chromium/src/third_party/blink/renderer/platform/fonts/font_data_cache.h

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
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 * in the documentation and/or other materials provided with the
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 * this software without specific prior written permission.
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#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_FONT_DATA_CACHE_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_FONT_DATA_CACHE_H_

#include "third_party/blink/renderer/platform/fonts/font_platform_data.h"
#include "third_party/blink/renderer/platform/fonts/simple_font_data.h"
#include "third_party/blink/renderer/platform/wtf/hash_map.h"
#include "third_party/blink/renderer/platform/wtf/linked_hash_set.h"

namespace blink {

enum ShouldRetain { kRetain, kDoNotRetain };
enum PurgeSeverity { kPurgeIfNeeded, kForcePurge };

struct FontDataCacheKeyHash {
  STATIC_ONLY(FontDataCacheKeyHash);
  static unsigned GetHash(const FontPlatformData* platform_data) {
    return platform_data->GetHash();
  }

  static bool Equal(const FontPlatformData* a, const FontPlatformData* b) {
    const FontPlatformData* empty_value =
        reinterpret_cast<FontPlatformData*>(-1);

    if (a == empty_value)
      return b == empty_value;
    if (b == empty_value)
      return a == empty_value;

    if (!a || !b)
      return a == b;

    CHECK(a && b);

    return *a == *b;
  }

  static const bool safe_to_compare_to_empty_or_deleted = true;
};

class FontDataCache {
  USING_FAST_MALLOC(FontDataCache);

 public:
  FontDataCache() = default;

  scoped_refptr<SimpleFontData> Get(const FontPlatformData*,
                                    ShouldRetain = kRetain,
                                    bool subpixel_ascent_descent = false);
  bool Contains(const FontPlatformData*) const;
  void Release(const SimpleFontData*);

  // Purges items in FontDataCache according to provided severity.
  // Returns true if any removal of cache items actually occurred.
  bool Purge(PurgeSeverity);

 private:
  bool PurgeLeastRecentlyUsed(int count);

  typedef HashMap<const FontPlatformData*,
                  std::pair<scoped_refptr<SimpleFontData>, unsigned>,
                  FontDataCacheKeyHash>
      Cache;
  Cache cache_;
  LinkedHashSet<scoped_refptr<SimpleFontData>> inactive_font_data_;

  DISALLOW_COPY_AND_ASSIGN(FontDataCache);
};

}  // namespace blink

#endif