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 #include "prtime.h"
  19
  20 class gfxUserFontSet;
  21 class nsAtom;
  22 class nsPresContext;
  23 struct nsFont;
  24
  25 class nsFontCache final : public nsIObserver {
  26  public:
  27   nsFontCache() : mContext(nullptr) {}
  28
  29   NS_DECL_THREADSAFE_ISUPPORTS
  30   NS_DECL_NSIOBSERVER
  31
  32   void Init(nsPresContext* aContext);
  33   void Destroy();
  34
  35   already_AddRefed<nsFontMetrics> GetMetricsFor(
  36       const nsFont& aFont, const nsFontMetrics::Params& aParams);
  37
  38   void FontMetricsDeleted(const nsFontMetrics* aFontMetrics);
  39   void Compact();
  40
  41   // Flush aFlushCount oldest entries, or all if aFlushCount is negative
  42   void Flush(int32_t aFlushCount = -1);
  43
  44   void UpdateUserFonts(gfxUserFontSet* aUserFontSet);
  45
  46  protected:
  47   // If the array of cached entries is about to exceed this threshold,
  48   // we'll discard the oldest ones so as to keep the size reasonable.
  49   // In practice, the great majority of cache hits are among the last
  50   // few entries; keeping thousands of older entries becomes counter-
  51   // productive because it can then take too long to scan the cache.
  52   static constexpr int32_t kMaxCacheEntries = 128;
  53
  54   // Number of cache misses before we assume that a font fingerprinting attempt
  55   // is being made. Usually fingerprinters will lookup the same font-family
  56   // three times, as "sans-serif", "serif" and "monospace".
  57   static constexpr int32_t kFingerprintingCacheMissThreshold = 3 * 20;
  58   // We assume that fingerprinters will lookup a large number of fonts in a
  59   // short amount of time.
  60   static constexpr PRTime kFingerprintingTimeout =
  61       PRTime(PR_USEC_PER_SEC) * 3;  // 3 seconds
  62
  63   static_assert(kFingerprintingCacheMissThreshold < kMaxCacheEntries);
  64
  65   ~nsFontCache() = default;
  66
  67   nsPresContext* mContext;  // owner
  68   RefPtr<nsAtom> mLocaleLanguage;
  69
  70   // We may not flush older entries immediately the array reaches
  71   // kMaxCacheEntries length, because this usually happens on a stylo
  72   // thread where we can't safely delete metrics objects. So we allocate an
  73   // oversized autoarray buffer here, so that we're unlikely to overflow
  74   // it and need separate heap allocation before the flush happens on the
  75   // main thread.
  76   AutoTArray<nsFontMetrics*, kMaxCacheEntries * 2> mFontMetrics;
  77
  78   bool mFlushPending = false;
  79
  80   class FlushFontMetricsTask : public mozilla::Runnable {
  81    public:
  82     explicit FlushFontMetricsTask(nsFontCache* aCache)
  83         : mozilla::Runnable("FlushFontMetricsTask"), mCache(aCache) {}
  84     NS_IMETHOD Run() override {
  85       // Partially flush the cache, leaving the kMaxCacheEntries/2 most
  86       // recent entries.
  87       mCache->Flush(mCache->mFontMetrics.Length() - kMaxCacheEntries / 2);
  88       mCache->mFlushPending = false;
  89       return NS_OK;
  90     }
  91
  92    private:
  93     RefPtr<nsFontCache> mCache;
  94   };
  95
  96   PRTime mLastCacheMiss = 0;
  97   uint64_t mCacheMisses = 0;
  98   bool mReportedProbableFingerprinting = false;
  99 };
 100
 101 #endif /* _NS_FONTCACHE_H_ */