[tracing] Switch to new heap dump format.

base/trace_event/heap_profiler_stack_frame_deduplicator.cc

 // Copyright 2015 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.
 
 #include "base/trace_event/heap_profiler_stack_frame_deduplicator.h"
 
 #include <inttypes.h>
 #include <stddef.h>
 
 #include <string>
@@ skipping 10 matching lines @@
 StackFrameDeduplicator::FrameNode::FrameNode(StackFrame frame,
                                              int parent_frame_index)
     : frame(frame), parent_frame_index(parent_frame_index) {}
 StackFrameDeduplicator::FrameNode::FrameNode(const FrameNode& other) = default;
 StackFrameDeduplicator::FrameNode::~FrameNode() {}
 
 size_t StackFrameDeduplicator::FrameNode::EstimateMemoryUsage() const {
   return base::trace_event::EstimateMemoryUsage(children);
 }
 
-StackFrameDeduplicator::StackFrameDeduplicator() {}
+StackFrameDeduplicator::StackFrameDeduplicator() : last_appended_index_(0) {}
 StackFrameDeduplicator::~StackFrameDeduplicator() {}
 
 int StackFrameDeduplicator::Insert(const StackFrame* beginFrame,
                                    const StackFrame* endFrame) {
   int frame_index = -1;
   std::map<StackFrame, int>* nodes = &roots_;
 
   // Loop through the frames, early out when a frame is null.
   for (const StackFrame* it = beginFrame; it != endFrame; it++) {
     StackFrame frame = *it;
@@ skipping 18 matching lines @@
       // A tree node for this frame exists. Look for the next one.
       frame_index = node->second;
     }
 
     nodes = &frames_[frame_index].children;
   }
 
   return frame_index;
 }
 
-void StackFrameDeduplicator::AppendAsTraceFormat(std::string* out) const {
-  out->append("{");  // Begin the |stackFrames| dictionary.
-
-  int i = 0;
-  auto frame_node = begin();
-  auto it_end = end();
+void StackFrameDeduplicator::AppendIncrementally(TracedValue* traced_value) {
   std::string stringify_buffer;
 
-  while (frame_node != it_end) {
-    // The |stackFrames| format is a dictionary, not an array, so the
-    // keys are stringified indices. Write the index manually, then use
-    // |TracedValue| to format the object. This is to avoid building the
-    // entire dictionary as a |TracedValue| in memory.
-    SStringPrintf(&stringify_buffer, "\"%d\":", i);
-    out->append(stringify_buffer);
+  for (; last_appended_index_ < frames_.size(); ++last_appended_index_) {
+    const auto& frame_node = frames_[last_appended_index_];
+    traced_value->BeginDictionary();
 
-    std::unique_ptr<TracedValue> frame_node_value(new TracedValue);
-    const StackFrame& frame = frame_node->frame;
+    traced_value->SetInteger("id", last_appended_index_);
+
+    const StackFrame& frame = frame_node.frame;
     switch (frame.type) {
       case StackFrame::Type::TRACE_EVENT_NAME:
-        frame_node_value->SetString(
-            "name", static_cast<const char*>(frame.value));
+        traced_value->SetString("name", static_cast<const char*>(frame.value));
         break;
       case StackFrame::Type::THREAD_NAME:
         SStringPrintf(&stringify_buffer,
                       "[Thread: %s]",
                       static_cast<const char*>(frame.value));
-        frame_node_value->SetString("name", stringify_buffer);
+        traced_value->SetString("name", stringify_buffer);
         break;
       case StackFrame::Type::PROGRAM_COUNTER:
         SStringPrintf(&stringify_buffer,
                       "pc:%" PRIxPTR,
                       reinterpret_cast<uintptr_t>(frame.value));
-        frame_node_value->SetString("name", stringify_buffer);
+        traced_value->SetString("name", stringify_buffer);
         break;
     }
-    if (frame_node->parent_frame_index >= 0) {
-      SStringPrintf(&stringify_buffer, "%d", frame_node->parent_frame_index);
-      frame_node_value->SetString("parent", stringify_buffer);
+
+    if (frame_node.parent_frame_index >= 0) {
+      traced_value->SetInteger("parent", frame_node.parent_frame_index);

[Primiano Tucci (use gerrit), 2017/02/17 17:07:05]

do we have the guarantee that the parent is always emitted (or has been emitted
by the previous snapshots)?

[DmitrySkiba, 2017/02/23 07:17:19]

Yes, because we dump nodes_ sequentially, and in there parents always precede
children.

     }
-    frame_node_value->AppendAsTraceFormat(out);
 
-    i++;
-    frame_node++;
-
-    if (frame_node != it_end)
-      out->append(",");
+    traced_value->EndDictionary();
   }
-
-  out->append("}");  // End the |stackFrames| dictionary.
 }
 
 void StackFrameDeduplicator::EstimateTraceMemoryOverhead(
     TraceEventMemoryOverhead* overhead) {
   size_t memory_usage =
       EstimateMemoryUsage(frames_) + EstimateMemoryUsage(roots_);
   overhead->Add("StackFrameDeduplicator",
                 sizeof(StackFrameDeduplicator) + memory_usage);
 }
 
 }  // namespace trace_event
 }  // namespace base