WaitSet::wait does not return if data was send before WaitSet::attachState

[mossmaurice]

Required information

Operating system:
Ubuntu 20.04.3 LTS

Compiler version:
GCC 8.4.0

Affected release(s):

• master branch
• iceoryx Blueberry v2.0.2

Observed result or behaviour:
WaitSet::wait does not return when there is data in the queue aka hasData() / hasRespones() / hasRequests() returning true at the time of attaching an object to the WaitSet and without further notification.

Expected result or behaviour:
If data is available in the queue when attached, the WaitSet::wait should immediately return.

Conditions where it occurred / Performed steps:

The issue was uncovered while working on ros2/rmw_iceoryx#84 with request/response communication. The same problem should also occur with pub/sub communication, but I have not explicitly reproduced that.

1. Start app Alice with iox::popo::Server
2. Start app Bob with iox::popo::Client
3. Send a request with iox::popo::Client from app Bob
4. From app Alice iox::popo::Server sends response
5. Only now, app Bob creates a ìox::popo::WaitSet
6. App Bob attaches the client with iox::popo::ClientState::HAS_RESPONSE
7. App Bob then calls WaitSet::wait which never returns because the ConditionNotifier::notify() call and its trigger is missing for the data which is already stored in the queue

[mossmaurice]

Will be closed once merged on release_2.0 branch.