external/bsd/libc++/dist/libcxx/src/chrono.cpp

   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 // FIXME: We assume that clock_gettime(CLOCK_MONOTONIC) works on
 112 // non-apple systems.  Instead, we should check _POSIX_TIMERS and
 113 // _POSIX_MONOTONIC_CLOCK and fall back to something else if those
 114 // don't exist.
 115
 116 // Warning:  If this is not truly steady, then it is non-conforming.  It is
 117 //  better for it to not exist and have the rest of libc++ use system_clock
 118 //  instead.
 119
 120 steady_clock::time_point
 121 steady_clock::now() _NOEXCEPT
 122 {
 123     struct timespec tp;
 124     if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
 125         __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
 126     return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
 127 }
 128 #endif  // __APPLE__
 129
 130 }
 131
 132 _LIBCPP_END_NAMESPACE_STD