Linux多線程學習（七）sched_yield

sched_yield()這個函數可以使用另一個級別等於或高於當前線程的線程先運行。如果沒有符合條件的線程，那麼這個函數將會立刻返回然後繼續執行當前線程的程序。  

在成功完成之後返回零，否則返回-1.

看下面一個實例

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

#define            LOOPCONSTANT     1000
#define            THREADS          3

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

static void checkResults(char *string, int rc) {
  if (rc) {
    printf("Error on : %s, rc=%d",
           string, rc);
    exit(EXIT_FAILURE);
  }
  return;
}

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;} 編譯 gcc -o sched_yield -lphread sched_yield.c

運行結果 Enter Testcase - ./sched_yield

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