[sf-perl] conditional "no warnings 'threads'"

[Joseph Brenner]

> I think you have the condition backwards?

Could be, I didn't remember what David was going for.



On 8/1/20, yary <not.com at gmail.com> wrote:
> I think you have the condition backwards?
> my $test_mode;
> BEGIN { $test_mode=1 }
> no if $test_mode, qw[warnings threads];
>
>
>
> perldoc if
>
> *NAME*
>
>     if - "use" a Perl module if a condition holds
>
>
> *SYNOPSIS*
>
>         use if CONDITION, "MODULE", ARGUMENTS;
>
>         no  if CONDITION, "MODULE", ARGUMENTS;
>
> -y
>
>
> On Sat, Aug 1, 2020 at 3:10 AM David Christensen
> <dpchrist at holgerdanske.com>
> wrote:
>
>> sanfrancisco-pm:
>>
>> I have a Linux computer:
>>
>> 2020-07-31 23:24:49 dpchrist at tinkywinky ~/sandbox/perl
>> $ cat /etc/debian_version ; uname -a ; perl -v | head -n 3
>> 9.13
>> Linux tinkywinky 4.9.0-12-amd64 #1 SMP Debian 4.9.210-1+deb9u1
>> (2020-06-07) x86_64 GNU/Linux
>>
>> This is perl 5, version 24, subversion 1 (v5.24.1) built for
>> x86_64-linux-gnu-thread-multi
>> (with 90 registered patches, see perl -V for more detail)
>>
>>
>> I am working on a Perl 5 library that uses threads.  If code in a child
>> thread throws an exception, I want the exception message to be printed;
>> except during testing.
>>
>>
>> I have found that:
>>
>>      no warnings 'threads'
>>
>> when placed before, and in the same block as, threads->create() will
>> suppress printing of the exception message:
>>
>> 2020-07-31 23:43:08 dpchrist at tinkywinky ~/sandbox/perl
>> $ cat thread-exception.pl
>> #!perl
>>
>> use strict;
>> use warnings;
>> use threads;
>>
>> use Test::More;
>> use Test::Exception;
>>
>> our $thr;
>> our $test_mode;
>>
>> sub foo
>> {
>>      if ($test_mode) {
>>         no warnings 'threads';
>>
>>         $thr = threads->create(
>>             sub { die "hello, world!" }
>>         );
>>      } else {
>>         $thr = threads->create(
>>             sub { die "hello, world!" }
>>         );
>>      }
>> }
>>
>> ok foo, __FILE__ . __LINE__;                            # 1
>>
>> is $thr->join, undef, __FILE__ . __LINE__;              # 2
>>
>> like $thr->error, qr/hello/, __FILE__ . __LINE__;       # 3
>>
>> $test_mode = 1;
>>
>> ok foo, __FILE__ . __LINE__;                            # 4
>>
>> is $thr->join, undef, __FILE__ . __LINE__;              # 5
>>
>> like $thr->error, qr/hello/, __FILE__ . __LINE__;       # 6
>>
>> done_testing;
>>
>> 2020-07-31 23:43:11 dpchrist at tinkywinky ~/sandbox/perl
>> $ perl thread-exception.pl
>> Thread 1 terminated abnormally: hello, world! at thread-exception.pl
>> line 23.
>> ok 1 - thread-exception.pl28
>> ok 2 - thread-exception.pl30
>> ok 3 - thread-exception.pl32
>> ok 4 - thread-exception.pl36
>> ok 5 - thread-exception.pl38
>> ok 6 - thread-exception.pl40
>> 1..6
>>
>>
>> I was unable to figure out how to conditionally perform "no warnings
>> 'threads'" in the body of foo(), so I had to copy-and-paste the body
>> into both halves of an if-else conditional and disable warnings in one
>> block.  This is an ugly work-around.
>>
>>
>> I was hoping for:
>>
>>      no warnings 'threads' if $test_mode;       # BAD CODE
>>
>>
>> But, that code does not work;
>>
>> 2020-07-31 23:56:50 dpchrist at tinkywinky ~/sandbox/perl
>> $ cat no-warnings-threads-if-1.pl
>> #!perl
>>
>> use strict;
>> use warnings;
>>
>> no warnings 'threads' if 1;
>>
>> 2020-07-31 23:56:53 dpchrist at tinkywinky ~/sandbox/perl
>> $ perl no-warnings-threads-if-1.pl
>> syntax error at no-warnings-threads-if-1.pl line 6, near "'threads' if"
>> Execution of no-warnings-threads-if-1.pl aborted due to compilation
>> errors.
>>
>>
>> Any comments or suggestions?
>>
>>
>> David
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>>
>