Initialize and destroys condition variables.
Threads Library (libpthreads.a)
#include <pthread.h>
int pthread_cond_init (cond, attr)
pthread_cond_t *cond;
const pthread_condattr_t *attr;
int pthread_cond_destroy (cond)
pthread_cond_t *cond;
pthread_cond_t cond = PTHREAD_COND_INTITIALIZER;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. 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.
| Item | Description |
|---|---|
| cond | Pointer to the condition variable. |
| attr | Specifies the attributes of the condition. |
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.
The pthread_cond_init function will fail if:
| Item | Description |
|---|---|
| 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:
| Item | Description |
|---|---|
| EINVAL | The value specified by attr is invalid. |
The pthread_cond_destroy function may fail if:
| Item | Description |
|---|---|
| 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.