From: "vjoel (Joel VanderWerf)" <vjoel@...>
Date: 2013-03-20T02:21:49+09:00
Subject: [ruby-core:53552] [ruby-trunk - Bug #8125][Open] lost-tuple bug and fix for Rinda::TupleSpaceProxy.take


Issue #8125 has been reported by vjoel (Joel VanderWerf).

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Bug #8125: lost-tuple bug and fix for Rinda::TupleSpaceProxy.take
https://bugs.ruby-lang.org/issues/8125

Author: vjoel (Joel VanderWerf)
Status: Open
Priority: Normal
Assignee: 
Category: lib
Target version: 
ruby -v: ruby 2.0.0p0 (2013-02-24) [x86_64-linux]


=begin

Rinda::TupleSpaceProxy prevents tuple loss during #take by exposing a "port" object on the client that the remote side (the tuplespace server) pushes to, instead of relying on the method return value. Pushing to the port fails if the process that called #take has exited, so the tuple will not be deleted from the tuplespace server.

However, if the process has not exited, and the thread that called #take was interrupted, the port still exists and accepts push requests (in the main drb thread). In this case the tuple is deleted on the server and not available on the client.

This is frequently a problem when using irb and manually interrupting take calls. It would also be a problem when using timeouts.

A concise reproduction of the problem is in the attached thread-int.rb.

The bug can be fixed by the patch below, which replaces the port array with a custom object that rejects pushes if the call stack has been unwound.

Note that this patch combines naturally with the faster take patch in #8119.


  diff --git a/lib/rinda/rinda.rb b/lib/rinda/rinda.rb
  index 18e284a..057c61a 100644
  --- a/lib/rinda/rinda.rb
  +++ b/lib/rinda/rinda.rb
  @@ -206,6 +206,23 @@ module Rinda
     # TupleSpaceProxy allows a remote Tuplespace to appear as local.

     class TupleSpaceProxy
  +    class Port
  +      attr_reader :val
  +
  +      def initialize
  +        @open = true
  +      end
  +      
  +      def close
  +        @open = false
  +      end
  +
  +      def push val
  +        raise unless @open
  +        @val = val
  +        nil # so that val doesn't get marshalled again
  +      end
  +    end

       ##
       # Creates a new TupleSpaceProxy to wrap +ts+.
  @@ -222,6 +239,19 @@ module Rinda
       end

       ##
  +    # Safely takes +tuple+ from the proxied TupleSpace.  See TupleSpace#take.
  +    # Ensures that an interrupted thread will not become a lasting cause
  +    # of further data loss.
  +
  +    def take_safely(tuple, sec=nil, &block)
  +      port = Port.new
  +      @ts.move(DRbObject.new(port), tuple, sec, &block)
  +      port.val
  +    ensure
  +      port.close # don't let the DRb thread push to it when remote sends tuple
  +    end
  +
  +    ##
       # Takes +tuple+ from the proxied TupleSpace.  See TupleSpace#take.

       def take(tuple, sec=nil, &block)

=end



-- 
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