Simple, global cache optimised for concurrent accesses.
remove worker, add erase
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README.md
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README.md
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Booklet is a simple, global cache optimised for concurrent accesses.
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Booklets are designed for caching values that persist throughout your program's
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lifetime. Booklets can never be deleted, but offer thread-safe, atomic updates
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and fast concurrent reads.
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lifetime. Booklets are never automatically deleted or garbage collected. Call `erase`
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to reset a booklets' value to its default and remove internal references.
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They offer thread-safe, atomic updates and fast concurrent reads.
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Booklet is implemented using atomic compare-and-swap operations on top of a
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managed ETS table on Erlang, or a simple mutable reference on Javascript.
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src/booklet.gleam
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src/booklet.gleam
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/// A Booklet is an opaque, typed reference to a concurrent, atomic, global cache.
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///
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/// Booklets are designed for caching values that persist throughout your program's
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/// lifetime. Booklets can never be deleted, but offer thread-safe, atomic updates
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/// and fast concurrent reads.
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/// lifetime. Booklets are never automatically deleted or garbage collected. Call `erase`
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/// to reset a booklets' value to its default and remove internal references.
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///
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/// They offer thread-safe, atomic updates and fast concurrent reads.
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///
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/// Booklet is implemented using atomic compare-and-swap operations on top of a
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/// managed ETS table on Erlang, or a simple mutable reference on Javascript.
···
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) -> value
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/// Atomically replace the value stored in the booklet.
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pub fn set(in booklet: Booklet(value), to new_value: value) -> Nil {
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update(booklet, fn(_) { new_value })
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Nil
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}
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@external(erlang, "booklet_ffi", "set")
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@external(javascript, "./booklet_ffi.mjs", "set")
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pub fn set(in booklet: Booklet(value), to new_value: value) -> Nil
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/// Erase the value stored in a booklet, resetting it to it's default
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/// value provided to `new`.
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///
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/// On Erlang, this will remove the ETS Table entry.
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@external(erlang, "booklet_ffi", "erase")
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@external(javascript, "./booklet_ffi.mjs", "erase")
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pub fn erase(booklet: Booklet(value)) -> Nil
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src/booklet_ffi.erl
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src/booklet_ffi.erl
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-module(booklet_ffi).
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-behaviour(application).
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-export([start/2, stop/1]).
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-behaviour(supervisor).
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-export([init/1, start_worker/0]).
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-export([make/1, get/1, update/2]).
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-export([start/2, stop/1]).
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-export([make/1, get/1, set/2, update/2, erase/1]).
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% TODO: Query the worker again for the table if the table ref is invalid
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% TODO: store default_value inside the tuple so we can always recover
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-compile([no_auto_import]).
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% -- Public API ----------------------------------------------------------------
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make(DefaultValue) ->
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Table = get_table(),
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Key = make_ref(),
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true = ets:insert_new(Table, {Key, 0, DefaultValue}),
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{Table, Key}.
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{erlang:make_ref(), DefaultValue}.
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get({Table, Key}) ->
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ets:lookup_element(Table, Key, 3).
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get({Key, DefaultValue}) ->
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Table = persistent_term:get(?MODULE),
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try
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ets:lookup_element(Table, Key, 3)
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catch
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error:badarg ->
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DefaultValue
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end.
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set({Key, _}, Value) ->
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Table = persistent_term:get(?MODULE),
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true = ets:insert(Table, {Key, 0, Value}),
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nil.
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update({Table, Key}, Updater) ->
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[{Key, Rev, Value}] = ets:lookup(Table, Key),
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NewValue = Updater(Value),
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Pattern = {Key, Rev, '_'},
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Replacement = {const, {Key, Rev + 1, NewValue}},
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case ets:select_replace(Table, [{Pattern, [], [Replacement]}]) of
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0 -> update({Table, Key}, Updater);
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_ -> NewValue
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update({Key, DefaultValue} = Booklet, Updater) ->
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Table = persistent_term:get(?MODULE),
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case ets:lookup(Table, Key) of
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[{_, Rev, Value}] ->
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NewValue = Updater(Value),
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Replacement = {const, {Key, Rev + 1, NewValue}},
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case ets:select_replace(Table, [{{Key, Rev, '_'}, [], [Replacement]}]) of
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0 ->
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update(Booklet, Updater);
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_ ->
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NewValue
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end;
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[] ->
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NewValue = Updater(DefaultValue),
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case ets:insert_new(Table, {Key, 0, NewValue}) of
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true ->
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NewValue;
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false ->
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update(Booklet, Updater)
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end
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end.
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erase({Key, _}) ->
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Table = persistent_term:get(?MODULE),
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ets:delete(Table, Key),
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nil.
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% -- APPLICATION ---------------------------------------------------------------
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start(_StartType, _StartArgs) ->
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supervisor:start_link(?MODULE, supervisor).
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Table =
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ets:new(booklet,
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[set, public, {keypos, 1}, {write_concurrency, auto}, {read_concurrency, true}]),
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ok = persistent_term:put(?MODULE, Table),
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{ok, erlang:self()}.
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stop(_State) ->
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persistent_term:erase(?MODULE),
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ok.
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% -- SUPERVISOR ----------------------------------------------------------------
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init(supervisor) ->
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SupFlags = #{
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strategy => one_for_one,
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intensity => 6,
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period => 3600
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},
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ChildSpec = #{
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id => booklet,
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start => {?MODULE, start_worker, []},
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shutdown => brutal_kill
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},
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{ok, {SupFlags, [ChildSpec]}}.
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% -- CHILD ---------------------------------------------------------------------
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start_worker() ->
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Pid = spawn_link(fun worker/0),
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true = register(booklet, Pid),
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{ok, Pid}.
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worker() ->
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Table = ets:new(booklet, [set, public, {keypos, 1}, {write_concurrency, auto}, {read_concurrency, true}]),
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worker_loop(Table).
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worker_loop(Table) ->
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receive
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{get, From, Ref} -> From ! {Ref, Table}, worker_loop(Table);
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_ -> worker_loop(Table)
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end.
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get_table() ->
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Ref = make_ref(),
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booklet ! {get, self(), Ref},
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receive {Ref, Table} -> Table end.
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src/booklet_ffi.mjs
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src/booklet_ffi.mjs
···
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export function make(default_value) {
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return { value: default_value }
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return { value: default_value, default_value: default_value };
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}
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export function get(key) {
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return key.value
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return key.value;
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}
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export function set(key, value) {
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key.value = value;
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}
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export function update(key, updater) {
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const new_value = updater(key.value);
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key.value = new_value;
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return new_value;
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const new_value = updater(key.value);
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key.value = new_value;
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return new_value;
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}
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export function erase(key) {
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key.value = key.default_value;
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}