生產者消費者問題

生產者-消費者問題是一個經典的進程同步問題，該問題最早由Dijkstra提出，用以演示他提出的信號量機制。在同一個進程地址空間內執行的兩個線程。生產者線程生產物品，然后將物品放置在一個空緩沖區中供消費者線程消費。消費者線程從緩沖區中獲得物品，然后釋放緩沖區。當生產者線程生產物品時，如果沒有空緩沖區可用，那么生產者線程必須等待消費者線程釋放出一個空緩沖區。當消費者線程消費物品時，如果沒有滿的緩沖區，那么消費者線程將被阻塞，直到新的物品被生產出來。

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

const   unsigned   short   SIZE_OF_BUFFER   =   10;   //緩沖區長度 
unsigned   short   ProductID   =   0;         //產品號 
unsigned   short   ConsumeID   =   0;         //將被消耗的產品號 
unsigned   short   in   =   0;             //產品進緩沖區時的緩沖區下標 
unsigned   short   out   =   0;             //產品出緩沖區時的緩沖區下標 

int   g_buffer[SIZE_OF_BUFFER];         //緩沖區是個循環隊列 
bool   g_continue   =   true;             //控制程序結束 
HANDLE   g_hMutex;               //用於線程間的互斥 
HANDLE   g_hFullSemaphore;           //當緩沖區滿時迫使生產者等待 
HANDLE   g_hEmptySemaphore;           //當緩沖區空時迫使消費者等待 

DWORD   WINAPI   Producer(LPVOID);         //生產者線程 
DWORD   WINAPI   Consumer(LPVOID);         //消費者線程 

int   main() 
{ 
    //創建各個互斥信號 
    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); 

    //調整下面的數值，可以發現，當生產者個數多於消費者個數時， 
    //生產速度快，生產者經常等待消費者；反之，消費者經常等待   
    const   unsigned   short   PRODUCERS_COUNT   =   3;     //生產者的個數 
    const   unsigned   short   CONSUMERS_COUNT   =   1;     //消費者的個數 

    //總的線程數 
    const   unsigned   short   THREADS_COUNT   =   PRODUCERS_COUNT+CONSUMERS_COUNT; 

    HANDLE   hThreads[PRODUCERS_COUNT];   //各線程的handle 
    DWORD   producerID[CONSUMERS_COUNT];   //生產者線程的標識符 
    DWORD   consumerID[THREADS_COUNT];   //消費者線程的標識符 

    //創建生產者線程 
    for   (int   i=0;i <PRODUCERS_COUNT;++i){ 
        hThreads[i]=CreateThread(NULL,0,Producer,NULL,0,&producerID[i]); 
        if   (hThreads[i]==NULL)   return   -1; 
    } 
    //創建消費者線程 
    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()){   //按回車后終止程序運行 
            g_continue   =   false; 
        } 
    } 

    return   0; 
} 

//生產一個產品。簡單模擬了一下，僅輸出新產品的ID號 
void   Produce() 
{ 
    std::cerr   < <   "Producing   "   < <   ++ProductID   < <   "   ...   "; 
    std::cerr   < <   "Succeed "   < <   std::endl; 
} 

//把新生產的產品放入緩沖區 
void   Append() 
{ 
    std::cerr   < <   "Appending   a   product   ...   "; 
    g_buffer[in]   =   ProductID; 
    in   =   (in+1)%SIZE_OF_BUFFER; 
    std::cerr   < <   "Succeed "   < <   std::endl; 

    //輸出緩沖區當前的狀態 
    for   (int   i=0;i <SIZE_OF_BUFFER;++i){ 
        std::cout   < <   i   < < ":   "   < <   g_buffer[i]; 
        if   (i==in)   std::cout   < <   "   <--   生產 "; 
        if   (i==out)   std::cout   < <   "   <--   消費 "; 
        std::cout   < <   std::endl; 
    } 
} 

//從緩沖區中取出一個產品 
void   Take() 
{ 
    std::cerr   < <   "Taking   a   product   ...   "; 
    ConsumeID   =   g_buffer[out]; 
    out   =   (out+1)%SIZE_OF_BUFFER; 
    std::cerr   < <   "Succeed "   < <   std::endl; 

    //輸出緩沖區當前的狀態 
    for   (int   i=0;i <SIZE_OF_BUFFER;++i){ 
        std::cout   < <   i   < < ":   "   < <   g_buffer[i]; 
        if   (i==in)   std::cout   < <   "   <--   生產 "; 
        if   (i==out)   std::cout   < <   "   <--   消費 "; 
        std::cout   < <   std::endl; 
    } 
} 

//消耗一個產品 
void   Consume() 
{ 
    std::cerr   < <   "Consuming   "   < <   ConsumeID   < <   "   ...   "; 
    std::cerr   < <   "Succeed "   < <   std::endl; 
} 

//生產者 
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; 
} 

//消費者 
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; 
}