Subject: Re: syslog_r (Re: CVS commit: src/lib/libc)
To: None <>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-userlevel
Date: 10/27/2006 14:59:09
>> I believe we should avoid the word "reentrant",

Well, unless we really mean it.

>> [...] because the word "reentrant" may mean async-signal-safe in
>> some technical context.

Not quite; it's stronger than (my understanding of) async-signal-safe.
An async-signal-safe function may be called from a signal handler
without taking any particular precautions to make sure that the signal
can be delivered only at particular times - right?

A reentrant routine may be called at any point during its own
execution, for example from a signal handler (or hardware interrupt, in
environments where that makes sense), to unlimited depth.

>> For example, Wikipedia ( says:
>> 	To be reentrant, a function must hold no static data, must not
>> 	return a pointer to static data, must work only on the data
>> 	provided to it by the caller, and must not call non-reentrant
>> 	functions.

I think the Wikipedia is wrong.  There is nothing wrong with returning
pointers to static data in some cases.  For example,

const char *k_str(int code)
	switch (code) {
		case K_FOO: return("foo"); break;
		case K_BAR: return("bar"); break;
		case K_BAZ: return("baz"); break;
		default: return("?""?"); break;

is a totally reentrant function, even though it *always* returns a
pointer to static data.

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