image/DecodePool.h
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 466338 1c5d4e9652092cb2cbec3c42656486a09b84ec9f
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: 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/. */

/**
 * DecodePool manages the threads used for decoding raster images.
 */

#ifndef mozilla_image_DecodePool_h
#define mozilla_image_DecodePool_h

#include "mozilla/Mutex.h"
#include "mozilla/StaticPtr.h"
#include "nsCOMArray.h"
#include "nsCOMPtr.h"
#include "nsIEventTarget.h"
#include "nsIObserver.h"
#include "mozilla/RefPtr.h"
#include "nsStringFwd.h"

class nsIThread;
class nsIThreadPool;

namespace mozilla {
namespace image {

class Decoder;
class DecodePoolImpl;
class IDecodingTask;

/**
 * DecodePool is a singleton class that manages decoding of raster images. It
 * owns a pool of image decoding threads that are used for asynchronous
 * decoding.
 *
 * DecodePool allows callers to run a decoder, handling management of the
 * decoder's lifecycle and whether it executes on the main thread,
 * off-main-thread in the image decoding thread pool, or on some combination of
 * the two.
 */
class DecodePool final : public nsIObserver
{
public:
  NS_DECL_THREADSAFE_ISUPPORTS
  NS_DECL_NSIOBSERVER

  /// Initializes the singleton instance. Should be called from the main thread.
  static void Initialize();

  /// Returns the singleton instance.
  static DecodePool* Singleton();

  /// @return the number of processor cores we have available. This is not the
  /// same as the number of decoding threads we're actually using.
  static uint32_t NumberOfCores();

  /// True if the DecodePool is being shutdown. This may only be called by
  /// threads from the pool to check if they should keep working or not.
  bool IsShuttingDown() const;

  /// Ask the DecodePool to run @aTask asynchronously and return immediately.
  void AsyncRun(IDecodingTask* aTask);

  /**
   * Run @aTask synchronously if the task would prefer it. It's up to the task
   * itself to make this decision; @see IDecodingTask::ShouldPreferSyncRun(). If
   * @aTask doesn't prefer it, just run @aTask asynchronously and return
   * immediately.
   * @return true if the task was run sync, false otherwise.
   */
  bool SyncRunIfPreferred(IDecodingTask* aTask, const nsCString& aURI);

  /**
   * Run @aTask synchronously. This does not guarantee that @aTask will complete
   * synchronously. If, for example, @aTask doesn't yet have the data it needs to
   * run synchronously, it may recover by scheduling an async task to finish up
   * the work when the remaining data is available.
   */
  void SyncRunIfPossible(IDecodingTask* aTask, const nsCString& aURI);

  /**
   * Returns an event target interface to the DecodePool's I/O thread. Callers
   * who want to deliver data to workers on the DecodePool can use this event
   * target.
   *
   * @return An nsIEventTarget interface to the thread pool's I/O thread.
   */
  already_AddRefed<nsIEventTarget> GetIOEventTarget();

private:
  friend class DecodePoolWorker;

  DecodePool();
  virtual ~DecodePool();

  static StaticRefPtr<DecodePool> sSingleton;
  static uint32_t sNumCores;

  RefPtr<DecodePoolImpl> mImpl;

  // mMutex protects mIOThread.
  Mutex                         mMutex;
  nsCOMPtr<nsIThread>           mIOThread;
};

} // namespace image
} // namespace mozilla

#endif // mozilla_image_DecodePool_h