CODEWITHSUNDEEP
c++c++11
kreaon
kreaon

Reputation: 53

How to make shared_ptrs work with different threads?

lets say i have this code in main:

std::shared_ptr<std::string> command = std::make_shared<std::string>();
std::atomic<bool> done(true);
std::thread videoShow;

while (1) {
        std::getline(cin, *command);
        std::cout << *command;
        if ((*command).find("video") != std::string::npos) {
            if ((*command).find("start") != std::string::npos && done) {

                videoShow = std::thread(Video::showFrames, command, std::ref(done));
            }
        }
}

and this code in the function Video::showFrames:

void showFrames(std::shared_ptr<std::string> command, std::atomic<bool>& isDone){
     isDone = false;
     while (1) {
        std::cout << "this is command" << *command;
}
}

why if i write the command "video start" the output is:

this is command video start (first call to std::cout in main)
this is command
this is command ...

why is the call to *command in the 4th line of the function showFrames not working?

Upvotes: 0

Views: 120

Answers (1)

Joseph Larson
Joseph Larson

Reputation: 9058

This is kind of scary code to me. Your main is sitting their loading strings. Your worker thread is doing a fast-loop.

But the thread start up takes time. So let's say line 2 of your file has your video start string in it. Great. You spawn a thread. And then you immediately go do a fresh getline, trashing the old string you just read, before the thread has a chance to use it.

I'm not sure what you're really trying to do, but I see no reason to use the shared pointer. Just pass the string by value (let it get copied) and be done with it, it seems to me.

Upvotes: 1

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