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POHow to atomatically delete specs of terminated children in a dynamic supervisor
 

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    <p><em>No knowledge of USB needed for this question, just described it as it is to make the example more conrete.</em></p> <p>I'm trying to implement a dynamic supervisor for specific devices on a USB bus. These devices have addresses and appear and disappear during the lifetime of the system. </p> <p>For each device I need a dynamic child for my supervisor.</p> <p>These children are transient, so once they crash or terminate we don't restart them (because probably they are gone then).</p> <p>I have a process that scans the USB port at certain times and produces a list of all addresses of the USB devices I want to handle.</p> <p>I plan to call <code>supervisor:which_children/1</code> before each scan to find out which devices are present but have no child process running.</p> <p>In order to find out which addresses have children running I plan to create Id atoms for the childspec that contain the addresses (there are only a few addresses possible), e.g. <code>adr_12</code> if the child handles address <code>12</code>.</p> <p>When I try to start/restart missing children I have the somewhat ugly situation that the child specs are not automatically deleted when the transient child terminates or crashes (at least I think that it is so). So I would need code like this:</p> <pre><code>case supervisor:start_child(my_sup, Spec) of {error, already_present} -&gt; supervisor:restart_child(my_sup, Spec); Any -&gt; Any end </code></pre> <p>Then there is the problem that I don't know if <code>supervisor:which_children/1</code> also returns already terminated children.</p> <p>So it would be best if children would be deleted after they transiently terminate.</p> <p>Somehow all this feels inelegant to me so I'm asking myself (and you):</p> <p>How can I resolve this most elegantly?</p> <p>Is it better not to use a supervisor at all in this situation?</p>
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