share data between events

Question

share data between events

I tend to write a function like this:

library.getCookie(request.headers.cookie,function(cookies){
    db.query("SELECT name,lastupdate FROM session WHERE id=?",[cookies.SESSID],function(result){
        var action = require('./action');
        new action({
            data : result, 
            callback : function(){ // this callback's gonna run at the end of the request, after severals other db queries.
                require('fs').rename('/session/'+cookies.SESSID,'/session/'+require('crypto').randomBytes(20));
            }
        }).build();
    });   
});

I got a feeling that my cookies.SESSID is vunerable to race condition because it will be shared between severals IO events. If my concern is feasible, how can I fix my code?

node.js
race-condition

Answer 1

Declare the variables you want to pass to the more inner callback with var and you will stay safe. Otherwise you are just declaring them as implict global variables and each call of the function will overwrite the value you are expecting to get in the callback;

(the callback inside action could take the value of cookies not like the one you passed when you called the first time but a new value if the function is invoked before the first callback is solved)

I have just answered a similar question, with examples: Race condition and common mistakes