gecko-dev/xpcom/threads/nsThreadPool.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 "nsCOMArray.h"
#include "nsIClassInfoImpl.h"
#include "ThreadDelay.h"
#include "nsThreadPool.h"
#include "nsThreadManager.h"
#include "nsThread.h"
#include "nsMemory.h"
#include "nsAutoPtr.h"
#include "prinrval.h"
#include "mozilla/Logging.h"
#include "mozilla/SystemGroup.h"
#include "nsThreadSyncDispatch.h"

using namespace mozilla;

static LazyLogModule sThreadPoolLog("nsThreadPool");
#ifdef LOG
#undef LOG
#endif
#define LOG(args) MOZ_LOG(sThreadPoolLog, mozilla::LogLevel::Debug, args)

// DESIGN:
//  o  Allocate anonymous threads.
//  o  Use nsThreadPool::Run as the main routine for each thread.
//  o  Each thread waits on the event queue's monitor, checking for
//     pending events and rescheduling itself as an idle thread.

#define DEFAULT_THREAD_LIMIT 4
#define DEFAULT_IDLE_THREAD_LIMIT 1
#define DEFAULT_IDLE_THREAD_TIMEOUT PR_SecondsToInterval(60)

NS_IMPL_ADDREF(nsThreadPool)
NS_IMPL_RELEASE(nsThreadPool)
NS_IMPL_CLASSINFO(nsThreadPool, nullptr, nsIClassInfo::THREADSAFE,
                  NS_THREADPOOL_CID)
NS_IMPL_QUERY_INTERFACE_CI(nsThreadPool, nsIThreadPool, nsIEventTarget,
                           nsIRunnable)
NS_IMPL_CI_INTERFACE_GETTER(nsThreadPool, nsIThreadPool, nsIEventTarget)

nsThreadPool::nsThreadPool()
  : mMutex("[nsThreadPool.mMutex]")
  , mEventsAvailable(mMutex, "[nsThreadPool.mEventsAvailable]")
  , mThreadLimit(DEFAULT_THREAD_LIMIT)
  , mIdleThreadLimit(DEFAULT_IDLE_THREAD_LIMIT)
  , mIdleThreadTimeout(DEFAULT_IDLE_THREAD_TIMEOUT)
  , mIdleCount(0)
  , mStackSize(nsIThreadManager::DEFAULT_STACK_SIZE)
  , mShutdown(false)
{
  LOG(("THRD-P(%p) constructor!!!\n", this));
}

nsThreadPool::~nsThreadPool()
{
  // Threads keep a reference to the nsThreadPool until they return from Run()
  // after removing themselves from mThreads.
  MOZ_ASSERT(mThreads.IsEmpty());
}

nsresult
nsThreadPool::PutEvent(nsIRunnable* aEvent)
{
  nsCOMPtr<nsIRunnable> event(aEvent);
  return PutEvent(event.forget(), 0);
}

nsresult
nsThreadPool::PutEvent(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags)
{
  // Avoid spawning a new thread while holding the event queue lock...

  bool spawnThread = false;
  uint32_t stackSize = 0;
  {
    MutexAutoLock lock(mMutex);

    if (NS_WARN_IF(mShutdown)) {
      return NS_ERROR_NOT_AVAILABLE;
    }
    LOG(("THRD-P(%p) put [%d %d %d]\n", this, mIdleCount, mThreads.Count(),
         mThreadLimit));
    MOZ_ASSERT(mIdleCount <= (uint32_t)mThreads.Count(), "oops");

    // Make sure we have a thread to service this event.
    if (mThreads.Count() < (int32_t)mThreadLimit &&
        !(aFlags & NS_DISPATCH_AT_END) &&
        // Spawn a new thread if we don't have enough idle threads to serve
        // pending events immediately.
        mEvents.Count(lock) >= mIdleCount) {
      spawnThread = true;
    }

    mEvents.PutEvent(std::move(aEvent), EventPriority::Normal, lock);
    mEventsAvailable.Notify();
    stackSize = mStackSize;
  }

  auto delay = MakeScopeExit([&]() {
      // Delay to encourage the receiving task to run before we do work.
      DelayForChaosMode(ChaosFeature::TaskDispatching, 1000);
  });

  LOG(("THRD-P(%p) put [spawn=%d]\n", this, spawnThread));
  if (!spawnThread) {
    return NS_OK;
  }

  nsCOMPtr<nsIThread> thread;
  nsresult rv = NS_NewNamedThread(mThreadNaming.GetNextThreadName(mName),
                                  getter_AddRefs(thread), nullptr, stackSize);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return NS_ERROR_UNEXPECTED;
  }

  bool killThread = false;
  {
    MutexAutoLock lock(mMutex);
    if (mThreads.Count() < (int32_t)mThreadLimit) {
      mThreads.AppendObject(thread);
    } else {
      killThread = true;  // okay, we don't need this thread anymore
    }
  }
  LOG(("THRD-P(%p) put [%p kill=%d]\n", this, thread.get(), killThread));
  if (killThread) {
    // We never dispatched any events to the thread, so we can shut it down
    // asynchronously without worrying about anything.
    ShutdownThread(thread);
  } else {
    thread->Dispatch(this, NS_DISPATCH_NORMAL);
  }

  return NS_OK;
}

void
nsThreadPool::ShutdownThread(nsIThread* aThread)
{
  LOG(("THRD-P(%p) shutdown async [%p]\n", this, aThread));

  // This is either called by a threadpool thread that is out of work, or
  // a thread that attempted to create a threadpool thread and raced in
  // such a way that the newly created thread is no longer necessary.
  // In the first case, we must go to another thread to shut aThread down
  // (because it is the current thread).  In the second case, we cannot
  // synchronously shut down the current thread (because then Dispatch() would
  // spin the event loop, and that could blow up the world), and asynchronous
  // shutdown requires this thread have an event loop (and it may not, see bug
  // 10204784).  The simplest way to cover all cases is to asynchronously
  // shutdown aThread from the main thread.
  SystemGroup::Dispatch(TaskCategory::Other, NewRunnableMethod(
        "nsIThread::AsyncShutdown", aThread, &nsIThread::AsyncShutdown));
}

NS_IMETHODIMP
nsThreadPool::Run()
{
  LOG(("THRD-P(%p) enter %s\n", this, mName.BeginReading()));

  nsCOMPtr<nsIThread> current;
  nsThreadManager::get().GetCurrentThread(getter_AddRefs(current));

  bool shutdownThreadOnExit = false;
  bool exitThread = false;
  bool wasIdle = false;
  TimeStamp idleSince;

  nsCOMPtr<nsIThreadPoolListener> listener;
  {
    MutexAutoLock lock(mMutex);
    listener = mListener;
  }

  if (listener) {
    listener->OnThreadCreated();
  }

  do {
    nsCOMPtr<nsIRunnable> event;
    {
      MutexAutoLock lock(mMutex);

      event = mEvents.GetEvent(nullptr, lock);
      if (!event) {
        TimeStamp now = TimeStamp::Now();
        TimeDuration timeout = TimeDuration::FromMilliseconds(mIdleThreadTimeout);

        // If we are shutting down, then don't keep any idle threads
        if (mShutdown) {
          exitThread = true;
        } else {
          if (wasIdle) {
            // if too many idle threads or idle for too long, then bail.
            if (mIdleCount > mIdleThreadLimit ||
                (mIdleThreadTimeout != UINT32_MAX && (now - idleSince) >= timeout)) {
              exitThread = true;
            }
          } else {
            // if would be too many idle threads...
            if (mIdleCount == mIdleThreadLimit) {
              exitThread = true;
            } else {
              ++mIdleCount;
              idleSince = now;
              wasIdle = true;
            }
          }
        }

        if (exitThread) {
          if (wasIdle) {
            --mIdleCount;
          }
          shutdownThreadOnExit = mThreads.RemoveObject(current);
        } else {
          AUTO_PROFILER_LABEL("nsThreadPool::Run::Wait", IDLE);

          TimeDuration delta = timeout - (now - idleSince);
          LOG(("THRD-P(%p) %s waiting [%f]\n", this, mName.BeginReading(),
               delta.ToMilliseconds()));
          mEventsAvailable.Wait(delta);
          LOG(("THRD-P(%p) done waiting\n", this));
        }
      } else if (wasIdle) {
        wasIdle = false;
        --mIdleCount;
      }
    }
    if (event) {
      LOG(("THRD-P(%p) %s running [%p]\n", this, mName.BeginReading(), event.get()));

      // Delay event processing to encourage whoever dispatched this event
      // to run.
      DelayForChaosMode(ChaosFeature::TaskRunning, 1000);

      event->Run();
    }
  } while (!exitThread);

  if (listener) {
    listener->OnThreadShuttingDown();
  }

  if (shutdownThreadOnExit) {
    ShutdownThread(current);
  }

  LOG(("THRD-P(%p) leave\n", this));
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::DispatchFromScript(nsIRunnable* aEvent, uint32_t aFlags)
{
  nsCOMPtr<nsIRunnable> event(aEvent);
  return Dispatch(event.forget(), aFlags);
}

NS_IMETHODIMP
nsThreadPool::Dispatch(already_AddRefed<nsIRunnable> aEvent, uint32_t aFlags)
{
  LOG(("THRD-P(%p) dispatch [%p %x]\n", this, /* XXX aEvent*/ nullptr, aFlags));

  if (NS_WARN_IF(mShutdown)) {
    return NS_ERROR_NOT_AVAILABLE;
  }

  if (aFlags & DISPATCH_SYNC) {
    nsCOMPtr<nsIThread> thread;
    nsThreadManager::get().GetCurrentThread(getter_AddRefs(thread));
    if (NS_WARN_IF(!thread)) {
      return NS_ERROR_NOT_AVAILABLE;
    }

    RefPtr<nsThreadSyncDispatch> wrapper =
      new nsThreadSyncDispatch(thread.forget(), std::move(aEvent));
    PutEvent(wrapper);

    SpinEventLoopUntil([&, wrapper]() -> bool {
        return !wrapper->IsPending();
      });
  } else {
    NS_ASSERTION(aFlags == NS_DISPATCH_NORMAL ||
                 aFlags == NS_DISPATCH_AT_END, "unexpected dispatch flags");
    PutEvent(std::move(aEvent), aFlags);
  }
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t)
{
  return NS_ERROR_NOT_IMPLEMENTED;
}

NS_IMETHODIMP_(bool)
nsThreadPool::IsOnCurrentThreadInfallible()
{
  MutexAutoLock lock(mMutex);

  nsIThread* thread = NS_GetCurrentThread();
  for (uint32_t i = 0; i < static_cast<uint32_t>(mThreads.Count()); ++i) {
    if (mThreads[i] == thread) {
      return true;
    }
  }
  return false;
}

NS_IMETHODIMP
nsThreadPool::IsOnCurrentThread(bool* aResult)
{
  MutexAutoLock lock(mMutex);
  if (NS_WARN_IF(mShutdown)) {
    return NS_ERROR_NOT_AVAILABLE;
  }

  nsIThread* thread = NS_GetCurrentThread();
  for (uint32_t i = 0; i < static_cast<uint32_t>(mThreads.Count()); ++i) {
    if (mThreads[i] == thread) {
      *aResult = true;
      return NS_OK;
    }
  }
  *aResult = false;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::Shutdown()
{
  nsCOMArray<nsIThread> threads;
  nsCOMPtr<nsIThreadPoolListener> listener;
  {
    MutexAutoLock lock(mMutex);
    mShutdown = true;
    mEventsAvailable.NotifyAll();

    threads.AppendObjects(mThreads);
    mThreads.Clear();

    // Swap in a null listener so that we release the listener at the end of
    // this method. The listener will be kept alive as long as the other threads
    // that were created when it was set.
    mListener.swap(listener);
  }

  // It's important that we shutdown the threads while outside the event queue
  // monitor.  Otherwise, we could end up dead-locking.

  for (int32_t i = 0; i < threads.Count(); ++i) {
    threads[i]->Shutdown();
  }

  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::GetThreadLimit(uint32_t* aValue)
{
  *aValue = mThreadLimit;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetThreadLimit(uint32_t aValue)
{
  MutexAutoLock lock(mMutex);
  LOG(("THRD-P(%p) thread limit [%u]\n", this, aValue));
  mThreadLimit = aValue;
  if (mIdleThreadLimit > mThreadLimit) {
    mIdleThreadLimit = mThreadLimit;
  }

  if (static_cast<uint32_t>(mThreads.Count()) > mThreadLimit) {
    mEventsAvailable.NotifyAll();  // wake up threads so they observe this change
  }
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::GetIdleThreadLimit(uint32_t* aValue)
{
  *aValue = mIdleThreadLimit;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetIdleThreadLimit(uint32_t aValue)
{
  MutexAutoLock lock(mMutex);
  LOG(("THRD-P(%p) idle thread limit [%u]\n", this, aValue));
  mIdleThreadLimit = aValue;
  if (mIdleThreadLimit > mThreadLimit) {
    mIdleThreadLimit = mThreadLimit;
  }

  // Do we need to kill some idle threads?
  if (mIdleCount > mIdleThreadLimit) {
    mEventsAvailable.NotifyAll();  // wake up threads so they observe this change
  }
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::GetIdleThreadTimeout(uint32_t* aValue)
{
  *aValue = mIdleThreadTimeout;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetIdleThreadTimeout(uint32_t aValue)
{
  MutexAutoLock lock(mMutex);
  uint32_t oldTimeout = mIdleThreadTimeout;
  mIdleThreadTimeout = aValue;

  // Do we need to notify any idle threads that their sleep time has shortened?
  if (mIdleThreadTimeout < oldTimeout && mIdleCount > 0) {
    mEventsAvailable.NotifyAll();  // wake up threads so they observe this change
  }
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::GetThreadStackSize(uint32_t* aValue)
{
  MutexAutoLock lock(mMutex);
  *aValue = mStackSize;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetThreadStackSize(uint32_t aValue)
{
  MutexAutoLock lock(mMutex);
  mStackSize = aValue;
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::GetListener(nsIThreadPoolListener** aListener)
{
  MutexAutoLock lock(mMutex);
  NS_IF_ADDREF(*aListener = mListener);
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetListener(nsIThreadPoolListener* aListener)
{
  nsCOMPtr<nsIThreadPoolListener> swappedListener(aListener);
  {
    MutexAutoLock lock(mMutex);
    mListener.swap(swappedListener);
  }
  return NS_OK;
}

NS_IMETHODIMP
nsThreadPool::SetName(const nsACString& aName)
{
  {
    MutexAutoLock lock(mMutex);
    if (mThreads.Count()) {
      return NS_ERROR_NOT_AVAILABLE;
    }
  }

  mName = aName;
  return NS_OK;
}