[tracing] Adding task information to heap profiler

base/trace_event/heap_profiler_allocation_context_tracker.cc

Index: base/trace_event/heap_profiler_allocation_context_tracker.cc
diff --git a/base/trace_event/heap_profiler_allocation_context_tracker.cc b/base/trace_event/heap_profiler_allocation_context_tracker.cc
index 0aa54a84ed380f8ee7e8f669bd78532041943e14..518792c4a5034b448eb364d13c3b223da147a4dd 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.cc
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.cc
@@ -19,6 +19,7 @@ subtle::Atomic32 AllocationContextTracker::capture_enabled_ = 0;
 namespace {
 
 const size_t kMaxStackDepth = 128u;
+const size_t kMaxTaskDepth = 16u;
 AllocationContextTracker* const kInitializingSentinel =
     reinterpret_cast<AllocationContextTracker*>(-1);
 
@@ -51,6 +52,7 @@ AllocationContextTracker::GetInstanceForCurrentThread() {
 
 AllocationContextTracker::AllocationContextTracker() : thread_name_(nullptr) {
   pseudo_stack_.reserve(kMaxStackDepth);
+  task_contexts_.reserve(kMaxTaskDepth);
 }
 AllocationContextTracker::~AllocationContextTracker() {}
 
@@ -99,6 +101,20 @@ void AllocationContextTracker::PopPseudoStackFrame(StackFrame frame) {
   pseudo_stack_.pop_back();
 }
 
+void AllocationContextTracker::PushCurrentTaskContext(const char* context) {
+  DCHECK(context);
+  if (task_contexts_.size() < kMaxTaskDepth)

[oystein (OOO til 10th of July), 2016/03/29 21:28:35]

Shouldn't this be a DCHECK(task_contexts.size() < kMaxTaskDepth); instead? With
only NOTREACHED() in the else fork, that's effectively what it is.

[ssid, 2016/03/29 23:04:19]

if the code was:
DCHECK(task_contexts.size() < kMaxTaskDepth);
task_contexts_.push_back(context);

in the release builds, it can try to do a pushback and cause an infite loop
because of extra allocation and rentrancy. So, in release builds we just ignore
the push_back and show wrong result instead of crashing or deadlock.

Also, there is predecessor for this piece of code in
AllocationContextTracker::PushPseudoStackFrame line 78. Does the same thing.

[oystein (OOO til 10th of July), 2016/03/29 23:44:51]

Makes sense; thanks!

+    task_contexts_.push_back(context);
+  else
+    NOTREACHED();
+}
+
+void AllocationContextTracker::PopCurrentTaskContext(const char* context) {
+  DCHECK_EQ(context, task_contexts_.back())
+      << "Encountered an unmatched context end";
+  task_contexts_.pop_back();
+}
+
 // static
 AllocationContext AllocationContextTracker::GetContextSnapshot() {
   AllocationContext ctx;
@@ -125,7 +141,9 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
     std::fill(dst, dst_end, nullptr);
   }
 
-  ctx.type_name = nullptr;
+  // TODO(ssid): Fix crbug.com/594803 to add file name as 3rd dimension
+  // (component name) in the heap profiler and not piggy back on the type name.
+  ctx.type_name = task_contexts_.empty() ? nullptr : task_contexts_.back();
 
   return ctx;
 }