From: Gennady <gfb@...>
Date: 2004-05-28T02:01:37+09:00
Subject: Re: Mutex re-entrancy

You may want to use monitor.rb instead (from the standard ruby 
distribution), it is designed to be reentrant, while Mutex is not.

Gennady.

Martin Hart wrote:
> Hi all,
> 
> I am using a Mutex to protect a function, but I need to call into the
> function again from the same thread without deadlocking:
> 
> class A
>   def initialize
>     @m = Mutex.new
>   end
>   def a
>     @m.synchronize { b }
>   end
>   def b
>     @m.synchronize { puts "hello" }
>   end
> end
> A.new.a #-> deadlock
> 
> It seems to me that to achieve this, all i need to do is track which thread
> has the mutex locked, and allow access if the same thread requests it again:
> 
> class Mutex2
>   def initialize
>     @m = Mutex.new
>     @l = nil
>   end
>   def synchronize
>     if @l == Thread.current
>       yield
>     else
>       @m.synchronize {
>         @l = Thread.current
>         begin
>           yield
>         ensure
>           @l = nil
>         end
>       }
>     end
>   end
> end
> 
> q1) am i reinventing the wheel and/or making it square?
> q2) is this safe?
> 
> TIA
> Martin
> 
>