结束线程时资源释放

#include
int pthread_kill(pthread_t thread, int sig);
pthead_kill作用：发送信号给某线程（线程对信号进行处理）或检测某线程是否存活（参数sig指定为0）。

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>


static int a = 10;
pthread_mutex_t glock = PTHREAD_MUTEX_INITIALIZER;

static void sig_hdl(int signum)
{
     if(signum == SIGQUIT){
         printf("SIGQUIT received\n");
         pthread_exit(NULL);
     }
     else{
         printf("signal %d received\n", signum);
     }

     return;
}

void *do_w(void *args)
{
    struct sigaction sa_usr;
    sa_usr.sa_flags = 0;
    sa_usr.sa_handler = sig_hdl;
    sigaction(SIGQUIT, &sa_usr, NULL);

    do{
        pthread_mutex_lock(&glock);
        a++;
        sleep(5);
        pthread_mutex_unlock(&glock);
        sleep(1);
    }while(1);

    return NULL;
}

void *do_r(void *args)
{
    do{
        pthread_mutex_lock(&glock);
        printf("read a : %d\n", a);
        pthread_mutex_unlock(&glock);
        sleep(1);
    }while(1);

    return;
}

void main(void)
{
    pthread_t wid, rid;
    pthread_create(&rid, NULL, do_r, NULL);
    pthread_create(&wid, NULL, do_w, NULL);

    do{
        if (a > 13){
            pthread_kill(wid, SIGQUIT);
            break;
        }
    }while(1);

    pthread_join(rid, NULL);
    pthread_join(wid, NULL);

    return;
}

当主线程通过pthread_kill发送SIGQUIT信号给do_w线程，该信号的处理函数会调用pthread_exit线程退出。
若do_w线程在lock后unlock前收到SIGQUIT信号，则锁资源就没有释放，线程do_r就会堵塞无法继续执行。

在POSIX线程API中提供了一个pthread_cleanup_push()/pthread_cleanup_pop()函数对用于自动释放资源--从pthread_cleanup_push()的调用点到pthread_cleanup_pop()之间的程序段中的终止动作（包括调用pthread_exit()和取消点终止）都将执行pthread_cleanup_push()所指定的清理函数。

下面的代码，在do_w线程中加入了pthread_cleanup_push/pthread_cleanup_pop函数,用来解决线程退出时自动释放资源。

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>


static int a = 10;
pthread_mutex_t glock = PTHREAD_MUTEX_INITIALIZER;

static void sig_hdl(int signum)
{
     if(signum == SIGQUIT){
         printf("SIGQUIT received\n");
         pthread_exit(NULL);
     }
     else{
         printf("signal %d received\n", signum);
     }

     return;
}

void *do_w(void *args)
{
    struct sigaction sa_usr;
    sa_usr.sa_flags = 0;
    sa_usr.sa_handler = sig_hdl; //信号处理函数

    sigaction(SIGQUIT, &sa_usr, NULL);
    pthread_cleanup_push(pthread_mutex_unlock, (void *)&glock);
    do{
        pthread_mutex_lock(&glock);
        a++;
        sleep(5);
        pthread_mutex_unlock(&glock);
        sleep(1);
    }while(1);
    pthread_cleanup_pop(0);

    return NULL;
}

void *do_r(void *args)
{
    do{
        pthread_mutex_lock(&glock);
        printf("read a : %d\n", a);
        pthread_mutex_unlock(&glock);
        sleep(1);
    }while(1);

    return;
}

void main(void)
{
    pthread_t wid, rid;
    pthread_create(&rid, NULL, do_r, NULL);
    pthread_create(&wid, NULL, do_w, NULL);

    do{
        if (a > 13){
            pthread_kill(wid, SIGQUIT);
            break;
        }
    }while(1);

    pthread_join(rid, NULL);
    pthread_join(wid, NULL);

    return;
}