Wow64SuspendThread function (wow64apiset.h)

Suspends the specified WOW64 thread.


DWORD Wow64SuspendThread(
  HANDLE hThread



A handle to the thread that is to be suspended. The handle must have the THREAD_SUSPEND_RESUME access right. For more information, see Thread Security and Access Rights.

Return value

If the function succeeds, the return value is the thread's previous suspend count; otherwise, it is (DWORD) -1. To get extended error information, use the GetLastError function.


If the function succeeds, execution of the specified thread is suspended and the thread's suspend count is incremented. Suspending a thread causes the thread to stop executing user-mode (application) code.

This function is primarily designed for use by debuggers. It is not intended to be used for thread synchronization. Calling Wow64SuspendThread on a thread that owns a synchronization object, such as a mutex or critical section, can lead to a deadlock if the calling thread tries to obtain a synchronization object owned by a suspended thread. To avoid this situation, a thread within an application that is not a debugger should signal the other thread to suspend itself. The target thread must be designed to watch for this signal and respond appropriately.

Each thread has a suspend count (with a maximum value of MAXIMUM_SUSPEND_COUNT). If the suspend count is greater than zero, the thread is suspended; otherwise, the thread is not suspended and is eligible for execution. Calling Wow64SuspendThread causes the target thread's suspend count to be incremented. Attempting to increment past the maximum suspend count causes an error without incrementing the count.

The ResumeThread function decrements the suspend count of a suspended thread.

This function is intended for 64-bit applications. It is not supported on 32-bit Windows; such calls fail and set the last error code to ERROR_INVALID_FUNCTION. A 32-bit application can call this function on a WOW64 thread; the result is the same as calling the SuspendThread function.


Minimum supported client Windows Vista
Minimum supported server Windows Server 2008
Header wow64apiset.h
Library Kernel32.lib
DLL Kernel32.dll

See also