Issues are not created for some email messages due to thread visibility problems

Customers have reported situations in which issues are not being created for some incoming email. The log contains the following message, even though the service has been configured correctly:

[CreateIssueHandler] Cannot handle message as destination project is null.

This is most likely a thread visibility problem, since the CreateIssueHandler contains mutable data that is accessed in a non-threadsafe way (e.g. the project key). The fields are normally set in the handler's init(Map), which is called after the object has been published by the AbstractMessageHandlingService.

This should be fixed by employing a safe publication idiom in the AbstractMessageHandlingService:

• only publish the reference to the handler after calling init
• publish the reference using a volatile field, AtomicReference, or equivalent technique