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• wxpython - Running threads sequentially without blocking GUI

  - by ryantmer

  I've got a GUI script with all my wxPython code in it, and a separate testSequences module that has a bunch of tasks that I run based on input from the GUI. The tasks take a long time to complete (from 20 seconds to 3 minutes), so I want to thread them, otherwise the GUI locks up while they're running. I also need them to run one after another, since they all use the same hardware. (My rationale behind threading is simply to prevent the GUI from locking up.) I'd like to have a "Running" message (with varying number of periods after it, i.e. "Running", "Running.", "Running..", etc.) so the user knows that progress is occurring, even though it isn't visible. I'd like this script to run the test sequences in separate threads, but sequentially, so that the second thread won't be created and run until the first is complete. Since this is kind of the opposite of the purpose of threads, I can't really find any information on how to do this... Any help would be greatly appreciated. Thanks in advance! gui.py import testSequences from threading import Thread #wxPython code for setting everything up here... for j in range(5): testThread = Thread(target=testSequences.test1) testThread.start() while testThread.isAlive(): #wait until the previous thread is complete time.sleep(0.5) i = (i+1) % 4 self.status.SetStatusText("Running"+'.'*i) testSequences.py import time def test1(): for i in range(10): print i time.sleep(1) (Obviously this isn't the actual test code, but the idea is the same.)

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• Java Thread execution on same data

  - by AR89

  first of all here is the code, you can just copy an paste import java.util.ArrayList; public class RepetionCounter implements Runnable{ private int x; private int y; private int[][] matrix; private int xCounter; private int yCounter; private ArrayList<Thread> threadArray; private int rowIndex; private boolean[] countCompleted; public RepetionCounter(int x, int y, int [][]matrix) { this.x = x; this.y = y; this.matrix = matrix; this.threadArray = new ArrayList<Thread>(matrix.length); this.rowIndex = 0; for(int i = 0; i < matrix.length; i++){ threadArray.add(new Thread(this)); } countCompleted = new boolean[matrix.length]; } public void start(){ for (int i = 0; i < threadArray.size(); i++){ threadArray.get(i).start(); this.rowIndex++; } } public void count(int rowIndex) { for(int i = 0; i < matrix[rowIndex].length; i++){ if (matrix[rowIndex][i] == x){ this.xCounter++; } else if (matrix[rowIndex][i] == y){ this.yCounter++; } } } @Override public void run() { count(this.rowIndex); countCompleted[this.rowIndex] = true; } public int getxCounter() { return xCounter; } public void setxCounter(int xCounter) { this.xCounter = xCounter; } public int getyCounter() { return yCounter; } public void setyCounter(int yCounter) { this.yCounter = yCounter; } public boolean[] getCountCompleted() { return countCompleted; } public void setCountCompleted(boolean[] countCompleted) { this.countCompleted = countCompleted; } public static void main(String args[]){ int[][] matrix = {{0,2,1}, {2,3,4}, {3,2,0}}; RepetionCounter rc = new RepetionCounter(0, 2, matrix); rc.start(); boolean ready = false; while(!ready){ for(int i = 0; i < matrix.length; i++){ if (rc.getCountCompleted()[i]){ ready = true; } else { ready = false; } } } if (rc.getxCounter() > rc.getyCounter()){ System.out.println("Thre are more x than y"); } else {System.out.println("There are:"+rc.getxCounter()+" x and:"+rc.getyCounter()+" y"); } } } What I want this code to do: I give to the object a matrix and tow numbers, and I want to know how much times these two numbers occurs in the matrix. I create as many thread as the number of rows of the matrix (that' why there is that ArrayList), so in this object I have k threads (supposing k is the number of rows), each of them count the occurrences of the two numbers. The problem is: if I run it for the first time everything work, but if I try to execute it another time I get and IndexOutOfBoundException, or a bad count of the occurrences, the odd thing is that if I get the error, and modify the code, after that it will works again just for once. Can you explain to me why is this happening?

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• How can one use multi threading in php applications

  - by Steve Obbayi

  Is there a realistic way of implementing a multi-threaded model in php whether truly or just simulating it. Some time back it was suggested that you can force the operating system to load another instance of the php executable and handle other simultaneous processes. The problem with this is that when the php code finished executing the php instance remains in memory because there is no way to kill it from within php. so if you are simulating several threads you can imagine whats going to happen. So am still looking for a way multi-threading can be done or simulated effectively from within php. Any ideas?

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• Lowest possible context switch time

  - by S.M

  Is it possible to tell the processor that has the best context switch time ?

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• Why is my code stopping and not returning an exception?

  - by BeckyLou

  I have some code that starts a couple of threads to let them execute, then uses a while loop to check for the current time passing a set timeout period, or for the correct number of results to have been processed (by checking an int on the class object) (with a Thread.Sleep() to wait between loops) Once the while loop is set to exit, it calls Abort() on the threads and should return data to the function that calls the method. When debugging and stepping through the code, I find there can be exceptions in the code running on the separate threads, and in some cases I handle these appropriately, and at other times I don't want to do anything specific. What I have been seeing is that my code goes into the while loop and the thread sleeps, then nothing is returned from my function, either data or an exception. Code execution just stops completely. Any ideas what could be happening? Code sample: System.Threading.Thread sendThread = new System.Threading.Thread(new System.Threading.ThreadStart(Send)); sendThread.Start(); System.Threading.Thread receiveThread = new System.Threading.Thread(new System.Threading.ThreadStart(Receive)); receiveThread.Start(); // timeout Int32 maxSecondsToProcess = this.searchTotalCount * timeout; DateTime timeoutTime = DateTime.Now.AddSeconds(maxSecondsToProcess); Log("Submit() Timeout time: " + timeoutTime.ToString("yyyyMMdd HHmmss")); // while we're still waiting to receive results & haven't hit the timeout, // keep the threads going while (resultInfos.Count < this.searchTotalCount && DateTime.Now < timeoutTime) { Log("Submit() Waiting..."); System.Threading.Thread.Sleep(10 * 1000); // 1 minute } Log("Submit() Aborting threads"); // <== this log doesn't show up sendThread.Abort(); receiveThread.Abort(); return new List<ResultInfo>(this.resultInfos.Values);

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• how to differentiate between two threads

  - by mithun1538

  Hello everyone, I have the following code in my program: Thread getUsersist, getChatUsers; getUsersList = new Thread(this, "getOnlineUsers"); getUsersList.start(); getChatUsers = new Thread(this, "getChatUsers"); getChatUsers.start(); In run(), I wish to know which thread is using run(). If its "getOnlineUsers" i will do something, If it is "getChatUsers" I will do something else. So how do I know which thread is using run()?

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• Select calls seems to not time out.

  - by martsbradley

  HI Folks, I have a threaded C++ program where up to three threads are calling select on a three separate socket descriptors waiting for data to become available. Each thread handles one socket and adds it to the readfds with a timeout of 300 seconds. After select returns if there is data available I'm calling recv to read it. Is there anything that I need to be aware of with winsock and threads because for some reason after a number of hours the select calls all seem to be not timing out. Can a multi threaded program select from a number of threads without issue? I know that I should have one thread listening to all three sockets however that would be a large change for this app and I'm only looking to apply a bug fix. cheers, Martin.

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• Why is volatile not considered useful in multithreaded C or C++ programming?

  - by Michael E

  As demonstrated in this answer I recently posted, I seem to be confused about the utility (or lack thereof) of volatile in multi-threaded programming contexts. My understanding is this: any time a variable may be changed outside the flow of control of a piece of code accessing it, that variable should be declared to be volatile. Signal handlers, I/O registers, and variables modified by another thread all constitute such situations. So, if you have a global int foo, and foo is read by one thread and set atomically by another thread (probably using an appropriate machine instruction), the reading thread sees this situation in the same way it sees a variable tweaked by a signal handler or modified by an external hardware condition and thus foo should be declared volatile (or, for multithreaded situations, accessed with memory-fenced load, which is probably a better a solution). How and where am I wrong?

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• PHP thread pool?

  - by embedded

  I have scheduled a CRON job to run every 4 hours which needs to gather user accounts information. Now I want to speed things up and to split the work between several processes and to use one process to update the MySQL DB with the retrieved data from other processes. In JAVA I know that there is a thread pool which I can dedicate some threads to accomplish some work. how do I do it in PHP? Any advice is welcome. Thank

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• Cleanest Way to Invoke Cross-Thread Events

  - by Nick

  I find that the .NET event model is such that I'll often be raising an event on one thread and listening for it on another thread. I was wondering what the cleanest way to marshal an event from a background thread onto my UI thread is. Based on the community suggestions, I've used this: // earlier in the code mCoolObject.CoolEvent+= new CoolObjectEventHandler(mCoolObject_CoolEvent); // then private void mCoolObject_CoolEvent(object sender, CoolObjectEventArgs args) { if (InvokeRequired) { CoolObjectEventHandler cb = new CoolObjectEventHandler( mCoolObject_CoolEvent); Invoke(cb, new object[] { sender, args }); return; } // do the dirty work of my method here }

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• How to end a thread in perl

  - by user1672190

  I am new to perl and i have a question about perl thread. I am trying to create a new thread to check if the running function is timed out, and my way of doing it is as below. Logic is 1.create a new thread 2.run the main function and see if it is timed out, if ture, kill it Sample code: $exit_tread = false; # a flag to make sure timeout thread will run my $thr_timeout = threads->new( \&timeout ); execute main function here; $exit_thread = true # set the flag to true to force thread ends $thr_timeout->join(); #wait for the timeout thread ends Code of timeout function sub timeout { $timeout = false; my $start_time = time(); while (!$exit_thread) { sleep(1); last if (main function is executed); if (time() - $start_time >= configured time ) { logmsg "process is killed as request timed out"; _kill_remote_process(); $timeout = true; last; } } } now the code is running as i expected, but i am just not very clear if the code $exit_thread = true works because there is a "last" at the end of while loop. Can anybody give me a answer? Thanks

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• C# Threading and Sql Connections

  - by Jonathan M

  I have a method that attempts to update a sql server database in an ASP.NET application. If the update fails, it catches the exception and then queues the update in MSMQ, and then spins up a new thread that will later de-queue the pending update and try again. When the thread starts, it fails to open a database connection because it is attempting to connect using Network Service as the login. The sql connection is using Windows Authentication, and will work outside of the thread. If I put a breakpoint in the code that executes inside the new thread and check the Thread.CurrentPrincipal, it shows the Identity as being the correct user. Why is the sql connection attempting to be opened by the Network Service account? I can elaborate further is necessary. Thanks.

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• How do I run two threads in Ruby at the same time?

  - by Arcath

  Is there some way to run 2 threads at the same time? I want to have my app run its current function and then bring up another thread running another function, that can change variables in the first thread.

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• DispatcherOperations.Wait()

  - by Mark

  What happens if you call dispatcherOperation.Wait() on an operation that has already completed? Also, the docs say that it returns a DispatcherOperationStatus, but wouldn't that always be Completed since it (supposedly) doesn't return until it's done? I was trying to use it like this: private void Update() { while (ops.Count > 0) ops.Dequeue().Wait(); } public void Add(T item) { lock (sync) { if (dispatcher.CheckAccess()) { list.Add(item); OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item)); } else { ops.Enqueue(dispatcher.BeginInvoke(new Action<T>(Add), item)); } } } I'm using this in WPF, so all the Add operations have to occur on the UI thread, but I figured I could basically just queue them up without having to wait for it to switch threads, and then just call Update() before any read operations to ensure that the list is up to date, but my program started hanging.

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• Multi-threaded random_r is slower than single threaded version.

  - by Nixuz

  The following program is essentially the same the one described here. When I run and compile the program using two threads (NTHREADS == 2), I get the following run times: real 0m14.120s user 0m25.570s sys 0m0.050s When it is run with just one thread (NTHREADS == 1), I get run times significantly better even though it is only using one core. real 0m4.705s user 0m4.660s sys 0m0.010s My system is dual core, and I know random_r is thread safe and I am pretty sure it is non-blocking. When the same program is run without random_r and a calculation of cosines and sines is used as a replacement, the dual-threaded version runs in about 1/2 the time as expected. #include <pthread.h> #include <stdlib.h> #include <stdio.h> #define NTHREADS 2 #define PRNG_BUFSZ 8 #define ITERATIONS 1000000000 void* thread_run(void* arg) { int r1, i, totalIterations = ITERATIONS / NTHREADS; for (i = 0; i < totalIterations; i++){ random_r((struct random_data*)arg, &r1); } printf("%i\n", r1); } int main(int argc, char** argv) { struct random_data* rand_states = (struct random_data*)calloc(NTHREADS, sizeof(struct random_data)); char* rand_statebufs = (char*)calloc(NTHREADS, PRNG_BUFSZ); pthread_t* thread_ids; int t = 0; thread_ids = (pthread_t*)calloc(NTHREADS, sizeof(pthread_t)); /* create threads */ for (t = 0; t < NTHREADS; t++) { initstate_r(random(), &rand_statebufs[t], PRNG_BUFSZ, &rand_states[t]); pthread_create(&thread_ids[t], NULL, &thread_run, &rand_states[t]); } for (t = 0; t < NTHREADS; t++) { pthread_join(thread_ids[t], NULL); } free(thread_ids); free(rand_states); free(rand_statebufs); } I am confused why when generating random numbers the two threaded version performs much worse than the single threaded version, considering random_r is meant to be used in multi-threaded applications.

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• Understanding java's native threads and the jvm

  - by Moev4

  I understand that the jvm is itself an application that turns the bytecode of the java executable into native machine code, but when using native threads I have some questions that I just cannot seem to answer. Does every thread create their own instance of the jvm to handle their particular execution? If not then does the jvm have to have some way to schedule which thread it will handle next, if so wouldn't this render the multi-threaded nature of java useless since only one thread can be ran at a time?

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• Does Interlocked guarantee visibility to other threads in C# or do I still have to use volatile?

  - by Lirik

  I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Interlocked. This is needed in scenarios where other libraries, interfaces or hardware can access your variable and update it anytime, or need the most recent version. Does Interlocked guarantee visibility of the atomic operation to all threads, or do I still have to use the volatile keyword on the value in order to guarantee visibility of the change? Here is my example: public class CountDownLatch { private volatile int m_remain; // <--- do I need the volatile keyword there since I'm using Interlocked? private EventWaitHandle m_event; public CountDownLatch (int count) { Reset(count); } public void Reset(int count) { if (count < 0) throw new ArgumentOutOfRangeException(); m_remain = count; m_event = new ManualResetEvent(false); if (m_remain == 0) { m_event.Set(); } } public void Signal() { // The last thread to signal also sets the event. if (Interlocked.Decrement(ref m_remain) == 0) m_event.Set(); } public void Wait() { m_event.WaitOne(); } }

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• Python Terminated Thread Cannot Restart

  - by Mel Kaye

  Hello, I have a thread that gets executed when some action occurs. Given the logic of the program, the thread cannot possibly be started while another instance of it is still running. Yet when I call it a second time, I get a "RuntimeError: thread already started" error. I added a check to see if it is actually alive using the Thread.is_alive() function, and it is actually dead. What am I doing wrong? I can provide more details as are needed.

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• dao as a member of a servlet - normal?

  - by EugeneP

  I guess, DAO is thread safe, does not use any class members. So can it be used without any problem as a private field of a Servlet ? We need only one copy, and multiple threads can access it simultaneously, so why bother creating a local variable, right?

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• Why wait should always be in synchronized block

  - by diy

  Hi gents, We all know that in order to invoke Object.wait() , this call must be placed in synchronized block,otherwise,IllegalMonitorStateException is thrown.But what's the reason for making this restriction?I know that wait() releases the monitor, but why do we need to explicitly acquire the monitor by making particular block synchronized and then release the monitor by calling wait() ? What is the potential damage if it was possible to invoke wait() outside synch block, retaining it's semantics - suspending the caller thread ? Thanks in advance

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• Minimizing Java Thread Context Switching Overhead

  - by binil

  I have a Java application running on Sun 1.6 32-bit VM/Solaris 10 (x86)/Nahelem 8-core(2 threads per core). A specific usecase in the application is to respond to some external message. In my performance test environment, when I prepare and send the response in the same thread that receives the external input, I get about 50 us advantage than when I hand off the message to a separate thread to send the response. I use a ThreadPoolExecutor with a SynchronousQueue to do the handoff. In your experience what is the acceptable delay between scheduling a task to a thread pool and it getting picked up for execution? What ideas had worked for you in the past to try improve this?

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• Help me find article on Multi-threading and Event Handling in Java

  - by JDR

  I once read an article on how to properly write event handlers for multi-threading in Java, but I can't for the life of me find it anymore. It described the pitfalls and potentials for deadlocks that can occur when firing events (not Swing events mind you, but general events like model update notifications). To clarify, the situation would be as such: // let's say this is code from an MVC model somewhere public void setSomeProperty(String myProperty){ if(!this.myProperty.equals(myProperty)){ this.myProperty = myProperty; fireMyPropertyChangedEvent(...); } } The article described how passing control to arbitrary external listener code was a potential cause for deadlock. I now find myself in a situation where I need to fire such events in a multithreaded environment and I would very much like to read the article again to see what it has to say before I continue. Does anyone know the article I'm referring to? I believe it came as a (fairly short) PDF. It started off with an initial naive implementation and incrementally pointed out flaws and improved upon it. It ended with a sort of final proper-way-to-fire-multithreaded-events. I've searched endlessly in my browse history and on google, but all I could find were endless amounts topics on Swing event dispatch threads. Thank you.

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• How solve consumer/producer task using semaphores

  - by user1074896

  I have SimpleProducerConsumer class that illustrate consumer/producer problem (I am not sure that it's correct). public class SimpleProducerConsumer { private Stack<Object> stack = new Stack<Object>(); private static final int STACK_MAX_SIZE = 10; public static void main(String[] args) { SimpleProducerConsumer pc = new SimpleProducerConsumer(); new Thread(pc.new Producer(), "p1").start(); new Thread(pc.new Producer(), "p2").start(); new Thread(pc.new Consumer(), "c1").start(); new Thread(pc.new Consumer(), "c2").start(); new Thread(pc.new Consumer(), "c3").start(); } public synchronized void push(Object d) { while (stack.size() >= STACK_MAX_SIZE) try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } stack.push(new Object()); System.out.println("push " + Thread.currentThread().getName() + " " + stack.size()); notify(); } public synchronized Object pop() { while (stack.size() == 0) try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } try { Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } stack.pop(); System.out.println("pop " + Thread.currentThread().getName() + " " + stack.size()); notify(); return null; } class Consumer implements Runnable { @Override public void run() { while (true) { pop(); } } } class Producer implements Runnable { @Override public void run() { while (true) { push(new Object()); } } } } I found simple realization of semaphore(here:http://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html I know that there is concurrency package) How I need to change code to exchange java objects monitors to my custom semaphore. (To illustrate C/P problem using semaphores) Semaphore: class Semaphore { private int counter; public Semaphore() { this(0); } public Semaphore(int i) { if (i < 0) throw new IllegalArgumentException(i + " < 0"); counter = i; } public synchronized void release() { if (counter == 0) { notify(); } counter++; } public synchronized void acquire() throws InterruptedException { while (counter == 0) { wait(); } counter--; } }

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• Perl TCP Server handling multiple Client connections

  - by Matt

  I'll preface this by saying I have minimal experience with both Perl and Socket programming, so I appreciate any help I can get. I have a TCP Server which needs to handle multiple Client connections simultaneously and be able to receive data from any one of the Clients at any time and also be able to send data back to the Clients based on information it's received. For example, Client1 and Client2 connect to my Server. Client2 sends "Ready", the server interprets that and sends "Go" to Client1. The following is what I have written so far: my $sock = new IO::Socket::INET { LocalHost => $host, // defined earlier in code LocalPort => $port, // defined earlier in code Proto => 'tcp', Listen => SOMAXCONN, Reuse => 1, }; die "Could not create socket $!\n" unless $sock; while ( my ($new_sock,$c_addr) = $sock->accept() ) { my ($client_port, $c_ip) = sockaddr_in($c_addr); my $client_ipnum = inet_ntoa($c_ip); my $client_host = ""; my @threads; print "got a connection from $client_host", "[$client_ipnum]\n"; my $command; my $data; while ($data = <$new_sock>) { push @threads, async \&Execute, $data; } } sub Execute { my ($command) = @_; // if($command) = "test" { // send "go" to socket1 print "Executing command: $command\n"; system($command); } I know both of my while loops will be blocking and I need a way to implement my accept command as a thread, but I'm not sure the proper way of writing it.

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• boost thread pool

  - by Dtag

  I need a threadpool for my application, and I'd like to rely on standard (C++11 or boost) stuff as much as possible. I realize there is an unofficial(!) boost thread pool class, which basically solves what I need, however I'd rather avoid it because it is not in the boost library itself -- why is it still not in the core library after so many years? In some posts on this page and elsewhere, people suggested using boost::asio to achieve a threadpool like behavior. At first sight, that looked like what I wanted to do, however I found out that all implementations I have seen have no means to join on the currently active tasks, which makes it useless for my application. To perform a join, they send stop signal to all the threads and subsequently join them. However, that completely nullifies the advantage of threadpools in my use case, because that makes new tasks require the creation of a new thread. What I want to do is: ThreadPool pool(4); for (...) { for (int i=0;i<something;i++) pool.pushTask(...); pool.join(); // do something with the results } Can anyone suggest a solution (except for using the existing unofficial thread pool on sourceforge)? Is there anything in C++11 or core boost that can help me here? Thanks a lot

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