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  • simple process rollback question

    - by OckhamsRazor
    hi folks! while revising for an exam, i came across this simple question asking about rollbacks in processes. i understand how rollbacks occur, but i need some validation on my answer. The question: my confusion results from the fact that there is interprocess communication between the processes. does that change anything in terms of where to rollback? my answer would be R13, R23, R32 and R43. any help is greatly appreciated! thanks!

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  • C++ VB6 interfacing problem

    - by Roshan
    Hi, I'm tearing my hair out trying to solve this one, any insights will be much appreciated: I have a C++ exe which acquires data from some hardware in the main thread and processes it in another thread (thread 2). I use a c++ dll to supply some data processing functions which are called from thread 2. I have a requirement to make another set of data processing functions in VB6. I have thus created a VB6 dll, using the add-in vbAdvance to create a standard dll. When I call functions from within this VB6 dll from the main thread, everything works exactly as expected. When I call functions from this VB6 dll in thread 2, I get an access violation. I've traced the error to the CopyMemory command, it would seem that if this is used within the call from the main thread, it's fine but in a call from the process thread, it causes an exception. Why should this be so? As far as I understand, threads share the same address space. Here is the code from my VB dll Public Sub UserFunInterface(ByVal in1ptr As Long, ByVal out1ptr As Long, ByRef nsamples As Long) Dim myarray1() As Single Dim myarray2() As Single Dim i As Integer ReDim myarray1(0 To nsamples - 1) As Single ReDim myarray2(0 To nsamples - 1) As Single With tsa1din(0) ' defined as safearray1d in a global definitions module .cDims = 1 .cbElements = 4 .cElements = nsamples .pvData = in1ptr End With With tsa1dout .cDims = 1 .cbElements = 4 .cElements = nsamples .pvData = out1ptr End With CopyMemory ByVal VarPtrArray(myarray1), VarPtr(tsa1din(0)), 4 CopyMemory ByVal VarPtrArray(myarray2), VarPtr(tsa1dout), 4 For i = 0 To nsamples - 1 myarray2(i) = myarray1(i) * 2 Next i ZeroMemory ByVal VarPtrArray(myarray1), 4 ZeroMemory ByVal VarPtrArray(myarray2), 4 End Sub

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  • How to save objects using Multi-Threading in Core Data?

    - by Konstantin
    I'm getting some data from the web service and saving it in the core data. This workflow looks like this: get xml feed go over every item in that feed, create a new ManagedObject for every feed item download some big binary data for every item and save it into ManagedObject call [managedObjectContext save:] Now, the problem is of course the performance - everything runs on the main thread. I'd like to re-factor as much as possible to another thread, but I'm not sure where I should start. Is it OK to put everything (1-4) to the separate thread?

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  • Socket.Recieve Failing When Multithreaded

    - by Qua
    The following piece of code runs fine when parallelized to 4-5 threads, but starts to fail as the number of threads increase somewhere beyond 10 concurrentthreads int totalRecieved = 0; int recieved; StringBuilder contentSB = new StringBuilder(4000); while ((recieved = socket.Receive(buffer, SocketFlags.None)) > 0) { contentSB.Append(Encoding.ASCII.GetString(buffer, 0, recieved)); totalRecieved += recieved; } The Recieve method returns with zero bytes read, and if I continue calling the recieve method then I eventually get a 'An established connection was aborted by the software in your host machine'-exception. So I'm assuming that the host actually sent data and then closed the connection, but for some reason I never recieved it. I'm curious as to why this problem arises when there are a lot of threads. I'm thinking it must have something to do with the fact that each thread doesn't get as much execution time and therefore there are some idle time for the threads which causes this error. Just can't figure out why idle time would cause the socket not to recieve any data.

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  • How to approach parallel processing of messages?

    - by Dan
    I am redesigning the messaging system for my app to use intel threading building blocks and am stumped trying to decide between two possible approaches. Basically, I have a sequence of message objects and for each message type, a sequence of handlers. For each message object, I apply each handler registered for that message objects type. The sequential version would be something like this (pseudocode): for each message in message_sequence <- SEQUENTIAL for each handler in (handler_table for message.type) apply handler to message <- SEQUENTIAL The first approach which I am considering processes the message objects in turn (sequentially) and applies the handlers concurrently. Pros: predictable ordering of messages (ie, we are guaranteed a FIFO processing order) (potentially) lower latency of processing each message Cons: more processing resources available than handlers for a single message type (bad parallelization) bad use of processor cache since message objects need to be copied for each handler to use large overhead for small handlers The pseudocode of this approach would be as follows: for each message in message_sequence <- SEQUENTIAL parallel_for each handler in (handler_table for message.type) apply handler to message <- PARALLEL The second approach is to process the messages in parallel and apply the handlers to each message sequentially. Pros: better use of processor cache (keeps the message object local to all handlers which will use it) small handlers don't impose as much overhead (as long as there are other handlers also to be run) more messages are expected than there are handlers, so the potential for parallelism is greater Cons: Unpredictable ordering - if message A is sent before message B, they may both be processed at the same time, or B may finish processing before all of A's handlers are finished (order is non-deterministic) The pseudocode is as follows: parallel_for each message in message_sequence <- PARALLEL for each handler in (handler_table for message.type) apply handler to message <- SEQUENTIAL The second approach has more advantages than the first, but non-deterministic ordering is a big disadvantage.. Which approach would you choose and why? Are there any other approaches I should consider (besides the obvious third approach: parallel messages and parallel handlers, which has the disadvantages of both and no real redeeming factors as far as I can tell)? Thanks!

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  • For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue?

    - by Jonathan Allen
    For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue? Concerns: * My goal is to pull up to 100 items at a time and send them as a batch to the next step. * If I use a ConcurrentQueue, I have to manually cause it to go asleep when there is no work to be done. Otherwise I waste CPU cycles on spinning. * If I use a BlockingQueue and I only have 99 work items, it could indefinitely block until there the 100th item arrives. http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx

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  • Python - question regarding the concurrent use of `multiprocess`.

    - by orokusaki
    I want to use Python's multiprocessing to do concurrent processing without using locks (locks to me are the opposite of multiprocessing) because I want to build up multiple reports from different resources at the exact same time during a web request (normally takes about 3 seconds but with multiprocessing I can do it in .5 seconds). My problem is that, if I expose such a feature to the web and get 10 users pulling the same report at the same time, I suddenly have 60 interpreters open at the same time (which would crash the system). Is this just the common sense result of using multiprocessing, or is there a trick to get around this potential nightmare? Thanks

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  • How to interrupt a thread performing a blocking socket connect?

    - by Jason R
    I have some code that spawns a pthread that attempts to maintain a socket connection to a remote host. If the connection is ever lost, it attempts to reconnect using a blocking connect() call on its socket. Since the code runs in a separate thread, I don't really care about the fact that it uses the synchronous socket API. That is, until it comes time for my application to exit. I would like to perform some semblance of an orderly shutdown, so I use thread synchronization primitives to wake up the thread and signal for it to exit, then perform a pthread_join() on the thread to wait for it to complete. This works great, unless the thread is in the middle of a connect() call when I command the shutdown. In that case, I have to wait for the connect to time out, which could be a long time. This makes the application appear to take a long time to shut down. What I would like to do is to interrupt the call to connect() in some way. After the call returns, the thread will notice my exit signal and shut down cleanly. Since connect() is a system call, I thought that I might be able to intentionally interrupt it using a signal (thus making the call return EINTR), but I'm not sure if this is a robust method in a POSIX threads environment. Does anyone have any recommendations on how to do this, either using signals or via some other method? As a note, the connect() call is down in some library code that I cannot modify, so changing to a non-blocking socket is not an option.

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  • For Loop help In a Hash Cracker Homework.

    - by aaron burns
    On the homework I am working on we are making a hash cracker. I am implementing it so as to have my cracker. java call worker.java. Worker.java implements Runnable. Worker is to take the start and end of a list of char, the hash it is to crack, and the max length of the password that made the hash. I know I want to do a loop in run() BUT I cannot think of how I would do it so it would go to the given max pasword length. I have posted the code I have so far. Any directions or areas I should look into.... I thought there was a way to do this with a certain way to write the loop but I don't know or can't find the correct syntax. Oh.. also. In main I divide up so x amount of threads can be chosen and I know that as of write now it only works for an even number of the 40 possible char given. package HashCracker; import java.util.*; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; public class Cracker { // Array of chars used to produce strings public static final char[] CHARS = "abcdefghijklmnopqrstuvwxyz0123456789.,-!".toCharArray(); public static final int numOfChar=40; /* Given a byte[] array, produces a hex String, such as "234a6f". with 2 chars for each byte in the array. (provided code) */ public static String hexToString(byte[] bytes) { StringBuffer buff = new StringBuffer(); for (int i=0; i<bytes.length; i++) { int val = bytes[i]; val = val & 0xff; // remove higher bits, sign if (val<16) buff.append('0'); // leading 0 buff.append(Integer.toString(val, 16)); } return buff.toString(); } /* Given a string of hex byte values such as "24a26f", creates a byte[] array of those values, one byte value -128..127 for each 2 chars. (provided code) */ public static byte[] hexToArray(String hex) { byte[] result = new byte[hex.length()/2]; for (int i=0; i<hex.length(); i+=2) { result[i/2] = (byte) Integer.parseInt(hex.substring(i, i+2), 16); } return result; } public static void main(String args[]) throws NoSuchAlgorithmException { if(args.length==1)//Hash Maker { //create a byte array , meassage digestand put password into it //and get out a hash value printed to the screen using provided methods. byte[] myByteArray=args[0].getBytes(); MessageDigest hasher=MessageDigest.getInstance("SHA-1"); hasher.update(myByteArray); byte[] digestedByte=hasher.digest(); String hashValue=Cracker.hexToString(digestedByte); System.out.println(hashValue); } else//Hash Cracker { ArrayList<Thread> myRunnables=new ArrayList<Thread>(); int numOfThreads = Integer.parseInt(args[2]); int charPerThread=Cracker.numOfChar/numOfThreads; int start=0; int end=charPerThread-1; for(int i=0; i<numOfThreads; i++) { //creates, stores and starts threads. Runnable tempWorker=new Worker(start, end, args[1], Integer.parseInt(args[1])); Thread temp=new Thread(tempWorker); myRunnables.add(temp); temp.start(); start=end+1; end=end+charPerThread; } } } import java.util.*; public class Worker implements Runnable{ private int charStart; private int charEnd; private String Hash2Crack; private int maxLength; public Worker(int start, int end, String hashValue, int maxPWlength) { charStart=start; charEnd=end; Hash2Crack=hashValue; maxLength=maxPWlength; } public void run() { byte[] myHash2Crack_=Cracker.hexToArray(Hash2Crack); for(int i=charStart; i<charEnd+1; i++) { Cracker.numOfChar[i]////// this is where I am stuck. } } }

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  • My multithread program works slowly or appear deadlock on dual core machine, please help

    - by Shangping Guo
    I have a program with several threads, one thread will change a global when it exits itself and the other thread will repeatedly poll the global. No any protection on the globals. The program works fine on uni-processor. On dual core machine, it works for a while and then halt either on Sleep(0) or SuspendThread(). Would anyone be able to help me out on this? The code would be like this: Thread 1: do something... while(1) { ..... flag_thread1_running=false; SuspendThread(GetCurrentThread()); continue; } Thread 2 .... while(flag_thread1_running==false) Sleep(0); ....

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  • How to implement cancellable worker thread

    - by Arnold Zokas
    Hi, I'm trying to implement a cancellable worker thread using the new threading constructs in System.Threading.Tasks namespace. So far I have have come up with this implementation: public sealed class Scheduler { private CancellationTokenSource _cancellationTokenSource; public System.Threading.Tasks.Task Worker { get; private set; } public void Start() { _cancellationTokenSource = new CancellationTokenSource(); Worker = System.Threading.Tasks.Task.Factory.StartNew( () => RunTasks(_cancellationTokenSource.Token), _cancellationTokenSource.Token ); } private static void RunTasks(CancellationToken cancellationToken) { while (!cancellationToken.IsCancellationRequested) { Thread.Sleep(1000); // simulate work } } public void Stop() { try { _cancellationTokenSource.Cancel(); Worker.Wait(_cancellationTokenSource.Token); } catch (OperationCanceledException) { // OperationCanceledException is expected when a Task is cancelled. } } } When Stop() returns I expect Worker.Status to be TaskStatus.Canceled. My unit tests have shown that under certain conditions Worker.Status remains set to TaskStatus.Running. Is this a correct way to implement a cancellable worker thread?

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  • How to update GUI thread/class from worker thread/class?

    - by user315182
    First question here so hello everyone. The requirement I'm working on is a small test application that communicates with an external device over a serial port. The communication can take a long time, and the device can return all sorts of errors. The device is nicely abstracted in its own class that the GUI thread starts to run in its own thread and has the usual open/close/read data/write data basic functions. The GUI is also pretty simple - choose COM port, open, close, show data read or errors from device, allow modification and write back etc. The question is simply how to update the GUI from the device class? There are several distinct types of data the device deals with so I need a relatively generic bridge between the GUI form/thread class and the working device class/thread. In the GUI to device direction everything works fine with [Begin]Invoke calls for open/close/read/write etc. on various GUI generated events. I've read the thread here (How to update GUI from another thread in C#?) where the assumption is made that the GUI and worker thread are in the same class. Google searches throw up how to create a delegate or how to create the classic background worker but that's not at all what I need, although they may be part of the solution. So, is there a simple but generic structure that can be used? My level of C# is moderate and I've been programming all my working life, given a clue I'll figure it out (and post back)... Thanks in advance for any help.

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  • Are indivisible operations still indivisible on multiprocessor and multicore systems?

    - by Steve314
    As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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  • How to correctly stop thread which is using Control.Invoke

    - by codymanix
    I tried the following (pseudocode) but I always get a deadlock when Iam trying to stop my thread. The problem is that Join() waits for the thread to complete and a pending Invoke() operation is also waiting to complete. How can I solve this? Thread workerThread = new Thread(BackupThreadRunner); volatile bool cancel; // this is the thread worker routine void BackupThreadRunner() { while (!cancel) { DoStuff(); ReportProgress(); } } // main thread void ReportProgress() { if (InvokeRequired) { Invoke(ReportProgress); } UpdateStatusBarAndStuff(); } // main thread void DoCancel() { cancel=true; workerThread.Join(); }

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  • How to Perform Continues Iteration over Shared Dictionary in Multi-threaded Environment

    - by Mubashar Ahmad
    Dear Gurus. Note Pls do not tell me regarding alternative to custom session, Pls answer only relative to the Pattern Scenario I have Done Custom Session Management in my application(WCF Service) for this I have a Dictionary shared to all thread. When a specific function Gets called I add a New Session and Issue SessionId to the client so it can use that sessionId for rest of his calls until it calls another specific function, which terminates this session and removes the session from the Dictionary. Due to any reason Client may not call session terminator function so i have to implement time expiration logic so that i can remove all such sessions from the memory. For this I added a Timer Object which calls ClearExpiredSessions function after the specific period of time. which iterates on the dictionary. Problem: As this dictionary gets modified every time new client comes and leaves so i can't lock the whole dictionary while iterating over it. And if i do not lock the dictionary while iteration, if dictionary gets modified from other thread while iterating, Enumerator will throw exception on MoveNext(). So can anybody tell me what kind of Design i should follow in this case. Is there any standard pattern available.

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  • Bluetooth in Java Mobile: Handling connections that go out of range

    - by Albus Dumbledore
    I am trying to implement a server-client connection over the spp. After initializing the server, I start a thread that first listens for clients and then receives data from them. It looks like that: public final void run() { while (alive) { try { /* * Await client connection */ System.out.println("Awaiting client connection..."); client = server.acceptAndOpen(); /* * Start receiving data */ int read; byte[] buffer = new byte[128]; DataInputStream receive = client.openDataInputStream(); try { while ((read = receive.read(buffer)) > 0) { System.out.println("[Recieved]: " + new String(buffer, 0, read)); if (!alive) { return; } } } finally { System.out.println("Closing connection..."); receive.close(); } } catch (IOException e){ e.printStackTrace(); } } } It's working fine for I am able to receive messages. What's troubling me is how would the thread eventually die when a device goes out of range? Firstly, the call to receive.read(buffer) blocks so that the thread waits until it receives any data. If the device goes out of range, it would never proceed onward to check if meanwhile it has been interrupted. Secondly, it would never close the connection, i.e. the server would not accept the device once it goes back in range. Thanks! Any ideas would be highly appreciated! Merry Christmas!

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  • how to multithread on a python server

    - by user3732790
    HELP please i have this code import socket from threading import * import time HOST = '' # Symbolic name meaning all available interfaces PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print ('Socket created') s.bind((HOST, PORT)) print ('Socket bind complete') s.listen(10) print ('Socket now listening') def listen(conn): odata = "" end = 'end' while end == 'end': data = conn.recv(1024) if data != odata: odata = data print(data) if data == b'end': end = "" print("conection ended") conn.close() while True: time.sleep(1) conn, addr = s.accept() print ('Connected with ' + addr[0] + ':' + str(addr[1])) Thread.start_new_thread(listen,(conn)) and i would like it so that when ever a person comes onto the server it has its own thread. but i can't get it to work please someone help me. :_( here is the error code: Socket created Socket bind complete Socket now listening Connected with 127.0.0.1:61475 Traceback (most recent call last): File "C:\Users\Myles\Desktop\test recever - Copy.py", line 29, in <module> Thread.start_new_thread(listen,(conn)) AttributeError: type object 'Thread' has no attribute 'start_new_thread' i am on python version 3.4.0 and here is the users code: import socket #for sockets import time s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print('Socket Created') host = 'localhost' port = 8888 remote_ip = socket.gethostbyname( host ) print('Ip address of ' + host + ' is ' + remote_ip) #Connect to remote server s.connect((remote_ip , port)) print ('Socket Connected to ' + host + ' on ip ' + remote_ip) while True: message = input("> ") #Set the whole string s.send(message.encode('utf-8')) print ('Message send successfully') data = s.recv(1024) print(data) s.close

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  • Pointers to threads

    - by viswanathan
    Suppose i have pointer to a thread like this CWinThread *m_pThread = AfxBeginThread(StartThread, this, THREAD_PRIORITY_NORMAL, 0, 0); Now in my StartThread function assume i did all operations and the function returned like this UINT CClassThread::StartThread(LPVOID pVoid) { return true; } Will my m_pThread be invalid when the return statement is executed?

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  • Setting the default stack size on Linux globally for the program

    - by wowus
    So I've noticed that the default stack size for threads on linux is 8MB (if I'm wrong, PLEASE correct me), and, incidentally, 1MB on Windows. This is quite bad for my application, as on a 4-core processor that means 64 MB is space is used JUST for threads! The worst part is, I'm never using more than 100kb of stack per thread (I abuse the heap a LOT ;)). My solution right now is to limit the stack size of threads. However, I have no idea how to do this portably. Just for context, I'm using Boost.Thread for my threading needs. I'm okay with a little bit of #ifdef hell, but I'd like to know how to do it easily first. Basically, I want something like this (where windows_* is linked on windows builds, and posix_* is linked under linux builds) // windows_stack_limiter.c int limit_stack_size() { // Windows impl. return 0; } // posix_stack_limiter.c int limit_stack_size() { // Linux impl. return 0; } // stack_limiter.cpp int limit_stack_size(); static volatile int placeholder = limit_stack_size(); How do I flesh out those functions? Or, alternatively, am I just doing this entirely wrong? Remember I have no control over the actual thread creation (no new params to CreateThread on Windows), as I'm using Boost.Thread.

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  • C++ threaded class design from non-threaded class

    - by macs
    I'm working on a library doing audio encoding/decoding. The encoder shall be able to use multiple cores (i.e. multiple threads, using boost library), if available. What i have right now is a class that performs all encoding-relevant operations. The next step i want to take is to make that class threaded. So i'm wondering how to do this. I thought about writing a thread-class, creating n threads for n cores and then calling the encoder with the appropriate arguments. But maybe this is an overkill and there is no need for another class, so i'm going to make use of the "user interface" for thread-creation. I hope there are any suggestions.

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  • asp.net Background Threads Exception Handling

    - by Chris
    In my 3.5 .net web application I have a background thread that does a lot of work (the application is similar to mint.com in that it does a lot of account aggregation on background threads). I do extensive exception handling within the thread performing the aggregation but there's always the chance an unhandled exception will be thrown and my entire application will die. I've read some articles about this topic but they all seem fairly outdated and none of them implement a standard approach. Is there a standard approach to this nowadays? Is there any nicer way to handle this in ASP.NET 4.0?

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  • What is Erlang's concurrency model actually ?

    - by arun_suresh
    I was reading a paper recently Why Events are Bad. The paper is a comparative study of Event based and thread based highly concurrent servers and finally concludes stating that Threads are better than events in that scenario. I find that I am not able to classify what sort of concurrency model erlang exposes. Erlang provides Light Weight Processes, but those processes are suspended most of the time until it has received some event/message of some sort. /Arun

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  • Async call Objective C iphone

    - by Sam
    Hi guys, I'm trying to get data from a website- xml. Everything works fine. But the UIButton remains pressed until the xml data is returned and thus if theres a problem with the internet service, it cant be corrected and the app is virtually unusable. here are the calls: { AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate]; if(!appDelegate.XMLdataArray.count > 0){ [UIApplication sharedApplication].networkActivityIndicatorVisible = YES; [appDelegate GetApps]; //function that retrieves data from Website and puts into the array - XMLdataArray. } XMLViewController *controller = [[XMLViewController alloc] initWithNibName:@"MedGearsApps" bundle:nil]; [self.navigationController pushViewController:controller animated:YES]; [controller release]; } It works fine, but how can I make the view buttons functional with getting stuck. In other words, I just want the UIButton and other UIButtons to be functional whiles the thing works in the background. I heard about performSelectorInMainThread but i cant put it to practice correctly any help is appreciated :)

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