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

["Robert Jongbloed" <robert.jongbloed@xxxxxxxxxxx>]

OK, fixed in trunk.

Why it was that way for RTEMS and not every other platform is beyond me!


Robert Jongbloed
OPAL/OpenH323 Architect and Co-founder.


> -----Original Message-----
> From: openh323-devel-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:openh323-
> devel-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Thien Nguyen
> Sent: Tuesday, 19 August 2008 6:03 PM
> To: openh323-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: [Openh323-devel] Bug : PRandom::Number() is not thread-safe
> with VC++ compiler.
> 
> 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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