monitor message order

[Vladimir Sekissov]

Good day,

vances> If I have a process set up multiple monitors to another
vances> process is there any telling which monitor reference will
vances> be returned first?  FIFO? FILO? Random?

If I correctly understand source

erts/emulator/beam/erl_process.c 
erts/emulator/beam/bif.c
erts/emulator/beam/utils.c

the order is LIFO.

Reference consists from four cyclic counters so we can do simple test:

19> F1 = fun () -> receive stop -> exit(normal) end end.
#Fun<erl_eval.19.280769>

24> F2 = fun (Cont) ->
            receive
              Msg ->
                io:format("~p~n", [Msg]), Cont(Cont)
              after 5000 -> ok
            end
         end.
#Fun<erl_eval.5.123085357>

25> F3 = fun (Pid) ->
            lists:foreach(fun (_) -> erlang:monitor(process, Pid) end,
                          [1,2,3,4,5,6]),
            Pid ! stop,
            F2(F2)
         end.
27> F3(spawn(F1)).
{'DOWN',#Ref<0.0.0.11860>,process,<0.2289.0>,normal}
{'DOWN',#Ref<0.0.0.11859>,process,<0.2289.0>,normal}
{'DOWN',#Ref<0.0.0.11858>,process,<0.2289.0>,normal}
{'DOWN',#Ref<0.0.0.11857>,process,<0.2289.0>,normal}
{'DOWN',#Ref<0.0.0.11856>,process,<0.2289.0>,normal}
{'DOWN',#Ref<0.0.0.11855>,process,<0.2289.0>,normal}
ok

Best Regards,
Vladimir Sekissov

vances> 
vances> If I have a process set up multiple monitors to another
vances> process is there any telling which monitor reference will
vances> be returned first?  FIFO? FILO? Random?
vances> 
vances> I'm trying to keep track of the processes that have created
vances> resources on a server and garbage collect those resources
vances> when the process goes away without cleaning up after itself.
vances> 
vances> It's easy enough at first glance but I'm struggling with the
vances> order of operations as there are dependencies on these
vances> resources.  If I could be sure of the order of receipt of
vances> the 'DOWN' messages it would greatly simplify things.
vances> 
vances> 	-Vance