A quick puzzle about security and synchronization

Raymond Chen

This quick puzzle floated past one of our internal discussion groups.

// in process A
hEventA = CreateEvent(NULL, FALSE, TRUE, TEXT("MyNamedEvent"));
// in process B
hEventB = OpenEvent(EVENT_MODIFY_STATE, FALSE, TEXT("MyNamedEvent"));
WaitForSingleObject(hEventB, INFINITE);

In Process B, the OpenEvent succeeds, but the WaitForSingleObject returns immediately instead of waiting. Explain.

[Correction: I confused the matter by passing TRUE as the third parameter, thereby creating an event that is initially signalled. Change it to FALSE so that the event is created non-signalled, in which case the WaitForSingleObject would be expected to wait.]

Raymond Chen

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