63 lines
2.2 KiB
C++
63 lines
2.2 KiB
C++
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/*##############################################################################
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## Author: Shaun Reed ##
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## Legal: All Content (c) 2022 Shaun Reed, all rights reserved ##
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## About: An example of condition_variables in multithreaded C++ ##
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## ##
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## Contact: shaunrd0@gmail.com | URL: www.shaunreed.com | GitHub: shaunrd0 ##
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################################################################################
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*/
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#include <chrono>
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#include <condition_variable>
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#include <iostream>
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#include <mutex>
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#include <thread>
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static std::mutex mtx;
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std::condition_variable cv;
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bool processing = false;
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// Starts a job that waits for kick-off from main
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// + When job finishes, handoff result back to main via processing bool
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void job(int32_t & shared) {
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std::unique_lock uniqueLock(mtx);
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cv.wait(uniqueLock, []()->bool {return processing;});
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std::cout << std::this_thread::get_id()
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<< " thread_A: Initial value of shared = " << shared << std::endl;
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while (shared < INT32_MAX) {
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shared++;
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}
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// We're no longer processing data
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processing = false;
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std::cout << std::this_thread::get_id()
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<< " thread_A: Done working." << std::endl;
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uniqueLock.unlock(); // Important! Unlock uniqueLock before we notify
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// Notify main that we've finished, so it can proceed
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cv.notify_one();
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}
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int main(const int argc, const char * argv[]) {
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std::cout << "main() thread id: " << std::this_thread::get_id() << std::endl;
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int32_t share = 0;
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std::thread thread_A(job, std::ref(share));
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mtx.lock();
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std::this_thread::sleep_for(std::chrono::seconds(3));
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share = INT32_MAX / 2;
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processing = true;
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mtx.unlock();
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// Notify thread_A that its work can begin
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cv.notify_one();
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// Wait until thread_A finishes its work
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std::unique_lock uniqueLock(mtx);
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// Block execution until we are not processing
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cv.wait(uniqueLock, []()->bool { return !processing;});
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std::cout << std::this_thread::get_id() << " main(): final value of shared = "
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<< share << std::endl;
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thread_A.join();
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return 0;
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}
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