In operating systems, a semaphore is used to control access to shared resources. It is a variable or an abstract data type that is used to solve the critical section problem, which arises when multiple processes or threads need to access a shared resource simultaneously.
For example, when there are two person A and B wants to use one computer at the same time then comes the role of semaphore.
It indicates that the computer is free or is in use.
If it is free, it will set the counter as 1, and if it the counter is set to 0, it means the computer is in use.
The semaphore provides two main operations:
Wait (P) operation: When a process/thread wants to access the shared resource, it performs the wait operation on the semaphore. If the counter is greater than zero, the process/thread decrements the counter and continues accessing the resource. If the counter is zero, indicating that all resources are currently being used, the process/thread is put into a waiting state until a resource becomes available.
Signal (V) operation: After a process/thread completes its use of the shared resource, it performs the signal operation on the semaphore. This operation increments the counter, indicating that a resource has been released and is now available for other processes/threads to use. If any waiting processes/threads were blocked, one of them is awakened and allowed to proceed.
