1 files changed, 91 insertions, 0 deletions
diff --git a/parser/html/nsHtml5AtomTable.h b/parser/html/nsHtml5AtomTable.h
new file mode 100644
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+++ b/parser/html/nsHtml5AtomTable.h
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+/* 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 nsHtml5AtomTable_h
+#define nsHtml5AtomTable_h
+
+#include "nsHashKeys.h"
+#include "nsTHashtable.h"
+#include "nsAtom.h"
+#include "nsISerialEventTarget.h"
+
+#define RECENTLY_USED_PARSER_ATOMS_SIZE 31
+
+/**
+ * nsHtml5AtomTable provides non-locking lookup and creation of atoms for
+ * nsHtml5Parser or nsHtml5StreamParser.
+ *
+ * The hashtable holds dynamically allocated atoms that are private to an
+ * instance of nsHtml5Parser or nsHtml5StreamParser. (Static atoms are used on
+ * interned nsHtml5ElementNames and interned nsHtml5AttributeNames. Also, when
+ * the doctype name is 'html', that identifier needs to be represented as a
+ * static atom.)
+ *
+ * Each instance of nsHtml5Parser has a single instance of nsHtml5AtomTable,
+ * and each instance of nsHtml5StreamParser has a single instance of
+ * nsHtml5AtomTable. Dynamic atoms obtained from an nsHtml5AtomTable are valid
+ * for == comparison with each other or with atoms declared in nsHtml5Atoms
+ * within the nsHtml5Tokenizer and the nsHtml5TreeBuilder instances owned by
+ * the same nsHtml5Parser/nsHtml5StreamParser instance that owns the
+ * nsHtml5AtomTable instance.
+ *
+ * Dynamic atoms (atoms whose IsStatic() returns false) obtained from
+ * nsHtml5AtomTable must be re-obtained from another atom table when there's a
+ * need to migrate atoms from an nsHtml5Parser to its nsHtml5StreamParser
+ * (re-obtain from the other nsHtml5AtomTable), from an nsHtml5Parser to its
+ * owner nsHtml5Parser (re-obtain from the other nsHtml5AtomTable) or from the
+ * parser to the DOM (re-obtain from the application-wide atom table). To
+ * re-obtain an atom from another atom table, obtain a string from the atom
+ * using ToString(nsAString&) and look up an atom in the other table using that
+ * string.
+ *
+ * An instance of nsHtml5AtomTable that belongs to an nsHtml5Parser is only
+ * accessed from the main thread. An instance of nsHtml5AtomTable that belongs
+ * to an nsHtml5StreamParser is accessed both from the main thread and from the
+ * thread that executes the runnables of the nsHtml5StreamParser instance.
+ * However, the threads never access the nsHtml5AtomTable instance concurrently
+ * in the nsHtml5StreamParser case.
+ *
+ * Methods on the atoms obtained from nsHtml5AtomTable may be called on any
+ * thread, although they only need to be called on the main thread or on the
+ * thread working for the nsHtml5StreamParser when nsHtml5AtomTable belongs to
+ * an nsHtml5StreamParser.
+ *
+ * Dynamic atoms obtained from nsHtml5AtomTable are deleted when the
+ * nsHtml5AtomTable itself is destructed, which happens when the owner
+ * nsHtml5Parser or nsHtml5StreamParser is destructed.
+ */
+class nsHtml5AtomTable {
+ public:
+  nsHtml5AtomTable();
+  ~nsHtml5AtomTable();
+
+  // NOTE: We rely on mRecentlyUsedParserAtoms keeping alive the returned atom,
+  // but the caller is responsible to take a reference before calling GetAtom
+  // again.
+  nsAtom* GetAtom(const nsAString& aKey);
+
+  /**
+   * Empties the table.
+   */
+  void Clear() {
+    for (uint32_t i = 0; i < RECENTLY_USED_PARSER_ATOMS_SIZE; ++i) {
+      mRecentlyUsedParserAtoms[i] = nullptr;
+    }
+  }
+
+#ifdef DEBUG
+  void SetPermittedLookupEventTarget(nsISerialEventTarget* aEventTarget) {
+    mPermittedLookupEventTarget = aEventTarget;
+  }
+#endif
+
+ private:
+  RefPtr<nsAtom> mRecentlyUsedParserAtoms[RECENTLY_USED_PARSER_ATOMS_SIZE];
+#ifdef DEBUG
+  nsCOMPtr<nsISerialEventTarget> mPermittedLookupEventTarget;
+#endif
+};
+
+#endif  // nsHtml5AtomTable_h