Mutexes and WaitForSingleObject -> doesn´t wait ??

[Souldrift]

Hello, I just played around with mutexes and wrote the following piece of code:

HANDLE hMutex = CreateMutex(NULL, // no security descriptor needed in the beginning
TRUE, // not initial owner
"test"); // mutex name (hopefully unique)

DWORD err = WaitForSingleObject(hMutex, INFINITE);
if( err == WAIT_FAILED )
printf( "This shouldn´t happen." );
else
{
err = WaitForSingleObject(hMutex, INFINITE);
if( err == WAIT_FAILED )
printf( "This shouldn´t happen." );
else
printf( "This shouldn´t happen either." );
}

No I don´t understand why the second WaitForSingleObject()-call doesn´t block. Since I said to wait indefinitely, shouldn´t it do so because the mutex object is already in use? I guess, I have some general trouble understanding the mechanism here. How do I get the mutex to lock a code area up? Souldrift

[Michael Schubert]

Whay don't you use GetLastError() when the return value is WAIT_FAILED as the documentation suggests?

[Souldrift]

There is no error. The return value both times is 0. Which is fine with the first call, and I thought was odd with the second. But I just read somewhere else, that mutexes under windows don´t block inside the same thread. So that might be it. Souldrift

[CPallini]

Souldrift wrote:

No I don´t understand why the second WaitForSingleObject()-call doesn´t block. Since I said to wait indefinitely, shouldn´t it do so because the mutex object is already in use?

Souldrift wrote:

I guess, I have some general trouble understanding the mechanism here.

You're missing this ([^])

The thread that owns a mutex can specify the same mutex in repeated wait function calls without blocking its execution. Typically, you would not wait repeatedly for the same mutex, but this mechanism 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.

:)

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[My articles]

[Souldrift]

Yes, that was exactly it. Just found out a minute ago. Thanks a lot. Just tested it with threads and it seems to work allright :). Good day all. Souldrift