linux c编程：线程退出

在线程创建的时候pthread_exit都是调用的固定参数，我们先来看下如果用自动变量作为pthread_exit的参数时出现的问题

typedef struct foo{

    int a;

    int b;

    int c;

    int d;

}foo;

void printinfo(const char *s,const struct foo *fp){

    printf("%s",s);

    printf("structure at 0x%lx\n",(unsigned long)fp);

    printf("foo.a=%d\n",fp->a);

    printf("foo.b=%d\n",fp->b);

    printf("foo.c=%d\n",fp->c);

    printf("foo.d=%d\n",fp->d);

}

 

void printids(const char *s){

    pid_t pid;

    pthread_t tid;

    pid=getpid();

    tid=pthread_self();

    printf("%s pid %lu tid %lu (0x%lx)\n",s,(unsigned long)pid,(unsigned long)tid,(unsigned long)tid);

}

 

void *thr_fn2(void *arg){

    printf("threaqd 2:ID is %lu\n",(unsigned long)pthread_self());

    pthread_exit((void *)0);

}

 

void *thr_fn1(void *arg){

    foo f={1,2,3,4};

    printinfo("thread1:\n",&f);

    pthread_exit((void *)&f);

}

 

int main()

{

    pthread_t tid1,tid2;

    foo *fp;

    pthread_create(&tid1,NULL,thr_fn1,NULL);

    pthread_join(tid1,(void *)&fp);

    Sleep(1);

    printf("parent starting create thread2:\n");

    pthread_create(&tid2,NULL,thr_fn2,NULL);

    Sleep(1);

    printinfo("parent:\n",fp);

    return 0;

}

在这个程序中，调用pthread_join(tid1,(void *)&fp)的时候会将返回码赋值给fp参数。然后再父进程中调用fp。

执行结果：可以看到当父进程中试图访问已退出的第一个线程传给它的结构时，内存不在有效，因此得到了SIGSEGV信号

Thread1:

Structure at 0x2bfff04

foo.a=1

foo.b=2

foo.c=3

foo.d=4

parent starting create thread2

thread 2 : ID is 3

segmentation fault(core dumped)

 

线程可以安排它退出时需要调用的函数，这样的函数称为线程清理处理程序。

void thread_cleanup_push(void (*rtn)(void *), void *arg);

void pthread_cleanup_pop(int execute)

rtn是调用的函数，arg是传入的参数。

 

void cleanup(void *arg){

    printf("cleanup:%s\n",(char *)arg);

}

 

void *thr_fn2(void *arg){

    printf("thread2 start\n");

    pthread_cleanup_push(cleanup,"thread2 first handler");

    pthread_cleanup_push(cleanup,"thread2 second handler");

    printf("thread2 push complete\n");

    if (arg)

        pthread_exit((void *)2);

    pthread_cleanup_pop(0);

    pthread_cleanup_pop(0);

}

 

void *thr_fn1(void *arg){

    printf("thread1 start\n");

    pthread_cleanup_push(cleanup,"thread1 first handler");

    pthread_cleanup_push(cleanup,"thread1 second handler");

    printf("thread1 push complete\n");

    if (arg)

        return((void *)1);

    pthread_cleanup_pop(0);

    pthread_cleanup_pop(0);

}

int main()

{

    pthread_t tid1,tid2;

    void *tret;

    pthread_create(&tid1,NULL,thr_fn1,(void *)1);

    pthread_create(&tid2,NULL,thr_fn2,(void *)1);

    pthread_join(tid1,&tret);

    printf("thread 1 exit code %ld\n",(long)tret);

    pthread_join(tid2,&tret);

    printf("thread 2 exit code %ld\n",(long)tret);

    return 0;

}

运行结果如下：两个线程都正确的自动启动和退出了，但是只有第二个线程的清理处理程序被调用了，如果线程是通过从它的启动历程中返回(return)而不是pthread_exit的话，它的清理程序就不会调用