生产者消费者问题

生产者-消费者问题是一个经典的进程同步问题，该问题最早由Dijkstra提出，用以演示他提出的信号量机制。在同一个进程地址空间内执行的两个线程。生产者线程生产物品，然后将物品放置在一个空缓冲区中供消费者线程消费。消费者线程从缓冲区中获得物品，然后释放缓冲区。当生产者线程生产物品时，如果没有空缓冲区可用，那么生产者线程必须等待消费者线程释放出一个空缓冲区。当消费者线程消费物品时，如果没有满的缓冲区，那么消费者线程将被阻塞，直到新的物品被生产出来。

#include   <windows.h> 
#include   <iostream> 

const   unsigned   short   SIZE_OF_BUFFER   =   10;   //缓冲区长度 
unsigned   short   ProductID   =   0;         //产品号 
unsigned   short   ConsumeID   =   0;         //将被消耗的产品号 
unsigned   short   in   =   0;             //产品进缓冲区时的缓冲区下标 
unsigned   short   out   =   0;             //产品出缓冲区时的缓冲区下标 

int   g_buffer[SIZE_OF_BUFFER];         //缓冲区是个循环队列 
bool   g_continue   =   true;             //控制程序结束 
HANDLE   g_hMutex;               //用于线程间的互斥 
HANDLE   g_hFullSemaphore;           //当缓冲区满时迫使生产者等待 
HANDLE   g_hEmptySemaphore;           //当缓冲区空时迫使消费者等待 

DWORD   WINAPI   Producer(LPVOID);         //生产者线程 
DWORD   WINAPI   Consumer(LPVOID);         //消费者线程 

int   main() 
{ 
    //创建各个互斥信号 
    g_hMutex   =   CreateMutex(NULL,FALSE,NULL); 
    g_hFullSemaphore   =   CreateSemaphore(NULL,SIZE_OF_BUFFER-1,SIZE_OF_BUFFER-1,NULL); 
    g_hEmptySemaphore   =   CreateSemaphore(NULL,0,SIZE_OF_BUFFER-1,NULL); 

    //调整下面的数值，可以发现，当生产者个数多于消费者个数时， 
    //生产速度快，生产者经常等待消费者；反之，消费者经常等待   
    const   unsigned   short   PRODUCERS_COUNT   =   3;     //生产者的个数 
    const   unsigned   short   CONSUMERS_COUNT   =   1;     //消费者的个数 

    //总的线程数 
    const   unsigned   short   THREADS_COUNT   =   PRODUCERS_COUNT+CONSUMERS_COUNT; 

    HANDLE   hThreads[PRODUCERS_COUNT];   //各线程的handle 
    DWORD   producerID[CONSUMERS_COUNT];   //生产者线程的标识符 
    DWORD   consumerID[THREADS_COUNT];   //消费者线程的标识符 

    //创建生产者线程 
    for   (int   i=0;i <PRODUCERS_COUNT;++i){ 
        hThreads[i]=CreateThread(NULL,0,Producer,NULL,0,&producerID[i]); 
        if   (hThreads[i]==NULL)   return   -1; 
    } 
    //创建消费者线程 
    for   (int   i=0;i <CONSUMERS_COUNT;++i){ 
        hThreads[PRODUCERS_COUNT+i]=CreateThread(NULL,0,Consumer,NULL,0,&consumerID[i]); 
        if   (hThreads[i]==NULL)   return   -1; 
    } 

    while(g_continue){ 
        if(getchar()){   //按回车后终止程序运行 
            g_continue   =   false; 
        } 
    } 

    return   0; 
} 

//生产一个产品。简单模拟了一下，仅输出新产品的ID号 
void   Produce() 
{ 
    std::cerr   < <   "Producing   "   < <   ++ProductID   < <   "   ...   "; 
    std::cerr   < <   "Succeed "   < <   std::endl; 
} 

//把新生产的产品放入缓冲区 
void   Append() 
{ 
    std::cerr   < <   "Appending   a   product   ...   "; 
    g_buffer[in]   =   ProductID; 
    in   =   (in+1)%SIZE_OF_BUFFER; 
    std::cerr   < <   "Succeed "   < <   std::endl; 

    //输出缓冲区当前的状态 
    for   (int   i=0;i <SIZE_OF_BUFFER;++i){ 
        std::cout   < <   i   < < ":   "   < <   g_buffer[i]; 
        if   (i==in)   std::cout   < <   "   <--   生产 "; 
        if   (i==out)   std::cout   < <   "   <--   消费 "; 
        std::cout   < <   std::endl; 
    } 
} 

//从缓冲区中取出一个产品 
void   Take() 
{ 
    std::cerr   < <   "Taking   a   product   ...   "; 
    ConsumeID   =   g_buffer[out]; 
    out   =   (out+1)%SIZE_OF_BUFFER; 
    std::cerr   < <   "Succeed "   < <   std::endl; 

    //输出缓冲区当前的状态 
    for   (int   i=0;i <SIZE_OF_BUFFER;++i){ 
        std::cout   < <   i   < < ":   "   < <   g_buffer[i]; 
        if   (i==in)   std::cout   < <   "   <--   生产 "; 
        if   (i==out)   std::cout   < <   "   <--   消费 "; 
        std::cout   < <   std::endl; 
    } 
} 

//消耗一个产品 
void   Consume() 
{ 
    std::cerr   < <   "Consuming   "   < <   ConsumeID   < <   "   ...   "; 
    std::cerr   < <   "Succeed "   < <   std::endl; 
} 

//生产者 
DWORD     WINAPI   Producer(LPVOID   lpPara) 
{ 
    while(g_continue){ 
        WaitForSingleObject(g_hFullSemaphore,INFINITE); 
        WaitForSingleObject(g_hMutex,INFINITE); 
        Produce(); 
        Append(); 
        Sleep(1500); 
        ReleaseMutex(g_hMutex); 
        ReleaseSemaphore(g_hEmptySemaphore,1,NULL); 
    } 
    return   0; 
} 

//消费者 
DWORD     WINAPI   Consumer(LPVOID   lpPara) 
{ 
    while(g_continue){ 
        WaitForSingleObject(g_hEmptySemaphore,INFINITE); 
        WaitForSingleObject(g_hMutex,INFINITE); 
        Take(); 
        Consume(); 
        Sleep(1500); 
        ReleaseMutex(g_hMutex); 
        ReleaseSemaphore(g_hFullSemaphore,1,NULL); 
    } 
    return   0; 
}