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• VB.net Cross-Thread

  - by PandaNL

  Hello, I have a cmd command that needs to be executed, when the command starts it starts to fill a progressbar. When the cmd command is done the progressbar needs to fill up to 100. This is the code i use, but it gives me an error when the progressbar.Value = 100 comes up. Public Class Form1 Dim teller As Integer Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TimerProgressbar.Tick teller += 1 ProgressBar1.Value = teller If ProgressBar1.Value = ProgressBar1.Maximum Then TimerProgressbar.Stop() End If End Sub This are the tow commands in another private sub where the app is crashing on ProgressBar1.Value = 100 TimerProgressbar.Stop() When i debug it and i try it out it crashes on ProgressBar1.Value = 100 But when i build it under Windows 7 it runs fine without crashing, however a few people reported me it crashes on there Windows xp system. VB gives me a suggestions about Cross Thread, but i don't know how i could make it work with this.

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• Cross-thread operation not valid: Control accessed from a thread other than the thread it was create

  - by SilverHorse

  I have a scenario. (Windows Forms, C#, .NET) There is a main form which hosts some user control. The user control does some heavy data operation, such that if I directly call the Usercontrol_Load method the UI become nonresponsive for the duration for load method execution. To overcome this I load data on different thread (trying to change existing code as little as I can) I used a background worker thread which will be loading the data and when done will notify the application that it has done its work. Now came a real problem. All the UI (main form and its child usercontrols) was created on the primary main thread. In the LOAD method of the usercontrol I'm fetching data based on the values of some control (like textbox) on userControl. The pseudocode would look like this: //CODE 1 UserContrl1_LOadDataMethod() { if(textbox1.text=="MyName") <<======this gives exception { //Load data corresponding to "MyName". //Populate a globale variable List<string> which will be binded to grid at some later stage. } } The Exception it gave was Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on. To know more about this I did some googling and a suggestion came up like using the following code //CODE 2 UserContrl1_LOadDataMethod() { if(InvokeRequired) // Line #1 { this.Invoke(new MethodInvoker(UserContrl1_LOadDataMethod)); return; } if(textbox1.text=="MyName") //<<======Now it wont give exception** { //Load data correspondin to "MyName" //Populate a globale variable List<string> which will be binded to grid at some later stage } } BUT BUT BUT... it seems I'm back to square one. The Application again become nonresponsive. It seems to be due to the execution of line #1 if condition. The loading task is again done by the parent thread and not the third that I spawned. I don't know whether I perceived this right or wrong. I'm new to threading. How do I resolve this and also what is the effect of execution of Line#1 if block? The situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread. So only accessing the value so that the corresponding data can be fetched from the database.

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• WPF - Pausing the UI Thread?

  - by Rachel

  I have a tab control with draggable tabs. When the mouse is released it removes the selected tab from the tabControl and adds it to its new location. My problem is that the TabControl draws itself after removing the tab, and then again when adding the tab so there is a very noticeable flicker that shows the tab behind the tab being moved. Is there a way I can pause the UI thread so the tab control does not redraw until both the Remove and the Insert operations finish? Or perhaps some other alternative way of rearranging the tab items? The Drag/Drop operation exists in a separate code file as an Attached Property

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• My Thread Programs Crash

  - by zp26

  I have a problem with threads objectiveC. The line of code below contains the recv block the program waiting for a datum. My intention is to launch a thread parallel to the program so that this statement does not block any application. I put this code in my program but when active switch the program crashes. Enter the code. -(IBAction)Chat{ if(switchChat.on){ buttonInvio.enabled = TRUE; fieldInvio.enabled = TRUE; [NSThread detachNewThreadSelector:@selector(riceviDatiServer) toTarget:self withObject:nil]; } else { buttonInvio.enabled = FALSE; fieldInvio.enabled = FALSE; } -(void)riceviDatiServer{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init]; int ricevuti; NSString *datiRicevuti; ricevuti = recv(temp, &datiRicevuti, datiRicevuti.length, 0); labelRicezione.text = [[NSString alloc] initWithFormat:@"%s.... %d", datiRicevuti, ricevuti]; [pool release]; }

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• Help with porting thread functionality: Win32 --> .Net

  - by JimDaniel

  Hi, I am responsible for porting a class from legacy Win32 code to .Net and I have come across a threading model that I'm not sure how best to implement in .Net. Basically the Win32 has one worker thread, which calls WaitForMultipleObjects() and executes the particular piece of code when a particular object has been triggered. This has a sort of first-come-first-serve effect that I need to emulate in my own code. But I'm not sure how best to do this in .Net. Does anyone have any idea? I see that there is no equivalent of WaitForMultipleObjects() in .Net, only the ThreadPool class, which seems to provide most of what I need, but I'm not sure if it's the best, since I only have four objects total to wait and execute code for. Thanks, Daniel

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• Sync between local service with a thread and an activity

  - by Henrik

  Hello all, I'm trying to think of a way on how to sync in between a local service and the main activity. The local service has, A thread with a socket connection that could receive data at any time. A list/array with data. At any time the socket could receive data and add it to the list. The activity needs to display this data. So when the activity starts up it needs to attach or start the local service and fetch the list. It also needs to be notified if the list is updated. I think I would need to sync my list somehow so the local service does not add a new entry to it while the activity fetches the list when connecting to the service. Any ideas? Thanks.

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• Activate thread synchronically

  - by mayap

  Hi All, I'm using .Net 4.0 parallel library. The tasks I execute, ask to run some other task, sometimes synchronically and somethimes asynchronically, dependending on some conditions which are not known in advanced. For async call, i simply create new tasks and that's it. I don't know how to handly sync call: how to run it from the same thread, maybe that sync tasks will also ask to execute sync tasks recursively. all this issue is pretty new to me. thanks in advance.

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• Thread Suicide on Shutdown?

  - by yar

  I have a java.util.Timer running at a fixed interval. I have added a Runtime#addShutdownHook and it shuts down when the VM ends normally or abnormally. However, it keeps the VM alive when a main terminates, unless I insist by doing a System.exit in the main. Is there any way for me to check if I'm the last Thread standing, or some other way to avoid altering a main that would exit normally on finish? Note: I know a lot of people believe that java.util.Timer is deprecated (it's not), but unless your alternative helps me solve this problem...

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• Is MSDN referencing a system.thread, a worker thread, an io thread or all three?

  - by w0051977

  Please see the warning below taken from the StreamWriter class specification (http://msdn.microsoft.com/en-us/library/system.io.streamwriter.aspx): "Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." I understand that a W3WC process contains two thread pools i.e. worker threads and I/O threads. A worker thread could contain many threads of its own (if the application creates its own System.Thread instances). Does the warning only relate to System.Threads or does it relate to worker threads and I/O threads as well I.e. as the instance variables of the streamwriter class are not thread safe then does this mean that there would be problems if multiple worker threads access it eg if two users on two different web clients attempt to write to the log file at the same time, then could one lock out the other?

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• Thread Synchronization and Synchronization Primitives

  When considering synchronization in an application, the decision truly depends on what the application and its worker threads are going to do. I would use synchronization if two or more threads could possibly manipulate the same instance of an object at the same time. An example of this in C# can be demonstrated through the use of storing data in a static object. A static object is initialized once per application and the data within the object can be accessed by all threads. I would use the synchronization primitives to prevent any data from being manipulated by multiple threads simultaneously. This would reduce any data corruption from occurring within the object. On the other hand if all the threads used non static objects and were independent of the other tasks there would be no need to use synchronization. Synchronization Primitives in C#: Basic Blocking Locking Signaling Non-Blocking Synchronization Constructs The Basic Blocking methods include Sleep, Join, and Task.Wait.  These methods force threads to wait until other threads have completed. In addition, these methods can also force a thread to wait a set amount of time before continuing to work.   The Locking primitive prevents a thread from entering a critical section of code while another thread is in the same critical section.  If another thread attempts to enter a locked code, it will wait, until the code block is released. The Signaling primitive allows a thread to temporarily pause work until receiving a notification from another thread that it is ok to continue working. The Signaling primitive removes the need for polling.The Non-Blocking Synchronization Constructs protect access to a common field by calling upon processor primitives.

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• Boost::thread mutex issue: Try to lock, access violation

  - by user1419305

  I am currently learning how to multithread with c++, and for that im using boost::thread. I'm using it for a simple gameengine, running three threads. Two of the threads are reading and writing to the same variables, which are stored inside something i call PrimitiveObjects, basicly balls, plates, boxes etc. But i cant really get it to work, i think the problem is that the two threads are trying to access the same memorylocation at the same time, i have tried to avoid this using mutex locks, but for now im having no luck, this works some times, but if i spam it, i end up with this exception: First-chance exception at 0x00cbfef9 in TTTTT.exe: 0xC0000005: Access violation reading location 0xdddddded. Unhandled exception at 0x77d315de in TTTTT.exe: 0xC0000005: Access violation reading location 0xdddddded. These are the functions inside the object that im using for this, and the debugger is also blaming them for the exception. void PrimitiveObj::setPos(glm::vec3 in){ boost::mutex mDisposingMutex; boost::try_mutex::scoped_try_lock lock(mDisposingMutex); if ( lock) { position = in; boost::try_mutex::scoped_try_lock unlock(mDisposingMutex); } } glm::vec3 PrimitiveObj::getPos(){ boost::mutex myMutex; boost::try_mutex::scoped_try_lock lock(myMutex); if ( lock) { glm::vec3 curPos = position; boost::try_mutex::scoped_try_lock unlock(myMutex); return curPos; } return glm::vec3(0,0,0); } Any ideas?

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• Windows Live Family Safety Service keeps closing Start Menu

  - by Jim McKeeth

  Got my kids a new Toshiba Laptop for Christmas. I was setting it all up for them so it would be ready to go. Tonight I installed Windows Live Family Safety Parental Controls. In the process of testing I discovered that on all the accounts the Start Menu closes automatically within 3 seconds (or less) of opening. It seems that it happens every 3 seconds, so sometimes it is immediate, and if I open it again then it will stay open for a full 3 seconds. This of course is rather annoying, and I need to wrap it up so it is ready to go under the tree. I disabled the Windows Live Family Safety Service, and that fixed it. Enable it again and the behavior returns. Is this a feature of the service? Can I disable that feature and keep the other features?

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• Synchronizing issue: I want the main thread to be run before another thread but it sometimes doesn´t

  - by Rox

  I have done my own small concurrency framework (just for learning purposes) inspired by the java.util.concurrency package. This is about the Callable/Future mechanism. My code below is the whole one and is compilable and very easy to understand. My problem is that sometimes I run into a deadlock where the first thread (the main thread) awaits for a signal from the other thread. But then the other thread has already notified the main thread before the main thread went into waiting state, so the main thread cannot wake up. FutureTask.get() should always be run before FutureTask.run() but sometimes the run() method (which is called by new thread) runs before the get() method (which is called by main thread). I don´t know how I can prevent that. This is a pseudo code of how I want the two threads to be run. //From main thread: Executor.submit().get() (in get() the main thread waits for new thread to notify) ->submit() calls Executor.execute(FutureTask object) -> execute() starts new thread -> new thread shall notify `main thread` I cannot understand how the new thread can start up and run faster than the main thread that actually starts the new thread. Main.java: public class Main { public static void main(String[] args) { new ExecutorServiceExample(); } public Main() { ThreadExecutor executor = new ThreadExecutor(); Integer i = executor.submit(new Callable<Integer>() { @Override public Integer call() { return 10; } }).get(); System.err.println("Value: "+i); } } ThreadExecutor.java: public class ThreadExecutor { public ThreadExecutor() {} protected <V> RunnableFuture<V> newTaskFor(Callable c) { return new FutureTask<V>(c); } public <V> Future<V> submit(Callable<V> task) { if (task == null) throw new NullPointerException(); RunnableFuture<V> ftask = newTaskFor(task); execute(ftask); return ftask; } public void execute(Runnable r) { new Thread(r).start(); } } FutureTask.java: import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; import java.util.logging.Level; import java.util.logging.Logger; public class FutureTask<V> implements RunnableFuture<V> { private Callable<V> callable; private volatile V result; private ReentrantLock lock = new ReentrantLock(); private Condition condition = lock.newCondition(); public FutureTask(Callable callable) { if (callable == null) throw new NullPointerException(); this.callable = callable; } @Override public void run() { acquireLock(); System.err.println("RUN"+Thread.currentThread().getName()); V v = this.callable.call(); set(v); condition.signal(); releaseLock(); } @Override public V get() { acquireLock(); System.err.println("GET "+Thread.currentThread().getName()); try { condition.await(); } catch (InterruptedException ex) { Logger.getLogger(FutureTask.class.getName()).log(Level.SEVERE, null, ex); } releaseLock(); return this.result; } public void set(V v) { this.result = v; } private void acquireLock() { lock.lock(); } private void releaseLock() { lock.unlock(); } } And the interfaces: public interface RunnableFuture<V> extends Runnable, Future<V> { @Override void run(); } public interface Future<V> { V get(); } public interface Callable<V> { V call(); }

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• Have main thread wait for a boost thread complete a task (but not finish).

  - by JAKE6459

  I have found plenty on making one thread wait for another to finish executing before continuing, but that is not what I wanted to do. I am not very familiar with using any multi-threading apis but right now I'm trying to learn boost. My situation is that I am using my main thread (the starting one from int main()) to create an instance of a class that is in charge of interacting with the main GUI. A class function is then called that creates a boost thread which in turn creates the GUI and runs the message pump. The thing I want to do is when my main thread calls the classes member function to create the GUI, I don't want that function to return until I tell it to from the newly created thread. This way my main thread can't continue and call more functions from the GUI class that interact with the GUI thread until that thread has completed GUI creation and entered the message loop. I think I may be able to figure it out if it was multiple boost thread objects interacting with each other, but when it is the main thread (non-boost object) interacting with a boost thread object, I get lost. Eventually I want a loop in my main thread to call a class function (among other tasks) to check if the user as entered any new input into the GUI (buy any changes detected by the message loop being updated into a struct and changing a bool to tell the main thread in the class function a change has occurred). Any suggestions for any of this would be greatly appreciated. This is the member function called by the main thread. int ANNGUI::CreateGUI() { GUIMain = new Main(); GUIThread = new boost::thread(boost::bind(&Main::MainThreadFunc, GUIMain)); return 0; }; This is the boost thread starting function. void Main::MainThreadFunc() { ANNVariables = new GUIVariables; WndProc = new WindowProcedure; ANNWindowsClass = new WindowsClass(ANNVariables, WndProc); ANNWindow = new MainWindow(ANNVariables); GUIMessagePump = new MessagePump; ANNWindow-ShowWindows(); while(true) { GUIMessagePump-ProcessMessage(); } }; BTW, everything compiles fine and when I run it, it works I just put a sleep() in the main thread so I can play with the GUI a little.

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• Identity.Name is disposed in a IIS7 Asp.NET MVC application Thread

  - by vIceBerg

  I have made the smallest demo project to illustrate my problem. You can download the sources Here Visual Studio 2008, .NET 3.5, IIS7, Windows 7 Ultimate 32 bits. The IIS Website is configured ONLY for Windows Authentication in an Integreated pipeline app pool (DefaultAppPool). Here's the problem. I have an Asp.NET MVC 2 application. In an action, I start a thread. The View returns. The thread is doing it's job... but it needs to access Thread.CurrentPrincipal.Identity.Name BANG The worker process of IIS7 stops. I have a window that says: "Visual Studio Just-In-Time Debugger An unhandled exception ('System.Object.DisposedException') occured in w3wp.exe [5524]" I checked with the debugger and the Thread.CurrentPrincipal.Identity is valid, but the Name property is disposed. If I put a long wait in the action before it returns the view, then the Thread can do it's job and the Identity.Name is not disposed. So I think the Name gets disposed when the view is returned. For the sake of the discussion, here's the code that the thread runs (but you can also download the demo project. The link is on top of this post): private void Run() { const int SECTOWAIT = 3; //wait SECTOWAIT seconds long end = DateTime.Now.Ticks + (TimeSpan.TicksPerSecond * SECTOWAIT); while (DateTime.Now.Ticks <= end) continue; //Check the currentprincipal. BANG!!!!!!!!!!!!! var userName = Thread.CurrentPrincipal.Identity.Name; } Here's the code that starts the thread public void Start() { Thread thread = new Thread(new ParameterizedThreadStart(ThreadProc)); thread.SetApartmentState(ApartmentState.MTA); thread.Name = "TestThread"; thread.Start(this); } static void ThreadProc(object o) { try { Builder builder = (Builder)o; builder.Run(); } catch (Exception ex) { throw; } } So... what am i doing wrong? Thanks

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• Pass a Message From Thread to Update UI

  - by Jay Dee

  Ive created a new thread for a file browser. The thread reads the contents of a directory. What I want to do is update the UI thread to draw a graphical representation of the files and folders. I know I can't update the UI from within a new thread so what I want to do is: whilst the file scanning thread iterates through a directories files and folders pass a file path string back to the UI thread. The handler in the UI thread then draws the graphical representation of the file passed back. public class New_Project extends Activity implements Runnable { private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { Log.d("New Thread","Proccess Complete."); Intent intent = new Intent(); setResult(RESULT_OK, intent); finish(); } }; public void getFiles(){ //if (!XMLEFunctions.canReadExternal(this)) return; pd = ProgressDialog.show(this, "Reading Directory.", "Please Wait...", true, false); Log.d("New Thread","Called"); Thread thread = new Thread(this); thread.start(); } public void run() { Log.d("New Thread","Reading Files"); getFiles(); handler.sendEmptyMessage(0); } public void getFiles() { for (int i=0;i<=allFiles.length-1;i++){ //I WANT TO PASS THE FILE PATH BACK TU A HANDLER IN THE UI //SO IT CAN BE DRAWN. **passFilePathBackToBeDrawn(allFiles[i].toString());** } } }

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• Connection Pooling vs Per-Thread JDBC Connection

  - by java_geek

  Which of these approaches is better ?

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• thread local stroage macosx

  - by anon

  http://developer.apple.com/mac/library/documentation/DeveloperTools/gcc-4.0.1/gcc/Thread_002dLocal.html Documents __thread yet my g++ compalins that __thread is not suppoted on my arch (Leopard on Macbookpro). Why is this? And how do I get around it?

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• VB.net: Is my Thread Safe List Solution actually safe?

  - by Shiftbit

  I've added teh following Extensions to my Project in order to create a thread safe list: Extensions If I want to conduct a simple operation on my list <Extension()> _ Public Sub Action(Of T)(ByVal list As List(Of T), ByVal action As Action(Of List(Of T))) SyncLock (list) action(list) End SyncLock End Sub If I want to pass it more than one parameter I could simply extend it with more items... <Extension()> _ Public Sub Action(Of T)(ByVal list As List(Of T), ByVal action As Action(Of List(Of T), T), ByVal item As T) SyncLock (list) Action(list, item) End SyncLock End Sub Actions I have created the following Action Examples: Private Sub Read(Of T)(ByVal list As List(Of T)) Console.WriteLine("Read") For Each item As T In list Console.WriteLine(item.ToString) Thread.Sleep(10) Next End Sub and also one that takes a parameter: Private Sub Write(Of T)(ByVal list As List(Of T), ByVal item As T) Thread.Sleep(100) list.Add(item) Console.WriteLine("Write") End Sub Initiating Then in my various threads I will call my Actions with: list.Action(AddressOf Read) or list.Action(AddressOf Write2, 10) Are these Extenxion methods thread safe or do you have other recommendations?

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• How do I make a background thread in Java that allows the main application to exit completely? This

  - by Bob

  I have a Java application that creates a new thread to do some work. I can launch the new thread with no problems. When the "main" program terminates, I want the thread I created to keep running - which it does... But the problem is, when I run the main application from Eclipse or from Ant under Windows, control doesn't return unless the background process is killed. If I fork the main java process in ant, I want control to return to ant once the main thread is done with its work... But as it is, ant continues to wait until both the main process and the created thread are both terminated. How do I launch the thread in the background such that control will return to ant when the "main" application is finished? (By the way, when I run the same application under Linux, I am able to do this with no problems).

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• Java Thread - Memory consistency errors

  - by Yatendra Goel

  I was reading a Sun's tutorial on Concurrency. But I couldn't understand exactly what memory consistency errors are? I googled about that but didn't find any helpful tutorial or article about that. I know that this question is a subjective one, so you can provide me links to articles on the above topic. It would be great if you explain it with a simple example.

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• Exception injection: Throwing an exception in other thread

  How to abort a non-cooperating thread by an exception

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• Thread safe GUI programming

  - by James

  I have been programming Java with swing for a couple of years now, and always accepted that GUI interactions had to happen on the Event Dispatch Thread. I recently started to use GTK+ for C applications and was unsurprised to find that GUI interactions had to be called on gtk_main. Similarly, I looked at SWT to see in what ways it was different to Swing and to see if it was worth using, and again found the UI thread idea, and I am sure that these 3 are not the only toolkits to use this model. I was wondering if there is a reason for this design i.e. what is the reason for keeping UI modifications isolated to a single thread. I can see why some modifications may cause issues (like modifying a list while it is being drawn), but I do not see why these concerns pass on to the user of the API. Is there a limit imposed by an operating system? Is there a good reason these concerns are not 'hidden' (i.e. some form of synchronization that is invisible to the user)? Is there any (even purely conceptual) way of creating a thread safe graphics library, or is such a thing actually impossible? I found this http://blogs.operationaldynamics.com/andrew/software/gnome-desktop/gtk-thread-awareness which seems to describe GTK differently to how I understood it (although my understanding was the same as many people's) How does this differ to other toolkits? Is it possible to implement this in Swing (as the EDT model does not actually prevent access from other threads, it just often leads to Exceptions)

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• Another thread pool

  A simple thread pool with minimal dependencies

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• How to do thread management in C++?

  - by Dipan Mehta

  We use pthread for thread management in C based systems. pthread is in general compilable by C++ compiler (like g++). However, what are the better ways of abstractions for threads in C++? Also, for making any system to be working in a multi-threaded system, it is also important to make thread safe. What are the standard libraries that requires alternative (installs) to be thread safe or are they unsafe for multi-threaded environments? Is smart pointers, templates require special measures to make it safe? What are the best practices for the thread managements in C++?

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