Perl procedural return two stack call levels - perl

Question

My question is similar to:
Is it possible for a Perl subroutine to force its caller to return?
but I need procedural method.
I want to program some message procedure with return, example essential code:
sub PrintMessage {
#this function can print to the screen and both to logfile
print "Script message: $_[0]\n";
}
sub ReturnMessage {
PrintMessage($_[0]);
return $_[2]; # <-- we thinking about *this* return
}
sub WorkingProc {
PrintMessage("Job is started now");
#some code
PrintMessage("processed 5 items");
# this should return from WorkingProc with given exitcode
ReturnMessage("too many items!",5) if $items>100;
#another code
ReturnMessage("time exceded!",6) if $timespent>3600;
PrintMessage("All processed succesfully");
return 0;
}
my $ExitCode=WorkingProc();
#finish something
exit $ExitCode
Idea is, how to use return inside ReturnMessage function to exit with specified code from WorkingProc function? Notice, ReturnMessage function is called from many places.

Answer 1

This isn't possible. However, you can explicitly return:
sub WorkingProc {
PrintMessage("Job is started now");
...
PrintMessage("processed 5 items");
# this returns from WorkingProc with given exitcode
return ReturnMessage("to much items!", 5) if $items > 100;
...
return ReturnMessage("time exceded!", 6) if $timespent > 3600;
PrintMessage("All processed succesfully");
return 0;
}
A sub can have any number of return statements, so this isn't an issue.
Such a solution is preferable to hacking through the call stack, because the control flow is more obvious to the reader. What you were dreaming of was a kind of GOTO, which most people not writing C or BASIC etc. have given up 45 years ago.
Your code relies on exit codes to determine errors in subroutines. *Sigh*. Perl has an exception system which is fairly backwards, but still more advanced than that.
Throw a fatal error with die "Reason", or use Carp and croak "Reason". Catch errors with the Try::Tiny or TryCatch modules.
sub WorkingProc {
PrintMessage("Job is started now");
...
PrintMessage("processed 5 items");
# this should return from WorkingProc with given exitcode
die "Too much items!" if $items > 100;
...
die "Time exceeded" if $timespent > 3600;
PrintMessage("All processed succesfully");
return 0;
}
WorkingProc();
If an error is thrown, this will exit with a non-zero status.

Answer 2

The approach that springs to mind for non-local return is to throw an exception (die) from the innermost function.
You'll then need to have some wrapping code to handle it at the top level. You could devise a set of utility routines to automatically set that up.

Answer 3

Using Log::Any and Log::Any::Adapter in conjunction with Exception::Class allow you to put all the pieces together with minimum fuss and maximum flexibility:
#!/usr/bin/env perl
package My::Worker;
use strict; use warnings;
use Const::Fast;
use Log::Any qw($log);
use Exception::Class (
JobException => { fields => [qw( exit_code )] },
TooManyItemsException => {
isa => 'JobException',
description => 'The worker was given too many items to process',
},
TimeExceededException => {
isa => 'JobException',
description => 'The worker spent too much time processing items',
},
);
sub work {
my $jobid = shift;
my $items = shift;
const my $ITEM_LIMIT => 100;
const my $TIME_LIMIT => 10;
$log->infof('Job %s started', $jobid);
shift #$items for 1 .. 5;
$log->info('Processed 5 items');
if (0.25 > rand) {
# throw this one with 25% probability
if (#$items > $ITEM_LIMIT) {
TooManyItemsException->throw(
error => sprintf(
'%d items remain. Limit is %d.',
scalar #$items, $ITEM_LIMIT,
),
exit_code => 5,
);
}
}
{ # simulate some work that might take more than 10 seconds
local $| = 1;
for (1 .. 40) {
sleep 1 if 0.3 > rand;
print '.';
}
print "\n";
}
my $time_spent = time - $^T;
($time_spent > $TIME_LIMIT) and
TimeExceededException->throw(
error => sprintf (
'Spent %d seconds. Limit is %d.',
$time_spent, $TIME_LIMIT,
),
exit_code => 6);
$log->info('All processed succesfully');
return;
}
package main;
use strict; use warnings;
use Log::Any qw( $log );
use Log::Any::Adapter ('Stderr');
eval { My::Worker::work(exceptional_job => [1 .. 200]) };
if (my $x = JobException->caught) {
$log->error($x->description);
$log->error($x->error);
exit $x->exit_code;
}
Sample output:
Job exceptional_job started
Processed 5 items
........................................
The worker spent too much time processing items
Spent 12 seconds. Limit is 10.
or
Job exceptional_job started
Processed 5 items
The worker was given too many items to process
195 items remain. Limit is 100.