components/tracing/proto/events_chunk.proto

// 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.

syntax = "proto2";
option optimize_for = LITE_RUNTIME;

package tracing.proto;

// An EventsChunk is a fixed portion of the trace ring buffer which is written
// exclusively by one writer (almost always 1 writer == 1 thread). It contains
// a variable number of variable-sized events. Events can be fragmented across
// several chunks.

message EventsChunk {
  // Chunks produced by the same trace writer have the same writer_id. This
  // allows to identify the next chunk for a writer (thread) in the ring buffer.
  optional uint32 writer_id = 1;

  // A monotonic counter within the writer, to establish sequencing of chunks.
  optional uint32 seq_id = 2;

  // Each event is a byte sequence that encapsulates the bytes for a single
  // Event (see event.proto) or an incomplete fragment.
  // Why this isn't just a "repeated Events" field? An Event can spawn across
  // several chunks. In this case the reader has to first glue the byte
  // sequences together and then process the event.
  repeated bytes events = 3;

  // The first entry of |events| is a fragment which continues from the previous
  // chunk.
  optional bool first_event_continues_from_prev_chunk = 4;

  // The last entry of |events| is a fragment and contiues into the next chunk.
  optional bool last_event_continues_on_next_chunk = 5;
}