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e7b3b3140d
Everything that goes in a PLDHashtable (and its derivatives, like nsTHashtable) needs to inherit from PLDHashEntryHdr. But through a lack of enforcement, copy constructors for these derived classes didn't explicitly invoke the copy constructor for PLDHashEntryHdr (and the compiler didn't invoke the copy constructor for us). Instead, PLDHashTable explicitly copied around the bits that the copy constructor would have. The current setup has two problems: 1) Derived classes should be using move construction, not copy construction, since anything that's shuffling hash table keys/entries around will be using move construction. 2) Derived classes should take responsibility for transferring bits of superclass state around, and not rely on something else to handle that. The second point is not a huge problem for PLDHashTable (PLDHashTable only has to copy PLDHashEntryHdr's bits in a single place), but future hash table implementations that might move entries around more aggressively would have to insert compensation code all over the place. Additionally, if moving entries is implemented via memcpy (which is quite common), PLDHashTable copying around bits *again* is inefficient. Let's fix all these problems in one go, by: 1) Explicitly declaring the set of constructors that PLDHashEntryHdr implements (and does not implement). In particular, the copy constructor is deleted, so any derived classes that attempt to make themselves copyable will be detected at compile time: the compiler will complain that the superclass type is not copyable. This change on its own will result in many compiler errors, so... 2) Change any derived classes to implement move constructors instead of copy constructors. Note that some of these move constructors are, strictly speaking, unnecessary, since the relevant classes are moved via memcpy in nsTHashtable and its derivatives.
109 lines
3.8 KiB
C++
109 lines
3.8 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsHtml5AtomTable_h
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#define nsHtml5AtomTable_h
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#include "nsHashKeys.h"
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#include "nsTHashtable.h"
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#include "nsAtom.h"
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#include "nsISerialEventTarget.h"
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#define RECENTLY_USED_PARSER_ATOMS_SIZE 31
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class nsHtml5AtomEntry : public nsStringHashKey
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{
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public:
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explicit nsHtml5AtomEntry(KeyTypePointer aStr);
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nsHtml5AtomEntry(nsHtml5AtomEntry&& aOther);
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~nsHtml5AtomEntry();
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inline nsAtom* GetAtom() { return mAtom; }
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private:
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nsDynamicAtom* mAtom;
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};
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/**
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* nsHtml5AtomTable provides non-locking lookup and creation of atoms for
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* nsHtml5Parser or nsHtml5StreamParser.
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*
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* The hashtable holds dynamically allocated atoms that are private to an
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* instance of nsHtml5Parser or nsHtml5StreamParser. (Static atoms are used on
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* interned nsHtml5ElementNames and interned nsHtml5AttributeNames. Also, when
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* the doctype name is 'html', that identifier needs to be represented as a
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* static atom.)
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*
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* Each instance of nsHtml5Parser has a single instance of nsHtml5AtomTable,
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* and each instance of nsHtml5StreamParser has a single instance of
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* nsHtml5AtomTable. Dynamic atoms obtained from an nsHtml5AtomTable are valid
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* for == comparison with each other or with atoms declared in nsHtml5Atoms
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* within the nsHtml5Tokenizer and the nsHtml5TreeBuilder instances owned by
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* the same nsHtml5Parser/nsHtml5StreamParser instance that owns the
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* nsHtml5AtomTable instance.
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*
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* Dynamic atoms (atoms whose IsStatic() returns false) obtained from
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* nsHtml5AtomTable must be re-obtained from another atom table when there's a
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* need to migrate atoms from an nsHtml5Parser to its nsHtml5StreamParser
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* (re-obtain from the other nsHtml5AtomTable), from an nsHtml5Parser to its
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* owner nsHtml5Parser (re-obtain from the other nsHtml5AtomTable) or from the
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* parser to the DOM (re-obtain from the application-wide atom table). To
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* re-obtain an atom from another atom table, obtain a string from the atom
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* using ToString(nsAString&) and look up an atom in the other table using that
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* string.
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*
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* An instance of nsHtml5AtomTable that belongs to an nsHtml5Parser is only
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* accessed from the main thread. An instance of nsHtml5AtomTable that belongs
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* to an nsHtml5StreamParser is accessed both from the main thread and from the
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* thread that executes the runnables of the nsHtml5StreamParser instance.
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* However, the threads never access the nsHtml5AtomTable instance concurrently
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* in the nsHtml5StreamParser case.
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*
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* Methods on the atoms obtained from nsHtml5AtomTable may be called on any
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* thread, although they only need to be called on the main thread or on the
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* thread working for the nsHtml5StreamParser when nsHtml5AtomTable belongs to
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* an nsHtml5StreamParser.
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*
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* Dynamic atoms obtained from nsHtml5AtomTable are deleted when the
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* nsHtml5AtomTable itself is destructed, which happens when the owner
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* nsHtml5Parser or nsHtml5StreamParser is destructed.
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*/
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class nsHtml5AtomTable
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{
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public:
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nsHtml5AtomTable();
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~nsHtml5AtomTable();
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/**
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* Obtains the atom for the given string in the scope of this atom table.
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*/
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nsAtom* GetAtom(const nsAString& aKey);
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/**
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* Empties the table.
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*/
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void Clear()
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{
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for (uint32_t i = 0; i < RECENTLY_USED_PARSER_ATOMS_SIZE; ++i) {
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mRecentlyUsedParserAtoms[i] = nullptr;
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}
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mTable.Clear();
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}
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#ifdef DEBUG
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void SetPermittedLookupEventTarget(nsISerialEventTarget* aEventTarget)
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{
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mPermittedLookupEventTarget = aEventTarget;
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}
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#endif
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private:
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nsTHashtable<nsHtml5AtomEntry> mTable;
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nsAtom* mRecentlyUsedParserAtoms[RECENTLY_USED_PARSER_ATOMS_SIZE];
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#ifdef DEBUG
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nsCOMPtr<nsISerialEventTarget> mPermittedLookupEventTarget;
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#endif
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};
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#endif // nsHtml5AtomTable_h
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