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-module(rexi_monitor).
-export([start/1, stop/1]).
-include_lib("eunit/include/eunit.hrl").
%% @doc spawn_links a process which monitors the supplied list of items and
%% returns the process ID. If a monitored process exits, the caller will
%% receive a {rexi_DOWN, MonitoringPid, DeadPid, Reason} message.
-spec start([pid() | atom() | {atom(),node()}]) -> pid().
start(Procs) ->
Parent = self(),
spawn_link(fun() ->
[erlang:monitor(process, P) || P <- Procs],
wait_monitors(Parent)
end).
%% @doc Cleanly shut down the monitoring process and flush all rexi_DOWN
%% messages from our mailbox.
-spec stop(pid()) -> ok.
stop(MonitoringPid) ->
MonitoringPid ! {self(), shutdown},
flush_down_messages().
%% internal functions %%
wait_monitors(Parent) ->
receive
{'DOWN', _, process, Pid, Reason} ->
Parent ! {rexi_DOWN, self(), Pid, Reason},
wait_monitors(Parent);
{Parent, shutdown} ->
ok
end.
flush_down_messages() ->
receive {rexi_DOWN, _, _, _} ->
flush_down_messages()
after 0 ->
ok
end.
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