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Operating Systems: Virtualization, Concurrency & Persistence

Semaphores: A Definition

Explore the concept of semaphores as synchronization tools in concurrency. Understand how sem_wait() and sem_post() manipulate semaphore values, manage thread waiting and signaling, and ensure proper access control among threads within a process.

We'll cover the following...

A semaphore is an object with an integer value that we can manipulate with two routines; in the POSIX standard, these routines are ...

C++
#include <semaphore.h>
sem_t s;
sem_init(&s, 0, 1);

In the code, we declare a semaphore s and initialize it to the value 1 by passing 1 in as the third argument. The second argument to sem_init() will be set to 0 in all of the examples we’ll see; this indicates that the semaphore is shared between threads in the same process. See the man page for details on ...