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%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2020. All Rights Reserved.
%%
%% 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.
%%
%% %CopyrightEnd%
%%
-module(pool).
%% Supplies a computational pool of processors.
%% The chief user interface function here is get_node()
%% Which returns the name of the nodes in the pool
%% with the least load !!!!
%% This function is callable from any node including the master
%% That is part of the pool
%% nodes are scheduled on a per usage basis and per load basis,
%% Whenever we use a node, we put at the end of the queue, and whenever
%% a node report a change in load, we insert it accordingly
% User interface Exports ...
-export([start/1,
start/2,
stop/0,
get_nodes/0,
get_nodes_and_load/0,
get_node/0,
pspawn/3,
attach/1,
pspawn_link/3]).
%% Internal Exports
-export([statistic_collector/0,
do_spawn/4,
init/1,
handle_call/3,
handle_cast/2,
handle_info/2,
terminate/2]).
%% User interface
%% Start up using the .hosts.erlang file
-spec start(Name) -> Nodes when
Name :: atom(),
Nodes :: [node()].
start(Name) ->
start(Name,[]).
-spec start(Name, Args) -> Nodes when
Name :: atom(),
Args :: string(),
Nodes :: [node()].
start(Name, Args) when is_atom(Name) ->
_ = gen_server:start({global, pool_master}, pool, [], []),
Hosts = net_adm:host_file(),
Nodes = start_nodes(Hosts, Name, Args),
lists:foreach(fun attach/1, Nodes),
Nodes.
%%
%% Interface functions ...
%%
-spec get_nodes() -> [node()].
get_nodes() ->
get_elements(2, get_nodes_and_load()).
-spec attach(Node) -> 'already_attached' | 'attached' when
Node :: node().
attach(Node) ->
gen_server:call({global, pool_master}, {attach, Node}).
get_nodes_and_load() ->
gen_server:call({global, pool_master}, get_nodes).
-spec get_node() -> node().
get_node() ->
gen_server:call({global, pool_master}, get_node).
-spec pspawn(Mod, Fun, Args) -> pid() when
Mod :: module(),
Fun :: atom(),
Args :: [term()].
pspawn(M, F, A) ->
gen_server:call({global, pool_master}, {spawn, group_leader(), M, F, A}).
-spec pspawn_link(Mod, Fun, Args) -> pid() when
Mod :: module(),
Fun :: atom(),
Args :: [term()].
pspawn_link(M, F, A) ->
spawn_link(get_node(), M, F, A).
start_nodes([], _, _) -> [];
start_nodes([Host|Tail], Name, Args) ->
case slave:start(Host, Name, Args) of
{error, {already_running, Node}} ->
io:format("Can't start node on host ~w due to ~w~n",[Host, {already_running, Node}]),
[Node | start_nodes(Tail, Name, Args)];
{error, R} ->
io:format("Can't start node on host ~w due to ~w~n",[Host, R]),
start_nodes(Tail, Name, Args);
{ok, Node} ->
[Node | start_nodes(Tail, Name, Args)]
end.
-spec stop() -> 'stopped'.
stop() ->
gen_server:call({global, pool_master}, stop).
get_elements(_Pos,[]) -> [];
get_elements(Pos,[E|T]) -> [element(Pos,E) | get_elements(Pos,T)].
stop_em([]) -> stopped;
stop_em([N|Tail]) ->
rpc:cast(N, erlang, halt, []),
stop_em(Tail).
init([]) ->
process_flag(trap_exit, true),
spawn_link(pool, statistic_collector, []),
{ok,[{0,node()}]}.
handle_call(get_nodes, _From, Nodes)->
{reply, Nodes, Nodes};
handle_call(get_node, _From, [{Load,N}|Tail]) ->
{reply, N, Tail++[{Load+1, N}]};
handle_call({attach, Node}, _From, Nodes) ->
case lists:keymember(Node, 2, Nodes) of
true ->
{reply, already_attached, Nodes};
false ->
erlang:monitor_node(Node, true),
spawn_link(Node, pool, statistic_collector, []),
{reply, attached, Nodes++[{999999,Node}]}
end;
handle_call({spawn, Gl, M, F, A}, _From, Nodes) ->
{reply, N, NewNodes} = handle_call(get_node, _From, Nodes),
Pid = spawn(N, pool, do_spawn, [Gl, M, F, A]),
{reply, Pid, NewNodes};
handle_call(stop, _From, Nodes) ->
%% clean up in terminate/2
{stop, normal, stopped, Nodes}.
handle_cast(_, Nodes) ->
{noreply, Nodes}.
handle_info({Node,load,Load}, Nodes) ->
Nodes2 = insert_node({Load,Node}, Nodes),
{noreply, Nodes2};
handle_info({nodedown, Node}, Nodes) ->
{noreply, lists:keydelete(Node, 2, Nodes)};
handle_info(_, Nodes) -> %% The EXIT signals etc.etc
{noreply, Nodes}.
terminate(_Reason, Nodes) ->
N = lists:delete(node(), get_elements(2, Nodes)),
stop_em(N),
ok.
-spec do_spawn(pid(), module(), atom(), [term()]) -> term().
do_spawn(Gl, M, F, A) ->
group_leader(Gl, self()),
apply(M, F, A).
insert_node({Load,Node},[{L,Node}|Tail]) when Load > L ->
%% We have a raised load here
pure_insert({Load,Node},Tail);
insert_node({Load,Node},[{L,N}|Tail]) when Load =< L ->
%% Move forward in the list
T = lists:keydelete(Node,2,[{L,N}|Tail]),
[{Load,Node} | T];
insert_node(Ln,[H|T]) ->
[H | insert_node(Ln,T)];
insert_node(X,[]) -> % Can't happen
error_logger:error_msg("Pool_master: Bad node list X=~w\n", [X]),
exit(crash).
pure_insert({Load,Node},[]) ->
[{Load,Node}];
pure_insert({Load,Node},[{L,N}|Tail]) when Load < L ->
[{Load,Node}, {L,N} | Tail];
pure_insert(L,[H|T]) -> [H|pure_insert(L,T)].
%% Really should not measure the contributions from
%% the background processes here .... which we do :-(
%% We don't have to monitor the master, since we're slaves anyway
statistic_collector() ->
statistic_collector(5).
statistic_collector(0) -> exit(normal);
statistic_collector(I) ->
timer:sleep(300),
case global:whereis_name(pool_master) of
undefined ->
statistic_collector(I-1);
M ->
stat_loop(M, 999999)
end.
%% Do not tell the master about our load if it has not changed
stat_loop(M, Old) ->
timer:sleep(2000),
case statistics(run_queue) of
Old ->
stat_loop(M, Old);
NewLoad ->
M ! {node(), load, NewLoad}, %% async
stat_loop(M, NewLoad)
end.
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