用 Erlang 的 gb_trees 实现了一个 memcached
最近蛋疼在用 Erlang 写 web 程序，这货是存 session 用的
定时器部分是拍脑袋拍的，不知道正规的实现应该是什么样子，想到这样，就这么写了..
-module(cache).
-behaviour(gen_server).
-export([start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
-export([set/2, set/3, get/1, del/1]).
start_link() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
set(K, V, T) ->
gen_server:call(?SERVER, {set, K, V, T}).
set(K, V) ->
gen_server:call(?SERVER, {set, K, V}).
get(K) ->
gen_server:call(?SERVER, {get, K}).
del(K) ->
gen_server:call(?SERVER, {del, K}).
init([]) ->
{ok, gb_trees:empty()}.
handle_call({set, K, V, T}, _From, Tree) ->
case gb_trees:lookup(K, Tree) of
none ->
none;
{value, {V, forever}} ->
none;
{value, {V, OldTRef}} ->
timer:cancel(OldTRef)
end,
{ok, TRef} = timer:apply_after(T * 1000, ?MODULE, del, [K]),
Tree2 = gb_trees:enter(K, {V, TRef}, Tree),
{reply, {ok, K, V}, Tree2};
handle_call({set, K, V}, _From, Tree) ->
case gb_trees:lookup(K, Tree) of
none ->
none;
{value, {V, forever}} ->
none;
{value, {V, OldTRef}} ->
timer:cancel(OldTRef)
end,
Tree2 = gb_trees:enter(K, {V, forever}, Tree),
{reply, {ok, K, V}, Tree2};
handle_call({get, K}, _From, Tree) ->
Reply = case gb_trees:lookup(K, Tree) of
none ->
none;
{value, {Value, _}} ->
{ok, Value}
end,
{reply, Reply, Tree};
handle_call({del, K}, _From, Tree) ->
Tree2 = gb_trees:delete_any(K, Tree),
{reply, {ok, K}, Tree2}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
