semaphores, classic problems
semaphores, classic problems
semaphores, classic problems
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Semaphores (Dijkstra 1965)<br />
• Slightly more abstract primitives<br />
• A semaphore is a non-negative integer variable<br />
with two atomic operations:<br />
– Passeren (wait): P(s) decrements s by 1 if possible,<br />
otherwise it waits until s becomes positive, then<br />
decrements it.<br />
– Verhogen (signal): V(s) increments s by one.<br />
• The operations are atomic: no other process is<br />
allowed to access the semaphore during a P or V<br />
operation, unless the P operation is blocked.<br />
Computing Systems<br />
http://www.cs.caltech.edu/cs134/cs134a October 10, 2001
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