DCE for the HP e3000 (B3821-90002)

Programming with Kernel Threads

Threads Synchronization and Communication

Chapter 5

Threads Synchronization and Communication

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 DCE Threads Service provides

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. You use a

condition variable to block one or more threads until some 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)

Refer to the OSF DCE Application Development Guide (B3190-90036) and the OSF DCE

Application Development Reference (B3190-90032) for detailed information on threads

synchronization and communication.