gfx/src/nsFontCache.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef _NS_FONTCACHE_H_
   7 #define _NS_FONTCACHE_H_
   8
   9 #include <stdint.h>
  10 #include <sys/types.h>
  11 #include "mozilla/RefPtr.h"
  12 #include "nsCOMPtr.h"
  13 #include "nsFontMetrics.h"
  14 #include "nsIObserver.h"
  15 #include "nsISupports.h"
  16 #include "nsTArray.h"
  17 #include "nsThreadUtils.h"
  18
  19 class gfxUserFontSet;
  20 class nsAtom;
  21 class nsPresContext;
  22 struct nsFont;
  23
  24 class nsFontCache final : public nsIObserver {
  25  public:
  26   nsFontCache() : mContext(nullptr) {}
  27
  28   NS_DECL_THREADSAFE_ISUPPORTS
  29   NS_DECL_NSIOBSERVER
  30
  31   void Init(nsPresContext* aContext);
  32   void Destroy();
  33
  34   already_AddRefed<nsFontMetrics> GetMetricsFor(
  35       const nsFont& aFont, const nsFontMetrics::Params& aParams);
  36
  37   void FontMetricsDeleted(const nsFontMetrics* aFontMetrics);
  38   void Compact();
  39
  40   // Flush aFlushCount oldest entries, or all if aFlushCount is negative
  41   void Flush(int32_t aFlushCount = -1);
  42
  43   void UpdateUserFonts(gfxUserFontSet* aUserFontSet);
  44
  45  protected:
  46   // If the array of cached entries is about to exceed this threshold,
  47   // we'll discard the oldest ones so as to keep the size reasonable.
  48   // In practice, the great majority of cache hits are among the last
  49   // few entries; keeping thousands of older entries becomes counter-
  50   // productive because it can then take too long to scan the cache.
  51   static const int32_t kMaxCacheEntries = 128;
  52
  53   ~nsFontCache() = default;
  54
  55   nsPresContext* mContext;  // owner
  56   RefPtr<nsAtom> mLocaleLanguage;
  57
  58   // We may not flush older entries immediately the array reaches
  59   // kMaxCacheEntries length, because this usually happens on a stylo
  60   // thread where we can't safely delete metrics objects. So we allocate an
  61   // oversized autoarray buffer here, so that we're unlikely to overflow
  62   // it and need separate heap allocation before the flush happens on the
  63   // main thread.
  64   AutoTArray<nsFontMetrics*, kMaxCacheEntries * 2> mFontMetrics;
  65
  66   bool mFlushPending = false;
  67
  68   class FlushFontMetricsTask : public mozilla::Runnable {
  69    public:
  70     explicit FlushFontMetricsTask(nsFontCache* aCache)
  71         : mozilla::Runnable("FlushFontMetricsTask"), mCache(aCache) {}
  72     NS_IMETHOD Run() override {
  73       // Partially flush the cache, leaving the kMaxCacheEntries/2 most
  74       // recent entries.
  75       mCache->Flush(mCache->mFontMetrics.Length() - kMaxCacheEntries / 2);
  76       mCache->mFlushPending = false;
  77       return NS_OK;
  78     }
  79
  80    private:
  81     RefPtr<nsFontCache> mCache;
  82   };
  83 };
  84
  85 #endif /* _NS_FONTCACHE_H_ */