求教APUE上的一个多线程程序（中文第二版p335）。。。。。。。

kidda 2014-12-30 10:18:02

问题是：主线程中已经对互斥量lock加锁，此时新线程如何还能加锁并处理SIGQUIT？（我在注释表明了两处上锁位置）



#include "apue.h"

#include <pthread.h>



int         quitflag;   /* set nonzero by thread */

sigset_t    mask;



pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

pthread_cond_t wait = PTHREAD_COND_INITIALIZER;



void *

thr_fn(void *arg)

{

    int err, signo;



    for (;;) {

        err = sigwait(&mask, &signo);

        if (err != 0)

            err_exit(err, "sigwait failed");

        switch (signo) {

        case SIGINT:

            printf("\ninterrupt\n");

            break;



        case SIGQUIT:

            pthread_mutex_lock(&lock);                         //主线程已经锁住，新线程在这里如何加锁？？？？

            quitflag = 1;

            pthread_mutex_unlock(&lock);

            pthread_cond_signal(&wait);

            return(0);



        default:

            printf("unexpected signal %d\n", signo);

            exit(1);

        }

    }

}

int

main(void)

{

    int         err;

    sigset_t    oldmask;

    pthread_t   tid;



    sigemptyset(&mask);

    sigaddset(&mask, SIGINT);

    sigaddset(&mask, SIGQUIT);

    if ((err = pthread_sigmask(SIG_BLOCK, &mask, &oldmask)) != 0)

        err_exit(err, "SIG_BLOCK error");



    err = pthread_create(&tid, NULL, thr_fn, 0);

    if (err != 0)

        err_exit(err, "can't create thread");



    pthread_mutex_lock(&lock);                                                                //主线程加锁

    while (quitflag == 0)

        pthread_cond_wait(&wait, &lock);

    pthread_mutex_unlock(&lock);



    /* SIGQUIT has been caught and is now blocked; do whatever */

    quitflag = 0;



    /* reset signal mask which unblocks SIGQUIT */

    if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)

        err_sys("SIG_SETMASK error");

    exit(0);

}