135 lines · cpp
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-exception6//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_MEAN20#define NOMINMAX21#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 // see38 // https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps39 // 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 always43 // 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-getsystemtimepreciseasfiletime59 // GetSystemTimePreciseAsFileTime60 // This function is best suited for high-resolution time-of-day61 // measurements, or time stamps that are synchronized to UTC62 [[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-getprocesstimes95 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-getthreadtimes99 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-filetime107 // It is not recommended that you add and subtract values from the FILETIME108 // structure to obtain relative times. Instead, you should copy the low- and109 // high-order parts of the file time to a ULARGE_INTEGER structure, perform110 // 64-bit arithmetic on the QuadPart member, and copy the LowPart and111 // 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 internal134} // namespace LIBC_NAMESPACE_DECL135