互斥锁mutex

https://blog.csdn.net/rqc112233/article/details/50015069

//g++ mute.cpp -o mute -g -lrt -lpthread
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <syslog.h>

static pthread_mutex_t testlock;
pthread_t test_thread;

void *test(void *)
{
    pthread_mutex_lock(&testlock);
    printf("thread Test() 
");
    syslog(LOG_DEBUG, "thread Test() 
");
    pthread_mutex_unlock(&testlock);
}

int main()
{
    openlog("syslog",  LOG_PID, LOG_DAEMON);
    pthread_mutex_init(&testlock, NULL);
    pthread_mutex_lock(&testlock);

    printf("Main lock 
");
    syslog(LOG_DEBUG, "Main lock 
");
    pthread_create(&test_thread, NULL, &test, NULL);
    sleep(3); //更加明显的观察到是否执行了创建线程的互斥锁
    printf("Main unlock 
");
    syslog(LOG_DEBUG, "Main unlock 
");
    pthread_mutex_unlock(&testlock);
    sleep(1);
    printf("Main after sleep 
");
    syslog(LOG_DEBUG, "Main after sleep 
");
    pthread_join(test_thread, NULL);
    pthread_mutex_destroy(&testlock);
    closelog();
    return 0;
}

小技巧:借助syslog 记录时间  cat /var/log/syslog

输出:

Jul  5 16:23:24 Linux syslog[19982]: Main lock
Jul  5 16:23:27 Linux syslog[19982]: Main unlock
Jul  5 16:23:27 Linux syslog[19982]: thread Test()
Jul  5 16:23:28 Linux syslog[19982]: Main after sleep

 稍微改下:

//g++ mute.cpp -o mute -g -lrt -lpthread
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <syslog.h>

static pthread_mutex_t testlock;
pthread_t test_thread;

void *test(void *)
{
    pthread_mutex_lock(&testlock);
    printf("thread Test() 
");
    syslog(LOG_DEBUG, "thread Test() 
");
    sleep(2); //更加明显的观察到是否执行了创建线程的互斥锁
    pthread_mutex_unlock(&testlock);
}

int main()
{
    openlog("syslog",  LOG_PID, LOG_DAEMON);
    pthread_mutex_init(&testlock, NULL);
    pthread_mutex_lock(&testlock);

    printf("Main lock 
");
    syslog(LOG_DEBUG, "Main lock 
");
    pthread_create(&test_thread, NULL, &test, NULL);
    sleep(3); //更加明显的观察到是否执行了创建线程的互斥锁
    printf("Main unlock 
");
    syslog(LOG_DEBUG, "Main unlock 
");
    pthread_mutex_unlock(&testlock);
    sleep(1);
    pthread_mutex_lock(&testlock);
    printf("Main after sleep 
");
    syslog(LOG_DEBUG, "Main after sleep 
");
    pthread_mutex_unlock(&testlock);
    pthread_join(test_thread, NULL);
    pthread_mutex_destroy(&testlock);
    closelog();
    return 0;
}

输出为:

Jul  6 10:31:40 Linux syslog[2498]: Main lock
Jul  6 10:31:43 Linux syslog[2498]: Main unlock
Jul  6 10:31:43 Linux syslog[2498]: thread Test()
Jul  6 10:31:45 Linux syslog[2498]: Main after sleep

主线程初始化互斥锁和上锁, 然后创建子线程, sleep 3s, 

子线程会卡在pthread_mutex_lock(&testlock);直到主线程解锁

主线程解锁后, 子线程持有锁, sleep 2s ,  主线程sleep 1s, 

主线程会卡在pthread_mutex_lock(&testlock);直到子线程解锁

阻塞的方式等待子线程结束.销毁锁

JAVA版本:

  public boolean waitDone() {
            final Object waitDoneLock = new Object();
            final Runnable unlockRunnable = new Runnable() {
                @Override
                public void run() {
                    synchronized (waitDoneLock) {
                        waitDoneLock.notifyAll();
                    }
                }
            };

            synchronized (waitDoneLock) {
                mCameraHandler.post(unlockRunnable);
                try {
                    waitDoneLock.wait();
                } catch (InterruptedException ex) {
                    QLog.v(TAG, "waitDone interrupted");
                    return false;
                }
            }
            return true;
        }

        public boolean waitDone(long timeout) {
            final Object waitDoneLock = new Object();
            final Runnable unlockRunnable = new Runnable() {
                @Override
                public void run() {
                    synchronized (waitDoneLock) {
                        waitDoneLock.notifyAll();
                    }
                }
            };

            synchronized (waitDoneLock) {
                mCameraHandler.post(unlockRunnable);
                try {
                    waitDoneLock.wait(timeout);
                    mCameraHandler.removeCallbacks(unlockRunnable);
                } catch (InterruptedException ex) {
                    QLog.v(TAG, "waitDone interrupted");
                    return false;
                }
            }
            return true;
        }