Eric 的小站

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#include <condition_variable>
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#include <iostream>
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#include <mutex>
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#include <string>
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#include <thread>
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std::mutex m;
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std::condition_variable cv;
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std::string data;
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bool ready = false;
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bool processed = false;
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void worker_thread()
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{
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    // wait until main() sends data
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    std::unique_lock lk(m);
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    cv.wait(lk, []{ return ready; });
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    // after the wait, we own the lock
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    std::cout << "Worker thread is processing data\n";
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    data += " after processing";
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    // send data back to main()
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    processed = true;
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    std::cout << "Worker thread signals data processing completed\n";
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    // manual unlocking is done before notifying, to avoid waking up
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    // the waiting thread only to block again (see notify_one for details)
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    lk.unlock();
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    cv.notify_one();
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}
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int main()
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{
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    std::thread worker(worker_thread);
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    data = "Example data";
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    // send data to the worker thread
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    {
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        std::lock_guard lk(m);
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        ready = true;
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        std::cout << "main() signals data ready for processing\n";
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    }
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    cv.notify_one();
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    // wait for the worker
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    {
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        std::unique_lock lk(m);
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        cv.wait(lk, []{ return processed; });
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    }
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    std::cout << "Back in main(), data = " << data << '\n';
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    worker.join();
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}

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main() signals data ready for processing
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Worker thread is processing data
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Worker thread signals data processing completed
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Back in main(), data = Example data after processing