Implement convinience `mem3:ping/2` function

Sometimes in operations it is helpful to re-establish connection between
erlang nodes. Usually it is achieved by calling `net_adm:ping/1`. However
the `ping` function provided by OTP uses `infinity` timeout. Which causes
indefinite hang in some cases. This PR adds convinience function to be
used instead of `net_adm:ping/1`.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/mem3/src/mem3.erl b/src/mem3/src/mem3.erl
index 7033faf4b..de633006a 100644
--- a/src/mem3/src/mem3.erl
+++ b/src/mem3/src/mem3.erl
@@ -21,6 +21,7 @@
 -export([live_shards/2]).
 -export([belongs/2, owner/3]).
 -export([get_placement/1]).
+-export([ping/1, ping/2]).
 
 %% For mem3 use only.
 -export([name/1, node/1, range/1, engine/1]).
@@ -28,6 +29,8 @@
 -include_lib("mem3/include/mem3.hrl").
 -include_lib("couch/include/couch_db.hrl").
 
+-define(PING_TIMEOUT_IN_MS, 60000).
+
 start() ->
     application:start(mem3).
 
@@ -331,6 +334,27 @@ engine(Opts) when is_list(Opts) ->
             []
     end.
 
+%% Check whether a node is up or down
+%%  side effect: set up a connection to Node if there not yet is one.
+
+-spec ping(Node :: atom()) -> pong | pang.
+
+ping(Node) ->
+    ping(Node, ?PING_TIMEOUT_IN_MS).
+
+-spec ping(Node :: atom(), Timeout :: pos_integer()) -> pong | pang.
+
+ping(Node, Timeout) when is_atom(Node) ->
+    %% The implementation of the function is copied from
+    %% lib/kernel/src/net_adm.erl with addition of a Timeout
+    case catch gen:call({net_kernel, Node},
+            '$gen_call', {is_auth, node()}, Timeout) of
+        {ok, yes} -> pong;
+        _ ->
+            erlang:disconnect_node(Node),
+            pang
+    end.
+
 -ifdef(TEST).
 
 -include_lib("eunit/include/eunit.hrl").