mirror of
https://github.com/classilla/tenfourfox.git
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161 lines
5.7 KiB
C++
161 lines
5.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* 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 nsStringBuffer_h__
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#define nsStringBuffer_h__
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#include "mozilla/Atomics.h"
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#include "mozilla/MemoryReporting.h"
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template<class T> struct already_AddRefed;
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/**
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* This structure precedes the string buffers "we" allocate. It may be the
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* case that nsTAString::mData does not point to one of these special
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* buffers. The mFlags member variable distinguishes the buffer type.
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*
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* When this header is in use, it enables reference counting, and capacity
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* tracking. NOTE: A string buffer can be modified only if its reference
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* count is 1.
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*/
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class nsStringBuffer
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{
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private:
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friend class CheckStaticAtomSizes;
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mozilla::Atomic<int32_t> mRefCount;
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uint32_t mStorageSize;
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public:
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/**
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* Allocates a new string buffer, with given size in bytes and a
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* reference count of one. When the string buffer is no longer needed,
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* it should be released via Release.
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*
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* It is up to the caller to set the bytes corresponding to the string
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* buffer by calling the Data method to fetch the raw data pointer. Care
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* must be taken to properly null terminate the character array. The
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* storage size can be greater than the length of the actual string
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* (i.e., it is not required that the null terminator appear in the last
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* storage unit of the string buffer's data).
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*
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* @return new string buffer or null if out of memory.
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*/
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static already_AddRefed<nsStringBuffer> Alloc(size_t aStorageSize);
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/**
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* Resizes the given string buffer to the specified storage size. This
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* method must not be called on a readonly string buffer. Use this API
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* carefully!!
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*
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* This method behaves like the ANSI-C realloc function. (i.e., If the
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* allocation fails, null will be returned and the given string buffer
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* will remain unmodified.)
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*
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* @see IsReadonly
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*/
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static nsStringBuffer* Realloc(nsStringBuffer* aBuf, size_t aStorageSize);
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/**
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* Increment the reference count on this string buffer.
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*/
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void NS_FASTCALL AddRef();
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/**
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* Decrement the reference count on this string buffer. The string
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* buffer will be destroyed when its reference count reaches zero.
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*/
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void NS_FASTCALL Release();
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/**
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* This method returns the string buffer corresponding to the given data
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* pointer. The data pointer must have been returned previously by a
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* call to the nsStringBuffer::Data method.
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*/
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static nsStringBuffer* FromData(void* aData)
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{
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return reinterpret_cast<nsStringBuffer*>(aData) - 1;
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}
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/**
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* This method returns the data pointer for this string buffer.
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*/
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void* Data() const
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{
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return const_cast<char*>(reinterpret_cast<const char*>(this + 1));
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}
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/**
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* This function returns the storage size of a string buffer in bytes.
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* This value is the same value that was originally passed to Alloc (or
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* Realloc).
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*/
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uint32_t StorageSize() const
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{
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return mStorageSize;
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}
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/**
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* If this method returns false, then the caller can be sure that their
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* reference to the string buffer is the only reference to the string
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* buffer, and therefore it has exclusive access to the string buffer and
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* associated data. However, if this function returns true, then other
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* consumers may rely on the data in this buffer being immutable and
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* other threads may access this buffer simultaneously.
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*/
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bool IsReadonly() const
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{
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return mRefCount > 1;
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}
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/**
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* The FromString methods return a string buffer for the given string
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* object or null if the string object does not have a string buffer.
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* The reference count of the string buffer is NOT incremented by these
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* methods. If the caller wishes to hold onto the returned value, then
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* the returned string buffer must have its reference count incremented
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* via a call to the AddRef method.
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*/
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static nsStringBuffer* FromString(const nsAString& aStr);
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static nsStringBuffer* FromString(const nsACString& aStr);
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/**
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* The ToString methods assign this string buffer to a given string
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* object. If the string object does not support sharable string
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* buffers, then its value will be set to a copy of the given string
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* buffer. Otherwise, these methods increment the reference count of the
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* given string buffer. It is important to specify the length (in
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* storage units) of the string contained in the string buffer since the
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* length of the string may be less than its storage size. The string
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* must have a null terminator at the offset specified by |len|.
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*
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* NOTE: storage size is measured in bytes even for wide strings;
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* however, string length is always measured in storage units
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* (2-byte units for wide strings).
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*/
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void ToString(uint32_t aLen, nsAString& aStr, bool aMoveOwnership = false);
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void ToString(uint32_t aLen, nsACString& aStr, bool aMoveOwnership = false);
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/**
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* This measures the size only if the StringBuffer is unshared.
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*/
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size_t SizeOfIncludingThisIfUnshared(mozilla::MallocSizeOf aMallocSizeOf) const;
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/**
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* This measures the size regardless of whether the StringBuffer is
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* unshared.
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*
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* WARNING: Only use this if you really know what you are doing, because
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* it can easily lead to double-counting strings. If you do use them,
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* please explain clearly in a comment why it's safe and won't lead to
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* double-counting.
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*/
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size_t SizeOfIncludingThisEvenIfShared(mozilla::MallocSizeOf aMallocSizeOf) const;
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};
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#endif /* !defined(nsStringBuffer_h__ */
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