dom/ipc/PreallocatedProcessManager.h
author Kartikaya Gupta <kgupta@mozilla.com>
Mon, 06 May 2019 22:14:40 +0000
changeset 531641 7748746bf2feda8edd0cabfdaff88b7faf059ad5
parent 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1548568 - Cleanup to remove unused guid parameter in callback. r=botond Differential Revision: https://phabricator.services.mozilla.com/D29688

/* -*- 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/. */

#ifndef mozilla_PreallocatedProcessManager_h
#define mozilla_PreallocatedProcessManager_h

#include "base/basictypes.h"
#include "mozilla/AlreadyAddRefed.h"

namespace mozilla {
namespace dom {
class ContentParent;
}  // namespace dom

/**
 * This class manages a ContentParent that it starts up ahead of any particular
 * need.  You can then call Take() to get this process and use it.  Since we
 * already started it up, it should be ready for use faster than if you'd
 * created the process when you needed it.
 *
 * This class watches the dom.ipc.processPrelaunch.enabled pref.  If it changes
 * from false to true, it preallocates a process.  If it changes from true to
 * false, it kills the preallocated process, if any.
 *
 * We don't expect this pref to flip between true and false in production, but
 * flipping the pref is important for tests.
 */
class PreallocatedProcessManager final {
  typedef mozilla::dom::ContentParent ContentParent;

 public:
  /**
   * Before first paint we don't want to allocate any processes in the
   * background. To avoid that, the PreallocatedProcessManager won't start up
   * any processes while there is a blocker active.
   */
  static void AddBlocker(ContentParent* aParent);
  static void RemoveBlocker(ContentParent* aParent);

  /**
   * Take the preallocated process, if we have one.  If we don't have one, this
   * returns null.
   *
   * If you call Take() twice in a row, the second call is guaranteed to return
   * null.
   *
   * After you Take() the preallocated process, you need to call one of the
   * Allocate* functions (or change the dom.ipc.processPrelaunch pref from
   * false to true) before we'll create a new process.
   */
  static already_AddRefed<ContentParent> Take();

  static bool Provide(ContentParent* aParent);

 private:
  PreallocatedProcessManager();
  DISALLOW_EVIL_CONSTRUCTORS(PreallocatedProcessManager);
};

}  // namespace mozilla

#endif  // defined mozilla_PreallocatedProcessManager_h