1 //===------------------------- chrono.cpp ---------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 #include <sys/time.h> //for gettimeofday and timeval
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
20 _LIBCPP_BEGIN_NAMESPACE_STD
27 system_clock::time_point
28 system_clock::now() _NOEXCEPT
32 return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
36 system_clock::to_time_t(const time_point& t) _NOEXCEPT
38 return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
41 system_clock::time_point
42 system_clock::from_time_t(time_t t) _NOEXCEPT
44 return system_clock::time_point(seconds(t));
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.
55 // MachInfo.numer / MachInfo.denom is often 1 on the latest equipment. Specialize
56 // for that case as an optimization.
58 #pragma GCC visibility push(hidden)
64 return mach_absolute_time();
69 compute_steady_factor()
71 mach_timebase_info_data_t MachInfo;
72 mach_timebase_info(&MachInfo);
73 return static_cast<double>(MachInfo.numer) / MachInfo.denom;
80 static const double factor = compute_steady_factor();
81 return static_cast<steady_clock::rep>(mach_absolute_time() * factor);
84 typedef steady_clock::rep (*FP)();
90 mach_timebase_info_data_t MachInfo;
91 mach_timebase_info(&MachInfo);
92 if (MachInfo.numer == MachInfo.denom)
93 return &steady_simplified;
97 #pragma GCC visibility pop
99 steady_clock::time_point
100 steady_clock::now() _NOEXCEPT
102 static FP fp = init_steady_clock();
103 return time_point(duration(fp()));
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
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
116 steady_clock::time_point
117 steady_clock::now() _NOEXCEPT
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));
128 _LIBCPP_END_NAMESPACE_STD