Asynchronous process handler in node

Question

Which process handles async or simultaneous work to happen in node js. Is there any specific api that takes care of all these events to happen in queue?

Answer 1

Is there any specific api that takes care of all these events to happen in queue?

No, not accessible from Javascript. The event queue is completely under the covers. You don't access it directly.

The implementation of asynchronous operations is all handled in native code. When an async operation completes, its native code calls an internal C++ API that inserts the completion event into the node.js event queue. If no Javascript is currently running in node.js at that moment, then inserting the item in the event queue will trigger it to get pulled out of the queue and the callback associated with it will be run. If Javascript is running at the moment, it will stay in the event queue until the current piece of running Javascript finishes at which point the interpreter will check the event queue, see there is an event in there and will pull that event out and run the callback associated with that event.

Which process handles async or simultaneous work to happen in node js.

It is not entirely clear what you mean by this. Each node.js function that is asynchronous has its own implementation. Networking uses OS-level event driven networking (not threads). Async file I/O uses a native thread pool. Timers use OS level timers. Some other asynchronous operation will have its own implementation and do it some other way as it completely depends upon what the async operation is for who it will accomplish its work.

The only three ways (I know of) for you to write your own asynchronous operation are:

1. Compose your own operation entirely using existing asynchronous operations such as request this data from another server, then write it to this file.

2. Use native code to write your own node.js add-on that can expose an asynchronous interface and use native code to implement that asynchronous interface in whatever manner is most appropriate for your operation.

3. Run some other process and communicate back the result from that other process. This can be some other program written in any language or it can be Javascript that you run in another node.js process.

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Now, there are a few ways you can influence the event queue timing of some things from Javascript. For example, setTimeout(fn, t), process.nextTick(fn) and setImmediate(fn) all have slightly different ways they insert your callback function into the event queue that determines what (that is already in the event queue) they run before or after. But, these by themselves just schedule a callback sometime in the future - they don't actually implement an asynchronous operation that accomplishes some tasks in a non-blocking way.

You may want to read some of these references:

The Node.js Event Loop, Timers, and process.nextTick()

setImmediate() vs nextTick() vs setTimeout(fn,0) – in depth explanation

Demystifying Asynchronous Programming Part 1: Node.js Event Loop

Answer 2

You might be thinking of child_process.spawn().

From the NodeJS documentation

The child_process.spawn(), child_process.fork(), child_process.exec(), and child_process.execFile() methods all follow the idiomatic asynchronous programming pattern typical of other Node.js APIs.

Each of the methods returns a ChildProcess instance. These objects implement the Node.js EventEmitter API, allowing the parent process to register listener functions that are called when certain events occur during the life cycle of the child process.

The child_process.exec() and child_process.execFile() methods additionally allow for an optional callback function to be specified that is invoked when the child process terminates.