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hi everyone,

This ones makes me scratch my head : I'm using the following script on
Windows and it looks like I can run two instances of it
simultaneously...which means that I have 2 servers listening on the
same port.

#!/usr/bin/perl -w
use strict;
use Socket;
my $port = 8080;
my $proto = getprotobyname('tcp');
socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
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: $!";
print "Server : server started on port $port\n";
while(1) {}

I was expecting an error like "port already in use". Am I doing
something wrong ?

<> wrote in message
news: oups.com...
> hi everyone,
>
> This ones makes me scratch my head : I'm using the following script on
> Windows and it looks like I can run two instances of it
> simultaneously...which means that I have 2 servers listening on the
> same port.
>

I have just been bitten by the same thing on Windows 2000 - during the
tidying up of some server and client scripts. I started getting inconsistent
behaviour that really had me puzzled (and irate) ... until I realised I had
four instances of the server script running concurrently - all listening to
the same port.

Not sure of the "approved" method for determining whether a port is in use.
As an interim measure I'm doing the following in an attempt to make sure I
don't make the same mistake again:

my $server_port = '2004'; # or whatever
my $netstat = `netstat -an`;
if($netstat =~ /:$server_port\s/) {die "Port already in use"}
# Followed by code to create the server listening on
# port $server_port

Cheers,
Rob

Sisyphus wrote:

>
> <> wrote in message
> news: oups.com...
>> hi everyone,
>>
>> This ones makes me scratch my head : I'm using the following script on
>> Windows and it looks like I can run two instances of it
>> simultaneously...which means that I have 2 servers listening on the
>> same port.

[...]

> Not sure of the "approved" method for determining whether a port is in
> use.

As filehandles, sockets are flock-able. An exclusive lock in the
server should do:

flock $server, LOCK_EX | LOCK_NB or die "port in use";

(Untested, I can't open the port another time in the first place.)

Anno

"Anno Siegel" <> wrote in message
..
..
>
> > Not sure of the "approved" method for determining whether a port is in
> > use.
>
> As filehandles, sockets are flock-able. An exclusive lock in the
> server should do:
>
> flock $server, LOCK_EX | LOCK_NB or die "port in use";
>

Also not sure about the use of flock() on Win32. When I insert the above
code into my server script (which runs with warnings pragma enabled) it dies
with:

Argument "LOCK_OZ" isn't numeric in flock at file_server.plx line 35.
port in use at file_server.plx line 35.

Line 35 is simply the line that implements the above code - the port is
definitely not in use.

From 'perldoc -f flock' I find:
"Produces a fatal error if used on a machine that doesn't implement
flock(2), fcntl(2) locking, or lockf(3)."

'perldoc perlport' reports that fcntl() is not implemented on Win32, though
flock() *is* implemented ... not sure what to make of all that.

Sorry if I'm being dumb.

Cheers,
Rob

wrote:
> hi everyone,
>
> This ones makes me scratch my head : I'm using the following script on
> Windows and it looks like I can run two instances of it
> simultaneously...which means that I have 2 servers listening on the
> same port.
>
> #!/usr/bin/perl -w
> use strict;
> use Socket;
> my $port = 8080;
> my $proto = getprotobyname('tcp');
> socket(Server, PF_INET, SOCK_STREAM, $proto) || die "socket: $!";
> setsockopt(Server, SOL_SOCKET, SO_REUSEADDR, pack("l", 1)) || die
> "setsockopt: $!";

Get rid of the SO_REUSEADDR. IIRC this will have the disadvantage that you
may have to wait a bit before you can reopen the socket after a close.

> bind(Server, sockaddr_in($port, INADDR_ANY)) || die "bind: $!";
> listen(Server,SOMAXCONN) || die "listen: $!";
> print "Server : server started on port $port\n";
> while(1) {}
>
> I was expecting an error like "port already in use". Am I doing
> something wrong ?
>

You might find IO::Socket easier to use.

Thomas

--
$/=$,,$_=<DATA>,s,(.*),$1,see;__END__
s,^(.*\043),,mg,@_=map{[split'']}split;{#>J~.>_an~>>e~......>r~
$_=$_[$%][$"];y,<~>^,-++-,?{$/=--$|?'"':#..u.t.^.o.P.r.>ha~.e..
'%',s,(.),\$$/$1=1,,$;=$_}:/\w/?{y,_, ,,#..>s^~ht<._..._..c....
print}:y,.,,||last,,,,,,$_=$;;eval,redo}#.....>.e. r^.>l^..>k^.-

"Thomas Kratz" <> wrote in message
..
..
>
> You might find IO::Socket easier to use.
>

Yes - that's what *I* use - but it still permits multiple instances of
servers to be listening on the same port.

Seems to be a Win32 thing - on linux I find it's not possible to run
multiple instances of the same server script. I get the fatal error "Address
already in use".

Even with the latest CPAN release of IO, the behaviour persists on Win32.
Should this be submitted as a bug to
http://rt.cpan.org/Public/Dist/Display.html?Name=IO ?

Cheers,
Rob

Sisyphus wrote:

>
> "Anno Siegel" <> wrote in message
> .
> .
>>
>> > Not sure of the "approved" method for determining whether a port is in
>> > use.
>>
>> As filehandles, sockets are flock-able. An exclusive lock in the
>> server should do:
>>
>> flock $server, LOCK_EX | LOCK_NB or die "port in use";
>>
>
> Also not sure about the use of flock() on Win32. When I insert the above
> code into my server script (which runs with warnings pragma enabled) it
> dies with:
>
> Argument "LOCK_OZ" isn't numeric in flock at file_server.plx line 35.
> port in use at file_server.plx line 35.

LOCK_OZ? Whazzat? Some windowy specialty?

> Line 35 is simply the line that implements the above code - the port is
> definitely not in use.
>
> From 'perldoc -f flock' I find:
> "Produces a fatal error if used on a machine that doesn't implement
> flock(2), fcntl(2) locking, or lockf(3)."
>
> 'perldoc perlport' reports that fcntl() is not implemented on Win32,
> though flock() *is* implemented ... not sure what to make of all that.

I have no personal experience with Windows, but I thought that file
locking worked.

Anno

Looks like the use of netstat before the binding is the most "direct"
solution...

Here is the same script with IO::Socket (the problem is the same but
the script is shorter

#!/usr/bin/perl -w
use strict;
use IO::Socket;
my $port=8080;
my $server = IO::Socket::INET->new(Proto => 'tcp',
LocalPort => $port,
Listen => SOMAXCONN,
Reuse => 1);
die "can't setup server" unless $server;
print "Server : server started on port $port\n";
while(1) {}

Quoth :
> Sisyphus wrote:
>
> >
> > <> wrote in message
> > news: oups.com...
> >> hi everyone,
> >>
> >> This ones makes me scratch my head : I'm using the following script on
> >> Windows and it looks like I can run two instances of it
> >> simultaneously...which means that I have 2 servers listening on the
> >> same port.
>
> [...]
>
> > Not sure of the "approved" method for determining whether a port is in
> > use.
>
> As filehandles, sockets are flock-able.

I *seriously* doubt if they are on Win32. Sockets on Win32 are not
ordinary filehandles, perl just fakes them up to look like it.

To the OP: remove the SO_REUSEADDR. Winsock is *COMPLETELY* broken;
among other things, SO_REUSEADDR doesn't mean 'allow another process to
bind again after the socket is closed but before the wait period' but
actually means 'bind to this port even if there is another process bound
there, at which point both sockets become non-deterministic' !!

See http://msdn.microsoft.com/library/de.../library/en-us
/winsock/winsock/using_so_reuseaddr_and_so_exclusiveaddruse.asp

(please excuse the wrapping).

Ben

--
'Deserve [death]? I daresay he did. Many live that deserve death. And some die
that deserve life. Can you give it to them? Then do not be too eager to deal
out death in judgement. For even the very wise cannot see all ends.'

"Anno Siegel" <> wrote in message
..
..
>
> LOCK_OZ? Whazzat? Some windowy specialty?
>

or maybe an Aussie specialty

>
> I have no personal experience with Windows, but I thought that file
> locking worked.
>

Heh ... I had this notion that it worked on Win32 without even being
specifically invoked

Btw, I (inadvertently) omitted some relevant info from my reply - if I run
under strictures I get:

Bareword "LOCK_EX" not allowed while "strict subs" in use at file_server.plx
line 35.
Bareword "LOCK_NB" not allowed while "strict subs" in use at file_server.plx
line 35.

Without strictures the error is as I reported.

I tried not supplying a second argument, but perl insists that a second arg
be supplied. I'm not feeling very energetic about this at the moment ....
maybe later

Cheers,
Rob