nsGkAtoms.h - mozsearch

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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 nsGkAtoms_h___

#define nsGkAtoms_h___

#include "nsAtom.h"

// Static atoms are structured carefully to satisfy a lot of constraints.

//

// - We have ~2300 static atoms.

//

// - We want them to be constexpr so they end up in .rodata, and thus shared

//   between processes, minimizing memory usage.

//

// - We need them to be in an array, so we can iterate over them (for

//   registration and lookups).

//

// - Each static atom has a string literal associated with it. We can't use a

//   pointer to the string literal because then the atoms won't end up in

//   .rodata. Therefore the string literals and the atoms must be arranged in a

//   way such that a numeric index can be used instead. This numeric index

//   (nsStaticAtom::mStringOffset) must be computable at compile-time to keep

//   the static atom constexpr. It should also not be too large (a uint32_t is

//   reasonable).

//

// - Each static atom stores the hash value of its associated string literal;

//   it's used in various ways. The hash value must be specified at

//   compile-time, to keep the static atom constexpr.

//

// - As well as accessing each static atom via array indexing, we need an

//   individual pointer, e.g. nsGkAtoms::foo. We want this to be constexpr so

//   it doesn't take up any space in memory.

//

// - The array of static atoms can't be in a .h file, because it's a huge

//   constexpr expression, which would blow out compile times. But the

//   individual pointers for the static atoms must be in a .h file so they are

//   public.

//

// nsGkAtoms below defines static atoms in a way that satisfies these

// constraints. It uses nsGkAtomList.h, which defines the names and values of

// the atoms. nsGkAtomList.h is generated by StaticAtoms.py and has entries

// that look like this:

//

//   GK_ATOM(a, "a", 0x01234567, nsStaticAtom, Atom)

//   GK_ATOM(bb, "bb", 0x12345678, nsCSSPseudoElementStaticAtom,

//           PseudoElementAtom)

//   GK_ATOM(Ccc, "Ccc", 0x23456789, nsCSSAnonBoxPseudoStaticAtom,

//           InheritingAnonBoxAtom)

//

// Comments throughout this file and nsGkAtoms.cpp show how these entries get

// expanded by macros.

// Trivial subclasses of nsStaticAtom so that function signatures can require

// an atom from a specific atom list.

#define DEFINE_STATIC_ATOM_SUBCLASS(name_)                              \

  class name_ : public nsStaticAtom {                                   \

   public:                                                              \

    constexpr name_(uint32_t aLength, uint32_t aHash, uint32_t aOffset, \

                    bool aIsAsciiLowercase)                             \

        : nsStaticAtom(aLength, aHash, aOffset, aIsAsciiLowercase) {}   \

};

DEFINE_STATIC_ATOM_SUBCLASS(nsCSSAnonBoxPseudoStaticAtom)

DEFINE_STATIC_ATOM_SUBCLASS(nsCSSPseudoElementStaticAtom)

#undef DEFINE_STATIC_ATOM_SUBCLASS