c++ 多线程编程demo

最佳实践：（摘录《c++高级编程 27.13 线程设计和最佳实践》）

使用并行标准库算法
终止应用程序前，确保所有thread对象都不是可joinable的
最好的同步就是没有同步（各线程只读取共享数据，不写入）
尝试使用单线程的所有权模式（一个线程拥有数据的独有权，处理完再传递给另一个线程）
在可能时使用原子类型和操作
使用锁保护可变的共享数据
尽快释放锁
不要手动获取多个锁，应该使用std::lock或std::try_lock(获取多个锁顺序要一致)
使用多线程的分析器
使用RAII锁对象（lock_guard、unique_loce、shared_lock、scoped_lock）
了解调试器的对线程支持特性
使用线程池，不动态创建和销毁大量线程
使用高级线程库（TBB、PPL）

I/O多路复用
https://zhuanlan.zhihu.com/p/115220699

几个多线程常用demo代码：

#include <atomic>
#include <latch>
#include <barrier>
#include <semaphore>
#include <future>
#include <iostream>
#include <thread>
#include <chrono>using namespace std::chrono_literals;void counter(int id, int numIterations)
{for (int i{ 0 }; i < numIterations; i++) {std::cout << "Counter " << id << " has value " << i << std::endl;}
}void increment(std::atomic<int>& counter)
{for (int i{ 0 }; i < 100; i++) {++counter;std::this_thread::sleep_for(std::chrono::microseconds(1));}
}void increment_ref(int& counter)
{std::atomic_ref<int> atomicCounter{ counter };for (int i{ 0 }; i < 100; i++) {++atomicCounter;std::this_thread::sleep_for(std::chrono::microseconds(1));}
}class Counter
{
public:Counter(int id, int numIterations) :m_id{ id }, m_numIterations{ numIterations } {}void operator()() const noexcept{for (int i{ 0 }; i < m_numIterations; ++i) {std::lock_guard lock{ ms_mutex };std::cout << "Counter " << m_id << " has value " << i << std::endl;}}void process() {for (int i{ 0 }; i < m_numIterations; ++i) {std::unique_lock lock{ ms_timed_mutex ,200ms };if (lock) {std::cout << "Counter " << m_id << " has value " << i << std::endl;}}}private:int m_id;int m_numIterations;inline static std::mutex ms_mutex;inline static std::timed_mutex ms_timed_mutex;
};int k;
thread_local int n;void counter_k(int id)
{std::cout << std::format("Thread {}:k={},n={}\n ",id, k,n);++k;++n;std::cout << std::format("Thread {}:k={},n={}\n ", id, k, n);
}void doSomeWork()
{throw std::runtime_error{" Exception from thread"};
}void threadFunc(std::exception_ptr& err)
{try {doSomeWork();}catch (...) {err = std::current_exception();}
}void doWorkInThread()
{std::exception_ptr error;std::thread te{ threadFunc,std::ref(error) };te.join();if (error) {std::rethrow_exception(error);}
}int main()
{std::cout.sync_with_stdio(false);std::thread t1{ counter, 1, 6 };std::thread t2{ counter, 2, 4 };t1.join();t2.join();std::thread t3{ Counter{3, 10} };t3.join();Counter c{ 4, 5 };std::thread t4{ std::ref(c) };t4.join();int id{ 5 };int numIterations{ 6 };std::thread t5{ [id, numIterations]() {for (int i{ 0 }; i < numIterations; ++i) {std::cout << "Counter " << id << " has value " << i << std::endl;}} };t5.join();Counter c1{ 6, 5 };std::thread t6{ &Counter::process,&c1 };t6.join();std::thread t11{ counter_k ,1};t11.join();std::thread t12{ counter_k ,2};t12.join();// jthread c++20 ,destory finish joinstd::jthread job{ [](std::stop_token token) {while (!token.stop_requested()) {std::cout << "running\n";Sleep(100);}}};Sleep(1000);job.request_stop();std::cout << "stop running\n";// catch error from threadtry {doWorkInThread();}catch (const std::exception& e) {std::cout << "Main thread caught:" << e.what()<< std::endl;}// atomicstd::atomic<int> counter{ 0 };int con{0};std::vector<std::thread> threads;for (int i{ 0 }; i < 10; ++i) {threads.push_back(std::thread{ increment,std::ref(counter) });threads.push_back(std::thread{ increment_ref,std::ref(con) });}for (auto& t : threads) {t.join();}std::cout << "Result:" << counter << std::endl;std::cout << "Result:" << con << std::endl;std::atomic<int> value{0};std::thread job1{ [&value]() {std::cout << "wait value:" << value << std::endl;value.wait(value);std::cout << "value:" << value << std::endl;} };std::this_thread::sleep_for(std::chrono::seconds(2));value = 1;value.notify_all();job1.join();// 同步控制 latchstd::latch startlatch{10};std::vector<std::jthread> threads_;for (int i{ 0 }; i < 10;i++) {threads_.push_back(std::jthread{ [&startlatch, id = i]() {std::this_thread::sleep_for(20ms);std::cout << "latch:" << id << std::endl;startlatch.count_down();startlatch.wait();std::cout << "latch:finish" << id << std::endl;}});}startlatch.wait();std::cout << "latch:finish";threads_.clear();// 同步控制 latchconst auto workers = { "anil", "busara", "carl" };auto on_completion = []() noexcept {static const char* phase = "... done\n" \"Cleaning up...\n";std::cout << phase;phase = "... done\n";};std::barrier sync_point(workers.size(),on_completion);auto work = [&](const std::string& name) {std::string product = "  " + name + " worked\n";std::cout << product; // ok, op<< call is atomicsync_point.arrive_and_wait();product = "  " + name + " cleaned\n";std::cout << product;sync_point.arrive_and_wait();};std::cout << "Starting...\n";for (auto const& worker : workers) {threads_.push_back(std::jthread{ work,worker });}// semaphorethreads_.clear();std::counting_semaphore sp{4};for (int i{ 0 }; i < 20; i++) {threads_.push_back(std::jthread{ [&sp,id = i]() {sp.acquire();std::cout << "thread..."<< id << "\n";std::this_thread::sleep_for(100ms);sp.release();}});}// future and promisestd::promise<int> m_;std::future<int> theFuture{m_.get_future()};std::thread t{ [](std::promise<int> p) { p.set_value(12); }, std::move(m_) };auto va = theFuture.get();std::cout << "the future value:" << va << std::endl;t.join();// 条件变量std::mutex m_mu;std::unique_lock<std::mutex> lock(m_mu);std::condition_variable con_var;std::atomic<int> ca{0};std::async(std::launch::async, [&ca]() {std::cout << "thread the value in: \n";std::this_thread::sleep_for(3s);std::cout << "change the value end: \n";ca = 5;});std::cout << "wait the value: \n";con_var.wait(lock, [&ca]() { return (ca > 0); });std::cout << "wait the value finish:" << ca << std::endl;// packaged_taskstd::packaged_task task{ []() { return 12; } };std::future fur{ task.get_future() };std::thread tt{std::move(task)};auto re = fur.get();std::cout << "wait the task value:" << re << std::endl;tt.join();// shared_futurestd::promise<void> tP1, tP2;std::promise<int> signalP;std::shared_future<int> sf{ signalP.get_future().share() };auto fun1 = [&tP1, sf]() {tP1.set_value();auto p{sf.get()};std::cout << "thread1 get value:" << p << std::endl;};auto fun2 = [&tP2, sf]() {tP2.set_value();auto p{ sf.get() };std::cout << "thread1 get value:" << p << std::endl;};auto res2{ std::async(std::launch::async,fun2) };tP1.get_future().wait();tP2.get_future().wait();signalP.set_value(22);return 1;
}

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