ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
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17.3. Communicating over TCPProblemYou want to read or write data over a TCP connection. SolutionThis recipe assumes you're using the Internet to communicate. For TCP-like communication within a single machine, see Recipe 17.6. Use print SERVER "What is your name?\n"; chomp ($response = <SERVER>); Or, use defined (send(SERVER, $data_to_send, $flags)) or die "Can't send : $!\n"; recv(SERVER, $data_read, $maxlen, $flags) or die "Can't receive: $!\n"; Or, use the corresponding methods on an IO::Socket object: use IO::Socket; $server->send($data_to_send, $flags) or die "Can't send: $!\n"; $server->recv($data_read, $flags) or die "Can't recv: $!\n"; To find out whether data can be read or written, use the use IO::Select; $select = IO::Select->new(); $select->add(*FROM_SERVER); $select->add($to_client); @read_from = $select->can_read($timeout); foreach $socket (@read_from) { # read the pending data from $socket } DiscussionSockets handle two completely different types of I/O, each with attendant pitfalls and benefits. The normal Perl I/O functions used on files (except for Awareness of buffering issues is particularly important in socket programming. That's because buffering, while designed to enhance performance, can interfere with the interactive feel that some programs require. Gathering input with < > may try to read more data from the socket than is yet available as it looks for a record separator. Both For line-based clients and servers, this is probably okay, so long as you turn on autoflushing for output. Newer versions of IO::Socket do this automatically on the anonymous filehandles returned by But stdio isn't the only source of buffering. Output ( use Socket; require "sys/socket.ph"; # for &TCP_NODELAY setsockopt(SERVER, SOL_SOCKET, &TCP_NODELAY, 1) or die "Couldn't disable Nagle's algorithm: $!\n"; Re-enable it with: setsockopt(SERVER, SOL_SOCKET, &TCP_NODELAY, 0) or die "Couldn't enable Nagle's algorithm: $!\n"; In most cases, TCP_NODELAY isn't something you need. TCP buffering is there for a reason, so don't disable it unless your application is one of the few real-time packet-intensive situations that need to. Load in TCP_NODELAY from sys/socket.ph, a file that isn't automatically installed with Perl, but can be easily built. See Recipe 12.14 for details. Because buffering is such an issue, you have the $rin = ''; # initialize bitmask vec($rin, fileno(SOCKET), 1) = 1; # mark SOCKET in $rin # repeat calls to vec() for each socket to check $timeout = 10; # wait ten seconds $nfound = select($rout = $rin, undef, undef, $timeout); if (vec($rout, fileno(SOCKET),1)){ # data to be read on SOCKET } The four arguments to The function changes the bitmask arguments passed to it, so that when it returns, the only bits set correspond to filehandles ready for I/O. This leads to the common strategy of assigning an input mask ( You can specify a timeout of 0 to poll (check without blocking). Some beginning programmers think that blocking is bad, so they write programs that "busy wait" - they poll and poll and poll and poll. When a program blocks, the operating system recognizes that the process is pending on input and gives CPU time to other programs until input is available. When a program busy-waits, the system can't let it sleep because it's always doing something - checking for input! Occasionally, polling is the right thing to do, but far more often it's not. A timeout of Because A full explanation of the exceptional data tested for with the third bitmask in Other See AlsoThe
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