Using photon::semaphore on AWS EC2, `signal` latency is high.

Using photon::semaphore on AWS EC2, `signal` latency is high.

I have using `photon::semaphore` on AWS EC2. I found `signal` function may cost 300~600ms. I don't know what happens and why `signal` cost so long. I'm seeking assistance in understanding the cause and debugging strategies🙏.

Start by reproducing the reported 300–600 ms `photon::semaphore` `signal` latency on AWS EC2 and inspect the semaphore signaling path. Use the reproduction to identify the cause and document debugging findings or a clearly scoped fix; the issue does not name specific files or tests.

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