1 files changed, 101 insertions, 0 deletions
diff --git a/gfx/src/nsFontCache.h b/gfx/src/nsFontCache.h
new file mode 100644
index 0000000000..794eb0fae0
--- /dev/null
+++ b/gfx/src/nsFontCache.h
@@ -0,0 +1,101 @@
+/* -*- Mode: C++; tab-width: 8; 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/. */
+
+#ifndef _NS_FONTCACHE_H_
+#define _NS_FONTCACHE_H_
+
+#include <stdint.h>
+#include <sys/types.h>
+#include "mozilla/RefPtr.h"
+#include "nsCOMPtr.h"
+#include "nsFontMetrics.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+#include "prtime.h"
+
+class gfxUserFontSet;
+class nsAtom;
+class nsPresContext;
+struct nsFont;
+
+class nsFontCache final : public nsIObserver {
+ public:
+  nsFontCache() : mContext(nullptr) {}
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  void Init(nsPresContext* aContext);
+  void Destroy();
+
+  already_AddRefed<nsFontMetrics> GetMetricsFor(
+      const nsFont& aFont, const nsFontMetrics::Params& aParams);
+
+  void FontMetricsDeleted(const nsFontMetrics* aFontMetrics);
+  void Compact();
+
+  // Flush aFlushCount oldest entries, or all if aFlushCount is negative
+  void Flush(int32_t aFlushCount = -1);
+
+  void UpdateUserFonts(gfxUserFontSet* aUserFontSet);
+
+ protected:
+  // If the array of cached entries is about to exceed this threshold,
+  // we'll discard the oldest ones so as to keep the size reasonable.
+  // In practice, the great majority of cache hits are among the last
+  // few entries; keeping thousands of older entries becomes counter-
+  // productive because it can then take too long to scan the cache.
+  static constexpr int32_t kMaxCacheEntries = 128;
+
+  // Number of cache misses before we assume that a font fingerprinting attempt
+  // is being made. Usually fingerprinters will lookup the same font-family
+  // three times, as "sans-serif", "serif" and "monospace".
+  static constexpr int32_t kFingerprintingCacheMissThreshold = 3 * 20;
+  // We assume that fingerprinters will lookup a large number of fonts in a
+  // short amount of time.
+  static constexpr PRTime kFingerprintingTimeout =
+      PRTime(PR_USEC_PER_SEC) * 3;  // 3 seconds
+
+  static_assert(kFingerprintingCacheMissThreshold < kMaxCacheEntries);
+
+  ~nsFontCache() = default;
+
+  nsPresContext* mContext;  // owner
+  RefPtr<nsAtom> mLocaleLanguage;
+
+  // We may not flush older entries immediately the array reaches
+  // kMaxCacheEntries length, because this usually happens on a stylo
+  // thread where we can't safely delete metrics objects. So we allocate an
+  // oversized autoarray buffer here, so that we're unlikely to overflow
+  // it and need separate heap allocation before the flush happens on the
+  // main thread.
+  AutoTArray<nsFontMetrics*, kMaxCacheEntries * 2> mFontMetrics;
+
+  bool mFlushPending = false;
+
+  class FlushFontMetricsTask : public mozilla::Runnable {
+   public:
+    explicit FlushFontMetricsTask(nsFontCache* aCache)
+        : mozilla::Runnable("FlushFontMetricsTask"), mCache(aCache) {}
+    NS_IMETHOD Run() override {
+      // Partially flush the cache, leaving the kMaxCacheEntries/2 most
+      // recent entries.
+      mCache->Flush(mCache->mFontMetrics.Length() - kMaxCacheEntries / 2);
+      mCache->mFlushPending = false;
+      return NS_OK;
+    }
+
+   private:
+    RefPtr<nsFontCache> mCache;
+  };
+
+  PRTime mLastCacheMiss = 0;
+  uint64_t mCacheMisses = 0;
+  bool mReportedProbableFingerprinting = false;
+};
+
+#endif /* _NS_FONTCACHE_H_ */