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diff --git a/mozglue/misc/TimeStamp_darwin.cpp b/mozglue/misc/TimeStamp_darwin.cpp
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//
+// Implement TimeStamp::Now() with mach_absolute_time
+//
+// The "tick" unit for mach_absolute_time is defined using mach_timebase_info() which
+// gives a conversion ratio to nanoseconds. For more information see Apple's QA1398.
+//
+// This code is inspired by Chromium's time_mac.cc. The biggest
+// differences are that we explicitly initialize using
+// TimeStamp::Initialize() instead of lazily in Now() and that
+// we store the time value in ticks and convert when needed instead
+// of storing the time value in nanoseconds.
+
+#include <mach/mach_time.h>
+#include <sys/time.h>
+#include <sys/sysctl.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "mozilla/TimeStamp.h"
+
+// Estimate of the smallest duration of time we can measure.
+static uint64_t sResolution;
+static uint64_t sResolutionSigDigs;
+
+static const uint64_t kNsPerMs = 1000000;
+static const uint64_t kUsPerSec = 1000000;
+static const double kNsPerMsd = 1000000.0;
+static const double kNsPerSecd = 1000000000.0;
+
+static bool gInitialized = false;
+static double sNsPerTick;
+
+static uint64_t
+ClockTime()
+{
+ // mach_absolute_time is it when it comes to ticks on the Mac. Other calls
+ // with less precision (such as TickCount) just call through to
+ // mach_absolute_time.
+ //
+ // At the time of writing mach_absolute_time returns the number of nanoseconds
+ // since boot. This won't overflow 64bits for 500+ years so we aren't going
+ // to worry about that possiblity
+ return mach_absolute_time();
+}
+
+static uint64_t
+ClockResolutionNs()
+{
+ uint64_t start = ClockTime();
+ uint64_t end = ClockTime();
+ uint64_t minres = (end - start);
+
+ // 10 total trials is arbitrary: what we're trying to avoid by
+ // looping is getting unlucky and being interrupted by a context
+ // switch or signal, or being bitten by paging/cache effects
+ for (int i = 0; i < 9; ++i) {
+ start = ClockTime();
+ end = ClockTime();
+
+ uint64_t candidate = (start - end);
+ if (candidate < minres) {
+ minres = candidate;
+ }
+ }
+
+ if (0 == minres) {
+ // measurable resolution is either incredibly low, ~1ns, or very
+ // high. fall back on NSPR's resolution assumption
+ minres = 1 * kNsPerMs;
+ }
+
+ return minres;
+}
+
+namespace mozilla {
+
+double
+BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks)
+{
+ MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
+ return (aTicks * sNsPerTick) / kNsPerSecd;
+}
+
+double
+BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks)
+{
+ MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
+ // don't report a value < mResolution ...
+ int64_t valueSigDigs = sResolution * (aTicks / sResolution);
+ // and chop off insignificant digits
+ valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
+ return (valueSigDigs * sNsPerTick) / kNsPerSecd;
+}
+
+int64_t
+BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds)
+{
+ MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
+ double result = (aMilliseconds * kNsPerMsd) / sNsPerTick;
+ if (result > INT64_MAX) {
+ return INT64_MAX;
+ } else if (result < INT64_MIN) {
+ return INT64_MIN;
+ }
+
+ return result;
+}
+
+int64_t
+BaseTimeDurationPlatformUtils::ResolutionInTicks()
+{
+ MOZ_ASSERT(gInitialized, "calling TimeDuration too early");
+ return static_cast<int64_t>(sResolution);
+}
+
+void
+TimeStamp::Startup()
+{
+ if (gInitialized) {
+ return;
+ }
+
+ mach_timebase_info_data_t timebaseInfo;
+ // Apple's QA1398 suggests that the output from mach_timebase_info
+ // will not change while a program is running, so it should be safe
+ // to cache the result.
+ kern_return_t kr = mach_timebase_info(&timebaseInfo);
+ if (kr != KERN_SUCCESS) {
+ MOZ_RELEASE_ASSERT(false, "mach_timebase_info failed");
+ }
+
+ sNsPerTick = double(timebaseInfo.numer) / timebaseInfo.denom;
+
+ sResolution = ClockResolutionNs();
+
+ // find the number of significant digits in sResolution, for the
+ // sake of ToSecondsSigDigits()
+ for (sResolutionSigDigs = 1;
+ !(sResolutionSigDigs == sResolution ||
+ 10 * sResolutionSigDigs > sResolution);
+ sResolutionSigDigs *= 10);
+
+ gInitialized = true;
+
+ return;
+}
+
+void
+TimeStamp::Shutdown()
+{
+}
+
+TimeStamp
+TimeStamp::Now(bool aHighResolution)
+{
+ return TimeStamp(ClockTime());
+}
+
+// Computes and returns the process uptime in microseconds.
+// Returns 0 if an error was encountered.
+
+uint64_t
+TimeStamp::ComputeProcessUptime()
+{
+ struct timeval tv;
+ int rv = gettimeofday(&tv, nullptr);
+
+ if (rv == -1) {
+ return 0;
+ }
+
+ int mib[] = {
+ CTL_KERN,
+ KERN_PROC,
+ KERN_PROC_PID,
+ getpid(),
+ };
+ u_int mibLen = sizeof(mib) / sizeof(mib[0]);
+
+ struct kinfo_proc proc;
+ size_t bufferSize = sizeof(proc);
+ rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
+
+ if (rv == -1) {
+ return 0;
+ }
+
+ uint64_t startTime =
+ ((uint64_t)proc.kp_proc.p_un.__p_starttime.tv_sec * kUsPerSec) +
+ proc.kp_proc.p_un.__p_starttime.tv_usec;
+ uint64_t now = (tv.tv_sec * kUsPerSec) + tv.tv_usec;
+
+ if (startTime > now) {
+ return 0;
+ }
+
+ return now - startTime;
+}
+
+} // namespace mozilla