NAME

pthread_cond_init - Creates a condition variable

SYNOPSIS

#include <pthread.h> int pthread_cond_init( pthread_cond_t *cond, pthread_condattr_t attr);

PARAMETERS

condCondition variable that is created. 

attrCondition variable attributes object that defines the characteristics of the condition variable created. If you specify pthread_condattr_default, default attributes are used. 

DESCRIPTION

The pthread_cond_init()  routine creates and initializes a condition variable. A condition variable is a synchronization object used in conjunction with a mutex. A mutex controls access to shared data; a condition variable allows threads to wait for that data to enter a defined state. The state is defined by a Boolean expression called a predicate. A condition variable is signaled or broadcast to indicate that a predicate might have become true. The broadcast operation indicates that all waiting threads need to resume and reevaluate the predicate. The signal operation is used when any one waiting thread can continue. If a thread that holds a mutex determines that the shared data is not in the correct state for it to proceed (the associated predicate is not true), it waits on a condition variable associated with the desired state. Waiting on the condition variable automatically releases the mutex so that other threads can modify or examine the shared data. When a thread modifies the state of the shared data so that a predicate might be true, it signals or broadcasts on the appropriate condition variable so that threads waiting for that predicate can continue. It is important that all threads waiting on a particular condition variable at any time hold the same mutex. If they do not, the behavior of the wait operation is unpredictable (an implementation can use the mutex to control internal access to the condition variable object). However, it is legal for a client to store condition variables and mutexes and later reuse them in different combinations. The client must ensure that no threads use the condition variable with the old mutex. At any time, an arbitrary number of condition variables can be associated with a single mutex, each representing a different predicate of the shared data protected by that mutex. Condition variables are not owned by a particular thread. Any associated storage is not automatically deallocated when the creating thread terminates.

RETURN VALUES

If the function fails, errno may be set to one of the following values:

RELATED INFORMATION

Functions: pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_signal(3), pthread_cond_timedwait(3), pthread_cond_wait(3). 

Hewlett-Packard Company  —  OSF DCE 1.1/HP DCE 1.5