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authorDan Gudmundsson <[email protected]>2017-11-20 15:23:24 +0100
committerDan Gudmundsson <[email protected]>2017-12-01 15:24:02 +0100
commitd4341cd249d728174fce580bd018e1e8b402d161 (patch)
treeda490e0cd419bf3413f4d55992e659e23ecbb6e7 /lib/kernel/src/kernel_refc.erl
parenta90b3712dcec20c96eeeecbabc2672ec67c7d89a (diff)
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kernel: add a resource reference counter
System resources/functionality may need to be reference counted to be handled correctly when used or enabled/disabled from more than one process or application. It is easier to handle this in erlang code than in erts, so make a process that deals with the housekeeping.
Diffstat (limited to 'lib/kernel/src/kernel_refc.erl')
-rw-r--r--lib/kernel/src/kernel_refc.erl139
1 files changed, 139 insertions, 0 deletions
diff --git a/lib/kernel/src/kernel_refc.erl b/lib/kernel/src/kernel_refc.erl
new file mode 100644
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+++ b/lib/kernel/src/kernel_refc.erl
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+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2017. 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(kernel_refc).
+
+-behaviour(gen_server).
+
+%% External exports
+-export([start_link/0, scheduler_wall_time/1]).
+%% Internal exports
+-export([init/1, handle_info/2, terminate/2]).
+-export([handle_call/3, handle_cast/2, code_change/3]).
+
+%%%-----------------------------------------------------------------
+%%% This module implements a process that handles reference counters for
+%%% various erts or other kernel resources which needs reference counting.
+%%%
+%%% Should not be documented nor used directly by user applications.
+%%%-----------------------------------------------------------------
+start_link() ->
+ gen_server:start_link({local,kernel_refc}, kernel_refc, [], []).
+
+-spec scheduler_wall_time(boolean()) -> boolean().
+scheduler_wall_time(Bool) ->
+ gen_server:call(kernel_refc, {scheduler_wall_time, self(), Bool}).
+
+%%-----------------------------------------------------------------
+%% Callback functions from gen_server
+%%-----------------------------------------------------------------
+
+-spec init([]) -> {'ok', map()} | {'stop', term()}.
+
+init([]) ->
+ resource(scheduler_wall_time, false),
+ {ok, #{scheduler_wall_time=>#{}}}.
+
+-spec handle_call(term(), term(), State) -> {'reply', term(), State}.
+handle_call({What, Who, false}, _From, State) ->
+ {Reply, Cnt} = do_stop(What, maps:get(What, State), Who),
+ {reply, Reply, State#{What:=Cnt}};
+handle_call({What, Who, true}, _From, State) ->
+ {Reply, Cnt} = do_start(What, maps:get(What, State), Who),
+ {reply, Reply, State#{What:=Cnt}};
+handle_call(_, _From, State) ->
+ {reply, badarg, State}.
+
+-spec handle_cast(term(), State) -> {'noreply', State}.
+handle_cast(_, State) ->
+ {noreply, State}.
+
+-spec handle_info(term(), State) -> {'noreply', State}.
+handle_info({'DOWN', _Ref, process, Pid, _}, State) ->
+ Cleanup = fun(Resource, Cnts) ->
+ cleanup(Resource, Cnts, Pid)
+ end,
+ {noreply, maps:map(Cleanup, State)};
+handle_info(_, State) ->
+ {noreply, State}.
+
+-spec terminate(term(), term()) -> 'ok'.
+terminate(_Reason, _State) ->
+ ok.
+
+-spec code_change(term(), State, term()) -> {'ok', State}.
+code_change(_OldVsn, State, _Extra) ->
+ {ok, State}.
+
+%%-----------------------------------------------------------------
+%% Internal functions
+%%-----------------------------------------------------------------
+
+do_start(Resource, Cnt, Pid) ->
+ case maps:get(Pid, Cnt, undefined) of
+ undefined ->
+ Ref = erlang:monitor(process, Pid),
+ case any(Cnt) of
+ true ->
+ {true, Cnt#{Pid=>{1, Ref}}};
+ false ->
+ resource(Resource, true),
+ {false, Cnt#{Pid=>{1, Ref}}}
+ end;
+ {N, Ref} ->
+ {true, Cnt#{Pid=>{N+1, Ref}}}
+ end.
+
+do_stop(Resource, Cnt0, Pid) ->
+ case maps:get(Pid, Cnt0, undefined) of
+ undefined ->
+ {any(Cnt0), Cnt0};
+ {1, Ref} ->
+ erlang:demonitor(Ref, [flush]),
+ Cnt = maps:remove(Pid, Cnt0),
+ case any(Cnt) of
+ true ->
+ {true, Cnt};
+ false ->
+ resource(Resource, false),
+ {true, Cnt}
+ end;
+ {N, Ref} ->
+ {true, Cnt0#{Pid=>{N-1, Ref}}}
+ end.
+
+cleanup(Resource, Cnt0, Pid) ->
+ case maps:is_key(Pid, Cnt0) of
+ true ->
+ Cnt = maps:remove(Pid, Cnt0),
+ case any(Cnt) of
+ true ->
+ Cnt;
+ false ->
+ resource(Resource, false),
+ Cnt
+ end;
+ false ->
+ Cnt0
+ end.
+
+any(Cnt) -> maps:size(Cnt) > 0.
+
+resource(scheduler_wall_time, Enable) ->
+ _ = erlang:system_flag(scheduler_wall_time, Enable).