Revision as of 16:10, 31 October 2008 (view source) rosettacode>Mwn3d (Added less technical description, roll back if I'm wrong.) ← Older edit		Revision as of 18:15, 31 October 2008 (view source) rosettacode>Mwn3d m (Typo, better wording) Newer edit →
Line 3: '''Semaphore''' is a synchronization object proposed by Edsger Dijkstra. A semaphore is characterized by a natural number ''k''. A [[task]] may atomically increase or decrease ''k''. When ''k'' reaches 0 the tasks attempting to decrease it are blocked. These are released in an unspecified order when other tasks increase ''k'', one per increment. The natural number ''k'' works like a count of available slots for resources. When you (asa task) want to use something (an object, a file, any resource) that can only be used by a limited number of tasks (usually one, but possibly more), you see if there are available slots (check the value of ''k''). If there are slots available (''k'' > 0), you ~~check~~take one ~~out~~ (decrement ''k''). When you're done with the resource, you ~~check~~free your slot ~~back in~~up (increment ''k''). If there were no slots available when you checked (''k'' = 0), you wait until one becomes available. A semaphore is considered a low-level synchronization primitive. They are exposed to deadlocking.

Semaphore: Difference between revisions

Semaphore (view source)