[OBSOLETE] tracing v2: introduce TraceBufferWriter

components/tracing/core/trace_ring_buffer.cc

Index: components/tracing/core/trace_ring_buffer.cc
diff --git a/components/tracing/core/trace_ring_buffer.cc b/components/tracing/core/trace_ring_buffer.cc
index 2a52bf61db1b64350f7d3e20a7f5acb4da63b2c1..510aaa4cf3c75aa5bd6985b2e6e20ac23632d574 100644
--- a/components/tracing/core/trace_ring_buffer.cc
+++ b/components/tracing/core/trace_ring_buffer.cc
@@ -10,7 +10,9 @@ namespace tracing {
 namespace v2 {
 
 TraceRingBuffer::TraceRingBuffer(uint8_t* begin, size_t size)
-    : num_chunks_(size / Chunk::kSize), current_chunk_idx_(0) {
+    : num_chunks_(size / Chunk::kSize),
+      num_chunks_taken_(0),
+      current_chunk_idx_(0) {
   DCHECK_GT(num_chunks_, 0u);
   DCHECK_EQ(0ul, reinterpret_cast<uintptr_t>(begin) % sizeof(uintptr_t));
   chunks_.reset(new Chunk[num_chunks_]);
@@ -23,7 +25,7 @@ TraceRingBuffer::TraceRingBuffer(uint8_t* begin, size_t size)
 
 TraceRingBuffer::~TraceRingBuffer() {}
 
-TraceRingBuffer::Chunk* TraceRingBuffer::TakeChunk() {
+TraceRingBuffer::Chunk* TraceRingBuffer::TakeChunk(uint32_t writer_id) {
   base::AutoLock lock(lock_);
   DCHECK_GT(num_chunks_, 0ul);
   DCHECK_LT(current_chunk_idx_, num_chunks_);
@@ -32,12 +34,15 @@ TraceRingBuffer::Chunk* TraceRingBuffer::TakeChunk() {
     current_chunk_idx_ = (current_chunk_idx_ + 1) % num_chunks_;
     if (!chunk->is_owned()) {
       chunk->Clear();
-      chunk->set_owner(base::PlatformThread::CurrentId());
+      DCHECK_NE(0u, writer_id);
+      chunk->set_owner(writer_id);
+      num_chunks_taken_++;
       return chunk;
     }
   }
 
   // Bankrupcy: there are more threads than chunks. All chunks were in flight.
+  DCHECK_EQ(num_chunks_, num_chunks_taken_);
   if (!bankrupcy_chunk_storage_) {
     bankrupcy_chunk_storage_.reset(new uint8_t[Chunk::kSize]);
     bankrupcy_chunk_.Initialize(&bankrupcy_chunk_storage_.get()[0]);
@@ -46,20 +51,26 @@ TraceRingBuffer::Chunk* TraceRingBuffer::TakeChunk() {
   return &bankrupcy_chunk_;
 }
 
-void TraceRingBuffer::ReturnChunk(TraceRingBuffer::Chunk* chunk,
-                                  uint32_t used_size) {
+void TraceRingBuffer::ReturnChunk(TraceRingBuffer::Chunk* chunk) {
+  // Returning a chunk without using it is quite odd, very likely a bug.
+  DCHECK_GT(chunk->used_size(), 0u);
+
   base::AutoLock lock(lock_);
-  chunk->set_used_size(used_size);
   chunk->clear_owner();
+  chunk->set_next_in_owner_list(nullptr);
+  num_chunks_taken_--;
 }
 
 TraceRingBuffer::Chunk::Chunk()
-    : begin_(nullptr), owner_(base::kInvalidThreadId) {}
+    : begin_(nullptr),
+      owner_(base::kInvalidThreadId),
+      next_in_owner_list_(nullptr) {}
 
 TraceRingBuffer::Chunk::~Chunk() {}
 
 void TraceRingBuffer::Chunk::Clear() {
   set_used_size(0);
+  set_next_in_owner_list(nullptr);
 }
 
 void TraceRingBuffer::Chunk::Initialize(uint8_t* begin) {