172 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_any;14 15// template <class Lock, class Rep, class Period, class Predicate>16// bool17// wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time,18// Predicate pred);19 20#include <condition_variable>21#include <atomic>22#include <cassert>23#include <chrono>24#include <mutex>25#include <thread>26 27#include "make_test_thread.h"28#include "test_macros.h"29 30template <class Mutex>31struct MyLock : std::unique_lock<Mutex> {32 using std::unique_lock<Mutex>::unique_lock;33};34 35template <class Function>36std::chrono::microseconds measure(Function f) {37 std::chrono::high_resolution_clock::time_point start = std::chrono::high_resolution_clock::now();38 f();39 std::chrono::high_resolution_clock::time_point end = std::chrono::high_resolution_clock::now();40 return std::chrono::duration_cast<std::chrono::microseconds>(end - start);41}42 43template <class Lock>44void test() {45 using Mutex = typename Lock::mutex_type;46 // Test unblocking via a call to notify_one() in another thread.47 //48 // To test this, we set a very long timeout in wait_for() and we try to minimize49 // the likelihood that we got awoken by a spurious wakeup by updating the50 // likely_spurious flag only immediately before we perform the notification.51 {52 std::atomic<bool> ready(false);53 std::atomic<bool> likely_spurious(true);54 auto timeout = std::chrono::seconds(3600);55 std::condition_variable_any cv;56 Mutex mutex;57 58 std::thread t1 = support::make_test_thread([&] {59 Lock lock(mutex);60 auto elapsed = measure([&] {61 ready = true;62 bool result = cv.wait_for(lock, timeout, [&] { return !likely_spurious; });63 assert(result); // return value should be true since we didn't time out64 });65 assert(elapsed < timeout);66 });67 68 std::thread t2 = support::make_test_thread([&] {69 while (!ready) {70 // spin71 }72 73 // Acquire the same mutex as t1. This ensures that the condition variable has started74 // waiting (and hence released that mutex).75 Lock lock(mutex);76 77 likely_spurious = false;78 lock.unlock();79 cv.notify_one();80 });81 82 t2.join();83 t1.join();84 }85 86 // Test unblocking via a timeout.87 //88 // To test this, we create a thread that waits on a condition variable with a certain89 // timeout, and we never awaken it. The "stop waiting" predicate always returns false,90 // which means that we can't get out of the wait via a spurious wakeup.91 {92 auto timeout = std::chrono::milliseconds(250);93 std::condition_variable_any cv;94 Mutex mutex;95 96 std::thread t1 = support::make_test_thread([&] {97 Lock lock(mutex);98 auto elapsed = measure([&] {99 bool result = cv.wait_for(lock, timeout, [] { return false; }); // never stop waiting (until timeout)100 assert(!result); // return value should be false since the predicate returns false after the timeout101 });102 assert(elapsed >= timeout);103 });104 105 t1.join();106 }107 108 // Test unblocking via a spurious wakeup.109 //110 // To test this, we set a fairly long timeout in wait_for() and we basically never111 // wake up the condition variable. This way, we are hoping to get out of the wait112 // via a spurious wakeup.113 //114 // However, since spurious wakeups are not required to even happen, this test is115 // only trying to trigger that code path, but not actually asserting that it is116 // taken. In particular, we do need to eventually ensure we get out of the wait117 // by standard means, so we actually wake up the thread at the end.118 {119 std::atomic<bool> ready(false);120 std::atomic<bool> awoken(false);121 auto timeout = std::chrono::seconds(3600);122 std::condition_variable_any cv;123 Mutex mutex;124 125 std::thread t1 = support::make_test_thread([&] {126 Lock lock(mutex);127 auto elapsed = measure([&] {128 ready = true;129 bool result = cv.wait_for(lock, timeout, [&] { return true; });130 awoken = true;131 assert(result); // return value should be true since we didn't time out132 });133 assert(elapsed < timeout); // can technically fail if t2 never executes and we timeout, but very unlikely134 });135 136 std::thread t2 = support::make_test_thread([&] {137 while (!ready) {138 // spin139 }140 141 // Acquire the same mutex as t1. This ensures that the condition variable has started142 // waiting (and hence released that mutex).143 Lock lock(mutex);144 lock.unlock();145 146 // Give some time for t1 to be awoken spuriously so that code path is used.147 std::this_thread::sleep_for(std::chrono::seconds(1));148 149 // We would want to assert that the thread has been awoken after this time,150 // however nothing guarantees us that it ever gets spuriously awoken, so151 // we can't really check anything. This is still left here as documentation.152 bool woke = awoken.load();153 assert(woke || !woke);154 155 // Whatever happened, actually awaken the condition variable to ensure the test156 // doesn't keep running until the timeout.157 cv.notify_one();158 });159 160 t2.join();161 t1.join();162 }163}164 165int main(int, char**) {166 test<std::unique_lock<std::mutex>>();167 test<std::unique_lock<std::timed_mutex>>();168 test<MyLock<std::mutex>>();169 test<MyLock<std::timed_mutex>>();170 return 0;171}172