Emilio Cobos Álvarez
fe182cca64
Make DOMString a regular nsAutoTString with some special methods for performance in some hot getters. For that, we need to change a bit nsTString: * Support for unowned buffers: Owned buffers now are represented by STRINGBUFFER|OWNED flags, rather than REFCOUNTED. * Inlining of the destructor: It showed up in profiles, it's also just a few instructions, so probably worth it. We could OOL the owned path I guess, if we wanted to. * Inlinling and reordering of NonVoidStringToJsval. Old code had special DOMString path inline with [buffer, literal, copy] paths, then out of line code with [literal, buffer, copy]. Instead, consolidate everything in a [buffer, literal, copy] inline path. Do the same for UTF8/Latin1 strings too for consistency. Differential Revision: https://phabricator.services.mozilla.com/D288148
104 lines
3.9 KiB
C++
104 lines
3.9 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 nsStringFlags_h
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#define nsStringFlags_h
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#include <stdint.h>
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#include "mozilla/TypedEnumBits.h"
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namespace mozilla {
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namespace detail {
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// NOTE: these flags are declared public _only_ for convenience inside
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// the string implementation. And they are outside of the string
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// class so that the type is the same for both narrow and wide
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// strings.
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// bits for mDataFlags
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enum class StringDataFlags : uint16_t {
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// Some terminology:
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//
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// "dependent buffer" A dependent buffer is one that the string class
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// does not own. The string class relies on some
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// external code to ensure the lifetime of the
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// dependent buffer.
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//
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// "refcounted buffer" A refcounted buffer is one that the string class
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// allocates. When it allocates a refcounted string
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// buffer, it allocates some additional space at
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// the beginning of the buffer for additional
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// fields, including a reference count and a
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// buffer length. See mozilla::StringBuffer.
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//
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// "adopted buffer" An adopted buffer is a raw string buffer
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// allocated on the heap (using moz_xmalloc)
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// of which the string class subsumes ownership.
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//
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// Some comments about the string data flags:
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//
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// The allocation type of mData is determined as follows:
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// * LITERAL: Points to a static string.
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// * INLINE: Points to our inline buffer, exclusive with other flags in
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// this list.
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// * STRINGBUFFER: Points to a (potentially dependent) StringBuffer.
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// * OWNED: Points to heap-allocated data, or to an StringBuffer that we
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// keep alive (depending on whether STRINGBUFFER) is set.
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//
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// If none of these flags are set, then the data pointer is dependent and
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// pointing to unknown data (it can also be dependent and pointing to a
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// STRINGBUFFER).
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//
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// STRINGBUFFER, OWNED, or INLINE imply TERMINATED. This is because
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// the string classes always allocate null-terminated buffers, and
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// non-terminated substrings are always dependent.
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//
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// VOIDED implies TERMINATED, and moreover it implies that mData
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// points to char_traits::sEmptyBuffer. Therefore, VOIDED is
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// mutually exclusive with STRINGBUFFER, OWNED, and INLINE.
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//
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// INLINE requires StringClassFlags::INLINE to be set on the type.
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// IsTerminated returns true
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TERMINATED = 1 << 0,
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// IsVoid returns true
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VOIDED = 1 << 1,
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// mData points to a heap-allocated, shareable StringBuffer. The buffer is
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// only owned iff OWNED is also set.
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STRINGBUFFER = 1 << 2,
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// mData points either to a heap-allocated, raw buffer, or to an owned
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// StringBuffer, iff STRINGBUFFER is also set.
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OWNED = 1 << 3,
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// mData points to a writable, inline buffer
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INLINE = 1 << 4,
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// mData points to a string literal; DataFlags::TERMINATED will also be set
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LITERAL = 1 << 5,
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// used to check for invalid flags -- all bits above the last item
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INVALID_MASK = (uint16_t)~((LITERAL << 1) - 1)
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};
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// bits for mClassFlags
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enum class StringClassFlags : uint16_t {
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// |this|'s buffer is inline, and requires the type to be binary-compatible
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// with nsTAutoStringN
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INLINE = 1 << 0,
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// |this| requires its buffer is null-terminated
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NULL_TERMINATED = 1 << 1,
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// used to check for invalid flags -- all bits above the last item
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INVALID_MASK = (uint16_t)~((NULL_TERMINATED << 1) - 1)
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};
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MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(StringDataFlags)
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MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(StringClassFlags)
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} // namespace detail
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} // namespace mozilla
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#endif
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