TI Evolving the UNIX System Interface to Support Multithreaded
Programs. 

OR SRC 

LT 21 

MN September 

DY 28 

YR 1987 

AU Paul R. McJones 

AU Garret F. Swart. 

PA 100 pages. 

AB Multiple threads (program counters executing in the same
address space) make it easier to write programs that deal with
related asynchronous activities and that execute faster on
shared-memory multiprocessors.  Supporting multiple threads
places new constraints on the design of operating system
interfaces.  Part I of this report presents guidelines for
designing (or redesigning) interfaces for multithreaded clients. 
We show how these guidelines were used to design an interface to
UNIX-compatible file and process management facilities in the
Topaz operating system.  Two implementations of this interface
are in everyday use: a native one for the Firefly multiprocessor,
and a layered one running within a UNIX process.  Part II is the
actual programmer's manual for the interface discussed in Part I. 

CO UNIX was designed to support client address spaces containing
exactly one program counter.  This assumption about a UNIX
process has had a remarkably pervasive influence on the interface
to the UNIX kernel.  This report documents a successful project
to provide an alternative interface, for multithreaded address
spaces, to the UNIX file and process facilities.  Single-threaded
processes using the UNIX kernel interface, and multithreaded
processes using the alternative, can cohabit the same system and
cooperate.  Part I of the report is a paper that discusses the
general issues and solutions.  Part II is a programmer's manual
for the new interface.  The inclusion of this second part will
allow the interested reader to answer quite detailed questions
about how the system may be used.  The techniques discussed in
Part I will apply to efforts to provide a more modern,
multithreaded interface to other operating systems with
single-threaded client interfaces.  Michael Schroeder