dom/ipc/PreallocatedProcessManager.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_PreallocatedProcessManager_h
   8 #define mozilla_PreallocatedProcessManager_h
   9
  10 #include "base/basictypes.h"
  11 #include "mozilla/dom/UniqueContentParentKeepAlive.h"
  12 #include "nsStringFwd.h"
  13
  14 namespace mozilla {
  15
  16 /**
  17  * This class manages a ContentParent that it starts up ahead of any particular
  18  * need.  You can then call Take() to get this process and use it.  Since we
  19  * already started it up, it should be ready for use faster than if you'd
  20  * created the process when you needed it.
  21  *
  22  * This class watches the dom.ipc.processPrelaunch.enabled pref.  If it changes
  23  * from false to true, it preallocates a process.  If it changes from true to
  24  * false, it kills the preallocated process, if any.
  25  *
  26  * We don't expect this pref to flip between true and false in production, but
  27  * flipping the pref is important for tests.
  28  */
  29 class PreallocatedProcessManagerImpl;
  30
  31 class PreallocatedProcessManager final {
  32   using ContentParent = mozilla::dom::ContentParent;
  33   using UniqueContentParentKeepAlive =
  34       mozilla::dom::UniqueContentParentKeepAlive;
  35
  36  public:
  37   static PreallocatedProcessManagerImpl* GetPPMImpl();
  38
  39   static bool Enabled();
  40
  41   /**
  42    * Before first paint we don't want to allocate any processes in the
  43    * background. To avoid that, the PreallocatedProcessManager won't start up
  44    * any processes while there is a blocker active.
  45    */
  46   static void AddBlocker(const nsACString& aRemoteType, ContentParent* aParent);
  47   static void RemoveBlocker(const nsACString& aRemoteType,
  48                             ContentParent* aParent);
  49
  50   /**
  51    * Take a preallocated process, if we have one. If we don't have a
  52    * preallocated process to return, this returns null.
  53    *
  54    * If we use a preallocated process, it will schedule the start of
  55    * another on Idle (AllocateOnIdle()).
  56    */
  57   static UniqueContentParentKeepAlive Take(const nsACString& aRemoteType);
  58
  59   /**
  60    * Note that a process was shut down, and should no longer be tracked as a
  61    * preallocated process.
  62    */
  63   static void Erase(ContentParent* aParent);
  64
  65  private:
  66   PreallocatedProcessManager();
  67   DISALLOW_EVIL_CONSTRUCTORS(PreallocatedProcessManager);
  68 };
  69
  70 }  // namespace mozilla
  71
  72 #endif  // defined mozilla_PreallocatedProcessManager_h