Can I drain the pending queue without running them?

Question

RepoPilot · Accepted Answer

Yes, you can drain the pending queue without running the tasks by calling `limit.clearQueue()`. This discards all pending promises that haven't started running yet.

From the README [readme.md:L96-L106]:
> Discard pending promises that are waiting to run.
>
> This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.
>
> Note: This does not cancel promises that are already running.

The implementation in [index.js:L86-L97] shows how it works:

```javascript
clearQueue: {
	value() {
		if (!rejectOnClear) {
			queue.clear();
			return;
		}

const abortError = AbortSignal.abort().reason;

while (queue.size > 0) {
			queue.dequeue().reject(abortError);
		}
	},
},
```

**Important note:** By default, pending promises are simply discarded and never settle. If you want pending promises to be explicitly rejected when cleared, you can enable the `rejectOnClear` option when creating the limiter [index.d.ts:L109-L115]:

```javascript
const limit = pLimit({concurrency: 1, rejectOnClear: true});
```

This is useful if you await the returned promises with `Promise.all`, so tasks don't remain unresolved after `clearQueue()` is called.

FOLLOW_UPS:
- What happens to currently running tasks after clearQueue()?
- How do I enable automatic rejection when clearing the queue?
- Can I drain the queue and check what was discarded?