apue- thread 线程学习(pthread_join,b

0x01 等待子线程返回结果

pthread_join 会阻塞当前线程, 直到子线程返回结果

#include "apue.h"
#include <pthread.h>

void *sub(void *arg) {
    printf("sub-thread-start ....\n");
    sleep(2);
    printf("sub-thread-end ....\n");
    pthread_exit((void *) 180);
}


int main(int argc, char *argv[]) {
    pthread_t p;
    void *rst;
    printf("main thread start ...\n");

    int e = pthread_create(&p, NULL, sub, NULL);
    if (e != 0)
        err_exit(e, "can't create thread");

    // main thread wait until get result from sub thread
    e = pthread_join(p, &rst);
    if (e != 0)
        err_exit(e, "can't joint thread");

    printf("main thread done %lu \n", (long)rst);
    exit(0);
}

• 运行结果:

main thread start ...
sub-thread-start ....
sub-thread-end ....
main thread done 180 

0x02 mutex 上锁超时

#include "apue.h"
#include <pthread.h>

int main(int argc, char *argv[]) {
    int e;
    struct timespec tout;
    struct tm *tmp;
    char buf[64];
    pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

    pthread_mutex_lock(&lock);
    printf("mutex is locked\n");

    clock_gettime(CLOCK_REALTIME, &tout);
    tmp = localtime(&tout.tv_sec);
    strftime(buf, sizeof(buf), "%r", tmp);
    printf("current time is %s\n", buf);

    tout.tv_sec += 5;

    // lock a mutex with timeout
    e = pthread_mutex_timedlock(&lock, &tout);
    clock_gettime(CLOCK_REALTIME, &tout);
    tmp = localtime(&tout.tv_sec);
    strftime(buf, sizeof(buf), "%r", tmp);
    printf("the time is now %s \n", buf);

    if (e == 0)
        printf("mutex locked again!\n");
    else
        printf("can't lock mutex again: %s\n", strerror(e));

    exit(0);
}

• 输出结果:

mutex is locked
current time is 10:38:44 AM
the time is now 10:38:49 AM 
can't lock mutex again: Connection timed out

0x03 线程组同步 barrier

• 启用一个barrier并指定线程数 : pthread_barrier_init(&b, NULL, TASK_CNT + 1);
• 每一个线程都会执行并等待到: pthread_barrier_wait(&b);
  当所有线程都到达这里后, 才都向后继续执行.

#include "apue.h"
#include <pthread.h>
#include <sys/time.h>


#define TASK_CNT ((unsigned int)5)

pthread_barrier_t b;

void *sub(void *arg) {
    printf("[%lu]thread running within : %lu seconds\n", pthread_self(), (long) arg);
    sleep((long) arg);
    printf("[%lu]thread done\n", pthread_self());
    pthread_barrier_wait(&b);
    pthread_exit((void *) 0);
}


int main(int argc, char *argv[]) {
    struct timeval start, end;
    long long startusec, endusec;
    double elapsed;
    int err;
    pthread_t tid;

    gettimeofday(&start, NULL);
    pthread_barrier_init(&b, NULL, TASK_CNT + 1);
    srandom(1);

    for (int i = 0; i < TASK_CNT; ++i) {
        err = pthread_create(&tid, NULL, sub, (void *) (random() % 10));
        if (err != 0)
            err_exit(err, "can't create thread");
    }
    pthread_barrier_wait(&b);

    gettimeofday(&end, NULL);
    startusec = start.tv_sec * 1000000 + start.tv_usec;
    endusec = end.tv_sec * 1000000 + end.tv_usec;
    elapsed = (double) (endusec - startusec) / 1000000.0;
    printf("all task took %.4f seconds\n", elapsed);

    exit(0);
}

• 结果:

[140526034429696]thread running within : 3 seconds
[140526017644288]thread running within : 7 seconds
[140526026036992]thread running within : 6 seconds
[140526009251584]thread running within : 5 seconds
[140526000858880]thread running within : 3 seconds
[140526034429696]thread done
[140526000858880]thread done
[140526009251584]thread done
[140526026036992]thread done
[140526017644288]thread done
sort took 7.0024 seconds