gecko-dev/xpcom/threads/ThreadEventTarget.cpp

/* -*- 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/. */

#include "ThreadEventTarget.h"
#include "mozilla/ThreadEventQueue.h"

#include "LeakRefPtr.h"
#include "nsComponentManagerUtils.h"
#include "nsThreadManager.h"
#include "nsThreadSyncDispatch.h"
#include "nsThreadUtils.h"
#include "nsXPCOMPrivate.h" // for gXPCOMThreadsShutDown

#ifdef MOZ_TASK_TRACER
#include "GeckoTaskTracer.h"
#include "TracedTaskCommon.h"
using namespace mozilla::tasktracer;
#endif

using namespace mozilla;

namespace {

class DelayedRunnable : public Runnable,
                        public nsITimerCallback
{
public:
  DelayedRunnable(already_AddRefed<nsIEventTarget> aTarget,
                  already_AddRefed<nsIRunnable> aRunnable,
                  uint32_t aDelay)
    : mozilla::Runnable("DelayedRunnable")
    , mTarget(aTarget)
    , mWrappedRunnable(aRunnable)
    , mDelayedFrom(TimeStamp::NowLoRes())
    , mDelay(aDelay)
  { }

  NS_DECL_ISUPPORTS_INHERITED

  nsresult Init()
  {
    nsresult rv;
    mTimer = do_CreateInstance(NS_TIMER_CONTRACTID, &rv);
    NS_ENSURE_SUCCESS(rv, rv);

    MOZ_ASSERT(mTimer);
    rv = mTimer->SetTarget(mTarget);

    NS_ENSURE_SUCCESS(rv, rv);
    return mTimer->InitWithCallback(this, mDelay, nsITimer::TYPE_ONE_SHOT);
  }

  nsresult DoRun()
  {
    nsCOMPtr<nsIRunnable> r = mWrappedRunnable.forget();
    return r->Run();
  }

  NS_IMETHOD Run() override
  {
    // Already ran?
    if (!mWrappedRunnable) {
      return NS_OK;
    }

    // Are we too early?
    if ((TimeStamp::NowLoRes() - mDelayedFrom).ToMilliseconds() < mDelay) {
      return NS_OK; // Let the nsITimer run us.
    }

    mTimer->Cancel();
    return DoRun();
  }

  NS_IMETHOD Notify(nsITimer* aTimer) override
  {
    // If we already ran, the timer should have been canceled.
    MOZ_ASSERT(mWrappedRunnable);
    MOZ_ASSERT(aTimer == mTimer);

    return DoRun();
  }

private:
  ~DelayedRunnable() {}

  nsCOMPtr<nsIEventTarget> mTarget;
  nsCOMPtr<nsIRunnable> mWrappedRunnable;
  nsCOMPtr<nsITimer> mTimer;
  TimeStamp mDelayedFrom;
  uint32_t mDelay;
};

NS_IMPL_ISUPPORTS_INHERITED(DelayedRunnable, Runnable, nsITimerCallback)

} // anonymous namespace

ThreadEventTarget::ThreadEventTarget(ThreadTargetSink* aSink,
                                     bool aIsMainThread)
  : mSink(aSink)
  , mIsMainThread(aIsMainThread)
{
  mVirtualThread = GetCurrentVirtualThread();
}

void
ThreadEventTarget::SetCurrentThread()
{
  mVirtualThread = GetCurrentVirtualThread();
}

NS_IMPL_ISUPPORTS(ThreadEventTarget,
                  nsIEventTarget,
                  nsISerialEventTarget)

NS_IMETHODIMP
ThreadEventTarget::DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags)
{
  return Dispatch(do_AddRef(aRunnable), aFlags);
}

NS_IMETHODIMP
ThreadEventTarget::Dispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags)
{
  // We want to leak the reference when we fail to dispatch it, so that
  // we won't release the event in a wrong thread.
  LeakRefPtr<nsIRunnable> event(Move(aEvent));
  if (NS_WARN_IF(!event)) {
    return NS_ERROR_INVALID_ARG;
  }

  if (gXPCOMThreadsShutDown && !mIsMainThread) {
    NS_ASSERTION(false, "Failed Dispatch after xpcom-shutdown-threads");
    return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
  }

#ifdef MOZ_TASK_TRACER
  nsCOMPtr<nsIRunnable> tracedRunnable = CreateTracedRunnable(event.take());
  (static_cast<TracedRunnable*>(tracedRunnable.get()))->DispatchTask();
  // XXX tracedRunnable will always leaked when we fail to disptch.
  event = tracedRunnable.forget();
#endif

  if (aFlags & DISPATCH_SYNC) {
    nsCOMPtr<nsIEventTarget> current = GetCurrentThreadEventTarget();
    if (NS_WARN_IF(!current)) {
      return NS_ERROR_NOT_AVAILABLE;
    }

    // XXX we should be able to do something better here... we should
    //     be able to monitor the slot occupied by this event and use
    //     that to tell us when the event has been processed.

    RefPtr<nsThreadSyncDispatch> wrapper =
      new nsThreadSyncDispatch(current.forget(), event.take());
    bool success = mSink->PutEvent(do_AddRef(wrapper), EventPriority::Normal); // hold a ref
    if (!success) {
      // PutEvent leaked the wrapper runnable object on failure, so we
      // explicitly release this object once for that. Note that this
      // object will be released again soon because it exits the scope.
      wrapper.get()->Release();
      return NS_ERROR_UNEXPECTED;
    }

    // Allows waiting; ensure no locks are held that would deadlock us!
    SpinEventLoopUntil([&, wrapper]() -> bool {
        return !wrapper->IsPending();
      });

    return NS_OK;
  }

  NS_ASSERTION(aFlags == NS_DISPATCH_NORMAL ||
               aFlags == NS_DISPATCH_AT_END, "unexpected dispatch flags");
  if (!mSink->PutEvent(event.take(), EventPriority::Normal)) {
    return NS_ERROR_UNEXPECTED;
  }
  return NS_OK;
}

NS_IMETHODIMP
ThreadEventTarget::DelayedDispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aDelayMs)
{
  NS_ENSURE_TRUE(!!aDelayMs, NS_ERROR_UNEXPECTED);

  RefPtr<DelayedRunnable> r = new DelayedRunnable(do_AddRef(this),
                                                  Move(aEvent),
                                                  aDelayMs);
  nsresult rv = r->Init();
  NS_ENSURE_SUCCESS(rv, rv);

  return Dispatch(r.forget(), NS_DISPATCH_NORMAL);
}

NS_IMETHODIMP
ThreadEventTarget::IsOnCurrentThread(bool* aIsOnCurrentThread)
{
  *aIsOnCurrentThread = IsOnCurrentThread();
  return NS_OK;
}

NS_IMETHODIMP_(bool)
ThreadEventTarget::IsOnCurrentThreadInfallible()
{
  // Rely on mVirtualThread being correct.
  MOZ_CRASH("IsOnCurrentThreadInfallible should never be called on nsIThread");
}