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• NHibernate correct way to reattach cached entity to different session

  - by Chris Marisic

  I'm using NHibernate to query a list of objects from my database. After I get the list of objects over them I iterate over the list of objects and apply a distance approximation algorithm to find the nearest object. I consider this function of getting the list of objects and apply the algorithm over them to be a heavy operation so I cache the object which I find from the algorithm in HttpRuntime.Cache. After this point whenever I'm given the supplied input again I can just directly pull the object from Cache instead of having to hit the database and traverse the list. My object is a complex object that has collections attached to it, inside the query where I return the full list of objects I don't bring back any of the sub collections eagerly so when I read my cached object I need lazy loading to work correctly to be able to display the object fully. Originally I tried using this to re-associate my cached object back to a new session _session.Lock(obj, LockMode.None); However when accessing the page concurrently from another instance I get the error Illegal attempt to associate a collection with two open sessions I then tried something different with _session.Merge(obj); However watching the output of this in NHProf shows that it is deleting and re-associating my object's contained collections with my object, which is not what I want although it seems to work fine. What is the correct way to do this? Neither of these seem to be right.

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• Why Firebug pretends that my stylesheet is calling my xmlrpc ?

  - by Rebol Tutorial

  Firebug shows a request which causes a huge delay to http://reboltutorial.com/wp-content/themes/minaflow/none Details below but I don't understand why it says it comes from xmlrpc and the stylesheet: Date Sun, 04 Apr 2010 16:10:02 GMT Server Apache X-Powered-By PHP/5.2.13 X-Pingback http://reboltutorial.com/xmlrpc.php Expires Wed, 11 Jan 1984 05:00:00 GMT Cache-Control no-cache, must-revalidate, max-age=0 Pragma no-cache Set-Cookie wordpress_test_cookie=WP+Cookie+check; path=/; domain=.reboltutorial.com Last-Modified Sun, 04 Apr 2010 16:10:03 GMT Vary Accept-Encoding Content-Encoding gzip Keep-Alive timeout=2, max=94 Connection Keep-Alive Transfer-Encoding chunked Content-Type text/html; charset=UTF-8 Requêtemise en page impression GET /wp-content/themes/minaflow/none HTTP/1.1 Host: reboltutorial.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; fr; rv:1.9.2) Gecko/20100115 Firefox/3.6 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Referer: http://reboltutorial.com/wp-content/themes/minaflow/style.css Cookie: _csoot=1267966575980; _csuid=4b6f27395991a2ff; wp-settings-1=editor%3Dhtml%26align%3Dleft%26m0%3Do%26m1%3Do%26m2%3Do%26m3%3Dc%26m4%3Do%26m5%3Dc%26m6%3Do%26m7%3Do%26m8%3Dc%26m9%3Dc%26m10%3Dc%26m11%3Do%26m12%3Dc%26m13%3Dc%26m14%3Dc%26m15%3Dc; wp-settings-time-1=1270384700; subscribe_checkbox_=unchecked; PHPSESSID=o70hjpjf7uj2hb4doe4k0o5co5; wordpress_test_cookie=WP+Cookie+check; xumgeqhxmhohxipF=Erjixxeeskfgnlba; SJECT=CKON; wordpress_=admin%7C1271592539%7C392c555d9051c6fa184074d8441cc472; wordpress_logged_in_=admin%7C1271592539%7C0e7a92bda53cc2f5afc32962237a1037; rcBDvgtspmuEsyzp=rmqjtFbCfheGCjBw; prli_click_15=creatingstandard; prli_visitor=m7928r

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• Javascript + PHP $_POST array empty

  - by Peterim

  While trying to send a POST request via xmlhttp.open("POST", "url", true) (javascript) to the server I get an empty $_POST array. Firebug shows that the data is being sent. Here is the data string from Firebug: a=1&q=151a45a150.... But $_POST['q'] returns nothing. The interesting thing is that file_get_contents('php://input') does have my data (the string above), but PHP somehow doesn't recognize it. Tried both $_POST and $_REQUEST, nothing works. Headers being sent: POST /test.php HTTP/1.1 Host: website.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us;q=0.7,en;q=0.3 Accept-Encoding: gzip,deflate Accept-Charset: utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Referer: http://website.com/ Content-Length: 156 Content-Type: text/plain; charset=UTF-8 Pragma: no-cache Cache-Control: no-cache Thank you for any suggestions.

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• Django + jquery : getting 301

  - by llazzaro

  Hello, I have tabs that calls via javascript urls of django to complete the "container" But i am getting 301, any idea why this is happening? Server misconfiguration? urls.py urlpatterns = patterns('', (r'^admin/', include(admin.site.urls)), (r'^list/', 'carsproj.cars.views.list'), ) view def list(request): if request.is_ajax(): return render_to_response('templates/generic_list.html', { 'items' : Cars.objects.all(), 'name' : 'List - Cars' }, context_instance = RequestContext(request)) javascript the_tabs.click(function(e){ var element = $(this); if(element.find('#overLine').length) return false; var bg = element.attr('class').replace('tab ',''); $('#overLine').remove(); $('<div>',{ id:'overLine', css:{ display:'none', width:element.outerWidth()-2, background:topLineColor[bg] || 'white' }}).appendTo(element).fadeIn('slow'); if(!element.data('cache')) { $('#contentHolder').html('<img src="/media/img/ajax_preloader.gif" width="64" height="64" class="preloader" />'); $.get(element.data('page'),function(msg){ $('#contentHolder').html(msg); element.data('cache',msg); }); } else $('#contentHolder').html(element.data('cache')); e.preventDefault(); }) Please tell me what more information you need, js code? template? url.py? I WILL EDIT THIS POST FOR ADD MORE DATA

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• Why does grails use hsqldb when I ask for mysql?

  - by John

  I'm following the racetrack example from Jason Rudolph's book at InfoQ, using grails-1.2.1. I got up to the part where I was to switch from hsqldb to mysql. I think I've deleted every reference to hsqldb in the DataSource.groovy file, but I get an exception and the stack trace shows it's still using hsqldb. DataSource.groovy dataSource { boolean pooled = true String driverClassName = "com.mysql.jdbc.Driver" String url = "jdbc:mysql://localhost/dfpc2" String dbCreate = "create" String username = "dfpc2" String password = "dfpc2" dialect = org.hibernate.dialect.MySQL5InnoDBDialect } hibernate { cache.use_second_level_cache=true cache.use_query_cache=true cache.provider_class='net.sf.ehcache.hibernate.EhCacheProvider' } // environment specific settings environments { development { } test { } production { } } When I grails run-app it all starts up with no errors. I can navigate to the home page. But when I click on one of the links, I get a stack trace: java.sql.SQLException: Table not found in statement [select this_.id as id0_0_, this_.version as version0_0_, this_.name as name0_0_, this_.variant as variant0_0_ from domainObject this_ limit ?] at org.hsqldb.jdbc.Util.throwError(Unknown Source) at org.hsqldb.jdbc.jdbcPreparedStatement.<init>(Unknown Source) at org.hsqldb.jdbc.jdbcConnection.prepareStatement(Unknown Source) at dfpc2.domainObjectController$_closure2.doCall(script1269434425504953491149.groovy:13) at dfpc2.domainObjectController$_closure2.doCall(script1269434425504953491149.groovy) at java.lang.Thread.run(Thread.java:619) My mysql database shows no tables created. (I don't think groovy's connected to mysql yet.) Things I've checked: mysql-connector-java-5.1.6.jar is in lib directory. I've tried grails clean I tried putting the dataSource info in the development environment (I haven't graduated to test or prod yet), but it seemed to make no difference. The stdout shows I'm using development env. I've googled for solutions, but the only solution I've found is when people don't change the test or production environments.

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• In Rails, a Sweeper isn't getting called in a Model-only setup

  - by charliepark

  I'm working on a Rails app, where I'm using page caching to store static html output. The caching works fine. I'm having trouble expiring the caches, though. I believe my problem is, in part, because I'm not expiring the cache from my controller. All of the actions necessary for this are being handled within the model. This seems like it should be doable, but all of the references to Model-based cache expiration that I'm finding seem to be out of date, or are otherwise not working. In my environment.rb file, I'm calling config.load_paths += %W( #{RAILS_ROOT}/app/sweepers ) And I have, in the /sweepers folder, a LinkSweeper file: class LinkSweeper < ActionController::Caching::Sweeper observe Link def after_update(link) clear_links_cache(link) end def clear_links_cache(link) # expire_page :controller => 'links', :action => 'show', :md5 => link.md5 expire_page '/l/'+ link.md5 + '.html' end end So ... why isn't it deleting the cached page when I update the model? (Process: using script/console, I'm selecting items from the database and saving them, but their corresponding pages aren't deleting from the cache), and I'm also calling the specific method in the Link model that would normally invoke the sweeper. Neither works. If it matters, the cached file is an md5 hash off a key value in the Links table. The cached page is getting stored as something like /l/45ed4aade64d427...99919cba2bd90f.html. Essentially, it seems as though the Sweeper isn't actually observing the Link. I also read (here) that it might be possible to simply add the sweeper to config.active_record.observers in environment.rb, but that didn't seem to do it (and I wasn't sure if the load_path of app/sweepers in environment.rb obviated that).

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• What's the best way to "shuffle" a table of database records?

  - by Darth

  Say that I have a table with a bunch of records, which I want to randomly present to users. I also want users to be able to paginate back and forth, so I have to perserve some sort of order, at least for a while. The application is basically only AJAX and it uses cache for already visited pages, so even if I always served random results, when the user tries to go back, he will get the previous page, because it will load from the local cache. The problem is, that if I return only random results, there might be some duplicates. Each page contains 6 results, so to prevent this, I'd have to do something like WHERE id NOT IN (1,2,3,4 ...) where I'd put all the previously loaded IDs. Huge downside of that solution is that it won't be possible to cache anything on the server side, as every user will request different data. Alternate solution might be to create another column for ordering the records, and shuffle it every insert time unit here. The problem here is, I'd need to set random number out of a sequence to every record in the table, which would take as many queries as there are records. I'm using Rails and MySQL if that's of any relevance.

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• How can I determine when an InnoDB table was last changed?

  - by David M

  I've had success in the past storing the (heavily) processed results of a database query in memcached, using the last update time of the underlying tables(s) as part of the cache key. For MyISAM tables, that last changed time is available in SHOW TABLE STATUS. Unfortunately, that's usually NULL for InnoDB tables. In MySQL 4.1, the ctime for an InnoDB in its SHOW TABLE STATUS line was usually its actual last update time, but that doesn't seem to be true for MySQL 5.1. There is a DATETIME field in the table, but it only shows when a row has been modified - it cannot show the deletion time of a row that's not there anymore! So, I really cannot use MAX(update_time). Here's the really tricky part. I have a number of replicas that I do reads from. Can I figure out the state of the table that doesn't rely on when the changes have actually been applied? My conclusion after working on this for a while is that it's not going to be possible to get this information as cheaply as I'd like. I'm probably going to cache data until the time that I expect the table to change (it's updated once a day), and let the query cache help out where it can.

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• Approach for caching data from data logger

  - by filip-fku

  Greetings, I've been working on a C#.NET app that interacts with a data logger. The user can query and obtain logs for a specified time period, and view plots of the data. Typically a new data log is created every minute and stores a measurement for a few parameters. To get meaningful information out of the logger, a reasonable number of logs need to be acquired - data for at least a few days. The hardware interface is a UART to USB module on the device, which restricts transfers to a maximum of about 30 logs/second. This becomes quite slow when reading in the data acquired over a number of days/weeks. What I would like to do is improve the perceived performance for the user. I realize that with the hardware speed limitation the user will have to wait for the full download cycle at least the first time they acquire a larger set of data. My goal is to cache all data seen by the app, so that it can be obtained faster if ever requested again. The approach I have been considering is to use a light database, like SqlServerCe, that can store the data logs as they are received. I am then hoping to first search the cache prior to querying a device for logs. The cache would be updated with any logs obtained by the request that were not already cached. Finally my question - would you consider this to be a good approach? Are there any better alternatives you can think of? I've tried to search SO and Google for reinforcement of the idea, but I mostly run into discussions of web request/content caching. Thanks for any feedback!

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• Error in FireFox Loading Images

  - by Brian

  Hello, Details of the app are: ASP.NET project, local web server, hosted in IIS locally, using latest FireFox, uses forms authentication. I'm getting a logon user name/pwd box when trying to access my local web server. Using the net panel in firebug, I see the issue is with an animated GIF, showing up as 401 unauthorized. I check the details and this is what I see for this URL: http://localhost/<virtual>/Images/loading.gif I'm getting the following: Response Headers: Server Microsoft-IIS/5.1 Date Thu, 17 Jun 2010 19:02:58 GMT WWW-Authenticate Negotiate NTLM Connection close Content-Length 4046 Content-Type text/html Request headers: Host localhost User-Agent Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3 ( .NET CLR 3.5.30729; .NET4.0E) Accept image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language en-us,en;q=0.5 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 115 Connection keep-alive Referer <correct referer> Cookie ASP.NET_SessionId=ux4bt345qjz4p3u1wm1zgmez; .ASPXFormsAuth=33F12B444040827B8ABF154EE4EDE43B6CA532432EB846987B355097E00256DF0955C76A37BC593EAA961747BF1CC1D8949FF63C6F2CA69D77213EB15B4EDFAF57A83D9E1F88AB8D821C3A09C07EA2EE; .ASPROLES=qTFrGteJydYAE3118WGXbhJthTDdjdtuQ06t4bYVrM1BwIfcEHU1HhnEcs7TqSOaV-fIN5MH3uO57oNVWXDvrhkZ8gQuURuUk_K0TpoR-DEFXuF953Gl9aIilKAdV211jutMNQmhkt2rdPE2tEhHs3pz953fADxjAOyZl7K-AqNvMk3yqJshhKHhJIf-ALMhWIYlrrKy0WsYznUwh3WCtPfzEBD5XzmXU8HVMJ2-ArLjBISuegvSmxvK1PuXBPhoMRMi9Ynaw6xi9ypGk-R6uN0ljOMCGkB2-20WUlFuP0xWTfac_zCTDT00pbpnyjtygnM-LShOXTrZ_mhoRuXfKYEYSodNihwD6SRr19Nm-8uZ5BQ-W81svM17S2C0vc0FaxtiuAcN_vHcsN1OEJeCuVfRjeqzo9xWEViupP3Vh6aOcCm6yrftgw5x94piuCJO7tCfXjJAw5RVUWDBBWv5gmid171F0k-_XZ0CSv7Gm2Eai1BRfogAqQ_MV3tyPv7XVEyJXRXqYGlf1JpkfTW8S8On4E05v9gx9RcdnKHZebiOZwbP1_ho9nG7pMwXysbhjxtxwZ-zLx-v11_rhZw_i5m7iNcLtt4BbFU-sb_crzMpCKGywHIc452Zp1E0kx1Rfx-2eUnaiLiCfGed-QqelO88NYTpJHttGKEfhFrDgmaIXZPJRtuZ-GrS6t3Vla-8qDAVb1p6ovPwoVT4z4BhQyFsk542gDx-uQDw6D0B6zo7lXfcOjtolUxDcLbETsNlYsexZaxFpRSbw7M1ldwL_k92P9wLPlv9mw4NtyhXKJesMu7GjquZuoBN3hO00AqJEe1tKFFtfrvbE5ZH7uNu7myNdtlxRPe3WZe7qukbqHo1 Pragma no-cache Cache-Control no-cache Any ideas? Thanks.

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• Entity framework with Linq to Entities performance

  - by mare

  If I have a static method like this public static string GetTicClassificationTitle(string classI, string classII, string classIII) { using (TicDatabaseEntities ticdb = new TicDatabaseEntities()) { var result = from classes in ticdb.Classifications where classes.ClassI == classI where classes.ClassII == classII where classes.ClassIII == classIII select classes.Description; return result.FirstOrDefault(); } } and use this method in various places in foreach loops or just plain calling it numerous times, does it create and open new connection every time? If so, how can I tackle this? Should I cache the results somewhere, like in this case, I would cache the entire Classifications table in Memory Cache? And then do queries vs this cached object? Or should I make TicDatabaseEntities variable static and initialize it at class level? Should my class be static if it contains only static methods? Because right now it is not.. Also I've noticed that if I return result.First() instead of FirstOrDefault() and the query does not find a match, it will issue an exception (with FirstOrDefault() there is no exception, it returns null). Thank you for clarification.

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• Client-Side caching on IIS7 doesn't seem to work

  - by thomasbtv

  I have set content caching on a specific folder by following the local web.config method. I don't think it works, and I would like to fix this. I activate the cache using the IIS / HTTP Headers / Common headers feature. I set them to 1 day of expiration. I opened a page with Google Chrome in private navigation, and then open the Network tab in the console. The first time I load the page, everything loads from the site, obviously. If I refresh the page, I see 2 types of loading in the Network console: the files from Google and Facebook and such have a status of 200, and a size of (from cache). the files from the folder for which I set the caching have a status of 304 and their size is displayed. So, I guess the caching setting doesn't work? Or does the 304 response means that it's loaded from the cache? If they aren't, how can I make it work ? Thanks !

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• Spring.net customer namespace parser

  - by ListenToRick

  I have a customer parser which looks like this: [NamespaceParser( Namespace = "http://mysite/schema/cache", SchemaLocationAssemblyHint = typeof(CacheNamespaceParser ), SchemaLocation = "/cache.xsd" ) ] public class CacheNamespaceParser : NamespaceParserSupport { public override void Init() { RegisterObjectDefinitionParser("cache", new CacheParser ()); } } public class CacheParser : AbstractSimpleObjectDefinitionParser { protected override Type GetObjectType(XmlElement element) { return typeof(CacheDefinition); } protected override void DoParse(XmlElement element, ObjectDefinitionBuilder builder) { } protected override bool ShouldGenerateIdAsFallback { get { return true; } } } in the web config i have the following configuration.... <spring> <parsers> <parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data"/> <parser type="App.Web.CacheNamespaceParser, WebApp" /> </parsers> When I run the project I get the following error: An error occurred creating the configuration section handler for spring/parsers: Invalid resource name. Name has to be in 'assembly:<assemblyName>/<namespace>/<resourceName>' format. I put a break point in the CacheNamespaceParser init method and it is called. If I remove from the web config all is well! Any ideas whats wrong

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• Hadoop File Read

  - by user3684584

  Hadoop Distributed Cache Wordcount example in hadoop 2.2.0. Copied file into hdfs filesystem to be used inside setup of mapper class. protected void setup(Context context) throws IOException,InterruptedException { Path[] uris = DistributedCache.getLocalCacheFiles(context.getConfiguration()); cacheData=new HashMap(); for(Path urifile: uris) { try { BufferedReader readBuffer1 = new BufferedReader(new FileReader(urifile.toString())); String line; while ((line=readBuffer1.readLine())!=null) { System.out.println("**************"+line); cacheData.put(line,line); } readBuffer1.close(); } catch (Exception e) { System.out.println(e.toString()); } } } Inside Driver Main class Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs(); if (otherArgs.length != 3) { System.err.println("Usage: wordcount <in> <out>"); System.exit(2); } Job job = new Job(conf, "word_count"); job.setJarByClass(WordCount.class); job.setMapperClass(Map.class); job.setReducerClass(Reduce.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(otherArgs[0])); Path outputpath=new Path(otherArgs[1]); outputpath.getFileSystem(conf).delete(outputpath,true); FileOutputFormat.setOutputPath(job,outputpath); System.out.println("CachePath****************"+otherArgs[2]); DistributedCache.addCacheFile(new URI(otherArgs[2]),job.getConfiguration()); System.exit(job.waitForCompletion(true) ? 0 : 1); But getting exception java.io.FileNotFoundException: file:/home/user12/tmp/mapred/local/1408960542382/cache (No such file or directory) So Cache functionality not working properly. Any Idea ?

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• Help me make a jquery AJAXed divs' links work like an iframe.

  - by Dave

  I want to make a few divs on the same page work similar to iframes. Each will load a URL which contains links. When you click on those links I want an AJAX request to go out and replace the div's html with new html from the page of the clicked link. It will be very similar to surfing a page inside an iframe. Here is my code to initially load the divs (this code works): onload: $.ajax({ url: "http://www.foo.com/videos.php", cache: false, success: function(html){ $("#HowToVideos").replaceWith(html); } }); $.ajax({ url: "http://www.foo.com/projects.php", cache: false, success: function(html){ $("#HowToProjects").replaceWith(html); } }); This is a sample of code that I'm not quite sure how to implement but explains the concept. Could I get some help with some selectors(surround in ?'s) and or let me know what is the correct way of doing this? I also want to display a loading icon, which I need to know where the right place to place the function is. $(".ajaxarea a").click(function(){ var linksURL = this.href; // var ParentingAjaxArea = $(this).closest(".ajaxarea");; $.ajax({ url: linksURL, cache: false, success: function(html){ $(ParentingAjaxArea).replaceWith(html); } }); return false; }); $(".ajaxarea").ajaxStart(function(){ // show loading icon });

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• Is Safari on iOS 6 caching $.ajax results?

  - by user1684978

  Since the upgrade to iOS 6, we are seeing Safari's web view take the liberty of caching $.ajax calls. This is in the context of a PhoneGap application so it is using the Safari WebView. Our $.ajax calls are POST methods and we have cache set to false {cache:false}, but still this is happening. We tried manually adding a timestamp to the headers but it did not help. We did more research and found that Safari is only returning cached results for web services that have a function signature that is static and does not change from call to call. For instance, imagine a function called something like: getNewRecordID(intRecordType) This function receives the same input parameters over and over again, but the data it returns should be different every time. Must be in Apple's haste to make iOS 6 zip along impressively they got too happy with the cache settings. Has anyone else seen this behavior on iOS 6? If so, what exactly is causing it? The workaround that we found was to modify the function signature to be something like this: getNewRecordID(intRecordType, strTimestamp) and then always pass in a timestamp parameter as well, and just discard that value on the server side. This works around the issue. I hope this helps some other poor soul who spends 15 hours on this issue like I did!

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• Design patterns for Caching Images in a MVC?

  - by Onema

  Hi, I'm designing an image cache system that will be used in an MVC CMS. The main purpose of the image cacher is to modify images: scale, crop, etc and cache them in the client site. I have created an image cache Model and Mapper that interact with the Database, to keep track of the images and know what kind of actions have been applied to them (scale, crop, etc). In addition to the Model and Mapper I have created a ImageCacher Class that is used by the API to manage the Model and image creation based on arguments passed by the client site, this class creates the images and generates the links to the images for the View. A coworker argued that I need to include the functionality of this last Class inside the Model, as the bulk of the logic should go in the model. I respectfully disagree with him since I feel the model's responsibility is to deal with the information about the images cached at the database level, and the responsibility of the ImageCacher Class is to create the url/image that we will be caching (keeping the single responsibility principle). In addition to this I believe that a model should not have Presentation-related features, like creating or showing images. Does anyone have any insight on this? is there a particular design pattern that would make this division of tasks clear and and the image cacher reusable? Should I add all the logic in the Model? Thank you.

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• Lazy load images in UITableViewCell

  - by lostInTransit

  Hi I have some 50 custom cells in my UITableView. I want to display an image and a label in the cells where I get the images from URLs. I want to do a lazy load of images so the UI does not freeze up while the images are being loaded. I tried getting the images in separate threads but I have to load each image every time a cell becomes visible again (Otherwise reuse of cells shows old images) Apps like Facebook load images only for cells currently visible and once the images are loaded, they are not loaded again. Can someone please tell me how to duplicate this behavior. Thanks. Edit Trying to cache images in an NSMutableDictionary object creates problems when the user scrolls fast. I am getting images only when scrolling completely stops and clearing out the cache on memory warning. But the app invariably gets a memory warning (due to size of images being cached) and clears the cache before reloading. If scrolling is very fast, it crashes. Any other suggestions are welcome

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• jQuery Code Only Fires On Hard Refresh?

  - by Rob Vanders

  The XFBML version of the Facebook Registration plugin only loads HTTPS. I need it to load HTTP so my form does not call a security error mismatch between domains. I wrote this code to get the SRC and rewrite it with out HTTPS It works fine on the first load, however on Chrome and Safari it only loads the first time and on HARD refreshes. It does not load on standard reloads or by pressing "enter" on the address bar. Here is the code $(window).load(function () { // Replace HTTPS with HTTP when frame has loaded $(".subscribe iframe").each(function(){ var source = $(this).attr("src"); //alert(source); var sourceNew = source.replace("https", "http"); // change https to http alert(sourceNew); $(this).attr("src", sourceNew); }); }); I have .HTACCESS set to disable server cache <Files *> Header set Cache-Control: "private, pre-check=0, post-check=0, max-age=0" Header set Expires: 0 Header set Pragma: no-cache </Files> What is causing this to not fire reliably? Thanks

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• How can I get size in bytes of an object sent using RMI?

  - by Lucas Batistussi

  I'm implementing a cache server with MongoDB and ConcurrentHashMap java class. When there are available space to put object in memory, it will put at. Otherwise, the object will be saved in a mongodb database. Is allowed that user specify a size limit in memory (this should not exceed heap size limit obviously!) for the memory cache. The clients can use the cache service connecting through RMI. I need to know the size of each object to verify if a new incoming object can be put into memory. I searched over internet and i got this solution to get size: public long getObjectSize(Object o){ try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(o); oos.close(); return bos.size(); } catch (Exception e) { return Long.MAX_VALUE; } } This solution works very well. But, in terms of memory use doesn't solve my problem. :( If many clients are verifying the object size at same time this will cause stack overflow, right? Well... some people can say: Why you don't get the specific object size and store it in memory and when another object is need to put in memory check the object size? This is not possible because the objects are variable in size. :( Someone can help me? I was thinking in get socket from RMI communication, but I don't know how to do this...

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• What is an efficient way to serve images (PHP)?

  - by Scarface

  Hey guys currently I am thinking of serving images using an image handler script. I have two sources of images. One is from my web images folder where images that are used to construct my site interface are served. The other is in each users images folder where they can store their own images. I was thinking of giving each user image a unique id and then searching that id with the image handler script and serving the image, and changing the file name. The problem is that my site images folder does not have any information in the database and thus has no ids, should I just serve directly? Also this way of serving user images does not seem like the most efficient. If anyone has any suggestions I would really appreciate it. $sql="SELECT username,file_name FROM images WHERE id=?"; $stmt=$conn->prepare($sql); $result=$stmt->execute(array($ID)); while($row = $stmt->fetch(PDO::FETCH_ASSOC)){ $image_name = $row['file_name']; $username = $row['username']; } $path="$username/images/$image_name"; header("Expires: -1"); header("Cache-Control: no-store, no-cache, must-revalidate"); header("Cache-Control: post-check=0, pre-check=0", false); readfile($path);

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• postfix: Temporary lookup failure

  - by mk_89

  I have followed the tutorials step by step for installing and configuring postfix https://help.ubuntu.com/community/Postfix https://help.ubuntu.com/community/PostfixBasicSetupHowto I am trying to test the services to whether Temporary lookup failure error telnet localhost 25 250 2.1.0 Ok rcpt to: fmaster@localhost 451 4.3.0 <fmaster@localhost>: Temporary lookup failure rcpt to: info@localhost 451 4.3.0 <info@localhost>: Temporary lookup failure I have tried searching the web but I have found no solutions, why am I getting this problem? mail.log Sep 24 01:03:05 bookcdb postfix/smtpd[21055]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <info@localhost>: Temporary lookup failure; from=<root@localhost> to=<info@localhost> proto=ESMTP helo=<localhost> Sep 24 01:03:19 bookcdb postfix/smtpd[21055]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <root@localhost>: Temporary lookup failure; from=<root@localhost> to=<root@localhost> proto=ESMTP helo=<localhost> Sep 24 01:08:19 bookcdb postfix/smtpd[21055]: timeout after RCPT from unknown[::1] Sep 24 01:08:19 bookcdb postfix/smtpd[21055]: disconnect from unknown[::1] Sep 24 01:10:49 bookcdb postfix/anvil[21059]: statistics: max connection rate 1/60s for (smtp:::1) at Sep 24 01:00:49 Sep 24 01:10:49 bookcdb postfix/anvil[21059]: statistics: max connection count 1 for (smtp:::1) at Sep 24 01:00:49 Sep 24 01:10:49 bookcdb postfix/anvil[21059]: statistics: max cache size 1 at Sep 24 01:00:49 Sep 24 01:15:36 bookcdb postfix/smtpd[22175]: error: open database /var/lib/mailman/data/aliases.db: No such file or directory Sep 24 01:15:36 bookcdb postfix/smtpd[22175]: warning: hostname localhost does not resolve to address ::1: No address associated with hostname Sep 24 01:15:36 bookcdb postfix/smtpd[22175]: connect from unknown[::1] Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: error: open database /etc/postfix/transport.db: No such file or directory Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport lookup error for "root@localhost" Sep 24 01:15:55 bookcdb postfix/trivial-rewrite[22195]: warning: transport_maps lookup failure Sep 24 01:15:59 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:15:59 bookcdb postfix/trivial-rewrite[22195]: warning: hash:/etc/postfix/transport lookup error for "fmaster@localhost" Sep 24 01:15:59 bookcdb postfix/trivial-rewrite[22195]: warning: transport_maps lookup failure Sep 24 01:15:59 bookcdb postfix/smtpd[22175]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <fmaster@localhost>: Temporary lookup failure; from=<root@localhost> to=<fmaster@localhost> proto=ESMTP helo=<localhost> Sep 24 01:16:30 postfix/smtpd[22175]: last message repeated 5 times Sep 24 01:16:30 bookcdb postfix/smtpd[22175]: disconnect from unknown[::1] Sep 24 01:19:50 bookcdb postfix/anvil[22177]: statistics: max connection rate 1/60s for (smtp:::1) at Sep 24 01:15:36 Sep 24 01:19:50 bookcdb postfix/anvil[22177]: statistics: max connection count 1 for (smtp:::1) at Sep 24 01:15:36 Sep 24 01:19:50 bookcdb postfix/anvil[22177]: statistics: max cache size 1 at Sep 24 01:15:36 Sep 24 01:20:32 bookcdb postfix/qmgr[21039]: D0C596E0B34: from=<[email protected]>, size=442, nrcpt=1 (queue active) Sep 24 01:20:32 bookcdb postfix/qmgr[21039]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 01:20:32 bookcdb postfix/error[22402]: D0C596E0B34: to=<[email protected]>, relay=none, delay=5369, delays=5369/0.01/0/0.09, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 01:24:16 bookcdb postfix/smtpd[22573]: error: open database /var/lib/mailman/data/aliases.db: No such file or directory Sep 24 01:24:16 bookcdb postfix/smtpd[22573]: warning: hostname localhost does not resolve to address ::1: No address associated with hostname Sep 24 01:24:16 bookcdb postfix/smtpd[22573]: connect from unknown[::1] Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: error: open database /etc/postfix/transport.db: No such file or directory Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "root@localhost" Sep 24 01:24:43 bookcdb postfix/trivial-rewrite[22594]: warning: transport_maps lookup failure Sep 24 01:25:14 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:25:14 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "[email protected]" Sep 24 01:25:14 bookcdb postfix/trivial-rewrite[22594]: warning: transport_maps lookup failure Sep 24 01:25:14 bookcdb postfix/smtpd[22573]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <[email protected]>: Temporary lookup failure; from=<root@localhost> to=<[email protected]> proto=ESMTP helo=<localhost> Sep 24 01:25:32 bookcdb postfix/qmgr[21039]: 2E5C36E0A07: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 01:25:32 bookcdb postfix/qmgr[21039]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 01:25:32 bookcdb postfix/qmgr[21039]: 0EA3A6E0ACC: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 01:25:32 bookcdb postfix/error[22631]: 2E5C36E0A07: to=<[email protected]>, orig_to=<root>, relay=none, delay=30203, delays=30203/0.01/0/0.1, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 01:25:32 bookcdb postfix/error[22632]: 0EA3A6E0ACC: to=<[email protected]>, orig_to=<root>, relay=none, delay=30115, delays=30115/0.01/0/0.11, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 01:25:58 bookcdb postfix/smtpd[22573]: warning: non-SMTP command from unknown[::1]: subject: fdf Sep 24 01:25:58 bookcdb postfix/smtpd[22573]: disconnect from unknown[::1] Sep 24 01:26:01 bookcdb postfix/smtpd[22573]: warning: hostname localhost does not resolve to address ::1: No address associated with hostname Sep 24 01:26:01 bookcdb postfix/smtpd[22573]: connect from unknown[::1] Sep 24 01:26:10 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:26:10 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "root@locahost" Sep 24 01:26:10 bookcdb postfix/trivial-rewrite[22594]: warning: transport_maps lookup failure Sep 24 01:26:37 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:26:37 bookcdb postfix/trivial-rewrite[22594]: warning: hash:/etc/postfix/transport lookup error for "fmaster@localhost" Sep 24 01:26:37 bookcdb postfix/trivial-rewrite[22594]: warning: transport_maps lookup failure Sep 24 01:26:37 bookcdb postfix/smtpd[22573]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <fmaster@localhost>: Temporary lookup failure; from=<root@locahost> to=<fmaster@localhost> proto=SMTP Sep 24 01:26:45 bookcdb postfix/smtpd[22573]: disconnect from unknown[::1] Sep 24 01:30:05 bookcdb postfix/anvil[22575]: statistics: max connection rate 1/60s for (smtp:::1) at Sep 24 01:24:16 Sep 24 01:30:05 bookcdb postfix/anvil[22575]: statistics: max connection count 1 for (smtp:::1) at Sep 24 01:24:16 Sep 24 01:30:05 bookcdb postfix/anvil[22575]: statistics: max cache size 1 at Sep 24 01:24:16 Sep 24 01:34:57 bookcdb dovecot: master: Dovecot v2.0.19 starting up (core dumps disabled) Sep 24 01:35:02 bookcdb amavis[1009]: starting. /usr/sbin/amavisd-new at mail.bookcdb.com amavisd-new-2.6.5 (20110407), Unicode aware Sep 24 01:35:02 bookcdb amavis[1009]: Perl version 5.014002 Sep 24 01:35:05 bookcdb amavis[1155]: Net::Server: Group Not Defined. Defaulting to EGID '114 114' Sep 24 01:35:05 bookcdb amavis[1155]: Net::Server: User Not Defined. Defaulting to EUID '108' Sep 24 01:35:05 bookcdb amavis[1155]: Module Amavis::Conf 2.208 Sep 24 01:35:05 bookcdb amavis[1155]: Module Archive::Zip 1.30 Sep 24 01:35:05 bookcdb amavis[1155]: Module BerkeleyDB 0.49 Sep 24 01:35:05 bookcdb amavis[1155]: Module Compress::Zlib 2.033 Sep 24 01:35:05 bookcdb amavis[1155]: Module Convert::TNEF 0.17 Sep 24 01:35:05 bookcdb amavis[1155]: Module Convert::UUlib 1.4 Sep 24 01:35:05 bookcdb amavis[1155]: Module Crypt::OpenSSL::RSA 0.27 Sep 24 01:35:05 bookcdb amavis[1155]: Module DB_File 1.821 Sep 24 01:35:05 bookcdb amavis[1155]: Module Digest::MD5 2.51 Sep 24 01:35:05 bookcdb amavis[1155]: Module Digest::SHA 5.61 Sep 24 01:35:05 bookcdb amavis[1155]: Module IO::Socket::INET6 2.69 Sep 24 01:35:05 bookcdb amavis[1155]: Module MIME::Entity 5.502 Sep 24 01:35:05 bookcdb amavis[1155]: Module MIME::Parser 5.502 Sep 24 01:35:05 bookcdb amavis[1155]: Module MIME::Tools 5.502 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::DKIM::Signer 0.39 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::DKIM::Verifier 0.39 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::Header 2.08 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::Internet 2.08 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::SPF v2.008 Sep 24 01:35:05 bookcdb amavis[1155]: Module Mail::SpamAssassin 3.003002 Sep 24 01:35:05 bookcdb amavis[1155]: Module Net::DNS 0.66 Sep 24 01:35:05 bookcdb amavis[1155]: Module Net::Server 0.99 Sep 24 01:35:05 bookcdb amavis[1155]: Module NetAddr::IP 4.058 Sep 24 01:35:05 bookcdb amavis[1155]: Module Socket6 0.23 Sep 24 01:35:05 bookcdb amavis[1155]: Module Time::HiRes 1.972101 Sep 24 01:35:05 bookcdb amavis[1155]: Module URI 1.59 Sep 24 01:35:05 bookcdb amavis[1155]: Module Unix::Syslog 1.1 Sep 24 01:35:05 bookcdb amavis[1155]: Amavis::DB code loaded Sep 24 01:35:05 bookcdb amavis[1155]: Amavis::Cache code loaded Sep 24 01:35:05 bookcdb amavis[1155]: SQL base code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: SQL::Log code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: SQL::Quarantine NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: Lookup::SQL code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: Lookup::LDAP code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: AM.PDP-in proto code loaded Sep 24 01:35:05 bookcdb amavis[1155]: SMTP-in proto code loaded Sep 24 01:35:05 bookcdb amavis[1155]: Courier proto code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: SMTP-out proto code loaded Sep 24 01:35:05 bookcdb amavis[1155]: Pipe-out proto code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: BSMTP-out proto code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: Local-out proto code loaded Sep 24 01:35:05 bookcdb amavis[1155]: OS_Fingerprint code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: ANTI-VIRUS code loaded Sep 24 01:35:05 bookcdb amavis[1155]: ANTI-SPAM code loaded Sep 24 01:35:05 bookcdb amavis[1155]: ANTI-SPAM-EXT code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: ANTI-SPAM-C code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: ANTI-SPAM-SA code loaded Sep 24 01:35:05 bookcdb amavis[1155]: Unpackers code loaded Sep 24 01:35:05 bookcdb amavis[1155]: DKIM code loaded Sep 24 01:35:05 bookcdb amavis[1155]: Tools code NOT loaded Sep 24 01:35:05 bookcdb amavis[1155]: Found $file at /usr/bin/file Sep 24 01:35:05 bookcdb amavis[1155]: No $altermime, not using it Sep 24 01:35:05 bookcdb amavis[1155]: Internal decoder for .mail Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .F Sep 24 01:35:05 bookcdb amavis[1155]: Found decoder for .Z at /bin/uncompress Sep 24 01:35:05 bookcdb amavis[1155]: Internal decoder for .gz Sep 24 01:35:05 bookcdb amavis[1155]: Found decoder for .bz2 at /bin/bzip2 -d Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .lzo tried: lzop -d Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .rpm tried: rpm2cpio.pl, rpm2cpio Sep 24 01:35:05 bookcdb amavis[1155]: Found decoder for .cpio at /bin/pax Sep 24 01:35:05 bookcdb amavis[1155]: Found decoder for .tar at /bin/pax Sep 24 01:35:05 bookcdb amavis[1155]: Found decoder for .deb at /usr/bin/ar Sep 24 01:35:05 bookcdb amavis[1155]: Internal decoder for .zip Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .7z tried: 7zr, 7za, 7z Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .rar tried: unrar-free Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .arj tried: arj, unarj Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .arc tried: nomarch, arc Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .zoo tried: zoo Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .lha Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .doc tried: ripole Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .cab tried: cabextract Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .tnef Sep 24 01:35:05 bookcdb amavis[1155]: Internal decoder for .tnef Sep 24 01:35:05 bookcdb amavis[1155]: No decoder for .exe tried: unrar-free; arj, unarj Sep 24 01:35:05 bookcdb amavis[1155]: Using primary internal av scanner code for ClamAV-clamd Sep 24 01:35:05 bookcdb amavis[1155]: Found secondary av scanner ClamAV-clamscan at /usr/bin/clamscan Sep 24 01:35:05 bookcdb amavis[1155]: Creating db in /var/lib/amavis/db/; BerkeleyDB 0.49, libdb 5.1 Sep 24 01:35:05 bookcdb postgrey[1219]: Process Backgrounded Sep 24 01:35:05 bookcdb postgrey[1219]: 2012/09/24-01:35:05 postgrey (type Net::Server::Multiplex) starting! pid(1219) Sep 24 01:35:05 bookcdb postgrey[1219]: Using default listen value of 128 Sep 24 01:35:05 bookcdb postgrey[1219]: Binding to TCP port 10023 on host localhost#012 Sep 24 01:35:05 bookcdb postgrey[1219]: Setting gid to "116 116" Sep 24 01:35:05 bookcdb postgrey[1219]: Setting uid to "110" Sep 24 01:35:06 bookcdb spamd[1231]: logger: removing stderr method Sep 24 01:35:08 bookcdb spamd[1233]: spamd: server started on port 783/tcp (running version 3.3.2) Sep 24 01:35:08 bookcdb spamd[1233]: spamd: server pid: 1233 Sep 24 01:35:08 bookcdb spamd[1233]: spamd: server successfully spawned child process, pid 1238 Sep 24 01:35:08 bookcdb spamd[1233]: spamd: server successfully spawned child process, pid 1240 Sep 24 01:35:08 bookcdb spamd[1233]: prefork: child states: SI Sep 24 01:35:08 bookcdb spamd[1233]: prefork: child states: II Sep 24 01:35:15 bookcdb postfix/master[1729]: daemon started -- version 2.9.3, configuration /etc/postfix Sep 24 01:36:08 bookcdb postfix/smtpd[1995]: error: open database /var/lib/mailman/data/aliases.db: No such file or directory Sep 24 01:36:08 bookcdb postfix/smtpd[1995]: warning: hostname localhost does not resolve to address ::1: No address associated with hostname Sep 24 01:36:08 bookcdb postfix/smtpd[1995]: connect from unknown[::1] Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: error: open database /etc/postfix/transport.db: No such file or directory Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport lookup error for "*" Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport lookup error for "root@localhost" Sep 24 01:36:51 bookcdb postfix/trivial-rewrite[1999]: warning: transport_maps lookup failure Sep 24 01:37:00 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:37:00 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport lookup error for "fmaster@localhost" Sep 24 01:37:00 bookcdb postfix/trivial-rewrite[1999]: warning: transport_maps lookup failure Sep 24 01:37:00 bookcdb postfix/smtpd[1995]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <fmaster@localhost>: Temporary lookup failure; from=<root@localhost> to=<fmaster@localhost> proto=SMTP Sep 24 01:37:28 bookcdb dovecot: imap-login: Login: user=<mkadiri89>, method=PLAIN, rip=::1, lip=::1, mpid=2730, secured Sep 24 01:37:28 bookcdb dovecot: imap(mkadiri89): Disconnected: Logged out bytes=44/697 Sep 24 01:37:29 bookcdb dovecot: imap-login: Login: user=<mkadiri89>, method=PLAIN, rip=::1, lip=::1, mpid=2732, secured Sep 24 01:37:29 bookcdb dovecot: imap(mkadiri89): Disconnected: Logged out bytes=464/1303 Sep 24 01:37:29 bookcdb dovecot: imap-login: Login: user=<mkadiri89>, method=PLAIN, rip=::1, lip=::1, mpid=2734, secured Sep 24 01:37:29 bookcdb dovecot: imap(mkadiri89): Disconnected: Logged out bytes=117/1395 Sep 24 01:37:31 bookcdb dovecot: imap-login: Login: user=<mkadiri89>, method=PLAIN, rip=::1, lip=::1, mpid=2737, secured Sep 24 01:37:31 bookcdb dovecot: imap(mkadiri89): Disconnected: Logged out bytes=117/1395 Sep 24 01:37:49 bookcdb dovecot: imap-login: Login: user=<root>, method=PLAIN, rip=::1, lip=::1, mpid=2739, secured Sep 24 01:37:49 bookcdb dovecot: imap: Error: user root: Invalid settings in userdb: userdb returned 0 as uid Sep 24 01:37:49 bookcdb dovecot: imap: Error: Invalid user settings. Refer to server log for more information. Sep 24 01:37:54 bookcdb dovecot: imap-login: Login: user=<root>, method=PLAIN, rip=::1, lip=::1, mpid=2741, secured Sep 24 01:37:54 bookcdb dovecot: imap: Error: user root: Invalid settings in userdb: userdb returned 0 as uid Sep 24 01:37:54 bookcdb dovecot: imap: Error: Invalid user settings. Refer to server log for more information. Sep 24 01:38:04 bookcdb dovecot: imap-login: Login: user=<info>, method=PLAIN, rip=::1, lip=::1, mpid=2743, secured Sep 24 01:38:04 bookcdb dovecot: imap(info): Disconnected: Logged out bytes=44/697 Sep 24 01:38:04 bookcdb dovecot: imap-login: Login: user=<info>, method=PLAIN, rip=::1, lip=::1, mpid=2745, secured Sep 24 01:38:04 bookcdb dovecot: imap(info): Disconnected: Logged out bytes=464/1303 Sep 24 01:38:04 bookcdb dovecot: imap-login: Login: user=<info>, method=PLAIN, rip=::1, lip=::1, mpid=2747, secured Sep 24 01:38:04 bookcdb dovecot: imap(info): Disconnected: Logged out bytes=117/1395 Sep 24 01:38:55 bookcdb postfix/smtpd[1995]: disconnect from unknown[::1] Sep 24 01:38:58 bookcdb postfix/smtpd[1995]: warning: hostname localhost does not resolve to address ::1: No address associated with hostname Sep 24 01:38:58 bookcdb postfix/smtpd[1995]: connect from unknown[::1] Sep 24 01:39:11 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport is unavailable. open database /etc/postfix/transport.db: No such file or directory Sep 24 01:39:11 bookcdb postfix/trivial-rewrite[1999]: warning: hash:/etc/postfix/transport lookup error for "info@localhost" Sep 24 01:39:11 bookcdb postfix/trivial-rewrite[1999]: warning: transport_maps lookup failure Sep 24 01:39:37 bookcdb postfix/smtpd[1995]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <fmaster@localhost>: Temporary lookup failure; from=<info@localhost> to=<fmaster@localhost> proto=SMTP Sep 24 01:39:47 bookcdb postfix/smtpd[1995]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <fmaster@localhost>: Temporary lookup failure; from=<info@localhost> to=<fmaster@localhost> proto=SMTP Sep 24 01:40:13 bookcdb postfix/smtpd[1995]: NOQUEUE: reject: RCPT from unknown[::1]: 451 4.3.0 <info@localhost>: Temporary lookup failure; from=<info@localhost> to=<info@localhost> proto=SMTP Sep 24 01:43:08 bookcdb postfix/smtpd[1995]: disconnect from unknown[::1] Sep 24 01:46:08 bookcdb postfix/anvil[1998]: statistics: max connection rate 1/60s for (smtp:::1) at Sep 24 01:36:08 Sep 24 01:46:08 bookcdb postfix/anvil[1998]: statistics: max connection count 1 for (smtp:::1) at Sep 24 01:36:08 Sep 24 01:46:08 bookcdb postfix/anvil[1998]: statistics: max cache size 1 at Sep 24 01:36:08 Sep 24 01:48:05 bookcdb dovecot: imap-login: Login: user=<info>, method=PLAIN, rip=::1, lip=::1, mpid=2805, secured Sep 24 01:48:05 bookcdb dovecot: imap(info): Disconnected: Logged out bytes=85/681 Sep 24 01:51:30 bookcdb dovecot: imap-login: Login: user=<info>, method=PLAIN, rip=::1, lip=::1, mpid=2815, secured Sep 24 01:51:30 bookcdb dovecot: imap(info): Disconnected: Logged out bytes=117/1395 Sep 24 02:05:15 bookcdb postfix/qmgr[1745]: 2EA006E0B32: from=<[email protected]>, size=439, nrcpt=1 (queue active) Sep 24 02:05:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 02:05:15 bookcdb postfix/qmgr[1745]: E76996E09B2: from=<[email protected]>, size=439, nrcpt=1 (queue active) Sep 24 02:05:15 bookcdb postfix/error[2842]: 2EA006E0B32: to=<[email protected]>, relay=none, delay=8391, delays=8391/0.05/0/0.09, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 02:05:16 bookcdb postfix/error[2843]: E76996E09B2: to=<[email protected]>, relay=none, delay=8416, delays=8416/0.03/0/0.11, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 02:30:15 bookcdb postfix/qmgr[1745]: D0C596E0B34: from=<[email protected]>, size=442, nrcpt=1 (queue active) Sep 24 02:30:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 02:30:15 bookcdb postfix/error[2914]: D0C596E0B34: to=<[email protected]>, relay=none, delay=9551, delays=9551/0.01/0/0.08, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 02:35:15 bookcdb postfix/qmgr[1745]: 2E5C36E0A07: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 02:35:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 02:35:15 bookcdb postfix/qmgr[1745]: 0EA3A6E0ACC: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 02:35:15 bookcdb postfix/error[2926]: 2E5C36E0A07: to=<[email protected]>, orig_to=<root>, relay=none, delay=34386, delays=34386/0.03/0/0.1, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 02:35:15 bookcdb postfix/error[2927]: 0EA3A6E0ACC: to=<[email protected]>, orig_to=<root>, relay=none, delay=34299, delays=34298/0.02/0/0.12, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 03:15:15 bookcdb postfix/qmgr[1745]: 2EA006E0B32: from=<[email protected]>, size=439, nrcpt=1 (queue active) Sep 24 03:15:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 03:15:15 bookcdb postfix/qmgr[1745]: E76996E09B2: from=<[email protected]>, size=439, nrcpt=1 (queue active) Sep 24 03:15:15 bookcdb postfix/error[3025]: 2EA006E0B32: to=<[email protected]>, relay=none, delay=12590, delays=12590/0.01/0/0.07, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 03:15:15 bookcdb postfix/error[3026]: E76996E09B2: to=<[email protected]>, relay=none, delay=12616, delays=12616/0.01/0/0.09, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 03:40:15 bookcdb postfix/qmgr[1745]: D0C596E0B34: from=<[email protected]>, size=442, nrcpt=1 (queue active) Sep 24 03:40:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 03:40:15 bookcdb postfix/error[3097]: D0C596E0B34: to=<[email protected]>, relay=none, delay=13752, delays=13752/0.01/0/0.07, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 03:45:15 bookcdb postfix/qmgr[1745]: 2E5C36E0A07: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 03:45:15 bookcdb postfix/qmgr[1745]: warning: connect to transport private/smtp-amavis: No such file or directory Sep 24 03:45:15 bookcdb postfix/qmgr[1745]: 0EA3A6E0ACC: from=<[email protected]>, size=438, nrcpt=1 (queue active) Sep 24 03:45:15 bookcdb postfix/error[3129]: 2E5C36E0A07: to=<[email protected]>, orig_to=<root>, relay=none, delay=38586, delays=38586/0.01/0/0.09, dsn=4.3.0, status=deferred (mail transport unavailable) Sep 24 03:45:15 bookcdb postfix/error[3130]: 0EA3A6E0ACC: to=<[email protected]>, orig_to=<root>, relay=none, delay=38498, delays=38498/0.01/0/0.08, dsn=4.3.0, status=deferred (mail transport unavailable) postconf -n alias_database = hash:/etc/aliases alias_maps = hash:/etc/aliases, hash:/var/lib/mailman/data/aliases append_dot_mydomain = no biff = no broken_sasl_auth_clients = yes config_directory = /etc/postfix content_filter = smtp-amavis:[127.0.0.1]:10024 home_mailbox = Maildir/ inet_interfaces = all inet_protocols = all mailbox_command = mailbox_size_limit = 0 mailman_destination_recipient_limit = 1 mydestination = server1.bookcdb.com, bookcdb.com, localhost.bookcdb.com, localho st, bookcdb.com myhostname = server1.bookcdb.com mynetworks = 127.0.0.0/8 myorigin = /etc/mailname readme_directory = no recipient_delimiter = + relay_domains = lists.bookcdb.com relayhost = smtp_tls_note_starttls_offer = yes smtp_tls_security_level = may smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,rejec t_unauth_destination smtpd_sasl_auth_enable = yes smtpd_sasl_local_domain = smtpd_sasl_security_options = noanonymous smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem smtpd_tls_auth_only = no smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt smtpd_tls_key_file = /etc/ssl/private/smtpd.key smtpd_tls_loglevel = 1 smtpd_tls_received_header = yes smtpd_tls_security_level = may smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtpd_tls_session_cache_timeout = 3600s smtpd_use_tls = yes tls_random_source = dev:/dev/urandom transport_maps = hash:/etc/postfix/transport

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• C#/.NET Little Wonders: The ConcurrentDictionary

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In this series of posts, we will discuss how the concurrent collections have been developed to help alleviate these multi-threading concerns.  Last week’s post began with a general introduction and discussed the ConcurrentStack<T> and ConcurrentQueue<T>.  Today's post discusses the ConcurrentDictionary<T> (originally I had intended to discuss ConcurrentBag this week as well, but ConcurrentDictionary had enough information to create a very full post on its own!).  Finally next week, we shall close with a discussion of the ConcurrentBag<T> and BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. Recap As you'll recall from the previous post, the original collections were object-based containers that accomplished synchronization through a Synchronized member.  While these were convenient because you didn't have to worry about writing your own synchronization logic, they were a bit too finely grained and if you needed to perform multiple operations under one lock, the automatic synchronization didn't buy much. With the advent of .NET 2.0, the original collections were succeeded by the generic collections which are fully type-safe, but eschew automatic synchronization.  This cuts both ways in that you have a lot more control as a developer over when and how fine-grained you want to synchronize, but on the other hand if you just want simple synchronization it creates more work. With .NET 4.0, we get the best of both worlds in generic collections.  A new breed of collections was born called the concurrent collections in the System.Collections.Concurrent namespace.  These amazing collections are fine-tuned to have best overall performance for situations requiring concurrent access.  They are not meant to replace the generic collections, but to simply be an alternative to creating your own locking mechanisms. Among those concurrent collections were the ConcurrentStack<T> and ConcurrentQueue<T> which provide classic LIFO and FIFO collections with a concurrent twist.  As we saw, some of the traditional methods that required calls to be made in a certain order (like checking for not IsEmpty before calling Pop()) were replaced in favor of an umbrella operation that combined both under one lock (like TryPop()). Now, let's take a look at the next in our series of concurrent collections!For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here. ConcurrentDictionary – the fully thread-safe dictionary The ConcurrentDictionary<TKey,TValue> is the thread-safe counterpart to the generic Dictionary<TKey, TValue> collection.  Obviously, both are designed for quick – O(1) – lookups of data based on a key.  If you think of algorithms where you need lightning fast lookups of data and don’t care whether the data is maintained in any particular ordering or not, the unsorted dictionaries are generally the best way to go. Note: as a side note, there are sorted implementations of IDictionary, namely SortedDictionary and SortedList which are stored as an ordered tree and a ordered list respectively.  While these are not as fast as the non-sorted dictionaries – they are O(log2 n) – they are a great combination of both speed and ordering -- and still greatly outperform a linear search. Now, once again keep in mind that if all you need to do is load a collection once and then allow multi-threaded reading you do not need any locking.  Examples of this tend to be situations where you load a lookup or translation table once at program start, then keep it in memory for read-only reference.  In such cases locking is completely non-productive. However, most of the time when we need a concurrent dictionary we are interleaving both reads and updates.  This is where the ConcurrentDictionary really shines!  It achieves its thread-safety with no common lock to improve efficiency.  It actually uses a series of locks to provide concurrent updates, and has lockless reads!  This means that the ConcurrentDictionary gets even more efficient the higher the ratio of reads-to-writes you have. ConcurrentDictionary and Dictionary differences For the most part, the ConcurrentDictionary<TKey,TValue> behaves like it’s Dictionary<TKey,TValue> counterpart with a few differences.  Some notable examples of which are: Add() does not exist in the concurrent dictionary. This means you must use TryAdd(), AddOrUpdate(), or GetOrAdd().  It also means that you can’t use a collection initializer with the concurrent dictionary. TryAdd() replaced Add() to attempt atomic, safe adds. Because Add() only succeeds if the item doesn’t already exist, we need an atomic operation to check if the item exists, and if not add it while still under an atomic lock. TryUpdate() was added to attempt atomic, safe updates. If we want to update an item, we must make sure it exists first and that the original value is what we expected it to be.  If all these are true, we can update the item under one atomic step. TryRemove() was added to attempt atomic, safe removes. To safely attempt to remove a value we need to see if the key exists first, this checks for existence and removes under an atomic lock. AddOrUpdate() was added to attempt an thread-safe “upsert”. There are many times where you want to insert into a dictionary if the key doesn’t exist, or update the value if it does.  This allows you to make a thread-safe add-or-update. GetOrAdd() was added to attempt an thread-safe query/insert. Sometimes, you want to query for whether an item exists in the cache, and if it doesn’t insert a starting value for it.  This allows you to get the value if it exists and insert if not. Count, Keys, Values properties take a snapshot of the dictionary. Accessing these properties may interfere with add and update performance and should be used with caution. ToArray() returns a static snapshot of the dictionary. That is, the dictionary is locked, and then copied to an array as a O(n) operation.  GetEnumerator() is thread-safe and efficient, but allows dirty reads. Because reads require no locking, you can safely iterate over the contents of the dictionary.  The only downside is that, depending on timing, you may get dirty reads. Dirty reads during iteration The last point on GetEnumerator() bears some explanation.  Picture a scenario in which you call GetEnumerator() (or iterate using a foreach, etc.) and then, during that iteration the dictionary gets updated.  This may not sound like a big deal, but it can lead to inconsistent results if used incorrectly.  The problem is that items you already iterated over that are updated a split second after don’t show the update, but items that you iterate over that were updated a split second before do show the update.  Thus you may get a combination of items that are “stale” because you iterated before the update, and “fresh” because they were updated after GetEnumerator() but before the iteration reached them. Let’s illustrate with an example, let’s say you load up a concurrent dictionary like this: 1: // load up a dictionary. 2: var dictionary = new ConcurrentDictionary<string, int>(); 3:  4: dictionary["A"] = 1; 5: dictionary["B"] = 2; 6: dictionary["C"] = 3; 7: dictionary["D"] = 4; 8: dictionary["E"] = 5; 9: dictionary["F"] = 6; Then you have one task (using the wonderful TPL!) to iterate using dirty reads: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); And one task to attempt updates in a separate thread (probably): 1: // attempt updates in a separate thread 2: var updateTask = new Task(() => 3: { 4: // iterates, and updates the value by one 5: foreach (var pair in dictionary) 6: { 7: dictionary[pair.Key] = pair.Value + 1; 8: } 9: }); Now that we’ve done this, we can fire up both tasks and wait for them to complete: 1: // start both tasks 2: updateTask.Start(); 3: iterationTask.Start(); 4:  5: // wait for both to complete. 6: Task.WaitAll(updateTask, iterationTask); Now, if I you didn’t know about the dirty reads, you may have expected to see the iteration before the updates (such as A:1, B:2, C:3, D:4, E:5, F:6).  However, because the reads are dirty, we will quite possibly get a combination of some updated, some original.  My own run netted this result: 1: F:6 2: E:6 3: D:5 4: C:4 5: B:3 6: A:2 Note that, of course, iteration is not in order because ConcurrentDictionary, like Dictionary, is unordered.  Also note that both E and F show the value 6.  This is because the output task reached F before the update, but the updates for the rest of the items occurred before their output (probably because console output is very slow, comparatively). If we want to always guarantee that we will get a consistent snapshot to iterate over (that is, at the point we ask for it we see precisely what is in the dictionary and no subsequent updates during iteration), we should iterate over a call to ToArray() instead: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary.ToArray()) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); The atomic Try…() methods As you can imagine TryAdd() and TryRemove() have few surprises.  Both first check the existence of the item to determine if it can be added or removed based on whether or not the key currently exists in the dictionary: 1: // try add attempts an add and returns false if it already exists 2: if (dictionary.TryAdd("G", 7)) 3: Console.WriteLine("G did not exist, now inserted with 7"); 4: else 5: Console.WriteLine("G already existed, insert failed."); TryRemove() also has the virtue of returning the value portion of the removed entry matching the given key: 1: // attempt to remove the value, if it exists it is removed and the original is returned 2: int removedValue; 3: if (dictionary.TryRemove("C", out removedValue)) 4: Console.WriteLine("Removed C and its value was " + removedValue); 5: else 6: Console.WriteLine("C did not exist, remove failed."); Now TryUpdate() is an interesting creature.  You might think from it’s name that TryUpdate() first checks for an item’s existence, and then updates if the item exists, otherwise it returns false.  Well, note quite... It turns out when you call TryUpdate() on a concurrent dictionary, you pass it not only the new value you want it to have, but also the value you expected it to have before the update.  If the item exists in the dictionary, and it has the value you expected, it will update it to the new value atomically and return true.  If the item is not in the dictionary or does not have the value you expected, it is not modified and false is returned. 1: // attempt to update the value, if it exists and if it has the expected original value 2: if (dictionary.TryUpdate("G", 42, 7)) 3: Console.WriteLine("G existed and was 7, now it's 42."); 4: else 5: Console.WriteLine("G either didn't exist, or wasn't 7."); The composite Add methods The ConcurrentDictionary also has composite add methods that can be used to perform updates and gets, with an add if the item is not existing at the time of the update or get. The first of these, AddOrUpdate(), allows you to add a new item to the dictionary if it doesn’t exist, or update the existing item if it does.  For example, let’s say you are creating a dictionary of counts of stock ticker symbols you’ve subscribed to from a market data feed: 1: public sealed class SubscriptionManager 2: { 3: private readonly ConcurrentDictionary<string, int> _subscriptions = new ConcurrentDictionary<string, int>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public void AddSubscription(string tickerKey) 7: { 8: // add a new subscription with count of 1, or update existing count by 1 if exists 9: var resultCount = _subscriptions.AddOrUpdate(tickerKey, 1, (symbol, count) => count + 1); 10:  11: // now check the result to see if we just incremented the count, or inserted first count 12: if (resultCount == 1) 13: { 14: // subscribe to symbol... 15: } 16: } 17: } Notice the update value factory Func delegate.  If the key does not exist in the dictionary, the add value is used (in this case 1 representing the first subscription for this symbol), but if the key already exists, it passes the key and current value to the update delegate which computes the new value to be stored in the dictionary.  The return result of this operation is the value used (in our case: 1 if added, existing value + 1 if updated). Likewise, the GetOrAdd() allows you to attempt to retrieve a value from the dictionary, and if the value does not currently exist in the dictionary it will insert a value.  This can be handy in cases where perhaps you wish to cache data, and thus you would query the cache to see if the item exists, and if it doesn’t you would put the item into the cache for the first time: 1: public sealed class PriceCache 2: { 3: private readonly ConcurrentDictionary<string, double> _cache = new ConcurrentDictionary<string, double>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public double QueryPrice(string tickerKey) 7: { 8: // check for the price in the cache, if it doesn't exist it will call the delegate to create value. 9: return _cache.GetOrAdd(tickerKey, symbol => GetCurrentPrice(symbol)); 10: } 11:  12: private double GetCurrentPrice(string tickerKey) 13: { 14: // do code to calculate actual true price. 15: } 16: } There are other variations of these two methods which vary whether a value is provided or a factory delegate, but otherwise they work much the same. Oddities with the composite Add methods The AddOrUpdate() and GetOrAdd() methods are totally thread-safe, on this you may rely, but they are not atomic.  It is important to note that the methods that use delegates execute those delegates outside of the lock.  This was done intentionally so that a user delegate (of which the ConcurrentDictionary has no control of course) does not take too long and lock out other threads. This is not necessarily an issue, per se, but it is something you must consider in your design.  The main thing to consider is that your delegate may get called to generate an item, but that item may not be the one returned!  Consider this scenario: A calls GetOrAdd and sees that the key does not currently exist, so it calls the delegate.  Now thread B also calls GetOrAdd and also sees that the key does not currently exist, and for whatever reason in this race condition it’s delegate completes first and it adds its new value to the dictionary.  Now A is done and goes to get the lock, and now sees that the item now exists.  In this case even though it called the delegate to create the item, it will pitch it because an item arrived between the time it attempted to create one and it attempted to add it. Let’s illustrate, assume this totally contrived example program which has a dictionary of char to int.  And in this dictionary we want to store a char and it’s ordinal (that is, A = 1, B = 2, etc).  So for our value generator, we will simply increment the previous value in a thread-safe way (perhaps using Interlocked): 1: public static class Program 2: { 3: private static int _nextNumber = 0; 4:  5: // the holder of the char to ordinal 6: private static ConcurrentDictionary<char, int> _dictionary 7: = new ConcurrentDictionary<char, int>(); 8:  9: // get the next id value 10: public static int NextId 11: { 12: get { return Interlocked.Increment(ref _nextNumber); } 13: } Then, we add a method that will perform our insert: 1: public static void Inserter() 2: { 3: for (int i = 0; i < 26; i++) 4: { 5: _dictionary.GetOrAdd((char)('A' + i), key => NextId); 6: } 7: } Finally, we run our test by starting two tasks to do this work and get the results… 1: public static void Main() 2: { 3: // 3 tasks attempting to get/insert 4: var tasks = new List<Task> 5: { 6: new Task(Inserter), 7: new Task(Inserter) 8: }; 9:  10: tasks.ForEach(t => t.Start()); 11: Task.WaitAll(tasks.ToArray()); 12:  13: foreach (var pair in _dictionary.OrderBy(p => p.Key)) 14: { 15: Console.WriteLine(pair.Key + ":" + pair.Value); 16: } 17: } If you run this with only one task, you get the expected A:1, B:2, ..., Z:26.  But running this in parallel you will get something a bit more complex.  My run netted these results: 1: A:1 2: B:3 3: C:4 4: D:5 5: E:6 6: F:7 7: G:8 8: H:9 9: I:10 10: J:11 11: K:12 12: L:13 13: M:14 14: N:15 15: O:16 16: P:17 17: Q:18 18: R:19 19: S:20 20: T:21 21: U:22 22: V:23 23: W:24 24: X:25 25: Y:26 26: Z:27 Notice that B is 3?  This is most likely because both threads attempted to call GetOrAdd() at roughly the same time and both saw that B did not exist, thus they both called the generator and one thread got back 2 and the other got back 3.  However, only one of those threads can get the lock at a time for the actual insert, and thus the one that generated the 3 won and the 3 was inserted and the 2 got discarded.  This is why on these methods your factory delegates should be careful not to have any logic that would be unsafe if the value they generate will be pitched in favor of another item generated at roughly the same time.  As such, it is probably a good idea to keep those generators as stateless as possible. Summary The ConcurrentDictionary is a very efficient and thread-safe version of the Dictionary generic collection.  It has all the benefits of type-safety that it’s generic collection counterpart does, and in addition is extremely efficient especially when there are more reads than writes concurrently. Tweet Technorati Tags: C#, .NET, Concurrent Collections, Collections, Little Wonders, Black Rabbit Coder,James Michael Hare

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• Install a web certificate on an Android device

  - by martani_net

  To gain access to WIFI at university I have to login with my user/pass credentials. The certificate of their website (the local home page that asks for the credentials) is not recognized as a trusted certificate, so we install it separately on our computers. The problem is that I don't take my laptop with me often to university, so I usually want to connect using my HTC Magic, but I have no clue on how to install the certificate separately on Android, it is always rejected. [Edit2] : this is what is stated in their website Need for installation of official certificates CyberTrust validated by the CRU (http://www.cru.fr/wiki/scs/) The certificates contain information certified to generate encryption keys for data exchange, called "sensitive" as the password of a user. By connecting to CanalIP-UPMC, for example, the user must validate the identity of the server accepting the certificate appears on the screen in a "popup window". In reality, the user is unable to validate a certificate knowing, because a simple visual check of the license is impossible. Therefore, the certificates of the certification authority (CRU-Cybertrust Educationnal-ca.ca Cybertrust and-global-root-ca.ca) must be installed prior to the browser for the validity of the certificate server can be controlled automatically. Before you connect to the network-UPMC CanalIP you must register in your browser through the certification authority Cybertrust-Educationnal-ca.ca Download the Cybertrust-Educationnal-ca.ca, depending on your browser and select the link below : With Internet Explorer, click on the link following. With Firefox, click on the link following. With Safari, click the link following. If this procedure is not respected, a real risk is incurred by the user: that of being robbed password LDAP directory UPMC. A malicious server may in fact try very easily attack type "man-in-the-middle" by posing as the legitimate server at UPMC. The theft of a password allows the attacker to steal an identity for transactions over the Internet can engage the responsibility of the user trapped ... This is their website : http://www.canalip.upmc.fr/doc/Default.htm (in French, Google-translate it :)) Anyone knows how to install a web certificate on Android?

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• When tab groups are loaded, Firefox becomes unresponsible for minutes (Unresponsive script)

  - by unor

  I have several tab groups (~ 20) in Firefox. I can start the browser without any problems. However, as soon as I … click at the "Group tabs" icon in the toolbar, or right-click on a tab and hover over "Move to tab group", … Firefox becomes unresponsible/freezes for a rather long time (more than 2 minutes). It seems to load all tab groups (it doesn't load all the pages! I deactivated this in the settings). While this is happening, I get several "Unresponsive script" warnings, like: Script: chrome://global/content/bindings/tabbox.xml:0 (most of the time) Script: chrome://global/content/bindings/tabbox.xml:418 Script: chrome://browser/content/tabview.js:400 Script: chrome://browser/content/tabview.js:522 Script: resource://modules/sessionstore/SessionStore.jsm:3578 Script: resource:///components/PageThumbsProtocol.js:79 (rare) Script: resource://gre/modules/XPCOMUtils.jsm:323 (rare) (probably also other warnings, didn't record them yet, though) On all of these I click "Continue". After ~ 2-3 minutes and 3-5 warnings, I can use Firefox again. Now I can switch tab groups without any problems. Why is this happening? How can I prevent the long loading time? Is there maybe a about:config setting I could try? I started Firefox in Safe Mode (= without any add-ons): the problem still exists.

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