Semaphores (Avoiding Train Wrecks) Kevin O’Gorman CS April 2002

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = -1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = -1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = -1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. Success!

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Semaphores Re-Run

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 1

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. sem = 0

Signalling. A1 statement A2 sem.signal(). B1 sem.wait() B2 statement. Success!