Re: return from nested functions
On Wed, 1 Nov 2000, Paul J. Lucas wrote: If I'm a few levels deep into function calls, I'd liek to be able to do something like "return SERVER_ERROR" and have the entire call stack unwind and the current request stopped. Is there any way to do that? Not that this has anything to do with mod_perl really but ... Use exceptions. There's a section in the guide on them some crazy guy wrote ;) I recommend my Exception::Class module on CPAN. But I would do that, wouldn't I? -dave /*== www.urth.org We await the New Sun ==*/
Re: return from nested functions
On Wed, 1 Nov 2000 11:37:00 -0800 (PST), "Paul J. Lucas" wrote:
If I'm a few levels deep into function calls, I'd liek to be
able to do something like "return SERVER_ERROR" and have the
entire call stack unwind and the current request stopped.
Will something like this do what you need?
~Ben
eval
{
get as many levels deep into functions as you want
...
...
...
die("SERVER_ERROR");
...
...
...
};
$the_error = $@;
if ($the_error)
{
warn("Unwound stack because of $the_error");
}
Re: return from nested functions
Hi there, On Wed, 1 Nov 2000, Paul J. Lucas wrote: If I'm a few levels deep into function calls, I'd liek to be able to do something like "return SERVER_ERROR" and have the entire call stack unwind and the current request stopped. Is there any way to do that? It's called a 'goto' (and real programmers don't use it:). Or you could call a function which does the business and then calls mod_perl's exit() function, page 464 Eagle Book. Don't use an ordinary exit() from a mod_perl process because that abruptly kills the child, which is Bad News. 73, Ged.
Re: return from nested functions
On Wed, 1 Nov 2000, G.W. Haywood wrote: Or you could call a function which does the business and then calls mod_perl's exit() function, page 464 Eagle Book. I tried exit: the status code isn't preserved to downstream stacked handlers. - Paul
Re: return from nested functions
On Wed, 1 Nov 2000, Dave Rolsky wrote:
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
If I'm a few levels deep into function calls, I'd liek to be
able to do something like "return SERVER_ERROR" and have the
entire call stack unwind and the current request stopped.
Is there any way to do that?
Not that this has anything to do with mod_perl really but ...
Actually it does because the status code should be preserved to
downstream stacked handlers (and, my testing, it apparantly
isn't):
sub some_nested_function {
$r-status( SERVER_ERROR );
Apache-exit( 0 );
}
# in downstream.pm handler
sub handler {
# $r-status() is NOT SERVER_ERROR here
}
- Paul
Re: return from nested functions
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
If I'm a few levels deep into function calls, I'd liek to be
able to do something like "return SERVER_ERROR" and have the
entire call stack unwind and the current request stopped.
Is there any way to do that?
Definitely use exceptions. I prefer Error.pm for this (sorry, Dave!),
which allows your handler to simply be:
sub handler {
return try {
...
} catch Exception::RetCode with {
my $E = shift;
return $E-{code};
} other exceptions
;
}
And then anywhere within your code you can go:
throw Exception::RetCode ( code = SERVER_ERROR );
Of course there's a bit of setup to do beyond that, which I intend to
rewrite the section of the guide to detail real soon now (tm).
--
Matt/
/||** Director and CTO **
//||** AxKit.com Ltd ** ** XML Application Serving **
// ||** http://axkit.org ** ** XSLT, XPathScript, XSP **
// \\| // ** Personal Web Site: http://sergeant.org/ **
\\//
//\\
// \\
Re: return from nested functions
On Wed, 1 Nov 2000, Matt Sergeant wrote: Definitely use exceptions. I prefer Error.pm for this (sorry, Dave!), which allows your handler to simply be: That's no reason not to use Exception::Class. They are largely orthogonal. If you want to be able to declare your exception hierarchy at compile time and have it enforced (this is a good thing!) then check out Exception::Class. If you want Try/Catch syntax get Error.pm. Both of them come with Exception object implementations. I don't know about Error but with Exception::Class you don't have to use it (you could even use Error's, I think). -dave /*== www.urth.org We await the New Sun ==*/
Re: return from nested functions
On Wed, 1 Nov 2000, Matt Sergeant wrote:
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
If I'm a few levels deep into function calls, I'd liek to be
able to do something like "return SERVER_ERROR" and have the
entire call stack unwind and the current request stopped.
Is there any way to do that?
Definitely use exceptions.
It's rather cumbersome. Ideally, I want to be able to do:
sub foo {
if ( $serious_problem )
stop_now_dammit( SERVER_ERROR );
}
anywhere in the code like:
sub bar {
foo();
}
and I do *NOT* have to "catch" anything after the point of
call, i.e., every call of foo() is similar to an "assertion" in
C, i.e., if you get to the line of code after it, it worked; if
it didn't work, you never get to the line after it.
I suppose I want to do something like Apache-exit() but
preserve the response code so the normal Apache error handling
mechanism kicks in and handles the error.
- Paul
Re: return from nested functions
On Wed, 1 Nov 2000, Matt Sergeant wrote:
Definitely use exceptions. I prefer Error.pm for this (sorry, Dave!),
which allows your handler to simply be:
sub handler {
return try {
...
} catch Exception::RetCode with {
my $E = shift;
return $E-{code};
} other exceptions
;
}
Be very careful with nested try/catch blocks. Error.pm uses prototypes to
make these into anonymous subs, which is usually fine, but this leaks
memory like mad:
my $foo;
try {
something();
try {
$foo++;
};
} otherwise {
handle_error();
};
It's not Graham Barr's fault; that's just a byproduct of Perl's support
for closures (I think).
- Perrin
Re: return from nested functions
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
Ideally, I want to be able to do:
sub foo {
if ( $serious_problem )
stop_now_dammit( SERVER_ERROR );
}
anywhere in the code like:
sub bar {
foo();
}
and I do *NOT* have to "catch" anything after the point of
call, i.e., every call of foo() is similar to an "assertion" in
C, i.e., if you get to the line of code after it, it worked; if
it didn't work, you never get to the line after it.
I figured out that I can do this by having stop_now_dammit()
use $r-notes() to set a note of the status code, call
Apache-exit(), and have the downstream handler check the note.
If it's anything but OK, simply return that value and the
normal Apache error handline mechanism kicks in. :)
- Paul
Re: return from nested functions
even better: Apache-exit(SERVER_ERROR);. or die SERVER_ERROR;. this is
documented in the eagle book:
ch9 - The Apache::Constants Class
"...
While the HTTP constants are generally used as return codes from
handler subroutines, it is also possible to use the builtin die()
function to jump out of a handler with a status code that will be
propagated back to Apache. Example:
unless (-r _) {
die FORBIDDEN;
}
"
sterling
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
Ideally, I want to be able to do:
sub foo {
if ( $serious_problem )
stop_now_dammit( SERVER_ERROR );
}
anywhere in the code like:
sub bar {
foo();
}
and I do *NOT* have to "catch" anything after the point of
call, i.e., every call of foo() is similar to an "assertion" in
C, i.e., if you get to the line of code after it, it worked; if
it didn't work, you never get to the line after it.
I figured out that I can do this by having stop_now_dammit()
use $r-notes() to set a note of the status code, call
Apache-exit(), and have the downstream handler check the note.
If it's anything but OK, simply return that value and the
normal Apache error handline mechanism kicks in. :)
- Paul
Re: return from nested functions
On Wed, 1 Nov 2000, Paul J. Lucas wrote:
On Wed, 1 Nov 2000, John K. Sterling wrote:
even better: Apache-exit(SERVER_ERROR);
The documentation for exit() deosnt' explicitly say you can do
that. It mentions only "0" and "DONE" (see pp. 464-465).
it works though, Apache.xs:exit() passes the status value to
perl_util.c:perl_call_halt(), which checks:
int is_http_code =
((status = 100) (status 600) ERRSV_CAN_BE_HTTP);
...
if(is_http_code) {
croak("%d\n", status);
}
the croak() call is caught the same way 'die SERVER_ERROR' is.
or die SERVER_ERROR;
But that works. Thanks! :)
- Paul
Re: return from nested functions
On Wed, 1 Nov 2000, Dave Rolsky wrote: On Wed, 1 Nov 2000, Paul J. Lucas wrote: If I'm a few levels deep into function calls, I'd liek to be able to do something like "return SERVER_ERROR" and have the entire call stack unwind and the current request stopped. Is there any way to do that? Not that this has anything to do with mod_perl really but ... Use exceptions. There's a section in the guide on them some crazy guy wrote ;) I recommend my Exception::Class module on CPAN. But I would do that, wouldn't I? I'll second that recommendation, at citysearch we are using Exception::Class very successfully. We are able to trap all sorts of errors and the overhead is fairly small. Craig
