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 class nsHtml5AtomEntry : public nsStringHashKey
  16 {
  17 public:
  18   explicit nsHtml5AtomEntry(KeyTypePointer aStr);
  19   nsHtml5AtomEntry(const nsHtml5AtomEntry& aOther);
  20   ~nsHtml5AtomEntry();
  21   inline nsAtom* GetAtom() { return mAtom; }
  22
  23 private:
  24   nsDynamicAtom* mAtom;
  25 };
  26
  27 /**
  28  * nsHtml5AtomTable provides non-locking lookup and creation of atoms for
  29  * nsHtml5Parser or nsHtml5StreamParser.
  30  *
  31  * The hashtable holds dynamically allocated atoms that are private to an
  32  * instance of nsHtml5Parser or nsHtml5StreamParser. (Static atoms are used on
  33  * interned nsHtml5ElementNames and interned nsHtml5AttributeNames. Also, when
  34  * the doctype name is 'html', that identifier needs to be represented as a
  35  * static atom.)
  36  *
  37  * Each instance of nsHtml5Parser has a single instance of nsHtml5AtomTable,
  38  * and each instance of nsHtml5StreamParser has a single instance of
  39  * nsHtml5AtomTable. Dynamic atoms obtained from an nsHtml5AtomTable are valid
  40  * for == comparison with each other or with atoms declared in nsHtml5Atoms
  41  * within the nsHtml5Tokenizer and the nsHtml5TreeBuilder instances owned by
  42  * the same nsHtml5Parser/nsHtml5StreamParser instance that owns the
  43  * nsHtml5AtomTable instance.
  44  *
  45  * Dynamic atoms (atoms whose IsStatic() returns false) obtained from
  46  * nsHtml5AtomTable must be re-obtained from another atom table when there's a
  47  * need to migrate atoms from an nsHtml5Parser to its nsHtml5StreamParser
  48  * (re-obtain from the other nsHtml5AtomTable), from an nsHtml5Parser to its
  49  * owner nsHtml5Parser (re-obtain from the other nsHtml5AtomTable) or from the
  50  * parser to the DOM (re-obtain from the application-wide atom table). To
  51  * re-obtain an atom from another atom table, obtain a string from the atom
  52  * using ToString(nsAString&) and look up an atom in the other table using that
  53  * string.
  54  *
  55  * An instance of nsHtml5AtomTable that belongs to an nsHtml5Parser is only
  56  * accessed from the main thread. An instance of nsHtml5AtomTable that belongs
  57  * to an nsHtml5StreamParser is accessed both from the main thread and from the
  58  * thread that executes the runnables of the nsHtml5StreamParser instance.
  59  * However, the threads never access the nsHtml5AtomTable instance concurrently
  60  * in the nsHtml5StreamParser case.
  61  *
  62  * Methods on the atoms obtained from nsHtml5AtomTable may be called on any
  63  * thread, although they only need to be called on the main thread or on the
  64  * thread working for the nsHtml5StreamParser when nsHtml5AtomTable belongs to
  65  * an nsHtml5StreamParser.
  66  *
  67  * Dynamic atoms obtained from nsHtml5AtomTable are deleted when the
  68  * nsHtml5AtomTable itself is destructed, which happens when the owner
  69  * nsHtml5Parser or nsHtml5StreamParser is destructed.
  70  */
  71 class nsHtml5AtomTable
  72 {
  73 public:
  74   nsHtml5AtomTable();
  75   ~nsHtml5AtomTable();
  76
  77   /**
  78    * Obtains the atom for the given string in the scope of this atom table.
  79    */
  80   nsAtom* GetAtom(const nsAString& aKey);
  81
  82   /**
  83    * Empties the table.
  84    */
  85   void Clear()
  86   {
  87     for (uint32_t i = 0; i < RECENTLY_USED_PARSER_ATOMS_SIZE; ++i) {
  88       mRecentlyUsedParserAtoms[i] = nullptr;
  89     }
  90     mTable.Clear();
  91   }
  92
  93 #ifdef DEBUG
  94   void SetPermittedLookupEventTarget(nsISerialEventTarget* aEventTarget)
  95   {
  96     mPermittedLookupEventTarget = aEventTarget;
  97   }
  98 #endif
  99
 100 private:
 101   nsTHashtable<nsHtml5AtomEntry> mTable;
 102   nsAtom* mRecentlyUsedParserAtoms[RECENTLY_USED_PARSER_ATOMS_SIZE];
 103 #ifdef DEBUG
 104   nsCOMPtr<nsISerialEventTarget> mPermittedLookupEventTarget;
 105 #endif
 106 };
 107
 108 #endif // nsHtml5AtomTable_h