CreateWaitableTimer

The CreateWaitableTimer function creates or opens a waitable timer object.

HANDLE CreateWaitableTimer(
  LPSECURITY_ATTRIBUTES lpTimerAttributes, // SD
  BOOL bManualReset,                       // reset type
  LPCTSTR lpTimerName                      // object name
);

Parameters

lpTimerAttributes

[in] Pointer to a SECURITY_ATTRIBUTES structure that specifies a security descriptor for the new timer object and determines whether child processes can inherit the returned handle. If lpTimerAttributes is NULL, the timer object gets a default security descriptor and the handle cannot be inherited.

bManualReset

[in] Specifies the timer type. If bManualReset is TRUE, the timer is a manual-reset notification timer. Otherwise, the timer is a synchronization timer.

lpTimerName

[in] Pointer to a null-terminated string specifying the name of the timer object. The name is limited to MAX_PATH characters. Name comparison is case sensitive.

If the string specified in the lpTimerName parameter matches the name of an existing named timer object, the call returns successfully and the GetLastError function returns ERROR_ALREADY_EXISTS.

If lpTimerName is NULL, the timer object is created without a name.

If lpTimerName matches the name of an existing event, semaphore, mutex, job, or file-mapping object, the function fails and GetLastError returns ERROR_INVALID_HANDLE. This occurs because these objects share the same name space.

Terminal Services: The name can have a "Global\" or "Local\" prefix to explicitly create the object in the global or session name space. The remainder of the name can contain any character except the backslash character (\). For more information, see Kernel Object Name Spaces.

Windows 2000: On Windows 2000 systems without Terminal Services running, the "Global\" and "Local\" prefixes are ignored. The remainder of the name can contain any character except the backslash character.

Windows NT 4.0 and earlier, Windows 95/98: The name can contain any character except the backslash character.

Return Values

If the function succeeds, the return value is a handle to the timer object. If the named timer object exists before the function call, the function returns a handle to the existing object and GetLastError returns ERROR_ALREADY_EXISTS.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

The handle returned by CreateWaitableTimer is created with the TIMER_ALL_ACCESS access right. This handle can be used in any function that requires a handle to a timer object.

Any thread of the calling process can specify the timer object handle in a call to one of the wait functions.

Multiple processes can have handles to the same timer object, enabling use of the object for interprocess synchronization.

• A process created by the CreateProcess function can inherit a handle to a timer object if the lpTimerAttributes parameter of CreateWaitableTimer enables inheritance.
• A process can specify the timer object handle in a call to the DuplicateHandle function. The resulting handle can be used by another process.
• A process can specify the name of a timer object in a call to the OpenWaitableTimer or CreateWaitableTimer function.

Use the CloseHandle function to close the handle. The system closes the handle automatically when the process terminates. The timer object is destroyed when its last handle has been closed.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 98.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT/2000.

See Also

Synchronization Overview, Synchronization Functions, CancelWaitableTimer, CloseHandle, CreateProcess, DuplicateHandle, FILETIME, OpenWaitableTimer, SECURITY_ATTRIBUTES, SetWaitableTimer, Object Names