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Terminating a Thread

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Terminating a thread has the following results:

  • Any resources owned by the thread, such as windows and hooks, are freed.
  • The thread exit code is set.
  • The thread object is signaled.
  • If the thread is the only active thread in the process, the process is terminated. For more information, see Terminating a Process.

The GetExitCodeThread function returns the termination status of a thread. While a thread is executing, its termination status is STILL_ACTIVE. When a thread terminates, its termination status changes from STILL_ACTIVE to the exit code of the thread.

When a thread terminates, the state of the thread object changes to signaled, releasing any other threads that had been waiting for the thread to terminate. For more about synchronization, see Synchronizing Execution of Multiple Threads.

When a thread terminates, its thread object is not freed until all open handles to the thread are closed.

How Threads are Terminated

A thread executes until one of the following events occurs:

  • The thread calls the ExitThread function.
  • Any thread of the process calls the ExitProcess function.
  • The thread function returns.
  • Any thread calls the TerminateThread function with a handle to the thread.
  • Any thread calls the TerminateProcess function with a handle to the process.

The exit code for a thread is either the value specified in the call to ExitThread, ExitProcess, TerminateThread, or TerminateProcess, or the value returned by the thread function.

If a thread is terminated by ExitThread, the system calls the entry-point function of each attached DLL with a value indicating that the thread is detaching from the DLL (unless you call the DisableThreadLibraryCalls function). If a thread is terminated by ExitProcess, the DLL entry-point functions are invoked once, to indicate that the process is detaching. DLLs are not notified when a thread is terminated by TerminateThread or TerminateProcess. For more information about DLLs, see Dynamic-Link Libraries.

The TerminateThread and TerminateProcess functions should be used only in extreme circumstances, since they do not allow threads to clean up, do not notify attached DLLs, and do not free the initial stack. In addition, handles to objects owned by the thread are not closed until the process terminates. The following steps provide a better solution:

  • Create an event object using the CreateEvent function.
  • Create the threads.
  • Each thread monitors the event state by calling the WaitForSingleObject function. Use a wait time-out interval of zero.
  • Each thread terminates its own execution when the event is set to the signaled state (WaitForSingleObject returns WAIT_OBJECT_0).