V8 API Reference, 7.2.502.16 (for Deno 0.2.4)
trace-buffer.cc
1 // Copyright 2016 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #include "src/libplatform/tracing/trace-buffer.h"
6 
7 namespace v8 {
8 namespace platform {
9 namespace tracing {
10 
11 TraceBufferRingBuffer::TraceBufferRingBuffer(size_t max_chunks,
12  TraceWriter* trace_writer)
13  : max_chunks_(max_chunks) {
14  trace_writer_.reset(trace_writer);
15  chunks_.resize(max_chunks);
16 }
17 
18 TraceObject* TraceBufferRingBuffer::AddTraceEvent(uint64_t* handle) {
19  base::MutexGuard guard(&mutex_);
20  if (is_empty_ || chunks_[chunk_index_]->IsFull()) {
21  chunk_index_ = is_empty_ ? 0 : NextChunkIndex(chunk_index_);
22  is_empty_ = false;
23  auto& chunk = chunks_[chunk_index_];
24  if (chunk) {
25  chunk->Reset(current_chunk_seq_++);
26  } else {
27  chunk.reset(new TraceBufferChunk(current_chunk_seq_++));
28  }
29  }
30  auto& chunk = chunks_[chunk_index_];
31  size_t event_index;
32  TraceObject* trace_object = chunk->AddTraceEvent(&event_index);
33  *handle = MakeHandle(chunk_index_, chunk->seq(), event_index);
34  return trace_object;
35 }
36 
37 TraceObject* TraceBufferRingBuffer::GetEventByHandle(uint64_t handle) {
38  base::MutexGuard guard(&mutex_);
39  size_t chunk_index, event_index;
40  uint32_t chunk_seq;
41  ExtractHandle(handle, &chunk_index, &chunk_seq, &event_index);
42  if (chunk_index >= chunks_.size()) return nullptr;
43  auto& chunk = chunks_[chunk_index];
44  if (!chunk || chunk->seq() != chunk_seq) return nullptr;
45  return chunk->GetEventAt(event_index);
46 }
47 
48 bool TraceBufferRingBuffer::Flush() {
49  base::MutexGuard guard(&mutex_);
50  // This flushes all the traces stored in the buffer.
51  if (!is_empty_) {
52  for (size_t i = NextChunkIndex(chunk_index_);; i = NextChunkIndex(i)) {
53  if (auto& chunk = chunks_[i]) {
54  for (size_t j = 0; j < chunk->size(); ++j) {
55  trace_writer_->AppendTraceEvent(chunk->GetEventAt(j));
56  }
57  }
58  if (i == chunk_index_) break;
59  }
60  }
61  trace_writer_->Flush();
62  // This resets the trace buffer.
63  is_empty_ = true;
64  return true;
65 }
66 
67 uint64_t TraceBufferRingBuffer::MakeHandle(size_t chunk_index,
68  uint32_t chunk_seq,
69  size_t event_index) const {
70  return static_cast<uint64_t>(chunk_seq) * Capacity() +
71  chunk_index * TraceBufferChunk::kChunkSize + event_index;
72 }
73 
74 void TraceBufferRingBuffer::ExtractHandle(uint64_t handle, size_t* chunk_index,
75  uint32_t* chunk_seq,
76  size_t* event_index) const {
77  *chunk_seq = static_cast<uint32_t>(handle / Capacity());
78  size_t indices = handle % Capacity();
79  *chunk_index = indices / TraceBufferChunk::kChunkSize;
80  *event_index = indices % TraceBufferChunk::kChunkSize;
81 }
82 
83 size_t TraceBufferRingBuffer::NextChunkIndex(size_t index) const {
84  if (++index >= max_chunks_) index = 0;
85  return index;
86 }
87 
88 TraceBufferChunk::TraceBufferChunk(uint32_t seq) : seq_(seq) {}
89 
90 void TraceBufferChunk::Reset(uint32_t new_seq) {
91  next_free_ = 0;
92  seq_ = new_seq;
93 }
94 
95 TraceObject* TraceBufferChunk::AddTraceEvent(size_t* event_index) {
96  *event_index = next_free_++;
97  return &chunk_[*event_index];
98 }
99 
100 TraceBuffer* TraceBuffer::CreateTraceBufferRingBuffer(
101  size_t max_chunks, TraceWriter* trace_writer) {
102  return new TraceBufferRingBuffer(max_chunks, trace_writer);
103 }
104 
105 } // namespace tracing
106 } // namespace platform
107 } // namespace v8
Definition: libplatform.h:13