https://build.spring.io/browse/INTSAMPLES-NIGHTLY-2342 The `TcpClientServerDemoTest.testMultiPlex()` relies on the `HashSet.size()` for assertion meanwhile that property is not `volatile`. Since we change the state of the `HashSet` from other threads the non-`volatile` property is not reliable source of information. * Change the test-case to use `LinkedBlockingQueue` instead of `HashSet` which uses `AtomicInteger` to track its `size`