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这3点很简单嘛！！！不就是调用pthread_create创建线程。代码如下：
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
#include<errno.h>
#include<unistd.h>
int g_Flag=0;
void* thread1(void*);
void* thread2(void*);
/*
* when program is started, a single thread is created, called the initial thread or main thread.
* Additional threads are created by pthread_create.
* So we just need to create two thread in main().
*/
int main(int argc, char** argv)
{
printf("enter mainn");
pthread_t tid1, tid2;
int rc1=0, rc2=0;
rc2 = pthread_create(&tid2, NULL, thread2, NULL);
if(rc2 != 0)
printf("%s: %dn",__func__, strerror(rc2));
rc1 = pthread_create(&tid1, NULL, thread1, &tid2);
if(rc1 != 0)
printf("%s: %dn",__func__, strerror(rc1));
printf("leave mainn");
exit(0);
}
/*
* thread1() will be execute by thread1, after pthread_create()
* it will set g_Flag = 1;
*/
void* thread1(void* arg)
{
printf("enter thread1n");
printf("this is thread1, g_Flag: %d, thread id is %un",g_Flag, (unsigned int)pthread_self());
g_Flag = 1;
printf("this is thread1, g_Flag: %d, thread id is %un",g_Flag, (unsigned int)pthread_self());
printf("leave thread1n");
pthread_exit(0);
}
/*
* thread2() will be execute by thread2, after pthread_create()
* it will set g_Flag = 2;
*/
void* thread2(void* arg)
{
printf("enter thread2n");
printf("this is thread2, g_Flag: %d, thread id is %un",g_Flag, (unsigned int)pthread_self());
g_Flag = 2;
printf("this is thread1, g_Flag: %d, thread id is %un",g_Flag, (unsigned int)pthread_self());
printf("leave thread2n");
pthread_exit(0);
}
这样就完成了1）、2）、3）这三点要求。编译执行得如下结果：
netsky@ubuntu:~/workspace/pthead_test$ gcc -lpthread test.c
如果程序中使用到了pthread库中的函数，除了要#include<pthread.h>，在编译的时候还有加上-lpthread 选项。
netsky@ubuntu:~/workspace/pthead_test$ ./a.out
enter main
enter thread2
this is thread2, g_Flag: 0, thread id is 3079588720
this is thread1, g_Flag: 2, thread id is 3079588720
leave thread2
leave main
enter thread1
this is thread1, g_Flag: 2, thread id is 3071196016
this is thread1, g_Flag: 1, thread id is 3071196016
leave thread1
但是运行结果不一定是上面的，还有可能是：
netsky@ubuntu:~/workspace/pthead_test$ ./a.out
enter main
leave main
enter thread1
this is thread1, g_Flag: 0, thread id is 3069176688
this is thread1, g_Flag: 1, thread id is 3069176688
leave thread1
或者是：
netsky@ubuntu:~/workspace/pthead_test$ ./a.out
enter main
leave main
等等。这也很好理解因为，这取决于主线程main函数何时终止，线程thread1、thread2是否能够来得急执行它们的函数。这也是多线程编程时要注意的问题，因为有可能一个线程会影响到整个进程中的所有其它线程！如果我们在main函数退出前，sleep()一段时间，就可以保证thread1、thread2来得及执行。 （编辑：南平站长网）
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