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      1 //===------------------------- chrono.cpp ---------------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is dual licensed under the MIT and the University of Illinois Open
      6 // Source Licenses. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #include "chrono"
     11 #include <sys/time.h>        //for gettimeofday and timeval
     12 #ifdef __APPLE__
     13 #include <mach/mach_time.h>  // mach_absolute_time, mach_timebase_info_data_t
     14 #else  /* !__APPLE__ */
     15 #include <cerrno>  // errno
     16 #include <system_error>  // __throw_system_error
     17 #include <time.h>  // clock_gettime, CLOCK_MONOTONIC
     18 #endif  // __APPLE__
     19 
     20 _LIBCPP_BEGIN_NAMESPACE_STD
     21 
     22 namespace chrono
     23 {
     24 
     25 // system_clock
     26 
     27 const bool system_clock::is_steady;
     28 
     29 system_clock::time_point
     30 system_clock::now() _NOEXCEPT
     31 {
     32     timeval tv;
     33     gettimeofday(&tv, 0);
     34     return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
     35 }
     36 
     37 time_t
     38 system_clock::to_time_t(const time_point& t) _NOEXCEPT
     39 {
     40     return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
     41 }
     42 
     43 system_clock::time_point
     44 system_clock::from_time_t(time_t t) _NOEXCEPT
     45 {
     46     return system_clock::time_point(seconds(t));
     47 }
     48 
     49 // steady_clock
     50 
     51 const bool steady_clock::is_steady;
     52 
     53 #ifdef __APPLE__
     54 //   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
     55 //   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
     56 //   are run time constants supplied by the OS.  This clock has no relationship
     57 //   to the Gregorian calendar.  It's main use is as a high resolution timer.
     58 
     59 // MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
     60 //   for that case as an optimization.
     61 
     62 #pragma GCC visibility push(hidden)
     63 
     64 static
     65 steady_clock::rep
     66 steady_simplified()
     67 {
     68     return static_cast<steady_clock::rep>(mach_absolute_time());
     69 }
     70 
     71 static
     72 double
     73 compute_steady_factor()
     74 {
     75     mach_timebase_info_data_t MachInfo;
     76     mach_timebase_info(&MachInfo);
     77     return static_cast<double>(MachInfo.numer) / MachInfo.denom;
     78 }
     79 
     80 static
     81 steady_clock::rep
     82 steady_full()
     83 {
     84     static const double factor = compute_steady_factor();
     85     return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
     86 }
     87 
     88 typedef steady_clock::rep (*FP)();
     89 
     90 static
     91 FP
     92 init_steady_clock()
     93 {
     94     mach_timebase_info_data_t MachInfo;
     95     mach_timebase_info(&MachInfo);
     96     if (MachInfo.numer == MachInfo.denom)
     97         return &steady_simplified;
     98     return &steady_full;
     99 }
    100 
    101 #pragma GCC visibility pop
    102 
    103 steady_clock::time_point
    104 steady_clock::now() _NOEXCEPT
    105 {
    106     static FP fp = init_steady_clock();
    107     return time_point(duration(fp()));
    108 }
    109 
    110 #else  // __APPLE__
    111 // Warning:  If this is not truly steady, then it is non-conforming.  It is
    112 //  better for it to not exist and have the rest of libc++ use system_clock
    113 //  instead.
    114 
    115 steady_clock::time_point
    116 steady_clock::now() _NOEXCEPT
    117 {
    118 #if (defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0) && \
    119     (defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK > 0)
    120     struct timespec tp;
    121     if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
    122         __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
    123     return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
    124 #else
    125 #warning According to unistd.h, there is no monotonic clock on this system so \
    126          we are falling back to std::system_clock (which may not be \
    127          monotonic, and therefore may not be conforming).
    128     return time_point(system_clock::now().time_since_epoch());
    129 #endif
    130 }
    131 #endif  // __APPLE__
    132 
    133 }
    134 
    135 _LIBCPP_END_NAMESPACE_STD
    136