nsBaseAppShell.cpp

/* -*- 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"
#include "nsExceptionHandler.h"
#include "nsThreadUtils.h"
#include "nsIObserverService.h"
#include "nsServiceManagerUtils.h"
#include "mozilla/Services.h"
#include "nsXULAppAPI.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),
      mProcessedGeckoEvents(false) {}

nsBaseAppShell::~nsBaseAppShell() = default;

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

  if (XRE_UseNativeEventProcessing()) {
    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(); }

// 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() {
  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();  // 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("DummyEvent");

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

void nsBaseAppShell::IncrementEventloopNestingLevel() {
  ++mEventloopNestingLevel;
  CrashReporter::SetEventloopNestingLevel(mEventloopNestingLevel);
}

void nsBaseAppShell::DecrementEventloopNestingLevel() {
  --mEventloopNestingLevel;
  CrashReporter::SetEventloopNestingLevel(mEventloopNestingLevel);
}

// 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;
}