tor-browser

The Tor Browser
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TimeStamp.cpp (4362B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 /*
      8 * Implementation of the OS-independent methods of the TimeStamp class
      9 */
     10 
     11 #include "mozilla/TimeStamp.h"
     12 #include "mozilla/Uptime.h"
     13 #include <string.h>
     14 #include <stdlib.h>
     15 
     16 namespace mozilla {
     17 
     18 /**
     19 * Wrapper class used to initialize static data used by the TimeStamp class
     20 */
     21 struct TimeStampInitialization {
     22  /**
     23   * First timestamp taken when the class static initializers are run. This
     24   * timestamp is used to sanitize timestamps coming from different sources.
     25   */
     26  TimeStamp mFirstTimeStamp;
     27 
     28  /**
     29   * Timestamp representing the time when the process was created. This field
     30   * is populated lazily the first time this information is required and is
     31   * replaced every time the process is restarted.
     32   */
     33  TimeStamp mProcessCreation;
     34 
     35  TimeStampInitialization() {
     36    TimeStamp::Startup();
     37    mFirstTimeStamp = TimeStamp::Now();
     38    // On Windows < 10, initializing the uptime requires `mFirstTimeStamp` to be
     39    // valid.
     40    mozilla::InitializeUptime();
     41  }
     42 
     43  ~TimeStampInitialization() { TimeStamp::Shutdown(); }
     44 };
     45 
     46 MOZ_RUNINIT static TimeStampInitialization sInitOnce;
     47 
     48 MFBT_API TimeStamp TimeStamp::ProcessCreation() {
     49  if (sInitOnce.mProcessCreation.IsNull()) {
     50    char* mozAppRestart = getenv("MOZ_APP_RESTART");
     51    TimeStamp ts;
     52 
     53    /* When calling PR_SetEnv() with an empty value the existing variable may
     54     * be unset or set to the empty string depending on the underlying platform
     55     * thus we have to check if the variable is present and not empty. */
     56    if (mozAppRestart && (strcmp(mozAppRestart, "") != 0)) {
     57      /* Firefox was restarted, use the first time-stamp we've taken as the new
     58       * process startup time. */
     59      ts = sInitOnce.mFirstTimeStamp;
     60    } else {
     61      TimeStamp now = Now();
     62      uint64_t uptime = ComputeProcessUptime();
     63 
     64      ts = now - TimeDuration::FromMicroseconds(static_cast<double>(uptime));
     65 
     66      if ((ts > sInitOnce.mFirstTimeStamp) || (uptime == 0)) {
     67        ts = sInitOnce.mFirstTimeStamp;
     68      }
     69    }
     70 
     71    sInitOnce.mProcessCreation = ts;
     72  }
     73 
     74  return sInitOnce.mProcessCreation;
     75 }
     76 
     77 void TimeStamp::RecordProcessRestart() {
     78  sInitOnce.mProcessCreation = TimeStamp();
     79 }
     80 
     81 MFBT_API TimeStamp TimeStamp::FirstTimeStamp() {
     82  return sInitOnce.mFirstTimeStamp;
     83 }
     84 
     85 class TimeStampTests {
     86  // Check that nullity is set/not set correctly.
     87  static_assert(TimeStamp{TimeStampValue{0}}.IsNull());
     88  static_assert(!TimeStamp{TimeStampValue{1}}.IsNull());
     89 
     90  // Check that some very basic comparisons work correctly.
     91  static constexpr uint64_t sMidTime = (uint64_t)1 << 63;
     92  static_assert(TimeStampValue{sMidTime + 5} > TimeStampValue{sMidTime - 5});
     93  static_assert(TimeStampValue{sMidTime + 5} >= TimeStampValue{sMidTime - 5});
     94  static_assert(TimeStampValue{sMidTime - 5} < TimeStampValue{sMidTime + 5});
     95  static_assert(TimeStampValue{sMidTime - 5} <= TimeStampValue{sMidTime + 5});
     96  static_assert(TimeStampValue{sMidTime} == TimeStampValue{sMidTime});
     97  static_assert(TimeStampValue{sMidTime} >= TimeStampValue{sMidTime});
     98  static_assert(TimeStampValue{sMidTime} <= TimeStampValue{sMidTime});
     99  static_assert(TimeStampValue{sMidTime - 5} != TimeStampValue{sMidTime + 5});
    100 
    101  // Check that comparisons involving very large and very small TimeStampValue's
    102  // work correctly. This may seem excessive, but these asserts would have
    103  // failed in the past due to a comparison such as "a > b" being implemented as
    104  // "<cast to signed 64-bit value>(a - b) > 0". When a-b didn't fit into a
    105  // signed 64-bit value, this would have given an incorrect result.
    106  static_assert(TimeStampValue{UINT64_MAX} > TimeStampValue{1});
    107  static_assert(TimeStampValue{1} < TimeStampValue{UINT64_MAX});
    108 
    109  // NOTE/TODO: It would be nice to add some additional tests here that involve
    110  // arithmetic between TimeStamps and TimeDurations (and verifying some of the
    111  // special behaviors in some cases such as not wrapping around below zero) but
    112  // that is not possible right now because those operators are not constexpr.
    113 };
    114 
    115 }  // namespace mozilla