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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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  • handling activity destruction in multithreaded android app

    - by Jayesh
    Hi, I have a multithreded app where background threads are used to load data over network or from disk/db. Every once in a while user will perform some action e.g. fetch news over network, which will spawn a background AsyncTask, but for some reason user will quit the app (press back button so that activity gets destroyed). In most such scenarios, I make appropriate checks in the background thread after it returns from n/w i/o, so that it won't crash by accessing members of the activity that is destroyed by now. However some corner cases are left where crashes happen, because the background thread would access some member of activity that is now null. Do other Android developers have some generic/recommended framework to handle such scenarios? These are the times when I wish android would have guaranteed termination of all threads when activity destroys (in the same way that regular linux process cleans up when it's quit)... but I guess Android devs had good reasons for not exposing process lifetimes through the api.

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  • java thread - run() and start() methods

    - by JavaUser
    Please explain the output of the below code: If I call th1.run() ,the output is EXTENDS RUN RUNNABLE RUN If I call th1.start() , the output is : RUNNABLE RUN EXTENDS RUN Why this inconsistency . Please explain. class ThreadExample extends Thread{ public void run(){ System.out.println("EXTENDS RUN"); } } class ThreadExampleRunnable implements Runnable { public void run(){ System.out.println("RUNNABLE RUN "); } } class ThreadExampleMain{ public static void main(String[] args){ ThreadExample th1 = new ThreadExample(); //th1.start(); th1.run(); ThreadExampleRunnable th2 = new ThreadExampleRunnable(); th2.run(); } }

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  • My python program always brings down my internet connection after several hours running, how do I debug and fix this problem?

    - by Shane
    I'm writing a python script checking/monitoring several server/websites status(response time and similar stuff), it's a GUI program and I use separate thread to check different server/website, and the basic structure of each thread is using an infinite while loop to request that site every random time period(15 to 30 seconds), once there's changes in website/server each thread will start a new thread to do a thorough check(requesting more pages and similar stuff). The problem is, my internet connection always got blocked/jammed/messed up after several hours running of this script, the situation is, from my script side I got urlopen error timed out each time it's requesting a page, and from my FireFox browser side I cannot open any site. But the weird thing is, the moment I close my script my Internet connection got back on immediately which means now I can surf any site through my browser, so it must be the script causing all the problem. I've checked the program carefully and even use del to delete any connection once it's used, still get the same problem. I only use urllib2, urllib, mechanize to do network requests. Anybody knows why such thing happens? How do I debug this problem? Is there a tool or something to check my network status once such situation occurs? It's really bugging me for a while... By the way I'm behind a VPN, does it have something to do with this problem? Although I don't think so because my network always get back on once the script closed, and the VPN connection never drops(as it appears) during the whole process.

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  • non blocking client server chat application in java using nio

    - by Amith
    I built a simple chat application using nio channels. I am very much new to networking as well as threads. This application is for communicating with server (Server / Client chat application). My problem is that multiple clients are not supported by the server. How do I solve this problem? What's the bug in my code? public class Clientcore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void coreClient() { System.out.println("please enter the text"); BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in)); SocketChannel sc = null; try { sc = SocketChannel.open(); sc.configureBlocking(false); sc.connect(new InetSocketAddress(8888)); int i=0; while (!sc.finishConnect()) { } for(int ii=0;ii>-22;ii++) { System.out.println("Enter the text"); String HELLO_REQUEST =stdin.readLine().toString(); if(HELLO_REQUEST.equalsIgnoreCase("end")) { break; } System.out.println("Sending a request to HelloServer"); ByteBuffer buffer = ByteBuffer.wrap(HELLO_REQUEST.getBytes()); sc.write(buffer); } } catch (IOException e) { e.printStackTrace(); } finally { if (sc != null) { try { sc.close(); } catch (Exception e) { e.printStackTrace(); } } } } public void run() { try { coreClient(); } catch(Exception ej) { ej.printStackTrace(); }}} public class ServerCore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void run() { try { coreServer(); } catch(Exception ej) { ej.printStackTrace(); } } private void coreServer() { try { ServerSocketChannel ssc = ServerSocketChannel.open(); try { ssc.socket().bind(new InetSocketAddress(8888)); while (true) { sckt_manager=SelectorProvider.provider().openSelector(); ssc.configureBlocking(false); SocketChannel sc = ssc.accept(); register_server(ssc,SelectionKey.OP_ACCEPT); if (sc == null) { } else { System.out.println("Received an incoming connection from " + sc.socket().getRemoteSocketAddress()); printRequest(sc); System.err.println("testing 1"); String HELLO_REPLY = "Sample Display"; ByteBuffer buffer = ByteBuffer.wrap(HELLO_REPLY.getBytes()); System.err.println("testing 2"); sc.write(buffer); System.err.println("testing 3"); sc.close(); }}} catch (IOException e) { e.printStackTrace(); } finally { if (ssc != null) { try { ssc.close(); } catch (IOException e) { e.printStackTrace(); } } } } catch(Exception E) { System.out.println("Ex in servCORE "+E); } } private static void printRequest(SocketChannel sc) throws IOException { ReadableByteChannel rbc = Channels.newChannel(sc.socket().getInputStream()); WritableByteChannel wbc = Channels.newChannel(System.out); ByteBuffer b = ByteBuffer.allocate(1024); // read 1024 bytes while (rbc.read(b) != -1) { b.flip(); while (b.hasRemaining()) { wbc.write(b); System.out.println(); } b.clear(); } } public void register_server(ServerSocketChannel ssc,int selectionkey_ops)throws Exception { ssc.register(sckt_manager,selectionkey_ops); }} public class HelloClient { public void coreClientChat() { Clientcore t=new Clientcore(); new Thread(t).start(); } public static void main(String[] args)throws Exception { HelloClient cl= new HelloClient(); cl.coreClientChat(); }} public class HelloServer { public void coreServerChat() { ServerCore t=new ServerCore(); new Thread(t).start(); } public static void main(String[] args) { HelloServer st= new HelloServer(); st.coreServerChat(); }}

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  • can a python script know that another instance of the same script is running... and then talk to it?

    - by Justin Grant
    I'd like to prevent multiple instances of the same long-running python command-line script from running at the same time, and I'd like the new instance to be able to send data to the original insance before the new instance commits suicide. How can I do this in a cross-platform way? Specifically, I'd like to enable the following behavior: "foo.py" is launched from the command line, and it will stay running for a long time-- days or weeks until the machine is rebooted or the parent process kills it. every few minutes the same script is launched again, but with different command-line parameters when launched, the script should see if any other instances are running. if other instances are running, then instance #2 should send its command-line parameters to instance #1, and then instance #2 should exit. instance #1, if it receives command-line parameters from another script, should spin up a new thread and (using the command-line parameters sent in the step above) start performing the work that instance #2 was going to perform. So I'm looking for two things: how can a python program know another instance of itself is running, and then how can one python command-line program communicate with another? Making this more complicated, the same script needs to run on both Windows and Linux, so ideally the solution would use only the Python standard library and not any OS-specific calls. Although if I need to have a Windows codepath and an *nix codepath (and a big if statement in my code to choose one or the other), that's OK if a "same code" solution isn't possible. I realize I could probably work out a file-based approach (e.g. instance #1 watches a directory for changes and each instance drops a file into that directory when it wants to do work) but I'm a little concerned about cleaning up those files after a non-graceful machine shutdown. I'd ideally be able to use an in-memory solution. But again I'm flexible, if a persistent-file-based approach is the only way to do it, I'm open to that option. More details: I'm trying to do this because our servers are using a monitoring tool which supports running python scripts to collect monitoring data (e.g. results of a database query or web service call) which the monitoring tool then indexes for later use. Some of these scripts are very expensive to start up but cheap to run after startup (e.g. making a DB connection vs. running a query). So we've chosen to keep them running in an infinite loop until the parent process kills them. This works great, but on larger servers 100 instances of the same script may be running, even if they're only gathering data every 20 minutes each. This wreaks havoc with RAM, DB connection limits, etc. We want to switch from 100 processes with 1 thread to one process with 100 threads, each executing the work that, previously, one script was doing. But changing how the scripts are invoked by the monitoring tool is not possible. We need to keep invocation the same (launch a process with different command-line parameters) but but change the scripts to recognize that another one is active, and have the "new" script send its work instructions (from the command line params) over to the "old" script.

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  • Should I pass a SqlDataReader by reference or not when passing it out to multiple threads.

    - by deroby
    Hi all, being new to c# I've run into this 'conundrum' when passing around a SqlDataReader between different threads. Without going into too much detail, the idea is to have a main thread fetching data from the database (a large recordset) and then have a helper-task run through this record by record and doing some stuff based upon the contents of this. There is no feedback to the recordset, it simply wades through until no records are left. This works fine, but given the nature of the job at hand it should be possible to have this job spread over different threads (CPUs) to maximize throughput (the order of execution is of no significance). The question then becomes, when I pass this recordset in a SqlDataReader, do I have to use ref or not ? It kind of boils down to the question : if I pass the object around without specifying ref, won't it create new copies in memory and have records processed n times ? Or, don't I risk having the record-position being moved forward while not all fields have been fully read yet ? The latter seems more like a 'data racing' issue and probably is covered by the lock()ing mechanism (or not?). My initial take on the problem was that it doesn't really hurt passing the variable using ref, yet as a colleague put it : "you only need ref when you're doing something wrong" =) Additionally using ref restricts me from applying a Using() construction too which isn't very nice either. I thus create a "basic" project that tackles the same approach but without the ref notation. Tests so far show that it works flawlessly on a Core2Duo (2cpu) using any number of threads, yet I'm still a bit wary... What do you experts think about this ? Use ref or not ? You can find the test-project here as it seems I can't upload it to this question directly ?!? ps: it's just a test-project and I'm new to c#, so please be gentle on me when breaking down the code =P

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  • Multi-Threaded Application - Help with some pseudo code!!

    - by HonorGod
    I am working on a multi-threaded application and need help with some pseudo-code. To make it simpler for implementation I will try to explain that in simple terms / test case. Here is the scenario - I have an array list of strings (say 100 strings) I have a Reader Class that reads the strings and passes them to a Writer Class that prints the strings to the console. Right now this runs in a Single Thread Model. I wanted to make this multi-threaded but with the following features - Ability to set MAX_READERS Ability to set MAX_WRITERS Ability to set BATCH_SIZE So basically the code should instantiate those many Readers and Writers and do the work in parallel. Any pseudo code will really be helpful to keep me going!

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  • Terminal-based snake game: input thread manipulates output

    - by enlightened
    I'm writing a snake game for the terminal, i.e. output via print. The following works just fine: while status[snake_monad] do print to_string draw canvas, compose_all([ frame, specs, snake_to_hash(snake[snake_monad]) ]) turn! snake_monad, get_dir move! snake_monad, specs sleep 0.25 end But I don't want the turn!ing to block, of course. So I put it into a new Thread and let it loop: Thread.new do loop do turn! snake_monad, get_dir end end while status[snake_monad] do ... # no turn! here ... end Which also works logically (the snake is turning), but the output is somehow interspersed with newlines. As soon as I kill the input thread (^C) it looks normal again. So why and how does the thread have any effect on my output? And how do I work around this issue? (I don't know much about threads, even less about them in ruby. Input and output concurrently on the same terminal make the matter worse, I guess...) Also (not really important): Wanting my program as pure as possible, would it be somewhat easily possible to get the input non-blockingly while passing everything around? Thank you!

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  • Threads to make video out of images

    - by masood
    updates: I think/ suspect the imageIO is not thread safe. shared by all threads. the read() call might use resources that are also shared. Thus it will give the performance of a single thread no matter how many threads used. ? if its correct . what is the solution (in practical code) Single request and response model at one time do not utilizes full network/internet bandwidth, thus resulting in low performance. (benchmark is of half speed utilization or even lower) This is to make a video out of an IP cam that gives a new image on each request. http://149.5.43.10:8001/snapshot.jpg It makes a delay of 3 - 8 seconds no matter what I do. Changed thread no. and thread time intervals, debugged the code by System.out.println statements to see if threads work. All seems normal. Any help? Please show some practical code. You may modify mine. This code works (javascript) with much smoother frame rate and max bandwidth usage. but the later code (java) dont. same 3 to 8 seconds gap. <!DOCTYPE html> <html> <head> <script type="text/javascript"> (function(){ var img="/*url*/"; var interval=50; var pointer=0; function showImg(image,idx) { if(idx<=pointer) return; document.body.replaceChild(image,document.getElementsByTagName("img")[0]); pointer=idx; preload(); } function preload() { var cache=null,idx=0;; for(var i=0;i<5;i++) { idx=Date.now()+interval*(i+1); cache=new Image(); cache.onload=(function(ele,idx){return function(){showImg(ele,idx);};})(cache,idx); cache.src=img+"?"+idx; } } window.onload=function(){ document.getElementsByTagName("img")[0].onload=preload; document.getElementsByTagName("img")[0].src="/*initial url*/"; }; })(); </script> </head> <body> <img /> </body> </html> and of java (with problem) : package camba; import java.applet.Applet; import java.awt.Button; import java.awt.Graphics; import java.awt.Image; import java.awt.Label; import java.awt.Panel; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.net.URL; import java.security.Timestamp; import java.util.Date; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicBoolean; import javax.imageio.ImageIO; public class Camba extends Applet implements ActionListener{ Image img; TextField textField; Label label; Button start,stop; boolean terminate = false; long viewTime; public void init(){ label = new Label("please enter camera URL "); add(label); textField = new TextField(30); add(textField); start = new Button("Start"); add(start); start.addActionListener(this); stop = new Button("Stop"); add(stop); stop.addActionListener(this); } public void actionPerformed(ActionEvent e){ Button source = (Button)e.getSource(); if(source.getLabel() == "Start"){ for (int i = 0; i < 7; i++) { myThread(50*i); } System.out.println("start..."); } if(source.getLabel() == "Stop"){ terminate = true; System.out.println("stop..."); } } public void paint(Graphics g) { update(g); } public void update(Graphics g){ try{ viewTime = System.currentTimeMillis(); g.drawImage(img, 100, 100, this); } catch(Exception e) { e.printStackTrace(); } } public void myThread(final int sleepTime){ new Thread(new Runnable() { public void run() { while(!terminate){ try { TimeUnit.MILLISECONDS.sleep(sleepTime); } catch (InterruptedException ex) { ex.printStackTrace(); } long requestTime= 0; Image tempImage = null; try { URL pic = null; requestTime= System.currentTimeMillis(); pic = new URL(getDocumentBase(), textField.getText()); tempImage = ImageIO.read(pic); } catch(Exception e) { e.printStackTrace(); } if(requestTime >= /*last view time*/viewTime){ img = tempImage; Camba.this.repaint(); } } }}).start(); System.out.println("thread started..."); } }

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  • Why does every thread in my application use a different hibernate session?

    - by Ittai
    Hi, I have a web-application which uses hibernate and for some reason every thread (httprequest or other threads related to queueing) uses a different session. I've implemented a HibernateSessionFactory class which looks like this: public class HibernateSessionFactory { private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>(); private static Configuration configuration = new AnnotationConfiguration(); private static org.hibernate.SessionFactory sessionFactory; static { try { configuration.configure(configFile); sessionFactory = configuration.buildSessionFactory(); } catch (Exception e) {} } private HibernateSessionFactory() {} public static Session getSession() throws HibernateException { Session session = (Session) threadLocal.get(); if (session == null || !session.isOpen()) { if (sessionFactory == null) { rebuildSessionFactory();//This method basically does what the static init block does } session = (sessionFactory != null) ? sessionFactory.openSession(): null; threadLocal.set(session); } return session; } //More non relevant methods here. Now from my testing it seems that the threadLocal member is indeed initialized only once when the class is first loaded by the JVM but for some reason when different threads access the getSession() method they use different sessions. When a thread first accesses this class (Session) threadLocal.get(); will return null but as expected all other access requests will yeild the same session. I'm not sure how this can be happening as the threadLocal variable is final and the method threadLocal.set(session) is only used in the above context (which I'm 99.9% sure has to yeild a non null session as I would have encountered a NullPointerException at a different part of my app). I'm not sure this is relevant but these are the main parts of my hibernate.cfg.xml file: <hibernate-configuration> <session-factory> <property name="connection.url">someURL</property> <property name="connection.driver_class"> com.microsoft.sqlserver.jdbc.SQLServerDriver</property> <property name="dialect">org.hibernate.dialect.SQLServerDialect</property> <property name="hibernate.connection.isolation">1</property> <property name="hibernate.connection.username">User</property> <property name="hibernate.connection.password">Password</property> <property name="hibernate.connection.pool_size">10</property> <property name="show_sql">false</property> <property name="current_session_context_class">thread</property> <property name="hibernate.hbm2ddl.auto">update</property> <property name="hibernate.cache.use_second_level_cache">false</property> <property name="hibernate.cache.provider_class">org.hibernate.cache.NoCacheProvider</property> <!-- Mapping files --> I'd appreciate any help granted and of course if anyone has any questions I'd be happy to clarify. Ittai

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  • C++ Thread Safe Integer

    - by Paul Ridgway
    Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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  • Are memory barriers necessary for atomic reference counting shared immutable data?

    - by Dietrich Epp
    I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

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  • Task.wait not working as I imagined

    - by user2357446
    I am trying to download a file, wait for the file to finish downloading, and then read the file afterwards. I have the following methods to do this: private async Task startDownload(string link, string savePath) { WebClient client = new WebClient(); client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged); client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted); await client.DownloadFileTaskAsync(new Uri(link), savePath); } private void checkUpdateButton_Click(object sender, EventArgs e) { Task task = Task.Factory.StartNew(() => startDownload(versionLink, versionSaveTo)); task.Wait(); if (task.IsCompleted) { checkVersion(); } } The checkVersion() method reads the file that was downloaded. This is throwing an IOException saying that the file is in use by something else and cannot be read. I thought that having task.Wait would prevent the rest of the method from executing until the task was finished?

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  • Is this a correct way to stop Execution Task

    - by Yan Cheng CHEOK
    I came across code to stop execution's task. private final ExecutorService executor = Executors.newSingleThreadExecutor(); public void stop() { executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (!Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; } I realize that, it is possible for Runnable to be in forever loop, as Unknown fun may Thread.sleep, clear the interrupt flag and ignore the InterruptedException Unknown fun may Thread.interrupted, clear the interrupt flag. I was wondering, is the following way correct way to fix the code? private final ExecutorService executor = Executors.newSingleThreadExecutor(); private volatile boolean flag = true; public void stop() { flag = false; executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (flag && !Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; }

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  • How to prevent the other threads from accessing a method when one thread is accessing a method?

    - by geeta
    I want to search for a string in 10 files and write the matching lines to a single file. I wrote the matching lines from each file to 10 output files(o/p file1,o/p file2...) and then copied those to a single file using 10 threads. But the output single file has mixed output(one line from o/p file1,another line from o/p file 2 etc...) because its accessed simultaneously by many threads. If I wait for all threads to complete and then write the single file it will be much slower. I want the output file to be written by one thread at a time. What should i do? My source code:(only writing to single file method) public void WriteSingle(File output_file,File final_output) throws IOException { synchronized(output_file){ System.out.println("Writing Single file"); FileOutputStream fo = new FileOutputStream(final_output,true); FileChannel fi = fo.getChannel(); FileInputStream fs = new FileInputStream(output_file); FileChannel fc = fs.getChannel(); int maxCount = (64 * 1024 * 1024) - (32 * 1024); long size = fc.size(); long position = 0; while (position < size) { position += fc.transferTo(position, maxCount, fi); } } }

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  • Why in the following code the output is different when I compile or run it more than once

    - by Sanjeev
    class Name implements Runnable { public void run() { for (int x = 1; x <= 3; x++) { System.out.println("Run by " + Thread.currentThread().getName() + ", x is " + x); } } } public class Threadtest { public static void main(String [] args) { // Make one Runnable Name nr = new Name(); Thread one = new Thread(nr); Thread two = new Thread(nr); Thread three = new Thread(nr); one.setName("A"); two.setName("B"); three.setName("C"); one.start(); two.start(); three.start(); } } The answer is different while compiling and running more then one time I don't know why? any idea.

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  • performSelectorInBackground, notify other viewcontroller when done.

    - by Michiel
    Hi, I have a method used to save an image when the user clicks Save. I use performSelectorInBackground to save the image, the viewcontroller is popped and the previous viewcontroller is shown. I want the table (on the previousUIViewController) to reload its data when the imagesaving is done. How can I do this? The save method is called like this: [self performSelectorInBackground:@selector(saveImage) withObject:nil]; [self.navigationController popViewControllerAnimated:YES];

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  • Efficiently display file status when using background thread

    - by schmoopy
    How can i efficiently display the status of a file when using a background thread? For instance, lets say i have a 100MB file: when i do the code below via a thread (just as an example) it runs in about 1 min: foreach(byte b in file.bytes) { WriteByte(b, xxx); } But... if i want to update the user i have to use a delegate to update the UI from the main thread, the code below takes - FOREVER - literally i don't know how long im still waiting, ive created this post and its not even 30% done. int total = file.length; int current = 0; foreach(byte b in file.bytes) { current++; UpdateCurrentFileStatus(current, total); WriteByte(b, xxx); } public delegate void UpdateCurrentFileStatus(int cur, int total); public void UpdateCurrentFileStatus(int cur, int total) { // Check if invoke required, if so create instance of delegate // the update the UI if(this.InvokeRequired) { } else { UpdateUI(...) } }

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  • Need help understanding .net ThreadPool

    - by Meredith
    I am trying to understand what ThreadPool does, I have this .NET example: class Program { static void Main() { int c = 2; // Use AutoResetEvent for thread management AutoResetEvent[] arr = new AutoResetEvent[50]; for (int i = 0; i < arr.Length; ++i) { arr[i] = new AutoResetEvent(false); } // Set the number of minimum threads ThreadPool.SetMinThreads(c, 4); // Enqueue 50 work items that run the code in this delegate function for (int i = 0; i < arr.Length; i++) { ThreadPool.QueueUserWorkItem(delegate(object o) { Thread.Sleep(100); arr[(int)o].Set(); // Signals completion }, i); } // Wait for all tasks to complete WaitHandle.WaitAll(arr); } } Does this run 50 "tasks", in groups of 2 (int c) until they all finish? Or I am not understanding what it really does.

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  • C - How to use both aio_read() and aio_write().

    - by Slav
    I implement game server where I need to both read and write. So I accept incoming connection and start reading from it using aio_read() but when I need to send something, I stop reading using aio_cancel() and then use aio_write(). Within write's callback I resume reading. So, I do read all the time but when I need to send something - I pause reading. It works for ~20% of time - in other case call to aio_cancel() fails with "Operation now in progress" - and I cannot cancel it (even within permanent while cycle). So, my added write operation never happens. How to use these functions well? What did I missed? EDIT: Used under Linux 2.6.35. Ubuntu 10 - 32 bit. Example code: void handle_read(union sigval sigev_value) { /* handle data or disconnection */ } void handle_write(union sigval sigev_value) { /* free writing buffer memory */ } void start() { const int acceptorSocket = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in addr; memset(&addr, 0, sizeof(struct sockaddr_in)); addr.sin_family = AF_INET; addr.sin_addr.s_addr = INADDR_ANY; addr.sin_port = htons(port); bind(acceptorSocket, (struct sockaddr*)&addr, sizeof(struct sockaddr_in)); listen(acceptorSocket, SOMAXCONN); struct sockaddr_in address; socklen_t addressLen = sizeof(struct sockaddr_in); for(;;) { const int incomingSocket = accept(acceptorSocket, (struct sockaddr*)&address, &addressLen); if(incomingSocket == -1) { /* handle error ... */} else { //say socket to append outcoming messages at writing: const int currentFlags = fcntl(incomingSocket, F_GETFL, 0); if(currentFlags < 0) { /* handle error ... */ } if(fcntl(incomingSocket, F_SETFL, currentFlags | O_APPEND) == -1) { /* handle another error ... */ } //start reading: struct aiocb* readingAiocb = new struct aiocb; memset(readingAiocb, 0, sizeof(struct aiocb)); readingAiocb->aio_nbytes = MY_SOME_BUFFER_SIZE; readingAiocb->aio_fildes = socketDesc; readingAiocb->aio_buf = mySomeReadBuffer; readingAiocb->aio_sigevent.sigev_notify = SIGEV_THREAD; readingAiocb->aio_sigevent.sigev_value.sival_ptr = (void*)mySomeData; readingAiocb->aio_sigevent.sigev_notify_function = handle_read; if(aio_read(readingAiocb) != 0) { /* handle error ... */ } } } } //called at any time from server side: send(void* data, const size_t dataLength) { //... some thread-safety precautions not needed here ... const int cancellingResult = aio_cancel(socketDesc, readingAiocb); if(cancellingResult != AIO_CANCELED) { //this one happens ~80% of the time - embracing previous call to permanent while cycle does not help: if(cancellingResult == AIO_NOTCANCELED) { puts(strerror(aio_return(readingAiocb))); // "Operation now in progress" /* don't know what to do... */ } } //otherwise it's okay to send: else { aio_write(...); } }

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