[PATCH] D27429: [Chrono][Darwin] On Darwin use CLOCK_UPTIME_RAW instead of CLOCK_MONOTONIC
Bruno Cardoso Lopes via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Wed Jan 4 16:30:57 PST 2017
bruno updated this revision to Diff 83158.
bruno added a comment.
Thanks for the reviews. @howard.hinnant thanks for the great explanation & examples.
Attached a new version of the patch, addressing all suggestions. The logic became a bit simpler after Saleem's r290804, which already moved the CLOCK_MONOTONIC to be the last condition.
On top of that, I also conditionalized the presence of `clock_gettime`, which isn't available before 10.12 on macosx and specific versions on other apple platforms. Check that by looking at the deployment target.
https://reviews.llvm.org/D27429
Files:
src/chrono.cpp
Index: src/chrono.cpp
===================================================================
--- src/chrono.cpp
+++ src/chrono.cpp
@@ -12,6 +12,28 @@
#include "system_error" // __throw_system_error
#include <time.h> // clock_gettime, CLOCK_MONOTONIC and CLOCK_REALTIME
+#if (__APPLE__)
+#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 101200
+#define _LIBCXX_USE_CLOCK_GETTIME
+#endif
+#elif defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ >= 100000
+#define _LIBCXX_USE_CLOCK_GETTIME
+#endif
+#elif defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ >= 100000
+#define _LIBCXX_USE_CLOCK_GETTIME
+#endif
+#elif defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__)
+#if __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ >= 30000
+#define _LIBCXX_USE_CLOCK_GETTIME
+#endif
+#endif // __ENVIRONMENT_.*_VERSION_MIN_REQUIRED__
+#else
+#define _LIBCXX_USE_CLOCK_GETTIME
+#endif // __APPLE__
+
#if defined(_LIBCPP_WIN32API)
#define WIN32_LEAN_AND_MEAN
#define VC_EXTRA_LEAN
@@ -70,16 +92,16 @@
static_cast<__int64>(ft.dwLowDateTime)};
return time_point(duration_cast<duration>(d - nt_to_unix_epoch));
#else
-#ifdef CLOCK_REALTIME
+#if defined(_LIBCXX_USE_CLOCK_GETTIME) && defined(CLOCK_REALTIME)
struct timespec tp;
if (0 != clock_gettime(CLOCK_REALTIME, &tp))
__throw_system_error(errno, "clock_gettime(CLOCK_REALTIME) failed");
return time_point(seconds(tp.tv_sec) + microseconds(tp.tv_nsec / 1000));
-#else // !CLOCK_REALTIME
+#else
timeval tv;
gettimeofday(&tv, 0);
return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
-#endif // CLOCK_REALTIME
+#endif // _LIBCXX_USE_CLOCK_GETTIME && CLOCK_REALTIME
#endif
}
@@ -106,6 +128,18 @@
#if defined(__APPLE__)
+// Darwin libc versions >= 1133 provide ns precision via CLOCK_UPTIME_RAW
+#if defined(_LIBCXX_USE_CLOCK_GETTIME) && defined(CLOCK_UPTIME_RAW)
+steady_clock::time_point
+steady_clock::now() _NOEXCEPT
+{
+ struct timespec tp;
+ if (0 != clock_gettime(CLOCK_UPTIME_RAW, &tp))
+ __throw_system_error(errno, "clock_gettime(CLOCK_UPTIME_RAW) failed");
+ return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
+}
+
+#else
// mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
// nanoseconds since the computer booted up. MachInfo.numer and MachInfo.denom
// are run time constants supplied by the OS. This clock has no relationship
@@ -157,6 +191,7 @@
static FP fp = init_steady_clock();
return time_point(duration(fp()));
}
+#endif // defined(_LIBCXX_USE_CLOCK_GETTIME) && defined(CLOCK_UPTIME_RAW)
#elif defined(_LIBCPP_WIN32API)
@@ -175,6 +210,13 @@
#elif defined(CLOCK_MONOTONIC)
+// On Apple platforms only CLOCK_UPTIME_RAW or mach_absolute_time are able to
+// time functions in the nanosecond range. Thus, they are the only acceptable
+// implementations of steady_clock.
+#ifdef __APPLE__
+#error "Never use CLOCK_MONOTONIC for steady_clock::now on Apple platforms"
+#endif
+
steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
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