%T JCSP\-Poison: Safe Termination of CSP Process Networks
%A  Bernhard H.C. Sputh,  Alastair R. Allen
%E  Jan F. Broenink,  Herman Roebbers,  Johan P. E. Sunter, Peter H. Welch,  David C. Wood
%B Communicating Process Architectures 2005
%X This paper presents a novel technique for safe partial or
   complete process network termination. The idea is to have
   two types of termination messages / poison: LocalPoison and
   GlobalPoison. Injecting GlobalPoison into a process network
   results in a safe termination of the whole process network.
   In contrast, injected LocalPoison only terminates all
   processes until it is filtered out by Poison\-Filtering
   Channels. This allows the creation of termination domains
   inside a process network. To make handling of a termination
   message easy, it is delivered as an exception and not as a
   normal message. The necessary Poisonable\- and
   Poison\-Filtering\-Channels have been modelled in CSP and
   checked using FDR. A proof of concept implementation for
   Communicating Sequential Processes for Java (JCSP) has been
   developed and refined. Previously, JCSP offered no safe way
   to terminate the process network. When the user terminated
   the program, the Java Virtual Machine (JVM) simply stops all
   threads (processes), without giving the processes the chance
   to perform clean up operations. A similar technique is used
   to perform partial termination of process networks in JCSP,
   making it unsafe as well. The technique presented in this
   paper is not limited to JCSP, but can easily be ported to
   other CSP environments. Partial process network termination
   can be applied in the area of Software Defined Radio (SDR),
   because SDR systems need to be able to change their signal
   processing algorithms during runtime.