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From: jimc@ucla-cs.UUCP
Newsgroups: net.lang.c++
Subject: Re: Re-entrancy Re-visited
Message-ID: <9691@ucla-cs.ARPA>
Date: Thu, 6-Mar-86 20:35:31 EST
Article-I.D.: ucla-cs.9691
Posted: Thu Mar  6 20:35:31 1986
Date-Received: Sun, 9-Mar-86 00:22:10 EST
References: <34200005@orstcs.UUCP>
Reply-To: jimc@ucla-cs.UUCP (Jim Carter)
Organization: UCLA Computer Science Department
Lines: 31

In article <34200005@orstcs.UUCP> nathan@orstcs.UUCP (nathan) writes:
>Under certain C compilers, I can write a complex-number library
>whose functions are usable both in main-line code and in signal
>routines.  It would not be at all portable.  C is not a fully
>re-entrant language.
>
>What galls is that *most* of the language is!  It's only in the
>area of structure handling that the specification is too loose
>to permit portability of programs which need re-entrancy.
>
>If, in the language specification, it doesn't say that
>interrupts won't mess up mainline code's variables, then I as
>a programmer can't count on that fact -- and any program I write
>which needs it is immediately, irreparably nonportable.
>
The draft "C" standard, X3J11/85-138, section B.2.3 "Signals and Exceptions",
states:
   Functions must be implemented such that they may be interrupted at any time
by a signal, and may be called by a signal handler with no alteration to data
with automatic storage duration belonging to earlier invocations...
   The functions in the standard library are not guaranteed to be reentrant...

As for the latter part, I believe it refers to things like asctime that
store results in a static string.  I have recommended a wording change to
"Certain library functions, explicitly noted in the standard, may not be
reentrant."

-- 
James F. Carter            (213) 206-1306
UCLA-SEASnet; 2567 Boelter Hall; 405 Hilgard Ave.; Los Angeles, CA 90024
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