[DocDB] Thread pool worker could miss added task

[spolitov]

Jira Link: DB-17504

Description

When a thread pool worker becomes idle, it follows these steps:

1. Checks the task queue
2. Adds itself to the waiting workers list
3. Waits on a condition variable for new work

However, a race condition can occur if a task is added to the queue immediately after the worker checks it but before it begins waiting. This results in:

• The worker waiting on the condition variable
• While the task queue is non-empty (causing a potential deadlock)

Issue Type

kind/bug

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