Kacheong Poon wrote:
I want to gather some info about what apps expect from setting
the SO_LINGER option with a non-zero linger time on a TCP socket.
Suppose after the specified linger timeout, some data still cannot
be sent or some data has not been ack'ed by the peer. In this
case, the close() will return an error as documented. But what do
apps expect the underlying TCP connection will behave? AFAIK,
there is no Solaris document which states what will happen to
the underlying TCP connection. Do apps expect that the connection
will be aborted after the timeout, the same behavior if a zero linger
time is set?
Yes of course. And Oracle does seem to describe the behavior in both
Java and Solaris documentation.
http://download.oracle.com/javase/1,5.0/docs/api/java/net/SocketOptions.html#SO_LINGER
SO_LINGER
static final int *SO_LINGER*
Specify a linger-on-close timeout. This option disables/enables
immediate return from a *close()* of a TCP Socket. Enabling this
option with a non-zero Integer /timeout/ means that a *close()* will
block pending the transmission and acknowledgement of all data
written to the peer, at which point the socket is closed
/gracefully/. *Upon reaching the linger timeout, the socket is
closed /forcefully/*, with a TCP RST. Enabling the option with a
timeout of zero does a forceful close immediately. If the specified
timeout value exceeds 65,535 it will be reduced to 65,535.
Valid only for TCP: SocketImpl
*See Also:*
Solaris: setsockopt(3SOCKET)
The SO_LINGER option controls the action taken when unsent
messages are queued on a socket and a close(2) is performed.
If the socket promises reliable delivery of data and
SO_LINGER is set, the system will block the thread on the
close() attempt until it is able to transmit the data *or
until it decides it is unable to deliver the information (a
timeout period, termed the linger interval, is specified in
the setsockopt() call when SO_LINGER is requested)*. If
SO_LINGER is disabled and a close() is issued, the system
will process the close() in a manner that allows the thread
to continue as quickly as possible.
Rao.
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