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// 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"
// Fwd declaration from the generated components/tracing/proto/event.pbzero.h.
namespace pbzero {
namespace tracing {
namespace proto {
class Event;
} // namespace proto
} // namespace tracing
} // namespace pbzero
namespace tracing {
namespace v2 {
using TraceEventHandle = ProtoZeroMessageHandle<pbzero::tracing::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_
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