[Openh323-devel] Bug : PRandom::Number() is not thread-safe with VC++ compiler.

[Thien Nguyen <thienpnguyen@xxxxxxxxx>]

Dear OpenH323 developers,

With VC++ compiler ( and some other compilers), the static object at block scope is not thread-safe. 

http://blogs.msdn.com/oldnewthing/archive/2004/03/08/85901.aspx


Therefore, the following method is not thread-safe.

// pwlib/src/ptclib/random.cxx

unsigned PRandom::Number()
{
#ifndef P_RTEMS
  static PMutex mutex;  //  <-- not thread-safe
#endif
  PWaitAndSignal wait(mutex); 

  static PRandom rand;
  return rand;
}

Here is a "error" scenario :

   a. First thread comes and try to initialize the static object "PMutex mutex" but not finish this task.

   b. Second thread comes and thinks that the static object PMutex mutex was initialize. Therefore, it excecutes "PWaitAndSignal wait(mutex)" : bug will happen because the mutex is not completely  initialized.

Suggestion : move "static PMutex mutex;" into file scope.

Thank for reading.



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