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% Copyright 2010 Cloudant
%
% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-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(),
Nodes = [node() | nodes()],
{Mon, Skip} = lists:partition(fun(P) -> should_monitor(P, Nodes) end,
Procs),
spawn_link(fun() ->
[notify_parent(Parent, P, noconnect) || P <- Skip],
[erlang:monitor(process, P) || P <- Mon],
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 %%
notify_parent(Parent, Pid, Reason) ->
erlang:send(Parent, {rexi_DOWN, self(), Pid, Reason}).
should_monitor(Pid, Nodes) when is_pid(Pid) ->
lists:member(node(Pid), Nodes);
should_monitor({_, Node}, Nodes) ->
lists:member(Node, Nodes).
wait_monitors(Parent) ->
receive
{'DOWN', _, process, Pid, Reason} ->
notify_parent(Parent, 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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