rabbit_writer.erl

%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (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.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developer of the Original Code is VMware, Inc.
%% Copyright (c) 2007-2012 VMware, Inc.  All rights reserved.
%%

-module(rabbit_writer).
-include("rabbit.hrl").
-include("rabbit_framing.hrl").

-export([start/5, start_link/5, start/6, start_link/6]).
-export([send_command/2, send_command/3,
         send_command_sync/2, send_command_sync/3,
         send_command_and_notify/4, send_command_and_notify/5]).
-export([internal_send_command/4, internal_send_command/6]).

%% internal
-export([mainloop/1, mainloop1/1]).

-record(wstate, {sock, channel, frame_max, protocol, reader,
                 stats_timer, pending}).

-define(HIBERNATE_AFTER, 5000).

%%---------------------------------------------------------------------------

-ifdef(use_specs).

-spec(start/5 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         non_neg_integer(), rabbit_types:protocol(), pid())
        -> rabbit_types:ok(pid())).
-spec(start_link/5 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         non_neg_integer(), rabbit_types:protocol(), pid())
        -> rabbit_types:ok(pid())).
-spec(start/6 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         non_neg_integer(), rabbit_types:protocol(), pid(), boolean())
        -> rabbit_types:ok(pid())).
-spec(start_link/6 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         non_neg_integer(), rabbit_types:protocol(), pid(), boolean())
        -> rabbit_types:ok(pid())).
-spec(send_command/2 ::
        (pid(), rabbit_framing:amqp_method_record()) -> 'ok').
-spec(send_command/3 ::
        (pid(), rabbit_framing:amqp_method_record(), rabbit_types:content())
        -> 'ok').
-spec(send_command_sync/2 ::
        (pid(), rabbit_framing:amqp_method_record()) -> 'ok').
-spec(send_command_sync/3 ::
        (pid(), rabbit_framing:amqp_method_record(), rabbit_types:content())
        -> 'ok').
-spec(send_command_and_notify/4 ::
        (pid(), pid(), pid(), rabbit_framing:amqp_method_record())
        -> 'ok').
-spec(send_command_and_notify/5 ::
        (pid(), pid(), pid(), rabbit_framing:amqp_method_record(),
         rabbit_types:content())
        -> 'ok').
-spec(internal_send_command/4 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         rabbit_framing:amqp_method_record(), rabbit_types:protocol())
        -> 'ok').
-spec(internal_send_command/6 ::
        (rabbit_net:socket(), rabbit_channel:channel_number(),
         rabbit_framing:amqp_method_record(), rabbit_types:content(),
         non_neg_integer(), rabbit_types:protocol())
        -> 'ok').

-endif.

%%---------------------------------------------------------------------------

start(Sock, Channel, FrameMax, Protocol, ReaderPid) ->
    start(Sock, Channel, FrameMax, Protocol, ReaderPid, false).

start_link(Sock, Channel, FrameMax, Protocol, ReaderPid) ->
    start_link(Sock, Channel, FrameMax, Protocol, ReaderPid, false).

start(Sock, Channel, FrameMax, Protocol, ReaderPid, ReaderWantsStats) ->
    State = initial_state(Sock, Channel, FrameMax, Protocol, ReaderPid,
                          ReaderWantsStats),
    {ok, proc_lib:spawn(?MODULE, mainloop, [State])}.

start_link(Sock, Channel, FrameMax, Protocol, ReaderPid, ReaderWantsStats) ->
    State = initial_state(Sock, Channel, FrameMax, Protocol, ReaderPid,
                          ReaderWantsStats),
    {ok, proc_lib:spawn_link(?MODULE, mainloop, [State])}.

initial_state(Sock, Channel, FrameMax, Protocol, ReaderPid, ReaderWantsStats) ->
    (case ReaderWantsStats of
         true  -> fun rabbit_event:init_stats_timer/2;
         false -> fun rabbit_event:init_disabled_stats_timer/2
     end)(#wstate{sock      = Sock,
                  channel   = Channel,
                  frame_max = FrameMax,
                  protocol  = Protocol,
                  reader    = ReaderPid,
                  pending   = []},
          #wstate.stats_timer).

mainloop(State) ->
    try
        mainloop1(State)
    catch
        exit:Error -> #wstate{reader = ReaderPid, channel = Channel} = State,
                      ReaderPid ! {channel_exit, Channel, Error}
    end,
    done.

mainloop1(State = #wstate{pending = []}) ->
    receive
        Message -> ?MODULE:mainloop1(handle_message(Message, State))
    after ?HIBERNATE_AFTER ->
            erlang:hibernate(?MODULE, mainloop, [State])
    end;
mainloop1(State) ->
    receive
        Message -> ?MODULE:mainloop1(handle_message(Message, State))
    after 0 ->
            ?MODULE:mainloop1(flush(State))
    end.

handle_message({send_command, MethodRecord}, State) ->
    internal_send_command_async(MethodRecord, State);
handle_message({send_command, MethodRecord, Content}, State) ->
    internal_send_command_async(MethodRecord, Content, State);
handle_message({'$gen_call', From, {send_command_sync, MethodRecord}}, State) ->
    State1 = flush(internal_send_command_async(MethodRecord, State)),
    gen_server:reply(From, ok),
    State1;
handle_message({'$gen_call', From, {send_command_sync, MethodRecord, Content}},
               State) ->
    State1 = flush(internal_send_command_async(MethodRecord, Content, State)),
    gen_server:reply(From, ok),
    State1;
handle_message({send_command_and_notify, QPid, ChPid, MethodRecord}, State) ->
    State1 = internal_send_command_async(MethodRecord, State),
    rabbit_amqqueue:notify_sent(QPid, ChPid),
    State1;
handle_message({send_command_and_notify, QPid, ChPid, MethodRecord, Content},
               State) ->
    State1 = internal_send_command_async(MethodRecord, Content, State),
    rabbit_amqqueue:notify_sent(QPid, ChPid),
    State1;
handle_message({'DOWN', _MRef, process, QPid, _Reason}, State) ->
    rabbit_amqqueue:notify_sent_queue_down(QPid),
    State;
handle_message({inet_reply, _, ok}, State) ->
    rabbit_event:ensure_stats_timer(State, #wstate.stats_timer, emit_stats);
handle_message({inet_reply, _, Status}, _State) ->
    exit({writer, send_failed, Status});
handle_message(emit_stats, State = #wstate{reader = ReaderPid}) ->
    ReaderPid ! ensure_stats,
    rabbit_event:reset_stats_timer(State, #wstate.stats_timer);
handle_message(Message, _State) ->
    exit({writer, message_not_understood, Message}).

%%---------------------------------------------------------------------------

send_command(W, MethodRecord) ->
    W ! {send_command, MethodRecord},
    ok.

send_command(W, MethodRecord, Content) ->
    W ! {send_command, MethodRecord, Content},
    ok.

send_command_sync(W, MethodRecord) ->
    call(W, {send_command_sync, MethodRecord}).

send_command_sync(W, MethodRecord, Content) ->
    call(W, {send_command_sync, MethodRecord, Content}).

send_command_and_notify(W, Q, ChPid, MethodRecord) ->
    W ! {send_command_and_notify, Q, ChPid, MethodRecord},
    ok.

send_command_and_notify(W, Q, ChPid, MethodRecord, Content) ->
    W ! {send_command_and_notify, Q, ChPid, MethodRecord, Content},
    ok.

%%---------------------------------------------------------------------------

call(Pid, Msg) ->
    {ok, Res} = gen:call(Pid, '$gen_call', Msg, infinity),
    Res.

%%---------------------------------------------------------------------------

assemble_frame(Channel, MethodRecord, Protocol) ->
    rabbit_binary_generator:build_simple_method_frame(
      Channel, MethodRecord, Protocol).

assemble_frames(Channel, MethodRecord, Content, FrameMax, Protocol) ->
    MethodName = rabbit_misc:method_record_type(MethodRecord),
    true = Protocol:method_has_content(MethodName), % assertion
    MethodFrame = rabbit_binary_generator:build_simple_method_frame(
                    Channel, MethodRecord, Protocol),
    ContentFrames = rabbit_binary_generator:build_simple_content_frames(
                      Channel, Content, FrameMax, Protocol),
    [MethodFrame | ContentFrames].

tcp_send(Sock, Data) ->
    rabbit_misc:throw_on_error(inet_error,
                               fun () -> rabbit_net:send(Sock, Data) end).

internal_send_command(Sock, Channel, MethodRecord, Protocol) ->
    ok = tcp_send(Sock, assemble_frame(Channel, MethodRecord, Protocol)).

internal_send_command(Sock, Channel, MethodRecord, Content, FrameMax,
                      Protocol) ->
    ok = lists:foldl(fun (Frame,     ok) -> tcp_send(Sock, Frame);
                         (_Frame, Other) -> Other
                     end, ok, assemble_frames(Channel, MethodRecord,
                                              Content, FrameMax, Protocol)).

internal_send_command_async(MethodRecord,
                            State = #wstate{channel   = Channel,
                                            protocol  = Protocol,
                                            pending   = Pending}) ->
    Frame = assemble_frame(Channel, MethodRecord, Protocol),
    maybe_flush(State#wstate{pending = [Frame | Pending]}).

internal_send_command_async(MethodRecord, Content,
                            State = #wstate{channel   = Channel,
                                            frame_max = FrameMax,
                                            protocol  = Protocol,
                                            pending   = Pending}) ->
    Frames = assemble_frames(Channel, MethodRecord, Content, FrameMax,
                             Protocol),
    maybe_flush(State#wstate{pending = [Frames | Pending]}).

%% This magic number is the tcp-over-ethernet MSS (1460) minus the
%% minimum size of a AMQP basic.deliver method frame (24) plus basic
%% content header (22). The idea is that we want to flush just before
%% exceeding the MSS.
-define(FLUSH_THRESHOLD, 1414).

maybe_flush(State = #wstate{pending = Pending}) ->
    case iolist_size(Pending) >= ?FLUSH_THRESHOLD of
        true  -> flush(State);
        false -> State
    end.

flush(State = #wstate{pending = []}) ->
    State;
flush(State = #wstate{sock = Sock, pending = Pending}) ->
    ok = port_cmd(Sock, lists:reverse(Pending)),
    State#wstate{pending = []}.

%% gen_tcp:send/2 does a selective receive of {inet_reply, Sock,
%% Status} to obtain the result. That is bad when it is called from
%% the writer since it requires scanning of the writers possibly quite
%% large message queue.
%%
%% So instead we lift the code from prim_inet:send/2, which is what
%% gen_tcp:send/2 calls, do the first half here and then just process
%% the result code in handle_message/2 as and when it arrives.
%%
%% This means we may end up happily sending data down a closed/broken
%% socket, but that's ok since a) data in the buffers will be lost in
%% any case (so qualitatively we are no worse off than if we used
%% gen_tcp:send/2), and b) we do detect the changed socket status
%% eventually, i.e. when we get round to handling the result code.
%%
%% Also note that the port has bounded buffers and port_command blocks
%% when these are full. So the fact that we process the result
%% asynchronously does not impact flow control.
port_cmd(Sock, Data) ->
    true = try rabbit_net:port_command(Sock, Data)
           catch error:Error -> exit({writer, send_failed, Error})
           end,
    ok.