[libc][time][windows] implement clock_getres (#118931)

libc/config/windows/entrypoints.txt

@@ -98,6 +98,7 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # time.h entrypoints
     libc.src.time.time
+    libc.src.time.clock_getres
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

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

@@ -1,10 +1,20 @@
+add_header_library(
+  performance_counter 
+  HDRS
+    performance_counter.h
+  DEPENDS
+    libc.src.__support.CPP.atomic
+    libc.src.__support.common
+)
+
 add_object_library(
   clock_gettime
   HDRS
     ../clock_gettime.h
   SRCS
     clock_gettime.cpp
   DEPENDS
+    .performance_counter
     libc.hdr.types.struct_timespec
     libc.hdr.types.clockid_t
     libc.hdr.errno_macros

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

@@ -14,30 +14,14 @@
 #include "src/__support/macros/optimization.h"
 #include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
+#include "src/__support/time/windows/performance_counter.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;
@@ -53,12 +37,12 @@ ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
     // 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.
+    // Yes. performance_counter 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 freq = performance_counter::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;

libc/src/__support/time/windows/performance_counter.h

@@ -0,0 +1,35 @@
+//===--- Cached Performance Counter Frequency  ----------------------------===//
+//
+// 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 "src/__support/CPP/atomic.h"
+#include "src/__support/common.h"
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <Windows.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace performance_counter {
+LIBC_INLINE 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;
+}
+} // namespace performance_counter
+} // namespace LIBC_NAMESPACE_DECL

libc/src/time/CMakeLists.txt

@@ -151,3 +151,10 @@ add_entrypoint_object(
   DEPENDS
     .${LIBC_TARGET_OS}.gettimeofday
 )
+
+add_entrypoint_object(
+  clock_getres
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.clock_getres
+)

libc/src/time/clock_getres.h

@@ -0,0 +1,21 @@
+//===-- Implementation header of clock_getres -------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC_TIME_CLOCK_GETRES_H
+#define LLVM_LIBC_SRC_TIME_CLOCK_GETRES_H
+
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_timespec.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int clock_getres(clockid_t clockid, timespec *tp);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_TIME_CLOCK_GETRES_H

libc/src/time/windows/CMakeLists.txt

@@ -0,0 +1,13 @@
+add_entrypoint_object(
+    clock_getres
+    SRCS
+        clock_getres.cpp
+    DEPENDS
+        libc.src.__support.time.windows.performance_counter
+        libc.src.__support.time.units
+        libc.src.__support.common
+        libc.src.__support.macros.optimization
+        libc.hdr.time_macros
+        libc.hdr.types.time_t
+        libc.hdr.types.struct_timespec
+)

libc/src/time/windows/clock_getres.cpp

@@ -0,0 +1,110 @@
+//===-- Windows implementation of clock_getres ------------------*- 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/errno_macros.h"
+#include "hdr/time_macros.h"
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_timespec.h"
+
+#include "src/__support/CPP/limits.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/time/units.h"
+#include "src/__support/time/windows/performance_counter.h"
+#include "src/errno/libc_errno.h"
+#include "src/time/clock_getres.h"
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <Windows.h>
+
+// add in dependencies for GetSystemTimeAdjustmentPrecise
+#pragma comment(lib, "mincore.lib")
+
+namespace LIBC_NAMESPACE_DECL {
+LLVM_LIBC_FUNCTION(int, clock_getres, (clockid_t id, struct timespec *res)) {
+  using namespace time_units;
+  // POSIX allows nullptr to be passed as res, in which case the function should
+  // do nothing.
+  if (res == nullptr)
+    return 0;
+  constexpr unsigned long long HNS_PER_SEC = 1_s_ns / 100ULL;
+  constexpr unsigned long long SEC_LIMIT =
+      cpp::numeric_limits<decltype(res->tv_sec)>::max();
+  // For CLOCK_MONOTONIC, we are using performance counter
+  // https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
+  // Hence, the resolution is given by the performance counter frequency.
+  // For CLOCK_REALTIME, the precision is given by
+  // GetSystemTimeAdjustmentPrecise
+  // (https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeadjustmentprecise)
+  // For CLOCK_PROCESS_CPUTIME_ID, CLOCK_THREAD_CPUTIME_ID, the precision is
+  // given by GetSystemTimeAdjustment
+  // (https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimeadjustment)
+  switch (id) {
+  default:
+    libc_errno = EINVAL;
+    return -1;
+
+  case CLOCK_MONOTONIC: {
+    long long freq = performance_counter::get_ticks_per_second();
+    __builtin_assume(freq != 0);
+    // division of 1 second by frequency, rounded up.
+    long long tv_sec = static_cast<long long>(freq == 1);
+    long long tv_nsec =
+        LIBC_LIKELY(freq != 1) ? 1ll + ((1_s_ns - 1ll) / freq) : 0ll;
+    // not possible to overflow tv_sec, tv_nsec
+    res->tv_sec = static_cast<decltype(res->tv_sec)>(tv_sec);
+    res->tv_nsec = static_cast<decltype(res->tv_nsec)>(tv_nsec);
+    break;
+  }
+
+  case CLOCK_REALTIME: {
+    [[clang::uninitialized]] DWORD64 time_adjustment;
+    [[clang::uninitialized]] DWORD64 time_increment;
+    [[clang::uninitialized]] BOOL time_adjustment_disabled;
+    if (!::GetSystemTimeAdjustmentPrecise(&time_adjustment, &time_increment,
+                                          &time_adjustment_disabled)) {
+      libc_errno = EINVAL;
+      return -1;
+    }
+    DWORD64 tv_sec = time_increment / HNS_PER_SEC;
+    DWORD64 tv_nsec = (time_increment % HNS_PER_SEC) * 100ULL;
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      libc_errno = EOVERFLOW;
+      return -1;
+    }
+    res->tv_sec = static_cast<decltype(res->tv_sec)>(tv_sec);
+    res->tv_nsec = static_cast<decltype(res->tv_nsec)>(tv_nsec);
+    break;
+  }
+  case CLOCK_PROCESS_CPUTIME_ID:
+  case CLOCK_THREAD_CPUTIME_ID: {
+    [[clang::uninitialized]] DWORD time_adjustment;
+    [[clang::uninitialized]] DWORD time_increment;
+    [[clang::uninitialized]] BOOL time_adjustment_disabled;
+    if (!::GetSystemTimeAdjustment(&time_adjustment, &time_increment,
+                                   &time_adjustment_disabled)) {
+      libc_errno = EINVAL;
+      return -1;
+    }
+    DWORD hns_per_sec = static_cast<DWORD>(HNS_PER_SEC);
+    DWORD sec_limit = static_cast<DWORD>(SEC_LIMIT);
+    DWORD tv_sec = time_increment / hns_per_sec;
+    DWORD tv_nsec = (time_increment % hns_per_sec) * 100UL;
+    if (LIBC_UNLIKELY(tv_sec > sec_limit)) {
+      libc_errno = EOVERFLOW;
+      return -1;
+    }
+    res->tv_sec = static_cast<decltype(res->tv_sec)>(tv_sec);
+    res->tv_nsec = static_cast<decltype(res->tv_nsec)>(tv_nsec);
+    break;
+  }
+  }
+  return 0;
+}
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/time/CMakeLists.txt

@@ -71,11 +71,21 @@ add_libc_test(
   SUITE
     libc_time_unittests
   SRCS
-  clock_gettime_test.cpp
+    clock_gettime_test.cpp
   DEPENDS
     libc.src.time.clock_gettime
 )
 
+add_libc_test(
+  clock_getres_test
+  SUITE
+    libc_time_unittests
+  SRCS
+    clock_getres_test.cpp
+  DEPENDS
+    libc.src.time.clock_getres
+)
+
 add_libc_unittest(
   difftime_test
   SUITE

libc/test/src/time/clock_getres_test.cpp

@@ -0,0 +1,55 @@
+//===-- Unittests for clock_getres- ---------------------------------------===//
+//
+// 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/time/clock_getres.h"
+#include "test/UnitTest/ErrnoSetterMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Fails;
+using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
+
+TEST(LlvmLibcClockGetRes, Invalid) {
+  timespec tp;
+  EXPECT_THAT(LIBC_NAMESPACE::clock_getres(-1, &tp), Fails(EINVAL));
+}
+
+TEST(LlvmLibcClockGetRes, NullSpec) {
+  EXPECT_THAT(LIBC_NAMESPACE::clock_getres(CLOCK_REALTIME, nullptr),
+              Succeeds());
+}
+
+TEST(LlvmLibcClockGetRes, Realtime) {
+  timespec tp;
+  EXPECT_THAT(LIBC_NAMESPACE::clock_getres(CLOCK_REALTIME, &tp), Succeeds());
+  EXPECT_GE(tp.tv_sec, static_cast<decltype(tp.tv_sec)>(0));
+  EXPECT_GE(tp.tv_nsec, static_cast<decltype(tp.tv_nsec)>(0));
+}
+
+TEST(LlvmLibcClockGetRes, Monotonic) {
+  timespec tp;
+  ASSERT_THAT(LIBC_NAMESPACE::clock_getres(CLOCK_MONOTONIC, &tp), Succeeds());
+  EXPECT_GE(tp.tv_sec, static_cast<decltype(tp.tv_sec)>(0));
+  EXPECT_GE(tp.tv_nsec, static_cast<decltype(tp.tv_nsec)>(0));
+}
+
+TEST(LlvmLibcClockGetRes, ProcessCpuTime) {
+  timespec tp;
+  ASSERT_THAT(LIBC_NAMESPACE::clock_getres(CLOCK_PROCESS_CPUTIME_ID, &tp),
+              Succeeds());
+  EXPECT_GE(tp.tv_sec, static_cast<decltype(tp.tv_sec)>(0));
+  EXPECT_GE(tp.tv_nsec, static_cast<decltype(tp.tv_nsec)>(0));
+}
+
+TEST(LlvmLibcClockGetRes, ThreadCpuTime) {
+  timespec tp;
+  ASSERT_THAT(LIBC_NAMESPACE::clock_getres(CLOCK_THREAD_CPUTIME_ID, &tp),
+              Succeeds());
+  EXPECT_GE(tp.tv_sec, static_cast<decltype(tp.tv_sec)>(0));
+  EXPECT_GE(tp.tv_nsec, static_cast<decltype(tp.tv_nsec)>(0));
+}