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/******************************************************************************
 * 描述：
 *     應(yīng)用Pthreads條件變量的實(shí)例代碼，主線程創(chuàng)建三個線程，其中兩個為“count”變量做
 * 加法運(yùn)算，第三個線程監(jiān)視“count”的值。當(dāng)“count”達(dá)到一個限定值，等待線程準(zhǔn)備接收來
 * 自于兩個加法線程中一個的信號，等待 線程喚醒后更改“count”的值。程序繼續(xù)運(yùn)行直到加法
 * 線程達(dá)到TCOUNT的值。最后，主程序打印出count的值。
 ******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

#define NUM_THREADS  3
#define TCOUNT 5       //單線程輪詢次數(shù)
#define COUNT_LIMIT 7  //發(fā)送信號的次數(shù)
int count = 0; //全局的累加量

pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *inc_count(void *t) {
    int i;
    long my_id = (long) t;

    for (i = 0; i < TCOUNT; i++) {
        pthread_mutex_lock(&count_mutex);
        count++;
        /*
         * 檢查count的值，如果條件滿足就發(fā)信號給等待線程
         * 注意，此處是用信號量鎖定的。
         * */
        if (count < COUNT_LIMIT) {
            printf("inc_count(): thread %ld, count = %d  Threshold reached. ",
                    my_id, count);
            pthread_cond_signal(&count_threshold_cv);
            printf("Just sent signal.\n");
        }
        printf("inc_count(): thread %ld, count = %d, unlocking mutex\n", my_id,
                count);
        pthread_mutex_unlock(&count_mutex);

        /*為線程輪詢互斥鎖增加延時*/
        sleep(1);
    }
    pthread_exit(NULL);
}

void *watch_count(void *t) {
    long my_id = (long) t;
    printf("Starting watch_count(): thread %ld\n", my_id);

    /*鎖定互斥量并等待信號，注意，pthread_cond_wait函數(shù)在等待時將自動以自動原子方式
     * 解鎖互斥量。還有，請注意，如果等待線程運(yùn)行到等待函數(shù)之前已經(jīng)滿足COUNT_LIMIT的
     * 條件判斷，輪詢會忽略掉等待函數(shù)，
     * */
    while (count < COUNT_LIMIT) {
        pthread_mutex_lock(&count_mutex);
        printf("watch_count(): thread %ld going into wait...\n", my_id);
        pthread_cond_wait(&count_threshold_cv, &count_mutex);
        printf("watch_count(): thread %ld Condition signal received.\n", my_id);

        printf("watch_count(): thread %ld count now = %d.\n", my_id, count);
        pthread_mutex_unlock(&count_mutex);
    }
    pthread_exit(NULL);
}

int main(int argc, char *argv[]) {
    int i;
    long t1 = 1, t2 = 2, t3 = 3;
    pthread_t threads[3];
    pthread_attr_t attr;

    /*初始化互斥量和條件變量對象*/
    pthread_mutex_init(&count_mutex, NULL);
    pthread_cond_init(&count_threshold_cv, NULL);

    /*創(chuàng)建線程時設(shè)為可連接狀態(tài)，便于移植*/
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
    pthread_create(&threads[0], &attr, watch_count, (void *) t1);
    pthread_create(&threads[1], &attr, inc_count, (void *) t2);
    pthread_create(&threads[2], &attr, inc_count, (void *) t3);

    /* 等待所有線程完成*/
    for (i = 1; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }
   /*發(fā)送信號給監(jiān)聽線程*/
    pthread_cond_signal(&count_threshold_cv); 
    pthread_join(threads[0],NULL);
    printf("Main(): Waited on %d threads. Final value of count = %d. Done.\n",
            NUM_THREADS, count);

    /*清除并退出 */
    pthread_attr_destroy(&attr);
    pthread_mutex_destroy(&count_mutex);
    pthread_cond_destroy(&count_threshold_cv);
    pthread_exit(NULL);
}