gecko-dev/dom/ipc/PreallocatedProcessManager.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 "mozilla/PreallocatedProcessManager.h"
#include "mozilla/ClearOnShutdown.h"
#include "mozilla/Preferences.h"
#include "mozilla/Unused.h"
#include "mozilla/dom/ContentParent.h"
#include "mozilla/dom/ScriptSettings.h"
#include "nsIPropertyBag2.h"
#include "ProcessPriorityManager.h"
#include "nsServiceManagerUtils.h"
#include "nsIXULRuntime.h"

// This number is fairly arbitrary ... the intention is to put off
// launching another app process until the last one has finished
// loading its content, to reduce CPU/memory/IO contention.
#define DEFAULT_ALLOCATE_DELAY 1000

using namespace mozilla::hal;
using namespace mozilla::dom;

namespace mozilla {
/**
 * This singleton class implements the static methods on
 * PreallocatedProcessManager.
 */
class PreallocatedProcessManagerImpl final : public nsIObserver {
 public:
  static PreallocatedProcessManagerImpl* Singleton();

  NS_DECL_ISUPPORTS
  NS_DECL_NSIOBSERVER

  // See comments on PreallocatedProcessManager for these methods.
  void AddBlocker(ContentParent* aParent);
  void RemoveBlocker(ContentParent* aParent);
  already_AddRefed<ContentParent> Take();
  bool Provide(ContentParent* aParent);

 private:
  static mozilla::StaticRefPtr<PreallocatedProcessManagerImpl> sSingleton;
  static uint32_t sPrelaunchDelayMS;

  PreallocatedProcessManagerImpl();
  ~PreallocatedProcessManagerImpl();
  DISALLOW_EVIL_CONSTRUCTORS(PreallocatedProcessManagerImpl);

  void Init();

  bool CanAllocate();
  void AllocateAfterDelay();
  void AllocateOnIdle();
  void AllocateNow();

  void RereadPrefs();
  void Enable();
  void Disable();
  void CloseProcess();

  void ObserveProcessShutdown(nsISupports* aSubject);

  bool mEnabled;
  bool mShutdown;
  bool mLaunchInProgress;
  RefPtr<ContentParent> mPreallocatedProcess;
  nsTHashtable<nsUint64HashKey> mBlockers;

  bool IsEmpty() const { return !mPreallocatedProcess && !mLaunchInProgress; }
};

/* static */
StaticRefPtr<PreallocatedProcessManagerImpl>
    PreallocatedProcessManagerImpl::sSingleton;
/* static */
uint32_t PreallocatedProcessManagerImpl::sPrelaunchDelayMS = 0;

/* static */
PreallocatedProcessManagerImpl* PreallocatedProcessManagerImpl::Singleton() {
  MOZ_ASSERT(NS_IsMainThread());
  if (!sSingleton) {
    sSingleton = new PreallocatedProcessManagerImpl();
    sSingleton->Init();
    ClearOnShutdown(&sSingleton);
  }

  return sSingleton;
}

NS_IMPL_ISUPPORTS(PreallocatedProcessManagerImpl, nsIObserver)

PreallocatedProcessManagerImpl::PreallocatedProcessManagerImpl()
    : mEnabled(false), mShutdown(false), mLaunchInProgress(false) {}

PreallocatedProcessManagerImpl::~PreallocatedProcessManagerImpl() {
  // This shouldn't happen, because the promise callbacks should
  // hold strong references, but let't make absolutely sure:
  MOZ_RELEASE_ASSERT(!mLaunchInProgress);
}

void PreallocatedProcessManagerImpl::Init() {
  Preferences::AddUintVarCache(&sPrelaunchDelayMS,
                               "dom.ipc.processPrelaunch.delayMs",
                               DEFAULT_ALLOCATE_DELAY);
  Preferences::AddStrongObserver(this, "dom.ipc.processPrelaunch.enabled");
  // We have to respect processCount at all time. This is especially important
  // for testing.
  Preferences::AddStrongObserver(this, "dom.ipc.processCount");
  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
  if (os) {
    os->AddObserver(this, "ipc:content-shutdown",
                    /* weakRef = */ false);
    os->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID,
                    /* weakRef = */ false);
    os->AddObserver(this, "profile-change-teardown",
                    /* weakRef = */ false);
  }
  RereadPrefs();
}

NS_IMETHODIMP
PreallocatedProcessManagerImpl::Observe(nsISupports* aSubject,
                                        const char* aTopic,
                                        const char16_t* aData) {
  if (!strcmp("ipc:content-shutdown", aTopic)) {
    ObserveProcessShutdown(aSubject);
  } else if (!strcmp("nsPref:changed", aTopic)) {
    // The only other observer we registered was for our prefs.
    RereadPrefs();
  } else if (!strcmp(NS_XPCOM_SHUTDOWN_OBSERVER_ID, aTopic) ||
             !strcmp("profile-change-teardown", aTopic)) {
    Preferences::RemoveObserver(this, "dom.ipc.processPrelaunch.enabled");
    Preferences::RemoveObserver(this, "dom.ipc.processCount");
    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
    if (os) {
      os->RemoveObserver(this, "ipc:content-shutdown");
      os->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
      os->RemoveObserver(this, "profile-change-teardown");
    }
    // Let's prevent any new preallocated processes from starting. ContentParent
    // will handle the shutdown of the existing process and the
    // mPreallocatedProcess reference will be cleared by the ClearOnShutdown of
    // the manager singleton.
    mShutdown = true;
  } else {
    MOZ_ASSERT(false);
  }

  return NS_OK;
}

void PreallocatedProcessManagerImpl::RereadPrefs() {
  if (mozilla::BrowserTabsRemoteAutostart() &&
      Preferences::GetBool("dom.ipc.processPrelaunch.enabled")) {
    Enable();
  } else {
    Disable();
  }

  if (ContentParent::IsMaxProcessCountReached(
          NS_LITERAL_STRING(DEFAULT_REMOTE_TYPE))) {
    CloseProcess();
  }
}

already_AddRefed<ContentParent> PreallocatedProcessManagerImpl::Take() {
  if (!mEnabled || mShutdown) {
    return nullptr;
  }

  if (mPreallocatedProcess) {
    // The preallocated process is taken. Let's try to start up a new one soon.
    ProcessPriorityManager::SetProcessPriority(mPreallocatedProcess,
                                               PROCESS_PRIORITY_FOREGROUND);
    AllocateOnIdle();
  }

  return mPreallocatedProcess.forget();
}

bool PreallocatedProcessManagerImpl::Provide(ContentParent* aParent) {
  // This will take the already-running process even if there's a
  // launch in progress; if that process hasn't been taken by the
  // time the launch completes, the new process will be shut down.
  if (mEnabled && !mShutdown && !mPreallocatedProcess) {
    mPreallocatedProcess = aParent;
  }

  // We might get a call from both NotifyTabDestroying and NotifyTabDestroyed
  // with the same ContentParent. Returning true here for both calls is
  // important to avoid the cached process to be destroyed.
  return aParent == mPreallocatedProcess;
}

void PreallocatedProcessManagerImpl::Enable() {
  if (mEnabled) {
    return;
  }

  mEnabled = true;
  AllocateAfterDelay();
}

void PreallocatedProcessManagerImpl::AddBlocker(ContentParent* aParent) {
  uint64_t childID = aParent->ChildID();
  MOZ_ASSERT(!mBlockers.Contains(childID));
  mBlockers.PutEntry(childID);
}

void PreallocatedProcessManagerImpl::RemoveBlocker(ContentParent* aParent) {
  uint64_t childID = aParent->ChildID();
  // This used to assert that the blocker existed, but preallocated
  // processes aren't blockers anymore because it's not useful and
  // interferes with async launch, and it's simpler if content
  // processes don't need to remember whether they were preallocated.
  // (And preallocated processes can't AddBlocker when taken, because
  // it's possible for a short-lived process to be recycled through
  // Provide() and Take() before reaching RecvFirstIdle.)
  mBlockers.RemoveEntry(childID);
  if (IsEmpty() && mBlockers.IsEmpty()) {
    AllocateAfterDelay();
  }
}

bool PreallocatedProcessManagerImpl::CanAllocate() {
  return mEnabled && mBlockers.IsEmpty() && IsEmpty() && !mShutdown &&
         !ContentParent::IsMaxProcessCountReached(
             NS_LITERAL_STRING(DEFAULT_REMOTE_TYPE));
}

void PreallocatedProcessManagerImpl::AllocateAfterDelay() {
  if (!mEnabled) {
    return;
  }

  NS_DelayedDispatchToCurrentThread(
      NewRunnableMethod("PreallocatedProcessManagerImpl::AllocateOnIdle", this,
                        &PreallocatedProcessManagerImpl::AllocateOnIdle),
      sPrelaunchDelayMS);
}

void PreallocatedProcessManagerImpl::AllocateOnIdle() {
  if (!mEnabled) {
    return;
  }

  NS_DispatchToCurrentThreadQueue(
      NewRunnableMethod("PreallocatedProcessManagerImpl::AllocateNow", this,
                        &PreallocatedProcessManagerImpl::AllocateNow),
      EventQueuePriority::Idle);
}

void PreallocatedProcessManagerImpl::AllocateNow() {
  if (!CanAllocate()) {
    if (mEnabled && !mShutdown && IsEmpty() && !mBlockers.IsEmpty()) {
      // If it's too early to allocate a process let's retry later.
      AllocateAfterDelay();
    }
    return;
  }

  RefPtr<PreallocatedProcessManagerImpl> self(this);
  mLaunchInProgress = true;

  ContentParent::PreallocateProcess()->Then(
      GetCurrentThreadSerialEventTarget(), __func__,

      [self, this](const RefPtr<ContentParent>& process) {
        mLaunchInProgress = false;
        if (CanAllocate()) {
          mPreallocatedProcess = process;
        } else {
          process->ShutDownProcess(ContentParent::SEND_SHUTDOWN_MESSAGE);
        }
      },

      [self, this](ContentParent::LaunchError err) {
        mLaunchInProgress = false;
      });
}

void PreallocatedProcessManagerImpl::Disable() {
  if (!mEnabled) {
    return;
  }

  mEnabled = false;
  CloseProcess();
}

void PreallocatedProcessManagerImpl::CloseProcess() {
  if (mPreallocatedProcess) {
    mPreallocatedProcess->ShutDownProcess(ContentParent::SEND_SHUTDOWN_MESSAGE);
    mPreallocatedProcess = nullptr;
  }
}

void PreallocatedProcessManagerImpl::ObserveProcessShutdown(
    nsISupports* aSubject) {
  nsCOMPtr<nsIPropertyBag2> props = do_QueryInterface(aSubject);
  NS_ENSURE_TRUE_VOID(props);

  uint64_t childID = CONTENT_PROCESS_ID_UNKNOWN;
  props->GetPropertyAsUint64(NS_LITERAL_STRING("childID"), &childID);
  NS_ENSURE_TRUE_VOID(childID != CONTENT_PROCESS_ID_UNKNOWN);

  if (mPreallocatedProcess && childID == mPreallocatedProcess->ChildID()) {
    mPreallocatedProcess = nullptr;
  }

  mBlockers.RemoveEntry(childID);
}

inline PreallocatedProcessManagerImpl* GetPPMImpl() {
  return PreallocatedProcessManagerImpl::Singleton();
}

/* static */
void PreallocatedProcessManager::AddBlocker(ContentParent* aParent) {
  GetPPMImpl()->AddBlocker(aParent);
}

/* static */
void PreallocatedProcessManager::RemoveBlocker(ContentParent* aParent) {
  GetPPMImpl()->RemoveBlocker(aParent);
}

/* static */
already_AddRefed<ContentParent> PreallocatedProcessManager::Take() {
  return GetPPMImpl()->Take();
}

/* static */
bool PreallocatedProcessManager::Provide(ContentParent* aParent) {
  return GetPPMImpl()->Provide(aParent);
}

}  // namespace mozilla