xpcom/threads/nsILabelableRunnable.h
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 436218 9e7267c06e4e7fb037e539809b409519ea3d63c0
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1402247 - Use encoding_rs for XPCOM string encoding conversions. r=Nika,erahm,froydnj. Correctness improvements: * UTF errors are handled safely per spec instead of dangerously truncating strings. * There are fewer converter implementations. Performance improvements: * The old code did exact buffer length math, which meant doing UTF math twice on each input string (once for length calculation and another time for conversion). Exact length math is more complicated when handling errors properly, which the old code didn't do. The new code does UTF math on the string content only once (when converting) but risks allocating more than once. There are heuristics in place to lower the probability of reallocation in cases where the double math avoidance isn't enough of a saving to absorb an allocation and memcpy. * Previously, in UTF-16 <-> UTF-8 conversions, an ASCII prefix was optimized but a single non-ASCII code point pessimized the rest of the string. The new code tries to get back on the fast ASCII path. * UTF-16 to Latin1 conversion guarantees less about handling of out-of-range input to eliminate an operation from the inner loop on x86/x86_64. * When assigning to a pre-existing string, the new code tries to reuse the old buffer instead of first releasing the old buffer and then allocating a new one. * When reallocating from the new code, the memcpy covers only the data that is part of the logical length of the old string instead of memcpying the whole capacity. (For old callers old excess memcpy behavior is preserved due to bogus callers. See bug 1472113.) * UTF-8 strings in XPConnect that are in the Latin1 range are passed to SpiderMonkey as Latin1. New features: * Conversion between UTF-8 and Latin1 is added in order to enable faster future interop between Rust code (or otherwise UTF-8-using code) and text node and SpiderMonkey code that uses Latin1. MozReview-Commit-ID: JaJuExfILM9

/* -*- 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 nsILabelableRunnable_h
#define nsILabelableRunnable_h

#include "mozilla/Maybe.h"
#include "mozilla/UniquePtr.h"
#include "nsHashKeys.h"
#include "nsISupports.h"
#include "nsTHashtable.h"

namespace mozilla {
class SchedulerGroup;
}

#define NS_ILABELABLERUNNABLE_IID \
{ 0x40da1ea1, 0x0b81, 0x4249, \
  { 0x96, 0x46, 0x61, 0x92, 0x23, 0x39, 0xc3, 0xe8 } }

// In some cases, it is not possible to assign a SchedulerGroup to a runnable
// when it is dispatched. For example, the vsync runnable affects whichever tabs
// happen to be in the foreground when the vsync runs. The nsILabelableRunnable
// interfaces makes it possible to query a runnable to see what SchedulerGroups
// it could belong to if it ran right now. For vsyncs, for example, this would
// return whichever tabs are foreground at the moment.
//
// This interface should be used very sparingly. In general, it is far
// preferable to label a runnable when it is dispatched since that gives the
// scheduler more flexibility and will improve performance.
//
// To use this interface, QI a runnable to nsILabelableRunnable and then call
// GetAffectedSchedulerGroups.
class nsILabelableRunnable : public nsISupports
{
public:
  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ILABELABLERUNNABLE_IID);

  class SchedulerGroupSet
  {
    friend class nsILabelableRunnable;

    using MultipleSchedulerGroups =
      nsTHashtable<nsRefPtrHashKey<mozilla::SchedulerGroup>>;

    RefPtr<mozilla::SchedulerGroup> mSingle;
    mozilla::Maybe<MultipleSchedulerGroups> mMulti;

  public:
    void Put(mozilla::SchedulerGroup* aGroup);

    void Clear();

    void SetIsRunning(bool aIsRunning);
  };

  // Returns true if the runnable can be labeled right now. In this case,
  // aGroups will contain the set of SchedulerGroups that can be affected by the
  // runnable. If this returns false, no assumptions can be made about which
  // SchedulerGroups are affected by the runnable.
  virtual bool GetAffectedSchedulerGroups(SchedulerGroupSet& aGroups) = 0;

  // Returns true if the runnable can be labeled right now and none of its
  // affected scheduler groups is running.
  bool IsReadyToRun();
};

NS_DEFINE_STATIC_IID_ACCESSOR(nsILabelableRunnable, NS_ILABELABLERUNNABLE_IID);

#endif // nsILabelableRunnable_h