Messages getting lost in erlang

Question

I am having some issues with messages in erlang that get lost.

The code that I am using works 100% correct when I use it manually, only when my code is used in a 'load test' where I test the code in parallel with a lot of requests, some messages are never received at the receiver part. When logging all the steps and values of the parameters, I found out that the address where I send the message to, is the correct one. Also the message itself has no problems.

My question is the following: is there knowledge of this 'losing of messages' in erlang yet, could this be some bug in erlang itself?

I could post some code that I am using if needed, but I don't think it would add a lot of value to this question in particular.

UPDATE: the main parts of my application. This is quite a lot of code to illustrate my problem, but I can not reproduce my problem in a simplified version. The application is an allocation system, i.e. it will reserve collections of cells in a grid in parallel. The important parts are: the globalManager, an actor that will control the entire allocation system. The rowManager will manage one row of the entire grid and will lock that row when a reservation is made. When a region of cells has to be reserved, the function request_specific_cells is called. This function will send a reservation request to all rowmanagers of whom the row has to be modified. When the row manager has reserved the region in its row it will send a confirmation to the globalManager. When all rowmanagers have send the confirmation, a confirmation will be send to the process that initiated the request, when one of the managers failed, the globalmanager will send a failure.

    globalManager(Grid) ->
    receive
        {Pid, request_specific_cells, ReservationId, Coordinates, Ctr, XX} ->
            NewGrid = request_specific_cells(Grid, Pid, ReservationId, Coordinates, Ctr, XX);

        {Pid, confirm_region, ResId, Rid, Sid, Region, Section, Ctr, XX} ->
            NewGrid = confirm_region(Grid, Pid, ResId, Rid, Sid, Region, Section, Ctr, XX);

        {Pid, failed_region, Rid, Region, Ctr, XX} ->
            NewGrid = failed_region(Grid, Pid, Rid, Region, Ctr, XX);

        Else ->
            erlang:display({unexpectedMessage, actor, Else}),
            NewGrid = Grid
    end,
    globalManager(NewGrid).


request_specific_cells(Grid, Pid, ReservationId, Coordinates, Ctr, XX) ->
    {{Width, Height}, GridRows, MaxAllocationSize, FreeCells, {UnspecificRequests, NextId}, PendingRequests, BlockedRows} = Grid,
    {X, Y, W, H} = Coordinates,
    Rows         = lists:seq(Y,Y+H-1),
    % Is one of the blocks that have to be reserved currently blocked?
    BlockedRow   = lists:foldl(fun(B, Acc) -> Acc xor search_list(B,BlockedRows) end, false, Rows),
    Request      = lists:keyfind(ReservationId, 1, UnspecificRequests),
    {ReservationId, _} = Request,
    % Now we need the addresses of the sections in which the regions has to be reserved.
    SubSectionIds = [ SPid || {_,SPid} <- [ lists:keyfind(Row, 1, GridRows) || Row <- Rows]],
    % Storing request enables us to rollback if one of the registrations fails.
    NewPendingRequests = PendingRequests ++ [{length(PendingRequests), 0, lists:map(fun(S) -> {S,null} end, SubSectionIds)}],
    % Send a registration command with the needed section to each corresponding section manager.
    [SPid ! {self(), request, Pid, ReservationId, length(PendingRequests), Coordinates, Ctr, XX} || SPid<- SubSectionIds],
    NewBlockedRows = Rows ++ BlockedRows,
    {{Width, Height}, GridRows, MaxAllocationSize, FreeCells, {UnspecificRequests, NextId}, NewPendingRequests, NewBlockedRows}
    end.


confirm_region(Grid, Pid, URid, Rid, Sid, Region, Section, Cttr, XX) ->
    {Dimensions, GridRows, MaxAllocationSize, FreeCells, {UnspecificRequests, NextId}, PendingRequests, BlockedRows} = Grid,
    {_,RY,_,_} = Region,
    if
        % All blocks have confirmed the reservation so the entire request is successful
        (Ctr+1) == length(Spids) -> 
                NewUnspecificRequests = lists:keydelete(URid, 1, UnspecificRequests),
                NewPendingRequests = lists:keydelete(Rid, 1, PendingRequests),
                NewSpids = lists:keyreplace(Sid, 1, Spids, {Sid, Section}),
                [Spid ! {self(), confirm_region, Sec} || {Spid, Sec} <- NewSpids],
                Pid ! {self(), request_specific_cells, Rid, success};
        true -> 
                NewUnspecificRequests = UnspecificRequests,
                % Safe the region that has to be marked/rolled back in the row
                NewSpids = lists:keyreplace(Sid, 1, Spids, {Sid, Section}),
                % Increase counter of confirmations
                NewPendingRequests = lists:keyreplace(Rid, 1, PendingRequests, {Rid, Ctr+1, NewSpids})
    end,
    NewBlockedRows = delete_list(RY, BlockedRows)
    {Dimensions, GridRows, MaxAllocationSize, FreeCells, {NewUnspecificRequests, NextId}, NewPendingRequests, NewBlockedRows}.



rowManager(Row) ->
    receive
        {Mid, request, Pid, URid, Rid, Region, Ctr, XX} ->
            NewRow = request_region(Row, Mid, Pid, URid, Rid, Region, Ctr, XX);
        Else ->
            erlang:display({unexpectedMessage, rowManager, Else}),
            NewRow = Row
    end,

    rowManager(NewRow).

request_region(Row, Mid, Pid, URid, Rid, Coordinates, Ctr, XX) ->
    {RY, Content, Modified} = Row,
    {X,_,W,_}    = Coordinates,
    if
        Modified == false -> 
                Free = region_is_empty({X,1,W,1}, Content),
                if
                    Free -> NewModified = true,
                            NewContent = mark_region({X,1,W,1}, Content, reserved),
                            Mid ! {Pid, confirm_region, URid, Rid, self(), Coordinates, {X,1,W,1}, Ctr, XX};
                    true -> NewModified = false,
                            NewContent = Content,
                            Mid ! {Pid, failed_region, Rid, Coordinates, Ctr, XX}
                end;
        true -> NewModified = false,
                NewContent = Content,
                Mid ! {Pid, failed_region, Rid, Coordinates, Ctr, XX}
    end,
    {RY, NewContent, NewModified}.

This code will be used by the reserver:

request_specific_cells(FollowUpPid, ReservationId, {X, Y, Width, Height}, Ctr, XX) ->
   FollowUpPid ! {self(), request_specific_cells, ReservationId, {X, Y, Width, Height}, Ctr, XX},
   receive
      {FollowUpPid, request_specific_cells, ReservationId, SuccessOrFailure} ->
        SuccessOrFailure
end.

I think that this receiver dies before an answer was received because I know that

Pid ! {self(), request_specific_cells, Rid, success}

from the confirm/9 function is always executed with the correct values, but is not always received at the function.

Messages getting lost in erlang

Answers (1)

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