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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/. */
/*
* Implementation of the OS-independent methods of the TimeStamp class
*/
#include "mozilla/TimeStamp.h"
#include "mozilla/Uptime.h"
#include <string.h>
#include <stdlib.h>
namespace mozilla {
/**
* Wrapper class used to initialize static data used by the TimeStamp class
*/
struct TimeStampInitialization {
/**
* First timestamp taken when the class static initializers are run. This
* timestamp is used to sanitize timestamps coming from different sources.
*/
TimeStamp mFirstTimeStamp;
/**
* Timestamp representing the time when the process was created. This field
* is populated lazily the first time this information is required and is
* replaced every time the process is restarted.
*/
TimeStamp mProcessCreation;
TimeStampInitialization() {
TimeStamp::Startup();
mFirstTimeStamp = TimeStamp::Now();
// On Windows < 10, initializing the uptime requires `mFirstTimeStamp` to be
// valid.
mozilla::InitializeUptime();
}
~TimeStampInitialization() { TimeStamp::Shutdown(); }
};
static TimeStampInitialization sInitOnce;
MFBT_API TimeStamp TimeStamp::ProcessCreation() {
if (sInitOnce.mProcessCreation.IsNull()) {
char* mozAppRestart = getenv("MOZ_APP_RESTART");
TimeStamp ts;
/* When calling PR_SetEnv() with an empty value the existing variable may
* be unset or set to the empty string depending on the underlying platform
* thus we have to check if the variable is present and not empty. */
if (mozAppRestart && (strcmp(mozAppRestart, "") != 0)) {
/* Firefox was restarted, use the first time-stamp we've taken as the new
* process startup time. */
ts = sInitOnce.mFirstTimeStamp;
} else {
TimeStamp now = Now();
uint64_t uptime = ComputeProcessUptime();
ts = now - TimeDuration::FromMicroseconds(static_cast<double>(uptime));
if ((ts > sInitOnce.mFirstTimeStamp) || (uptime == 0)) {
ts = sInitOnce.mFirstTimeStamp;
}
}
sInitOnce.mProcessCreation = ts;
}
return sInitOnce.mProcessCreation;
}
void TimeStamp::RecordProcessRestart() {
sInitOnce.mProcessCreation = TimeStamp();
}
MFBT_API TimeStamp TimeStamp::FirstTimeStamp() {
return sInitOnce.mFirstTimeStamp;
}
class TimeStampTests {
// Check that nullity is set/not set correctly.
static_assert(TimeStamp{TimeStampValue{0}}.IsNull());
static_assert(!TimeStamp{TimeStampValue{1}}.IsNull());
// Check that some very basic comparisons work correctly.
static constexpr uint64_t sMidTime = (uint64_t)1 << 63;
static_assert(TimeStampValue{sMidTime + 5} > TimeStampValue{sMidTime - 5});
static_assert(TimeStampValue{sMidTime + 5} >= TimeStampValue{sMidTime - 5});
static_assert(TimeStampValue{sMidTime - 5} < TimeStampValue{sMidTime + 5});
static_assert(TimeStampValue{sMidTime - 5} <= TimeStampValue{sMidTime + 5});
static_assert(TimeStampValue{sMidTime} == TimeStampValue{sMidTime});
static_assert(TimeStampValue{sMidTime} >= TimeStampValue{sMidTime});
static_assert(TimeStampValue{sMidTime} <= TimeStampValue{sMidTime});
static_assert(TimeStampValue{sMidTime - 5} != TimeStampValue{sMidTime + 5});
// Check that comparisons involving very large and very small TimeStampValue's
// work correctly. This may seem excessive, but these asserts would have
// failed in the past due to a comparison such as "a > b" being implemented as
// "<cast to signed 64-bit value>(a - b) > 0". When a-b didn't fit into a
// signed 64-bit value, this would have given an incorrect result.
static_assert(TimeStampValue{UINT64_MAX} > TimeStampValue{1});
static_assert(TimeStampValue{1} < TimeStampValue{UINT64_MAX});
// NOTE/TODO: It would be nice to add some additional tests here that involve
// arithmetic between TimeStamps and TimeDurations (and verifying some of the
// special behaviors in some cases such as not wrapping around below zero) but
// that is not possible right now because those operators are not constexpr.
};
} // namespace mozilla
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