As you may have gathered, the Timeout IO::Socket::INET option is expected to apply only to connect and accept -- and some people doubt whether even that works on Win32... but more on that, below.

For sysread and syswrite I know of three ways to introduce a time-out:

1. use alarm and a signal handler. I've seen an eval wrapped around a read or write operation, with a signal handler that dies. A quick experiment suggests this is not necessary, an ALRM signal causes sysread to return with an EINTR "soft" error. However, alarm doesn't appear to work on Win32 -- I cannot find chapter and verse on this limitation, but I can say when I tried it (perl 5.10.0, ActivePerl Build 1002 283697) it did not work.

2. socket options SO_RCVTIMEO and SO_SNDTIMEO seem to offer exactly what's required. Unfortunately the POSIX (1003.1, 2004) specification says "not all implementations allow this option to be set", which isn't encouraging -- life is complicated enough, already. When I tried it, Linux (2.6.27.7-53) rejected the attempt to $sock->sockopt(SO_RCVTIMEO, 10) :-(

3. the final way is to use select, which may seem to be hard work, but is actually straighforward and has the advantage of working ! The following will read from an open socket $sock until it is closed by the far end, or nothing arrives for ten seconds, or some error occurs:

     my $select = IO::Select->new($sock) ;
     my $buffer = '' ;
     my $rc ;
     while (1) {
       $! = undef ;               # no error, yet
       if ($select->can_read(10)) {
         $rc = sysread($sock, $buffer, 64*1024, length($buffer));
         next if $rc ;            # continue if not error and not "eof"
         last if defined($rc) ;   # exit if "eof"
       }
       else {
         $rc = $! ? undef : 1 ;   # $rc == undef if error, == 1 if time o
   +ut
         last if $rc ;            # exit if time out
       } ;
   
       redo if $! == EAGAIN ;     # Not really expected, even with non-bl
   +ocking
       redo if $! == EINTR ;      # Signals !
   
       last ;                     # exit on "hard" error
     } ;
   
     # Now: $rc == 0 => no error, == 1 => timed out, == undef => error
   [download]

   and something similar should work for syswrite. Note that it is not necessary to set the socket non-blocking in order to use select, or for sysread to return with a partial result -- but it won't hurt to set the socket non-blocking.

At some time in the past IO::Socket may have used alarm to implement time-out for connect/new and for accept. However, current implementation (v1.31) uses IO::Select, and works happily on Win32. (Looking at the ChangeLog, this appears to have been the case since v1.15, Sun 19 Jan 1997.)

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