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  • Protecting critical sections based on a condition in C#

    - by NAADEV
    Hello, I'm dealing with a courious scenario. I'm using EntityFramework to save (insert/update) into a SQL database in a multithreaded environment. The problem is i need to access database to see whether a register with a particular key has been already created in order to set a field value (executing) or it's new to set a different value (pending). Those registers are identified by a unique guid. I've solved this problem by setting a lock since i do know entity will not be present in any other process, in other words, i will not have same guid in different processes and it seems to be working fine. It looks something like that: static readonly object LockableObject = new object(); static void SaveElement(Entity e) { lock(LockableObject) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } But this implies when i have a huge ammount of requests to be saved, they will be queued. I wonder if there is something like that (please, take it just as an idea): static void SaveElement(Entity e) { (using ThisWouldBeAClassToProtectBasedOnACondition protector = new ThisWouldBeAClassToProtectBasedOnACondition(e => e.UniqueId) { Entity e2 = Repository.FindByKey(e); if (e2 != null) { Repository.Insert(e2); } else { Repository.Update(e2); } } } The idea would be having a kind of protection that protected based on a condition so each entity e would have its own lock based on e.UniqueId property. Any idea?

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  • What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

    - by Tom Morris
    I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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  • Phonegap Android application exiting - but not really - when home button is pressed

    - by Lucas T
    I have created an Phonegap 1.5/Android application. My client reports that, when he leaves the app using the Home button, and then relaunches it using the app icon, the app relaunches from the start instead of resuming. However, when he holds the home button, the app appears in the running apps, and when he accesses the app through this menu, the app resumes in the expected way. I thought this could be linked to the app being automatically closed by the OS due to a lack of memory, but if that was the case the app shouldn't appear in the running apps. I could not reproduce the bug on my Sony Ericsson XPERIA with Android 2.3.4, the client has experienced this behaviour on a Motorola Defy and on another phone (i'll add the reference of the other phone and the OS versions as soon as I get them). The initialization process of the app is declared this way : window.addEventListener('load', function(){ document.addEventListener('deviceready', _onDeviceReady, false); }, false); Could this be fixed by attaching the processes to other events (although I doubt it, the app really seems to be relaunched from the start) ? Is there a declaration to make in the Android Manifest to prevent this behavior ? Is that a known bug in some Android phones/versions ?

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  • Is there a way to validate the presence of Javadoc and/or inline code comments?

    - by Chris Aldrich
    We are trying to put quality code processes in place for a large project I am working on. Right now a lot of developers are not putting in Javadoc or in-line code comments into their code. Ok right now. But it will severely hurt us in the very near future. We are using Maven 2.0.9 as our build tool, as well as Hudson for Continuous Integration. We are using Subversion as our source versioning tool/code repository, Rational Application Developer and Rational Softare Architect (essentially Eclipse) 7.5.1 as our IDE's, and then Subclipse as our Eclipse plug-in to connect to SVN. Is there a plug-in or a way to validate that a developer put in Javadoc and/or in-line code comments in order to allow a commit to SVN? This isn't intended to be a substitute for good code reviews, but merely a help to make sure that developers are reminded to add this documentation before committing. We are still intending on conducting code reviews that would also review documentation. Has anyone found any plug-ins for something like this? Any links? Any ideas?

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  • Custom UIButton Memory Management in dealloc

    - by ddawber
    I am hoping to clarify the processes going on here. I have created a subclass of UIButton whose init method looks like this: - (id)initWithTitle:(NSString *)title frame:(CGRect)btnFrame { self = [UIButton buttonWithType:UIButtonTypeCustom]; [self setTitle:title forState:UIControlStateNormal]; self.frame = btnFrame; return self; } In my view controller I am creating one of these buttons and adding it as a subview: myButton = [[CustomButton alloc] initWithTitle:@"Title" frame:someFrame]; [self.view addSubview:myButton]; In the view controller's dealloc method I log the retain count of my button: - (void)dealloc { NSLog(@"RC: %d", [myButton retainCount]); //RC = 2 [super dealloc]; NSLog(@"RC: %d", [myButton retainCount]); //RC = 1 } The way I understand it, myButton is not actually retained, even though I invoked it using alloc, because in my subclass I created an autorelease button (using buttonWithType:). In dealloc, does this mean that, when dealloc is called the superview releases the button and its retain count goes down to 1? The button has not yet been autoreleased? Or do I need to get that retain count down to zero after calling [super dealloc]? Cheers.

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  • Yeoman 'grunt test' fails on clean project with 'port already in use'

    - by XMLilley
    With: Mac OS 10.8.4 Node 0.10.12 npm 1.3.1 grunt-cli 0.1.9 yo 1.0.0-rc.1 bower 0.9.2 [email protected] I encounter the following error with a clean yo angular project, followed by grunt server then grunt test: Running "connect:test" (connect) task Fatal error: Port 9000 is already in use by another process. I'm new to Yeoman and am stumped. I've deleted my original project and created a new one in a fresh folder just to make sure I wasn't overlooking any invisible configs. I restarted the machine to make sure I wasn't running any temporary server processes I had forgotten about. After all attempts, the basic server starts fine, attaches to Chrome, and the watcher updates the browser on any changes. (Notably, the server is running on 9000, which seems odd for the test-runner to also be trying to use 9000.) But I get that same error on attempting to start the test runner. Is this something I can fix, or an issue I should report to the Yeoman team? Thanks.

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  • Limit CPU usage of a process

    - by jb
    I have a service running which periodically checks a folder for a file and then processes it. (Reads it, extracts the data, stores it in sql) So I ran it on a test box and it took a little longer thaan expected. The file had 1.6 million rows, and it was still running after 6 hours (then I went home). The problem is the box it is running on is now absolutely crippled - remote desktop was timing out so I cant even get on it to stop the process, or attach a debugger to see how far through etc. It's solidly using 90%+ CPU, and all other running services or apps are suffering. The code is (from memory, may not compile): List<ItemDTO> items = new List<ItemDTO>(); using (StreamReader sr = fileInfo.OpenText()) { while (!sr.EndOfFile) { string line = sr.ReadLine() try { string s = line.Substring(0,8); double y = Double.Parse(line.Substring(8,7)); //If the item isnt already in the collection, add it. if (items.Find(delegate(ItemDTO i) { return (i.Item == s); }) == null) items.Add(new ItemDTO(s,y)); } catch { /*Crash*/ } } return items; } - So I am working on improving the code (any tips appreciated). But it still could be a slow affair, which is fine, I've no problems with it taking a long time as long as its not killing my server. So what I want from you fine people is: 1) Is my code hideously un-optimized? 2) Can I limit the amount of CPU my code block may use? Cheers all

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  • Why does the JSF action tag handler in JSP invoke rendering immediately after creation?

    - by Pentius
    Dear fellows, I read the article "Improving JSF by Dumping JSP" from Hans Bergsten. There I read the following: The JSP container processes the page and invokes the JSF action tag handlers as they are encountered. A JSF tag handler looks for the JSF component it represents in the component tree. If it can't find the component, it creates it and adds it to the component tree. It then asks the component to render itself. and furthermore On the first request, the action creates its component and asks it to render itself. I understand that the immediate rendering after the creation of the component is the problem here (The reference to the input component can't be resolved in the example). That's one point, why JSF doesn't fit with JSP. But it reads as if the action tag handler itself would ask the component to render. Or is it JSP that triggers the rendering directly after the action tag handler created the component. If it is the action tag handler, I don't understand, why this is the fault of JSP. What is different here than from JSF intended? Thanks for your help, I need this for my thesis.

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  • Some images fails to load on Windows Server 2008

    - by Guffa
    I have an application running on a Windows Server 2008, that is processing uploaded images. Currently it successfully processes about 8000 images per day, creating 11 different sizes of each image. The problem that I have is that sometimes the application fails to load some images, I get the error "System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+.". The upload only accepts files with a JPEG extension (jpg/jpeg/jpe) or with a JPEG MIME type, and from what I can tell those images are really JPEG images. If I look at the image file in windows explorer on the server, it can successfully extract the thumbnail from the file, but if I try to open it, I get the error message "This is not a valid bitmap file, or it's format is not currently supported." from Paint. If I copy the image to my own computer, running Windows 7, there is no problem opening the image. It works in Paint, Windows Photo Viewer, Adobe Bridge, and Photoshop. If I try to load the image using Image.FromStream the same way as in the application running on the server, it loads just fine. (I have copied the file back to the server, and it still doesn't work, so there is nothing in the copying process that changes it.) When I look at the image information in Bridge, I see that the images are created using Picasa 3.0, but other than that I can't see anything special about them. I haven't yet found anyone having the same problem, or any known problems like this with the Picasa application. Has anyone had any similar problem, or know if there is something special about images created using Picasa? Is there any image codec that needs installing on the server to handle all kinds of JPEG images?

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  • Performing measures within the execution of a c++ code every t milliseconds

    - by user506901
    Given a while loop and the function ordering as follows: int k=0; int total=100; while(k<total){ doSomething(); if(approx. t milliseconds elapsed) { measure(); } ++k; } I want to perform 'measure' every t-th milliseconds. However, since 'doSomething' can be close to the t-th millisecond from the last execution, it is acceptable to perform the measure after approximately t milliseconds elapsed from the last measure. My question is: how could this be achieved? One solution would be to set timer to zero, and measure it after every 'doSomething'. When it is withing the acceptable range, I perform measures, and reset. However, I'm not which c++ function I should use for such a task. As I can see, there are certain functions, but the debate on which one is the most appropriate is outside of my understanding. Note that some of the functions actually take into account the time taken by some other processes, but I want my timer to only measure the time of the execution of my c++ code (I hope that is clear). Another thing is the resolution of the measurements, as pointed out below. Suppose the medium option of those suggested.

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  • What about parallelism across network using multiple PCs?

    - by MainMa
    Parallel computing is used more and more, and new framework features and shortcuts make it easier to use (for example Parallel extensions which are directly available in .NET 4). Now what about the parallelism across network? I mean, an abstraction of everything related to communications, creation of processes on remote machines, etc. Something like, in C#: NetworkParallel.ForEach(myEnumerable, () => { // Computing and/or access to web ressource or local network database here }); I understand that it is very different from the multi-core parallelism. The two most obvious differences would probably be: The fact that such parallel task will be limited to computing, without being able for example to use files stored locally (but why not a database?), or even to use local variables, because it would be rather two distinct applications than two threads of the same application, The very specific implementation, requiring not just a separate thread (which is quite easy), but spanning a process on different machines, then communicating with them over local network. Despite those differences, such parallelism is quite possible, even without speaking about distributed architecture. Do you think it will be implemented in a few years? Do you agree that it enables developers to easily develop extremely powerfull stuff with much less pain? Example: Think about a business application which extracts data from the database, transforms it, and displays statistics. Let's say this application takes ten seconds to load data, twenty seconds to transform data and ten seconds to build charts on a single machine in a company, using all the CPU, whereas ten other machines are used at 5% of CPU most of the time. In a such case, every action may be done in parallel, resulting in probably six to ten seconds for overall process instead of forty.

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  • Capturing wildcards in java generics

    - by Rollerball
    From this orcale java tutorial: The WildcardError example produces a capture error when compiled: import java.util.List; public class WildcardError { void foo(List<?> i) { i.set(0, i.get(0)); } } After this error demonstration, they fix the problem by using a helper method: public class WildcardFixed { void foo(List<?> i) { fooHelper(i); } // Helper method created so that the wildcard can be captured // through type inference. private <T> void fooHelper(List<T> l) { l.set(0, l.get(0)); } } First, they say that the list input parameter (i) is seen as an Object: In this example, the compiler processes the i input parameter as being of type Object. Why then i.get(0) does not return an Object? if it was already passed in as such? Furthermore what is the point of using a <?> when then you have to use an helper method using <T>. Would not be better using directly which can be inferred?

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  • LINQ extention SelectMany in 3.5 vs 4.0?

    - by Moberg
    Hi When I saw Darins suggestion here .. IEnumerable<Process> processes = new[] { "process1", "process2" } .SelectMany(Process.GetProcessesByName); ( http://stackoverflow.com/questions/3059667/process-getprocessesbyname/3059733#3059733 ) .. I was a bit intrigued and I tried it in VS2008 with .NET 3.5 - and it did not compiling unless I changed it to .. IEnumerable<Process> res = new string[] { "notepad", "firefox", "outlook" } .SelectMany(s => Process.GetProcessesByName(s)); Having read some Darins answers before I suspected that it was me that were the problem, and when I later got my hands on a VS2010 with.NET 4.0 - as expected - the original suggestion worked beautifully. My question is : What have happend from 3.5 to 4.0 that makes this (new syntax) possible? Is it the extentionmethods that have been extended(hmm) or new rules for lambda syntax or? I've tried to search but my google-fu was not strong enough. Please forgive if the question is a bit naive and note that I've taged it as beginner :)

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  • Processing a database queue across multiple threads - design advice

    - by rwmnau
    I have a SQL Server table full of orders that my program needs to "follow up" on (call a webservice to see if something has been done with them). My application is multi-threaded, and could have instances running on multiple servers. Currently, every so often (on a Threading timer), the process selects 100 rows, at random (ORDER BY NEWID()), from the list of "unconfirmed" orders and checks them, marking off any that come back successfully. The problem is that there's a lot of overlap between the threads, and between the different processes, and their's no guarantee that a new order will get checked any time soon. Also, some orders will never be "confirmed" and are dead, which means that they get in the way of orders that need to be confirmed, slowing the process down if I keep selecting them over and over. What I'd prefer is that all outstanding orders get checked, systematically. I can think of two easy ways do this: The application fetches one order to check at a time, passing in the last order it checked as a parameter, and SQL Server hands back the next order that's unconfirmed. More database calls, but this ensures that every order is checked in a reasonable timeframe. However, different servers may re-check the same order in succession, needlessly. The SQL Server keeps track of the last order it asked a process to check up on, maybe in a table, and gives a unique order to every request, incrementing its counter. This involves storing the last order somewhere in SQL, which I wanted to avoid, but it also ensures that threads won't needlessly check the same orders at the same time Are there any other ideas I'm missing? Does this even make sense? Let me know if I need some clarification.

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  • Scalability 101: How can I design a scalable web application using PHP?

    - by Legend
    I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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  • reporting tool/viewer for large datasets

    - by FrustratedWithFormsDesigner
    I have a data processing system that generates very large reports on the data it processes. By "large" I mean that a "small" execution of this system produces about 30 MB of reporting data when dumped into a CSV file and a large dataset is about 130-150 MB (I'm sure someone out there has a bigger idea of "large" but that's not the point... ;) Excel has the ideal interface for the report consumers in the form of its Data Lists: users can filter and segment the data on-the-fly to see the specific details that they are interested in - they can also add notes and markup to the reports, create charts, graphs, etc... They know how to do all this and it's much easier to let them do it if we just give them the data. Excel was great for the small test datasets, but it cannot handle these large ones. Does anyone know of a tool that can provide a similar interface as Excel data lists, but that can handle much larger files? The next tool I tried was MS Access, and found that the Access file bloats hugely (30 MB input file leads to about 70 MB Access file, and when I open the file, run a report and close it the file's at 120-150 MB!), the import process is slow and very manual (currently, the CSV files are created by the same plsql script that runs the main process so there's next to no intervention on my part). I also tried an Access database with linked tables to the database tables that store the report data and that was many times slower (for some reason, sqlplus could query and generate the report file in a minute or soe while Access would take anywhere from 2-5 minutes for the same data) (If it helps, the data processing system is written in PL/SQL and runs on Oracle 10g.)

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  • can this problem be solved with a single SQL query?

    - by PierrOz
    I have the two following tables (with some sample datas) LOGS: ID | SETID | DATE ======================== 1 | 1 | 2010-02-25 2 | 2 | 2010-02-25 3 | 1 | 2010-02-26 4 | 2 | 2010-02-26 5 | 1 | 2010-02-27 6 | 2 | 2010-02-27 7 | 1 | 2010-02-28 8 | 2 | 2010-02-28 9 | 1 | 2010-03-01 STATS: ID | OBJECTID | FREQUENCY | STARTID | ENDID ============================================= 1 | 1 | 0.5 | 1 | 5 2 | 2 | 0.6 | 1 | 5 3 | 3 | 0.02 | 1 | 5 4 | 4 | 0.6 | 2 | 6 5 | 5 | 0.6 | 2 | 6 6 | 6 | 0.4 | 2 | 6 7 | 1 | 0.35 | 3 | 7 8 | 2 | 0.6 | 3 | 7 9 | 3 | 0.03 | 3 | 7 10 | 4 | 0.6 | 4 | 8 11 | 5 | 0.6 | 4 | 8 7 | 1 | 0.45 | 5 | 9 8 | 2 | 0.6 | 5 | 9 9 | 3 | 0.02 | 5 | 9 Every day new logs are analyzed on different sets of objects and stored in table LOGS. Among other processes, some statistics are computed on the objects contained into these sets and the result are stored in table STATS. These statistic are computed through several logs (identified by the STARTID and ENDID columns). So, what could be the SQL query that would give me the latest computed stats for all the objects with the corresponding log dates. In the given example, the result rows would be: OBJECTID | SETID | FREQUENCY | STARTDATE | ENDDATE ====================================================== 1 | 1 | 0.45 | 2010-02-27 | 2010-03-01 2 | 1 | 0.6 | 2010-02-27 | 2010-03-01 3 | 1 | 0.02 | 2010-02-27 | 2010-03-01 4 | 2 | 0.6 | 2010-02-26 | 2010-02-28 5 | 2 | 0.6 | 2010-02-26 | 2010-02-28 So, the most recent stats for set 1 are computed with logs from feb 27 to march 1 whereas stats for set 2 are computed from feb 26 to feb 28. object 6 is not in the results rows as there is no stat on it within the last period of time. Last thing, I use MySQL. Any Idea ?

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  • How can I efficiently manipulate 500k records in SQL Server 2005?

    - by cdeszaq
    I am getting a large text file of updated information from a customer that contains updates for 500,000 users. However, as I am processing this file, I often am running into SQL Server timeout errors. Here's the process I follow in my VB application that processes the data (in general): Delete all records from temporary table (to remove last month's data) (eg. DELETE * FROM tempTable) Rip text file into the temp table Fill in extra information into the temp table, such as their organization_id, their user_id, group_code, etc. Update the data in the real tables based on the data computed in the temp table The problem is that I often run commands like UPDATE tempTable SET user_id = (SELECT user_id FROM myUsers WHERE external_id = tempTable.external_id) and these commands frequently time out. I have tried bumping the timeouts up to as far as 10 minutes, but they still fail. Now, I realize that 500k rows is no small number of rows to manipulate, but I would think that a database purported to be able to handle millions and millions of rows should be able to cope with 500k pretty easily. Am I doing something wrong with how I am going about processing this data? Please help. Any and all suggestions welcome.

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  • Parallel doseq for Clojure

    - by andrew cooke
    I haven't used multithreading in Clojure at all so am unsure where to start. I have a doseq whose body can run in parallel. What I'd like is for there always to be 3 threads running (leaving 1 core free) that evaluate the body in parallel until the range is exhausted. There's no shared state, nothing complicated - the equivalent of Python's multiprocessing would be just fine. So something like: (dopar 3 [i (range 100)] ; repeated 100 times in 3 parallel threads... ...) Where should I start looking? Is there a command for this? A standard package? A good reference? So far I have found pmap, and could use that (how do I restrict to 3 at a time? looks like it uses 32 at a time - no, source says 2 + number of processors), but it seems like this is a basic primitive that should already exist somewhere. clarification: I really would like to control the number of threads. I have processes that are long-running and use a fair amount of memory, so creating a large number and hoping things work out OK isn't a good approach (example which uses a significant chunk available mem). update: Starting to write a macro that does this, and I need a semaphore (or a mutex, or an atom i can wait on). Do semaphores exist in Clojure? Or should I use a ThreadPoolExecutor? It seems odd to have to pull so much in from Java - I thought parallel programming in Clojure was supposed to be easy... Maybe I am thinking about this completely the wrong way? Hmmm. Agents?

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  • unbuffered I/O in Linux

    - by stuck
    I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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  • Efficient database access when dealing with multiple abstracted repositories

    - by Nathan Ridley
    I want to know how most people are dealing with the repository pattern when it involves hitting the same database multiple times (sometimes transactionally) and trying to do so efficiently while maintaining database agnosticism and using multiple repositories together. Let's say we have repositories for three different entities; Widget, Thing and Whatsit. Each repository is abstracted via a base interface as per normal decoupling design processes. The base interfaces would then be IWidgetRepository, IThingRepository and IWhatsitRepository. Now we have our business layer or equivalent (whatever you want to call it). In this layer we have classes that access the various repositories. Often the methods in these classes need to do batch/combined operations where multiple repositories are involved. Sometimes one method may make use of another method internally, while that method can still be called independently. What about, in this scenario, when the operation needs to be transactional? Example: class Bob { private IWidgetRepository _widgetRepo; private IThingRepository _thingRepo; private IWhatsitRepository _whatsitRepo; public Bob(IWidgetRepository widgetRepo, IThingRepository thingRepo, IWhatsitRepository whatsitRepo) { _widgetRepo = widgetRepo; _thingRepo= thingRepo; _whatsitRepo= whatsitRepo; } public void DoStuff() { _widgetRepo.StoreSomeStuff(); _thingRepo.ReadSomeStuff(); _whatsitRepo.SaveSomething(); } public void DoOtherThing() { _widgetRepo.UpdateSomething(); DoStuff(); } } How do I keep my access to that database efficient and not have a constant stream of open-close-open-close on connections and inadvertent invocation of MSDTS and whatnot? If my database is something like SQLite, standard mechanisms like creating nested transactions are going to inherently fail, yet the business layer should not have to be concerning itself with such things. How do you handle such issues? Does ADO.Net provide simple mechanisms to handle this or do most people end up wrapping their own custom bits of code around ADO.Net to solve these types of problems?

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  • C# threading solution for long queries

    - by Eddie
    Senerio We have an application that records incidents. An external database needs to be queried when an incident is approved by a supervisor. The queries to this external database are sometimes taking a while to run. This lag is experienced through the browser. Possible Solution I want to use threading to eliminate the simulated hang to the browser. I have used the Thread class before and heard about ThreadPool. But, I just found BackgroundWorker in this post. MSDN states: The BackgroundWorker class allows you to run an operation on a separate, dedicated thread. Time-consuming operations like downloads and database transactions can cause your user interface (UI) to seem as though it has stopped responding while they are running. When you want a responsive UI and you are faced with long delays associated with such operations, the BackgroundWorker class provides a convenient solution. Is BackgroundWorker the way to go when handling long running queries? What happens when 2 or more BackgroundWorker processes are ran simultaneously? Is it handled like a pool?

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  • How to limit TCP writes to particular size and then block untlil the data is read

    - by ustulation
    {Qt 4.7.0 , VS 2010} I have a Server written in Qt and a 3rd party client executable. Qt based server uses QTcpServer and QTcpSocket facilities (non-blocking). Going through the articles on TCP I understand the following: the original implementation of TCP mentioned the negotiable window size to be a 16-bit value, thus maximum being 65535 bytes. But implementations often used the RFC window-scale-extension that allows the sliding window size to be scalable by bit-shifting to yield a maximum of 1 gigabyte. This is implementation defined. This could have resulted in majorly different window sizes on receiver and sender end as the server uses Qt facilities without hardcoding any window size limit. Client 1st asks for all information it can based on the previous messages from the server before handling the new (accumulating) incoming messages. So at some point Server receives a lot of messages each asking for data of several MB's. This the server processes and puts it into the sender buffer. Client however is unable to handle the messages at the same pace and it seems that client’s receiver buffer is far smaller (65535 bytes maybe) than sender’s transmit window size. The messages thus get accumulated at sender’s end until the sender’s buffer is full too after which the TCP writes on sender would block. This however does not happen as sender buffer is much larger. Hence this manifests as increase in memory consumption on the sender’s end. To prevent this from happening, I used Qt’s socket’s waitForBytesWritten() with timeout set to -1 for infinite waiting period. This as I see from the behaviour blocks the thread writing TCP data until the data has actually been sensed by the receiver’s window (which will happen when earlier messages have been processed by the client at application level). This has caused memory consumption at Server end to be almost negligible. is there a better alternative to this (in Qt) if i want to restrict the memory consumption at server end to say x MB's? Also please point out if any of my understandings is incorrect.

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  • Why do I need to close fds when reading and writing to the pipe?

    - by valentimsousa
    However, what if one of my processes needs to continuously write to the pipe while the other pipe needs to read? This example seems to work only for one write and one read. I need multi read and write void executarComandoURJTAG(int newSock) { int input[2], output[2], estado, d; pid_t pid; char buffer[256]; char linha[1024]; pipe(input); pipe(output); pid = fork(); if (pid == 0) {// child close(0); close(1); close(2); dup2(input[0], 0); dup2(output[1], 1); dup2(output[1], 2); close(input[1]); close(output[0]); execlp("jtag", "jtag", NULL); } else { // parent close(input[0]); close(output[1]); do { read(newSock, linha, 1024); /* Escreve o buffer no pipe */ write(input[1], linha, strlen(linha)); close(input[1]); while ((d = read(output[0], buffer, 255))) { //buffer[d] = '\0'; write(newSock, buffer, strlen(buffer)); puts(buffer); } write(newSock, "END", 4); } while (strcmp(linha, "quit") != 0); } }

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  • Set request attributes when a Form is POSTed

    - by ssahmed555
    Is there any way to set request attributes (not parameters) when a form is posted? The problem I am trying to solve is: I have a JSP page displaying some data in a couple of dropdown lists. When the form is posted, my Controller servlet processes this request (based on the parameters set/specified in the form) and redirects to the same JSP page that is supposed to display addition details. I now want to display the same/earlier data in the dropdown lists without having to recompute or recalculate to get that same data. And in the said JSP page, the dropdown lists in the form are populated by data that is specified through request attributes. Right now, after the Form is POSTed and I am redirected to the same JSP page the dropdown lists are empty because the necessary request attributes are not present. I am quite the n00b when it comes to web apps, so an obvious & easy solution to this problem escapes me at the moment! I am open to suggestions on how to restructure the control flow in the Servlet. Some details about this app: standard Servlet + JSP, JSTL, running in Apache Tomcat 6.0. Thanks.

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