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• File based caching under PHP

  - by azatoth

  I've been using http://code.google.com/p/phpbrowscap/ for a project, and it usually works nice. But a few times it's cache, which is plain php-files (see http://code.google.com/p/phpbrowscap/source/browse/trunk/browscap/Browscap.php#372 et. al.), has been "zeroed", i.e. the whole cache file has become large blob of NULLs. Instead of trying to find out why the files become NULL, I though perhaps it might be better to change the caching strategy to something more resilient. So I do wonder if you has any good ideas what would be a good solution; I've been looking at http://www.jongales.com/blog/2009/02/18/simple-file-based-php-cache-class/ and http://www.phpclasses.org/package/313-PHP-Cache-arbitrary-data-in-files-.html and I also though of just saving an serialized array to the file instead of pure php as it's been doing now; But I'm uncertain what approach I should target here. I'm grateful for any insight into this area of technology, as I know it's complex from a performance point of view.

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• converting a timestring to a duration

  - by radman

  Hi, At the moment I am trying to read in a timestring formatted and create a duration from that. I am currently trying to use the boost date_time time_duration class to read and store the value. boost date_time provides a method time_duration duration_from_string(std::string) that allows a time_duration to be created from a time string and it accepts strings formatted appropriately ("[-]h[h][:mm][:ss][.fff]".). Now this method works fine if you use a correctly formatted time string. However if you submit something invalid like "ham_sandwich" or "100" then you will still be returned a time_duration that is not valid. Specifically if you try to pass it to a standard output stream then an assertion will occur. My question is: Does anyone know how to test the validity of the boost time_duration? and failing that can you suggest another method of reading a timestring and getting a duration from it? Note: I have tried the obvious testing methods that time_duration provides; is_not_a_date_time(), is_special() etc and they don't pick up that there is an issue. Using boost 1.38.0

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• What arguments to use to explain why SQL Server is far better then a flat file

  - by jamone

  The higher ups in my company were told by good friends that flat files are the way to go, and we should switch from SQL Server to them for everything we do. We have over 300 servers and hundreds of different databases. From just the few I'm involved with we have 10 billion records in quite a few of them with upwards of 100k new records a day and who knows how many updates... Me and a couple others need to come up with a response saying why we shouldn't do this. Most of our stuff is ASP.NET with some legacy ASP. We thought that making a simple console app that tests/times the same interactions between a flat file (stored on the network) and SQL over the network doing large inserts, searches, updates etc along with things like network disconnects randomly. This would show them how bad flat files can be especially when you are dealing with millions of records. What things should I use in my response? What should I do with my demo code to illustrate this? My sort list so far: Security Concurrent access Performance with large amounts of data Amount of time to do such a massive rewrite/switch Lack of transactions PITA to map relational data to flat files NTFS doesn't support tons of files in a directory well I fear that this will be a great post on the Daily WTF someday if I can't stop it now.

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• Scope of "library" methods

  - by JS

  Hello, I'm apparently laboring under a poor understanding of Python scoping. Perhaps you can help. Background: I'm using the 'if name in "main"' construct to perform "self-tests" in my module(s). Each self test makes calls to the various public methods and prints their results for visual checking as I develop the modules. To keep things "purdy" and manageable, I've created a small method to simplify the testing of method calls: def pprint_vars(var_in): print("%s = '%s'" % (var_in, eval(var_in))) Calling pprint_vars with: pprint_vars('some_variable_name') prints: some_variable_name = 'foo' All fine and good. Problem statement: Not happy to just KISS, I had the brain-drizzle to move my handy-dandy 'pprint_vars' method into a separate file named 'debug_tools.py' and simply import 'debug_tools' whenever I wanted access to 'pprint_vars'. Here's where things fall apart. I would expect import debug_tools foo = bar debug_tools.pprint_vars('foo') to continue working its magic and print: foo = 'bar' Instead, it greets me with: NameError: name 'some_var' is not defined Irrational belief: I believed (apparently mistakenly) that import puts imported methods (more or less) "inline" with the code, and thus the variable scoping rules would remain similar to if the method were defined inline. Plea for help: Can someone please correct my (mis)understanding of scoping regards imports? Thanks, JS

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• _dl_runtime_resolve -- When do the shared objects get loaded in to memory?

  - by windfinder

  We have a message processing system with high performance demands. Recently we have noticed that the first message takes many times longer then subsequent messages. A bunch of transformation and message augmentation happens as this goes through our system, much of it done by way of external lib. I just profiled this issue (using callgrind), comparing a "run" of just one message with a "run" of many messages (providing a baseline of comparison). The main difference I see is the function "do_lookup_x" taking up a huge amount of time. Looking at the various calls to this function, they all seem to be called by the common function: _dl_runtime_resolve. Not sure what this function does, but to me this looks like the first time the various shared libraries are being used, and are then being loaded in to memory by the ld. Is this a correct assumption? That the binary will not load the shared libraries in to memory until they are being prepped for use, therefore we will see a massive slowdown on the first message, but on none of the subsequent? How do we go about avoiding this? Note: We operate on the microsecond scale.

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• SQL Server full text query across multiple tables - why so slow?

  - by Mikey Cee

  Hi. I'm trying to understand the performance of an SQL Server 2008 full-text query I am constructing. The following query, using a full-text index, returns the correct results immediately: SELECT O.ID, O.Name FROM dbo.EventOccurrence O WHERE FREETEXT(O.Name, 'query') ie, all EventOccurrences with the word 'query' in their name. And the following query, using a full-text index from a different table, also returns straight away: SELECT V.ID, V.Name FROM dbo.Venue V WHERE FREETEXT(V.Name, 'query') ie. all Venues with the word 'query' in their name. But if I try to join the tables and do both full-text queries at once, it 12 seconds to return: SELECT O.ID, O.Name FROM dbo.EventOccurrence O INNER JOIN dbo.Event E ON O.EventID = E.ID INNER JOIN dbo.Venue V ON E.VenueID = V.ID WHERE FREETEXT(E.Name, 'search') OR FREETEXT(V.Name, 'search') Here is the execution plan: http://uploadpad.com/files/query.PNG From my reading, I didn't think it was even possible to make a free text query across multiple tables in this way, so I'm not sure I am understanding this correctly. Note that if I remove the WHERE clause from this last query then it returns all results within a second, so it's definitely the full-text that is causing the issue here. Can someone explain (i) why this is so slow and (ii) if this is even supported / if I am even understanding this correctly. Thanks in advance for your help.

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• URL equals and checking Internet access

  - by James P.

  On http://java.sun.com/j2se/1.5.0/docs/api/java/net/URL.html it states that: Compares this URL for equality with another object. If the given object is not a URL then this method immediately returns false. Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file. Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null. Since hosts comparison requires name resolution, this operation is a blocking operation. Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP. According to this, equals will only work if name resolution is possible. Since I can't be sure that a computer has internet access at a given time, should I just use Strings to store addresses instead? Also, how do I go about testing if access is available when requested?

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• How to access a TextView element in a BroadcastReceiver

  - by ric03uec

  Hello, I am testing a simple widget in android and using Alarms to update a TextView at regular intervals. The problem is that in the BroadcastReceiver class I cannot access the TextView element, which I want to get updated when the alarm expires. The class is being called properly because the Toast i have put there is giving the appropriate message. The following code is from the class where I configure the widget and set the timers. public void onCreate(Bundle bundle) { super.onCreate(bundle); Intent intent = getIntent(); Bundle extras = intent.getExtras(); if(extras != null){ mWidgetId = extras.getInt(AppWidgetManager.EXTRA_APPWIDGET_ID, AppWidgetManager.INVALID_APPWIDGET_ID); AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(WidgetConfigure.this); RemoteViews views = new RemoteViews(WidgetConfigure.this.getPackageName(), R.layout.widget_layout); views.setTextViewText(R.id.quote, "Widget Loaded From Activity"); appWidgetManager.updateAppWidget(mWidgetId, views); setTimer(); //set the timers... setResult();// set the result... } } Now i want to update the same TextView when the BroadCastReceiver is called after the timer expires. I have tried the code provided in the ExampleAppWidget example provided in android api demos and that isnt working out. How can i set the required text? Thankx in advance

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• Sending and receiving IM messages via controller in Rails

  - by Grnbeagle

  Hi, I need a way to handle XMPP communication in my Rails app. My requirements are: Keep an instance of XMPP client running and logged in as one specific user (my bot user) Trigger an event from a controller to send a message and wait for a reply. The message is sent to another machine equipped with a bot so that the reply is supposed to be returned quickly. I installed xmpp4r and backgrounDrb similar to what's described here, but backgrounDrb seems to have evolved and I couldn't get it to wait for a reply. If it has to happen asynchronously, I am willing to use a server-push technology to notify the browser when the reply arrives. To give you a better idea, here are snippets of my code: (In controller) class ServicesController < ApplicationController layout 'simple' def index render :text => "index" end def show @my_service = Service.find(params[:id]) worker = MiddleMan.worker(:jabber_agent_worker) worker.send_request(:arg => {:jid => "someuser@someserver", :cmd => "help"}) render :text => "testing" end end (In worker script) require 'xmpp4r' require 'logger' class JabberAgentWorker < BackgrounDRb::MetaWorker set_worker_name :jabber_agent_worker def create(args = nil) jid = Jabber::JID.new('myagent@myserver') @client = Jabber::Client.new(jid) @client.connect @client.auth('pass') @client.send(Jabber::Presence.new.set_show(:chat).set_status('BackgrounDRb')) @client.add_message_callback do |message| logger.info("**** messaged received: #{message}") # never reaches here end end def send_request(args = nil) to_jid = Jabber::JID.new(args[:jid]) message = Jabber::Message::new(to_jid, args[:cmd]).set_type(:normal).set_id('1') @client.send(message) end end If anyone can tell me any of the following, I'd much appreciate it: issue with my backgrounDrb usage other background process alternatives appropriate for XMPP interactions other ways of achieving this Thanks in advance.

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• How to receive Email in JEE application

  - by Hank

  Obviously it's not so difficult to send out emails from a JEE application via JavaMail. What I am interested in is the best pattern to receive emails (notification bounces, mostly)? I am not interested in IMAP/POP3-based approaches (polling the inbox) - my application shall react to inbound emails. One approach I could think of would be Keep existing MTA (postfix on linux in my case) - ops team already knows how to configure / operate it For every mail that arrives, spawn a Java app that receives the data and sends it off via JMS. I could do this via an entry in /etc/aliases like myuser: "|/path/to/javahelper" with javahelper calling the Java app, passing STDIN along. MDB (part of JEE application) receives JMS message, parses it, detects bounce message and acts accordingly. Another approach could be Open a listening network socket on port 25 on the JEE application container. Associate a SessionBean with the socket. Bean is part of JEE application and can parse/detect bounces/handle the messages directly. Keep existing MTA as inbound relay, do all its security/spam filtering, but forward emails to myuser (that pass the filter) to the JEE application container, port 25. The first approach I have done before (albeit in a different language/setup). From a performance and (perceived) cleanliness point of view, I think the second approach is better, but it would require me to provide a proper SMTP transport implementation. Also, I don't know if it's at all possible to connect a network socket with a bean... What is your recommendation? Do you have details about the second approach?

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• Should java try blocks be scoped as tightly as possible?

  - by isme

  I've been told that there is some overhead in using the Java try-catch mechanism. So, while it is necessary to put methods that throw checked exception within a try block to handle the possible exception, it is good practice performance-wise to limit the size of the try block to contain only those operations that could throw exceptions. I'm not so sure that this is a sensible conclusion. Consider the two implementations below of a function that processes a specified text file. Even if it is true that the first one incurs some unnecessary overhead, I find it much easier to follow. It is less clear where exactly the exceptions come from just from looking at statements, but the comments clearly show which statements are responsible. The second one is much longer and complicated than the first. In particular, the nice line-reading idiom of the first has to be mangled to fit the readLine call into a try block. What is the best practice for handling exceptions in a funcion where multiple exceptions could be thrown in its definition? This one contains all the processing code within the try block: void processFile(File f) { try { // construction of FileReader can throw FileNotFoundException BufferedReader in = new BufferedReader(new FileReader(f)); // call of readLine can throw IOException String line; while ((line = in.readLine()) != null) { process(line); } } catch (FileNotFoundException ex) { handle(ex); } catch (IOException ex) { handle(ex); } } This one contains only the methods that throw exceptions within try blocks: void processFile(File f) { FileReader reader; try { reader = new FileReader(f); } catch (FileNotFoundException ex) { handle(ex); return; } BufferedReader in = new BufferedReader(reader); String line; while (true) { try { line = in.readLine(); } catch (IOException ex) { handle(ex); break; } if (line == null) { break; } process(line); } }

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• Project management: Implementing custom errors in VS compilation process

  - by David Lively

  Like many architects, I've developed coding standards through years of experience to which I expect my developers to adhere. This is especially a problem with the crowd that believes that three or four years of experience makes you a senior-level developer.Approaching this as a training and code review issue has generated limited success. So, I was thinking that it would be great to be able to add custom compile-time errors to the build process to more strictly enforce this and other guidelines. For instance, we use stored procedures for ALL database access, which provides procedure-level security, db encapsulation (table structure is hidden from the app), and other benefits. (Note: I am not interested in starting a debate about this.) Some developers prefer inline SQL or parametrized queries, and that's fine - on their own time and own projects. I'd like a way to add a compilation check that finds, say, anything that looks like string sql = "insert into some_table (col1,col2) values (@col1, @col2);" and generates an error or, in certain circumstances, a warning, with a message like Inline SQL and parametrized queries are not permitted. Or, if they use the var keyword var x = new MyClass(); Variable definitions must be explicitly typed. Do Visual Studio and MSBuild provide a way to add this functionality? I'm thinking that I could use a regular expression to find unacceptable code and generate the correct error, but I'm not sure what, from a performance standpoint, is the best way to to integrate this into the build process. We could add a pre- or post-build step to run a custom EXE, but how can I return line- and file-specifc errors? Also, I'd like this to run after compilation of each file, rather than post-link. Is a regex the best way to perform this type of pattern matching, or should I go crazy and run the code through a C# parser, which would allow node-level validation via the parse tree? I'd appreciate suggestions and tales of prior experience.

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• How to manage sessions in NHibernate unit tests?

  - by Ben

  I am a little unsure as to how to manage sessions within my nunit test fixtures. In the following test fixture, I am testing a repository. My repository constructor takes in an ISession (since I will be using session per request in my web application). In my test fixture setup I configure NHibernate and build the session factory. In my test setup I create a clean SQLite database for each test executed. [TestFixture] public class SimpleRepository_Fixture { private static ISessionFactory _sessionFactory; private static Configuration _configuration; [TestFixtureSetUp] // called before any tests in fixture are executed public void TestFixtureSetUp() { _configuration = new Configuration(); _configuration.Configure(); _configuration.AddAssembly(typeof(SimpleObject).Assembly); _sessionFactory = _configuration.BuildSessionFactory(); } [SetUp] // called before each test method is called public void SetupContext() { new SchemaExport(_configuration).Execute(true, true, false); } [Test] public void Can_add_new_simpleobject() { var simpleObject = new SimpleObject() { Name = "Object 1" }; using (var session = _sessionFactory.OpenSession()) { var repo = new SimpleObjectRepository(session); repo.Save(simpleObject); } using (var session =_sessionFactory.OpenSession()) { var repo = new SimpleObjectRepository(session); var fromDb = repo.GetById(simpleObject.Id); Assert.IsNotNull(fromDb); Assert.AreNotSame(simpleObject, fromDb); Assert.AreEqual(simpleObject.Name, fromDb.Name); } } } Is this a good approach or should I be handling the sessions differently? Thanks Ben

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• Blackberry app stuck trying to access a server.

  - by Tejaswi Yerukalapudi

  Hi, I've built a ASP.NET webservice and I'm trying to access it from a Blackberry. I've been testing it out with multiple devices and the simulator and it works fine, but there's just the one Blackberry 9000 (It's not the model, I've tried it out with another Blackberry 9000), and it's stuck waiting for a response from the server. Relevant section of the code that accesses this - System.out.println("IN ntwk access thread, start point"); HttpConnection connection = (HttpConnection)Connector.open(serviceURL + WSNAME); connection.setRequestMethod(HttpConnection.POST); connection.setRequestProperty("Content-type", "application/x-www-form-urlencoded"); connection.setRequestProperty("Content-length", Integer.toString(postData1.length)); OutputStream requestOutput = connection.openOutputStream(); requestOutput.write(postData1); requestOutput.close(); final int responseCode = connection.getResponseCode(); if(responseCode!= HttpConnection.HTTP_OK) { //Process the error condition } // Request succeeded process the data. It seems to be getting stuck after connection.getResponseCode(). Is there some way I can verify what's going wrong with this particular device? Thanks, Teja

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• Technology and language for a stable Digital Audio Workstation development

  - by Kill KRT

  Hi, I'm designing a cross platform (Windows/Linux/OS X) application, something like a digital audio workstation. I'd like to create a software where users have a fully featured sequencer (multiple tracks with automation) and where it is possible to create instruments using a visual language (as Pure Data/Max MSP). Ehm... I know that I've already posted a question about a related issue... But in order to decide which technology I should use, I think I'd better to make more investigation. I'm a quite experted user of audio trackers (Renoise, Protracker,...) and sequencers (FL Studio, Cubase 5), but I didn't ever try to develop even a basic audio tracker. I know just the basic theory of mixing sound and know how basically a DSP works. My questions are: Where I can find a good tutorial/guide/book about this issue? Do you think using C# (with NAudio) could dramatically reduce performance? I know C++ would be the best choice, but I find C# so elegant and easy to build and port, while C++ is so powerful and fast, but there are too #define and bad things for my taste! ;-) Thank you.

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• Help with jQuery Ajax calling ASMX which returns string.

  - by Jason Evans

  Hi there. I have the following jQuery ajax call setup: function Testing() { var result = ''; $.ajax({ url: 'BookingUtils.asmx/GetNonBookableSlots', dataType: 'text', error: function(error) { alert('GetNonBookableSlots Error'); }, success: function(data) { alert('GetNonBookableSlots'); result = data; } }); return result; } Here is the web service I'm trying to call: [WebMethod] public string GetNonBookableSlots() { return "fhsdfuhsiufhsd"; } When I run the jQuery code, there is no error or success event fired (none of the alerts are called). In fact, nothing happens at all, the javascript code just moves on to return statement at the end. I put a breakpoint in the web service code and it does get hit, but when I leave that method I end up on the return statement anyway. Can someone give me some tips on how I should be configuring the ajax call correctly, as I feel that I'm doing this wrong. The webservice just needs to return a string, no XML or JSON involved. Cheers. Jas.

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• Vehicle License Plate Detection

  - by Ash

  Hey all Basically for my final project at university, I'm developing a vehicle license plate detection application. Now I consider myself an intermediate programmer, however my mathematics knowledge lacks anything above secondary school, therefore producing detection formulae is basically impossible. I've spend a good amount of time looking up academic papers such as: http://www.scribd.com/doc/266575/Detecting-Vehicle-License-Plates-in-Images http://www.cic.unb.br/~mylene/PI_2010_2/ICIP10/pdfs/0003945.pdf http://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-b05.pdf When it comes to the maths, I'm lost. Due to this testing various graphic images proved productive, for example: to However this approach is only catered to that particular image, and if the techniques were applied to different images, I'm sure a different, most likely poorer conversion would occur. I've read about a formula called the bottom hat morphology transform, which according to the first does the following: "Basically, the trans- formation keeps all the dark details of the picture, and eliminates everything else (including bigger dark regions and light regions)." Sadly I can't find much information on this, however the image within the documentation near the end of the report shows it's effectiveness. I'm aware this is complicated and vast, I'd just appreciate a little advice, even in terms of what transformation techniques I should focus on developing, or algorithm regarding edge detection or pixel detection. Few things I need to add Developing in C Sharp Confining the project to UK registration plates only I can basically choose the images to convert as a demonstration Thanks

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• Execute process conditionally in Windows PowerShell (e.g. the && and || operators in Bash)

  - by Dustin

  I'm wondering if anybody knows of a way to conditionally execute a program depending on the exit success/failure of the previous program. Is there any way for me to execute a program2 immediately after program1 if program1 exits successfully without testing the LASTEXITCODE variable? I tried the -band and -and operators to no avail, though I had a feeling they wouldn't work anyway, and the best substitute is a combination of a semicolon and an if statement. I mean, when it comes to building a package somewhat automatically from source on Linux, the && operator can't be beaten: # Configure a package, compile it and install it ./configure && make && sudo make install PowerShell would require me to do the following, assuming I could actually use the same build system in PowerShell: # Configure a package, compile it and install it .\configure ; if ($LASTEXITCODE -eq 0) { make ; if ($LASTEXITCODE -eq 0) { sudo make install } } Sure, I could use multiple lines, save it in a file and execute the script, but the idea is for it to be concise (save keystrokes). Perhaps it's just a difference between PowerShell and Bash (and even the built-in Windows command prompt which supports the && operator) I'll need to adjust to, but if there's a cleaner way to do it, I'd love to know.

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• rookie MySql question about paging; Is one query enough?

  - by Camran

  I have managed to get paging to work, almost. I want to display to the user, total nr of records found, and the currently displayed records. Ex: 4000 found, displaying 0-100. I am testing this with the nr 2 (because I don't have that many records, have like 20). So I am using LIMIT $start, $nr_results; Do I have to make two queries in order to display the results the way I want, one query fetching all records and then make a mysql_num_rows to get all records, then the one with the LIMIT ? I have this: mysql_num_rows($qry_result); $total_pages = ceil($num_total / $res_per_page); //$res_per_page==2 and $num_total = 2 if ($p - 10 < 1) { $pagemin=1; } else { $pagemin = $p - 10; } if ($p + 10 $total_pages) { $pagemax = $total_pages; } else { $pagemax = $p + 10; } Here is the query: SELECT mt.*, fordon.*, boende.*, elektronik.*, business.*, hem_inredning.*, hobby.* FROM classified mt LEFT JOIN fordon ON fordon.classified_id = mt.classified_id LEFT JOIN boende ON boende.classified_id = mt.classified_id LEFT JOIN elektronik ON elektronik.classified_id = mt.classified_id LEFT JOIN business ON business.classified_id = mt.classified_id LEFT JOIN hem_inredning ON hem_inredning.classified_id = mt.classified_id LEFT JOIN hobby ON hobby.classified_id = mt.classified_id ORDER BY modify_date DESC LIMIT 0, 2 Thanks, if you need more input let me know. Basically Q is, do I have to make two queries?

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• iPhone: Using dispatch_after to mimick NSTimer

  - by Joseph Tura

  Don't know a whole lot about blocks. How would you go about mimicking a repeating NSTimer with dispatch_after? My problem is that I want to "pause" a timer when the app moves to the background, but subclassing NSTimer does not seem to work. I tried something which seems to work. I cannot judge its performance implications or whether it could be greatly optimized. Any input is welcome. #import "TimerWithPause.h" @implementation TimerWithPause @synthesize timeInterval; @synthesize userInfo; @synthesize invalid; @synthesize invocation; + (TimerWithPause *)scheduledTimerWithTimeInterval:(NSTimeInterval)aTimeInterval target:(id)aTarget selector:(SEL)aSelector userInfo:(id)aUserInfo repeats:(BOOL)aTimerRepeats { TimerWithPause *timer = [[[TimerWithPause alloc] init] autorelease]; timer.timeInterval = aTimeInterval; NSMethodSignature *signature = [[aTarget class] instanceMethodSignatureForSelector:aSelector]; NSInvocation *aInvocation = [NSInvocation invocationWithMethodSignature:signature]; [aInvocation setSelector:aSelector]; [aInvocation setTarget:aTarget]; [aInvocation setArgument:&timer atIndex:2]; timer.invocation = aInvocation; timer.userInfo = aUserInfo; if (!aTimerRepeats) { timer.invalid = YES; } [timer fireAfterDelay]; return timer; } - (void)fireAfterDelay { dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, self.timeInterval * NSEC_PER_SEC); dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); dispatch_after(delay, queue, ^{ [invocation performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:NO]; if (!invalid) { [self fireAfterDelay]; } }); } - (void)invalidate { invalid = YES; [invocation release]; invocation = nil; [userInfo release]; userInfo = nil; } - (void)dealloc { [self invalidate]; [super dealloc]; } @end

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• Is there a practical benefit to casting a NULL pointer to an object and calling one of its member fu

  - by zdawg

  Ok, so I know that technically this is undefined behavior, but nonetheless, I've seen this more than once in production code. And please correct me if I'm wrong, but I've also heard that some people use this "feature" as a somewhat legitimate substitute of a lacking aspect of the current C++ standard, namely, the inability to obtain the address (well, offset really) of a member function. For example, this is out of a popular implementation of a PCRE (Perl-compatible Regular Expression) library: #ifndef offsetof #define offsetof(p_type,field) ((size_t)&(((p_type *)0)->field)) #endif One can debate whether the exploitation of such a language subtlety in a case like this is valid or not, or even necessary, but I've also seen it used like this: struct Result { void stat() { if(this) // do something... else // do something else... } }; // ...somewhere else in the code... ((Result*)0)->stat(); This works just fine! It avoids a null pointer dereference by testing for the existence of this, and it does not try to access class members in the else block. So long as these guards are in place, it's legitimate code, right? So the question remains: Is there a practical use case, where one would benefit from using such a construct? I'm especially concerned about the second case, since the first case is more of a workaround for a language limitation. Or is it? PS. Sorry about the C-style casts, unfortunately people still prefer to type less if they can.

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• A standard set of questions to ask an interviewer?

  - by Rob Wells

  We have had many questions for interviewers to ask interviewees. But none addressing information flow in the other direction, interviewee to interviewer. Just an indirect question about "deal breakers" and one about "finding dream jobs". What I'm after is when you're interviewing at a company do you have a set of questions that you like to ask to help get a feel for the company and the work environment? I have a series of questions that I like to ask that range from the development environment to testing techniques to how the team get on together. Anything else you'd like to ask? Edit: I moved my original list of interviewer questions to my answer below. I've also gone through the other answers and added the ones thought were useful in to that answer. The answer is community wiki so feel free to add anything useful. N.B. This is my first cut of categories. Feel free to modify/add/etc. the categories. Or to recategorise the questions themselves.

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• Collision of dot and line in 2D space

  - by Anderiel

  So i'm trying to make my first game on android. The thing is i have a small moving ball and i want it to bounce from a line that i drew. For that i need to find if the x,y of the ball are also coordinates of one dot from the line. I tried to implement these equations about lines x=a1 + t*u1 y=a2 + t*u2 = (x-a1)/u1=(y-a2)/u2 (t=t which has to be if the point is on the line) where x and y are the coordinates im testing, dot[a1,a2] is a dot that is on the line and u(u1,u2) is the vector of the line. heres the code: public boolean Collided() { float u1 =Math.abs(Math.round(begin_X)-Math.round(end_X)); float u2 =Math.abs(Math.round(begin_Y)-Math.round(end_Y)); float t_x =Math.round((elect_X - begin_X)/u1); float t_y =Math.round((elect_Y - begin_Y)/u2); if(t_x==t_y) { return true; } else { return false; } } points [begin_X,end_X] and [begin_Y,end_Y] are the two points from the line and [elect_X,elect_Y] are the coordinates of the ball theoreticaly it should work, but in the reality the ball most of the time just goes straigth through the line or bounces somewhere else where it shouldnt

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• JTA or LOCAL transactions in JPA2+Hibernate 3.6.0?

  - by Pangea

  We are in the process of re-thinking our tech stack and below are our choices (We can't live without Spring and Hibernate due to the complexity etc of the app). We are also moving from J2EE 1.4 to JEE 5. Tech stack JEE 5 JPA 2.0 (I know JEE 5 only supports JPA 1.0 but we want to use Hibernate as the JPA provider) Hibernate 3.6.0 (We already have lots of hbm files with custom types etc. so we doesn't want to migrate them at this time to JPA. This means we want both jpa/hbm mappings work together and hence the Hibernate as the JPA provider instead of using the default that comes with App Server) Now the problems is that I want to stick with local transactions but other team members want to use JTA. I have been working with J2EE for last 9 years and I've heard time and again people suggesting to stick with local transactions if I doesn't need two phase commits. This is not only for performance reasons but debugging/troubleshooting a local transaction is lot easier than a distributed transaction. My suggestion is to use spring declarative transaction management + local transactions (HibernateTransactionManager) I want to make sure if I am being paranoid or I have a valid point. I'd like to hear what the rest of the JEE world thinks. Thank you.

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• How can i get HWND of external application's listview? In Windows Api using c++

  - by Marko29

  So i am trying to make app to get content of my explorer listviews and get item text etc.. from it but here are the problems... If i inspect windows explorer folder(using spy++) with listview, just for testing purposes i will use random folder. It shows me that caption of the window is "FolderView" with class "SysListView32" and the top level window where this listview is nested is called "reference", this is also the title of windows explorer folder where all the files are. So what i do is.. HWND hWndLV = FindWindow(NULL, TEXT("reference")); // first i get hwnd of the main window, this is where listview window is also nested according to spy++, thats why i do this first. HWND child = FindWindowEx(hWndLV, NULL,NULL,TEXT("FolderView")); // trying to get hwnd of the listview here but it fails, same happens if i also put the class name along as HWND child = FindWindowEx(hWndLV, NULL,TEXT("SysListView32"),TEXT("FolderView")); I am using bool test = IsWindow(child); to test for fail, also VS debugger shows 0x0000000000 each time so i am sure i am reading results well. So i am stuck on this probably simple thing for most of people:( p.s. i am on vista64(if that matters anyhow) edit: It appears that this function works only if i search the first nested level of a parent window i am searching. So i assume what i need is a way to get handle with some sort of deep nested level search. I also tried to go step by step by defining hwnd of every parent then i use findwindowex on it but oh boy then i get to the point where there are 5 nested windows all with the same name and only one of them contains my listview, so nice uh?

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