inter-process lock via ngx.shared.DICT.add/delete

[Russell Sullivan]

I need a nginx-wide (i.e. multiple processes) lock.

My plan is to use a ngx.shared.DICT and methods: add (w/ sleep on failure) and delete around the non 'thread"-safe code

pseudocode would be:

local finished = false; 

while (not finished) do

  local success, err, forcible = ngx.shared.DICT.add("LOCK", 1);  

  if (not success and err == "exists") then

    ngx.sleep(0);    -- LOCK FAILED TRY AGAIN (NEXT NGINX EVENT LOOP)

  else

    finished = true; -- LOCK SUCCESS

  end

end

<<CODE>>

ngx.shared.DICT.delete("LOCK");

Will this work correctly? (conceptually: i.e. ignore that its pseudo-code and that I dont check all errors from the add() call)

Is it a hack? Are there some bad side effects (other than on lock fail the co-routine sleeping some)?

Is there a better way to do this

thanks :)

[tokers]

Hi!

I think the https://github.com/openresty/lua-resty-lock is the best choice which is light-weight. Actually it also based on the ngx.shared.DICT.

[Russell Sullivan]

@tokers THANKS ... I somehow missed finding lua-resty-lock :)

always better to use something established and tested than to build your own