linux c編程：線程退出

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線上程建立的時候pthread_exit都是調用的固定參數，我們先來看下如果用自動變數作為pthread_exit的參數時出現的問題

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;

}

在這個程式中，調用pthread_join(tid1,(void *)&fp)的時候會將返回碼賦值給fp參數。然後再父進程中調用fp。

執行結果：可以看到當父進程中試圖訪問已退出的第一個線程傳給它的結構時，記憶體不在有效，因此得到了SIGSEGV訊號

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)

 

線程可以俺怕它退出時需要調用的函數，這樣的函數稱為線程清理處理常式。

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

void pthread_cleanup_pop(int execute)

rtn是調用的函數，arg是傳入的參數。

 

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;

}

運行結果如下：兩個線程都正確的自動啟動和退出了，但是只有第二個線程的清理處理常式被調用了，如果線程是通過從它的啟動曆程中返回(return)而不是pthread_exit的話，它的清理程式就不會調用

 

linux c編程：線程退出