text: //===----------------------------------------------------------------------===//
  //
  // 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: libcpp-has-no-threads
  
  // ALLOW_RETRIES: 2
  
  // This test uses the POSIX header <sys/time.h> which Windows doesn't provide
  // UNSUPPORTED: windows
  
  // This test depends on signal behaviour until r210210, so some system libs
  // don't pass.
  //
  // XFAIL: with_system_cxx_lib=macosx10.11
  // XFAIL: with_system_cxx_lib=macosx10.10
  // XFAIL: with_system_cxx_lib=macosx10.9
  
  // <thread>
  
  // template <class Rep, class Period>
  //   void sleep_for(const chrono::duration<Rep, Period>& rel_time);
  
  #include <thread>
  #include <cstdlib>
  #include <cassert>
  #include <cstring>
  #include <signal.h>
  #include <sys/time.h>
  
  #include "test_macros.h"
  
  void sig_action(int) {}
  
  int main(int, char**)
  {
      int ec;
      struct sigaction action;
      action.sa_handler = &sig_action;
      sigemptyset(&action.sa_mask);
      action.sa_flags = 0;
  
      ec = sigaction(SIGALRM, &action, nullptr);
      assert(!ec);
  
      struct itimerval it;
      std::memset(&it, 0, sizeof(itimerval));
      it.it_value.tv_sec = 0;
      it.it_value.tv_usec = 250000;
      // This will result in a SIGALRM getting fired resulting in the nanosleep
      // inside sleep_for getting EINTR.
      ec = setitimer(ITIMER_REAL, &it, nullptr);
      assert(!ec);
  
      typedef std::chrono::system_clock Clock;
      typedef Clock::time_point time_point;
      std::chrono::milliseconds ms(500);
      time_point t0 = Clock::now();
      std::this_thread::sleep_for(ms);
      time_point t1 = Clock::now();
      std::chrono::nanoseconds ns = (t1 - t0) - ms;
      std::chrono::nanoseconds err = 5 * ms / 100;
      // The time slept is within 5% of 500ms
      assert(std::abs(ns.count()) < err.count());
  
    return 0;
  }
  