klips/cpp/multithreading/conditions/driver.cpp

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