xpcom/threads/SystemGroup.h
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 422445 0acc77eb92c6372cb73f441d2753c77068d87c2f
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 mozilla_SystemGroup_h
#define mozilla_SystemGroup_h

#include "mozilla/TaskCategory.h"
#include "mozilla/SchedulerGroup.h"

// The SystemGroup should be used for dispatching runnables that don't need to
// touch web content. Runnables dispatched to the SystemGroup are run in order
// relative to each other, but their order relative to other runnables is
// undefined.

namespace mozilla {

class SystemGroup
{
 public:
  // This method is safe to use from any thread.
  static nsresult Dispatch(TaskCategory aCategory,
                           already_AddRefed<nsIRunnable>&& aRunnable);

  // This method is safe to use from any thread.
  static nsISerialEventTarget* EventTargetFor(TaskCategory aCategory);

  // Must be called on the main thread. The AbstractThread can always be used
  // off the main thread.
  static AbstractThread* AbstractMainThreadFor(TaskCategory aCategory);

  static void InitStatic();
  static void Shutdown();

  // Returns true if SystemGroup has been initialized.
  static bool Initialized();
};

} // namespace mozilla

#endif // mozilla_SystemGroup_h