- Createthread example
- Handle createthread windows
- Windows threads
- Createthread waitforsingleobject
Synchronization is a very hot topic in all threading subjects. Almost all the programs using threading are in some way will be implementing a synchronization object in their source. Windows provides a number of synchronization objects and objects that are wait able on the synchronization objects. WaitForSingleObject is one such wait able object. This WaitForSingleObject is a single object wait function. It requires a handle to be supplied as a parameter for it to wait on. The handle can be from objects like a thread, event, mutex, semaphore etc. Once these objects are signaled, then WaitForSingleObject function returns immediately. When this is set to a specified amount of time, the function WaitForSingleObject returns either when it is signaled or when the time specified has elapsed. The biggest advantage or use of WaitForSingleObject is when there are a lot of threads used and there is a need to track if all of them are complete. For example there might be a program while closing, might need to exit all the threads, close all pipes, sockets etc. In such cases, we can put a wait using WaitForSingleObject and exit once all of them give a green signal and then close the program. A small sample is provided using a thread, an event object on which the WaitForSingleObject function waits and exits after it becomes signaled. As above the function WaitForSingleObject can be made to wait on all synchronization objects. WaitForSingleobject can also be used in small timer implementations because of its ability to wait for a specified amount of time.
Createthread exampleWindows Supported. WaitForSingleObject halts program execution temporarily, until either a specified object enters a signaled state or a specified timeout period elapses. This function allows a program to wait until something else has happened before execution continues. The mutex is now owned by the calling thread and is in a nonsignaled state. Use GetLastError to get the error code. This handle can refer to one of the following types of objects: Change Notification Console Input Event Job is signaled when the job has finished Mutex Process is signaled when the process has terminated Semaphore Thread is signaled when the thread has terminated Waitable timer dwMilliseconds The timeout interval to wait for. Wait until the user has closed the window before continuing with the example. The example begins when the user clicks button Command1. Obviously, to use this example, you need to place a command button named Command1 on a form window. With sei ' Size of the structure. End With ' Open the file using its associated program. LastDllError ' could also be used instead, if you wish. Select Case sei. Print "An unexpected error occured. This allows the DoEvents VB function to be called, preventing ' our program from appearing to lock up while it waits. Print "Notepad or whatever program was opened has just closed. Back to the Function list. Back to the Reference section. E-mail: vbapi vbapi.
Lpthread_start_routineThe WaitForSingleObject function returns when one of the following occurs: The specified object is in the signaled state. The time-out interval elapses. For a list of the object types whose handles can be specified, see the following Remarks section. For more information, see Standard Access Rights. The function returns if the interval elapses, even if the object's state is nonsignaled. If dwMilliseconds is zero, the function tests the object's state and returns immediately. Return Values If the function succeeds, the return value indicates the event that caused the function to return. This value can be one of the following. To get extended error information, call GetLastError. The WaitForSingleObject function checks the current state of the specified object. If the object's state is nonsignaled, the calling thread enters an efficient wait state. The thread consumes very little processor time while waiting for the object state to become signaled or the time-out interval to elapse. Before returning, a wait function modifies the state of some types of synchronization objects. Modification occurs only for the object whose signaled state caused the function to return. For example, the count of a semaphore object is decreased by one. Use caution when calling the wait functions and code that directly or indirectly creates windows. If a thread creates any windows, it must process messages. Message broadcasts are sent to all windows in the system. A thread that uses a wait function with no time-out interval may cause the system to become deadlocked. Windows CE: Windows CE does not support waiting for semaphores, change notification objects, console input, and timers. Windows NT: Requires version 3. Windows: Requires Windows 95 or later. Windows CE: Requires version 1. Header: Declared in winbase. Import Library: Use kernel The specified object is a mutex object that was not released by the thread that owned the mutex object before the owning thread terminated. Ownership of the mutex object is granted to the calling thread, and the mutex is set to nonsignaled.
CreateremotethreadAdded a sentence for clarity. See also the short follow-up post. Synchronize seems so handy, and yet because it must use WaitForSingleObjectis so fraught with complications. Simpler than fiddling with synchronisation primitives, right? Everyone knows threading is hard, so use the well-tested thread utilities where you can? The basic problem is that these calls can cause deadlocks, if you ever call them from a thread that has its own message loop and windows. And other libraries can create their own windows as well, such as the ADO libraries. So what causes the deadlock? BackgroundThread used TThread. Synchronize to periodically update the UI status about a background database process it was running. Behind the scenes, a second window was automatically created by Windows once we had the first window in the thread, and this one had the class name IME. This would signal an event which the main thread would check periodically from its message loop. Eventually it would call the RefreshStatus procedure. Where are we going? Well, if the main thread receives a message that it then decides to send on to other windows in the process, while BackgroundThread is getting ready to synchronize, we can end up in a deadlock. Remember, this is just one possible scenario which can trigger a deadlock. We can see that the main thread has sent a message somewhere. It turns out it has sent a message to a window in the same thread The window handle c is just the Edit window :. So why is it stalling? First, we find the process details:. And we can see the first thread has the address a Highlighted above there is a call to win32k! This is passed the address of a window at bbe And when we look at that, we see the following:. And window d01fe is the IME window for the other, deadlocked thread! Why is the kernel sending a message to another thread here and now? And without a timeout? Next was to figure out why we were getting that. After a fair bit of exploration, I looked at little harder at the call stack, and decided to investigate the parameters for xxxActivateKeyboardLayout :. That sounds pretty suspicious! However, the issue can still arise if you ever use that flag in your own code when calling ActivateKeyboardLayout. Synchronizewhich unfortunately by design cannot be robust against deadlocks. The blog post describes exactly what is happening. Thanks Eric. Just changing a factor of the problem without understanding the root cause is not a good programming practice. And in this situation, the root cause of the deadlock was certainly unexpected. Furthermore, this model of thread synchronisation — using TThread.
WinthreadTo wait for multiple objects, use WaitForMultipleObjects. A handle to the object. For a list of the object types whose handles can be specified, see the following Remarks section. For more information, see Standard Access Rights. The time-out interval, in milliseconds. If a nonzero value is specified, the function waits until the object is signaled or the interval elapses. If dwMilliseconds is zero, the function does not enter a wait state if the object is not signaled; it always returns immediately. For example, the timeout does keep counting down while the computer is asleep. For example, the timeout does not keep counting down while the computer is asleep. If the function succeeds, the return value indicates the event that caused the function to return. It can be one of the following values. The WaitForSingleObject function checks the current state of the specified object. If the object's state is nonsignaled, the calling thread enters the wait state until the object is signaled or the time-out interval elapses. The function modifies the state of some types of synchronization objects. Modification occurs only for the object whose signaled state caused the function to return. For example, the count of a semaphore object is decreased by one. For an example, see Using Mutex Objects. Synchronization Functions. Wait Functions. Skip to main content. Contents Exit focus mode. If this handle is closed while the wait is still pending, the function's behavior is undefined. Return value If the function succeeds, the return value indicates the event that caused the function to return. Ownership of the mutex object is granted to the calling thread and the mutex state is set to nonsignaled. If the mutex was protecting persistent state information, you should check it for consistency. To get extended error information, call GetLastError. The WaitForSingleObject function can wait for the following objects: Change notification Console input Event Memory resource notification Mutex Process Semaphore Thread Waitable timer Use caution when calling the wait functions and code that directly or indirectly creates windows. If a thread creates any windows, it must process messages. Message broadcasts are sent to all windows in the system. A thread that uses a wait function with no time-out interval may cause the system to become deadlocked. Examples For an example, see Using Mutex Objects. Is this page helpful? Yes No. Any additional feedback?
Handle createthread windows
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