133 lines
3.3 KiB
C++
133 lines
3.3 KiB
C++
//===------------------------- chrono.cpp ---------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "chrono"
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#include <sys/time.h> //for gettimeofday and timeval
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#ifdef __APPLE__
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#include <mach/mach_time.h> // mach_absolute_time, mach_timebase_info_data_t
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#else /* !__APPLE__ */
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#include <cerrno> // errno
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#include <system_error> // __throw_system_error
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#include <time.h> // clock_gettime, CLOCK_MONOTONIC
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#endif // __APPLE__
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_LIBCPP_BEGIN_NAMESPACE_STD
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namespace chrono
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{
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// system_clock
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const bool system_clock::is_steady;
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system_clock::time_point
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system_clock::now() _NOEXCEPT
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{
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timeval tv;
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gettimeofday(&tv, 0);
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return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
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}
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time_t
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system_clock::to_time_t(const time_point& t) _NOEXCEPT
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{
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return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
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}
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system_clock::time_point
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system_clock::from_time_t(time_t t) _NOEXCEPT
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{
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return system_clock::time_point(seconds(t));
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}
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// steady_clock
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const bool steady_clock::is_steady;
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#ifdef __APPLE__
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// mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
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// nanoseconds since the computer booted up. MachInfo.numer and MachInfo.denom
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// are run time constants supplied by the OS. This clock has no relationship
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// to the Gregorian calendar. It's main use is as a high resolution timer.
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// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment. Specialize
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// for that case as an optimization.
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#pragma GCC visibility push(hidden)
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static
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steady_clock::rep
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steady_simplified()
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{
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return static_cast<steady_clock::rep>(mach_absolute_time());
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}
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static
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double
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compute_steady_factor()
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{
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mach_timebase_info_data_t MachInfo;
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mach_timebase_info(&MachInfo);
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return static_cast<double>(MachInfo.numer) / MachInfo.denom;
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}
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static
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steady_clock::rep
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steady_full()
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{
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static const double factor = compute_steady_factor();
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return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
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}
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typedef steady_clock::rep (*FP)();
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static
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FP
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init_steady_clock()
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{
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mach_timebase_info_data_t MachInfo;
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mach_timebase_info(&MachInfo);
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if (MachInfo.numer == MachInfo.denom)
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return &steady_simplified;
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return &steady_full;
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}
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#pragma GCC visibility pop
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steady_clock::time_point
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steady_clock::now() _NOEXCEPT
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{
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static FP fp = init_steady_clock();
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return time_point(duration(fp()));
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}
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#else // __APPLE__
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// FIXME: We assume that clock_gettime(CLOCK_MONOTONIC) works on
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// non-apple systems. Instead, we should check _POSIX_TIMERS and
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// _POSIX_MONOTONIC_CLOCK and fall back to something else if those
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// don't exist.
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// Warning: If this is not truly steady, then it is non-conforming. It is
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// better for it to not exist and have the rest of libc++ use system_clock
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// instead.
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steady_clock::time_point
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steady_clock::now() _NOEXCEPT
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{
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struct timespec tp;
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if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
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__throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
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return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
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}
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#endif // __APPLE__
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}
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_LIBCPP_END_NAMESPACE_STD
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