Revert of tracing v2: Introduce TraceBufferWriter

components/tracing/core/trace_buffer_writer.h

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef COMPONENTS_TRACING_CORE_TRACE_BUFFER_WRITER_H_
-#define COMPONENTS_TRACING_CORE_TRACE_BUFFER_WRITER_H_
-
-#include "base/macros.h"
-#include "components/tracing/core/proto_zero_message.h"
-#include "components/tracing/core/proto_zero_message_handle.h"
-#include "components/tracing/core/scattered_stream_writer.h"
-#include "components/tracing/core/trace_ring_buffer.h"
-#include "components/tracing/tracing_export.h"
-
-namespace tracing {
-
-// TODO(primiano): in next CL the Event class will just come from the C++
-// header generated by the ProtoZero plugin.
-namespace proto {
-class Event : public v2::ProtoZeroMessage {};
-}
-
-namespace v2 {
-
-using TraceEventHandle = ProtoZeroMessageHandle<proto::Event>;
-
-// This class is the entry-point to add events to the TraceRingBuffer.
-// It acts as a glue layer between the protobuf classes (ProtoZeroMessage) and
-// the chunked trace ring buffer (TraceRingBuffer). This class is deliberately
-// NOT thread safe. The expected design is that each thread owns an instance of
-// TraceBufferWriter and that trace events produced on one thread are not passed
-// to other threads.
-class TRACING_EXPORT TraceBufferWriter
-    : public ScatteredStreamWriter::Delegate {
- public:
-  // |trace_ring_buffer| is the underlying ring buffer for taking and returning
-  // chunks. |writer_id| is an identifier, unique for each instance, which is
-  // appended to the header of each chunk. Its purpose is to allow the importer
-  // to reconstruct the logical sequence of chunks for a given writer. Think to
-  // this as a thread-id (just, in rare cases, some threads can have more than
-  // one writer).
-  TraceBufferWriter(TraceRingBuffer* trace_ring_buffer, uint32_t writer_id);
-  ~TraceBufferWriter() override;
-
-  // Adds a new event and returns a handle to it. The new event is valid (can be
-  // populated) until the next call to AddEvent(). The new event is finalized
-  // and fully committed to the ring buffer on the next call to AddEvent() or
-  // when the returned handle goes out of scope, whichever comes first.
-  TraceEventHandle AddEvent();
-
-  // ScatteredStreamWriter::Delegate implementation.
-  // Called by the ProtoZeroMessage's ScatteredStreamWriter when the caller
-  // tries to append a new field and the write overflows the current chunk.
-  ContiguousMemoryRange GetNewBuffer() override;
-
-  // Finalize the pending event (if any) and returns back all chunks to the
-  // |trace_ring_buffer_|.
-  void Flush();
-
-  const ScatteredStreamWriter& stream_writer() const { return stream_writer_; }
-
-  uint32_t writer_id() const { return writer_id_; }
-
- private:
-  void FinalizeCurrentEvent();
-  void FinalizeCurrentChunk(bool is_fragmenting_event);
-  ContiguousMemoryRange AcquireNewChunk(bool event_continues_from_prev_chunk);
-  uint8_t* WriteEventPreambleForNewChunk(uint8_t* begin);
-
-  TraceRingBuffer* trace_ring_buffer_;
-
-  // Unique id of this writer (see comment in the ctor).
-  const uint32_t writer_id_;
-
-  // Monotonic counter (within the scope of writer_id_) of chunks.
-  uint32_t chunk_seq_id_;
-
-  // The last chunk acquired from the ring buffer. nullptr before the first call
-  // to AddEvent(). Each instance can own more than one chunk at any given time
-  // (to deal with messages larger than a chunk). This is being tracked through
-  // the singly linked list Chunk::next_in_owner_list().
-  TraceRingBuffer::Chunk* chunk_;
-
-  // Used to work out how many bytes for the current |event_| lie in the current
-  // |chunk_|.
-  uint8_t* event_data_start_in_current_chunk_;
-
-  ScatteredStreamWriter stream_writer_;
-
-  // This field should be a proto::Event. However, ProtoZeroMessage subclasses
-  // are stateless by design. This avoids to pull the full tree of autogenerated
-  // headers for the stub classes and reduce build time.
-  ProtoZeroMessage event_;
-
-  DISALLOW_COPY_AND_ASSIGN(TraceBufferWriter);
-};
-
-}  // namespace v2
-}  // namespace tracing
-
-#endif  // COMPONENTS_TRACING_CORE_TRACE_BUFFER_WRITER_H_