Add 'src/ioq/' from commit 'e641a740978447f0b29785580e46d2e30e822001'

git-subtree-dir: src/ioq
git-subtree-mainline: c8a5757c33c8f782d935fce2f804cb745bf77b4a
git-subtree-split: e641a740978447f0b29785580e46d2e30e822001

5 files changed, 257 insertions, 0 deletions

diff --git a/src/ioq/.gitignore b/src/ioq/.gitignore
new file mode 100644
index 000000000..21cf3d388
--- /dev/null
+++ b/src/ioq/.gitignore
@@ -0,0 +1,2 @@
+.rebar
+ebin/
diff --git a/src/ioq/src/ioq.app.src b/src/ioq/src/ioq.app.src
new file mode 100644
index 000000000..65ea50d6d
--- /dev/null
+++ b/src/ioq/src/ioq.app.src
@@ -0,0 +1,21 @@
+% 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.
+
+{application,ioq, [
+    {description, "I/O prioritizing engine"},
+    {vsn, git},
+    {registered,[]},
+    {applications,[kernel,stdlib,config]},
+    {mod,{ioq_app,[]}},
+    {env, []},
+    {modules,[ioq,ioq_app,ioq_sup]}
+]}.
diff --git a/src/ioq/src/ioq.erl b/src/ioq/src/ioq.erl
new file mode 100644
index 000000000..81d94a36f
--- /dev/null
+++ b/src/ioq/src/ioq.erl
@@ -0,0 +1,189 @@
+% 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.
+
+-module(ioq).
+-behaviour(gen_server).
+-behaviour(config_listener).
+
+-export([start_link/0, call/3]).
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2, code_change/3, terminate/2]).
+
+% config_listener api
+-export([handle_config_change/5, handle_config_terminate/3]).
+
+-define(RELISTEN_DELAY, 5000).
+
+-record(state, {
+    concurrency,
+    ratio,
+    interactive=queue:new(),
+    background=queue:new(),
+    running=[]
+}).
+
+-record(request, {
+    fd,
+    msg,
+    priority,
+    from,
+    ref
+}).
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+call(Fd, Msg, Metadata) ->
+    Priority = io_class(Msg, Metadata),
+    case bypass(Priority) of
+        true ->
+            gen_server:call(Fd, Msg);
+        false ->
+            queued_call(Fd, Msg, Priority)
+    end.
+
+bypass(Priority) ->
+    config:get("ioq.bypass", atom_to_list(Priority)) =:= "true".
+
+io_class({prompt, _}, _) ->
+    os_process;
+io_class({data, _}, _) ->
+    os_process;
+io_class(_, {interactive, _}) ->
+    read;
+io_class(_, {db_update, _}) ->
+    write;
+io_class(_, {view_update, _, _}) ->
+    view_update;
+io_class(_, {internal_repl, _}) ->
+    shard_sync;
+io_class(_, {db_compact, _}) ->
+    compaction;
+io_class(_, {view_compact, _, _}) ->
+    compaction;
+io_class(_, _) ->
+    other.
+
+queued_call(Fd, Msg, Priority) ->
+    Request = #request{fd=Fd, msg=Msg, priority=Priority, from=self()},
+    try
+        gen_server:call(?MODULE, Request, infinity)
+    catch
+        exit:{noproc,_} ->
+            gen_server:call(Fd, Msg, infinity)
+    end.
+
+init(_) ->
+    ok = config:listen_for_changes(?MODULE, nil),
+    State = #state{},
+    {ok, read_config(State)}.
+
+read_config(State) ->
+    Ratio = list_to_float(config:get("ioq", "ratio", "0.01")),
+    Concurrency = list_to_integer(config:get("ioq", "concurrency", "10")),
+    State#state{concurrency=Concurrency, ratio=Ratio}.
+
+handle_call(#request{}=Request, From, State) ->
+    {noreply, enqueue_request(Request#request{from=From}, State), 0}.
+
+handle_cast(change, State) ->
+    {noreply, read_config(State)};
+handle_cast(_Msg, State) ->
+    {noreply, State}.
+
+handle_info({Ref, Reply}, State) ->
+    case lists:keytake(Ref, #request.ref, State#state.running) of
+        {value, Request, Remaining} ->
+            erlang:demonitor(Ref, [flush]),
+            gen_server:reply(Request#request.from, Reply),
+            {noreply, State#state{running=Remaining}, 0};
+        false ->
+            {noreply, State, 0}
+    end;
+handle_info({'DOWN', Ref, _, _, Reason}, State) ->
+    case lists:keytake(Ref, #request.ref, State#state.running) of
+        {value, Request, Remaining} ->
+            gen_server:reply(Request#request.from, {'EXIT', Reason}),
+            {noreply, State#state{running=Remaining}, 0};
+        false ->
+            {noreply, State, 0}
+    end;
+handle_info(restart_config_listener, State) ->
+    ok = config:listen_for_changes(?MODULE, nil),
+    {noreply, State};
+handle_info(timeout, State) ->
+    {noreply, maybe_submit_request(State)}.
+
+handle_config_change("ioq", _, _, _, _) ->
+    {ok, gen_server:cast(?MODULE, change)};
+handle_config_change(_, _, _, _, _) ->
+    {ok, nil}.
+
+handle_config_terminate(_Server, stop, _State) ->
+    ok;
+handle_config_terminate(_Server, _Reason, _State) ->
+    erlang:send_after(?RELISTEN_DELAY, whereis(?MODULE), restart_config_listener).
+
+code_change(_Vsn, State, _Extra) ->
+    {ok, State}.
+
+terminate(_Reason, _State) ->
+    ok.
+
+enqueue_request(#request{priority=compaction}=Request, #state{}=State) ->
+    State#state{background=queue:in(Request, State#state.background)};
+enqueue_request(#request{priority=shard_sync}=Request, #state{}=State) ->
+    State#state{background=queue:in(Request, State#state.background)};
+enqueue_request(#request{}=Request, #state{}=State) ->
+    State#state{interactive=queue:in(Request, State#state.interactive)}.
+
+maybe_submit_request(#state{concurrency=Concurrency, running=Running}=State)
+  when length(Running) < Concurrency ->
+    case make_next_request(State) of
+        State ->
+            State;
+        NewState when length(Running) >= Concurrency - 1 ->
+            NewState;
+        NewState ->
+            maybe_submit_request(NewState)
+    end;
+maybe_submit_request(State) ->
+    State.
+
+make_next_request(#state{}=State) ->
+    case {queue:is_empty(State#state.background), queue:is_empty(State#state.interactive)} of
+        {true, true} ->
+            State;
+        {true, false} ->
+            choose_next_request(#state.interactive, State);
+        {false, true} ->
+            choose_next_request(#state.background, State);
+        {false, false} ->
+            case couch_rand:uniform() < State#state.ratio of
+                true ->
+                    choose_next_request(#state.background, State);
+                false ->
+                    choose_next_request(#state.interactive, State)
+            end
+    end.
+
+choose_next_request(Index, State) ->
+    case queue:out(element(Index, State)) of
+        {empty, _} ->
+            State;
+        {{value, Request}, Q} ->
+            submit_request(Request, setelement(Index, State, Q))
+    end.
+
+submit_request(#request{}=Request, #state{}=State) ->
+    Ref = erlang:monitor(process, Request#request.fd),
+    Request#request.fd ! {'$gen_call', {self(), Ref}, Request#request.msg},
+    State#state{running = [Request#request{ref=Ref} | State#state.running]}.
diff --git a/src/ioq/src/ioq_app.erl b/src/ioq/src/ioq_app.erl
new file mode 100644
index 000000000..2e6d75acb
--- /dev/null
+++ b/src/ioq/src/ioq_app.erl
@@ -0,0 +1,21 @@
+% 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.
+
+-module(ioq_app).
+-behaviour(application).
+-export([start/2, stop/1]).
+
+start(_StartType, _StartArgs) ->
+    ioq_sup:start_link().
+
+stop(_State) ->
+    ok.
diff --git a/src/ioq/src/ioq_sup.erl b/src/ioq/src/ioq_sup.erl
new file mode 100644
index 000000000..c4d04a9e4
--- /dev/null
+++ b/src/ioq/src/ioq_sup.erl
@@ -0,0 +1,24 @@
+% 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.
+
+-module(ioq_sup).
+-behaviour(supervisor).
+-export([start_link/0, init/1]).
+
+%% Helper macro for declaring children of supervisor
+-define(CHILD(I, Type), {I, {I, start_link, []}, permanent, 5000, Type, [I]}).
+
+start_link() ->
+    supervisor:start_link({local, ?MODULE}, ?MODULE, []).
+
+init([]) ->
+    {ok, { {one_for_one, 5, 10}, [?CHILD(ioq, worker)]}}.