gfxGradientCache.cpp

/* -*- 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 "mozilla/gfx/2D.h"
#include "nsTArray.h"
#include "PLDHashTable.h"
#include "nsExpirationTracker.h"
#include "nsClassHashtable.h"
#include "mozilla/SystemGroup.h"
#include "gfxGradientCache.h"
#include <time.h>

namespace mozilla {
namespace gfx {

using namespace mozilla;

struct GradientCacheKey : public PLDHashEntryHdr {
  typedef const GradientCacheKey& KeyType;
  typedef const GradientCacheKey* KeyTypePointer;
  enum { ALLOW_MEMMOVE = true };
  const nsTArray<GradientStop> mStops;
  ExtendMode mExtend;
  BackendType mBackendType;

  GradientCacheKey(const nsTArray<GradientStop>& aStops, ExtendMode aExtend,
                   BackendType aBackendType)
      : mStops(aStops), mExtend(aExtend), mBackendType(aBackendType) {}

  explicit GradientCacheKey(const GradientCacheKey* aOther)
      : mStops(aOther->mStops),
        mExtend(aOther->mExtend),
        mBackendType(aOther->mBackendType) {}

  GradientCacheKey(GradientCacheKey&& aOther) = default;

  union FloatUint32 {
    float f;
    uint32_t u;
  };

  static PLDHashNumber HashKey(const KeyTypePointer aKey) {
    PLDHashNumber hash = 0;
    FloatUint32 convert;
    hash = AddToHash(hash, int(aKey->mBackendType));
    hash = AddToHash(hash, int(aKey->mExtend));
    for (uint32_t i = 0; i < aKey->mStops.Length(); i++) {
      hash = AddToHash(hash, aKey->mStops[i].color.ToABGR());
      // Use the float bits as hash, except for the cases of 0.0 and -0.0 which
      // both map to 0
      convert.f = aKey->mStops[i].offset;
      hash = AddToHash(hash, convert.f ? convert.u : 0);
    }
    return hash;
  }

  bool KeyEquals(KeyTypePointer aKey) const {
    bool sameStops = true;
    if (aKey->mStops.Length() != mStops.Length()) {
      sameStops = false;
    } else {
      for (uint32_t i = 0; i < mStops.Length(); i++) {
        if (mStops[i].color.ToABGR() != aKey->mStops[i].color.ToABGR() ||
            mStops[i].offset != aKey->mStops[i].offset) {
          sameStops = false;
          break;
        }
      }
    }

    return sameStops && (aKey->mBackendType == mBackendType) &&
           (aKey->mExtend == mExtend);
  }
  static KeyTypePointer KeyToPointer(KeyType aKey) { return &aKey; }
};

/**
 * This class is what is cached. It need to be allocated in an object separated
 * to the cache entry to be able to be tracked by the nsExpirationTracker.
 * */
struct GradientCacheData {
  GradientCacheData(GradientStops* aStops, GradientCacheKey&& aKey)
      : mStops(aStops), mKey(std::move(aKey)) {}

  GradientCacheData(GradientCacheData&& aOther) = default;

  nsExpirationState* GetExpirationState() { return &mExpirationState; }

  nsExpirationState mExpirationState;
  const RefPtr<GradientStops> mStops;
  GradientCacheKey mKey;
};

/**
 * This class implements a cache with no maximum size, that retains the
 * gfxPatterns used to draw the gradients.
 *
 * The key is the nsStyleGradient that defines the gradient, and the size of the
 * gradient.
 *
 * The value is the gfxPattern, and whether or not we perform an optimization
 * based on the actual gradient property.
 *
 * An entry stays in the cache as long as it is used often. As long as a cache
 * entry is in the cache, all the references it has are guaranteed to be valid:
 * the nsStyleRect for the key, the gfxPattern for the value.
 */
class GradientCache final : public nsExpirationTracker<GradientCacheData, 4> {
 public:
  GradientCache()
      : nsExpirationTracker<GradientCacheData, 4>(
            MAX_GENERATION_MS, "GradientCache",
            SystemGroup::EventTargetFor(TaskCategory::Other)) {
    srand(time(nullptr));
  }

  virtual void NotifyExpired(GradientCacheData* aObject) override {
    // This will free the gfxPattern.
    RemoveObject(aObject);
    mHashEntries.Remove(aObject->mKey);
  }

  GradientCacheData* Lookup(const nsTArray<GradientStop>& aStops,
                            ExtendMode aExtend, BackendType aBackendType) {
    GradientCacheData* gradient =
        mHashEntries.Get(GradientCacheKey(aStops, aExtend, aBackendType));

    if (gradient) {
      MarkUsed(gradient);
    }

    return gradient;
  }

  // Returns true if we successfully register the gradient in the cache, false
  // otherwise.
  bool RegisterEntry(GradientCacheData* aValue) {
    nsresult rv = AddObject(aValue);
    if (NS_FAILED(rv)) {
      // We are OOM, and we cannot track this object. We don't want stall
      // entries in the hash table (since the expiration tracker is responsible
      // for removing the cache entries), so we avoid putting that entry in the
      // table, which is a good things considering we are short on memory
      // anyway, we probably don't want to retain things.
      return false;
    }
    mHashEntries.Put(aValue->mKey, aValue);
    return true;
  }

 protected:
  static const uint32_t MAX_GENERATION_MS = 10000;
  /**
   * FIXME use nsTHashtable to avoid duplicating the GradientCacheKey.
   * https://bugzilla.mozilla.org/show_bug.cgi?id=761393#c47
   */
  nsClassHashtable<GradientCacheKey, GradientCacheData> mHashEntries;
};

static GradientCache* gGradientCache = nullptr;

GradientStops* gfxGradientCache::GetGradientStops(
    const DrawTarget* aDT, nsTArray<GradientStop>& aStops, ExtendMode aExtend) {
  if (!gGradientCache) {
    gGradientCache = new GradientCache();
  }
  GradientCacheData* cached =
      gGradientCache->Lookup(aStops, aExtend, aDT->GetBackendType());
  if (cached && cached->mStops) {
    if (!cached->mStops->IsValid()) {
      gGradientCache->NotifyExpired(cached);
    } else {
      return cached->mStops;
    }
  }

  return nullptr;
}

already_AddRefed<GradientStops> gfxGradientCache::GetOrCreateGradientStops(
    const DrawTarget* aDT, nsTArray<GradientStop>& aStops, ExtendMode aExtend) {
  if (aDT->IsRecording()) {
    return aDT->CreateGradientStops(aStops.Elements(), aStops.Length(),
                                    aExtend);
  }

  RefPtr<GradientStops> gs = GetGradientStops(aDT, aStops, aExtend);
  if (!gs) {
    gs = aDT->CreateGradientStops(aStops.Elements(), aStops.Length(), aExtend);
    if (!gs) {
      return nullptr;
    }
    GradientCacheData* cached = new GradientCacheData(
        gs, GradientCacheKey(aStops, aExtend, aDT->GetBackendType()));
    if (!gGradientCache->RegisterEntry(cached)) {
      delete cached;
    }
  }
  return gs.forget();
}

void gfxGradientCache::PurgeAllCaches() {
  if (gGradientCache) {
    gGradientCache->AgeAllGenerations();
  }
}

void gfxGradientCache::Shutdown() {
  delete gGradientCache;
  gGradientCache = nullptr;
}

}  // namespace gfx
}  // namespace mozilla