Tracks whether the stream is waiting for an allocation to the stream flow control window, to the connection flow control window or not waiting for an allocation and only issues allocation notifications when the stream is known to be waiting for the notification.

It is possible for a stream to be waiting for a connection allocation when a stream allocation is made. Therefore this class tracks the type of allocation that the stream is waiting for to ensure that notifications are correctly triggered.

With the implementation at the time of writing, it is not possible for a stream to receive an unexpected connection notification as these are only issues to streams in the backlog and a stream must be waiting for a connection allocation in order to be placed on the backlog. However, as a precaution, this class protects against unexpected connection notifications.

It is important for asynchronous processing not to notify unless a notification is expected else a dispatch will be performed unnecessarily which may lead to unexpected results.

A previous implementation used separate locks for the stream and connection notifications. However, correct handling of allocation waiting requires holding the stream lock when making the decision to wait. Therefore both allocations need to wait on the Stream.