Post on 02-Jan-2016
description
How to Place Timeouts on Sockets (1)
Using SIGALRM signalConnection timeout 기간의 축소 Response timeout
advio/dgclitimeo3.c lib/connect_timeo.c
alarm() 은 초 단위setitimer() 는 micro sec 단위 설정 가능 ( 실제는 msec 단위로 동작 )
How to Place Timeouts on Sockets (2)
Using select with timeoutadvio/dgclitimeo1.c lib/readable_timeo.c
How to Place Timeouts on Sockets (3)
Using SO_RCVTIMEO and SO_SNDTIMEO socket options Caution: timeout applies to all I/O operations for the
socket descriptor
advio/dgclitimeo2.c
Socket and Standard I/O
Buffering in Standard I/O library fully buffered: all stream except for terminal devices line buffered : terminal devices unbuffered: stderr
Caution Socket 에 standard I/O functions(fgets, fputs) 를 쓰면
fully buffered 됨
Generic Socket Options(1)
SO_BROADCAST Enable the ability of the process to send broadcast messages Application must set this option before broadcasting
SO_DEBUG Kernel keeps track of detailed information about all the packets
sent or received by TCP for the socket SO_DONTROUTE
Bypass the normal routing mechanism The packet is directed to the appropriate local interface. If the
local interface cannot be determined (i.e. destination is not on the same network), ENETUNREACH is returned.
SO_ERROR Get the value of pending error Socket 에 error 가 발생하면 , so_error (pending error) 에 먼저
setting 하고 나서 errno 에 setting 함
Generic Socket Options(2)
SO_KEEPALIVE Enforce TCP to send a keepalive probe automatically to the peer
if no data has been exchanged for 2 hours (to detect if the peer host crashes)
Peer’s response is either ACK: everything is OK (application is not notified) RST: the peer host has crashed and rebooted. Socket’s pending
error = ECONNRESET and socket is closed No response: send 8 additional probes, 75 sec apart (totally, 11mim
and 15sec). Listen the peer’s response. Still no response ETIMEOUT and socket is closed Receives ICMP error, EHOSTUNREACH or …
To shorten probe period Use TCP_KEEPALIVE option (Not all implementation support this
option). But, this will affect all sockets on the host. Or, implement your own heartbeat mechanism.
Default Operation of close
Any data remaining in the socket send buffer is sent. Close returns immediately without receiving ACK.
Client cannot know whether the data has been delivered correctly to the server !!!
Generic Socket Options(3) SO_LINGER: linger when the socket is closed
Data type for option value
If l_onoff = 0, default close(). i.e. return immediately, but the remaining data is delivered to the peer
else linger when the socket is closed If l_linger==0, TCP aborts the connection. i.e. TCP discards any
data still remaining in the socket send buffer and sends an RST to the peer.
else linger when the socket is closed. Any data still remaining in the socket send buffer is sent. But, if linger time expires, return EWOULDBLOCK and any remaining data is discarded.
Generic Socket Options(4) SO_OOBINLINE
OOB data will be placed in the normal input queue SO_RCVBUF and SO_SNDBUF
Set or get socket send buffer size / socket receive buffer size TCP:
advertise receive buffer(window) to the peer sliding window mechanism(flow control) buffer size 3 * MSS
UDP: typical send buffer size 9000, receive buffer size 40,000, If data received > available receive buffer, datagram is discarded
Capacity of full-duplex pipe (bandwidth-delay product) bandwidth * RTT (<= 64KB)
SO_RCVLOWAT, SO_SNDLOWAT: socket low water mark data in socket receive buffer >= SO_RCVLOWAT readable available space in socket send buffer >= SO_SNDLOWAT writable SO_RCVLOWAT = 1, SO_SNDLOWAT = 2048 by default
SO_RCVTIMEO, SO_SNDTIMEO: socket time out for receiving and sending message
Generic Socket Options(6) SO_REUSEADDR: reuse the established port
Allows a listening server to start and bind its well-known port even if previously established connections exist that use this port
Allows multiple instances of the same server to be started on the same port as long as each instance binds a different local IP address hosting multiple HTTP servers using IP alias technique
Allows a single process to bind the same port to multiple socket as long as each bind specifies a different local IP address
Allows completely duplicate bindings when same IP address and port are already bound to another socket. Used with multicasting to allow the same application to be
run multiple times on the same host when the SO_REUSEPORT option is not supported
TCP Socket Options
TCP_KEEPALIVE: specifies the idle time in seconds for the connection before TCP starts sending keepalive probes 7200 sec (2 hours), default Effective only when SO_KEEPALIVE socket option is enabled
TCP_MAXSEG: fetch or set MSS for TCP connection TCP_NODELAY
e.g) rlogin, telnet Nagle algorithm / delayed algorithm disabled TCP’s Nagle algorithm
No small packet( < MSS ) will not be sent until the existing data is ACKed
TCP’s delayed ACK algorithm piggyback: TCP sends an ACK after some small amount of time( 50 ~
200msec)