Linux 线程的互斥和等待 pthread_mutex_lock/pthread_mutex_unlock pthread_cond_wait/pthread_cond_signal

多线程中比较常见的是生产者，消费者的模式。而实现它并不复杂，通过 pthread_mutex_lock/pthread_mutex_unlock pthread_cond_wait/pthread_cond_signal 就可以达到目的：

非常容易犯的错误是，忘记对 mutex 和 mwait 的初始化，有时候会出现非常难以发现的问题。

#include <pthread.h>

pthread_mutex_t mutex;
pthread_cond_t mwait;

bool exit_sign;

void init() {

　pthread_mutex_init(mutex, NULL);
　pthread_cond_init(mwait, NULL);

}

void relese() {

exit_sign = 1;

pthread_mutex_unlock(mutex);

pthread_cond_signal(mwait);

pthread_mutex_destroy(mutex);
pthread_cond_destroy(mwait);

}

void pushD(D *data) {
    pthread_mutex_lock(&D_mutex);
    if (D_queue.size() >= maxQueueSize) {
        delete (D_queue.front());
        D_queue.pop();
　　 }

    D_queue.push(data);
    pthread_mutex_unlock(&mutex);
    pthread_cond_signal(&mwait);
    return 0;
}

D* popD() {
    pthread_mutex_lock(&mutex);
    D *d = NULL;
    while (D_queue.size() <= 0 && !exit_sign) {
        pthread_cond_wait(&mwait, &mutex);
    }

    if (exit_sign) {
        return NULL;
    }
    d = D_queue.front();
    D_queue.pop();
    pthread_mutex_unlock(&mutex);
    return d;
}