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• What the difference between deadlock avoidance and deadlock prevention?

  - by skydoor

  I met two terms and are they the same thing or different thing?

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• C# Threads.Abort()

  - by Betamoo

  If a thread is running a function func1 that calls another function func2 inside it... Then I called thread.Abort() Will this stop func1 only OR func1 and func2 and all the functions func1 has called?? Thanks Edit: Here are more detail: func1 is called in a new thread, it continuously calls func2 on regular basis... func2 begin doing some work only if some array is not null.. it finishes it and return When supervisor wants to save data, it aborts Thread of func1- and then makes array null, saves data, then fill in the array with new one.. and starts Thread with func1 again.. Sometimes exception is raised because array is null in func2.. so func1 abort did not affect func2

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• How to simulate an unhandled exception in Java

  - by Martin Wiboe

  Hi, I am creating some multi-threaded code, and I have created a JobDispatcher class that creates threads. I want this object to handle any unhandled exceptions in the worker threads, and so I am using Thread.setUncaughtExceptionHandler(this); Now, I would like to test this functionality - how can I generate an unhandled exception in the run() method of my worker object? Thanks, Martin

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• Thread safe lazy contruction of a singleton in C++

  - by pauldoo

  Is there a way to implement a singleton object in C++ that is: Lazily constructed in a thread safe manner (two threads might simultaneously be the first user of the singleton - it should still only be constructed once). Doesn't rely on static variables being constructed beforehand (so the singleton object is itself safe to use during the construction of static variables). (I don't know my C++ well enough, but is it the case that integral and constant static variables are initialized before any code is executed (ie, even before static constructors are executed - their values may already be "initialized" in the program image)? If so - perhaps this can be exploited to implement a singleton mutex - which can in turn be used to guard the creation of the real singleton..) Excellent, it seems that I have a couple of good answers now (shame I can't mark 2 or 3 as being the answer). There appears to be two broad solutions: Use static initialisation (as opposed to dynamic initialisation) of a POD static varible, and implementing my own mutex with that using the builtin atomic instructions. This was the type of solution I was hinting at in my question, and I believe I knew already. Use some other library function like pthread_once or boost::call_once. These I certainly didn't know about - and am very grateful for the answers posted.

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• Why can't I use an Action to a ThreadStart?

  - by Rookian

  Both are delegates and have the same signature, but I can not use Action as ThreadStart. Why? Action doIt; doIt = () => MyMethod("test"); Thread t; t = new Thread(doIt); t.Start(); but this seams to work: Thread t; t = new Thread(() => MyMethod("test")); t.Start();

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• What is difference between Thread Affinity and Process affinity ?

  - by DotNetBeginner

  What is difference between Thread Affinity and Process affinity ? If I have two Threads and I have duel core machine then is it possible to run these two threads parallely on the two cores ? If I use processor affinity Mask then I can control execution of a process on the cores but when I have to run threads on a particular core how can I make these threads core specific ? A very simple example will be appreciated.

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• Async Socket Listener on separate thread - VB.net

  - by TheHockeyGeek

  I am trying to use the code from Microsoft for an Async Socket connection. It appears the listener runs in the main thread locking the GUI. I am new at both socket connections and multi-threading all at the same time. Having a hard time getting my mind wrapped around this all at once. The code used is at http://msdn.microsoft.com/en-us/library/fx6588te.aspx Using this example, how can I move the listener to its own thread? Public Shared Sub Main() ' Data buffer for incoming data. Dim bytes() As Byte = New [Byte](1023) {} ' Establish the local endpoint for the socket. Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName()) Dim ipAddress As IPAddress = ipHostInfo.AddressList(1) Dim localEndPoint As New IPEndPoint(ipAddress, 11000) ' Create a TCP/IP socket. Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) ' Bind the socket to the local endpoint and listen for incoming connections. listener.Bind(localEndPoint) listener.Listen(100)

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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• WCF service and COM interop callback

  - by Sjblack

  I have a COM object that creates an instance of a WCF service and passes a handle to itself as a callback. The com object is marked/initialized as MTA. The problem being every instance of the WCF service that makes a call to the callback occurs on the same thread so they are being processed one at a time which is causing session timeouts under a heavy load. The WCF service is session based not sure if that makes any difference.

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• Cocoa Touch - Display an Activity Indicator while loading a UITabBar View

  - by Aurum Aquila

  I have a UITabBar Application with two views that load large amounts of data from the web in their "viewWillAppear" methods. I want to show a progress bar or an activity indicator while this data is being retrieved, to make sure the user knows the app isn't frozen. I am aware that this has been asked before. I simply need some clarification on what seems to be a rather good solution. I have implimented the code in the example. The question's original asker later solved their problem, by putting the retrieval of data into another "thread". I understand the concept of threads, but I do not know how I would impliment this. With research, I have found that I need to move all of my heavy data retrieval into a background thread, as all of the UI updating occurs in the main thread. If one would be so kind as to provide an example for me, I would be very appreciative. I can provide parts of my existing code as necessary.

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• Me.Invoke in VB.NET doesn't actually "Invoke" - threads stall on Invoke statement

  - by rwmnau

  I've got the following code: Public Delegate Sub SetStatusBarTextDelegate(ByVal StatusText As String) Private Sub SetStatusBarText(ByVal StatusText As String) If Me.InvokeRequired Then Me.Invoke(New SetStatusBarTextDelegate(AddressOf SetStatusBarText), StatusText) Else Me.labelScanningProgress.Text = StatusText End If End Sub The problem is that, when I call the "SetStatusBarText" sub from another thread, InvokeRequired is True (as it should be), but then my threads stall on the Me.Invoke statement - pausing execution shows them all just sitting there, not actually invoking anything. Any thoughts about why the threads seem to be afraid of the Invoke?

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• Variable mysteriously changing value

  - by Eitan

  I am making a simple tcp/ip chat program for practicing threads and tcp/ip. I was using asynchronous methods but had a problem with concurrency so I went to threads and blocking methods (not asynchronous). I have two private variables defined in the class, not static: string amessage = string.Empty; int MessageLength; and a Thread private Thread BeginRead; Ok so I call a function called Listen ONCE when the client starts: public virtual void Listen(int byteLength) { var state = new StateObject {Buffer = new byte[byteLength]}; BeginRead = new Thread(ReadThread); BeginRead.Start(state); } and finally the function to receive commands and process them, I'm going to shorten it because it is really long: private void ReadThread(object objectState) { var state = (StateObject)objectState; int byteLength = state.Buffer.Length; while (true) { var buffer = new byte[byteLength]; int len = MySocket.Receive(buffer); if (len <= 0) return; string content = Encoding.ASCII.GetString(buffer, 0, len); amessage += cleanMessage.Substring(0, MessageLength); if (OnRead != null) { var e = new CommandEventArgs(amessage); OnRead(this, e); } } } Now, as I understand it only one thread at a time will enter BeginRead, I call Receive, it blocks until I get data, and then I process it. The problem: the variable amessage will change it's value between statements that do not touch or alter the variable at all, for example at the bottom of the function at: if (OnRead != null) "amessage" will be equal to 'asdf' and at if (OnRead != null) "amessage" will be equal to qwert. As I understand it this is indicative of another thread changing the value/running asynchronously. I only spawn one thread to do the receiving and the Receive function is blocking, how could there be two threads in this function and if there is only one thread how does amessage's value change between statements that don't affect it's value. As a side note sorry for spamming the site with these questions but I'm just getting a hang of this threading story and it's making me want to sip cyanide. Thanks in advance. EDIT: Here is my code that calls the Listen Method in the client: public void ConnectClient(string ip,int port) { client.Connect(ip,port); client.Listen(5); } and in the server: private void Accept(IAsyncResult result) { var client = new AbstractClient(MySocket.EndAccept(result)); var e = new CommandEventArgs(client, null); Clients.Add(client); client.Listen(5); if (OnClientAdded != null) { var target = (Control) OnClientAdded.Target; if (target != null && target.InvokeRequired) target.Invoke(OnClientAdded, this, e); else OnClientAdded(this, e); } client.OnRead += OnRead; MySocket.BeginAccept(new AsyncCallback(Accept), null); } All this code is in a class called AbstractClient. The client inherits the Abstract client and when the server accepts a socket it create's it's own local AbstractClient, in this case both modules access the functions above however they are different instances and I couldn't imagine threads from different instances combining especially as no variable is static.

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• Why does Python's math.factorial not play nice with threads?

  - by W1N9Zr0

  Why does math.factorial act so weird in a thread? Here is an example, it creates three threads: thread that just sleeps for a while thread that increments an int for a while thread that does math.factorial on a large number. It calls start on the threads, then join with a timeout The sleep and spin threads work as expected and return from start right away, and then sit in the join for the timeout. The factorial thread on the other hand does not return from start until it runs to the end! import sys from threading import Thread from time import sleep, time from math import factorial # Helper class that stores a start time to compare to class timed_thread(Thread): def __init__(self, time_start): Thread.__init__(self) self.time_start = time_start # Thread that just executes sleep() class sleep_thread(timed_thread): def run(self): sleep(15) print "st DONE:\t%f" % (time() - time_start) # Thread that increments a number for a while class spin_thread(timed_thread): def run(self): x = 1 while x < 120000000: x += 1 print "sp DONE:\t%f" % (time() - time_start) # Thread that calls math.factorial with a large number class factorial_thread(timed_thread): def run(self): factorial(50000) print "ft DONE:\t%f" % (time() - time_start) # the tests print print "sleep_thread test" time_start = time() st = sleep_thread(time_start) st.start() print "st.start:\t%f" % (time() - time_start) st.join(2) print "st.join:\t%f" % (time() - time_start) print "sleep alive:\t%r" % st.isAlive() print print "spin_thread test" time_start = time() sp = spin_thread(time_start) sp.start() print "sp.start:\t%f" % (time() - time_start) sp.join(2) print "sp.join:\t%f" % (time() - time_start) print "sp alive:\t%r" % sp.isAlive() print print "factorial_thread test" time_start = time() ft = factorial_thread(time_start) ft.start() print "ft.start:\t%f" % (time() - time_start) ft.join(2) print "ft.join:\t%f" % (time() - time_start) print "ft alive:\t%r" % ft.isAlive() And here is the output on Python 2.6.5 on CentOS x64: sleep_thread test st.start: 0.000675 st.join: 2.006963 sleep alive: True spin_thread test sp.start: 0.000595 sp.join: 2.010066 sp alive: True factorial_thread test ft DONE: 4.475453 ft.start: 4.475589 ft.join: 4.475615 ft alive: False st DONE: 10.994519 sp DONE: 12.054668 I've tried this on python 2.6.5 on CentOS x64, 2.7.2 on Windows x86 and the factorial thread does not return from start on either of them until the thread is done executing. I've also tried this with PyPy 1.8.0 on Windows x86, and there result is slightly different. The start does return immediately, but then the join doesn't time out! sleep_thread test st.start: 0.001000 st.join: 2.001000 sleep alive: True spin_thread test sp.start: 0.000000 sp DONE: 0.197000 sp.join: 0.236000 sp alive: False factorial_thread test ft.start: 0.032000 ft DONE: 9.011000 ft.join: 9.012000 ft alive: False st DONE: 12.763000

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• Does JavaME and/or Proguard reorder assignments?

  - by chrisdew

  This is a simplified example - I have two threads: Can JavaME and/Proguard ever reorder the obX = ... statements, such that thread_B will have a null pointer exception at ob2.someMethod? thread_A: Object ob1 = null; Object ob2 = null; ... ob1 = something1; ob2 = something2; thread_B: if (ob2 != null) { ob1.someMethod(); ... } P.S. I do realise that synchronising these will avoid the issue. Synchronisation has both a performance overhead, and more importantly, a chance to introduce deadlock.

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• Testing a Non-blocking Queue

  - by jsw

  I've ported the non-blocking queue psuedocode here to C#. The code below is meant as a near verbatim copy of the paper. What approach would you take to test the implementation? Note: I'm running in VS2010 so I don't have CHESS support yet. using System.Threading; #pragma warning disable 0420 namespace ConcurrentCollections { class QueueNodePointer<T> { internal QueueNode<T> ptr; internal QueueNodePointer() : this(null) { } internal QueueNodePointer(QueueNode<T> ptr) { this.ptr = ptr; } } class QueueNode<T> { internal T value; internal QueueNodePointer<T> next; internal QueueNode() : this(default(T)) { } internal QueueNode(T value) { this.value = value; this.next = new QueueNodePointer<T>(); } } public class ConcurrentQueue<T> { private volatile int count = 0; private QueueNodePointer<T> qhead = new QueueNodePointer<T>(); private QueueNodePointer<T> qtail = new QueueNodePointer<T>(); public ConcurrentQueue() { var node = new QueueNode<T>(); node.next.ptr = null; this.qhead.ptr = this.qtail.ptr = node; } public int Count { get { return this.count; } } public void Enqueue(T value) { var node = new QueueNode<T>(value); node.next.ptr = null; QueueNodePointer<T> tail; QueueNodePointer<T> next; while (true) { tail = this.qtail; next = tail.ptr.next; if (tail == this.qtail) { if (next.ptr == null) { var newtail = new QueueNodePointer<T>(node); if (Interlocked.CompareExchange(ref tail.ptr.next, newtail, next) == next) { Interlocked.Increment(ref this.count); break; } else { Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } } } } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(node), tail); } public T Dequeue() { T value; while (true) { var head = this.qhead; var tail = this.qtail; var next = head.ptr.next; if (head == this.qhead) { if (head.ptr == tail.ptr) { if (next.ptr == null) { return default(T); } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } else { value = next.ptr.value; var newhead = new QueueNodePointer<T>(next.ptr); if (Interlocked.CompareExchange(ref this.qhead, newhead, head) == head) { Interlocked.Decrement(ref this.count); break; } } } } return value; } } } #pragma warning restore 0420

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• Monitor.Wait, Pulse - When worker thread should conditionally behave as an actual worker thread

  - by Griever

  My particular scenario: - Main thread starts a worker thread. - Main thread needs to block itself until either worker thread is completed (yeah funny) or worker thread itself informs main thread to go on Alright, so what I did in main thread: wokerThread.Start(lockObj); lock(lockObj) Monitor.Wait(lockObj); Somewhere in worker thread: if(mainThreadShouldGoOn) lock(lockObj) Monitor.Pulse(lockObj); Also, at the end of worker thread: lock(lockObj) Monitor.Pulse(lockObj); So far, it's working perfect. But is it a good solution? Is there a better one?

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• Advantage of using Thread.Start vs QueueUserWorkItem

  - by Cheeso

  In multithreaded .NET programming, what are the decision criteria for using ThreadPool.QueueUserWorkItem versus starting my own thread via new Thread() and Thread.Start()? In a server app (let's say, an ASP.NET app or a WCF service) I think the ThreadPool is always there and available. What about in a client app, like a WinForms or WPF app? Is there a cost to spin up the thread pool? If I just want 3 or 4 threads to work for a short period on some computation, is it better to QUWI or to Thread.Start().

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• Basic Java Multi-Threading Question

  - by Veered

  When an object is instantiated in Java, is it bound to the thread that instantiated in? Because when I anonymously implement an interface in one thread, and pass it to another thread to be run, all of its methods are run in the original thread. If they are bound to their creation thread, is there anyway to create an object that will run in whatever thread calls it?

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• Does operator new allocate on THREAD heap?

  - by Jonas Byström

  My problem seems to be this: heap data allocated by one thread (that later dies) seems to die as well. As so: Thread X: starts Thread Y: starts Thread X: ptr = new some bytes Thread X: dies Thread Y: tries to use ptr - and crashes! So far, I've only seen this problem on Darwin (Mac OS 10.5 and 10.6), but haven't tried more other platforms than Windows and Linux (Ubuntu) where it works as expected. I've had this problem for some time, so any know-how or more information about this is highly appreciated!

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• Multi-Threading - Cleanup strategy at program end

  - by weismat

  What is the best way to finish a multi-threaded application in a clean way? I am starting several socket connections from the main thread in seperate sockets and wait until the end of my business day in the main thread and use currently System.Environment.Exit(0) to terminate it. This leads to an unhandled execption in one of the childs. Should I stop the threads from the list? I have been reluctant to implement any real stopping in the childs yet, thus I am wondering about the best practice. The sockets are all wrapped nicely with proper destructors for logging out and closing, but it still leads to errors.

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• Using SetThreadAffinityMask function imported from kernel32.dll in C # code.

  - by DotNetBeginner

  I am trying to set Thread Affinity using SetThreadAffinityMask function imported from kernel32.dll in C # code of mine. This is how I import SetThreadAffinityMask function from "kernel32.dll" in my C# .net code [DllImport("kernel32.dll")] static extern IntPtr SetThreadAffinityMask(IntPtr hThread, IntPtr dwThreadAffinityMask); I am creating 3 threads Thread t1=new Thread(some delegate); Thread t2=new Thread(some delegate); Thread t3=new Thread(some delegate); I wish to set Thread affinity for t1,t2 & t3 for which I am using SetThreadAffinityMask function. But I am not getting how to pass parameters to this function. SetThreadAffinityMask takes two parameters 1. HANDLE hThread 2. DWORD_PTR dwThreadAffinityMask Please help me in using SetThreadAffinityMask function in C# Thanks in advance !

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• Java - How to detect that the internet connection has got disconnected through a java desktop applic

  - by Yatendra Goel

  I am developing a Java Desktop Application that access internet. It is a multi-threaded application, each thread do the same work (means each thread is an instance of same Thread class). Now, as all the threads need internet connection to be active, there should be some mechanism that detects whether an internet connection is active or not. Q1. How to detect whether the internet connection is active or not? Q2. Where to implement this internet-status-check-mechanism code? Should I start a separate thread for checking internet status regularly and notifies all the threads when the status changes from one state to another? Or should I let each thread check for the internet-status itself? Q3. This issue should be a very common issue as every application accessing an internet should deal with this problem. So how other developers usually deal with this problem? Q4. If you could give me a reference to a good demo application that addresses this issue then it would greatly help me.

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• Parallelism in Python

  - by fmark

  What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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• Thread Proc for an instancable class?

  - by user146780

  Basically I have a class and it is instincable (not static). Basically I want the class to be able to generate its own threads and manage its own stuff. I don't want to make a global callback for each instance I make, this doesnt seem clean and proper to me. What is the proper way of doing what I want. If I try to pass the threadproc to CreateThread and it is the proc from a class instance the compiler says I cannot do this. What is the best way of achieving what I want? Thanks

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• How can I make these images download on a separate thread?

  - by Andy Barlow

  I have the following code running on my Android device. It works great and displays my list items wonderfully. It's also clever in the fact it only downloads the data when it's needed by the ArrayAdapter. However, whilst the download of the thumbnail is occurring, the entire list stalls and you cannot scroll until it's finished downloading. Is there any way of threading this so it'll still scroll happily, maybe show a place holder for the downloading image, finish the download, and then show? Any help with this would be really appreciated. private class CatalogAdapter extends ArrayAdapter<SingleQueueResult> { private ArrayList<SingleQueueResult> items; //Must research what this actually does! public CatalogAdapter(Context context, int textViewResourceId, ArrayList<SingleQueueResult> items) { super(context, textViewResourceId, items); this.items = items; } /** This overrides the getview of the ArrayAdapter. It should send back our new custom rows for the list */ @Override public View getView(int position, View convertView, ViewGroup parent) { View v = convertView; if (v == null) { LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE); v = vi.inflate(R.layout.mylists_rows, null); } final SingleQueueResult result = items.get(position); // Sets the text inside the rows as they are scrolled by! if (result != null) { TextView title = (TextView)v.findViewById(R.id.mylist_title); TextView format = (TextView)v.findViewById(R.id.mylist_format); title.setText(result.getTitle()); format.setText(result.getThumbnail()); // Download Images ImageView myImageView = (ImageView)v.findViewById(R.id.mylist_thumbnail); downloadImage(result.getThumbnail(), myImageView); } return v; } } // This should run in a seperate thread public void downloadImage(String imageUrl, ImageView myImageView) { try { url = new URL(imageUrl); URLConnection conn = url.openConnection(); conn.connect(); InputStream is = conn.getInputStream(); BufferedInputStream bis = new BufferedInputStream(is); Bitmap bm = BitmapFactory.decodeStream(bis); bis.close(); is.close(); myImageView.setImageBitmap(bm); } catch (IOException e) { /* Reset to Default image on any error. */ //this.myImageView.setImageDrawable(getResources().getDrawable(R.drawable.default)); } }

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