NAME

pthread_cond_init, pthread_cond_destroy - initialise and destroy condition variables

 SYNOPSIS

#include <pthread.h>

int pthread_cond_init(pthread_cond_t *cond,
    const pthread_condattr_t *attr);
int pthread_cond_destroy(pthread_cond_t *cond);
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

 DESCRIPTION

The function pthread_cond_init() initialises the condition variable referenced by cond with attributes referenced by attr. If attr is NULL, the default condition variable attributes are used; the effect is the same as passing the address of a default condition variable attributes object. Upon successful initialisation, the state of the condition variable becomes initialised.

Attempting to initialise an already initialised condition variable results in undefined behaviour.

The function pthread_cond_destroy() destroys the given condition variable specified by cond; the object becomes, in effect, uninitialised. An implementation may cause pthread_cond_destroy() to set the object referenced by cond to an invalid value. A destroyed condition variable object can be re-initialised using pthread_cond_init(); the results of otherwise referencing the object after it has been destroyed are undefined.

It is safe to destroy an initialised condition variable upon which no threads are currently blocked. Attempting to destroy a condition variable upon which other threads are currently blocked results in undefined behaviour.

In cases where default condition variable attributes are appropriate, the macro PTHREAD_COND_INITIALIZER can be used to initialise condition variables that are statically allocated. The effect is equivalent to dynamic initialisation by a call to pthread_cond_init() with parameter attr specified as NULL, except that no error checks are performed.

 RETURN VALUE

If successful, the pthread_cond_init() and pthread_cond_destroy() functions return zero. Otherwise, an error number is returned to indicate the error. The [EBUSY] and [EINVAL] error checks, if implemented, act as if they were performed immediately at the beginning of processing for the function and caused an error return prior to modifying the state of the condition variable specified by cond.

 ERRORS

The pthread_cond_init() function will fail if:

[EAGAIN]

The system lacked the necessary resources (other than memory) to initialise another condition variable.

[ENOMEM]

Insufficient memory exists to initialise the condition variable.

The pthread_cond_init() function may fail if:

[EBUSY]

The implementation has detected an attempt to re-initialise the object referenced by cond, a previously initialised, but not yet destroyed, condition variable.

[EINVAL]

The value specified by attr is invalid.

The pthread_cond_destroy() function may fail if:

[EBUSY]

The implementation has detected an attempt to destroy the object referenced by cond while it is referenced (for example, while being used in a pthread_cond_wait() or pthread_cond_timedwait()) by another thread.

[EINVAL]

The value specified by cond is invalid.

These functions will not return an error code of [EINTR].

 EXAMPLES

None.

 APPLICATION USAGE

None.

 FUTURE DIRECTIONS

None.

 SEE ALSO

pthread_cond_signal(), pthread_cond_broadcast(), pthread_cond_wait(), pthread_cond_timedwait(), <pthread.h>.

DERIVATION

Derived from the POSIX Threads Extension (1003.1c-1995)