widget/nsBaseAppShell.cpp
author Chris H-C <chutten@mozilla.com>
Mon, 04 Jul 2016 11:16:05 -0400
changeset 312997 df28918fe2361f0b54ca9ce4773a29c4c0675d06
parent 294851 fcc0936b576daa150697671849a191009ca33811
permissions -rw-r--r--
bug 1218576 - Support remote accumulation via JS histograms. r=gfritzsche The JS histograms, too, need to dispatch their accumulations from child to parent. JSHistograms_Add now only supports histograms that are in gHistogramsMap or that were created in the parent process. After bug 1288745, maybe we'll be able to change this to be less convoluted. MozReview-Commit-ID: 3qTH89YKbGP

/* -*- Mode: c++; tab-width: 2; indent-tabs-mode: nil; -*- */
/* 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 "base/message_loop.h"

#include "nsBaseAppShell.h"
#if defined(MOZ_CRASHREPORTER)
#include "nsExceptionHandler.h"
#endif
#include "nsThreadUtils.h"
#include "nsIObserverService.h"
#include "nsServiceManagerUtils.h"
#include "mozilla/Services.h"

// When processing the next thread event, the appshell may process native
// events (if not in performance mode), which can result in suppressing the
// next thread event for at most this many ticks:
#define THREAD_EVENT_STARVATION_LIMIT PR_MillisecondsToInterval(10)

NS_IMPL_ISUPPORTS(nsBaseAppShell, nsIAppShell, nsIThreadObserver, nsIObserver)

nsBaseAppShell::nsBaseAppShell()
  : mSuspendNativeCount(0)
  , mEventloopNestingLevel(0)
  , mBlockedWait(nullptr)
  , mFavorPerf(0)
  , mNativeEventPending(false)
  , mStarvationDelay(0)
  , mSwitchTime(0)
  , mLastNativeEventTime(0)
  , mEventloopNestingState(eEventloopNone)
  , mRunning(false)
  , mExiting(false)
  , mBlockNativeEvent(false)
{
}

nsBaseAppShell::~nsBaseAppShell()
{
}

nsresult
nsBaseAppShell::Init()
{
  // Configure ourselves as an observer for the current thread:

  nsCOMPtr<nsIThreadInternal> threadInt =
      do_QueryInterface(NS_GetCurrentThread());
  NS_ENSURE_STATE(threadInt);

  threadInt->SetObserver(this);

  nsCOMPtr<nsIObserverService> obsSvc =
    mozilla::services::GetObserverService();
  if (obsSvc)
    obsSvc->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
  return NS_OK;
}

// Called by nsAppShell's native event callback
void
nsBaseAppShell::NativeEventCallback()
{
  if (!mNativeEventPending.exchange(false))
    return;

  // If DoProcessNextNativeEvent is on the stack, then we assume that we can
  // just unwind and let nsThread::ProcessNextEvent process the next event.
  // However, if we are called from a nested native event loop (maybe via some
  // plug-in or library function), then go ahead and process Gecko events now.
  if (mEventloopNestingState == eEventloopXPCOM) {
    mEventloopNestingState = eEventloopOther;
    // XXX there is a tiny risk we will never get a new NativeEventCallback,
    // XXX see discussion in bug 389931.
    return;
  }

  // nsBaseAppShell::Run is not being used to pump events, so this may be
  // our only opportunity to process pending gecko events.

  nsIThread *thread = NS_GetCurrentThread();
  bool prevBlockNativeEvent = mBlockNativeEvent;
  if (mEventloopNestingState == eEventloopOther) {
    if (!NS_HasPendingEvents(thread))
      return;
    // We're in a nested native event loop and have some gecko events to
    // process.  While doing that we block processing native events from the
    // appshell - instead, we want to get back to the nested native event
    // loop ASAP (bug 420148).
    mBlockNativeEvent = true;
  }

  IncrementEventloopNestingLevel();
  EventloopNestingState prevVal = mEventloopNestingState;
  NS_ProcessPendingEvents(thread, THREAD_EVENT_STARVATION_LIMIT);
  mProcessedGeckoEvents = true;
  mEventloopNestingState = prevVal;
  mBlockNativeEvent = prevBlockNativeEvent;

  // Continue processing pending events later (we don't want to starve the
  // embedders event loop).
  if (NS_HasPendingEvents(thread))
    DoProcessMoreGeckoEvents();

  DecrementEventloopNestingLevel();
}

// Note, this is currently overidden on windows, see comments in nsAppShell for
// details.
void
nsBaseAppShell::DoProcessMoreGeckoEvents()
{
  OnDispatchedEvent(nullptr);
}


// Main thread via OnProcessNextEvent below
bool
nsBaseAppShell::DoProcessNextNativeEvent(bool mayWait)
{
  // The next native event to be processed may trigger our NativeEventCallback,
  // in which case we do not want it to process any thread events since we'll
  // do that when this function returns.
  //
  // If the next native event is not our NativeEventCallback, then we may end
  // up recursing into this function.
  //
  // However, if the next native event is not our NativeEventCallback, but it
  // results in another native event loop, then our NativeEventCallback could
  // fire and it will see mEventloopNestingState as eEventloopOther.
  //
  EventloopNestingState prevVal = mEventloopNestingState;
  mEventloopNestingState = eEventloopXPCOM;

  IncrementEventloopNestingLevel();
  bool result = ProcessNextNativeEvent(mayWait);
  DecrementEventloopNestingLevel();

  mEventloopNestingState = prevVal;
  return result;
}

//-------------------------------------------------------------------------
// nsIAppShell methods:

NS_IMETHODIMP
nsBaseAppShell::Run(void)
{
  NS_ENSURE_STATE(!mRunning);  // should not call Run twice
  mRunning = true;

  nsIThread *thread = NS_GetCurrentThread();

  MessageLoop::current()->Run();

  NS_ProcessPendingEvents(thread);

  mRunning = false;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::Exit(void)
{
  if (mRunning && !mExiting) {
    MessageLoop::current()->Quit();
  }
  mExiting = true;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::FavorPerformanceHint(bool favorPerfOverStarvation,
                                     uint32_t starvationDelay)
{
  mStarvationDelay = PR_MillisecondsToInterval(starvationDelay);
  if (favorPerfOverStarvation) {
    ++mFavorPerf;
  } else {
    --mFavorPerf;
    mSwitchTime = PR_IntervalNow();
  }
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::SuspendNative()
{
  ++mSuspendNativeCount;
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::ResumeNative()
{
  --mSuspendNativeCount;
  NS_ASSERTION(mSuspendNativeCount >= 0, "Unbalanced call to nsBaseAppShell::ResumeNative!");
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::GetEventloopNestingLevel(uint32_t* aNestingLevelResult)
{
  NS_ENSURE_ARG_POINTER(aNestingLevelResult);

  *aNestingLevelResult = mEventloopNestingLevel;

  return NS_OK;
}

//-------------------------------------------------------------------------
// nsIThreadObserver methods:

// Called from any thread
NS_IMETHODIMP
nsBaseAppShell::OnDispatchedEvent(nsIThreadInternal *thr)
{
  if (mBlockNativeEvent)
    return NS_OK;

  if (mNativeEventPending.exchange(true))
    return NS_OK;

  // Returns on the main thread in NativeEventCallback above
  ScheduleNativeEventCallback();
  return NS_OK;
}

// Called from the main thread
NS_IMETHODIMP
nsBaseAppShell::OnProcessNextEvent(nsIThreadInternal *thr, bool mayWait)
{
  if (mBlockNativeEvent) {
    if (!mayWait)
      return NS_OK;
    // Hmm, we're in a nested native event loop and would like to get
    // back to it ASAP, but it seems a gecko event has caused us to
    // spin up a nested XPCOM event loop (eg. modal window), so we
    // really must start processing native events here again.
    mBlockNativeEvent = false;
    if (NS_HasPendingEvents(thr))
      OnDispatchedEvent(thr); // in case we blocked it earlier
  }

  PRIntervalTime start = PR_IntervalNow();
  PRIntervalTime limit = THREAD_EVENT_STARVATION_LIMIT;

  // Unblock outer nested wait loop (below).
  if (mBlockedWait)
    *mBlockedWait = false;

  bool *oldBlockedWait = mBlockedWait;
  mBlockedWait = &mayWait;

  // When mayWait is true, we need to make sure that there is an event in the
  // thread's event queue before we return.  Otherwise, the thread will block
  // on its event queue waiting for an event.
  bool needEvent = mayWait;
  // Reset prior to invoking DoProcessNextNativeEvent which might cause
  // NativeEventCallback to process gecko events.
  mProcessedGeckoEvents = false;

  if (mFavorPerf <= 0 && start > mSwitchTime + mStarvationDelay) {
    // Favor pending native events
    PRIntervalTime now = start;
    bool keepGoing;
    do {
      mLastNativeEventTime = now;
      keepGoing = DoProcessNextNativeEvent(false);
    } while (keepGoing && ((now = PR_IntervalNow()) - start) < limit);
  } else {
    // Avoid starving native events completely when in performance mode
    if (start - mLastNativeEventTime > limit) {
      mLastNativeEventTime = start;
      DoProcessNextNativeEvent(false);
    }
  }

  while (!NS_HasPendingEvents(thr) && !mProcessedGeckoEvents) {
    // If we have been asked to exit from Run, then we should not wait for
    // events to process.  Note that an inner nested event loop causes
    // 'mayWait' to become false too, through 'mBlockedWait'.
    if (mExiting)
      mayWait = false;

    mLastNativeEventTime = PR_IntervalNow();
    if (!DoProcessNextNativeEvent(mayWait) || !mayWait)
      break;
  }

  mBlockedWait = oldBlockedWait;

  // Make sure that the thread event queue does not block on its monitor, as
  // it normally would do if it did not have any pending events.  To avoid
  // that, we simply insert a dummy event into its queue during shutdown.
  if (needEvent && !mExiting && !NS_HasPendingEvents(thr)) {
    DispatchDummyEvent(thr);
  }

  return NS_OK;
}

bool
nsBaseAppShell::DispatchDummyEvent(nsIThread* aTarget)
{
  NS_ASSERTION(NS_IsMainThread(), "Wrong thread!");

  if (!mDummyEvent)
    mDummyEvent = new mozilla::Runnable();

  return NS_SUCCEEDED(aTarget->Dispatch(mDummyEvent, NS_DISPATCH_NORMAL));
}

void
nsBaseAppShell::IncrementEventloopNestingLevel()
{
  ++mEventloopNestingLevel;
#if defined(MOZ_CRASHREPORTER)
  CrashReporter::SetEventloopNestingLevel(mEventloopNestingLevel);
#endif
}

void
nsBaseAppShell::DecrementEventloopNestingLevel()
{
  --mEventloopNestingLevel;
#if defined(MOZ_CRASHREPORTER)
  CrashReporter::SetEventloopNestingLevel(mEventloopNestingLevel);
#endif
}

// Called from the main thread
NS_IMETHODIMP
nsBaseAppShell::AfterProcessNextEvent(nsIThreadInternal *thr,
                                      bool eventWasProcessed)
{
  return NS_OK;
}

NS_IMETHODIMP
nsBaseAppShell::Observe(nsISupports *subject, const char *topic,
                        const char16_t *data)
{
  NS_ASSERTION(!strcmp(topic, NS_XPCOM_SHUTDOWN_OBSERVER_ID), "oops");
  Exit();
  return NS_OK;
}