Question

In Erlang, is it possible to have a cleanup function automatically called when all references to a resource go away? For example, will the native file handle that is opened by calling file:open/2 ever be closed if file:close/1 is never called? If this is possible, how is it done? If not possible, are there Erlang idioms that make resources leaks like this not an issue?

Answer 1

From the file documentation:

IoDevice is really the pid of the process which handles the file. This process is linked to the process which originally opened the file. If any process to which the IoDevice is linked terminates, the file will be closed and the process itself will be terminated. An IoDevice returned from this call can be used as an argument to the IO functions (see io(3)).

So, if the process that opened the file dies, the file will be closed automatically.

If you are using OTP and you want to be absolutely sure your file was closed when your process dies, add file:close to the terminate function. Of course your gen_* must be attached to a supervisor.