pick: clear futures when all task finished

[foxspy]

issue: #385
related: #387

[mergify]

@foxspy 🔍 Important: PR Classification Needed!

For efficient project management and a seamless review process, it's essential to classify your PR correctly. Here's how:

1. If you're fixing a bug, label it as kind/bug.
2. For small tweaks (less than 20 lines without altering any functionality), please use kind/improvement.
3. Significant changes that don't modify existing functionalities should be tagged as kind/enhancement.
4. Adjusting APIs or changing functionality? Go with kind/feature.

For any PR outside the kind/improvement category, ensure you link to the associated issue using the format: “issue: #”.

Thanks for your efforts and contribution to the community!.

[foxspy]

/kind bug

[liliu-z]

/lgtm

[liliu-z]

/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: foxspy, liliu-z

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[yellow-shine]

/run-e2e

[mergify]

@foxspy e2e jenkins job failed, comment /run-e2e can trigger the job again.

[foxspy]

/run-e2e