palemoon-dev/platform/widget/nsIdleService.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:expandtab:shiftwidth=2:tabstop=2:
 */
/* 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/. */

#include "nsIdleService.h"
#include "nsString.h"
#include "nsIObserverService.h"
#include "nsIServiceManager.h"
#include "nsDebug.h"
#include "nsCOMArray.h"
#include "nsXULAppAPI.h"
#include "prinrval.h"
#include "mozilla/Logging.h"
#include "prtime.h"
#include "mozilla/dom/ContentChild.h"
#include "mozilla/Services.h"
#include "mozilla/Preferences.h"
#include "mozilla/Telemetry.h"
#include <algorithm>

using namespace mozilla;

// interval in milliseconds between internal idle time requests.
#define MIN_IDLE_POLL_INTERVAL_MSEC (5 * PR_MSEC_PER_SEC) /* 5 sec */

// After the twenty four hour period expires for an idle daily, this is the
// amount of idle time we wait for before actually firing the idle-daily
// event.
#define DAILY_SIGNIFICANT_IDLE_SERVICE_SEC (3 * 60)

// In cases where it's been longer than twenty four hours since the last
// idle-daily, this is the shortend amount of idle time we wait for before
// firing the idle-daily event.
#define DAILY_SHORTENED_IDLE_SERVICE_SEC 60

// Pref for last time (seconds since epoch) daily notification was sent.
#define PREF_LAST_DAILY "idle.lastDailyNotification"

// Number of seconds in a day.
#define SECONDS_PER_DAY 86400

// MAX_DELTA_SEC * 1000 should be less than UINT32_MAX to prevent overflow on
// converting from sec to msec
#define MAX_DELTA_SEC (SECONDS_PER_DAY * 10)

static PRLogModuleInfo *sLog = nullptr;

#define LOG_TAG "GeckoIdleService"

// Use this to find previously added observers in our array:
class IdleListenerComparator
{
public:
  bool Equals(IdleListener a, IdleListener b) const
  {
    return (a.observer == b.observer) &&
           (a.reqIdleTime == b.reqIdleTime);
  }
};

////////////////////////////////////////////////////////////////////////////////
//// nsIdleServiceDaily

NS_IMPL_ISUPPORTS(nsIdleServiceDaily, nsIObserver, nsISupportsWeakReference)

NS_IMETHODIMP
nsIdleServiceDaily::Observe(nsISupports *,
                            const char *aTopic,
                            const char16_t *)
{
  MOZ_LOG(sLog, LogLevel::Debug,
         ("nsIdleServiceDaily: Observe '%s' (%d)",
          aTopic, mShutdownInProgress));

  if (strcmp(aTopic, "profile-after-change") == 0) {
    // We are back. Start sending notifications again.
    mShutdownInProgress = false;
    return NS_OK;
  }

  if (strcmp(aTopic, "xpcom-will-shutdown") == 0 ||
      strcmp(aTopic, "profile-change-teardown") == 0) {
    mShutdownInProgress = true;
  }

  if (mShutdownInProgress || strcmp(aTopic, OBSERVER_TOPIC_ACTIVE) == 0) {
    return NS_OK;
  }
  MOZ_ASSERT(strcmp(aTopic, OBSERVER_TOPIC_IDLE) == 0);

  MOZ_LOG(sLog, LogLevel::Debug,
         ("nsIdleServiceDaily: Notifying idle-daily observers"));

  // Send the idle-daily observer event
  nsCOMPtr<nsIObserverService> observerService =
    mozilla::services::GetObserverService();
  NS_ENSURE_STATE(observerService);
  (void)observerService->NotifyObservers(nullptr,
                                         OBSERVER_TOPIC_IDLE_DAILY,
                                         nullptr);

  // Notify the category observers.
  nsCOMArray<nsIObserver> entries;
  mCategoryObservers.GetEntries(entries);
  for (int32_t i = 0; i < entries.Count(); ++i) {
    (void)entries[i]->Observe(nullptr, OBSERVER_TOPIC_IDLE_DAILY, nullptr);
  }

  // Stop observing idle for today.
  (void)mIdleService->RemoveIdleObserver(this, mIdleDailyTriggerWait);

  // Set the last idle-daily time pref.
  int32_t nowSec = static_cast<int32_t>(PR_Now() / PR_USEC_PER_SEC);
  Preferences::SetInt(PREF_LAST_DAILY, nowSec);

  // Force that to be stored so we don't retrigger twice a day under
  // any circumstances.
  nsIPrefService* prefs = Preferences::GetService();
  if (prefs) {
    prefs->SavePrefFile(nullptr);
  }

  MOZ_LOG(sLog, LogLevel::Debug,
         ("nsIdleServiceDaily: Storing last idle time as %d sec.", nowSec));

  // Note the moment we expect to get the next timer callback
  mExpectedTriggerTime  = PR_Now() + ((PRTime)SECONDS_PER_DAY *
                                      (PRTime)PR_USEC_PER_SEC);

  MOZ_LOG(sLog, LogLevel::Debug,
         ("nsIdleServiceDaily: Restarting daily timer"));

  // Start timer for the next check in one day.
  (void)mTimer->InitWithFuncCallback(DailyCallback,
                                     this,
                                     SECONDS_PER_DAY * PR_MSEC_PER_SEC,
                                     nsITimer::TYPE_ONE_SHOT);

  return NS_OK;
}

nsIdleServiceDaily::nsIdleServiceDaily(nsIIdleService* aIdleService)
  : mIdleService(aIdleService)
  , mTimer(do_CreateInstance(NS_TIMER_CONTRACTID))
  , mCategoryObservers(OBSERVER_TOPIC_IDLE_DAILY)
  , mShutdownInProgress(false)
  , mExpectedTriggerTime(0)
  , mIdleDailyTriggerWait(DAILY_SIGNIFICANT_IDLE_SERVICE_SEC)
{
}

void
nsIdleServiceDaily::Init()
{
  // First check the time of the last idle-daily event notification. If it
  // has been 24 hours or higher, or if we have never sent an idle-daily,
  // get ready to send an idle-daily event. Otherwise set a timer targeted
  // at 24 hours past the last idle-daily we sent.

  int32_t nowSec = static_cast<int32_t>(PR_Now() / PR_USEC_PER_SEC);
  int32_t lastDaily = Preferences::GetInt(PREF_LAST_DAILY, 0);
  if (lastDaily < 0 || lastDaily > nowSec) {
    // The time is bogus, use default.
    lastDaily = 0;
  }
  int32_t secondsSinceLastDaily = nowSec - lastDaily;

  MOZ_LOG(sLog, LogLevel::Debug,
         ("nsIdleServiceDaily: Init: seconds since last daily: %d",
          secondsSinceLastDaily));

  // If it has been twenty four hours or more or if we have never sent an
  // idle-daily event get ready to send it during the next idle period.
  if (secondsSinceLastDaily > SECONDS_PER_DAY) {
    // Check for a "long wait", e.g. 48-hours or more.
    bool hasBeenLongWait = (lastDaily &&
                            (secondsSinceLastDaily > (SECONDS_PER_DAY * 2)));

    MOZ_LOG(sLog, LogLevel::Debug,
           ("nsIdleServiceDaily: has been long wait? %d",
            hasBeenLongWait));

    // StageIdleDaily sets up a wait for the user to become idle and then
    // sends the idle-daily event.
    StageIdleDaily(hasBeenLongWait);
  } else {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("nsIdleServiceDaily: Setting timer a day from now"));

    // According to our last idle-daily pref, the last idle-daily was fired
    // less then 24 hours ago. Set a wait for the amount of time remaining.
    int32_t milliSecLeftUntilDaily = (SECONDS_PER_DAY - secondsSinceLastDaily)
      * PR_MSEC_PER_SEC;

    MOZ_LOG(sLog, LogLevel::Debug,
           ("nsIdleServiceDaily: Seconds till next timeout: %d",
            (SECONDS_PER_DAY - secondsSinceLastDaily)));

    // Mark the time at which we expect this to fire. On systems with faulty
    // timers, we need to be able to cross check that the timer fired at the
    // expected time.
    mExpectedTriggerTime  = PR_Now() +
      (milliSecLeftUntilDaily * PR_USEC_PER_MSEC);

    (void)mTimer->InitWithFuncCallback(DailyCallback,
                                       this,
                                       milliSecLeftUntilDaily,
                                       nsITimer::TYPE_ONE_SHOT);
  }

  // Register for when we should terminate/pause
  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
  if (obs) {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("nsIdleServiceDaily: Registering for system event observers."));
    obs->AddObserver(this, "xpcom-will-shutdown", true);
    obs->AddObserver(this, "profile-change-teardown", true);
    obs->AddObserver(this, "profile-after-change", true);
  }
}

nsIdleServiceDaily::~nsIdleServiceDaily()
{
  if (mTimer) {
    mTimer->Cancel();
    mTimer = nullptr;
  }
}


void
nsIdleServiceDaily::StageIdleDaily(bool aHasBeenLongWait)
{
  NS_ASSERTION(mIdleService, "No idle service available?");
  MOZ_LOG(sLog, LogLevel::Debug,
          ("nsIdleServiceDaily: Registering Idle observer callback "
           "(short wait requested? %d)", aHasBeenLongWait));

  mIdleDailyTriggerWait = (aHasBeenLongWait ?
                             DAILY_SHORTENED_IDLE_SERVICE_SEC :
                             DAILY_SIGNIFICANT_IDLE_SERVICE_SEC);
  (void)mIdleService->AddIdleObserver(this, mIdleDailyTriggerWait);
}

// static
void
nsIdleServiceDaily::DailyCallback(nsITimer* aTimer, void* aClosure)
{
  MOZ_LOG(sLog, LogLevel::Debug,
          ("nsIdleServiceDaily: DailyCallback running"));

  nsIdleServiceDaily* self = static_cast<nsIdleServiceDaily*>(aClosure);

  // Check to be sure the timer didn't fire early.
  PRTime now = PR_Now();
  if (self->mExpectedTriggerTime && now < self->mExpectedTriggerTime) {
    // Timer returned early, reschedule to the appropriate time.
    PRTime delayTime = self->mExpectedTriggerTime - now;

    // Add 10 ms to ensure we don't undershoot, and never get a "0" timer.
    delayTime += 10 * PR_USEC_PER_MSEC;

    MOZ_LOG(sLog, LogLevel::Debug, ("nsIdleServiceDaily: DailyCallback resetting timer to %lld msec",
                        delayTime / PR_USEC_PER_MSEC));

    (void)self->mTimer->InitWithFuncCallback(DailyCallback,
                                             self,
                                             delayTime / PR_USEC_PER_MSEC,
                                             nsITimer::TYPE_ONE_SHOT);
    return;
  }

  // Register for a short term wait for idle event. When this fires we fire
  // our idle-daily event.
  self->StageIdleDaily(false);
}


/**
 * The idle services goal is to notify subscribers when a certain time has
 * passed since the last user interaction with the system.
 *
 * On some platforms this is defined as the last time user events reached this
 * application, on other platforms it is a system wide thing - the preferred
 * implementation is to use the system idle time, rather than the application
 * idle time, as the things depending on the idle service are likely to use
 * significant resources (network, disk, memory, cpu, etc.).
 *
 * When the idle service needs to use the system wide idle timer, it typically
 * needs to poll the idle time value by the means of a timer.  It needs to
 * poll fast when it is in active idle mode (when it has a listener in the idle
 * mode) as it needs to detect if the user is active in other applications.
 *
 * When the service is waiting for the first listener to become idle, or when
 * it is only monitoring application idle time, it only needs to have the timer
 * expire at the time the next listener goes idle.
 *
 * The core state of the service is determined by:
 *
 * - A list of listeners.
 *
 * - A boolean that tells if any listeners are in idle mode.
 *
 * - A delta value that indicates when, measured from the last non-idle time,
 *   the next listener should switch to idle mode.
 *
 * - An absolute time of the last time idle mode was detected (this is used to
 *   judge if we have been out of idle mode since the last invocation of the
 *   service.
 *
 * There are four entry points into the system:
 *
 * - A new listener is registered.
 *
 * - An existing listener is deregistered.
 *
 * - User interaction is detected.
 *
 * - The timer expires.
 *
 * When a new listener is added its idle timeout, is compared with the next idle
 * timeout, and if lower, that time is stored as the new timeout, and the timer
 * is reconfigured to ensure a timeout around the time the new listener should
 * timeout.
 *
 * If the next idle time is above the idle time requested by the new listener
 * it won't be informed until the timer expires, this is to avoid recursive
 * behavior and to simplify the code.  In this case the timer will be set to
 * about 10 ms.
 *
 * When an existing listener is deregistered, it is just removed from the list
 * of active listeners, we don't stop the timer, we just let it expire.
 *
 * When user interaction is detected, either because it was directly detected or
 * because we polled the system timer and found it to be unexpected low, then we
 * check the flag that tells us if any listeners are in idle mode, if there are
 * they are removed from idle mode and told so, and we reset our state
 * caculating the next timeout and restart the timer if needed.
 *
 * ---- Build in logic
 *
 * In order to avoid restarting the timer endlessly, the timer function has
 * logic that will only restart the timer, if the requested timeout is before
 * the current timeout.
 *
 */


////////////////////////////////////////////////////////////////////////////////
//// nsIdleService

namespace { 
nsIdleService* gIdleService;
} // namespace

already_AddRefed<nsIdleService>
nsIdleService::GetInstance()
{
  RefPtr<nsIdleService> instance(gIdleService);
  return instance.forget();
}

nsIdleService::nsIdleService() : mCurrentlySetToTimeoutAt(TimeStamp()),
                                 mIdleObserverCount(0),
                                 mDeltaToNextIdleSwitchInS(MAX_DELTA_SEC),
                                 mLastUserInteraction(TimeStamp::Now())
{
  if (sLog == nullptr)
    sLog = PR_NewLogModule("idleService");
  MOZ_ASSERT(!gIdleService);
  gIdleService = this;
  if (XRE_IsParentProcess()) {
    mDailyIdle = new nsIdleServiceDaily(this);
    mDailyIdle->Init();
  }
}

nsIdleService::~nsIdleService()
{
  if(mTimer) {
    mTimer->Cancel();
  }


  MOZ_ASSERT(gIdleService == this);
  gIdleService = nullptr;
}

NS_IMPL_ISUPPORTS(nsIdleService, nsIIdleService, nsIIdleServiceInternal)

NS_IMETHODIMP
nsIdleService::AddIdleObserver(nsIObserver* aObserver, uint32_t aIdleTimeInS)
{
  NS_ENSURE_ARG_POINTER(aObserver);
  // We don't accept idle time at 0, and we can't handle idle time that are too
  // high either - no more than ~136 years.
  NS_ENSURE_ARG_RANGE(aIdleTimeInS, 1, (UINT32_MAX / 10) - 1);

  if (XRE_IsContentProcess()) {
    dom::ContentChild* cpc = dom::ContentChild::GetSingleton();
    cpc->AddIdleObserver(aObserver, aIdleTimeInS);
    return NS_OK;
  }

  MOZ_LOG(sLog, LogLevel::Debug,
       ("idleService: Register idle observer %p for %d seconds",
        aObserver, aIdleTimeInS));

  // Put the time + observer in a struct we can keep:
  IdleListener listener(aObserver, aIdleTimeInS);

  if (!mArrayListeners.AppendElement(listener)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  // Create our timer callback if it's not there already.
  if (!mTimer) {
    nsresult rv;
    mTimer = do_CreateInstance(NS_TIMER_CONTRACTID, &rv);
    NS_ENSURE_SUCCESS(rv, rv);
  }

  // Check if the newly added observer has a smaller wait time than what we
  // are waiting for now.
  if (mDeltaToNextIdleSwitchInS > aIdleTimeInS) {
    // If it is, then this is the next to move to idle (at this point we
    // don't care if it should have switched already).
    MOZ_LOG(sLog, LogLevel::Debug,
          ("idleService: Register: adjusting next switch from %d to %d seconds",
           mDeltaToNextIdleSwitchInS, aIdleTimeInS));

    mDeltaToNextIdleSwitchInS = aIdleTimeInS;
  }

  // Ensure timer is running.
  ReconfigureTimer();

  return NS_OK;
}

NS_IMETHODIMP
nsIdleService::RemoveIdleObserver(nsIObserver* aObserver, uint32_t aTimeInS)
{

  NS_ENSURE_ARG_POINTER(aObserver);
  NS_ENSURE_ARG(aTimeInS);

  if (XRE_IsContentProcess()) {
    dom::ContentChild* cpc = dom::ContentChild::GetSingleton();
    cpc->RemoveIdleObserver(aObserver, aTimeInS);
    return NS_OK;
  }

  IdleListener listener(aObserver, aTimeInS);

  // Find the entry and remove it, if it was the last entry, we just let the
  // existing timer run to completion (there might be a new registration in a
  // little while.
  IdleListenerComparator c;
  nsTArray<IdleListener>::index_type listenerIndex = mArrayListeners.IndexOf(listener, 0, c);
  if (listenerIndex != mArrayListeners.NoIndex) {
    if (mArrayListeners.ElementAt(listenerIndex).isIdle)
      mIdleObserverCount--;
    mArrayListeners.RemoveElementAt(listenerIndex);
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: Remove observer %p (%d seconds), %d remain idle",
            aObserver, aTimeInS, mIdleObserverCount));

    return NS_OK;
  }

  // If we get here, we haven't removed anything:
  MOZ_LOG(sLog, LogLevel::Warning, 
         ("idleService: Failed to remove idle observer %p (%d seconds)",
          aObserver, aTimeInS));

  return NS_ERROR_FAILURE;
}

NS_IMETHODIMP
nsIdleService::ResetIdleTimeOut(uint32_t idleDeltaInMS)
{
  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: Reset idle timeout (last interaction %u msec)",
          idleDeltaInMS));

  // Store the time
  mLastUserInteraction = TimeStamp::Now() -
                         TimeDuration::FromMilliseconds(idleDeltaInMS);

  // If no one is idle, then we are done, any existing timers can keep running.
  if (mIdleObserverCount == 0) {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: Reset idle timeout: no idle observers"));
    return NS_OK;
  }

  // Mark all idle services as non-idle, and calculate the next idle timeout.
  nsCOMArray<nsIObserver> notifyList;
  mDeltaToNextIdleSwitchInS = MAX_DELTA_SEC;

  // Loop through all listeners, and find any that have detected idle.
  for (uint32_t i = 0; i < mArrayListeners.Length(); i++) {
    IdleListener& curListener = mArrayListeners.ElementAt(i);

    // If the listener was idle, then he shouldn't be any longer.
    if (curListener.isIdle) {
      notifyList.AppendObject(curListener.observer);
      curListener.isIdle = false;
    }

    // Check if the listener is the next one to timeout.
    mDeltaToNextIdleSwitchInS = std::min(mDeltaToNextIdleSwitchInS,
                                       curListener.reqIdleTime);
  }

  // When we are done, then we wont have anyone idle.
  mIdleObserverCount = 0;

  // Restart the idle timer, and do so before anyone can delay us.
  ReconfigureTimer();

  int32_t numberOfPendingNotifications = notifyList.Count();

  // Bail if nothing to do.
  if (!numberOfPendingNotifications) {
    return NS_OK;
  }

  // Now send "active" events to all, if any should have timed out already,
  // then they will be reawaken by the timer that is already running.

  // We need a text string to send with any state change events.
  nsAutoString timeStr;

  timeStr.AppendInt((int32_t)(idleDeltaInMS / PR_MSEC_PER_SEC));

  // Send the "non-idle" events.
  while (numberOfPendingNotifications--) {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: Reset idle timeout: tell observer %p user is back",
            notifyList[numberOfPendingNotifications]));

    notifyList[numberOfPendingNotifications]->Observe(this,
                                                      OBSERVER_TOPIC_ACTIVE,
                                                      timeStr.get());
  }
  return NS_OK;
}

NS_IMETHODIMP
nsIdleService::GetIdleTime(uint32_t* idleTime)
{
  // Check sanity of in parameter.
  if (!idleTime) {
    return NS_ERROR_NULL_POINTER;
  }

  // Polled idle time in ms.
  uint32_t polledIdleTimeMS;

  bool polledIdleTimeIsValid = PollIdleTime(&polledIdleTimeMS);

  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: Get idle time: polled %u msec, valid = %d",
          polledIdleTimeMS, polledIdleTimeIsValid));
  
  // timeSinceReset is in milliseconds.
  TimeDuration timeSinceReset = TimeStamp::Now() - mLastUserInteraction;
  uint32_t timeSinceResetInMS = timeSinceReset.ToMilliseconds();

  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: Get idle time: time since reset %u msec",
          timeSinceResetInMS));

  // If we did't get pulled data, return the time since last idle reset.
  if (!polledIdleTimeIsValid) {
    // We need to convert to ms before returning the time.
    *idleTime = timeSinceResetInMS;
    return NS_OK;
  }

  // Otherwise return the shortest time detected (in ms).
  *idleTime = std::min(timeSinceResetInMS, polledIdleTimeMS);

  return NS_OK;
}


bool
nsIdleService::PollIdleTime(uint32_t* /*aIdleTime*/)
{
  // Default behavior is not to have the ability to poll an idle time.
  return false;
}

bool
nsIdleService::UsePollMode()
{
  uint32_t dummy;
  return PollIdleTime(&dummy);
}

void
nsIdleService::StaticIdleTimerCallback(nsITimer* aTimer, void* aClosure)
{
  static_cast<nsIdleService*>(aClosure)->IdleTimerCallback();
}

void
nsIdleService::IdleTimerCallback(void)
{
  // Remember that we no longer have a timer running.
  mCurrentlySetToTimeoutAt = TimeStamp();

  // Find the last detected idle time.
  uint32_t lastIdleTimeInMS = static_cast<uint32_t>((TimeStamp::Now() -
                              mLastUserInteraction).ToMilliseconds());
  // Get the current idle time.
  uint32_t currentIdleTimeInMS;

  if (NS_FAILED(GetIdleTime(&currentIdleTimeInMS))) {
    MOZ_LOG(sLog, LogLevel::Info,
           ("idleService: Idle timer callback: failed to get idle time"));

    return;
  }

  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: Idle timer callback: current idle time %u msec",
          currentIdleTimeInMS));

  // Check if we have had some user interaction we didn't handle previously
  // we do the calculation in ms to lessen the chance for rounding errors to
  // trigger wrong results.
  if (lastIdleTimeInMS > currentIdleTimeInMS)
  {
    // We had user activity, so handle that part first (to ensure the listeners
    // don't risk getting an non-idle after they get a new idle indication.
    ResetIdleTimeOut(currentIdleTimeInMS);

    // NOTE: We can't bail here, as we might have something already timed out.
  }

  // Find the idle time in S.
  uint32_t currentIdleTimeInS = currentIdleTimeInMS / PR_MSEC_PER_SEC;

  // Restart timer and bail if no-one are expected to be in idle
  if (mDeltaToNextIdleSwitchInS > currentIdleTimeInS) {
    // If we didn't expect anyone to be idle, then just re-start the timer.
    ReconfigureTimer();
    return;
  }

  // We need to initialise the time to the next idle switch.
  mDeltaToNextIdleSwitchInS = MAX_DELTA_SEC;

  // Create list of observers that should be notified.
  nsCOMArray<nsIObserver> notifyList;

  for (uint32_t i = 0; i < mArrayListeners.Length(); i++) {
    IdleListener& curListener = mArrayListeners.ElementAt(i);

    // We are only interested in items, that are not in the idle state.
    if (!curListener.isIdle) {
      // If they have an idle time smaller than the actual idle time.
      if (curListener.reqIdleTime <= currentIdleTimeInS) {
        // Then add the listener to the list of listeners that should be
        // notified.
        notifyList.AppendObject(curListener.observer);
        // This listener is now idle.
        curListener.isIdle = true;
        // Remember we have someone idle.
        mIdleObserverCount++;
      } else {
        // Listeners that are not timed out yet are candidates for timing out.
        mDeltaToNextIdleSwitchInS = std::min(mDeltaToNextIdleSwitchInS,
                                           curListener.reqIdleTime);
      }
    }
  }

  // Restart the timer before any notifications that could slow us down are
  // done.
  ReconfigureTimer();

  int32_t numberOfPendingNotifications = notifyList.Count();

  // Bail if nothing to do.
  if (!numberOfPendingNotifications) {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: **** Idle timer callback: no observers to message."));
    return;
  }

  // We need a text string to send with any state change events.
  nsAutoString timeStr;
  timeStr.AppendInt(currentIdleTimeInS);

  // Notify all listeners that just timed out.
  while (numberOfPendingNotifications--) {
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: **** Idle timer callback: tell observer %p user is idle",
            notifyList[numberOfPendingNotifications]));

    notifyList[numberOfPendingNotifications]->Observe(this,
                                                      OBSERVER_TOPIC_IDLE,
                                                      timeStr.get());
  }
}

void
nsIdleService::SetTimerExpiryIfBefore(TimeStamp aNextTimeout)
{
  TimeDuration nextTimeoutDuration = aNextTimeout - TimeStamp::Now();

  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: SetTimerExpiryIfBefore: next timeout %0.f msec from now",
          nextTimeoutDuration.ToMilliseconds()));

  // Bail if we don't have a timer service.
  if (!mTimer) {
    return;
  }

  // If the new timeout is before the old one or we don't have a timer running,
  // then restart the timer.
  if (mCurrentlySetToTimeoutAt.IsNull() ||
      mCurrentlySetToTimeoutAt > aNextTimeout) {

    mCurrentlySetToTimeoutAt = aNextTimeout;

    // Stop the current timer (it's ok to try'n stop it, even it isn't running).
    mTimer->Cancel();

    // Check that the timeout is actually in the future, otherwise make it so.
    TimeStamp currentTime = TimeStamp::Now();
    if (currentTime > mCurrentlySetToTimeoutAt) {
      mCurrentlySetToTimeoutAt = currentTime;
    }

    // Add 10 ms to ensure we don't undershoot, and never get a "0" timer.
    mCurrentlySetToTimeoutAt += TimeDuration::FromMilliseconds(10);

    TimeDuration deltaTime = mCurrentlySetToTimeoutAt - currentTime;
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: IdleService reset timer expiry to %0.f msec from now",
            deltaTime.ToMilliseconds()));

    // Start the timer
    mTimer->InitWithFuncCallback(StaticIdleTimerCallback,
                                 this,
                                 deltaTime.ToMilliseconds(),
                                 nsITimer::TYPE_ONE_SHOT);

  }
}

void
nsIdleService::ReconfigureTimer(void)
{
  // Check if either someone is idle, or someone will become idle.
  if ((mIdleObserverCount == 0) && MAX_DELTA_SEC == mDeltaToNextIdleSwitchInS) {
    // If not, just let any existing timers run to completion
    // And bail out.
    MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: ReconfigureTimer: no idle or waiting observers"));

    return;
  }

  // Find the next timeout value, assuming we are not polling.

  // We need to store the current time, so we don't get artifacts from the time
  // ticking while we are processing.
  TimeStamp curTime = TimeStamp::Now();

  TimeStamp nextTimeoutAt = mLastUserInteraction +
                            TimeDuration::FromSeconds(mDeltaToNextIdleSwitchInS);

  TimeDuration nextTimeoutDuration = nextTimeoutAt - curTime;

  MOZ_LOG(sLog, LogLevel::Debug,
         ("idleService: next timeout %0.f msec from now",
          nextTimeoutDuration.ToMilliseconds()));

  // Check if we should correct the timeout time because we should poll before.
  if ((mIdleObserverCount > 0) && UsePollMode()) {
    TimeStamp pollTimeout =
        curTime + TimeDuration::FromMilliseconds(MIN_IDLE_POLL_INTERVAL_MSEC);

    if (nextTimeoutAt > pollTimeout) {
      MOZ_LOG(sLog, LogLevel::Debug,
           ("idleService: idle observers, reducing timeout to %lu msec from now",
            MIN_IDLE_POLL_INTERVAL_MSEC));

      nextTimeoutAt = pollTimeout;
    }
  }

  SetTimerExpiryIfBefore(nextTimeoutAt);
}