Nope, no locks needed in Node. This is one of the little joys of javascript: no threading at all. None. With Web Workers you can have processes, but there is

Nope, no locks needed in Node. This is one of the little joys of javascript: no threading at all. None. With Web Workers you can have processes, but there isn't shared state; everything is done through message passing. All parallelism is cooperative in javascript, meaning that you don't have to worry about control flow switching out from under you at arbitrary points, just when you explicitly yield it by returning from an event handler or from the top level of your program. Finally, to answer the grandparent question, the easiest answer is a promise group. A promise group is basically a promise that emits a success event once all of its child promises have emitted success events. There are a few implementations floating around, though it's just a handful of lines of code to write and makes for a good exercise. So assuming that A and B are rewritten to return promises (or wrapped, I believe that isaacs has a library which will wrap functions which take a callback to return a promise instead), you can do the following: var promise_a = do_A(); promise_a.onSuccess(do_C); var promise_b = do_B(); promise_b.onSuccess(do_D); var promise_group = new PromiseGroup([promise_a, promise_b]); promise_group.onSuccess(do_E);