Re: FW: Re: sigint, memoize

In article <020520042154490968%[email protected]>, _brian_d_foy
<[email protected]> wrote:

> In article <[email protected]>, Robert Spier
> <[email protected]> wrote:
> 
> > MJD sent this message a few months ago.  I meant to try and write
> > something up, but after three months, it's fallen off the bottom of my
> > todo list.
> 
> let me take a whack at it sometime this week.

cvs diff -u -d perlfaq8.pod
Index: perlfaq8.pod
===================================================================
RCS file: /cvs/public/perlfaq/perlfaq8.pod,v
retrieving revision 1.20
diff -u -d -r1.20 perlfaq8.pod
--- perlfaq8.pod        7 Feb 2004 04:29:50 -0000       1.20
+++ perlfaq8.pod        4 May 2004 13:41:05 -0000
@@ -413,31 +413,30 @@
 Signals are documented in L<perlipc/"Signals"> and the
 section on ``Signals'' in the Camel.
 
-Be warned that very few C libraries are re-entrant.  Therefore, if you
-attempt to print() in a handler that got invoked during another stdio
-operation your internal structures will likely be in an
-inconsistent state, and your program will dump core.  You can
-sometimes avoid this by using syswrite() instead of print().
-
-Unless you're exceedingly careful, the only safe things to do inside a
-signal handler are (1) set a variable and (2) exit.  In the first case,
-you should only set a variable in such a way that malloc() is not
-called (eg, by setting a variable that already has a value).
+You can set the values of the %SIG hash to be the functions you want 
+to handle the signal.  After perl catches the signal, it looks in %SIG
+for a key with the same name as the signal, then calls the subroutine
+value for that key.
 
-For example:
+       # as an anonymous subroutine
+
+       $SIG{INT} = sub { syswrite(STDERR, "ouch\n", 5 ) };
+
+       # or a reference to a function
+
+       $SIG{INT} = \&ouch;
+
+       # or the name of the function as a string
+
+       $SIG{INT} = "ouch"; 
 
-    $Interrupted = 0;  # to ensure it has a value
-    $SIG{INT} = sub {
-        $Interrupted++;
-       syswrite(STDERR, "ouch\n", 5);
-    }
+Perl versions before 5.8 had in its C source code signal handlers which
+would catch the signal and possibly run a Perl function that you had
set
+in %SIG.  This violated the rules of signal handling at that level
+causing perl to dump core. Since version 5.8.0, perl looks at %SIG
+*after* the signal has been caught, rather than while it is being
caught.
+Previous versions of this answer were incorrect.
 
-However, because syscalls restart by default, you'll find that if
-you're in a "slow" call, such as <FH>, read(), connect(), or
-wait(), that the only way to terminate them is by "longjumping" out;
-that is, by raising an exception.  See the time-out handler for a
-blocking flock() in L<perlipc/"Signals"> or the section on ``Signals''
-in the Camel book.
 
 =head2 How do I modify the shadow password file on a Unix system?

-- 
brian d foy, [email protected]