bthread signal & wait 问题咨询


在使用过程中，观察server侧的火焰图，此时brpc_worker thread的cpu基本打满。发现futex_wake、futex_wait占用的时间占比比较高，竞争锁成为了瓶颈。怀疑可能是由于调度不均衡，某些worker中的task较多，而一些worker的task较少，当这些task消费完之后每次都会调用wait，然后又快速被signal唤醒。同时也存在parking_lot中没有wait的线程但仍然在signal的场景。

这方面是否存在一些优化点，比如：
1. signal时判断是否存在wait状态的线程；
2. wait之前先尝试steal_task n 次，如果都失败再wait挂起线程；或者wait时设置timeout时间而不是每次都是永久wait，只能被signal主动唤醒。

Start by reading the bthread signal and wait paths and the parking_lot behavior described in the issue. Reproduce the reported futex_wake and futex_wait contention, then determine whether the proposed scheduling or wake-up changes are warranted; done should include an agreed optimization and evidence that contention improves.

Written by the indexing model from the issue text.