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Hi monks,

I've spent some time tracking down a strange problem in a daemon script - ultimately I've no-one to blame but myself, as I wasn't checking my return codes and/or $!, but I've found some surprising behaviour... Much reduced code:

#!/usr/bin/perl -w
use strict;
use IO::Socket::INET;
my $server =IO::Socket::INET->new(LocalPort => 4848, Listen=> 1,ReuseA
+ddr => 1) or die "listen: $!";
my $client;
USER: while($client= $server->accept()){
        if (my $pid = fork()){
                #parent
                close $client;
                $SIG{CHLD} = sub {};
        }else{
                print $client "hello, world!\n";
                select(undef,undef,undef,2);
                exit;
        }
}
warn "fell out of loop - $!";
[download]

The sleep in the child process causes SIGCHLD to be delivered to the parent when it is in blocking in accept(), and sure enough I get fell out of loop - Interrupted system call at /tmp/z.pl line 17.

I understand from chapter 16 of the Camel Book that this could happen with old, horrible Unices, but I'm surprised it happens with This is perl, v5.10.0 built for i486-linux-gnu-thread-multi on Debian 5.0.3

Can anyone shed some light on this?? An strace looks like it's going to work, but doesn't...

bind(3, {sa_family=AF_INET, sin_port=htons(4848), sin_addr=inet_addr("
+0.0.0.0")}, 16) = 0
listen(3, 1)                            = 0
accept(3, {sa_family=AF_INET, sin_port=htons(23694), sin_addr=inet_add
+r("127.0.0.1")}, [16]) = 4
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbffa26c8) = -1 EINVAL (Inval
+id argument)
_llseek(4, 0, 0xbffa2710, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbffa26c8) = -1 EINVAL (Inval
+id argument)
_llseek(4, 0, 0xbffa2710, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
fcntl64(4, F_SETFD, FD_CLOEXEC)         = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIG
+CHLD, child_tidptr=0xb7d9f908) = 5206
close(4)                                = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, {0x809a270, [], 0}, {SIG_DFL}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
accept(3, 0xbffa28c8, [4096])           = ? ERESTARTSYS (To be restart
+ed)
--- SIGCHLD (Child exited) @ 0 (0) ---
sigreturn()                             = ? (mask now [])
rt_sigprocmask(SIG_BLOCK, [CHLD], NULL, 8) = 0
rt_sigaction(SIGCHLD, NULL, {0x809a270, [], 0}, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [CHLD], NULL, 8) = 0
open("/usr/share/locale/locale.alias", O_RDONLY) = 4
fstat64(4, {st_mode=S_IFREG|0644, st_size=2586, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
+ 0) = 0xb7f7a000
read(4, "# Locale name alias data base.\n# "..., 4096) = 2586
read(4, ""..., 4096)                    = 0
close(4)                                = 0
munmap(0xb7f7a000, 4096)                = 0
open("/usr/share/locale/en_GB.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = 
+-1 ENOENT (No such file or directory)
open("/usr/share/locale/en_GB.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -
+1 ENOENT (No such file or directory)
open("/usr/share/locale/en_GB/LC_MESSAGES/libc.mo", O_RDONLY) = 4
fstat64(4, {st_mode=S_IFREG|0644, st_size=1474, ...}) = 0
mmap2(NULL, 1474, PROT_READ, MAP_PRIVATE, 4, 0) = 0xb7f7a000
close(4)                                = 0
open("/usr/share/locale/en.UTF-8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 
+ENOENT (No such file or directory)
open("/usr/share/locale/en.utf8/LC_MESSAGES/libc.mo", O_RDONLY) = -1 E
+NOENT (No such file or directory)
open("/usr/share/locale/en/LC_MESSAGES/libc.mo", O_RDONLY) = -1 ENOENT
+ (No such file or directory)
write(2, "fell out of loop - Interrupted sy"..., 65) = 65
close(3)                                = 0
exit_group(0)                           = ?
[download]

Thanks!

In reply to linux perl - interrupted system calls not restarted? by flipper

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