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 22 namespace chrono 23 { 24 25 // system_clock 26 27 system_clock::time_point 28 system_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 35 time_t 36 system_clock::to_time_t(const time_point& t) _NOEXCEPT 37 { 38 return time_t(duration_cast<seconds>(t.time_since_epoch()).count()); 39 } 40 41 system_clock::time_point 42 system_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 60 static 61 steady_clock::rep 62 steady_simplified() 63 { 64 return static_cast<steady_clock::rep>(mach_absolute_time()); 65 } 66 67 static 68 double 69 compute_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 76 static 77 steady_clock::rep 78 steady_full() 79 { 80 static const double factor = compute_steady_factor(); 81 return static_cast<steady_clock::rep>(mach_absolute_time() * factor); 82 } 83 84 typedef steady_clock::rep (*FP)(); 85 86 static 87 FP 88 init_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 99 steady_clock::time_point 100 steady_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. 115 116 steady_clock::time_point 117 steady_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