c++多线程小练习

#include <iostream> #include <thread> using namespace std; void func(string &s) { cout<<"hello,this is my thread,thread id is" <<this_thread::get_id()<<endl; } int main() { string s = "test"; thread th = thread(func,std::ref(s)); //以引用的方式传递参数 //th.detach(); //将线程剥离出主线程，失去对其控制 th.join(); cout<<"this is main thread"<<endl; } /********************************************************/ //function object struct A{ void operator() (){ cout<<"I'm A"<<endl; } } int main() { thread th = thread(A()); th.join(); } /******************************************************/ //lambda在多线程中的使用 //c++ lambda表达式详解：https://www.cnblogs.com/jimodetiantang/p/9016826.html int main() { string s = "test"; //[]为外部变量参数列表，()为参数列表 auto f = [&s](int a,int b){ cout<<s<<endl; cout<< a+b<<endl; }; //多线程的方式 thread f1 = thread([&s](int a,int b){ cout<<z<<" "<<a+b<<endl; },2,3); f1.join(); f(1,2); } /******************************************************/ //多线程时间效率的测量 //C++类模板 template <class T>：https://www.cnblogs.com/msymm/p/9750787.html template<class T> void measure(T&& func) { using namespace std::chrono; auto start = sysytem_clock::now(); func(); duration<double> diff_ = sysytem_clock::now() - start; cout<<diff_.count()<<"seconds"<<endl; } int main() { measure([](){ long long s =0; for(int i = 0; i<1000;i++) s+=i; cout<<s<<endl; }); } /********************************************************/ //多线程加速小测验 template <class T> void measure(T&& func) { using namespace std::chrono; auto start = system_clock::now(); func(); duration<double> diff = sysytem_clock::now() - start; cout<<"cost:"<<diff.count()<<" seconds"<<endl; } void sum(long start,long end,long& ans) { long s = 0; for(long i = start; i<end;i++) { s+=i; } ans = s; } long s = 1000000000; int main() { measure([](){ long ans1,ans2; thread t1 = thread(sum,0,s/2,std::ref(ans1)); thread t2 = thread(sum,s/2,s,std::ref(ans2)); t1.join(); t2.join(); cout<<ans1+ans2<<endl; }); measure([](){ long ans; sum(0,s,ans); cout<<ans<<endl; }); } /****************************************************/ //使用异步接口std::async和std::feature实现多线程 //参考博客：https://www.cnblogs.com/qicosmos/p/3534211.html #include <feature> template <class T> void measure(T&& func) { using namespace std::chrono; auto start = system_clock::now(); func(); duration<double> diff = sysytem_clock::now() - start; cout<<"cost:"<<diff.count()<<" seconds"<<endl; } long sum(long start,long end) { long s = 0; for(long i = start; i<end;i++) { s+=i; } return s; } const long s = 1000000; int main() { measure([](){ const int k =4; vector<future<long>> vf; vf.reverse(k); for(int i = 0; i<k;i++) { vf.push_back(std::async(sum, i == 0 ? 0 : (s/k)*i,(s/k)*(i+1))) } long ans=0; for(int i =0;i<k;i++) ans+=vf[i].get(); cout<<ans<<endl; }); } /***************************************************/ //c++中的互斥锁 std::mutex mtx; void sum(int &s) { mtx.lock(); for(long i = 0; i<1000;i++) { s++; } mtx.unlock(); } const long s = 1000000; int main() { measure([](){ const int k =4; int s{0}; vector<thread> vf; for(int i = 0; i<k;i++) { vf.emplace_back(sum, std::ref(s)); } for(int j =0;j<4;j++) { vf[j].join(); } cout<<s<<endl; }); }