//程式碼可直接編譯通過

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#define MAX_STOCK 20//容量
char g_storage[MAX_STOCK];
size_t g_stock = 0;//當前庫存
pthread_mutex_t g_mtx = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t g_full = PTHREAD_COND_INITIALIZER;
pthread_cond_t g_empty = PTHREAD_COND_INITIALIZER;
void show(const char* who,const char* op,char prod){
    printf("%s:",who);
    size_t i;
    for(i < 0;i < g_stock;++i)
        printf("%c",g_storage[i]);
    printf("%s%c\n",op,prod);
}
void* producer(void* arg)
{
    const char* who = (const char*)arg;
    for(;;){
        pthread_mutex_lock(&g_mtx);
        while(g_stock >= MAX_STOCK){//此處必須用while判斷，防止條件失效。試想兩個producer都阻塞在
            //wait上，之後一個被喚醒。生產之後，另一個又返回去生產，導致越界。
            printf("%s:full\n",who);
            pthread_cond_wait(&g_full,&g_mtx);
            //此函式阻塞,同時Mutex會解鎖,返回之前需重新獲取這把鎖
        }
        char prod = 'A' + rand()%26;
        show(who,"<-",prod);
        g_storage[g_stock++] = prod;
        pthread_cond_broadcast(&g_empty);
        pthread_mutex_unlock(&g_mtx);
        usleep((rand()%100)*1000);
    }
    return NULL;
}
void* customer(void* arg){
    const char* who = (const char*)arg;
    for(;;){
        pthread_mutex_lock(&g_mtx);
        while(!g_stock){
            printf("%s:空倉\n",who);
            pthread_cond_wait(&g_empty,&g_mtx);
            //g_empty初始化之後無訊號,之後進入阻塞.
        }
        char prod = g_storage[--g_stock];
        show(who,"->",prod);
        pthread_cond_broadcast(&g_full);//只有有執行緒阻塞的時候發訊號才有效.
        pthread_mutex_unlock(&g_mtx);
        usleep((rand()%100)*1000);
    }
    return NULL;
}
int main(void){
    srand(time(NULL));
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);
    pthread_t tid;
    pthread_create(&tid,&attr,producer,"prodecer1");
    pthread_create(&tid,&attr,producer,"prodecer2");
    pthread_create(&tid,&attr,customer,"customer1");
    pthread_create(&tid,&attr,customer,"customer2");
    getchar();
}

//pthread_cond_broadcast(&g_full)叫醒所有的，pthread_cond_signal(&g_full)只喚醒一個