libcxx/test/std/thread/thread.condition/thread.condition.condvarany/wait_for.pass.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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // UNSUPPORTED: no-threads, c++03
  10
  11 // <condition_variable>
  12
  13 // class condition_variable_any;
  14
  15 // template <class Lock, class Rep, class Period>
  16 //   cv_status
  17 //   wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);
  18
  19 #include <condition_variable>
  20 #include <atomic>
  21 #include <cassert>
  22 #include <chrono>
  23 #include <mutex>
  24 #include <thread>
  25
  26 #include "make_test_thread.h"
  27 #include "test_macros.h"
  28
  29 template <class Mutex>
  30 struct MyLock : std::unique_lock<Mutex> {
  31   using std::unique_lock<Mutex>::unique_lock;
  32 };
  33
  34 template <class Function>
  35 std::chrono::microseconds measure(Function f) {
  36   std::chrono::high_resolution_clock::time_point start = std::chrono::high_resolution_clock::now();
  37   f();
  38   std::chrono::high_resolution_clock::time_point end = std::chrono::high_resolution_clock::now();
  39   return std::chrono::duration_cast<std::chrono::microseconds>(end - start);
  40 }
  41
  42 template <class Lock>
  43 void test() {
  44   using Mutex = typename Lock::mutex_type;
  45   // Test unblocking via a call to notify_one() in another thread.
  46   //
  47   // To test this, we set a very long timeout in wait_for() and we wait
  48   // again in case we get awoken spuriously. Note that it can actually
  49   // happen that we get awoken spuriously and fail to recognize it
  50   // (making this test useless), but the likelihood should be small.
  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         do {
  63           std::cv_status result = cv.wait_for(lock, timeout);
  64           assert(result == std::cv_status::no_timeout);
  65         } while (likely_spurious);
  66       });
  67
  68       // This can technically fail if we have many spurious awakenings, but in practice the
  69       // tolerance is so high that it shouldn't be a problem.
  70       assert(elapsed < timeout);
  71     });
  72
  73     std::thread t2 = support::make_test_thread([&] {
  74       while (!ready) {
  75         // spin
  76       }
  77
  78       // Acquire the same mutex as t1. This blocks the condition variable inside its wait call
  79       // so we can notify it while it is waiting.
  80       Lock lock(mutex);
  81       cv.notify_one();
  82       likely_spurious = false;
  83       lock.unlock();
  84     });
  85
  86     t2.join();
  87     t1.join();
  88   }
  89
  90   // Test unblocking via a timeout.
  91   //
  92   // To test this, we create a thread that waits on a condition variable
  93   // with a certain timeout, and we never awaken it. To guard against
  94   // spurious wakeups, we wait again whenever we are awoken for a reason
  95   // other than a timeout.
  96   {
  97     auto timeout = std::chrono::milliseconds(250);
  98     std::condition_variable_any cv;
  99     Mutex mutex;
 100
 101     std::thread t1 = support::make_test_thread([&] {
 102       Lock lock(mutex);
 103       std::cv_status result;
 104       do {
 105         auto elapsed = measure([&] { result = cv.wait_for(lock, timeout); });
 106         if (result == std::cv_status::timeout)
 107           assert(elapsed >= timeout);
 108       } while (result != std::cv_status::timeout);
 109     });
 110
 111     t1.join();
 112   }
 113 }
 114
 115 int main(int, char**) {
 116   test<std::unique_lock<std::mutex>>();
 117   test<std::unique_lock<std::timed_mutex>>();
 118   test<MyLock<std::mutex>>();
 119   test<MyLock<std::timed_mutex>>();
 120   return 0;
 121 }