$shucks++;
die "Somebody sent me a SIG$signame";
}
- $SIG{INT} = __PACKAGE__ . "::catch_zap";
+ $SIG{INT} = __PACKAGE__ . "::catch_zap";
$SIG{INT} = \&catch_zap; # best strategy
Prior to Perl 5.8.0 it was necessary to do as little as you possibly
Sending a signal to a negative process ID means that you send the signal
to the entire Unix process group. This code sends a hang-up signal to all
-processes in the current process group, and also sets $SIG{HUP} to C<"IGNORE">
+processes in the current process group, and also sets $SIG{HUP} to C<"IGNORE">
so it doesn't kill itself:
# block scope for local
located in the subroutine C<code()>, which just prints some debugging
info to show that it works; it should be replaced with the real code.
- #!/usr/bin/perl -w
+ #!/usr/bin/perl
+
+ use strict;
+ use warnings;
use POSIX ();
use FindBin ();
use File::Basename ();
- use File::Spec::Functions;
+ use File::Spec::Functions qw(catfile);
$| = 1;
print "PID: $$\n";
print "ARGV: @ARGV\n";
my $count = 0;
- while (++$count) {
+ while (1) {
sleep 2;
- print "$count\n";
+ print ++$count, "\n";
}
}
opcode (e.g. a regular expression operation on a very large string) will
not be seen until the current opcode completes.
-If a signal of any given type fires multiple times during an opcode
+If a signal of any given type fires multiple times during an opcode
(such as from a fine-grained timer), the handler for that signal will
be called only once, after the opcode completes; all other
instances will be discarded. Furthermore, if your system's signal queue
SA_RESTART flag when installing %SIG handlers. This meant that
restartable system calls would continue rather than returning when
a signal arrived. In order to deliver deferred signals promptly,
-Perl 5.8.0 and later do I<not> use SA_RESTART. Consequently,
+Perl 5.8.0 and later do I<not> use SA_RESTART. Consequently,
restartable system calls can fail (with $! set to C<EINTR>) in places
where they previously would have succeeded.
The default C<:perlio> layer retries C<read>, C<write>
-and C<close> as described above; interrupted C<wait> and
+and C<close> as described above; interrupted C<wait> and
C<waitpid> calls will always be retried.
=item Signals as "faults"
to handle. Consider:
open(FH, "|bogus") || die "can't fork: $!";
- print FH "bang\n"; # neither necessary nor sufficient
+ print FH "bang\n"; # neither necessary nor sufficient
# to check print retval!
close(FH) || die "can't close: $!";
system doesn't have the setsid() function, open F</dev/tty> and use the
C<TIOCNOTTY> ioctl() on it instead. See tty(4) for details.
-Non-Unix users should check their C<< I<Your_OS>::Process >> module for
+Non-Unix users should check their C<< I<Your_OS>::Process >> module for
other possible solutions.
=head2 Safe Pipe Opens
}
} until defined $pid;
- if ($pid) { # I am the parent
+ if ($pid) { # I am the parent
print KID_TO_WRITE @some_data;
close(KID_TO_WRITE) || warn "kid exited $?";
} else { # I am the child
# drop permissions in setuid and/or setgid programs:
- ($EUID, $EGID) = ($UID, $GID);
- open (OUTFILE, "> $PRECIOUS")
+ ($EUID, $EGID) = ($UID, $GID);
+ open (OUTFILE, "> $PRECIOUS")
|| die "can't open $PRECIOUS: $!";
while (<STDIN>) {
print OUTFILE; # child's STDIN is parent's KID_TO_WRITE
}
It is very easy to dead-lock a process using this form of open(), or
-indeed with any use of pipe() with multiple subprocesses. The
+indeed with any use of pipe() with multiple subprocesses. The
example above is "safe" because it is simple and calls exec(). See
L</"Avoiding Pipe Deadlocks"> for general safety principles, but there
are extra gotchas with Safe Pipe Opens.
One would use either of these:
- open(PS_PIPE, "-|", "ps", "aux")
+ open(PS_PIPE, "-|", "ps", "aux")
|| die "can't open ps pipe: $!";
@ps_args = qw[ ps aux ];
Because there are more than three arguments to open(), forks the ps(1)
command I<without> spawning a shell, and reads its standard output via the
C<PS_PIPE> filehandle. The corresponding syntax to I<write> to command
-pipes is to use C<"|-"> in place of C<"-|">.
+pipes is to use C<"|-"> in place of C<"-|">.
This was admittedly a rather silly example, because you're using string
literals whose content is perfectly safe. There is therefore no cause to
=for TODO
Hold on, is this even true? First it says that socketpair() is avoided
-for portability, but then it says it probably won't work except on
+for portability, but then it says it probably won't work except on
Unixy systems anyway. Which one of those is true?
Here's an example of using open2():
PARENT_WTR->autoflush(1);
if ($pid = fork()) {
- close PARENT_RDR;
+ close PARENT_RDR;
close PARENT_WTR;
print CHILD_WTR "Parent Pid $$ is sending this\n";
chomp($line = <CHILD_RDR>);
waitpid($pid, 0);
} else {
die "cannot fork: $!" unless defined $pid;
- close CHILD_RDR;
+ close CHILD_RDR;
close CHILD_WTR;
chomp($line = <PARENT_RDR>);
print "Child Pid $$ just read this: '$line'\n";
print PARENT_WTR "Child Pid $$ is sending this\n";
- close PARENT_RDR;
+ close PARENT_RDR;
close PARENT_WTR;
exit(0);
}
One of the major problems with ancient, antemillennial socket code in Perl
was that it used hard-coded values for some of the constants, which
severely hurt portability. If you ever see code that does anything like
-explicitly setting C<$AF_INET = 2>, you know you're in for big trouble.
+explicitly setting C<$AF_INET = 2>, you know you're in for big trouble.
An immeasurably superior approach is to use the C<Socket> module, which more
reliably grants access to the various constants and functions you'll need.
conformant (be strict in what you provide), but they also recommend
accepting a lone "\012" on input (be lenient in what you require).
We haven't always been very good about that in the code in this manpage,
-but unless you're on a Mac from way back in its pre-Unix dark ages, you'll
+but unless you're on a Mac from way back in its pre-Unix dark ages, you'll
probably be ok.
=head2 Internet TCP Clients and Servers
my $proto = getprotobyname("tcp");
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
- setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
+ setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
|| die "setsockopt: $!";
bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
listen(Server, SOMAXCONN) || die "listen: $!";
my $paddr;
- $SIG{CHLD} = \&REAPER;
-
for ( ; $paddr = accept(Client, Server); close Client) {
my($port, $iaddr) = sockaddr_in($paddr);
my $name = gethostbyaddr($iaddr, AF_INET);
my $proto = getprotobyname("tcp");
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
- setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
+ setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1))
|| die "setsockopt: $!";
bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
listen(Server, SOMAXCONN) || die "listen: $!";
unless (defined($pid = fork())) {
logmsg "cannot fork: $!";
return;
- }
+ }
elsif ($pid) {
logmsg "begat $pid";
return; # I'm the parent
L</Deferred Signals (Safe Signals)> above) in Perl 5.8.0 means that
accept() might also be interrupted when the process receives a signal.
This typically happens when one of the forked subprocesses exits and
-notifies the parent process with a CHLD signal.
+notifies the parent process with a CHLD signal.
If accept() is interrupted by a signal, $! will be set to EINTR.
If this happens, we can safely continue to the next iteration of
the loop and another call to accept(). It is important that your
-signal handling code not modify the value of $!, or else this test
+signal handling code not modify the value of $!, or else this test
will likely fail. In the REAPER subroutine we create a local version
of $! before calling waitpid(). When waitpid() sets $! to ECHILD as
-it inevitably does when it has no more children waiting, it
+it inevitably does when it has no more children waiting, it
updates the local copy and leaves the original unchanged.
You should use the B<-T> flag to enable taint checking (see L<perlsec>)
printf "%-24s ", $host;
my $hisiaddr = inet_aton($host) || die "unknown host";
my $hispaddr = sockaddr_in($port, $hisiaddr);
- socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
+ socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
|| die "socket: $!";
connect(SOCKET, $hispaddr) || die "connect: $!";
my $rtime = pack("C4", ());
unless (defined($pid = fork())) {
logmsg "cannot fork: $!";
return;
- }
+ }
elsif ($pid) {
logmsg "begat $pid";
return; # I'm the parent
- }
+ }
else {
# I'm the child -- go spawn
}
manpage describes the low-level interface to sockets. Besides the obvious
functions in L<perlfunc>, you should also check out the F<modules> file at
your nearest CPAN site, especially
-L<http://www.cpan.org/modules/00modlist.long.html#ID5_Networking_>.
+L<http://www.cpan.org/modules/00modlist.long.html#ID5_Networking_>.
See L<perlmodlib> or best yet, the F<Perl FAQ> for a description
-of what CPAN is and where to get it if the previous link doesn't work
+of what CPAN is and where to get it if the previous link doesn't work
for you.
Section 5 of CPAN's F<modules> file is devoted to "Networking, Device
https://perl5.git.perl.org / perl5.git / blobdiff