sched_yield()--Yield Processor to Another Thread

 #include <sched.h>
 int sched_yield(void);

The sched_yield() function yields the processor from the currently executing thread to another ready-to-run, active thread of equal or higher priority.

If no threads of equal or higher priority are active and ready to run, sched_yield() returns immediately, and the calling thread continues to run until its time has expired.

Authorities and Locks

None.

Parameters

None.

Return Value

0

sched_yield() was successful.

value

sched_yield() was not successful. value is set to indicate the error condition.

Error Conditions

The sched_yield() API does not currently return an error.

Related Information

• The <pthread.h> header file. See Header files for Pthread functions.
  
  
• pthread_getschedparam()--Get Thread Scheduling Parameters

Example

See Code disclaimer information for information pertaining to code examples.

#define _MULTI_THREADED
#include <pthread.h>
#include <stdio.h>
#include <errno.h>
#include "check.h"

#define            LOOPCONSTANT     1000
#define            THREADS          3

pthread_mutex_t    mutex = PTHREAD_MUTEX_INITIALIZER;
int                i,j,k,l;

void *threadfunc(void *parm)
{
  int   loop = 0;
  int   localProcessingCompleted = 0;
  int   numberOfLocalProcessingBursts = 0;
  int   processingCompletedThisBurst = 0;
  int   rc;

  printf("Entered secondary thread\n");
  for (loop=0; loop<LOOPCONSTANT; ++loop) {
    rc = pthread_mutex_lock(&mutex);
    checkResults("pthread_mutex_lock()\n", rc);
    /* Perform some not so important processing */
    i++, j++, k++, l++;

    rc = pthread_mutex_unlock(&mutex);
    checkResults("pthread_mutex_unlock()\n", rc);
    /* This work is not too important. Also, we just released a lock
       and would like to ensure that other threads get a chance in
       a more co-operative manner. This is an admittedly contrived
       example with no real purpose for doing the sched_yield().
       */
    sched_yield();
  }
  printf("Finished secondary thread\n");
  return NULL;
}

int main(int argc, char **argv)
{
  pthread_t             threadid[THREADS];
  int                   rc=0;
  int                   loop=0;

  printf("Enter Testcase - %s\n", argv[0]);

  rc = pthread_mutex_lock(&mutex);
  checkResults("pthread_mutex_lock()\n", rc);

  printf("Creating %d threads\n", THREADS);
  for (loop=0; loop<THREADS; ++loop) {
    rc = pthread_create(&threadid[loop], NULL, threadfunc, NULL);
    checkResults("pthread_create()\n", rc);
  }

  sleep(1);
  rc = pthread_mutex_unlock(&mutex);
  checkResults("pthread_mutex_unlock()\n", rc);

  printf("Wait for results\n");
  for (loop=0; loop<THREADS; ++loop) {
    rc = pthread_join(threadid[loop], NULL);
    checkResults("pthread_join()\n", rc);
  }

  pthread_mutex_destroy(&mutex);

  printf("Main completed\n");
  return 0;
}

Output:

Enter Testcase - QP0WTEST/TPSCHY0
Creating 3 threads
Entered secondary thread
Entered secondary thread

Entered secondary thread
Wait for results
Finished secondary thread
Finished secondary thread
Finished secondary thread
Main completed