操作系统实验三程序分析

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

const unsigned short SIZE_OF_BUFFER = 2; //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 buffer[SIZE_OF_BUFFER]; //缓冲区是个循环队列
bool p_ccontinue = true; //控制程序结束
HANDLE Mutex; //用于线程间的互斥
HANDLE FullSemaphore; //当缓冲区满时迫使生产者等待
HANDLE EmptySemaphore; //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
//注意，互斥信号量和同步信号量的定义方法不同，互斥信号量调用的是 CreateMutex 函数，
//同步信号量调用的是 CreateSemaphore 函数，函数的返回值都是句柄。
    Mutex = CreateMutex(NULL,FALSE,NULL);
    EmptySemaphore = CreateSemaphore(NULL,SIZE_OF_BUFFER,SIZE_OF_BUFFER,NULL);
//将上句做如下修改，看看结果会怎样
//EmptySemaphore = CreateSemaphore(NULL,0,SIZE_OF_BUFFER-1,NULL);
    FullSemaphore = CreateSemaphore(NULL,0,SIZE_OF_BUFFER,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[THREADS_COUNT]; //各线程的 handle
    DWORD producerID[PRODUCERS_COUNT]; //生产者线程的标识符
    DWORD consumerID[CONSUMERS_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(p_ccontinue) {
        if(getchar()) { //按回车后终止程序运行
            p_ccontinue = 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::cout << std::endl<< "Producing " << ++ProductID << " ... ";
    std::cout << "Succeed" << std::endl;
}
//把新生产的产品放入缓冲区
void Append() {
    std::cerr << "Appending a product ... ";
    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 <<": " << 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 = buffer[out];
    buffer[out] = 0;
    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 <<": " << 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::cout << "Consuming " << ConsumeID << " ... ";
    std::cout << "Succeed" << std::endl;
}
//生产者
DWORD WINAPI Producer(LPVOID lpPara) {
    while(p_ccontinue) {
        WaitForSingleObject(EmptySemaphore,INFINITE); //p(empty);
        WaitForSingleObject(Mutex,INFINITE); //p(mutex);
        Produce();
        Append();
        Sleep(1500);
        ReleaseMutex(Mutex); //V(mutex);
        ReleaseSemaphore(FullSemaphore,1,NULL); //V(full);
    }
    return 0;
}
//消费者
DWORD WINAPI Consumer(LPVOID lpPara) {
    while(p_ccontinue) {
        WaitForSingleObject(FullSemaphore,INFINITE); //P(full);
        WaitForSingleObject(Mutex,INFINITE); //P(mutex);
        Take();
        Consume();
        Sleep(1500);
        ReleaseMutex(Mutex); //V(mutex);
        ReleaseSemaphore(EmptySemaphore,1,NULL); //V(empty);
    }
    return 0;
}

LPSECURITY_ATTRIBUTES lpMutexAttributes  //代表安全属性指针
BOOL bInitialOwner //代表布尔bInitialOwner
LPCTSTR lpName //代表LPCTSTR类型lpName