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Basics of Multithreading |
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It’s a concept that was introduced with the win32 style of application coding,
which allows multiple threads to run at the same time in a process or
application. The concurrent execution can be on different processors or in the
same processor in a time sliced manner. Each thread has its own stack and its own copy of the CPU registers. Other resources of the process are shared by all threads and while trying to access them it should be synchronized. Win32 provides a number of synchronization methods like 1. Semaphores 2. Critical section 3. Events 4. Mutexes These objects are either in the signaled or non-signaled state. By specifying the handle to any of these objects in a call to one of the wait functions would block the execution of the calling thread until the state of the specified object is signaled. This is different in case of a critical section we use the EnterCriticalSection to get hold of a critical section object. Some of the wait functions used in the above case is 1. WaitforSingleObject (single-object wait functions) 2. WaitForMultipleObject (multiple-object wait functions) 3. SignalObjectAndWait (Alertable wait functions) 4. RegisterWaitForSingleObject (Registered wait functions) The synchronization is needed for globally shared resources or data. And it is advisable to use global data only in time of need. We can make use of the Threads Local Storage capabilities to store per-thread data. And there are some TLS API (Tlsalloc, TlsGetValue, TlsSetValue and TlsFree) to access these information. When a new thread is created, a handle to the thread is returned. And it is valid until closed, even after the thread it represents has been terminated. The handle can be duplicated with the DuplicateHandle API. A thread also contains a thread ID which is unique to the thread and can be accessed using the API GetCurrentThreadID. It is important to note that no thread identifier will have a value 0 and is valid only until the thread is terminated. We could get a thread handle using the OpenThread API, if we are in possession of the thread identifier. A thread can suspend and resume its execution using the SuspendThread and ResumeThread APIs. Sleep or SleepEx are used to delay the execution of a thread for a specified interval of time. |
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| RELATED TOPICS | |||
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What is a thread? Thread Pools Thread Vs Process MultiThreading support in C++ and MFC Creating User-Interface Threads in MFC Creating worker Threads in MFC Terminating Threads Thread Synchronization Designing a Thread-safe class Semaphore in MFC Mutex in MFC Critical Section in MFC Event Objects in MFC CSingleLock and CMultiLock in MFC |
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