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
now()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
to_time_t(const time_point & 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
from_time_t(time_t t)44 system_clock::from_time_t(time_t t) _NOEXCEPT
45 {
46     return system_clock::time_point(seconds(t));
47 }
48 
49 #ifndef _LIBCPP_HAS_NO_MONOTONIC_CLOCK
50 // steady_clock
51 
52 const bool steady_clock::is_steady;
53 
54 #ifdef __APPLE__
55 //   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
56 //   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
57 //   are run time constants supplied by the OS.  This clock has no relationship
58 //   to the Gregorian calendar.  It's main use is as a high resolution timer.
59 
60 // MachInfo.numer / MachInfo.denom is often 1 on the latest equipment.  Specialize
61 //   for that case as an optimization.
62 
63 #pragma GCC visibility push(hidden)
64 
65 static
66 steady_clock::rep
steady_simplified()67 steady_simplified()
68 {
69     return static_cast<steady_clock::rep>(mach_absolute_time());
70 }
71 
72 static
73 double
compute_steady_factor()74 compute_steady_factor()
75 {
76     mach_timebase_info_data_t MachInfo;
77     mach_timebase_info(&MachInfo);
78     return static_cast<double>(MachInfo.numer) / MachInfo.denom;
79 }
80 
81 static
82 steady_clock::rep
steady_full()83 steady_full()
84 {
85     static const double factor = compute_steady_factor();
86     return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
87 }
88 
89 typedef steady_clock::rep (*FP)();
90 
91 static
92 FP
init_steady_clock()93 init_steady_clock()
94 {
95     mach_timebase_info_data_t MachInfo;
96     mach_timebase_info(&MachInfo);
97     if (MachInfo.numer == MachInfo.denom)
98         return &steady_simplified;
99     return &steady_full;
100 }
101 
102 #pragma GCC visibility pop
103 
104 steady_clock::time_point
now()105 steady_clock::now() _NOEXCEPT
106 {
107     static FP fp = init_steady_clock();
108     return time_point(duration(fp()));
109 }
110 
111 #else  // __APPLE__
112 // FIXME: if _LIBCPP_HAS_NO_MONOTONIC_CLOCK, then clock_gettime isn't going to
113 // work. It may be possible to fall back on something else, depending on the system.
114 
115 // Warning:  If this is not truly steady, then it is non-conforming.  It is
116 //  better for it to not exist and have the rest of libc++ use system_clock
117 //  instead.
118 
119 steady_clock::time_point
now()120 steady_clock::now() _NOEXCEPT
121 {
122     struct timespec tp;
123     if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
124         __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
125     return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
126 }
127 #endif  // __APPLE__
128 
129 #endif // !_LIBCPP_HAS_NO_MONOTONIC_CLOCK
130 
131 }
132 
133 _LIBCPP_END_NAMESPACE_STD
134