CS106L笔记：Multi-threading

Multi-threading

Thread

• threads are ways to parallelise execution

what’s the problem?

• DATA RACE!

• use LOCK!

//std::mutex mtx;
void greet(int id){
    //std::lock_guard<std::mutex> lg(mtx);
    cout<<"my name is "<<id<<endl;
}
int main(){
    cout<<"Greetings from my threads..."<<endl;
    std::thread thread1(greet,id1);
    std::thread thread2(greet,id2);
    thread1.join();
    thread2.join();
    cout<<"All greetings done!"<<endl;
    return 0;
}

• Data Racing is unpredictable!

use lock_guard to ensure the greeting is atomic:

std::mutex mtx;
void greet(int id){
    std::lock_guard<std::mutex> lg(mtx);
    cout<<"my name is "<<id<<endl;
}

use join to let the main wait the thread to finish

thread1.join();
thread2.join();

• the results seems fine!

//...work with vector if threads
vector<std::thread> threads;

for(size_t i=0; i < kNumThreads; ++i){
    threads.push_back(std::thread(greet,i));
}

for(std::thread& t: threads){
    t.join();
}
//...