storage/mozIStorageFunction.idl
author Kyle Huey <khuey@kylehuey.com>
Tue, 11 Aug 2015 06:10:46 -0700
changeset 257246 a13c1f26e351dd6251da641fe7a9eb53790fc2d0
parent 244681 ad01543457e739b4eee7a245e16734a3ecfd10ad
child 475212 020c8c871c0d3b3920fe95935cfef06501976c0f
permissions -rw-r--r--
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 "mozIStorageValueArray.idl"

interface mozIStorageConnection;
interface nsIArray;
interface nsIVariant;

/**
 * mozIStorageFunction is to be implemented by storage consumers that
 * wish to receive callbacks during the request execution.
 *
 * SQL can apply functions to values from tables. Examples of
 * such functions are MIN(a1,a2) or SQRT(num). Many functions are
 * implemented in SQL engine.
 *
 * This interface allows consumers to implement their own,
 * problem-specific functions.
 * These functions can be called from triggers, too.
 *
 */
[scriptable, function, uuid(9ff02465-21cb-49f3-b975-7d5b38ceec73)]
interface mozIStorageFunction : nsISupports {
  /**
   * onFunctionCall is called when execution of a custom
   * function should occur.
   * 
   * @param aNumArguments         The number of arguments
   * @param aFunctionArguments    The arguments passed in to the function
   *
   * @returns any value as Variant type.
   */

  nsIVariant onFunctionCall(in mozIStorageValueArray aFunctionArguments);
};