1.sleep(0)或者没有sleep
/* thread_test.c */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#define NUM_THREADS 4
pthread_mutex_t mutex;
void *PrintHello(void *args)
{
int thread_arg;
thread_arg = (int)(*((int*)args));
while(1)
{
// pthread_mutex_lock(&mutex);
// thread_arg = (int)(*((int*)args));
// pthread_mutex_unlock(&mutex);
if(1 == thread_arg)
{
printf("Hello from thread %d\n", thread_arg);
}
if(2 == thread_arg)
{
printf("Hello from thread %d\n", thread_arg);
}
sleep(0);
}
return NULL;
}
int main(void)
{
int rc,t;
pthread_t thread[NUM_THREADS];
pthread_mutex_init (&mutex, NULL);
for( t = 0; t < NUM_THREADS; t++)
{
printf("Creating thread %d\n", t);
//此处t变量的用法是方便大家调测代码的写法,实际使用会有问题,因为这个t是局部变量,
//函数执行完后马上释放,大家传递参数时需要使用全局变量或malloc出来的变量。
// 可写为 rc = pthread_create(&thread[t], NULL, PrintHello, (void*) t)
// 在线程中,为thread_arg = (int)arg;
rc = pthread_create(&thread[t], NULL, PrintHello, &t);
if (rc)
{
printf("ERROR; return code is %d\n", rc);
return EXIT_FAILURE;
}
}
for( t = 0; t < NUM_THREADS; t++)
pthread_join(thread[t], NULL);
return EXIT_SUCCESS;
}
编译命令:gcc thread_test.c -o thread_test -pthread
这种情况好像每次运行结果不同。有一次用sleep(0),最后只循环打印“Hello from thread 1”,thread 2抢不到cpu,一直没有打印;有一次没有用sleep,倒是打印一段时间的“Hello from thread 1”后再打印“Hello from thread 2”,thread1和thread2都能抢到cpu。
2.usleep(1)
一直交替打印“Hello from thread 1”和“Hello from thread 2”,基本上就是打印一次“Hello from thread 1”后接着再打印“Hello from thread 2”。
参考:
pthread_create_百度百科 (baidu.com)