path: root/xpcom/threads/nsIEventTarget.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 "nsISupports.idl"
#include "nsIRunnable.idl"
%{C++
#include "nsCOMPtr.h"
#include "mozilla/AlreadyAddRefed.h"
#include "mozilla/Atomics.h"

class nsITargetShutdownTask;
%}

native alreadyAddRefed_nsIRunnable(already_AddRefed<nsIRunnable>);
[ptr] native nsITargetShutdownTask(nsITargetShutdownTask);

[builtinclass, scriptable, uuid(a03b8b63-af8b-4164-b0e5-c41e8b2b7cfa)]
interface nsIEventTarget : nsISupports
{
  /* until we can get rid of all uses, keep the non-alreadyAddRefed<> version */
%{C++
    nsresult Dispatch(nsIRunnable* aEvent, uint32_t aFlags) {
      return Dispatch(nsCOMPtr<nsIRunnable>(aEvent).forget(), aFlags);
    }
%}

  /**
   * This flag specifies the default mode of event dispatch, whereby the event
   * is simply queued for later processing.  When this flag is specified,
   * dispatch returns immediately after the event is queued.
   */
  const unsigned long DISPATCH_NORMAL = 0;

  /**
   * This flag specifies the synchronous mode of event dispatch, in which the
   * dispatch method does not return until the event has been processed.
   *
   * NOTE: passing this flag to dispatch may have the side-effect of causing
   * other events on the current thread to be processed while waiting for the
   * given event to be processed.
   */
  const unsigned long DISPATCH_SYNC = 1;

  /**
   * This flag specifies that the dispatch is occurring from a running event
   * that was dispatched to the same event target, and that event is about to
   * finish.
   *
   * A thread pool can use this as an optimization hint to not spin up
   * another thread, since the current thread is about to become idle.
   *
   * These events are always async.
   */
  const unsigned long DISPATCH_AT_END = 2;

  /**
   * This flag specifies that the dispatched event may block the thread on
   * which it executes, usually by doing some sort of I/O.  This information
   * may be used by the event target to execute the job on a thread
   * specifically dedicated to doing I/O, leaving other threads available for
   * CPU-intensive work.
   */
  const unsigned long DISPATCH_EVENT_MAY_BLOCK = 4;

  /**
   * This flag specifies that the dispatched event should be delivered to the
   * target thread even if the thread has been configured to block dispatching
   * of runnables. This is generally done for threads which have their own
   * internal event loop, such as thread pools or the timer thread, and will not
   * service runnables dispatched to them until shutdown.
   */
  const unsigned long DISPATCH_IGNORE_BLOCK_DISPATCH = 8;

  /**
   * IsOnCurrentThread() should return true if events dispatched to this target
   * can possibly run on the current thread, and false otherwise. In the case
   * of an nsIEventTarget for a thread pool, it should return true on all
   * threads in the pool. In the case of a non-thread nsIEventTarget such as
   * ThrottledEventQueue, it should return true on the thread where events are
   * expected to be processed, even if no events from the queue are actually
   * being processed right now.
   *
   * When called on an nsISerialEventTarget, IsOnCurrentThread can be used to
   * ensure that no other thread has "ownership" of the event target. As such,
   * it's useful for asserting that an object is only used on a particular
   * thread. IsOnCurrentThread can't guarantee that the current event has been
   * dispatched through a particular event target.
   *
   * The infallible version of IsOnCurrentThread() is optimized to avoid a
   * virtual call for non-thread event targets. Thread targets should set
   * mThread to their virtual PRThread. Non-thread targets should leave
   * mThread null and implement IsOnCurrentThreadInfallible() to
   * return the correct answer.
   *
   * The fallible version of IsOnCurrentThread may return errors, such as during
   * shutdown. If it does not return an error, it should return the same result
   * as the infallible version. The infallible method should return the correct
   * result regardless of whether the fallible method returns an error.
   */
  %{C++
public:
  // Infallible. Defined in nsThreadUtils.cpp. Delegates to
  // IsOnCurrentThreadInfallible when mThread is null.
  bool IsOnCurrentThread();

protected:
  mozilla::Atomic<PRThread*> mThread;

  nsIEventTarget() : mThread(nullptr) {}
  %}
  // Note that this method is protected.  We define it through IDL, rather than
  // in a %{C++ block, to ensure that the correct method indices are recorded
  // for XPConnect purposes.
  [noscript,notxpcom] boolean isOnCurrentThreadInfallible();
  %{C++
public:
  %}

  // Fallible version of IsOnCurrentThread.
  boolean isOnCurrentThread();

  /**
   * Dispatch an event to this event target.  This function may be called from
   * any thread, and it may be called re-entrantly.
   *
   * @param event
   *   The alreadyAddRefed<> event to dispatch.
   *   NOTE that the event will be leaked if it fails to dispatch.
   * @param flags
   *   The flags modifying event dispatch.  The flags are described in detail
   *   below.
   *
   * @throws NS_ERROR_INVALID_ARG
   *   Indicates that event is null.
   * @throws NS_ERROR_UNEXPECTED
   *   Indicates that the thread is shutting down and has finished processing
   * events, so this event would never run and has not been dispatched.
   */
  [noscript, binaryname(Dispatch)] void dispatchFromC(in alreadyAddRefed_nsIRunnable event,
                                                      [default(DISPATCH_NORMAL)] in unsigned long flags);
  /**
   * Version of Dispatch to expose to JS, which doesn't require an alreadyAddRefed<>
   * (it will be converted to that internally)
   *
   * @param event
   *   The (raw) event to dispatch.
   * @param flags
   *   The flags modifying event dispatch.  The flags are described in detail
   *   below.
   *
   * @throws NS_ERROR_INVALID_ARG
   *   Indicates that event is null.
   * @throws NS_ERROR_UNEXPECTED
   *   Indicates that the thread is shutting down and has finished processing
   * events, so this event would never run and has not been dispatched.
   */
  [binaryname(DispatchFromScript)] void dispatch(in nsIRunnable event, in unsigned long flags);
  /**
   * Dispatch an event to this event target, but do not run it before delay
   * milliseconds have passed.  This function may be called from any thread.
   *
   * @param event
   *   The alreadyAddrefed<> event to dispatch.
   * @param delay
   *   The delay (in ms) before running the event.  If event does not rise to
   *   the top of the event queue before the delay has passed, it will be set
   *   aside to execute once the delay has passed.  Otherwise, it will be
   *   executed immediately.
   *
   * @throws NS_ERROR_INVALID_ARG
   *   Indicates that event is null.
   * @throws NS_ERROR_UNEXPECTED
   *   Indicates that the thread is shutting down and has finished processing
   * events, so this event would never run and has not been dispatched, or
   * that delay is zero.
   */
  [noscript] void delayedDispatch(in alreadyAddRefed_nsIRunnable event, in unsigned long delay);

  /**
   * Register an task to be run on this event target when it begins shutting
   * down.  Shutdown tasks may be run in any order, and this function may be
   * called from any thread.
   *
   * The event target may or may not continue accepting events during or after
   * the shutdown task. The precise behaviour here depends on the event target.
   *
   * @param task
   *   The task to be registered to the target thread.
   *   NOTE that unlike `dispatch`, this will not leak the task if it fails.
   *
   * @throws NS_ERROR_INVALID_ARG
   *   Indicates that task is null.
   * @throws NS_ERROR_NOT_IMPLEMENTED
   *   Indicates that this event target doesn't support shutdown tasks.
   * @throws NS_ERROR_UNEXPECTED
   *   Indicates that the thread is already shutting down, and no longer
   *   accepting events.
   */
  [noscript] void registerShutdownTask(in nsITargetShutdownTask task);

  /**
   * Unregisters an task previously registered with registerShutdownTask.  This
   * function may be called from any thread.
   *
   * @param task
   *   The task previously registered with registerShutdownTask
   *
   * @throws NS_ERROR_INVALID_ARG
   *   Indicates that task is null.
   * @throws NS_ERROR_NOT_IMPLEMENTED
   *   Indicates that this event target doesn't support shutdown tasks.
   * @throws NS_ERROR_UNEXPECTED
   *   Indicates that the thread is already shutting down, and no longer
   *   accepting events, or that the shutdown task cannot be found.
   */
  [noscript] void unregisterShutdownTask(in nsITargetShutdownTask task);
};

%{C++
// convenient aliases:
#define NS_DISPATCH_NORMAL nsIEventTarget::DISPATCH_NORMAL
#define NS_DISPATCH_SYNC   nsIEventTarget::DISPATCH_SYNC
#define NS_DISPATCH_AT_END nsIEventTarget::DISPATCH_AT_END
#define NS_DISPATCH_EVENT_MAY_BLOCK nsIEventTarget::DISPATCH_EVENT_MAY_BLOCK
#define NS_DISPATCH_IGNORE_BLOCK_DISPATCH nsIEventTarget::DISPATCH_IGNORE_BLOCK_DISPATCH

// Convenient NS_DECL variant that includes some C++-only methods.
#define NS_DECL_NSIEVENTTARGET_FULL                                   \
    NS_DECL_NSIEVENTTARGET                                            \
    /* Avoid hiding these methods */                                  \
    using nsIEventTarget::Dispatch;                                   \
    using nsIEventTarget::IsOnCurrentThread;
%}