pthread & signal

 pthread线程和信号

    所有的异步信号发到整个进程的所有线程（异步信号如kill, lwp_kill, sigsend, kill等调用产生的都是，异步信号也称为中断），而且所有线程共享信号的处理行为（即sigaction的设置，对于同一信号的设置，某一线程的更改会影响到所有线程）。但每个线程可以有自己的mask来阻止信号的发送，所以可以通过线程对mask的设置来决定信号发送到哪个线程。设置mask的函数为:

#include <signal.h>

int pthread_sigmask(int how, const sigset_t *restrict set, sigset_t *restrict oset)

此外，线程可以通过sleep（超过指定时间或调用的进程/线程捕捉到某个信号并从信号处理程序返回时，sleep返回）或者sigwait来等待一个或多个信号发生。

#include <signal.h>

int pthread_sigwait(const sigset_t *restrict set, int *restrict signop);

给进程发送信号可以调用kill，同样给线程调用信号可以使用pthread_kill

#include <signal.h>

int pthread_kill(pthread_t thread, int signo);

可以发送一个0的signo来检查线程是否存在，如果信号的默认行为是终止进程(例如SIGARLM)，那么把该信号发送给某个线程会杀掉整个进程的所有线程。

另外注意ALARM是进程资源，并且所有线程共享相同的ALARM，设置一个alarm()会发送SIGARLM信号给所有线程,所以他们不可能互补干扰的使用alarm()。

 

here comes an example:

/*threadsig.c*/
#include <signal.h>
#include <pthread.h>
#include <stdio.h>

void sighandler(int signo);

void *
thr1_fn(void *arg)
{
    pthread_t   tid = pthread_self();
    int     rc;

    printf("thread 1 with tid:%u\n", tid);
    rc = sleep(60);
    if (rc != 0)
        printf("thread 1... interrupted at %d second\n", 60 - rc);
    printf("thread 1 ends\n");
    return NULL;
}

void *
thr2_fn(void *arg)
{
    struct sigaction    action;
    pthread_t       tid = pthread_self();
    int         rc, err;

    printf("thread 2 with tid:%u\n", tid);

    action.sa_flags = 0;
    action.sa_handler = sighandler;

    err = sigaction(SIGALRM, &action, NULL);

    rc = sleep(60);
    if (rc != 0)
        printf("thread 2... interrupted at %d second\n", 60 - rc);
    printf("thread 2 ends\n");
    return NULL;
}

void *
thr3_fn(void *arg)
{
    pthread_t   tid = pthread_self();
    sigset_t    mask;
    int     rc, err;

    printf("thread 3 with tid%u\n", tid);


    sigemptyset(&mask); /* 初始化mask信号集 */

    sigaddset(&mask, SIGALRM);
    err = pthread_sigmask(SIG_BLOCK, &mask, NULL);
    if (err != 0)
    {
        printf("%d, %s/n", rc, strerror(rc));
        return NULL;
    }

    rc = sleep(60);
        if (rc != 0)
                printf("thread 3... interrupted at %d second\n", 60 - rc);
        printf("thread 3 ends\n");
        return NULL;

    return NULL;
}

int
main(void)
{
    int     rc, err;
    pthread_t   thr1, thr2, thr3, thrm = pthread_self();

    printf("thread main with pid %u\n", (unsigned int)thrm);
    err = pthread_create(&thr1, NULL, thr1_fn, NULL);
    if (err != 0) {
        printf("error in creating pthread:%d\t%s\n",err, strerror(rc));
        exit(1);
    }


/*  pthread_kill(thr1, SIGALRM);    send a SIGARLM signal to thr1 before thr2 set the signal handler, then the whole process will be terminated*/
    err = pthread_create(&thr2, NULL, thr2_fn, NULL);
    if (err != 0) {
        printf("error in creating pthread:%d\t%s\n",err, strerror(rc));
        exit(1);
    }

    err = pthread_create(&thr3, NULL, thr3_fn, NULL);
    if (err != 0) {
        printf("error in creating pthread:%d\t%s\n",err, strerror(rc));
        exit(1);
    }

    sleep(3);
    pthread_kill(thr1, SIGALRM);
    pthread_kill(thr2, SIGALRM);
    pthread_kill(thr3, SIGALRM);
    pthread_join(thr1, NULL);   /*wait for the threads to complete.*/
    pthread_join(thr2, NULL);
    pthread_join(thr3, NULL);
    printf("main ends\n");
    return 0;
}

void
sighandler(int signo)
{
    pthread_t   tid = pthread_self();

    printf("thread with pid:%u receive signo:%d\n", tid, signo);
    return;
}

luffy@luffy-laptop:~/workspace/myapue$ ./threadsig 

thread main with pid 3557979936

thread 1 with tid:3549923072

thread 2 with tid:3541530368

thread 3 with tid3533137664

thread with pid:3549923072 receive signo:14

thread with pid:3541530368 receive signo:14

thread 2... interrupted at 3 second

thread 1... interrupted at 3 second

thread 1 ends

thread 2 ends #then wait for 27 seconds and thread-3 ends

thread 3 ends

main ends

 

    thr2设置的信号处理程序 sighandler也应用到其他线程，thr3由于设置mask所有阻塞了SIGARLM信号。

 

Reference:

APUE

线程信号 http://blog.csdn.net/copal/article/details/5454279