# Function Reference

# _WinAPI_CreateMutex

Creates or opens a named or unnamed mutex object

#include <WinAPIProc.au3>
_WinAPI_CreateMutex ( $sMutex [, $bInitial = True [, $tSecurity = 0]] )

## Parameters

$sMutex | The name of the mutex object. Name comparisons are case sensitive.
$bInitial | [optional] Specifies whether the calling process obtains the initial ownership of the mutex object, valid values: True - The calling thread obtains initial ownership of the mutex object (Default). False - The calling thread does not obtain ownership of the mutex object.
$tSecurity | [optional] $tagSECURITY_ATTRIBUTES structure that specifies a security descriptor for the new mutex. If this parameter is 0 (Default), the mutex gets a default security descriptor.

## Return Value

Success: | The handle to the newly created mutex object.
Failure: | 0, call _WinAPI_GetLastError() to get extended error information.

## Remarks

If the mutex is a named mutex and the object existed before this function call, the return value is a handle to the existing object, _WinAPI_GetLastError() returns ERROR_ALREADY_EXISTS (183), $bInitial is ignored, and the calling thread is not granted ownership.
However, if the caller has limited access rights, the function will fail with ERROR_ACCESS_DENIED (5) and the caller should use the _WinAPI_OpenMutex() function.
Any process can specify the mutex-object handle in a call to one of the wait functions.
The single-object wait functions return when the state of the specified object is signaled.
The multiple-object wait functions can be instructed to return either when any one or when all of the specified objects are signaled.
When a wait function returns, the waiting thread is released to continue its execution.
Two or more processes can call _WinAPI_CreateMutex() to create the same named mutex.
The first process actually creates the mutex, and subsequent processes with sufficient access rights simply open a handle to the existing mutex.
This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first.
When using this technique, you should set the $bInitial parameter to False; otherwise, it can be difficult to be certain which process has initial ownership.
Use the _WinAPI_CloseHandle() function to close the handle.
The system closes the handle automatically when the process terminates.
The mutex object is destroyed when its last handle has been closed.

## Related

_WinAPI_CloseHandle, _WinAPI_OpenMutex

## See Also

Search CreateMutex in MSDN Library.