muad33b has asked for the wisdom of the Perl Monks concerning the following question:

The following code snippet does not time out: 
Use Net:SSH2;
<snip>
$ssh2 = Net::SSH2->new();
<snip>
$ssh2->connect($host,$port);
<snip>
$ssh2->auth_password($os_user,$os_pass);
<snip>
eval {
    local $SIG{ALRM} = sub { die "alarm\n"; };
    alarm (10);
    $ssh2->scp_get($remote, $local);
    alarm (0);
};

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However, the following works just fine: 
eval {
    local $SIG{ALRM} = sub { die "alarm\n"; };
    alarm (10);
    $buf = <>;
    alarm (0);
};
print "Timed out.\n" if ($@);

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I've googled around and seen some reference to a change in perl's eval handling in 5.8.x, as well as some reference to eval failing to timeout blocks of code involving network copys, etc... Any ideas what I have to do to get eval to do it's job here, and time out? Thanks...

Replies are listed 'Best First'.
Re: eval problem
by ikegami (Patriarch) on Jan 09, 2007 at 07:39 UTC

    In Perl, signals no longer interrupt opcodes, except for Perl IO operations. Perl checks if a signal was received between executing opcodes. Net:SSH2 is a wrapper for C library libssh2. libssh2 doesn't know anything about Perl. All the IO is done using C IO, not Perl IO, so alarm will not interrupt Net::SSH2 while it waits for libssh2 to return data.

    The reason for this change (and how to switch to the dangerous old system) is documented in Deferred Signals in perlipc.

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[d/l]
Re: eval problem
by diotalevi (Canon) on Jan 09, 2007 at 07:17 UTC

    Set the environment variable PERL_SIGNALS to "unsafe" to reenable the old behaviour. See perlipc for the scoop.

    ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊

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Re: eval problem
by ysth (Canon) on Jan 09, 2007 at 07:58 UTC
[reply]
      Ok, so after some more RTFM (thanks!) I ended up trying this option, as it seemed best, however, now when I try to implement Sys::SigAction's "timeout_call" - which gives the following example: 
         use Sys::SigAction qw( timeout_call );
   if ( timeout_call( 5 ,sub { $retval = DoSomething( @args ); } )
   {
      print "DoSomething() timed out\n" ;
   }

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      And I implemented this as, e.g.: 
      177       eval {
178               if ( timeout_call( 10, sub { $ret = system($mnt_cmd)
+; } )
179               {
180                      logit ("Couldn't get to $smbdest, and couldn'
+t mount it running $mnt_cmd");
181                      return 1;
182               }

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      I get the following error: 
      [support@hydra script]$ ./cfg_sucker.pl  
syntax error at ./cfg_sucker.pl line 179, near ") 
                        {"
syntax error at ./cfg_sucker.pl line 186, near "}"
Execution of ./cfg_sucker.pl aborted due to compilation errors.

      [download]
      What am I doing wrong syntactically? I've looged around, and this appears to be kosher?? TIA!
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[d/l]
[select]

        You have a missing close paren ')', Missing close curly '}' and missing final semicolon ';': 

        eval {
   if ( timeout_call( 10, sub { $ret = system($mnt_cmd); } )
#     1             2                                      2 ? 
   {
      logit("Couldn't get to $smbdest, and couldn't mount it running $
+mnt_cmd");
      return 1;
#  ?? missing '}'
}                 ## <<< missing ;

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        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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[d/l]

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