1 files changed, 115 insertions, 0 deletions
diff --git a/mozglue/misc/TimeStamp.cpp b/mozglue/misc/TimeStamp.cpp
new file mode 100644
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+++ b/mozglue/misc/TimeStamp.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/. */
+
+/*
+ * 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