ANSI C -- longjmp and volatiles

[Martin Minow]

This is one of a collection of comments on the Draft Standard, posted to
comp.lang.c for discussion before I mail a final draft to the Ansi C
committee.  Each message discusses one problem I have found with the Draft
Standard that I feel warrants a "no" vote.  Note that this message is my
personal opinion, and does not reflect on the opinions of my employer.

---- Problem:

Page 202, line 46ff. volatile objects will have indeterminate values if
longjmp() is called ``in contexts of signals, interrupts, and any of their
associated functions.''

---- Motivation:

If longjmp() is called from a signal handler, volatile objects may have
indeterminate values as they cannot always be updated by atomic (one machine
cycle) operations. It is unrealistic to require an implementation to lock
interrupts before modifying a volatile object.  The Standard should note that
volatile objects are indeterminate when longjmp() is called from an interrupt
or signal handler.

I would suspect that, in some implementations, longjmp() cannot be called
from interrupt or signal handlers.  I would recommend that this capability
be regarded as implementation-dependent.

----

Martin Minow
decvax!minow