Synchronization with POSIX Threads
Learn how to coordinate multiple POSIX threads safely using synchronization mechanisms such as mutexes, condition variables, semaphores, and barriers to control access to shared data and ensure correct concurrent execution.
Previously, we learned how multiple threads can execute concurrently within the same process using POSIX threads. Because these threads share the same memory space, they can read and modify the same variables. Without proper coordination, this can potentially lead to incorrect results.
In this lesson, we'll learn how synchronization by the pthreads library allows us to coordinate thread execution safely and predictably.
Mutual exclusion with mutexes
The most fundamental synchronization mechanism in pthreads is the mutex (short for mutual exclusion). A mutex protects a critical section, which is a portion of code that accesses shared data and must not be executed by more than one thread at a time. If one thread locks a mutex, any other thread attempting to lock the same mutex must wait until it is unlocked.
Consider a simple example in which multiple threads increment a shared counter: