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Operating Systems: Virtualization, Concurrency & Persistence

Locks

Explore how to use locks in the POSIX Thread API to protect critical sections and ensure correct operation in concurrent programs. Understand lock initialization, error checking, and different lock acquisition routines to manage thread synchronization effectively.

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Beyond thread creation and join, probably the next most useful set of functions provided by the POSIX threads library are those for providing mutual exclusion to a critical section via locks. The most basic pair of routines to use for this purpose is provided by the following:

C
int pthread_mutex_lock(pthread_mutex_t *mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);

Lock and unlock routines

The routines should be easy to understand and use. When you have a region of code that is a critical section and thus needs to be protected to ensure correct operation, locks are quite useful. You can probably imagine what the code looks like:

C
pthread_mutex_t lock;
pthread_mutex_lock(&lock);
x = x + 1; // or whatever your critical section is
pthread_mutex_unlock(&lock);

The intent of the code is as follows: if no other thread holds the lock when pthread_mutex_lock() is called, the thread ...