pthread_cond_init example c c++

NAME

pthread_cond_destroy, pthread_cond_init - destroy and initialize condition variables

SYNOPSIS

[THR]  #include <pthread.h>

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

DESCRIPTION

The pthread_cond_destroy() function shall destroy 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 reinitialized using pthread_cond_init(); the results of otherwise referencing the object after it has been destroyed are undefined.
It shall be 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.(pthread_cond_destroy, pthread_cond_init)
The pthread_cond_init() function shall initialize the condition variable referenced by cond with attributes referenced by attr. If attr is NULL, the default condition variable attributes shall be 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 shall become initialized.
Only cond itself may be used for performing synchronization. The result of referring to copies of cond in calls to pthread_cond_wait(),pthread_cond_timedwait(), pthread_cond_signal(), pthread_cond_broadcast(), and pthread_cond_destroy() is undefined.
Attempting to initialize an already initialized condition variable 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 shall be 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 VALUE of (pthread_cond_destroy, pthread_cond_init)

If successful, the pthread_cond_destroy() and pthread_cond_init() functions shall return zero; otherwise, an error number shall be returned to indicate the error.
The [EBUSY] and [EINVAL] error checks, if implemented, shall 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_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.

The pthread_cond_init() function shall 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 reinitialize the object referenced by cond, a previously initialized, but not yet destroyed, condition variable.

[EINVAL]

The value specified by attr is invalid.

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

EXAMPLES of (pthread_cond_destroy, pthread_cond_init)

Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.

#include <pthread.h>
#include <stdio.h>
#include "check.h"

pthread_cond_t              cond;

int main(int argc, char **argv)
{
  int                   rc=0;
  pthread_mutexattr_t   attr;

  printf("Entering testcase\n");

  printf("Create the condition using the condition attributes object\n");
  rc = pthread_cond_init(&cond, NULL);
  checkResults("pthread_cond_init()\n", rc);

  printf("- At this point, the condition with its default attributes\n");
  printf("- Can be used from any threads that want to use it\n");

  printf("Destroy condition\n");
  rc = pthread_cond_destroy(&cond);
  checkResults("pthread_cond_destroy()\n", rc);
 
  printf("Main completed\n");
  return 0;
}

Output:

Entering testcase
Create the condition using the condition attributes object
- At this point, the condition with its default attributes
- Can be used from any threads that want to use it
Destroy condition
Main completed