1//===--- clock_gettime windows implementation -------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "hdr/time_macros.h"
10
11#include "src/__support/CPP/atomic.h"
12#include "src/__support/CPP/bit.h"
13#include "src/__support/CPP/limits.h"
14#include "src/__support/macros/optimization.h"
15#include "src/__support/time/clock_gettime.h"
16#include "src/__support/time/units.h"
17#include "src/__support/time/windows/performance_counter.h"
18
19#define WIN32_LEAN_AND_MEAN
20#define NOMINMAX
21#include <Windows.h>
22
23namespace LIBC_NAMESPACE_DECL {
24namespace internal {
25ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
26 using namespace time_units;
27 constexpr unsigned long long HNS_PER_SEC = 1_s_ns / 100ULL;
28 constexpr long long SEC_LIMIT =
29 cpp::numeric_limits<decltype(ts->tv_sec)>::max();
30 ErrorOr<int> ret = 0;
31 switch (clockid) {
32 default:
33 ret = cpp::unexpected(EINVAL);
34 break;
35
36 case CLOCK_MONOTONIC: {
37 // see
38 // https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
39 // Is the performance counter monotonic (non-decreasing)?
40 // Yes. performance_counter does not go backward.
41 [[clang::uninitialized]] LARGE_INTEGER buffer;
42 // On systems that run Windows XP or later, the function will always
43 // succeed and will thus never return zero.
44 ::QueryPerformanceCounter(&buffer);
45 long long freq = performance_counter::get_ticks_per_second();
46 long long ticks = buffer.QuadPart;
47 long long tv_sec = ticks / freq;
48 long long tv_nsec = (ticks % freq) * 1_s_ns / freq;
49 if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
50 ret = cpp::unexpected(EOVERFLOW);
51 break;
52 }
53 ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
54 ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
55 break;
56 }
57 case CLOCK_REALTIME: {
58 // https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime
59 // GetSystemTimePreciseAsFileTime
60 // This function is best suited for high-resolution time-of-day
61 // measurements, or time stamps that are synchronized to UTC
62 [[clang::uninitialized]] FILETIME file_time;
63 [[clang::uninitialized]] ULARGE_INTEGER time;
64 ::GetSystemTimePreciseAsFileTime(&file_time);
65 time.LowPart = file_time.dwLowDateTime;
66 time.HighPart = file_time.dwHighDateTime;
67
68 // adjust to POSIX epoch (from Jan 1, 1601 to Jan 1, 1970)
69 constexpr unsigned long long POSIX_TIME_SHIFT =
70 (11644473600ULL * HNS_PER_SEC);
71 if (LIBC_UNLIKELY(POSIX_TIME_SHIFT > time.QuadPart)) {
72 ret = cpp::unexpected(EOVERFLOW);
73 break;
74 }
75 time.QuadPart -= (11644473600ULL * HNS_PER_SEC);
76 unsigned long long tv_sec = time.QuadPart / HNS_PER_SEC;
77 unsigned long long tv_nsec = (time.QuadPart % HNS_PER_SEC) * 100ULL;
78 if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
79 ret = cpp::unexpected(EOVERFLOW);
80 break;
81 }
82 ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
83 ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
84 break;
85 }
86 case CLOCK_PROCESS_CPUTIME_ID:
87 case CLOCK_THREAD_CPUTIME_ID: {
88 [[clang::uninitialized]] FILETIME creation_time;
89 [[clang::uninitialized]] FILETIME exit_time;
90 [[clang::uninitialized]] FILETIME kernel_time;
91 [[clang::uninitialized]] FILETIME user_time;
92 bool success;
93 if (clockid == CLOCK_PROCESS_CPUTIME_ID) {
94 // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getprocesstimes
95 success = ::GetProcessTimes(::GetCurrentProcess(), &creation_time,
96 &exit_time, &kernel_time, &user_time);
97 } else {
98 // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getthreadtimes
99 success = ::GetThreadTimes(::GetCurrentThread(), &creation_time,
100 &exit_time, &kernel_time, &user_time);
101 }
102 if (!success) {
103 ret = cpp::unexpected(EINVAL);
104 break;
105 }
106 // https://learn.microsoft.com/en-us/windows/win32/api/minwinbase/ns-minwinbase-filetime
107 // It is not recommended that you add and subtract values from the FILETIME
108 // structure to obtain relative times. Instead, you should copy the low- and
109 // high-order parts of the file time to a ULARGE_INTEGER structure, perform
110 // 64-bit arithmetic on the QuadPart member, and copy the LowPart and
111 // HighPart members into the FILETIME structure.
112 auto kernel_time_hns = cpp::bit_cast<ULARGE_INTEGER>(kernel_time);
113 auto user_time_hns = cpp::bit_cast<ULARGE_INTEGER>(user_time);
114 unsigned long long total_time_hns =
115 kernel_time_hns.QuadPart + user_time_hns.QuadPart;
116
117 unsigned long long tv_sec = total_time_hns / HNS_PER_SEC;
118 unsigned long long tv_nsec = (total_time_hns % HNS_PER_SEC) * 100ULL;
119
120 if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
121 ret = cpp::unexpected(EOVERFLOW);
122 break;
123 }
124
125 ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
126 ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
127
128 break;
129 }
130 }
131 return ret;
132}
133} // namespace internal
134} // namespace LIBC_NAMESPACE_DECL
135

source code of libc/src/__support/time/windows/clock_gettime.cpp