Programming Erlang, 2nd Edition

Monitors

Monitors are similar to links but with several significant differences.

• Monitors are unidirectional. If A monitors B and B dies, then A will be sent an exit message but not the other way around (recall that links were bidirectional, so if A and B were linked, the death of either process would result in the other process being informed).

• When a monitored process dies, a “down” message and not an exit signal is sent to the monitoring process. This means that the monitoring process does not have to become a system process in order to handle errors.

Monitors are used when you want asymmetry in error handling; links are used when you want symmetric error handling. Monitors are typically used by servers to monitor the behavior of clients. ...