stevensonmt
In the Elixir for Programmers course by @pragdave he asks the student to come up with a means of monitoring when children of a dynamic supervisor “goes away”. By “goes away” I assume that means exits gracefully or the node crashes out. I can easily monitor when nodes connect by implementing handle_info and when the the call to DynamicSupervisor.start_child occurs I follow it with a call to send(pid, DynamicSupervisor.which_children(my_supervisor_name)). I don’t yet have a graceful exit implemented for the game so right now I only have to handle when the node crashes out. Since this occurs without a message being sent to the supervisor I don’t know how to trigger a reaction to the event. Any suggestions?
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Actually it occurs to me that I might not have been killing or exiting the node in a reasonable way. I’m starting the supervisor in an IEX session, then in another terminal starting the child process. Then I ctrl-c to kill the IEX session of the child process. When running the observer on the supervisor I do not see any message coming into the supervisor, but the child process PID persists. So maybe as far as the VM is concerned nothing has happened?
The information in the observer for the child processes that are no longer active gives “status waiting” in Process Information tab but in the State tab “status” is “running” and Logged Events is an empty list.
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joaoevangelista
You can use a genserver to monitor the Node, the process where you call
Node.monitor/2will be the one responsible to monitoring it. If you call on a GenServer callback it will be the GenServer, then you can listen for messages on handle_info callback.Last Post!
stevensonmt
That’s what I’ve just done this morning. I had to set up a “NodeWatcher” GenServer that is started when the application starts. When a new game is started I check to see if there are any new nodes connected and if so add them to the NodeWatcher. The NodeWatcher runs Node.monitor/2 every time a node is added to its state. When the NodeWatcher receives a
{:nodedown, node}message I have ahandle_infocall that removes the node from the watcher’s state and outputs confirmation that it has been removed to the terminal. Ultimately I think I’d like to have the ability to keep games associated with nodes, and if a given node goes down it starts a timer for the game to shutdown if the node does not reconnect in x amount of time.