平湖模板网站建设公司,网页美工培训,聊城网站公司,贵州网站建设文章目录 前言CodeCode运行效果 分解讲解main()class ProducerConsumerProblemproduce()consumer() END 前言
生产者消费者问题_百度百科 (baidu.com) 生产者消费者问题 #xff08;英语#xff1a;Producer-consumer problem#xff09;#xff0c;也称有限缓冲问题… 文章目录 前言CodeCode运行效果 分解讲解main()class ProducerConsumerProblemproduce()consumer() END 前言
生产者消费者问题_百度百科 (baidu.com) 生产者消费者问题 英语Producer-consumer problem也称有限缓冲问题英语Bounded-buffer problem是一个多线程同步问题的经典案例。该问题描述了两个共享固定大小缓冲区的线程——即所谓的“生产者”和“消费者”——在实际运行时会发生的问题。生产者的主要作用是生成一定量的数据放到缓冲区中然后重复此过程。与此同时消费者也在缓冲区消耗这些数据。该问题的关键就是要保证生产者不会在缓冲区已经装满时加入数据消费者也不会在缓冲区为空时消耗数据。 Code
Code
#include condition_variable
#include iostream
#include mutex
#include queue
#include string
#include thread
#include vectorconstexpr int WORKERTHREAD_COUNT 3;class ProducerConsumerProblem {
private:// 任务队列std::queuestd::string m_queue;// mutexstd::mutex m_mutex;// condition_variablestd::condition_variable m_cv;public:/*** 生产者函数*/void produce(const int cnt) {printf((Produce Thread:%lld) start\n, std::this_thread::get_id());// RAII 自动解锁std::lock_guardstd::mutex lock(m_mutex);char buff[1024] {};for (int i 0; i cnt; i 1) {sprintf(buff, Produce[%02d], i);m_queue.push(buff);}// 唤醒所有消费者m_cv.notify_all();// 唤醒任意一个消费者// m_cv.notify_one();}/*** 消费者线程*/void consumer() {printf((Consumer Thread:%lld) start\n, std::this_thread::get_id());constexpr int SLEEP_TIME 5;std::string receiveBuffer;while (1) {// 比lock_guard更细致的控制力度std::unique_lockstd::mutex lock(m_mutex);/*** brief* 如果任务队列为空则等待** 为什么是循环判断* 条件变量虚假唤醒* 消费者线程被唤醒后* 缓存队列中没有数据** 条件变量 wait(mutex)的作用* 1. 把互斥锁解开* 2. 阻塞等待被唤醒* 3. 给互斥锁加锁* 等效写法* m_cv.wait(lock, [this]() { return !m_queue.empty(); });*/while (m_queue.empty()) {// 等待生产者唤醒printf((Thread:%lld) is waiting ~~~\n,std::this_thread::get_id());m_cv.wait(lock);}// 此时任务队列有数据且cv被唤醒// 消费者处理一个任务receiveBuffer m_queue.front();m_queue.pop();// 当前消费者线程获得数据手动解锁lock.unlock();// 模拟随机设定一个消费时间int solveTimeCost (rand() % SLEEP_TIME);printf((Thread:%lld) %s need %d seconds ...\n,std::this_thread::get_id(), receiveBuffer.c_str(),solveTimeCost);std::this_thread::sleep_for(std::chrono::seconds(solveTimeCost));}}
};int main() {srand(time(0));ProducerConsumerProblem obj;std::vectorstd::thread thdVec;for (int i 0; i WORKERTHREAD_COUNT; i 1) {// 只能move放入vector延长对象的生存周期auto thd std::thread(ProducerConsumerProblem::consumer, obj);thdVec.push_back(std::move(thd));thdVec[i].detach();}int cnt;// 通过这里的输入阻塞程序while (printf(Please input produce number:\n), std::cin cnt) {obj.produce(cnt);}return 0;
}运行效果
环境
g (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 7.3.0效果
分别输入2 10 3
Please input produce number:
(Consumer Thread:2) start
(Consumer Thread:3) start
(Consumer Thread:4) start
(Thread:2) is waiting ~~~
(Thread:3) is waiting ~~~
(Thread:4) is waiting ~~~
2
(Produce Thread:1) start
Please input produce number:
(Thread:4) Produce[00] need 1 seconds ...
(Thread:2) Produce[01] need 1 seconds ...
(Thread:3) is waiting ~~~
(Thread:4) is waiting ~~~
(Thread:2) is waiting ~~~
10
(Produce Thread:1) start
Please input produce number:
(Thread:2) Produce[00] need 2 seconds ...
(Thread:4) Produce[01] need 2 seconds ...
(Thread:3) Produce[02] need 1 seconds ...
(Thread:3) Produce[03] need 2 seconds ...
(Thread:2) Produce[04] need 4 seconds ...
(Thread:4) Produce[05] need 4 seconds ...
(Thread:3) Produce[06] need 4 seconds ...
(Thread:2) Produce[07] need 0 seconds ...
(Thread:2) Produce[08] need 4 seconds ...
(Thread:4) Produce[09] need 0 seconds ...
(Thread:4) is waiting ~~~
(Thread:3) is waiting ~~~
(Thread:2) is waiting ~~~
3
(Produce Thread:1) start
Please input produce number:
(Thread:4) Produce[00] need 4 seconds ...
(Thread:3) Produce[02] need 0 seconds ...
(Thread:3) is waiting ~~~
(Thread:2) Produce[01] need 4 seconds ...
(Thread:4) is waiting ~~~
(Thread:2) is waiting ~~~
^Z分解讲解
main()
int main() {// 设置随机数种子srand(time(0));// 采用对象成员函数的方式进行多线程ProducerConsumerProblem obj;std::vectorstd::thread thdVec;for (int i 0; i WORKERTHREAD_COUNT; i 1) {// 只能move放入vector延长对象的生存周期auto thd std::thread(ProducerConsumerProblem::consumer, obj);thdVec.push_back(std::move(thd));thdVec[i].detach();}// 通过手动输入生产物品int cnt;// 通过这里的输入阻塞程序while (printf(Please input produce number:\n), std::cin cnt) {obj.produce(cnt);}return 0;
}这里采用对象成员函数的形式创建线程因为成员函数的第一个参数是一个隐式的this因此写std::thread(ProducerConsumerProblem::consumer, obj);
注意std::thread只能move不能copy。
要将线程对象的生命周期延长因此移动到vector中。
为了让下文的code执行将线程进行分离detach()。
class ProducerConsumerProblem
class ProducerConsumerProblem {
private:// 任务队列std::queuestd::string m_queue;// mutexstd::mutex m_mutex;// condition_variablestd::condition_variable m_cv;public:/*** 生产者函数*/void produce(const int cnt) ;/*** 消费者函数*/void consumer() ;
};这里的核心数据结构就是std::condition_variable 通常配合std::unique_lock使用。
produce() void produce(const int cnt) {printf((Produce Thread:%lld) start\n, std::this_thread::get_id());// RAII 自动解锁std::lock_guardstd::mutex lock(m_mutex);char buff[1024] {};for (int i 0; i cnt; i 1) {sprintf(buff, Produce[%02d], i);m_queue.push(buff);}// 唤醒所有消费者m_cv.notify_all();// 唤醒任意一个消费者// m_cv.notify_one();}std::lock_guardstd::mutex可以做到最简单的构造时上锁析构时解锁。
notify_all()唤醒所有wait中的对象。
notify_one()唤醒一个wait中的对象。
consumer() void consumer() {printf((Consumer Thread:%lld) start\n, std::this_thread::get_id());constexpr int SLEEP_TIME 5;std::string receiveBuffer;while (1) {// 比lock_guard更细致的控制力度std::unique_lockstd::mutex lock(m_mutex);/// 最重要的部分while (m_queue.empty()) {// 等待生产者唤醒printf((Thread:%lld) is waiting ~~~\n,std::this_thread::get_id());m_cv.wait(lock);}// 此时任务队列有数据且cv被唤醒// 消费者处理一个任务receiveBuffer m_queue.front();m_queue.pop();// 当前消费者线程获得数据手动解锁lock.unlock();// 模拟随机设定一个消费时间int solveTimeCost (rand() % SLEEP_TIME);printf((Thread:%lld) %s need %d seconds ...\n,std::this_thread::get_id(), receiveBuffer.c_str(),solveTimeCost);std::this_thread::sleep_for(std::chrono::seconds(solveTimeCost));}}std::unique_lockstd::mutex居于更细致的操作力度可以手动上锁解锁。
m_cv.wait(lock);整个demo的核心
为什么是循环判断 条件变量虚假唤醒消费者线程被唤醒后缓存队列中没有数据重新进入wait 条件变量 wait(mutex)的作用 把互斥锁解开阻塞等待被唤醒给互斥锁加锁
在消费者在处理任务时可以让unique_lock主动解锁。 END
