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• Rendering to a single Bitmap object from multiple threads

  - by Lee Treveil

  What im doing is rendering a number of bitmaps to a single bitmap. There could be hundreds of images and the bitmap being rendered to could be over 1000x1000 pixels. Im hoping to speed up this process by using multiple threads but since the Bitmap object is not thread-safe it cant be rendered to directly concurrently. What im thinking is to split the large bitmap into sections per cpu, render them separately then join them back together at the end. I haven't done this yet incase you guys/girls have any better suggestions. Any ideas? Thanks

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• Whats wrong with my backgroundwork method

  - by diver-d

  I am trying to get a background worker process working in a wpf application. it creates 2 files then crashes. BackgroundWorker worker = new BackgroundWorker(); worker.DoWork += delegate(object s, DoWorkEventArgs args) { CreateFile(i.ToString()); }; worker.RunWorkerAsync(); private void CreateFile(string fileName) { string path = string.Format(@"{0}\{1}.txt", directory, fileName); using (StreamWriter sw = new StreamWriter(path)) { sw.WriteLine(fileName); } } I get this error " The requested operation cannot be performed on a file with a user-mapped section open." what am I doing wrong? Any help would be great

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• How to log correct context with Threadpool threads using log4net?

  - by myotherme

  I am trying to find a way to log useful context from a bunch of threads. The problem is that a lot of code is dealt with on Events that are arriving via threadpool threads (as far as I can tell) so their names are not in relation to any context. The problem can be demonstrated with the following code: class Program { private static readonly log4net.ILog log = log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType); static void Main(string[] args) { new Thread(TestThis).Start("ThreadA"); new Thread(TestThis).Start("ThreadB"); Console.ReadLine(); } private static void TestThis(object name) { var nameStr = (string)name; Thread.CurrentThread.Name = nameStr; log4net.ThreadContext.Properties["ThreadContext"] = nameStr; log4net.LogicalThreadContext.Properties["LogicalThreadContext"] = nameStr; log.Debug("From Thread itself"); ThreadPool.QueueUserWorkItem(x => log.Debug("From threadpool Thread: " + nameStr)); } } The Conversion pattern is: %date [%thread] %-5level %logger [%property] - %message%newline The output is like so: 2010-05-21 15:08:02,357 [ThreadA] DEBUG LogicalContextTest.Program [{LogicalThreadContext=ThreadA, log4net:HostName=xxx, ThreadContext=ThreadA}] - From Thread itself 2010-05-21 15:08:02,357 [ThreadB] DEBUG LogicalContextTest.Program [{LogicalThreadContext=ThreadB, log4net:HostName=xxx, ThreadContext=ThreadB}] - From Thread itself 2010-05-21 15:08:02,404 [7] DEBUG LogicalContextTest.Program [{log4net:HostName=xxx}] - From threadpool Thread: ThreadA 2010-05-21 15:08:02,420 [16] DEBUG LogicalContextTest.Program [{log4net:HostName=xxx}] - From threadpool Thread: ThreadB As you can see the last two rows have no Names of useful information to distinguish the 2 threads, other than manually adding the name to the message (which I want to avoid). How can I get the Name/Context into the log for the threadpool threads without adding it to the message at every call?

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• Does a multithreaded crawler in Python really speed things up?

  - by beagleguy

  Was looking to write a little web crawler in python. I was starting to investigate writing it as a multithreaded script, one pool of threads downloading and one pool processing results. Due to the GIL would it actually do simultaneous downloading? How does the GIL affect a web crawler? Would each thread pick some data off the socket, then move on to the next thread, let it pick some data off the socket, etc..? Basically I'm asking is doing a multi-threaded crawler in python really going to buy me much performance vs single threaded? thanks!

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• What are shared by multi threads in the same process?

  - by skydoor

  I found that each thread still has its own registers. Also has its own stack, but other threads can read and write the stack memory. My questions, what are shared by the multi threads in the same process? What I can imagine is 1) address space of the process; 2) stack, register; 3) variables Can any body elaborate it and add more?

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• Of these 3 methods for reading linked lists from shared memory, why is the 3rd fastest?

  - by Joseph Garvin

  I have a 'server' program that updates many linked lists in shared memory in response to external events. I want client programs to notice an update on any of the lists as quickly as possible (lowest latency). The server marks a linked list's node's state_ as FILLED once its data is filled in and its next pointer has been set to a valid location. Until then, its state_ is NOT_FILLED_YET. I am using memory barriers to make sure that clients don't see the state_ as FILLED before the data within is actually ready (and it seems to work, I never see corrupt data). Also, state_ is volatile to be sure the compiler doesn't lift the client's checking of it out of loops. Keeping the server code exactly the same, I've come up with 3 different methods for the client to scan the linked lists for changes. The question is: Why is the 3rd method fastest? Method 1: Round robin over all the linked lists (called 'channels') continuously, looking to see if any nodes have changed to 'FILLED': void method_one() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { Data* current_item = channel_cursors[i]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[i] = static_cast<Data*>(current_item->next_.get(segment)); } } } Method 1 gave very low latency when then number of channels was small. But when the number of channels grew (250K+) it became very slow because of looping over all the channels. So I tried... Method 2: Give each linked list an ID. Keep a separate 'update list' to the side. Every time one of the linked lists is updated, push its ID on to the update list. Now we just need to monitor the single update list, and check the IDs we get from it. void method_two() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { if(update_cursor->state_ == NOT_FILLED_YET) { continue; } ::uint32_t update_id = update_cursor->list_id_; Data* current_item = channel_cursors[update_id]; if(current_item->state_ == NOT_FILLED_YET) { std::cerr << "This should never print." << std::endl; // it doesn't continue; } log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[update_id] = static_cast<Data*>(current_item->next_.get(segment)); update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } } Method 2 gave TERRIBLE latency. Whereas Method 1 might give under 10us latency, Method 2 would inexplicably often given 8ms latency! Using gettimeofday it appears that the change in update_cursor-state_ was very slow to propogate from the server's view to the client's (I'm on a multicore box, so I assume the delay is due to cache). So I tried a hybrid approach... Method 3: Keep the update list. But loop over all the channels continuously, and within each iteration check if the update list has updated. If it has, go with the number pushed onto it. If it hasn't, check the channel we've currently iterated to. void method_three() { std::vector<Data*> channel_cursors; for(ChannelList::iterator i = channel_list.begin(); i != channel_list.end(); ++i) { Data* current_item = static_cast<Data*>(i->get(segment)->tail_.get(segment)); channel_cursors.push_back(current_item); } UpdateID* update_cursor = static_cast<UpdateID*>(update_channel.tail_.get(segment)); while(true) { for(std::size_t i = 0; i < channel_list.size(); ++i) { std::size_t idx = i; ACQUIRE_MEMORY_BARRIER; if(update_cursor->state_ != NOT_FILLED_YET) { //std::cerr << "Found via update" << std::endl; i--; idx = update_cursor->list_id_; update_cursor = static_cast<UpdateID*>(update_cursor->next_.get(segment)); } Data* current_item = channel_cursors[idx]; ACQUIRE_MEMORY_BARRIER; if(current_item->state_ == NOT_FILLED_YET) { continue; } found_an_update = true; log_latency(current_item->tv_sec_, current_item->tv_usec_); channel_cursors[idx] = static_cast<Data*>(current_item->next_.get(segment)); } } } The latency of this method was as good as Method 1, but scaled to large numbers of channels. The problem is, I have no clue why. Just to throw a wrench in things: if I uncomment the 'found via update' part, it prints between EVERY LATENCY LOG MESSAGE. Which means things are only ever found on the update list! So I don't understand how this method can be faster than method 2. The full, compilable code (requires GCC and boost-1.41) that generates random strings as test data is at: http://pastebin.com/e3HuL0nr

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• Best practices for Java logging from multiple threads?

  - by Jason S

  I want to have a diagnostic log that is produced by several tasks managing data. These tasks may be in multiple threads. Each task needs to write an element (possibly with subelements) to the log; get in and get out quickly. If this were a single-task situation I'd use XMLStreamWriter as it seems like the best match for simplicity/functionality without having to hold a ballooning XML document in memory. But it's not a single-task situation, and I'm not sure how to best make sure this is "threadsafe", where "threadsafe" in this application means that each log element should be written to the log correctly and serially (one after the other and not interleaved in any way). Any suggestions? I have a vague intuition that the way to go is to use a queue of log elements (with each one able to be produced quickly: my application is busy doing real work that's performance-sensitive), and have a separate thread which handles the log elements and sends them to a file so the logging doesn't interrupt the producers. The logging doesn't necessarily have to be XML, but I do want it to be structured and machine-readable. edit: I put "threadsafe" in quotes. Log4j seems to be the obvious choice (new to me but old to the community), why reinvent the wheel...

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• Lock-Free, Wait-Free and Wait-freedom algorithms for non-blocking multi-thread synchronization.

  - by GJ

  In multi thread programming we can find different terms for data transfer synchronization between two or more threads/tasks. When exactly we can say that some algorithem is: 1)Lock-Free 2)Wait-Free 3)Wait-Freedom I understand what means Lock-free but when we can say that some synchronization algorithm is Wait-Free or Wait-Freedom? I have made some code (ring buffer) for multi-thread synchronization and it use Lock-Free methods but: 1) Algorithm predicts maximum execution time of this routine. 2) Therad which call this routine at beginning set unique reference, what mean that is inside of this routine. 3) Other threads which are calling the same routine check this reference and if is set than count the CPU tick count (measure time) of first involved thread. If that time is to long interrupt the current work of involved thread and overrides him job. 4) Thread which not finished job because was interrupted from task scheduler (is reposed) at the end check the reference if not belongs to him repeat the job again. So this algorithm is not really Lock-free but there is no memory lock in use, and other involved threads can wait (or not) certain time before overide the job of reposed thread. Added RingBuffer.InsertLeft function: function TgjRingBuffer.InsertLeft(const link: pointer): integer; var AtStartReference: cardinal; CPUTimeStamp : int64; CurrentLeft : pointer; CurrentReference: cardinal; NewLeft : PReferencedPtr; Reference : cardinal; label TryAgain; begin Reference := GetThreadId + 1; //Reference.bit0 := 1 with rbRingBuffer^ do begin TryAgain: //Set Left.Reference with respect to all other cores :) CPUTimeStamp := GetCPUTimeStamp + LoopTicks; AtStartReference := Left.Reference OR 1; //Reference.bit0 := 1 repeat CurrentReference := Left.Reference; until (CurrentReference AND 1 = 0)or (GetCPUTimeStamp - CPUTimeStamp > 0); //No threads present in ring buffer or current thread timeout if ((CurrentReference AND 1 <> 0) and (AtStartReference <> CurrentReference)) or not CAS32(CurrentReference, Reference, Left.Reference) then goto TryAgain; //Calculate RingBuffer NewLeft address CurrentLeft := Left.Link; NewLeft := pointer(cardinal(CurrentLeft) - SizeOf(TReferencedPtr)); if cardinal(NewLeft) < cardinal(@Buffer) then NewLeft := EndBuffer; //Calcolate distance result := integer(Right.Link) - Integer(NewLeft); //Check buffer full if result = 0 then //Clear Reference if task still own reference if CAS32(Reference, 0, Left.Reference) then Exit else goto TryAgain; //Set NewLeft.Reference NewLeft^.Reference := Reference; SFence; //Try to set link and try to exchange NewLeft and clear Reference if task own reference if (Reference <> Left.Reference) or not CAS64(NewLeft^.Link, Reference, link, Reference, NewLeft^) or not CAS64(CurrentLeft, Reference, NewLeft, 0, Left) then goto TryAgain; //Calcolate result if result < 0 then result := Length - integer(cardinal(not Result) div SizeOf(TReferencedPtr)) else result := cardinal(result) div SizeOf(TReferencedPtr); end; //with end; { TgjRingBuffer.InsertLeft } RingBuffer unit you can find here: RingBuffer, CAS functions: FockFreePrimitives, and test program: RingBufferFlowTest Thanks in advance, GJ

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• calling concurrently Graphics.Draw and new Bitmap from memory in thread take long time

  - by Abdul jalil

  Example1 public partial class Form1 : Form { public Form1() { InitializeComponent(); pro = new Thread(new ThreadStart(Producer)); con = new Thread(new ThreadStart(Consumer)); } private AutoResetEvent m_DataAvailableEvent = new AutoResetEvent(false); Queue<Bitmap> queue = new Queue<Bitmap>(); Thread pro; Thread con ; public void Producer() { MemoryStream[] ms = new MemoryStream[3]; for (int y = 0; y < 3; y++) { StreamReader reader = new StreamReader("image"+(y+1)+".JPG"); BinaryReader breader = new BinaryReader(reader.BaseStream); byte[] buffer=new byte[reader.BaseStream.Length]; breader.Read(buffer,0,buffer.Length); ms[y] = new MemoryStream(buffer); } while (true) { for (int x = 0; x < 3; x++) { Bitmap bmp = new Bitmap(ms[x]); queue.Enqueue(bmp); m_DataAvailableEvent.Set(); Thread.Sleep(6); } } } public void Consumer() { Graphics g= pictureBox1.CreateGraphics(); while (true) { m_DataAvailableEvent.WaitOne(); Bitmap bmp = queue.Dequeue(); if (bmp != null) { // Bitmap bmp = new Bitmap(ms); g.DrawImage(bmp,new Point(0,0)); bmp.Dispose(); } } } private void pictureBox1_Click(object sender, EventArgs e) { con.Start(); pro.Start(); } } when Creating bitmap and Drawing to picture box are in seperate thread then Bitmap bmp = new Bitmap(ms[x]) take 45.591 millisecond and g.DrawImage(bmp,new Point(0,0)) take 41.430 milisecond when i make bitmap from memoryStream and draw it to picture box in one thread then Bitmap bmp = new Bitmap(ms[x]) take 29.619 and g.DrawImage(bmp,new Point(0,0)) take 35.540 the code is for Example 2 is why it take more time to draw and bitmap take time in seperate thread and how to reduce the time when processing in seperate thread. i am using ANTS performance profiler 4.3 public Form1() { InitializeComponent(); pro = new Thread(new ThreadStart(Producer)); con = new Thread(new ThreadStart(Consumer)); } private AutoResetEvent m_DataAvailableEvent = new AutoResetEvent(false); Queue<MemoryStream> queue = new Queue<MemoryStream>(); Thread pro; Thread con ; public void Producer() { MemoryStream[] ms = new MemoryStream[3]; for (int y = 0; y < 3; y++) { StreamReader reader = new StreamReader("image"+(y+1)+".JPG"); BinaryReader breader = new BinaryReader(reader.BaseStream); byte[] buffer=new byte[reader.BaseStream.Length]; breader.Read(buffer,0,buffer.Length); ms[y] = new MemoryStream(buffer); } while (true) { for (int x = 0; x < 3; x++) { // Bitmap bmp = new Bitmap(ms[x]); queue.Enqueue(ms[x]); m_DataAvailableEvent.Set(); Thread.Sleep(6); } } } public void Consumer() { Graphics g= pictureBox1.CreateGraphics(); while (true) { m_DataAvailableEvent.WaitOne(); //Bitmap bmp = queue.Dequeue(); MemoryStream ms= queue.Dequeue(); if (ms != null) { Bitmap bmp = new Bitmap(ms); g.DrawImage(bmp,new Point(0,0)); bmp.Dispose(); } } } private void pictureBox1_Click(object sender, EventArgs e) { con.Start(); pro.Start(); }

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• Form gets disposed somehow

  - by mnn

  I have a client-server application, in which I use classic Sockets and threads for receiving/sending data and listening for clients. The application works fine, but after some random time I get the ObjectDisposedException: System.ObjectDisposedException: Cannot access a disposed object. Object name: 'MainForm'. at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous) at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args) at System.Windows.Forms.Control.Invoke(Delegate method) That code is called from client Socket thread and I use Invoke() method to run the code on UI thread. I'm sure that I don't manually dispose the form nor using Close() (form is closed by user clicking Close button), so I don't know what could cause its disposing.

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• Java Backgroundworker: Scope of Widget to be updated unclear

  - by erlord

  Hi all, I am trying to understand the mechanism of org.jdesktop.swingx.BackgroundWorker. Their javadoc presents following example: final JLabel label; class MeaningOfLifeFinder implements BackgroundListener { public void doInBackground(BackgroundEvent evt) { String meaningOfLife = findTheMeaningOfLife(); evt.getWorker().publish(meaningOfLife); } public void process(BackgroundEvent evt) { label.setText("" + evt.getData()); } public void done(BackgroundEvent evt) {} public void started(BackgroundEvent evt) {} } (new MeaningOfLifeFinder()).execute(); Apart from the fact that I doubt the result will ever get published, I wonder how label is passed to the process method, where it is being updated. I thought it's scope is limited to the outside of the BackgroudListener implementation. Quite confused I am ... any answers for me? Thanks in advance

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• Sending message from working non-gui thread to the main window

  - by bartek

  I'm using WinApi. Is SendMessage/PostMessage a good, thread safe method of communicating with the main window? Suppose, the working thread is creating a bitmap, that must be displayed on the screen. The working thread allocates a bitmap, sends a message with a pointer to this bitmap and waits until GUI thread processes it (for example using SendMessage). The working thread shares no data with other threads. Am I running into troubles with such design? Are there any other possibilities that do not introduce thread synchronizing, locking etc. ?

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• Difference in output from use of synchronized keyword and join()

  - by user2964080

  I have 2 classes, public class Account { private int balance = 50; public int getBalance() { return balance; } public void withdraw(int amt){ this.balance -= amt; } } and public class DangerousAccount implements Runnable{ private Account acct = new Account(); public static void main(String[] args) throws InterruptedException{ DangerousAccount target = new DangerousAccount(); Thread t1 = new Thread(target); Thread t2 = new Thread(target); t1.setName("Ravi"); t2.setName("Prakash"); t1.start(); /* #1 t1.join(); */ t2.start(); } public void run(){ for(int i=0; i<5; i++){ makeWithdrawl(10); if(acct.getBalance() < 0) System.out.println("Account Overdrawn"); } } public void makeWithdrawl(int amt){ if(acct.getBalance() >= amt){ System.out.println(Thread.currentThread().getName() + " is going to withdraw"); try{ Thread.sleep(500); }catch(InterruptedException e){ e.printStackTrace(); } acct.withdraw(amt); System.out.println(Thread.currentThread().getName() + " has finished the withdrawl"); }else{ System.out.println("Not Enough Money For " + Thread.currentThread().getName() + " to withdraw"); } } } I tried adding synchronized keyword in makeWithdrawl method public synchronized void makeWithdrawl(int amt){ and I keep getting this output as many times I try Ravi is going to withdraw Ravi has finished the withdrawl Ravi is going to withdraw Ravi has finished the withdrawl Ravi is going to withdraw Ravi has finished the withdrawl Ravi is going to withdraw Ravi has finished the withdrawl Ravi is going to withdraw Ravi has finished the withdrawl Not Enough Money For Prakash to withdraw Not Enough Money For Prakash to withdraw Not Enough Money For Prakash to withdraw Not Enough Money For Prakash to withdraw Not Enough Money For Prakash to withdraw This shows that only Thread t1 is working... If I un-comment the the line saying t1.join(); I get the same output. So how does synchronized differ from join() ? If I don't use synchronize keyword or join() I get various outputs like Ravi is going to withdraw Prakash is going to withdraw Prakash has finished the withdrawl Ravi has finished the withdrawl Prakash is going to withdraw Ravi is going to withdraw Prakash has finished the withdrawl Ravi has finished the withdrawl Prakash is going to withdraw Ravi is going to withdraw Prakash has finished the withdrawl Ravi has finished the withdrawl Account Overdrawn Account Overdrawn Not Enough Money For Ravi to withdraw Account Overdrawn Not Enough Money For Prakash to withdraw Account Overdrawn Not Enough Money For Ravi to withdraw Account Overdrawn Not Enough Money For Prakash to withdraw Account Overdrawn So how does the output from synchronized differ from join() ?

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• java share data between thread

  - by ayush

  i have a java process that reads data from a socket server. Thus i have a BufferedReader and a PrintWriter object corresponding to that socket. Now in the same java process i have a multithreaded java server that accepts client connections. I want to achieve a functionality where all these clients that i accept can read data from the BufferedReader object that i mentioned above.(so that they can multiplex the data) How do i make these individual client threads read the data from BuffereReader single object? Sorry for the confusion.

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• How to give highest priority to events generated from main thread than those generated from secondar

  - by martjno

  I have a c++ application written in wxWidgets, which has a main thread (GUI) and a working thread (calculations). The working thread executes commands requested by the main thread and communicates the result to the main thread posting an event after every step of the processing. The problem is that when the working thread is sending many events consecutively, the gui requests made by the user (i.e. interrupt the processing clicking a button) won't be processed by the event handler until the working thread has finished. This is actually happening on OSX, on Windows it works perfectly. I've tried to wxThread::SetPriority and wxThread::Yield but nothing changes. It is working if I put wxThread::Sleep in the working thread, but this slows down very much the processing.

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• Core dump of a multithreaded program

  - by benjamin button

  Hi, i have regularly worked with single threaded programs. i never saw a multithreded program crashing since i havent worked on any. is there any difference between both teh core dumps? is there any additional information provided in the core dump of a multithreaded program when compared to a single threaded program?

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• deciding between subprocess, multiprocesser and thread in Python?

  - by user248237

  I'd like to parallelize my Python program so that it can make use of multiple processors on the machine that it runs on. My parallelization is very simple, in that all the parallel "threads" of the program are independent and write their output to separate files. I don't need the threads to exchange information but it is imperative that I know when the threads finish since some steps of my pipeline depend on their output. Portability is important, in that I'd like this to run on any Python version on Mac, Linux and Windows. Given these constraints, which is the most appropriate Python module for implementing this? I am tryign to decide between thread, subprocess and multiprocessing, which all seem to provide related functionality. Any thoughts on this? I'd like the simplest solution that's portable. Thanks.

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• How can I limit access to a particular class to one caller at a time in an ASMX web service?

  - by MusiGenesis

  I have a web service method in which I create a particular type of object, use it for a few seconds, and then dispose it. Because of problems arising from multiple threads creating and using instances of this class at the same time, I need to restrict the method so that only one caller at a time ever has one of these objects. To do this, I am creating a private static object: private static object _lock = new object(); ... and then inside the web service method I do this around the critical code: lock (_lock) { using (DangerousObject do = new DangerousObject()) { do.MakeABigMess(); do.CleanItUp(); } } I'm not sure this is working, though. Do I have this right? Will this code ensure that only one instance of DangerousObject is instantiated and in use at a time? Or does each caller get their own copy of _lock, rendering my code here laughable?

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• Swingworker producing duplicate output/output out of order?

  - by Stefan Kendall

  What is the proper way to guarantee delivery when using a SwingWorker? I'm trying to route data from an InputStream to a JTextArea, and I'm running my SwingWorker with the execute method. I think I'm following the example here, but I'm getting out of order results, duplicates, and general nonsense. Here is my non-working SwingWorker: class InputStreamOutputWorker extends SwingWorker<List<String>,String> { private InputStream is; private JTextArea output; public InputStreamOutputWorker(InputStream is, JTextArea output) { this.is = is; this.output = output; } @Override protected List<String> doInBackground() throws Exception { byte[] data = new byte[4 * 1024]; int len = 0; while ((len = is.read(data)) > 0) { String line = new String(data).trim(); publish(line); } return null; } @Override protected void process( List<String> chunks ) { for( String s : chunks ) { output.append(s + "\n"); } } }

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• Multi:Threading - Is this the right approach?

  - by HonorGod

  Experts - I need some advice in the following scenario. I have a configuration file with a list of tasks. Each task can have zero, one or more dependencies. I wanted to execute these tasks in parallel [right now they are being executed sequentially] The idea is to have a main program to read the configuration file and load all the tasks. Read individual tasks and give it to an executor [callable] that will perform the task and return results in a Future. When the task is submitted to the executor (thread) it will monitor for its dependencies to finish first and perform its own task. Is this the right approach? Are there any other better approaches using java 1.5 features?

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• What is the basic concept behind WaitHandle in C# .net threading ?

  - by DotNetBeginner

  What is the basic concept behind WaitHandle in C# .net threading ? Whats is its use ? When to use it ? What is the use of WaitAll and WaitAny methods inside it ?

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• Interrupt an Http Request blocked in read() on Android

  - by twk

  Using the Apache Http stack on Android, I'm trying to force a thread out of a call to read. This is what the stack looks like: OSNetworkSystem.receiveStreamImpl(FileDescriptor, byte[], int, int, int) line: not available [native method] OSNetworkSystem.receiveStream(FileDescriptor, byte[], int, int, int) line: 478 PlainSocketImpl.read(byte[], int, int) line: 565 SocketInputStream.read(byte[], int, int) line: 87 SocketInputBuffer(AbstractSessionInputBuffer).fillBuffer() line: 103 SocketInputBuffer(AbstractSessionInputBuffer).read(byte[], int, int) line: 134 IdentityInputStream.read(byte[], int, int) line: 86 EofSensorInputStream.read(byte[], int, int) line: 159 Fetcher.readStream() line: 89 I've tried InputStream.close(), Thread.Interrupt(), and HttpUriRequest.abort(), without any success. Any ideas? I'm also open to some kind of non-blocking IO, but I don't see any way to do that with the HttpUriRequest object. Thanks!

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• Why is my Map broken?

  - by Kirk

  Scenario: Creating a server which has Room objects which contain User objects. I want to store the rooms in a Map of some sort by Id (a string). Desired Behavior: When a user makes a request via the server, I should be able to look up the Room by id from the library and then add the user to the room, if that's what the request needs. Currently I use the static function in my Library.java class where the Map is stored to retrieve Rooms: public class Library { private static Hashtable<String, Rooms> myRooms = new Hashtable<String, Rooms>(); public static addRoom(String s, Room r) { myRooms.put(s, r); } public static Room getRoomById(String s) { return myRooms.get(s); } } In another class I'll do the equivalent of myRoom.addUser(user); What I'm observing using Hashtable, is that no matter how many times I add a user to the Room returned by getRoomById, the user is not in the room later. I thought that in Java, the object that was returned was essentially a reference to the data, the same object that was in the Hashtable with the same references; but, it isn't behaving like that. Is there a way to get this behavior? Maybe with a wrapper of some sort? Am I just using the wrong variant of map? Help?

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• Do condition variables still need a mutex if you're changing the checked value atomically?

  - by Joseph Garvin

  Here is the typical way to use a condition variable: // The reader(s) lock(some_mutex); if(protected_by_mutex_var != desired_value) some_condition.wait(some_mutex); unlock(some_mutex); // The writer lock(some_mutex); protected_by_mutex_var = desired_value; unlock(some_mutex); some_condition.notify_all(); But if protected_by_mutex_var is set atomically by say, a compare-and-swap instruction, does the mutex serve any purpose (other than that pthreads and other APIs require you to pass in a mutex)? Is it protecting state used to implement the condition? If not, is it safe then to do this?: // The writer protected_by_mutex_var = desired_value; some_condition.notify_all(); With the writer never directly interacting with the reader's mutex? If so, is it even necessary that different readers use the same mutex?

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• Why is (javax.servlet.)SingleThreadModel deprecated?

  - by saugata

  Why is javax.servlet.SingleThreadModel deprecated?

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