Supervisor callback for child normal exit

Question

I am creating a test app where is one supervisor with simple_one_for_one strategy and many worker children added dynamically to it. How to implement callback (or receive a message) in supervisor that will be called when child exit normally?

Main goal is to notify some other process that all supervised worker processes are done and it's time to show final report.

How to design such kind of behavior? Should I create my own behavior that combine supervisor and gen_server, or there is a way to do this with standard otp behaviors?

Answer 1

There are two ways to do such a notification. The first is to simply monitor the child from the beginning. By using erlang:monitor/2, a third party can whether a process is alive or not. When the monitored process dies, the result will be turned into a message that will give the reason for it to the monitoring process.

The other way could be to use a bit of message sending in the process' terminate/2 function (terminate/3 if it's a gen_fsm). This far more brittle because the terminate function will not be called in all circumstances.

The monitor option is far superior.