74 lines
2.7 KiB
C++
74 lines
2.7 KiB
C++
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// Fig. 17.14: LatchDemo.cpp
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// Coordinate threads with a std::latch object.
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#include <chrono>
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#include <fmt/format.h>
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#include <iostream>
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#include <latch>
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#include <random>
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#include <string_view>
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#include <thread>
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#include <vector>
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int main() {
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// set up random-number generation
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std::random_device rd;
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std::default_random_engine engine{rd()};
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std::uniform_int_distribution ints{2000, 3000};
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// latch that 3 threads must signal before the main thread continues
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std::latch mainLatch{3};
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// lambda representing the task to execute
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auto task{
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[&](std::string_view name, std::chrono::milliseconds workTime) {
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std::cout << fmt::format("Proceeding with {} work for {} ms.\n",
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name, workTime.count());
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// simulate work by sleeping
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std::this_thread::sleep_for(workTime);
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// show that task arrived at mainLatch
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std::cout << fmt::format("{} done; signals mainLatch.\n", name);
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mainLatch.count_down();
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}
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};
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std::vector<std::jthread> threads; // stores the threads
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std::cout << "Main starting three jthreads.\n";
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// start three jthreads
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for (int i{1}; i < 4; ++i) {
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// create jthread that calls task lambda,
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// passing a task name and work time
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threads.push_back(std::jthread{task,
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fmt::format("Task {}", i),
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std::chrono::milliseconds{ints(engine)}});
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}
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std::cout << "\nMain waiting for jthreads to reach the latch.\n\n";
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mainLatch.wait();
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std::cout << "\nAll jthreads reached the latch. Main working.\n";
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std::cout << "Showing that mainLatch is permanently open.\n";
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mainLatch.wait(); // latch is already open
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std::cout << "mainLatch is already open. Main continues.\n";
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}
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/************************************************************************
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* (C) Copyright 1992-2022 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The *
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* authors and publisher shall not be liable in any event for *
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* incidental or consequential damages in connection with, or arising *
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* out of, the furnishing, performance, or use of these programs. *
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***********************************************************************/
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