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 31
  14
  15 /**
  16  * nsHtml5AtomTable provides non-locking lookup and creation of atoms for
  17  * nsHtml5Parser or nsHtml5StreamParser.
  18  *
  19  * The hashtable holds dynamically allocated atoms that are private to an
  20  * instance of nsHtml5Parser or nsHtml5StreamParser. (Static atoms are used on
  21  * interned nsHtml5ElementNames and interned nsHtml5AttributeNames. Also, when
  22  * the doctype name is 'html', that identifier needs to be represented as a
  23  * static atom.)
  24  *
  25  * Each instance of nsHtml5Parser has a single instance of nsHtml5AtomTable,
  26  * and each instance of nsHtml5StreamParser has a single instance of
  27  * nsHtml5AtomTable. Dynamic atoms obtained from an nsHtml5AtomTable are valid
  28  * for == comparison with each other or with atoms declared in nsHtml5Atoms
  29  * within the nsHtml5Tokenizer and the nsHtml5TreeBuilder instances owned by
  30  * the same nsHtml5Parser/nsHtml5StreamParser instance that owns the
  31  * nsHtml5AtomTable instance.
  32  *
  33  * Dynamic atoms (atoms whose IsStatic() returns false) obtained from
  34  * nsHtml5AtomTable must be re-obtained from another atom table when there's a
  35  * need to migrate atoms from an nsHtml5Parser to its nsHtml5StreamParser
  36  * (re-obtain from the other nsHtml5AtomTable), from an nsHtml5Parser to its
  37  * owner nsHtml5Parser (re-obtain from the other nsHtml5AtomTable) or from the
  38  * parser to the DOM (re-obtain from the application-wide atom table). To
  39  * re-obtain an atom from another atom table, obtain a string from the atom
  40  * using ToString(nsAString&) and look up an atom in the other table using that
  41  * string.
  42  *
  43  * An instance of nsHtml5AtomTable that belongs to an nsHtml5Parser is only
  44  * accessed from the main thread. An instance of nsHtml5AtomTable that belongs
  45  * to an nsHtml5StreamParser is accessed both from the main thread and from the
  46  * thread that executes the runnables of the nsHtml5StreamParser instance.
  47  * However, the threads never access the nsHtml5AtomTable instance concurrently
  48  * in the nsHtml5StreamParser case.
  49  *
  50  * Methods on the atoms obtained from nsHtml5AtomTable may be called on any
  51  * thread, although they only need to be called on the main thread or on the
  52  * thread working for the nsHtml5StreamParser when nsHtml5AtomTable belongs to
  53  * an nsHtml5StreamParser.
  54  *
  55  * Dynamic atoms obtained from nsHtml5AtomTable are deleted when the
  56  * nsHtml5AtomTable itself is destructed, which happens when the owner
  57  * nsHtml5Parser or nsHtml5StreamParser is destructed.
  58  */
  59 class nsHtml5AtomTable {
  60  public:
  61   nsHtml5AtomTable();
  62   ~nsHtml5AtomTable();
  63
  64   // NOTE: We rely on mRecentlyUsedParserAtoms keeping alive the returned atom,
  65   // but the caller is responsible to take a reference before calling GetAtom
  66   // again.
  67   nsAtom* GetAtom(const nsAString& aKey);
  68
  69   /**
  70    * Empties the table.
  71    */
  72   void Clear() {
  73     for (uint32_t i = 0; i < RECENTLY_USED_PARSER_ATOMS_SIZE; ++i) {
  74       mRecentlyUsedParserAtoms[i] = nullptr;
  75     }
  76   }
  77
  78 #ifdef DEBUG
  79   void SetPermittedLookupEventTarget(nsISerialEventTarget* aEventTarget) {
  80     mPermittedLookupEventTarget = aEventTarget;
  81   }
  82 #endif
  83
  84  private:
  85   RefPtr<nsAtom> mRecentlyUsedParserAtoms[RECENTLY_USED_PARSER_ATOMS_SIZE];
  86 #ifdef DEBUG
  87   nsCOMPtr<nsISerialEventTarget> mPermittedLookupEventTarget;
  88 #endif
  89 };
  90
  91 #endif  // nsHtml5AtomTable_h