parser/html/nsHtml5AtomTable.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef nsHtml5AtomTable_h
   6 #define nsHtml5AtomTable_h
   7
   8 #include "nsHashKeys.h"
   9 #include "nsTHashtable.h"
  10 #include "nsAtom.h"
  11 #include "nsISerialEventTarget.h"
  12
  13 #define RECENTLY_USED_PARSER_ATOMS_SIZE 37
  14
  15 /*
  16  * nsHtml5AtomTable provides an atom cache for nsHtml5Parser and
  17  * nsHtml5StreamParser.
  18  *
  19  * An instance of nsHtml5AtomTable that belongs to an nsHtml5Parser is only
  20  * accessed from the main thread. An instance of nsHtml5AtomTable that belongs
  21  * to an nsHtml5StreamParser is accessed both from the main thread and from the
  22  * thread that executes the runnables of the nsHtml5StreamParser instance.
  23  * However, the threads never access the nsHtml5AtomTable instance concurrently
  24  * in the nsHtml5StreamParser case.
  25  *
  26  * Methods on the atoms obtained from nsHtml5AtomTable may be called on any
  27  * thread, although they only need to be called on the main thread or on the
  28  * thread working for the nsHtml5StreamParser when nsHtml5AtomTable belongs to
  29  * an nsHtml5StreamParser.
  30  *
  31  * Atoms cached by nsHtml5AtomTable are released when Clear() is called or when
  32  * the nsHtml5AtomTable itself is destructed, which happens when the owner
  33  * nsHtml5Parser or nsHtml5StreamParser is destructed.
  34  */
  35 class nsHtml5AtomTable {
  36  public:
  37   nsHtml5AtomTable();
  38   ~nsHtml5AtomTable();
  39
  40   // NOTE: We rely on mRecentlyUsedParserAtoms keeping alive the returned atom,
  41   // but the caller is responsible to take a reference before calling GetAtom
  42   // again.
  43   nsAtom* GetAtom(const nsAString& aKey);
  44
  45   /**
  46    * Empties the table.
  47    */
  48   void Clear() {
  49     for (uint32_t i = 0; i < RECENTLY_USED_PARSER_ATOMS_SIZE; ++i) {
  50       mRecentlyUsedParserAtoms[i] = nullptr;
  51     }
  52   }
  53
  54 #ifdef DEBUG
  55   void SetPermittedLookupEventTarget(nsISerialEventTarget* aEventTarget) {
  56     mPermittedLookupEventTarget = aEventTarget;
  57   }
  58 #endif
  59
  60  private:
  61   RefPtr<nsAtom> mRecentlyUsedParserAtoms[RECENTLY_USED_PARSER_ATOMS_SIZE];
  62 #ifdef DEBUG
  63   nsCOMPtr<nsISerialEventTarget> mPermittedLookupEventTarget;
  64 #endif
  65 };
  66
  67 #endif  // nsHtml5AtomTable_h