[tracing] Fix mising thread names in 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 fd4e21abe5d62d6594e6fd5bf56544228cce92f1..7d6ee5e36c677a0fdc403c8ba5bde909bc56db17 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.cc
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.cc
@@ -8,9 +8,14 @@
 #include <iterator>
 
 #include "base/atomicops.h"
+#include "base/threading/platform_thread.h"
 #include "base/threading/thread_local_storage.h"
 #include "base/trace_event/heap_profiler_allocation_context.h"
 
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+#include <sys/prctl.h>
+#endif
+
 namespace base {
 namespace trace_event {
 
@@ -33,6 +38,27 @@ void DestructAllocationContextTracker(void* alloc_ctx_tracker) {
   delete static_cast<AllocationContextTracker*>(alloc_ctx_tracker);
 }
 
+// Gets the thread name from kernel if available or returns a string with id.
+// This function intenionally leaks the allocated strings since they are used to
+// tag allocations even after the thread dies.
+const char* GetThreadName() {

[Primiano Tucci (use gerrit), 2016/05/17 19:38:43]

can you make this a void GetThreadName(char* out_name, size_t size) and move the
strdup down where you use it?
I can be ok with the strdup but I fear that in future somebody else calls this
and we multiply the leaks. 

[Dmitry Skiba, 2016/05/17 20:05:18]

Let's simply call function LeakThreadName(), and put annotation there? Right now
function knows how much buffer space it needs, by adding name/size arguments you
require callers to care about function's internals  (to justify 16 in your
example below).

[Primiano Tucci (use gerrit), 2016/05/17 20:46:12]

You could pass a std::string* as arugment and leak that.
Anyways LGTM both ways (either with the Leak in the name or leaking a
std::string).
You guys figure out. Just remember the annotation :)

[ssid, 2016/05/18 03:38:05]

Changed the name and added ANNOTATE_LEAKING_OBJECT_PTR.

+  char name[16];
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+  // If the thread name is not set, try to get it from prctl. Thread name might
+  // not be set in cases where the thread started before heap profiling was
+  // enabled.
+  int err = prctl(PR_GET_NAME, name);
+  if (!err) {
+    return strdup(name);

[Primiano Tucci (use gerrit), 2016/05/17 19:38:44]

once you move this, make sure you include leak_annotations.h and use
ANNOTATE_LEAKING_OBJECT_PTR(duped_str_ptr).
Otherwise your patch will be reverted as soon as it hits the asan bots :)

[ssid, 2016/05/18 03:38:05]

Done.

+  }
+#endif  // defined(OS_LINUX) || defined(OS_ANDROID)
+
+  // Use tid if we don't have a thread name.
+  snprintf(name, sizeof(name), "%lu",
+           static_cast<unsigned long>(PlatformThread::CurrentId()));
+  return strdup(name);

[Primiano Tucci (use gerrit), 2016/05/17 19:38:43]

instead of strduping twice what you want to do below is:

if(!thread_name_) {
 thread_name = new char[16];
 ANNOTATE_LEAKING_OBJECT_PTR(thread_name_);
 GetThreadName(&thread_name, sizeof(thread_name))
}

[ssid, 2016/05/18 03:38:05]

Keepin strdup twice.

+}
+
 }  // namespace
 
 // static
@@ -142,7 +168,15 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
   auto backtrace = std::begin(ctx.backtrace.frames);
   auto backtrace_end = std::end(ctx.backtrace.frames);
 
-  // Add the thread name as the first entry
+  if (!thread_name_) {
+    // Ignore the string allocation made by GetThreadName to avoid reentrancy.
+    ignore_scope_depth_++;
+    thread_name_ = GetThreadName();
+    DCHECK(thread_name_);
+    ignore_scope_depth_--;
+  }
+
+  // Add the thread name as the first entry in pseudo stack.
   if (thread_name_) {
     *backtrace++ = StackFrame::FromThreadName(thread_name_);
   }