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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: no-threads, c++03
// <condition_variable>
// class condition_variable;
// template <class Predicate>
// void wait(unique_lock<mutex>& lock, Predicate pred);
#include <condition_variable>
#include <atomic>
#include <cassert>
#include <mutex>
#include <thread>
#include "make_test_thread.h"
#include "test_macros.h"
int main(int, char**) {
// Test unblocking via a call to notify_one() in another thread.
//
// To test this, we try to minimize the likelihood that we got awoken by a
// spurious wakeup by updating the likely_spurious flag only immediately
// before we perform the notification.
{
std::atomic<bool> ready(false);
std::atomic<bool> likely_spurious(true);
std::condition_variable cv;
std::mutex mutex;
std::thread t1 = support::make_test_thread([&] {
std::unique_lock<std::mutex> lock(mutex);
ready = true;
cv.wait(lock, [&] { return !likely_spurious; });
});
std::thread t2 = support::make_test_thread([&] {
while (!ready) {
// spin
}
// Acquire the same mutex as t1. This ensures that the condition variable has started
// waiting (and hence released that mutex).
std::unique_lock<std::mutex> lock(mutex);
likely_spurious = false;
lock.unlock();
cv.notify_one();
});
t2.join();
t1.join();
}
// Test unblocking via a spurious wakeup.
//
// To test this, we basically never wake up the condition variable. This way, we
// are hoping to get out of the wait via a spurious wakeup.
//
// However, since spurious wakeups are not required to even happen, this test is
// only trying to trigger that code path, but not actually asserting that it is
// taken. In particular, we do need to eventually ensure we get out of the wait
// by standard means, so we actually wake up the thread at the end.
{
std::atomic<bool> ready(false);
std::atomic<bool> awoken(false);
std::condition_variable cv;
std::mutex mutex;
std::thread t1 = support::make_test_thread([&] {
std::unique_lock<std::mutex> lock(mutex);
ready = true;
cv.wait(lock, [&] { return true; });
awoken = true;
});
std::thread t2 = support::make_test_thread([&] {
while (!ready) {
// spin
}
// Acquire the same mutex as t1. This ensures that the condition variable has started
// waiting (and hence released that mutex).
std::unique_lock<std::mutex> lock(mutex);
lock.unlock();
// Give some time for t1 to be awoken spuriously so that code path is used.
std::this_thread::sleep_for(std::chrono::seconds(1));
// We would want to assert that the thread has been awoken after this time,
// however nothing guarantees us that it ever gets spuriously awoken, so
// we can't really check anything. This is still left here as documentation.
bool woke = awoken.load();
assert(woke || !woke);
// Whatever happened, actually awaken the condition variable to ensure the test finishes.
cv.notify_one();
});
t2.join();
t1.join();
}
return 0;
}
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