36.6 Connection Closure

The Ice run time may close a connection for many reasons, including the situa­tions listed below:

• When deactivating an object adapter or shutting down a communicator

• As required by active connection management (see Section 36.4)

• When initiated by an application (see Section 36.5.5)

• After a request times out (see Section 36.3.5)

• In response to an exception, such as a socket failure or protocol error.

In most cases, the Ice run time closes a connection gracefully as required by the Ice protocol (see Section 37.3.6). The Ice run time only closes a connection force­fully when a timeout occurs or when the application explicitly requests it.

36.6.1 Graceful Connection Closure

Gracefully closing a connection occurs in stages:

• In the process that initiates closure, incoming and outgoing requests that are in progress are allowed to complete, and then a close connection message is sent to the peer. Any incoming requests received after closure is initiated are silently discarded (but may be retried, as discussed in the next bullet). An attempt to make a new outgoing request on the connection results in a CloseConnectionException and an automatic retry (if enabled).

• Upon receipt of a close connection message, the Ice run time in the peer closes its end of the connection. Any outgoing requests still pending on that connec­tion fail with a CloseConnectionException. This exception indicates to the Ice run time that it is safe to retry those requests without violating at‑most-once semantics (see Section 32.22), assuming automatic retries have not been disabled.

• After detecting that the peer has closed the connection, the initiating Ice run time closes the connection.

36.6.2 Impact on Oneway Invocations

As discussed in Section 32.14, oneway invocations are generally considered reli­able because they are sent over a stream-oriented transport. However, it is quite possible for oneway requests to be silently discarded if a server has initiated graceful connection closure (see Section 36.6.1). Whereas graceful closure causes a discarded twoway request to receive a CloseConnectionException and eventu­ally be retried, the sender receives no notice about a discarded oneway request.

If an application makes assumptions about the reliability of oneway requests, it may be necessary to control the events surrounding connection closure as much as possible, for example by disabling active connection management (see Section 36.4) and avoiding explicit connection closures.