Re: SIGINT and system calls

You have a zombie problem. Call wait before exit in the signal handler.

You don't say what version of perl you use, but "safe" signals might be involved. That could prevent Ctrl-C from interrupting a blocking read in <CMD>. Your code looks fine.

You can break up the print <CMD>; by calling sysread, perhaps inside select.

# replaces print <CMD>;
vec( my $rin, fileno(*CMD), 1) = 1;
while (select my $rd = $rin, undef, undef, undef;) {
    my $bytes = sysread *CMD, my $buf, 4096;
    print $buf if 0 < $bytes;
    last if 1 > $bytes;
}

# wait added to lay the zombies
sub myhand() {
   print "Parent $$ caught SIGINT.\n";
   print "Parent $$ will KILL $pid.\n";

   kill INT, $pid;
   waitpid $pid;
   exit 0;
}
[download]

It's a potential problem that the signal handler is set before the child is launched. That makes the child inherit a handler that is clearly meant for the parent. If you changed the kill signal to the more proper SIGINT, the child would try to signal a nonexistent child.

After Compline,
Zaxo

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Re^2: SIGINT and system calls by Anonymous Monk on Jan 20, 2005 at 05:26 UTC
You monks are great! I am running ActiveState 5.8.6 on Windows. So here's what it translates into: $SIG{INT}=\&myhand; print "Parent pid = $$ \n"; $pid = open(CMD, "ping google.com -n 15 \|"); print "Ping running... pid = $pid \n\n"; # replaces print <CMD>; vec( my $rin, fileno(CMD), 1) = 1; while (select (my $rd = $rin, undef, undef, undef)) { my $bytes = sysread CMD, my $buf, 4096; print $buf if 0 < $bytes; } print "I am finished with my task. My results are: \n"; # where are my results stored if I want them in a variable? # print $results; # wait added to lay the zombies sub myhand() { print "Parent $$ caught SIGINT.\n"; print "Parent $$ will KILL $pid.\n"; kill 9, $pid; waitpid $pid, 0; exit 0; } [download] I am not sure if I completely understand what is happening with the output that you have shown -- it appears to me that it stays in the while loop and I can't get it to "I am finished with my task." Also, do one of those variables currently have the complete results (of the ping output in this case) or will I need to build a new variable if I want it STDOUT as well as in a variable to pass to another routine later? Thanks!!	[reply] [d/l]
Re^3: SIGINT and system calls by Zaxo (Archbishop) on Jan 20, 2005 at 05:43 UTC
I'm surprised that that works on windows. Both select and signals are pretty unixy for the windows ports to emulate. I didn't know they could do that at all. You're right that I omitted a way out of the while select loop. Probably `last if 1 > $bytes;` at the end of the loop would do it. I'll edit that into the original. Update: Yes, concatenation in the loop would work fine, or if you wanted to get fancy I think you could say, `my $result; while (select my $rd = $rin, undef, undef, 60) { my $bytes = sysread *CMD, substr($result, -1), 4096; last if 1 > $bytes; }` [download] Or else you could use the offset argument of sysread to position at the end of $result. The 60 second timeout is new, too. Adjust to taste. After Compline, Zaxo	[reply] [d/l]
Re^4: SIGINT and system calls by Anonymous Monk on Jan 20, 2005 at 05:59 UTC
That works well to break the loop. What about putting the results back into a variable (such as $results)? Do I need to do a concatenation in the `while( ... $results .= $buf; ... )` or is there a better way to store the output in a variable? `print "I am finished with my task. My results are: \n"; # where are my results stored if I want them in a variable? # print $results;` [download] Thanks again!	[reply] [d/l] [select]
Re^4: SIGINT and system calls by Anonymous Monk on Jan 20, 2005 at 17:20 UTC
I like the opportunity to get fancy, but I noticed an odd reaction of the sysread(). Using: `my $result; while (select my $rd = $rin, undef, undef, 60) { my $bytes = sysread CMD, substr($result, -1), 4096; last if 1 > $bytes; } ... print "I am finished with my task. My results are: \n"; print $result."\n";` [download] My output is: `I am finished with my task. My result are: Pinging google.com [216.239.37.99] with 32 bytes of data: Reply from 216.239.37.99:bytes=32 time=36ms TTL=244 Ping statistics for 216.239.37.99: Packets: Sent = 15, Received = 15, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 36ms, Maximum = 37ms, Average = 36ms` [download] What happened to all of the other lines from the ping (should be 15 result lines)? I would expect it to be: I am finished with my task. My result are: Pinging google.com [216.239.37.99] with 32 bytes of data: Reply from 216.239.37.99: bytes=32 time=37ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=36ms TTL=244 Reply from 216.239.37.99: bytes=32 time=37ms TTL=244 Reply from 216.239.37.99: bytes=32 time=37ms TTL=244 Reply from 216.239.37.99: bytes=32 time=37ms TTL=244 Ping statistics for 216.239.37.99: Packets: Sent = 15, Received = 15, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 36ms, Maximum = 37ms, Average = 36ms [download] What happens that makes the `$result` apparently overwrite the output of the `CMD`? I would still want to output the live results and set the variable, so would it be best to use the concatenation? I can't print `$result` in the loop, since that would contain all of the output, not just that loop's progress. Also, why is the sysread() length set to 4096. Does that have a significant value? Thanks!	[reply] [d/l] [select]