[tracing] Fix mising thread names in heap profiler

base/trace_event/heap_profiler_allocation_context_tracker.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_allocation_context_tracker.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/atomicops.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 {
 
 subtle::Atomic32 AllocationContextTracker::capture_mode_ =
     static_cast<int32_t>(AllocationContextTracker::CaptureMode::DISABLED);
 
 namespace {
 
 const size_t kMaxStackDepth = 128u;
 const size_t kMaxTaskDepth = 16u;
@@ skipping 111 matching lines @@
     ctx.backtrace.frame_count = 1;
     return ctx;
   }
 
   CaptureMode mode = static_cast<CaptureMode>(
       subtle::NoBarrier_Load(&capture_mode_));
 
   auto backtrace = std::begin(ctx.backtrace.frames);
   auto backtrace_end = std::end(ctx.backtrace.frames);
 
-  // Add the thread name as the first entry
+#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.
+  if (!thread_name_) {
+    // Ignore the string allocation and allocations from prctl to avoid

[Dmitry Skiba, 2016/05/13 18:34:06]

prctl is a syscall, there can be no reentrancy.

[ssid, 2016/05/13 20:48:08]

Ah yes, I thought it was causing reentrancy too. Fixed comment

+    // reentrancy.
+    ignore_scope_depth_++;
+    char* leaked_str = new char[16];
+    int err = prctl(PR_GET_NAME, leaked_str);
+    ignore_scope_depth_--;
+
+    if (err) {
+      // Set thread name to "Unknown" so that we call prctl only once per
+      // thread.
+      thread_name_ = "Unknown";

[Dmitry Skiba, 2016/05/13 18:34:06]

Let's format thread id instead. Hmm, and I think snprintf() can actually
allocate, so you might need reentrancy check anyway.

[ssid, 2016/05/13 20:48:08]

Hm, do you think it is useful to see a thread id instead of unknown? This also
causes an extra string leak and branching in the view.

+      free(leaked_str);

[Dmitry Skiba, 2016/05/13 18:34:06]

Use 'delete []' here since you allocated with new. Better approach might be to
start with stack array and then strdup() it on assignment to thread_name_.

[ssid, 2016/05/13 20:48:09]

Yes, fixed.

+    } else {
+      thread_name_ = leaked_str;
+    }
+  }
+#endif  // defined(OS_LINUX) || defined(OS_ANDROID)
+
+  // Add the thread name as the first entry in pseudo stack.
   if (thread_name_) {
     *backtrace++ = StackFrame::FromThreadName(thread_name_);
   }
 
   switch (mode) {
     case CaptureMode::DISABLED:
       {
         break;
       }
     case CaptureMode::PSEUDO_STACK:
@@ skipping 42 matching lines @@
 
   // 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;
 }
 
 }  // namespace trace_event
 }  // namespace base