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  • Mac Newbold's avatar
    New StateWait changes - the main point of all this is to move to our new · 2b2a306d
    Mac Newbold authored
    model of waiting for state changes. Before we were watching the database
    (which means we can only watch for terminal/stable/long-lived states, and
    have to poll the db). Now things that are waiting for states to change
    become event listeners, and watch the stream of events flow by, and don't
    have to do any polling. They can now watch for any state, and even
    sequences of states (ie a Shutdown followed by an Isup).
    To do this, there is now a cool library that encapsulates the
    functionality needed. To use it, you call initStateWait before you start
    the chain of events (ie before you call node reboot). Then do your stuff,
    and call waitForState() when you're ready to wait. It can be told to
    return periodically with the results so far, and you can cancel waiting
    for things. An example program called waitForState is in
    testbed/event/stated/ , and can also be used nicely as a command line tool
    that wraps up the library functionality.
    This also required the introduction of a TBFAILED event that can be sent
    when a node isn't going to make it to the state that someone may be
    waiting for. Ie if it gets wedged coming up, and stated retries, but
    eventually gives up on it, it sends this to let things know that the node
    is hozed and won't ever come up.
    Another thing that is part of this is that node_reboot moves (back) to the
    fully-event-driven model, where users call node reboot, and it does some
    checks and sends some events. Then stated calls node_reboot in "real mode"
    to actually do the work, and handles doing the appropriate retries until
    the node either comes up or is deemed "failed" and stated gives up on it.
    This means stated is also the gatekeeper of when you can and cannot reboot
    a node. (See mail archives for extensive discussions of the details.)
    A big part of the motivation for this was to get uninformed timeouts and
    retries out of os_load/os_setup and put them in stated where we can make a
    wiser choice. So os_load and os_setup now use this new stuff and don't
    have to worry about timing out on nodes and rebooting. Stated makes sure
    that they either come up, get retried, or fail to boot. tbrestart also
    underwent a similar change.