Promise.resolve() does not work correctly inside an inotify callback

[redneb]

Promise.resolve() returns an already resolved promise and therefore Promise.resolve().then(...) should execute the promise callback immediately. But when I try that from within an inotify callback, the promise callback never gets called. Here's a minimal example:

const Inotify = require("inotify").Inotify;

new Inotify().addWatch({
	path: ".",
	watch_for: Inotify.IN_ALL_EVENTS,
	callback: ev => {
		console.log("this is an inotify callback");
		Promise.resolve().then(() => {
			console.log("done");
		});
	},
});

When I run this with node v8.4.0 and do a touch . in a different terminal, I do not see done in the output.

[c4milo]

@redneb I don't think we have added support for promises yet. Any help is appreciated.

[redneb]

This issue is not about promises per se, nor I'm asking you to add support for promises to node-inotify. I am just pointing out that while the following piece of code:

console.log("hello");
Promise.resolve().then(() => {
	console.log("done");
});

works as expected when executed by itself (i.e. it produces two lines of output, hello and done)), when executed from within an inotify callback, it does not work as expected. So the behavior changes.

[redneb]

Here's another complete example that has the same problem and does not use promises at all:

const Inotify = require("inotify").Inotify;

new Inotify().addWatch({
	path: ".",
	watch_for: Inotify.IN_ALL_EVENTS,
	callback: ev => {
		console.log("hello");
		process.nextTick(() => {
			console.log("done");
		});
	},
});

I expect that every time the above program prints hello, it would be (almost) immediately followed by another line of output, done. But it doesn't. It's as if the next tick never happens.

[c4milo]

@redneb thanks for the detailed issue report! I'm looking into it and I will keep you posted here.

[c4milo]

@redneb, alright, I think I know what I need to do to fix this. I will find some time tonight to do it.

We need to change

node-inotify/src/bindings.cc

Line 278 in 15001bb

callback->Call(handle, 1, argv);

to use https://github.com/nodejs/nan/blob/master/doc/callback.md#api_nan_callback

[c4milo]

@redneb thanks again, the fix landed on v1.4.2.