Semaphore is a new type of variable introduced by E. W. Dijkstra. You may learn about semaphores in university. It is used to solve the Producer-Consumer Problem in Operation system design which I have learn in books "Modern Operating Systems " (second edition) by Andrew S. Tanenbaum. In that books the algorithm for semaphore is clearly defined and easy to understand. But I was always curious about that "Does this type of problem occur on our program?" rather than operating system design and "Where can I use it?". When I begin to learn linux programming I found the semaphore function under <semaphore.h> header and example program where semaphore is used to synchronize the thread.
In this article we look at the simplest type of semaphore, a binary semaphore that takes only values 0 or 1. There is also a more general semaphore that takes a wider range of values. Normally, semaphores are used to protect a piece of code so that only one thread of execution can run it at any one time.The semaphore functions do not start with pthread_,as most thread-specific functions do,but with sem_. Four basic semaphore functions are used in threads. They are all quite simple.
In this article we look at the simplest type of semaphore, a binary semaphore that takes only values 0 or 1. There is also a more general semaphore that takes a wider range of values. Normally, semaphores are used to protect a piece of code so that only one thread of execution can run it at any one time.The semaphore functions do not start with pthread_,as most thread-specific functions do,but with sem_. Four basic semaphore functions are used in threads. They are all quite simple.