127 lines
3.5 KiB
C++
127 lines
3.5 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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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 PROFILEJSONWRITER_H
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#define PROFILEJSONWRITER_H
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#include <ostream>
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#include <string>
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#include <string.h>
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#include "mozilla/JSONWriter.h"
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#include "mozilla/UniquePtr.h"
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class SpliceableChunkedJSONWriter;
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// On average, profile JSONs are large enough such that we want to avoid
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// reallocating its buffer when expanding. Additionally, the contents of the
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// profile are not accessed until the profile is entirely written. For these
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// reasons we use a chunked writer that keeps an array of chunks, which is
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// concatenated together after writing is finished.
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class ChunkedJSONWriteFunc : public mozilla::JSONWriteFunc
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{
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public:
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friend class SpliceableJSONWriter;
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ChunkedJSONWriteFunc() {
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AllocChunk(kChunkSize);
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}
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bool IsEmpty() const {
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MOZ_ASSERT_IF(!mChunkPtr, !mChunkEnd &&
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mChunkList.length() == 0 &&
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mChunkLengths.length() == 0);
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return !mChunkPtr;
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}
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void Write(const char* aStr) override;
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mozilla::UniquePtr<char[]> CopyData() const;
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void Take(ChunkedJSONWriteFunc&& aOther);
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private:
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void AllocChunk(size_t aChunkSize);
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static const size_t kChunkSize = 4096 * 512;
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// Pointer for writing inside the current chunk.
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//
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// The current chunk is always at the back of mChunkList, i.e.,
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// mChunkList.back() <= mChunkPtr <= mChunkEnd.
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char* mChunkPtr;
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// Pointer to the end of the current chunk.
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//
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// The current chunk is always at the back of mChunkList, i.e.,
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// mChunkEnd >= mChunkList.back() + mChunkLengths.back().
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char* mChunkEnd;
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// List of chunks and their lengths.
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//
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// For all i, the length of the string in mChunkList[i] is
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// mChunkLengths[i].
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mozilla::Vector<mozilla::UniquePtr<char[]>> mChunkList;
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mozilla::Vector<size_t> mChunkLengths;
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};
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struct OStreamJSONWriteFunc : public mozilla::JSONWriteFunc
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{
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explicit OStreamJSONWriteFunc(std::ostream& aStream)
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: mStream(aStream)
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{ }
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void Write(const char* aStr) override {
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mStream << aStr;
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}
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std::ostream& mStream;
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};
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class SpliceableJSONWriter : public mozilla::JSONWriter
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{
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public:
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explicit SpliceableJSONWriter(mozilla::UniquePtr<mozilla::JSONWriteFunc> aWriter)
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: JSONWriter(mozilla::Move(aWriter))
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{ }
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void StartBareList(CollectionStyle aStyle = SingleLineStyle) {
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StartCollection(nullptr, "", aStyle);
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}
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void EndBareList() {
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EndCollection("");
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}
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void NullElements(uint32_t aCount) {
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for (uint32_t i = 0; i < aCount; i++) {
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NullElement();
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}
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}
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void Splice(const ChunkedJSONWriteFunc* aFunc);
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void Splice(const char* aStr);
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// Takes the chunks from aFunc and write them. If move is not possible
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// (e.g., using OStreamJSONWriteFunc), aFunc's chunks are copied and its
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// storage cleared.
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virtual void TakeAndSplice(ChunkedJSONWriteFunc* aFunc);
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};
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class SpliceableChunkedJSONWriter : public SpliceableJSONWriter
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{
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public:
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explicit SpliceableChunkedJSONWriter()
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: SpliceableJSONWriter(mozilla::MakeUnique<ChunkedJSONWriteFunc>())
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{ }
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ChunkedJSONWriteFunc* WriteFunc() const {
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return static_cast<ChunkedJSONWriteFunc*>(JSONWriter::WriteFunc());
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}
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// Adopts the chunks from aFunc without copying.
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virtual void TakeAndSplice(ChunkedJSONWriteFunc* aFunc) override;
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};
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#endif // PROFILEJSONWRITER_H
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