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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_any;
// template <class Lock, class Rep, class Period, class Predicate>
// bool
// wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time,
// Predicate pred);
#include <condition_variable>
#include <atomic>
#include <cassert>
#include <chrono>
#include <mutex>
#include <thread>
#include "make_test_thread.h"
#include "test_macros.h"
template <class Mutex>
struct MyLock : std::unique_lock<Mutex> {
using std::unique_lock<Mutex>::unique_lock;
};
template <class Function>
std::chrono::microseconds measure(Function f) {
std::chrono::high_resolution_clock::time_point start = std::chrono::high_resolution_clock::now();
f();
std::chrono::high_resolution_clock::time_point end = std::chrono::high_resolution_clock::now();
return std::chrono::duration_cast<std::chrono::microseconds>(end - start);
}
template <class Lock>
void test() {
using Mutex = typename Lock::mutex_type;
// Test unblocking via a call to notify_one() in another thread.
//
// To test this, we set a very long timeout in wait_for() and 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);
auto timeout = std::chrono::seconds(3600);
std::condition_variable_any cv;
Mutex mutex;
std::thread t1 = support::make_test_thread([&] {
Lock lock(mutex);
auto elapsed = measure([&] {
ready = true;
bool result = cv.wait_for(lock, timeout, [&] { return !likely_spurious; });
assert(result); // return value should be true since we didn't time out
});
assert(elapsed < timeout);
});
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).
Lock lock(mutex);
likely_spurious = false;
lock.unlock();
cv.notify_one();
});
t2.join();
t1.join();
}
// Test unblocking via a timeout.
//
// To test this, we create a thread that waits on a condition variable with a certain
// timeout, and we never awaken it. The "stop waiting" predicate always returns false,
// which means that we can't get out of the wait via a spurious wakeup.
{
auto timeout = std::chrono::milliseconds(250);
std::condition_variable_any cv;
Mutex mutex;
std::thread t1 = support::make_test_thread([&] {
Lock lock(mutex);
auto elapsed = measure([&] {
bool result = cv.wait_for(lock, timeout, [] { return false; }); // never stop waiting (until timeout)
assert(!result); // return value should be false since the predicate returns false after the timeout
});
assert(elapsed >= timeout);
});
t1.join();
}
// Test unblocking via a spurious wakeup.
//
// To test this, we set a fairly long timeout in wait_for() and 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);
auto timeout = std::chrono::seconds(3600);
std::condition_variable_any cv;
Mutex mutex;
std::thread t1 = support::make_test_thread([&] {
Lock lock(mutex);
auto elapsed = measure([&] {
ready = true;
bool result = cv.wait_for(lock, timeout, [&] { return true; });
awoken = true;
assert(result); // return value should be true since we didn't time out
});
assert(elapsed < timeout); // can technically fail if t2 never executes and we timeout, but very unlikely
});
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).
Lock 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
// doesn't keep running until the timeout.
cv.notify_one();
});
t2.join();
t1.join();
}
}
int main(int, char**) {
test<std::unique_lock<std::mutex>>();
test<std::unique_lock<std::timed_mutex>>();
test<MyLock<std::mutex>>();
test<MyLock<std::timed_mutex>>();
return 0;
}
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