Mobile Data Types for Communicating Processes
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F.R.M. Barnes and P.H. Welch
PDPTA 2001, Las Vegas


Aliasing problems are a major source for error in traditional imperative
languages (such as C) and modern object-orientated languages (such as Java,
C++ and C#).  Add in concurrency and the problems compound exponentially.
Improperly synchronised access to shared (i.e. aliased) resources leads to
problems of race hazard, deadlock, livelock and starvation.  This paper
describes the binding into occam (a concurrent processing language based
on CSP) of a secure, dynamic and efficient way of sharing data between
parallel processes with minimal synchronisation overheads.  The key new
facilities provided are: a movement semantics for assignment and
communication, strict zero-aliasing, apparently dynamic memory allocation
and automatic zero-or-very-small-unit-time garbage collection.  With
occam becoming available on a variety of microprocessors for GUI building,
internet services and small-memory-footprint embedded products, these
capabilities are timely.  Lessons are drawn for concurrency back in OO
languages -- and especially for the JCSP (CSP for Java) package library.