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-module(channel_server).
-export([start/0]).
-export([alloc/0, free/1, stop/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-behaviour(gen_server).
-record(channel,{allocated, free}).
start() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
alloc() -> gen_server:call(?MODULE, {alloc}). %% 获取一个空闲频道
free(Ch)-> gen_server:call(?MODULE, {free, Ch}). %% 释放一个已用频道
stop() -> gen_server:call(?MODULE, stop).
init([]) -> %% 初始化allocated:已用频道；free:空闲频道
{ok, #channel{allocated = [], free = lists:seq(1,50)}}.
handle_call({alloc}, _From, Start) ->
%% io:format("alloc:==="),
{Allocated, [H|T]} = {Start#channel.allocated, Start#channel.free},
Reply = [H|Allocated],
NewStart = Start#channel{allocated=Reply, free=T},
{reply, Reply, NewStart};
handle_call({free, Ch}, _From, Start) ->
{Alloc, Free} = {Start#channel.allocated, Start#channel.free},
{_, Reply} = case lists:member(Ch, Alloc) of
true ->
A = lists:delete(Ch, Alloc),
B = [Ch|Free],
NewStart = Start#channel{allocated=A, free=B},
{A, B};
false ->
NewStart = Start#channel{allocated=Alloc, free=Free},
{Alloc, Free}
end,
{reply, Reply, NewStart};
handle_call(stop, _From, Start) ->
{stop, normal, stoped, Start}.
handle_cast(_Msg, Start) ->
{noreply, Start}.
handle_info(_Info, Start) ->
{noreply, Start}.
terminate(_Reason, _Start) ->
ok.
code_change(_OldVsn, Start, _Extra) ->
{ok, Start}.
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