chrono.cpp revision 227825 
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#if __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
22namespace chrono
23{
24
25// system_clock
26
27system_clock::time_point
28system_clock::now() _NOEXCEPT
29{
30    timeval tv;
31    gettimeofday(&tv, 0);
32    return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
33}
34
35time_t
36system_clock::to_time_t(const time_point& t) _NOEXCEPT
37{
38    return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
39}
40
41system_clock::time_point
42system_clock::from_time_t(time_t t) _NOEXCEPT
43{
44    return system_clock::time_point(seconds(t));
45}
46
47// steady_clock
48
49#if __APPLE__
50//   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
51//   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
52//   are run time constants supplied by the OS.  This clock has no relationship
53//   to the Gregorian calendar.  It's main use is as a high resolution timer.
54
55// MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
56//   for that case as an optimization.
57
58#pragma GCC visibility push(hidden)
59
60static
61steady_clock::rep
62steady_simplified()
63{
64    return mach_absolute_time();
65}
66
67static
68double
69compute_steady_factor()
70{
71    mach_timebase_info_data_t MachInfo;
72    mach_timebase_info(&MachInfo);
73    return static_cast<double>(MachInfo.numer) / MachInfo.denom;
74}
75
76static
77steady_clock::rep
78steady_full()
79{
80    static const double factor = compute_steady_factor();
81    return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
82}
83
84typedef steady_clock::rep (*FP)();
85
86static
87FP
88init_steady_clock()
89{
90    mach_timebase_info_data_t MachInfo;
91    mach_timebase_info(&MachInfo);
92    if (MachInfo.numer == MachInfo.denom)
93        return &steady_simplified;
94    return &steady_full;
95}
96
97#pragma GCC visibility pop
98
99steady_clock::time_point
100steady_clock::now() _NOEXCEPT
101{
102    static FP fp = init_steady_clock();
103    return time_point(duration(fp()));
104}
105
106#else  // __APPLE__
107// FIXME: We assume that clock_gettime(CLOCK_MONOTONIC) works on
108// non-apple systems.  Instead, we should check _POSIX_TIMERS and
109// _POSIX_MONOTONIC_CLOCK and fall back to something else if those
110// don't exist.
111
112// Warning:  If this is not truly steady, then it is non-conforming.  It is
113//  better for it to not exist and have the rest of libc++ use system_clock
114//  instead.
115
116steady_clock::time_point
117steady_clock::now() _NOEXCEPT
118{
119    struct timespec tp;
120    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
121        __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
122    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
123}
124#endif  // __APPLE__
125
126}
127
128_LIBCPP_END_NAMESPACE_STD
129