VM: Fix deadlock in time line recording.

runtime/vm/os_thread.h

 // Copyright (c) 2012, 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_OS_THREAD_H_
 #define VM_OS_THREAD_H_
 
 #include "platform/globals.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 229 matching lines @@
   // Returns the current thread and moves forward.
   OSThread* Next();
 
  private:
   OSThread* next_;
 };
 
 
 class Mutex {
  public:
-  Mutex();
+  explicit Mutex(bool recursive = false);

[Ivan Posva, 2015/12/09 16:34:57]

The class Mutex is defined to not ever be recursive. If we have such a case then
the algorithm needs to be updated.

[Florian Schneider, 2015/12/10 14:44:21]

What would break otherwise? I didn't see any tests failing, so at least there is
no test coverage of this assumption.

   ~Mutex();
 
   void Lock();
   bool TryLock();
   void Unlock();
 
 #if defined(DEBUG)
   bool IsOwnedByCurrentThread() const {
     return owner_ == OSThread::GetCurrentThreadId();
   }
@@ skipping 55 matching lines @@
 #endif  // defined(DEBUG)
 
   DISALLOW_COPY_AND_ASSIGN(Monitor);
 };
 
 
 }  // namespace dart
 
 
 #endif  // VM_OS_THREAD_H_