Quelle FileSystemTaskBase.h Sprache: C

/* -*- 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_dom_FileSystemTaskBase_h
#define mozilla_dom_FileSystemTaskBase_h

#include "mozilla/dom/FileSystemRequestParent.h"
#include "mozilla/dom/PFileSystemRequestChild.h"
#include "nsIGlobalObject.h"
#include "nsThreadUtils.h"

namespace mozilla {
class ErrorResult;

namespace dom {

class BlobImpl;
class FileSystemBase;
class FileSystemParams;

/*
* The base class to implement a Task class.
* The file system operations can only be performed in the parent process. In
* order to avoid duplicated code, we used PBackground for child-parent and
* parent-parent communications.
*
* The following diagram illustrates the how a API call from the content page
* starts a task and gets call back results.
*
* The left block is the call sequence inside any process loading content, while
* the right block is the call sequence only inside the parent process.
*
*       Page
*        |
*        | (1)
*  ______|_________________________     |    _________________________________
* |      |                          |   |   |                                 |
* |      |                          |   |   |                                 |
* |      V                          |  IPC  | PBackground thread on           |
* | [new FileSystemTaskChildBase()] |   |   | the parent process              |
* |         |                       |   |   |                                 |
* |         | (2)                   |       |                                 |
* |         V                       |  (3)  |                                 |
* |    [GetRequestParams]------------------->[new FileSystemTaskParentBase()] |
* |                                 |       |          |                      |
* |                                 |   |   |          | (4)   _____________  |
* |                                 |   |   |          |      |             | |
* |                                 |   |   |          |      | I/O Thread  | |
* |                                 |   |   |          |      |             | |
* |                                 |   |   |          ---------> [IOWork]  | |
* |                                 |  IPC  |                 |     |       | |
* |                                 |   |   |                 |     | (5)   | |
* |                                 |   |   |          -------------*       | |
* |                                 |   |   |          |      |_____|_______| |
* |                                 |   |   |          |  __________|_______  |
* |                                 |   |   |          | |          |       | |
* |                                 |   |   |          | | Main     |       | |
* |                                 |   |   |          | | Thread   |       | |
* |                                 |   |   |          | |          V       | |
* |                                 |   |   |          | | [MainThreadWork] | |
* |                                 |  IPC  |          | |   (5.1)  |       | |
* |                                 |   |   |          | |          |       | |
* |                                 |   |   |          |<------------       | |
* |                                 |   |   |          | |__________________| |
* |                                 |   |   |          V                      |
* |                                 |   |   |     [HandleResult]              |
* |                                 |   |   |          |                      |
* |                                 |       |          | (6)                  |
* |                                 |  (7)  |          V                      |
* |   [SetRequestResult]<---------------------[GetRequestResult]              |
* |       |                         |       |                                 |
* |       | (8)                     |   |   |                                 |
* |       V                         |   |   |                                 |
* |[HandlerCallback]                |  IPC  |                                 |
* |_______|_________________________|   |   |_________________________________|
*         |                             |
*         V
*        Page
*
* 1. From the process that is handling the request
* Child/Parent (it can be in any process):
*   (1) Call FileSystem API from content page with JS. Create a task and run.
*   The base constructor [FileSystemTaskChildBase()] of the task should be
*   called.
*   (2) Forward the task to the parent process through the IPC and call
*   [GetRequestParams] to prepare the parameters of the IPC.
* Parent:
*   (3) The parent process receives IPC and handle it in
*   FileystemRequestParent. Get the IPC parameters and create a task to run the
*   IPC task.
*   (4) The task operation will be performed in the member function of
* [IOWork]. A I/O  thread will be created to run that function. If error occurs
*   during the operation, call [SetError] to record the error and then abort.
*   (5) After finishing the task operation, call [HandleResult] to send the
*   result back to the child process though the IPC.
*   (5.1) Optional, we need to run some code in the main-thread.
*   (6) Call [GetRequestResult] request result to prepare the parameters of the
*   IPC. Because the formats of the error result for different task are the
*   same, FileSystemTaskChildBase can handle the error message without
*   interfering.
*   Each task only needs to implement its specific success result preparation
*   function -[GetSuccessRequestResult].
* Child/Parent:
*   (7) The process receives IPC and calls [SetRequestResult] to get the
*   task result. Each task needs to implement its specific success result
*   parsing function [SetSuccessRequestResult] to get the success result.
*   (8) Call [HandlerCallback] to send the task result to the content page.
*/
class FileSystemTaskChildBase : public PFileSystemRequestChild {
  friend class PFileSystemRequestChild;

public:
  NS_INLINE_DECL_REFCOUNTING(FileSystemTaskChildBase, final)

  /*
   * Start the task. It will dispatch all the information to the parent process,
   * PBackground thread. This method must be called from the owning thread.
   */
  void Start();

  /*
   * The error codes are defined in xpcom/base/ErrorList.h and their
   * corresponding error name and message are defined in dom/base/domerr.msg.
   */
  void SetError(const nsresult& aErrorCode);

  FileSystemBase* GetFileSystem() const;

  /*
   * After the task is completed, this function will be called to pass the task
   * result to the content page. This method is called in the owning thread.
   * Override this function to handle the call back to the content page.
   */
  virtual void HandlerCallback() = 0;

  bool HasError() const { return NS_FAILED(mErrorValue); }

protected:
  /*
   * To create a task to handle the page content request.
   */
  FileSystemTaskChildBase(nsIGlobalObject* aGlobalObject,
                          FileSystemBase* aFileSystem);

  virtual ~FileSystemTaskChildBase();

  /*
   * Wrap the task parameter to FileSystemParams for sending it through IPC.
   * It will be called when we need to forward a task from the child process to
   * the parent process. This method runs in the owning thread.
   * @param filesystem The string representation of the file system.
   */
  virtual FileSystemParams GetRequestParams(const nsString& aSerializedDOMPath,
                                            ErrorResult& aRv) const = 0;

  /*
   * Unwrap the IPC message to get the task success result.
   * It will be called when the task is completed successfully and an IPC
   * message is received in the child process and we want to get the task
   * success result. This method runs in the owning thread.
   */
  virtual void SetSuccessRequestResult(const FileSystemResponseValue& aValue,
                                       ErrorResult& aRv) = 0;

  // Overrides PFileSystemRequestChild
  virtual mozilla::ipc::IPCResult Recv__delete__(
      const FileSystemResponseValue& value) final;

  nsresult mErrorValue;
  RefPtr<FileSystemBase> mFileSystem;
  nsCOMPtr<nsIGlobalObject> mGlobalObject;

private:
  /*
   * Unwrap the IPC message to get the task result.
   * It will be called when the task is completed and an IPC message is received
   * in the content process and we want to get the task result. This runs on the
   * owning thread.
   */
  void SetRequestResult(const FileSystemResponseValue& aValue);
};

// This class is the 'alter ego' of FileSystemTaskChildBase in the PBackground
// world.
class FileSystemTaskParentBase : public Runnable {
public:
  FileSystemTaskParentBase()
      : Runnable("FileSystemTaskParentBase"),
        mErrorValue(NS_ERROR_NOT_INITIALIZED) {}

  /*
   * Start the task. This must be called from the PBackground thread only.
   */
  void Start();

  /*
   * The error codes are defined in xpcom/base/ErrorList.h and their
   * corresponding error name and message are defined in dom/base/domerr.msg.
   */
  void SetError(const nsresult& aErrorCode);

  /*
   * The function to perform task operation. It will be run on the I/O
   * thread of the parent process.
   * Overrides this function to define the task operation for individual task.
   */
  virtual nsresult IOWork() = 0;

  // In case `MainThreadNeeded()` returns true, the following method is called.
  virtual nsresult MainThreadWork() {
    MOZ_CRASH("This method should be implemented");
    return NS_OK;
  }

  // If this returns true, after I/O work, we schedule a runnable to the
  // main-thread before resolving the task on the PBackground one.
  virtual bool MainThreadNeeded() const { return false; };

  /*
   * Wrap the task success result to FileSystemResponseValue for sending it
   * through IPC. This method runs in the PBackground thread.
   * It will be called when the task is completed successfully and we need to
   * send the task success result back to the child process.
   */
  virtual FileSystemResponseValue GetSuccessRequestResult(
      ErrorResult& aRv) const = 0;

  /*
   * After finishing the task operation, handle the task result.
   * If it is an IPC task, send back the IPC result. It runs on the PBackground
   * thread.
   */
  void HandleResult();

  bool HasError() const { return NS_FAILED(mErrorValue); }

  NS_IMETHOD
  Run() override;

  virtual nsresult GetTargetPath(nsAString& aPath) const = 0;

private:
  /*
   * Wrap the task result to FileSystemResponseValue for sending it through IPC.
   * It will be called when the task is completed and we need to
   * send the task result back to the content. This runs on the PBackground
   * thread.
   */
  FileSystemResponseValue GetRequestResult() const;

protected:
  /*
   * To create a parent process task delivered from the child process through
   * IPC.
   */
  FileSystemTaskParentBase(FileSystemBase* aFileSystem,
                           const FileSystemParams& aParam,
                           FileSystemRequestParent* aParent);

  virtual ~FileSystemTaskParentBase();

  nsresult mErrorValue;
  RefPtr<FileSystemBase> mFileSystem;
  RefPtr<FileSystemRequestParent> mRequestParent;
  nsCOMPtr<nsIEventTarget> mBackgroundEventTarget;
};

}  // namespace dom
}  // namespace mozilla

#endif  // mozilla_dom_FileSystemTaskBase_h

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