🧵 Improve synchronization of connection_state transitions
#494
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If `disconnected?` returns true, the connection state is most likely already `logout`. But, just in case, we'll ensure it's set every time.
Net::IMAP#disconnect will still attempt to enter the logout state first, but it won't wait for the lock until after the socket has been shutdown.
The reciever thread should close the connection before it finishes, and `@sock.shutdown` should've been enough to trigger that. But this ensures the socket is closed right away, without needing to wait on whatever the receiver thread might be in the middle of doing.
It should always be safe to call `@sock.close` without external synchronization. And synchronizing here with could get stuck waiting e.g. for a response_handler looping in the receiver thread.
This should work both for TCPSocket and for OpenSSL::SSL::SSLSocket. Both will respond to `#to_io` with the TCPSocket.
Eventually the states will store small bits of information about each state on the state objects, e.g: which mailbox was selected or what caused the logout. So for `logout`, the first attempt wins and shouldn't be overwritten. For other states, like `selected`, the last attempt _should_ win. On the other hand, state transitions should be reworked so that: * state transitioning commands cannot run simultaneously * all state transitions are effected _inside_ the receiver thread
This pushes `ensure state_logout!` from the receiver's `Thread.start` down into `#receive_responses`. As a side-effect, this also pulls the state change inside the receiver thread's exception handling. But that's fine: it fits better inside `receive_responses`, and `state_logout!` really should never raise an exception anyway.
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Handles a few more connection_state synchronization issues I saw while working on #493.
While attempting to get the tests running under JRuby,
#disconnectwould sometimes deadlock. So, although I haven't seen that problem elsewhere and JRuby is still failing tests with another threading issue, this did get most tests passing for me (but not in CI).