A version of this page is also available for

Windows Embedded CE 6.0 R3


This function releases ownership of the specified mutex object.


BOOL ReleaseMutex(
  HANDLE hMutex


  • hMutex
    [in] Handle to the mutex object. The CreateMutex function returns this handle.

Return Value

Nonzero indicates success. Zero indicates failure. To get extended error information, call GetLastError.


The ReleaseMutex function fails if the calling thread does not own the mutex object.

A thread gets ownership of a mutex by specifying a handle to the mutex in one of the wait functions. The thread that creates a mutex object can also get immediate ownership without using one of the wait functions. When the owning thread no longer needs to own the mutex object, it calls the ReleaseMutex function.

While a thread has ownership of a mutex, it can specify the same mutex in additional wait-function calls without blocking its execution. This prevents a thread from deadlocking itself while waiting for a mutex that it already owns. However, to release its ownership, the thread must call ReleaseMutex once for each time that the mutex satisfied a wait function call.

Each object type, such as memory maps, semaphores, events, message queues, mutexes, and watchdog timers, has its own separate namespace. Empty strings, "", are handled as named objects. On Windows desktop-based platforms, synchronization objects all share the same namespace.


Header winbase.h
Library Nk.lib
Windows Embedded CE Windows CE 1.01 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also


Synchronization Functions