Win32 Mutex not waiting

I am creating an application that implements inter process communication. For this purpose I have set up a shared buffer, which seems to work fine. Now, I need a way for the data generating application (written in c++) to tell the data receiving application (written in freepascal/lazarus) when it should read the data.

I was trying to use a mutex for this purpose. I do not have much experience with windows api programming.

So, my problem is, in the FreePascal code below, the mutex won't wait. I can call the TMutex.Wait() function, it doesn't return an error or anything, but it simply won't wait.

constructor TMutex.Create(sName: AnsiString);

begin

  sName := 'Local\Mutex'+sName;

  hMutex := CreateMutexA(

        nil, // default access

      开发者_StackOverflow中文版;  True, // initially not owned

        PChar(sName)); // named mutex

  if hMutex = 0 then

  begin

    raise Exception.Create('mutex creation failed');

  end;

end;

destructor TMutex.Destroy;

begin

  CloseHandle(hMutex);

end;

procedure TMutex.Wait;

begin

  if (WaitForSingleObject(hMutex, INFINITE) <> 0) then ShowMessage('debug: wait returned something');

end;

procedure TMutex.Post;

begin

  ReleaseMutex(hMutex);

end;

It looks like your problem is at:

    True, // initially not owned

You have things backwards -- true means it initially IS owned, so waiting on it will return immediately.

you don't show us the code that calls the Wait, method of TMutex. however, you have to know that a mutex is reentrant: if a thread owns a mutex, it will always be granted access to it, thus a wait will never block. this is built into the mutex to avoid deadlocks.

try acquiring the mutex from another thread, the wait should block.