src/chrono.cpp

//===------------------------- chrono.cpp ---------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "chrono"
#include "cerrno"        // errno
#include "system_error"  // __throw_system_error
#include <time.h>        // clock_gettime, CLOCK_MONOTONIC and CLOCK_REALTIME
#include "include/apple_availability.h"

#if !defined(__APPLE__)
#define _LIBCPP_USE_CLOCK_GETTIME
#endif // __APPLE__

#if defined(_LIBCPP_WIN32API)
#define WIN32_LEAN_AND_MEAN
#define VC_EXTRA_LEAN
#include <windows.h>
#if _WIN32_WINNT >= _WIN32_WINNT_WIN8
#include <winapifamily.h>
#endif
#else
#if !defined(CLOCK_REALTIME) || !defined(_LIBCPP_USE_CLOCK_GETTIME)
#include <sys/time.h>        // for gettimeofday and timeval
#endif // !defined(CLOCK_REALTIME)
#endif // defined(_LIBCPP_WIN32API)

#if !defined(_LIBCPP_HAS_NO_MONOTONIC_CLOCK)
#if __APPLE__
#include <mach/mach_time.h>  // mach_absolute_time, mach_timebase_info_data_t
#elif !defined(_LIBCPP_WIN32API) && !defined(CLOCK_MONOTONIC)
#error "Monotonic clock not implemented"
#endif
#endif

#if defined(__unix__) &&  defined(__ELF__) && defined(_LIBCPP_HAS_COMMENT_LIB_PRAGMA)
#pragma comment(lib, "rt")
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

namespace chrono
{

// system_clock

const bool system_clock::is_steady;

system_clock::time_point
system_clock::now() _NOEXCEPT
{
#if defined(_LIBCPP_WIN32API)
  // FILETIME is in 100ns units
  using filetime_duration =
      _VSTD::chrono::duration<__int64,
                              _VSTD::ratio_multiply<_VSTD::ratio<100, 1>,
                                                    nanoseconds::period>>;

  // The Windows epoch is Jan 1 1601, the Unix epoch Jan 1 1970.
  static _LIBCPP_CONSTEXPR const seconds nt_to_unix_epoch{11644473600};

  FILETIME ft;
#if _WIN32_WINNT >= _WIN32_WINNT_WIN8
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
  GetSystemTimePreciseAsFileTime(&ft);
#else
  GetSystemTimeAsFileTime(&ft);
#endif
#else
  GetSystemTimeAsFileTime(&ft);
#endif

  filetime_duration d{(static_cast<__int64>(ft.dwHighDateTime) << 32) |
                       static_cast<__int64>(ft.dwLowDateTime)};
  return time_point(duration_cast<duration>(d - nt_to_unix_epoch));
#else
#if defined(_LIBCPP_USE_CLOCK_GETTIME) && defined(CLOCK_REALTIME)
  struct timespec tp;
  if (0 != clock_gettime(CLOCK_REALTIME, &tp))
    __throw_system_error(errno, "clock_gettime(CLOCK_REALTIME) failed");
  return time_point(seconds(tp.tv_sec) + microseconds(tp.tv_nsec / 1000));
#else
    timeval tv;
    gettimeofday(&tv, 0);
    return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
#endif // _LIBCPP_USE_CLOCK_GETTIME && CLOCK_REALTIME
#endif
}

time_t
system_clock::to_time_t(const time_point& t) _NOEXCEPT
{
    return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
}

system_clock::time_point
system_clock::from_time_t(time_t t) _NOEXCEPT
{
    return system_clock::time_point(seconds(t));
}

#ifndef _LIBCPP_HAS_NO_MONOTONIC_CLOCK
// steady_clock
//
// Warning:  If this is not truly steady, then it is non-conforming.  It is
//  better for it to not exist and have the rest of libc++ use system_clock
//  instead.

const bool steady_clock::is_steady;

#if defined(__APPLE__)

// Darwin libc versions >= 1133 provide ns precision via CLOCK_UPTIME_RAW
#if defined(_LIBCPP_USE_CLOCK_GETTIME) && defined(CLOCK_UPTIME_RAW)
steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
    struct timespec tp;
    if (0 != clock_gettime(CLOCK_UPTIME_RAW, &tp))
        __throw_system_error(errno, "clock_gettime(CLOCK_UPTIME_RAW) failed");
    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
}

#else
//   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
//   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
//   are run time constants supplied by the OS.  This clock has no relationship
//   to the Gregorian calendar.  It's main use is as a high resolution timer.

// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
//   for that case as an optimization.

static
steady_clock::rep
steady_simplified()
{
    return static_cast<steady_clock::rep>(mach_absolute_time());
}

static
double
compute_steady_factor()
{
    mach_timebase_info_data_t MachInfo;
    mach_timebase_info(&MachInfo);
    return static_cast<double>(MachInfo.numer) / MachInfo.denom;
}

static
steady_clock::rep
steady_full()
{
    static const double factor = compute_steady_factor();
    return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
}

typedef steady_clock::rep (*FP)();

static
FP
init_steady_clock()
{
    mach_timebase_info_data_t MachInfo;
    mach_timebase_info(&MachInfo);
    if (MachInfo.numer == MachInfo.denom)
        return &steady_simplified;
    return &steady_full;
}

steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
    static FP fp = init_steady_clock();
    return time_point(duration(fp()));
}
#endif // defined(_LIBCPP_USE_CLOCK_GETTIME) && defined(CLOCK_UPTIME_RAW)

#elif defined(_LIBCPP_WIN32API)

// https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx says:
//    If the function fails, the return value is zero. <snip>
//    On systems that run Windows XP or later, the function will always succeed 
//      and will thus never return zero.

static LARGE_INTEGER
__QueryPerformanceFrequency()
{
	LARGE_INTEGER val;
	(void) QueryPerformanceFrequency(&val);
	return val;
}

steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
  static const LARGE_INTEGER freq = __QueryPerformanceFrequency();

  LARGE_INTEGER counter;
  (void) QueryPerformanceCounter(&counter);
  return time_point(duration(counter.QuadPart * nano::den / freq.QuadPart));
}

#elif defined(CLOCK_MONOTONIC)

// On Apple platforms only CLOCK_UPTIME_RAW or mach_absolute_time are able to
// time functions in the nanosecond range. Thus, they are the only acceptable
// implementations of steady_clock.
#ifdef __APPLE__
#error "Never use CLOCK_MONOTONIC for steady_clock::now on Apple platforms"
#endif

steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
    struct timespec tp;
    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
        __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
}

#else
#error "Monotonic clock not implemented"
#endif

#endif // !_LIBCPP_HAS_NO_MONOTONIC_CLOCK

}

_LIBCPP_END_NAMESPACE_STD