Can I drain the pending queue without running them?

Question

RepoPilot · Accepted Answer

Yes, you can drain the pending queue without running the tasks using the `clearQueue()` method. This discards all pending promises that are waiting to run.

According to [index.d.ts:L19-L27], `clearQueue()` will:

> 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.

Here's a practical example from the test file [test.js:L182-L190]:

```javascript
const limit = pLimit(1);

Array.from({length: 1}, () => limit(() => delay(1000)));
Array.from({length: 3}, () => limit(() => delay(1000)));

await Promise.resolve();
t.is(limit.pendingCount, 3);
limit.clearQueue();
t.is(limit.pendingCount, 0);
```

After calling `clearQueue()`, the `pendingCount` drops to 0, meaning all pending tasks have been discarded without execution.

**Important note:** By default, pending promises never settle when cleared. However, if you enable the `rejectOnClear` option when creating the limiter, pending promises will be rejected with an `AbortError` [index.d.ts:L104-L108], which is recommended if you're awaiting the promises with `Promise.all`.

FOLLOW_UPS:
- How does `rejectOnClear` change queue clearing behavior?
- What's the difference between `activeCount` and `pendingCount`?
- Can I modify the concurrency limit dynamically?