note
tybalt89
<p>
sysread returning 0 means "connection was closed".
<br>
sysread returning undef means "connection is still open but no data is available at this time, or some other error".
<br><br>
Your code wasn't doing what you documented.
</p>
<code>
#!/usr/bin/perl
use diagnostics;
use strict 'subs';
use strict 'refs';
use Socket;
use IO::Handle;
my $child; #filehandle to child process
my $parent; #filehandle to parent process
my $pid; #Process ID of child process
# r e a d L i n e
# This expects to read one line (\n-terminated, but the newline is chomped).
# Returns the line, which will be empty if no characters are waiting to be read.
sub readLine {
my ($fh) = @_;
my $buf = '';
my $offset = 0;
my $cnt = 0;
my $stat;
do {
$stat = sysread $fh, $buf, 4096-$offset, $offset;
# die "sysread: $!\n" unless defined($stat);
return '' unless defined($stat); ############ DOING WHAT YOU DOCUMENTED
$offset += $stat;
} while ($stat and "\n" ne substr($buf, -1));
chomp $buf;
#print STDERR time%100, " #readLine returning <$buf>\n";
return $buf;
} #readLine()
# w r i t e L i n e
# Writes a buffer to the filehandle.
sub writeLine {
my ($fh, $buf) = @_;
my $offset = 0;
my $remaining = length($buf);
do {
my $stat = syswrite($fh, $buf, $remaining, $offset);
die "syswrite: $!\n" unless defined($stat);
$remaining -= $stat;
$offset += $stat;
} while (0 < $remaining);
} #writeLine()
socketpair($child, $parent, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
or die "socketpair: $!";
$child->autoflush(1);
$parent->autoflush(1);
$child->blocking(0) or die "blocking: $!\n"; ######### CHANGED
#$parent->blocking(0) or die "blocking: $!\n";
if ($pid = fork()) { #parent
close $parent or die "close: $!\n";
while (1) {
sleep 1;
print STDOUT time%100, ": polling child\n";
if (my $line = readLine($child)) {
print STDOUT time%100, ": received <$line>\n";
if ('E_O_F' eq $line) {
my $stat = wait;
die "wait returned $stat\n" unless $stat == $pid;
print STDOUT time%100, ": child reaped, parent exiting\n";
exit 0;
}
} else {
print STDOUT time%100, ": no input from child yet\n";
}
}
} else { #child
die "cannot fork: $!" unless defined $pid;
close $child or die "close: $!\n";
writeLine($parent, time%100 . ": child started\n");
sleep 6;
writeLine($parent, time%100 . ": child wrote again\n");
sleep 2;
writeLine($parent, "E_O_F\n"); #causes termination
close $parent or die "close: $!\n";
print STDOUT time%100, ": child exiting\n";
exit;
}
</code>
<p>
Outputs:
</p>
<c>
51: polling child
51: received <50: child started>
52: polling child
52: no input from child yet
53: polling child
53: no input from child yet
54: polling child
54: no input from child yet
55: polling child
55: no input from child yet
56: polling child
56: received <56: child wrote again>
57: polling child
57: no input from child yet
58: child exiting
58: polling child
58: received <E_O_F>
58: child reaped, parent exiting
</c>
<p>
Is this what you wanted?
</p>
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