Semaphore

Know the Vocabulary

This lesson uses the terms below many times. Read them once now, and come back here when a later section needs one.

• Semaphore: A counter of permits that controls how many threads may do something at the same time.
• Permit: One unit of permission. A thread needs a permit to go in, and it gives the permit back when it is done.
• Acquire: To take a permit. If no permit is free, the thread waits until one comes back.
• Release: To give a permit back. If threads are waiting, one of them can then take it.