gecko-dev/xpcom/threads/nsIThreadInternal.idl

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 "nsIThread.idl"

interface nsIThreadObserver;
interface nsIThreadEventFilter;

/**
 * The XPCOM thread object implements this interface, which allows a consumer
 * to observe dispatch activity on the thread.
 */
[scriptable, uuid(504e9e1f-70e1-4f33-a785-5840a4680414)]
interface nsIThreadInternal : nsIThread
{
  /**
   * Get/set the current thread observer (may be null).  This attribute may be
   * read from any thread, but must only be set on the thread corresponding to
   * this thread object.  The observer will be released on the thread
   * corresponding to this thread object after all other events have been
   * processed during a call to Shutdown.
   */
  attribute nsIThreadObserver observer;

  /**
   * The current recursion depth, 0 when no events are running, 1 when a single
   * event is running, and higher when nested events are running. Must only be
   * called on the target thread.
   */
  readonly attribute unsigned long recursionDepth;

  /**
   * Add an observer that will *only* receive onProcessNextEvent and
   * afterProcessNextEvent callbacks. Always called on the target thread, and
   * the implementation does not have to be threadsafe. Order of callbacks is
   * not guaranteed (i.e. afterProcessNextEvent may be called first depending on
   * whether or not the observer is added in a nested loop). Holds a strong ref.
   */
  void addObserver(in nsIThreadObserver observer);

  /**
   * Remove an observer added via the addObserver call. Once removed the
   * observer will never be called again by the thread.
   */
  void removeObserver(in nsIThreadObserver observer);
};

/**
 * This interface provides the observer with hooks to implement a layered
 * event queue.  For example, it is possible to overlay processing events
 * for a GUI toolkit on top of the events for a thread:
 *
 *   var NativeQueue;
 *   Observer = {
 *     onDispatchedEvent(thread) {
 *       NativeQueue.signal();
 *     }
 *     onProcessNextEvent(thread, mayWait, recursionDepth) {
 *       if (NativeQueue.hasNextEvent())
 *         NativeQueue.processNextEvent();
 *       while (mayWait && !thread.hasPendingEvent()) {
 *         NativeQueue.wait();
 *         NativeQueue.processNextEvent();
 *       }
 *     }
 *   };
 *
 * NOTE: The implementation of this interface must be threadsafe.
 * 
 * NOTE: It is valid to change the thread's observer during a call to an
 *       observer method.
 *
 * NOTE: Will be split into two interfaces soon: one for onProcessNextEvent and
 *       afterProcessNextEvent, then another that inherits the first and adds
 *       onDispatchedEvent.
 */
[scriptable, uuid(81D0B509-F198-4417-8020-08EB4271491F)]
interface nsIThreadObserver : nsISupports
{
  /**
   * This method is called after an event has been dispatched to the thread.
   * This method may be called from any thread. 
   *
   * @param thread
   *   The thread where the event is being dispatched.
   */
  void onDispatchedEvent(in nsIThreadInternal thread);

  /**
   * This method is called (from nsIThread::ProcessNextEvent) before an event
   * is processed.  This method is only called on the target thread.
   *
   * @param thread
   *   The thread being asked to process another event.
   * @param mayWait
   *   Indicates whether or not the method is allowed to block the calling
   *   thread.  For example, this parameter is false during thread shutdown.
   * @param recursionDepth
   *   Indicates the number of calls to ProcessNextEvent on the call stack in
   *   addition to the current call.
   */
  void onProcessNextEvent(in nsIThreadInternal thread, in boolean mayWait,
                          in unsigned long recursionDepth);

  /**
   * This method is called (from nsIThread::ProcessNextEvent) after an event
   * is processed.  This method is only called on the target thread.
   *
   * @param thread
   *   The thread that processed another event.
   * @param recursionDepth
   *   Indicates the number of calls to ProcessNextEvent on the call stack in
   *   addition to the current call.
   */
  void afterProcessNextEvent(in nsIThreadInternal thread,
                             in unsigned long recursionDepth);
};