[Tracing] V8 Tracing Controller

src/libplatform/tracing/trace-buffer.cc

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/libplatform/tracing/trace-buffer.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+TraceBufferRingBuffer::TraceBufferRingBuffer(size_t max_chunks,
+                                             TraceWriter* trace_writer)
+    : max_chunks_(max_chunks), is_empty_(true), current_chunk_seq_(1) {
+  trace_writer_.reset(trace_writer);
+  chunks_.resize(max_chunks);
+}
+
+TraceBufferRingBuffer::~TraceBufferRingBuffer() { Flush(); }
+
+TraceObject* TraceBufferRingBuffer::AddTraceEvent(uint64_t* handle) {
+  if (is_empty_ || chunks_[chunk_index_]->IsFull()) {
+    chunk_index_ = is_empty_ ? 0 : NextChunkIndex(chunk_index_);
+    is_empty_ = false;
+    auto& chunk = chunks_[chunk_index_];
+    if (chunk) {
+      chunk->Reset(current_chunk_seq_++);
+    } else {
+      chunk.reset(new TraceBufferChunk(current_chunk_seq_++));
+    }
+  }
+  auto& chunk = chunks_[chunk_index_];
+  size_t event_index;
+  TraceObject* trace_object = chunk->AddTraceEvent(&event_index);
+  *handle = MakeHandle(chunk_index_, chunk->seq(), event_index);
+  return trace_object;
+}
+
+TraceObject* TraceBufferRingBuffer::GetEventByHandle(uint64_t handle) {
+  size_t chunk_index, event_index;
+  uint32_t chunk_seq;
+  ExtractHandle(handle, &chunk_index, &chunk_seq, &event_index);
+  if (chunk_index >= chunks_.size()) return NULL;
+  auto& chunk = chunks_[chunk_index];
+  if (!chunk || chunk->seq() != chunk_seq) return NULL;
+  return chunk->GetEventAt(event_index);
+}
+
+bool TraceBufferRingBuffer::Flush() {
+  // This flushes all the traces stored in the buffer.
+  if (!is_empty_) {
+    for (size_t i = NextChunkIndex(chunk_index_);; i = NextChunkIndex(i)) {
+      if (auto& chunk = chunks_[i]) {
+        for (size_t j = 0; j < chunk->size(); ++j) {
+          trace_writer_->AppendTraceEvent(chunk->GetEventAt(j));
+        }
+      }
+      if (i == chunk_index_) break;
+    }
+  }
+  trace_writer_->Flush();
+  // This resets the trace buffer.
+  is_empty_ = true;
+  return true;
+}
+
+uint64_t TraceBufferRingBuffer::MakeHandle(size_t chunk_index,
+                                           uint32_t chunk_seq,
+                                           size_t event_index) const {
+  return static_cast<uint64_t>(chunk_seq) * Capacity() +
+         chunk_index * TraceBufferChunk::kChunkSize + event_index;
+}
+
+void TraceBufferRingBuffer::ExtractHandle(uint64_t handle, size_t* chunk_index,
+                                          uint32_t* chunk_seq,
+                                          size_t* event_index) const {
+  *chunk_seq = static_cast<uint32_t>(handle / Capacity());
+  size_t indices = handle % Capacity();
+  *chunk_index = indices / TraceBufferChunk::kChunkSize;
+  *event_index = indices % TraceBufferChunk::kChunkSize;
+}
+
+size_t TraceBufferRingBuffer::NextChunkIndex(size_t index) const {
+  if (++index >= max_chunks_) index = 0;
+  return index;
+}
+
+TraceBufferChunk::TraceBufferChunk(uint32_t seq) : next_free_(0), seq_(seq) {}
+
+void TraceBufferChunk::Reset(uint32_t new_seq) {
+  next_free_ = 0;
+  seq_ = new_seq;
+}
+
+TraceObject* TraceBufferChunk::AddTraceEvent(size_t* event_index) {
+  *event_index = next_free_++;
+  return &chunk_[*event_index];
+}
+
+TraceBuffer* TraceBuffer::CreateTraceBufferRingBuffer(
+    size_t max_chunks, TraceWriter* trace_writer) {
+  return new TraceBufferRingBuffer(max_chunks, trace_writer);
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8