Answer to quick puzzle about security and synchronization
As many people quickly figured out, the reason why the
WaitForSingleObject returns immediately
is that the call is failing.
The reason is that the second process opened the handle
grants permission to call
the fatally flawed
but it doesn’t include
which is necessary if you intend to synchronize on the object
(i.e., wait on it).
The fix is for Process B to ask for
SYNCHRONIZE access instead of
The fact that it’s happening in a second process is a red herring. You can put this code in the same process and it will fail/succeed in the same way:
HANDLE hEventA = CreateEvent(NULL, FALSE, TRUE, TEXT("MyNamedEvent")); HANDLE hEventB = OpenEvent(EVENT_MODIFY_STATE, FALSE, TEXT("MyNamedEvent")); WaitForSingleObject(hEventB, INFINITE); // fails
Indeed, the fact that the object is named is a red herring. It has nothing to do with named/unnamed objects.
HANDLE hEventA = CreateEvent(NULL, FALSE, TRUE, NULL); HANDLE hEventB; DuplicateHandle(GetCurrentProcess(), hEventA, GetCurrentProcess(), &hEventB, EVENT_MODIFY_STATE, FALSE, 0); WaitForSingleObject(hEventB, INFINITE); // fails
In all three cases, the fix is to change