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Threads Synchronization and Communication

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All threads in a process execute within a single address space and share resources. When threads share resources in an unsynchronized way, incorrect output can result from race conditions or thread scheduling anomalies. The Kernal Threads provide the following facilities and routines to synchronize thread access to shared resources.

Mutexes (Mutual Exclusion Objects)

Mutexes are used to synchronize access by multiple threads to a shared resource, allowing access by only one thread at a time. Routines for creating and managing mutexes are:

  • pthread_mutex_init(mutex,attr)

  • pthread_mutex_destroy(mutex)

  • pthread_mutex_lock(mutex)

  • pthread_mutex_trylock(mutex)

  • pthread_mutex_unlock(mutex)

Condition Variables

Condition variables provide an explicit communication vehicle between threads. A condition variable is a shared resource, and requires a mutex to protect it. A condition variable is used to block one or more threads until a condition becomes true, then any or all of the blocked threads can be unblocked. Routines for creating and managing condition variables are:

  • pthread_cond_init(cond,attr)

  • pthread_cond_broadcast(cond)

  • pthread_cond_signal(cond)

  • pthread_cond_wait(cond,mutex)

  • pthread_cond_destroy(cond)

Join Facility

The join facility is the simplest means of synchronizing threads, and uses neither shared resources or mutexes. The join facility causes the calling thread to wait until the specified thread finishes and returns a status value to the calling thread. Routines for joining and detaching threads are:

  • pthread_join(thread,status)

  • pthread_detach(thread)



Chapter 5 Programming with Kernel Threads

Threads Scheduling