If we want to give access to critical section to multiple threads one at a time then we use a Lock.
But what if we want to give access to more than one threads?
Here we use Semaphore.
Semaphore is nothing but a "permit machine".
- We define a Semaphore with number of allowed permits.
- So if we define a Semaphore with 3 permits then at a time only 3 threads can work on the CS.
- Rest of the threads will wait for the working threads to release the permit.
"A Semaphore manages a set of virtual permits; the initial number of permits is passed to the Semaphore constructor."
Semaphore Use cases:
- Limiting concurrent access to disk (as performance degrades due to competing disk seeks)
- Thread creation limiting
- JDBC connection pooling / limiting
- Network connection throttling
- Throttling CPU or memory intensive tasks