JIRA: https://jira.spring.io/browse/INT-3722
The TCP outbound gateway correlates replies based on the connection id.
When a `CachingClientConnectionFactory` is being used, the connection is
returned to the pool too early, and can be reused. It is possible that
the current thread then removes the "next" pending reply from the correlation map.
Add code to the `CachingClientConnectionFactory` so that the "self" close from the
connection (called after `onMessage`) is deferred and the actual close (return to cache)
is controlled by the gateway itself.
This mechanism will no longer be needed when INT-3654 is resolved (removal of the "self"
closing by connections). At that time, connection users (such as the gateway) will be
in complete control.
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