thread_12

#include <stdlib.h>
#include <pthread.h>
#include <stdio.h>
#include <sched.h>
int a = 0;
void *thread1(void *arg)
 {       
       // pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
        //如果把这行代码加上 a的值会改变的
         a = 10;
        printf("start thread (%u)\n", (unsigned)pthread_self());
 }
 int main(int argc, char *argv[])
{       
         pthread_t  t1, t2, t3;
         int ret, i;
        printf("main start\n");
        ret = pthread_create(&t1, NULL, thread1, NULL);
        if(ret != 0)
         {       
                 printf("create thread failed\n");
                exit(1);
         }
         pthread_cancel(t1);
        pthread_join(t1, NULL);
       sleep(3);
       printf("main end, a=%d\n", a);
     return 0;
 }
/*运行结果： 设置为异步模式，在没到达取消点之前就结束了，a没被改动。如果把13行注释，a会被改动。
main start
main end, a=0*/