/
kvs.erl
161 lines (149 loc) · 4.88 KB
/
kvs.erl
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-module(kvs).
-export([get/1, get/2, set/2, set/3, start/1, stop/0, store/1]).
-include("kvs.hrl").
%% @doc create N nodes in distributed key-value store
%% @spec start(integer()) -> started
start(N) ->
pg2:create(kvs),
lists:foreach(fun(_) ->
Store = #kvs_store{data=[],
pending_reads=[],
pending_writes=[]},
pg2:join(kvs, spawn(kvs, store, [Store]))
end, lists:seq(0, N)),
started.
%% @doc stop all pids in KVS process group
%% stop() -> stopped.
stop() ->
LocalFun = fun(X) -> erlang:node(X) == node() end,
LocalPids = lists:filter(LocalFun, pg2:get_members(kvs)),
lists:foreach(fun(Pid) ->
pg2:leave(kvs, Pid),
Pid ! stop
end, LocalPids),
stopped.
%% @doc retrieve value for key
%% @spec get(term()) -> value() | undefined
%% value = term()
get(Key) -> get(Key, ?TIMEOUT).
%% @doc retrieve value for key, with timeout
%% @spec get(term(), integer()) -> val() | timeout()
%% val = {ok, term()} | {ok, undefined}
%% timeout = {error, timeout}
get(Key, Timeout) ->
Pid = pg2:get_closest_pid(kvs),
Pid ! {self(), get, Key},
receive
{Pid, got, Value} ->
{ok, Value};
{error, Error} ->
{error, Error}
after
Timeout ->
{error, timeout}
end.
%% @doc update value for key
%% @spec set(term(), term()) -> {ok, updated} | {error, timeout}
set(Key, Val) -> set(Key, Val, ?TIMEOUT).
%% @doc update value for key, with timeout
%% @spec set(term(), term()) -> {ok, updated} | {error, timeout}
set(Key, Val, Timeout) ->
Pid = pg2:get_closest_pid(kvs),
Pid ! {self(), set, Key, Val},
receive
{Pid, received, {set, Key, Val}} ->
{ok, updated};
{error, Error} ->
{error, Error}
after
Timeout ->
{error, timeout}
end.
%% @doc implementation of distributed key-value store
%% @spec store(proplist()) -> term()
%% proplist = [{term(), term()}]
store(Store = #kvs_store{data=Data, pending_reads=Reads, pending_writes=Writes}) ->
receive
{Sender, get, Key} ->
% client interface for retrieving values
lists:foreach(fun(Pid) ->
Pid ! {self(), retrieve, Sender, Key}
end, pg2:get_members(kvs)),
% ?KVS_READS is required # of nodes to read from
% [] is used to collect read values
Reads2 = [{{Sender, Key}, {?KVS_READS, [], ts()}} | Reads],
store(Store#kvs_store{pending_reads=Reads2});
{Sender, retrieve, Client, Key} ->
Sender ! {self(), retrieved, Client, Key, proplists:get_value(Key, Data)},
store(Store);
{_Sender, retrieved, Client, Key, Value} ->
case proplists:get_value({Client, Key}, Reads) of
{0, Values, _Timestamp} ->
Freq = lists:foldr(fun(X, Acc) ->
case proplists:get_value(X, Acc) of
undefined -> [{X, 1} | Acc];
N -> [{X, N+1} | proplists:delete(X, Acc)]
end
end, [], Values),
[{Popular, _} | _ ] = lists:reverse(lists:keysort(2, Freq)),
Client ! {self(), got, Popular},
store(Store#kvs_store{
pending_reads=proplists:delete({Key, Value}, Reads)});
{Count, Values, Timestamp} ->
store(Store#kvs_store{
pending_reads=[{{Client, Key}, {Count-1, [Value | Values], Timestamp}} |
proplists:delete({Client, Key}, Reads)]})
end;
{Sender, set, Key, Value} ->
% client interface for updating values
lists:foreach(fun(Pid) ->
Pid ! {self(), update, Sender, Key, Value}
end, pg2:get_members(kvs)),
Writes2 = [{{Sender, Key}, {?KVS_WRITES, ts()}} | Writes],
store(Store#kvs_store{pending_writes=Writes2});
{Sender, update, Client, Key, Value} ->
% sent to all nodes by first receiving node
Sender ! {self(), updated, Client, Key, Value},
store(Store#kvs_store{data=[{Key, Value} |
proplists:delete(Key, Data)]});
{_Sender, updated, Client, Key, Value} ->
{Count, Timestamp} = proplists:get_value({Client, Key}, Writes),
case Count of
undefined ->
store(Store);
0 ->
Client ! {self(), received, {set, Key, Value}},
store(Store#kvs_store{
pending_writes=proplists:delete({Key, Value}, Writes)});
_ ->
store(Store#kvs_store{
pending_writes=[{{Client, Key}, {Count-1, Timestamp}} |
proplists:delete({Client, Key}, Writes)]})
end;
stop ->
ok
after
?KVS_POLL_PENDING ->
Writes2 = lists:filter(fun filter_writes/1, Writes),
Reads2 = lists:filter(fun filter_reads/1, Reads),
store(Store#kvs_store{pending_writes=Writes2, pending_reads=Reads2})
end.
filter_writes({{Client, _Key}, {_Count, Ts}}) ->
Now = ts(),
if Now > Ts + ?KVS_WRITE_TIMEOUT ->
Client ! {error, write_failed},
false;
true ->
true
end.
filter_reads({{Client, _Key}, {_Count, _Values, Ts}}) ->
Now = ts(),
if Now > Ts + ?KVS_READ_TIMEOUT ->
Client ! {error, read_failed},
false;
true ->
true
end.
ts() ->
{Mega, Sec, _} = erlang:now(),
(Mega * 1000000) + Sec.