Minor cleanup

runtime/vm/profiler.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PROFILER_H_
 #define VM_PROFILER_H_
 
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
 #include "vm/code_observers.h"
@@ skipping 20 matching lines @@
   static void Shutdown();
 
   static void SetSampleDepth(intptr_t depth);
   static void SetSamplePeriod(intptr_t period);
 
   static SampleBuffer* sample_buffer() {
     return sample_buffer_;
   }
 
   static void SampleAllocation(Thread* thread, intptr_t cid);
+
+  // SampleThread is called from inside the signal handler and hence it is very
+  // critical that the implementation of SampleThread does not do any of the
+  // following:
+  //   * Accessing TLS -- Because on Windows the callback will be running in a
+  //                      different thread.
+  //   * Allocating memory -- Because this takes locks which may already be
+  //                          held, resulting in a dead lock.
+  //   * Taking a lock -- See above.
   static void SampleThread(Thread* thread,
                            const InterruptedThreadState& state);
 
  private:
   static bool initialized_;
   static Monitor* monitor_;
 
   static SampleBuffer* sample_buffer_;
 
   friend class Thread;
@@ skipping 471 matching lines @@
 
  private:
   ZoneGrowableArray<ProcessedSample*> samples_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessedSampleBuffer);
 };
 
 }  // namespace dart
 
 #endif  // VM_PROFILER_H_