进程同步演示
一、实验目的
• 深入掌握进程同步机制——信号量机制的应用;
• 掌握Windows编程中信号量机制的使用方法;
• 可进行简单的信号量应用编程。
二、实验工具
Windows系统 + VisuaStudio2019
三、实验内容
1、复习教材上信号量机制的定义与应用,复习经典进程同步问题——生产者消费者问题及其同步方案;
2、验证后附的参考代码pc.cpp(生产者消费者问题),掌握Windows系统中信号量的定义与使用方法;
注意:
1)代码中 生产者 和 消费者 所做的工作 用过程Producer和Consumer描述,并通过创建线程的方法创建3个生产者线程和1个消费者线程,具体创建方法:CreateThread(NULL,0,Producer,NULL,0,&producerID[i]);其中第3个参数就是指定该线程所做的工作为过程Producer;
2)问题中设置了三个信号量g_hMutex(用于互斥访问临界区buffer)、g_hFullSemaphore、g_hEmptySemaphore(用于控制同步的资源信号量),先声明,再定义,最后使用。互斥信号量和资源信号量的定义方法不同:
g_hMutex = CreateMutex(NULL,FALSE,NULL); 互斥信号量最开始没有指定针对那个资源
g_hFullSemaphore = CreateSemaphore(NULL,SIZE_OF_BUFFER-1,SIZE_OF_BUFFER-1,NULL); 其中第2和3个参数为信号量的初始值和最大值
信号量的使用方法:WaitForSingleObject为信号量的P操作,每对一个信号量执行该操作,则信号量值减1,并判断减1后值是否仍大于等于0,如是则该操作成功,否则进程阻塞; ReleaseSemaphore为信号量的V操作,每执行一次将该信号量的值加1,并起到唤醒作用。如:
WaitForSingleObject(g_hFullSemaphore,INFINITE);
…
ReleaseSemaphore(g_hEmptySemaphore,1,NULL);
ReleaseMutex(g_hMutex);
3、撰写实验报告,请在实验报告中给出运行结果,并对程序功能进行分析,可截图
代码段
#define _CRT_SECURE_NO_WARNINGS
#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[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 (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;
}