man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

pthread_cond_init(3C)

Name

pthread_cond_init, pthread_cond_destroy - initialize or destroy condition variables

Synopsis

cc –mt [ flag... ] file... [ library... ]
#include <pthread.h>

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

Description

The function pthread_cond_init() initializes 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. See pthread_condattr_init(3C). Upon successful initialization, the state of the condition variable becomes initialized.

Attempting to initialize an already initialized condition variable results in undefined behavior.

The function pthread_cond_destroy() destroys the given condition variable specified by cond; the object becomes, in effect, uninitialized. 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-initialized using pthread_cond_init(); the results of otherwise referencing the object after it has been destroyed are undefined.

It is safe to destroy an initialized 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 behavior.

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

Return Values

If successful, the pthread_cond_init() and pthread_cond_destroy() functions return 0. 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 initialize another condition variable.

ENOMEM

Insufficient memory exists to initialize the condition variable.

The pthread_cond_init() function may fail if:

EBUSY

The implementation has detected an attempt to re-initialize the object referenced by cond, a previously initialized, 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.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe
Standard

See Also

pthread_cond_signal(3C), pthread_cond_broadcast(3C), pthread_cond_wait(3C), pthread_cond_timedwait(3C), pthread_condattr_init(3C), attributes(5), condition(5), standards(5)