这个函数可以使用另一个级别等于或高于当前线程的线程先运行。如果没有符合条件的线程，那么这个函数将会立刻返回然后继续执行当前线程的程序。
下面这个例子中，只是使用了 sched_yield这个函数，其实就实际效果上，并未体现出其真正的意义，主要旨在体会用法。
#define _MULTI_THREADED
#include <pthread.h>
#include <stdio.h>
#include <errno.h>
#define checkResults(string, val) { \
if(val){ \ printf("Failed with %d at %s", val, string); \
exit(1); \ } \ } #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; }