1 files changed, 45 insertions, 0 deletions
diff --git a/deps/rabbit/src/rabbit_mirror_queue_mode_exactly.erl b/deps/rabbit/src/rabbit_mirror_queue_mode_exactly.erl
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+++ b/deps/rabbit/src/rabbit_mirror_queue_mode_exactly.erl
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+%% This Source Code Form is subject to the terms of the Mozilla Public
+%% License, v. 2.0. If a copy of the MPL was not distributed with this
+%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
+%%
+%% Copyright (c) 2010-2020 VMware, Inc. or its affiliates.  All rights reserved.
+%%
+
+-module(rabbit_mirror_queue_mode_exactly).
+
+-include("rabbit.hrl").
+
+-behaviour(rabbit_mirror_queue_mode).
+
+-export([description/0, suggested_queue_nodes/5, validate_policy/1]).
+
+-rabbit_boot_step({?MODULE,
+                   [{description, "mirror mode exactly"},
+                    {mfa,         {rabbit_registry, register,
+                                   [ha_mode, <<"exactly">>, ?MODULE]}},
+                    {requires,    rabbit_registry},
+                    {enables,     kernel_ready}]}).
+
+description() ->
+    [{description, <<"Mirror queue to a specified number of nodes">>}].
+
+%% When we need to add nodes, we randomise our candidate list as a
+%% crude form of load-balancing. TODO it would also be nice to
+%% randomise the list of ones to remove when we have too many - we
+%% would have to take account of synchronisation though.
+suggested_queue_nodes(Count, MNode, SNodes, _SSNodes, Poss) ->
+    SCount = Count - 1,
+    {MNode, case SCount > length(SNodes) of
+                true  -> Cand = shuffle((Poss -- [MNode]) -- SNodes),
+                         SNodes ++ lists:sublist(Cand, SCount - length(SNodes));
+                false -> lists:sublist(SNodes, SCount)
+            end}.
+
+shuffle(L) ->
+    {_, L1} = lists:unzip(lists:keysort(1, [{rand:uniform(), N} || N <- L])),
+    L1.
+
+validate_policy(N) when is_integer(N) andalso N > 0 ->
+    ok;
+validate_policy(Params) ->
+    {error, "ha-mode=\"exactly\" takes an integer, ~p given", [Params]}.