[libc][windows] start time API implementation (#117775)

Add a `clock_gettime` emulation layer and use it to implement the `time`
entrypoint.

For windows, the monotonic clock is emulated using `QPC`.
The realtime clock is emulated using `GetSystemTimePreciseAsFileTime`.

libc/config/windows/entrypoints.txt

@@ -95,6 +95,9 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # errno.h entrypoints
     libc.src.errno.errno
+
+    # time.h entrypoints
+    libc.src.time.time
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

libc/hdr/CMakeLists.txt

@@ -135,10 +135,18 @@ add_proxy_header_library(
     libc.include.llvm-libc-macros.unistd_macros
 )
 
+if (WIN32)
+  set(windows_addtional_time_macros libc.include.llvm-libc-macros.windows.time_macros_ext)
+else()
+  set(windows_addtional_time_macros "")
+endif()
+
 add_proxy_header_library(
   time_macros
   HDRS
     time_macros.h
+  DEPENDS
+    ${windows_addtional_time_macros}
   FULL_BUILD_DEPENDS
     libc.include.time
     libc.include.llvm-libc-macros.time_macros

libc/hdr/time_macros.h

@@ -19,4 +19,10 @@
 
 #endif // LLVM_LIBC_FULL_BUILD
 
+// TODO: For now, on windows, let's always include the extension header.
+// We will need to decide how to export this header.
+#ifdef _WIN32
+#include "include/llvm-libc-macros/windows/time-macros-ext.h"
+#endif // _WIN32
+
 #endif // LLVM_LIBC_HDR_TIME_MACROS_H

libc/hdr/types/clockid_t.h

@@ -9,7 +9,8 @@
 #ifndef LLVM_LIBC_HDR_TYPES_CLOCKID_T_H
 #define LLVM_LIBC_HDR_TYPES_CLOCKID_T_H
 
-#ifdef LIBC_FULL_BUILD
+// TODO: we will need to decide how to export extension to windows.
+#if defined(LIBC_FULL_BUILD) || defined(_WIN32)
 
 #include "include/llvm-libc-types/clockid_t.h"
 

libc/include/llvm-libc-macros/windows/CMakeLists.txt

@@ -0,0 +1,6 @@
+add_header(
+  time_macros_ext
+  HDR
+    time-macros-ext.h
+)
+

libc/include/llvm-libc-macros/windows/time-macros-ext.h

@@ -0,0 +1,17 @@
+//===-- Windows Time Macros Extension -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H
+#define LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H
+
+#define CLOCK_MONOTONIC 0
+#define CLOCK_REALTIME 1
+#define CLOCK_PROCESS_CPUTIME_ID 2
+#define CLOCK_THREAD_CPUTIME_ID 3
+
+#endif // LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H

libc/src/CMakeLists.txt

@@ -13,6 +13,7 @@ add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(wchar)
+add_subdirectory(time)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(dirent)
@@ -40,5 +41,4 @@ add_subdirectory(setjmp)
 add_subdirectory(signal)
 add_subdirectory(spawn)
 add_subdirectory(threads)
-add_subdirectory(time)
 add_subdirectory(locale)

libc/src/__support/time/CMakeLists.txt

@@ -2,6 +2,13 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${LIBC_TARGET_OS})
 endif()
 
+add_object_library(
+  clock_gettime
+  ALIAS
+  DEPENDS
+    libc.src.__support.time.${LIBC_TARGET_OS}.clock_gettime
+)
+
 add_header_library(
   units
   HDRS

libc/src/__support/time/clock_gettime.h

@@ -6,21 +6,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
-#define LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
+#ifndef LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H
+#define LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H
 
 #include "hdr/types/clockid_t.h"
 #include "hdr/types/struct_timespec.h"
 #include "src/__support/error_or.h"
 
-#if defined(SYS_clock_gettime64)
-#include <linux/time_types.h>
-#endif
-
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts);
 } // namespace internal
 } // namespace LIBC_NAMESPACE_DECL
 
-#endif // LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
+#endif // LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H

libc/src/__support/time/linux/CMakeLists.txt

@@ -1,7 +1,7 @@
 add_object_library(
   clock_gettime
   HDRS
-    clock_gettime.h
+    ../clock_gettime.h
   SRCS
     clock_gettime.cpp
   DEPENDS

libc/src/__support/time/linux/clock_conversion.h

@@ -10,7 +10,7 @@
 #define LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_CONVERSION_H
 
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/__support/time/linux/clock_gettime.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "hdr/types/clockid_t.h"
 #include "hdr/types/struct_timespec.h"
 #include "src/__support/OSUtil/linux/vdso.h"

libc/src/__support/time/windows/CMakeLists.txt

@@ -0,0 +1,16 @@
+add_object_library(
+  clock_gettime
+  HDRS
+    ../clock_gettime.h
+  SRCS
+    clock_gettime.cpp
+  DEPENDS
+    libc.hdr.types.struct_timespec
+    libc.hdr.types.clockid_t
+    libc.hdr.errno_macros
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.CPP.atomic
+    libc.src.__support.CPP.limits
+)

libc/src/__support/time/windows/clock_gettime.cpp

@@ -0,0 +1,150 @@
+//===--- clock_gettime windows implementation -------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/time_macros.h"
+
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/CPP/limits.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/time/clock_gettime.h"
+#include "src/__support/time/units.h"
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <Windows.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+static long long get_ticks_per_second() {
+  static cpp::Atomic<long long> frequency = 0;
+  // Relaxed ordering is enough. It is okay to record the frequency multiple
+  // times. The store operation itself is atomic and the value must propagate
+  // as required by cache coherence.
+  auto freq = frequency.load(cpp::MemoryOrder::RELAXED);
+  if (!freq) {
+    [[clang::uninitialized]] LARGE_INTEGER buffer;
+    // On systems that run Windows XP or later, the function will always
+    // succeed and will thus never return zero.
+    ::QueryPerformanceFrequency(&buffer);
+    frequency.store(buffer.QuadPart, cpp::MemoryOrder::RELAXED);
+    return buffer.QuadPart;
+  }
+  return freq;
+}
+
+ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
+  using namespace time_units;
+  constexpr unsigned long long HNS_PER_SEC = 1_s_ns / 100ULL;
+  constexpr long long SEC_LIMIT =
+      cpp::numeric_limits<decltype(ts->tv_sec)>::max();
+  ErrorOr<int> ret = 0;
+  switch (clockid) {
+  default:
+    ret = cpp::unexpected(EINVAL);
+    break;
+
+  case CLOCK_MONOTONIC: {
+    // see
+    // https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
+    // Is the performance counter monotonic (non-decreasing)?
+    // Yes. QPC does not go backward.
+    [[clang::uninitialized]] LARGE_INTEGER buffer;
+    // On systems that run Windows XP or later, the function will always
+    // succeed and will thus never return zero.
+    ::QueryPerformanceCounter(&buffer);
+    long long freq = get_ticks_per_second();
+    long long ticks = buffer.QuadPart;
+    long long tv_sec = ticks / freq;
+    long long tv_nsec = (ticks % freq) * 1_s_ns / freq;
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+    break;
+  }
+  case CLOCK_REALTIME: {
+    // https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime
+    // GetSystemTimePreciseAsFileTime
+    // This function is best suited for high-resolution time-of-day
+    // measurements, or time stamps that are synchronized to UTC
+    [[clang::uninitialized]] FILETIME file_time;
+    [[clang::uninitialized]] ULARGE_INTEGER time;
+    ::GetSystemTimePreciseAsFileTime(&file_time);
+    time.LowPart = file_time.dwLowDateTime;
+    time.HighPart = file_time.dwHighDateTime;
+
+    // adjust to POSIX epoch (from Jan 1, 1601 to Jan 1, 1970)
+    constexpr unsigned long long POSIX_TIME_SHIFT =
+        (11644473600ULL * HNS_PER_SEC);
+    if (LIBC_UNLIKELY(POSIX_TIME_SHIFT > time.QuadPart)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    time.QuadPart -= (11644473600ULL * HNS_PER_SEC);
+    unsigned long long tv_sec = time.QuadPart / HNS_PER_SEC;
+    unsigned long long tv_nsec = (time.QuadPart % HNS_PER_SEC) * 100ULL;
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+    break;
+  }
+  case CLOCK_PROCESS_CPUTIME_ID:
+  case CLOCK_THREAD_CPUTIME_ID: {
+    [[clang::uninitialized]] FILETIME creation_time;
+    [[clang::uninitialized]] FILETIME exit_time;
+    [[clang::uninitialized]] FILETIME kernel_time;
+    [[clang::uninitialized]] FILETIME user_time;
+    bool success;
+    if (clockid == CLOCK_PROCESS_CPUTIME_ID) {
+      // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getprocesstimes
+      success = ::GetProcessTimes(::GetCurrentProcess(), &creation_time,
+                                  &exit_time, &kernel_time, &user_time);
+    } else {
+      // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getthreadtimes
+      success = ::GetThreadTimes(::GetCurrentThread(), &creation_time,
+                                 &exit_time, &kernel_time, &user_time);
+    }
+    if (!success) {
+      ret = cpp::unexpected(EINVAL);
+      break;
+    }
+    // https://learn.microsoft.com/en-us/windows/win32/api/minwinbase/ns-minwinbase-filetime
+    // It is not recommended that you add and subtract values from the FILETIME
+    // structure to obtain relative times. Instead, you should copy the low- and
+    // high-order parts of the file time to a ULARGE_INTEGER structure, perform
+    // 64-bit arithmetic on the QuadPart member, and copy the LowPart and
+    // HighPart members into the FILETIME structure.
+    auto kernel_time_hns = cpp::bit_cast<ULARGE_INTEGER>(kernel_time);
+    auto user_time_hns = cpp::bit_cast<ULARGE_INTEGER>(user_time);
+    unsigned long long total_time_hns =
+        kernel_time_hns.QuadPart + user_time_hns.QuadPart;
+
+    unsigned long long tv_sec = total_time_hns / HNS_PER_SEC;
+    unsigned long long tv_nsec = (total_time_hns % HNS_PER_SEC) * 100ULL;
+
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+
+    break;
+  }
+  }
+  return ret;
+}
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

libc/src/time/CMakeLists.txt

@@ -106,9 +106,15 @@ add_entrypoint_object(
 
 add_entrypoint_object(
   time
-  ALIAS
+  SRCS
+    time.cpp
+  HDRS
+    time_func.h
   DEPENDS
-    .${LIBC_TARGET_OS}.time
+    libc.hdr.time_macros
+    libc.hdr.types.time_t
+    libc.src.__support.time.clock_gettime
+    libc.src.errno.errno
 )
 
 add_entrypoint_object(

libc/src/time/linux/CMakeLists.txt

@@ -1,16 +1,3 @@
-add_entrypoint_object(
-  time
-  SRCS
-    time.cpp
-  HDRS
-    ../time_func.h
-  DEPENDS
-    libc.hdr.time_macros
-    libc.hdr.types.time_t
-    libc.src.__support.time.linux.clock_gettime
-    libc.src.errno.errno
-)
-
 add_entrypoint_object(
   timespec_get
   SRCS
@@ -20,7 +7,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.time_macros
     libc.hdr.types.struct_timespec
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 
@@ -34,7 +21,7 @@ add_entrypoint_object(
     libc.hdr.time_macros
     libc.hdr.types.clock_t
     libc.src.__support.time.units
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.__support.CPP.limits
     libc.src.errno.errno
 )
@@ -62,7 +49,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.types.clockid_t
     libc.hdr.types.struct_timespec
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 
@@ -75,7 +62,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.time_macros
     libc.hdr.types.suseconds_t
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.__support.time.units
     libc.src.errno.errno
 )

libc/src/time/linux/clock.cpp

@@ -11,7 +11,7 @@
 #include "src/__support/CPP/limits.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 #include "src/errno/libc_errno.h"
 

libc/src/time/linux/clock_gettime.cpp

@@ -9,7 +9,7 @@
 #include "src/time/clock_gettime.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/time/linux/gettimeofday.cpp

@@ -11,7 +11,7 @@
 #include "hdr/types/suseconds_t.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 #include "src/errno/libc_errno.h"
 

libc/src/time/linux/timespec_get.cpp

@@ -10,7 +10,7 @@
 #include "hdr/time_macros.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/time/time.cpp

@@ -9,14 +9,14 @@
 #include "hdr/time_macros.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 #include "src/time/time_func.h"
 
 namespace LIBC_NAMESPACE_DECL {
-
-LLVM_LIBC_FUNCTION(time_t, time, (time_t * tp)) {
-  // TODO: Use the Linux VDSO to fetch the time and avoid the syscall.
+// avoid inconsitent clang-format behavior
+using time_ptr_t = time_t *;
+LLVM_LIBC_FUNCTION(time_t, time, (time_ptr_t tp)) {
   struct timespec ts;
   auto result = internal::clock_gettime(CLOCK_REALTIME, &ts);
   if (!result.has_value()) {

libc/test/src/CMakeLists.txt

@@ -59,6 +59,7 @@ add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(wchar)
+add_subdirectory(time)
 
 # Depends on utilities in stdlib
 add_subdirectory(inttypes)
@@ -82,7 +83,6 @@ add_subdirectory(network)
 add_subdirectory(setjmp)
 add_subdirectory(signal)
 add_subdirectory(spawn)
-add_subdirectory(time)
 add_subdirectory(locale)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")

libc/test/src/__support/threads/linux/raw_mutex_test.cpp

@@ -12,7 +12,7 @@
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/threads/linux/raw_mutex.h"
 #include "src/__support/threads/sleep.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/stdlib/exit.h"
 #include "src/sys/mman/mmap.h"
 #include "src/sys/mman/munmap.h"

libc/test/src/time/CMakeLists.txt

@@ -157,8 +157,8 @@ add_libc_unittest(
   SRCS
     time_test.cpp
   DEPENDS
-    libc.include.time
     libc.src.time.time
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 

libc/test/src/time/time_test.cpp

@@ -9,8 +9,6 @@
 #include "src/time/time_func.h"
 #include "test/UnitTest/Test.h"
 
-#include <time.h>
-
 TEST(LlvmLibcTimeTest, SmokeTest) {
   time_t t1;
   time_t t2 = LIBC_NAMESPACE::time(&t1);

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -1471,13 +1471,13 @@ libc_support_library(
     }),
     deps = [
         ":__support_time",
-        ":__support_time_linux_clock_gettime",
+        ":__support_time_clock_gettime",
     ],
 )
 
 libc_support_library(
-    name = "__support_time_linux_clock_gettime",
-    hdrs = ["src/__support/time/linux/clock_gettime.h"],
+    name = "__support_time_clock_gettime",
+    hdrs = ["src/__support/time/clock_gettime.h"],
     target_compatible_with = select({
         "@platforms//os:linux": [],
         "//conditions:default": ["@platforms//:incompatible"],