160 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// UNSUPPORTED: no-threads, c++0310 11// <condition_variable>12 13// class condition_variable;14 15// template <class Rep, class Period, class Predicate>16// bool17// wait_for(unique_lock<mutex>& lock,18// const chrono::duration<Rep, Period>& rel_time,19// Predicate pred);20 21#include <condition_variable>22#include <atomic>23#include <cassert>24#include <chrono>25#include <mutex>26#include <thread>27 28#include "make_test_thread.h"29#include "test_macros.h"30 31template <class Function>32std::chrono::microseconds measure(Function f) {33 std::chrono::high_resolution_clock::time_point start = std::chrono::high_resolution_clock::now();34 f();35 std::chrono::high_resolution_clock::time_point end = std::chrono::high_resolution_clock::now();36 return std::chrono::duration_cast<std::chrono::microseconds>(end - start);37}38 39int main(int, char**) {40 // Test unblocking via a call to notify_one() in another thread.41 //42 // To test this, we set a very long timeout in wait_for() and we try to minimize43 // the likelihood that we got awoken by a spurious wakeup by updating the44 // likely_spurious flag only immediately before we perform the notification.45 {46 std::atomic<bool> ready(false);47 std::atomic<bool> likely_spurious(true);48 auto timeout = std::chrono::seconds(3600);49 std::condition_variable cv;50 std::mutex mutex;51 52 std::thread t1 = support::make_test_thread([&] {53 std::unique_lock<std::mutex> lock(mutex);54 auto elapsed = measure([&] {55 ready = true;56 bool result = cv.wait_for(lock, timeout, [&] { return !likely_spurious; });57 assert(result); // return value should be true since we didn't time out58 });59 assert(elapsed < timeout);60 });61 62 std::thread t2 = support::make_test_thread([&] {63 while (!ready) {64 // spin65 }66 67 // Acquire the same mutex as t1. This ensures that the condition variable has started68 // waiting (and hence released that mutex).69 std::unique_lock<std::mutex> lock(mutex);70 71 likely_spurious = false;72 lock.unlock();73 cv.notify_one();74 });75 76 t2.join();77 t1.join();78 }79 80 // Test unblocking via a timeout.81 //82 // To test this, we create a thread that waits on a condition variable with a certain83 // timeout, and we never awaken it. The "stop waiting" predicate always returns false,84 // which means that we can't get out of the wait via a spurious wakeup.85 {86 auto timeout = std::chrono::milliseconds(250);87 std::condition_variable cv;88 std::mutex mutex;89 90 std::thread t1 = support::make_test_thread([&] {91 std::unique_lock<std::mutex> lock(mutex);92 auto elapsed = measure([&] {93 bool result = cv.wait_for(lock, timeout, [] { return false; }); // never stop waiting (until timeout)94 assert(!result); // return value should be false since the predicate returns false after the timeout95 });96 assert(elapsed >= timeout);97 });98 99 t1.join();100 }101 102 // Test unblocking via a spurious wakeup.103 //104 // To test this, we set a fairly long timeout in wait_for() and we basically never105 // wake up the condition variable. This way, we are hoping to get out of the wait106 // via a spurious wakeup.107 //108 // However, since spurious wakeups are not required to even happen, this test is109 // only trying to trigger that code path, but not actually asserting that it is110 // taken. In particular, we do need to eventually ensure we get out of the wait111 // by standard means, so we actually wake up the thread at the end.112 {113 std::atomic<bool> ready(false);114 std::atomic<bool> awoken(false);115 auto timeout = std::chrono::seconds(3600);116 std::condition_variable cv;117 std::mutex mutex;118 119 std::thread t1 = support::make_test_thread([&] {120 std::unique_lock<std::mutex> lock(mutex);121 auto elapsed = measure([&] {122 ready = true;123 bool result = cv.wait_for(lock, timeout, [&] { return true; });124 awoken = true;125 assert(result); // return value should be true since we didn't time out126 });127 assert(elapsed < timeout); // can technically fail if t2 never executes and we timeout, but very unlikely128 });129 130 std::thread t2 = support::make_test_thread([&] {131 while (!ready) {132 // spin133 }134 135 // Acquire the same mutex as t1. This ensures that the condition variable has started136 // waiting (and hence released that mutex).137 std::unique_lock<std::mutex> lock(mutex);138 lock.unlock();139 140 // Give some time for t1 to be awoken spuriously so that code path is used.141 std::this_thread::sleep_for(std::chrono::seconds(1));142 143 // We would want to assert that the thread has been awoken after this time,144 // however nothing guarantees us that it ever gets spuriously awoken, so145 // we can't really check anything. This is still left here as documentation.146 bool woke = awoken.load();147 assert(woke || !woke);148 149 // Whatever happened, actually awaken the condition variable to ensure the test150 // doesn't keep running until the timeout.151 cv.notify_one();152 });153 154 t2.join();155 t1.join();156 }157 158 return 0;159}160