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-exception
6//
7//===----------------------------------------------------------------------===//
8
9// UNSUPPORTED: no-threads
10// UNSUPPORTED: c++03, c++11
11
12// <shared_mutex>
13
14// class shared_timed_mutex;
15
16// template <class Clock, class Duration>
17// bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
18
19#include <shared_mutex>
20#include <atomic>
21#include <cassert>
22#include <chrono>
23#include <thread>
24
25#include "make_test_thread.h"
26
27template <class Function>
28std::chrono::microseconds measure(Function f) {
29 std::chrono::high_resolution_clock::time_point start = std::chrono::high_resolution_clock::now();
30 f();
31 std::chrono::high_resolution_clock::time_point end = std::chrono::high_resolution_clock::now();
32 return std::chrono::duration_cast<std::chrono::microseconds>(end - start);
33}
34
35int main(int, char**) {
36 // Try to lock a mutex that is not locked yet. This should succeed immediately.
37 {
38 std::shared_timed_mutex m;
39 bool succeeded = m.try_lock_until(atime: std::chrono::steady_clock::now() + std::chrono::milliseconds(1));
40 assert(succeeded);
41 m.unlock();
42 }
43
44 // Try to lock an already-locked mutex for a long enough amount of time and succeed.
45 // This is technically flaky, but we use such long durations that it should pass even
46 // in slow or contended environments.
47 {
48 std::chrono::milliseconds const wait_time(500);
49 std::chrono::milliseconds const tolerance = wait_time * 3;
50 std::atomic<bool> ready(false);
51
52 std::shared_timed_mutex m;
53 m.lock();
54
55 std::thread t = support::make_test_thread([&] {
56 auto elapsed = measure([&] {
57 ready = true;
58 bool succeeded = m.try_lock_until(std::chrono::steady_clock::now() + wait_time);
59 assert(succeeded);
60 m.unlock();
61 });
62
63 // Ensure we didn't wait significantly longer than our timeout. This is technically
64 // flaky and non-conforming because an implementation is free to block for arbitrarily
65 // long, but any decent quality implementation should pass this test.
66 assert(elapsed - wait_time < tolerance);
67 });
68
69 // Wait for the thread to be ready to take the lock before we unlock it from here, otherwise
70 // there's a high chance that we're not testing the "locking an already locked" mutex use case.
71 // There is still technically a race condition here.
72 while (!ready)
73 /* spin */;
74 std::this_thread::sleep_for(rtime: wait_time / 5);
75
76 m.unlock(); // this should allow the thread to lock 'm'
77 t.join();
78 }
79
80 // Try to lock an already-locked mutex for a short amount of time and fail.
81 // Again, this is technically flaky but we use such long durations that it should work.
82 {
83 std::chrono::milliseconds const wait_time(10);
84 std::chrono::milliseconds const tolerance(750); // in case the thread we spawned goes to sleep or something
85
86 std::shared_timed_mutex m;
87 m.lock();
88
89 std::thread t = support::make_test_thread([&] {
90 auto elapsed = measure([&] {
91 bool succeeded = m.try_lock_until(std::chrono::steady_clock::now() + wait_time);
92 assert(!succeeded);
93 });
94
95 // Ensure we failed within some bounded time.
96 assert(elapsed - wait_time < tolerance);
97 });
98
99 t.join();
100
101 m.unlock();
102 }
103
104 return 0;
105}
106

source code of libcxx/test/std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_until.pass.cpp