CreateMutex

Namespace: WinBase.h

Header: synchapi.h

Synopsis

HANDLE CreateMutexA(
    LPSECURITY_ATTRIBUTES lpMutexAttributes,
    BOOL                  bInitialOwner,
    LPCSTR                lpName
);

HANDLE CreateMutexW(
    LPSECURITY_ATTRIBUTES lpMutexAttributes,
    BOOL                  bInitialOwner,
    LPCWSTR               lpName
);

#ifdef UNICODE
#define CreateMutex  CreateMutexW
#else
#define CreateMutex  CreateMutexA
#endif

Parameters

Parameter	Description
`lpMutexAttributes`	Pointer to a `SECURITY_ATTRIBUTES` structure that determines whether the returned handle can be inherited by child processes. `NULL` for default.
`bInitialOwner`	If `TRUE`, the calling thread obtains immediate ownership of the mutex.
`lpName`	Optional name of the mutex object. Must be `NULL` or a null‑terminated string. If a mutex with the same name exists, the function opens a handle to the existing mutex.

Return Value

If the function succeeds, the return value is a handle to the newly created mutex object. If the function fails, the return value is NULL. Call GetLastError for extended error information.

Remarks

A mutex can be used for inter‑process synchronization when created with a name.
To release ownership, call ReleaseMutex. Failing to release a mutex results in a deadlock.
When the last handle to a mutex is closed, the system destroys the mutex object.

Example

#include <windows.h>
#include <stdio.h>

int main(void)
{
    HANDLE hMutex = CreateMutexA(
        NULL,          // default security attributes
        FALSE,         // not owned initially
        "Global\\MyMutex"
    );

    if (hMutex == NULL) {
        printf("CreateMutex failed: %lu\n", GetLastError());
        return 1;
    }

    // Wait for ownership
    DWORD dwWait = WaitForSingleObject(hMutex, INFINITE);
    if (dwWait == WAIT_OBJECT_0) {
        printf("Mutex acquired, doing work...\\n");
        // Critical section
        Sleep(2000);
        ReleaseMutex(hMutex);
    }

    CloseHandle(hMutex);
    return 0;
}