Fix ServerTiming in Threads, use single subscriber #45964
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jhawthorn
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casperisfine
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| @mutex.synchronize do |
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I think we could use double checked locking to avoid synchronizing that mutex on every request.
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I'd prefer readability here, and I think it's a safe bet that anyone enabling this (presumably only in development) isn't too concerned with performance.
I could see revisiting this if we make this more production-appropriate (sampling a small set of useful topics), but that would likely look different from this.
casperisfine
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Sep 8, 2022
Previously ActionDispatch::ServerTiming would subscribe and unsubscribe on each request. This could cause issues with the internal stacks of ActiveSupport::Notifications, particlularly under the previous AS::N implementation which used thread-local stacks for every subscriber (the new implementation has mostly mitigated this). Additionally, the previous ServerTiming implementation did not report metrics correctly in a multi-threaded environment. This commit works around both of these issues by using a single global subscription, which collects events into a per-thread Array.
These are not intended for user consumption
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Fix ServerTiming in Threads, use single subscriber
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Previously ActionDispatch::ServerTiming would subscribe and unsubscribe on each request. This could cause issues with the internal stacks of ActiveSupport::Notifications, particlularly under the previous AS::N implementation which used thread-local stacks for every subscriber (the new implementation has mostly mitigated this).
Additionally, the previous ServerTiming implementation did not report metrics correctly in a multi-threaded environment.
This commit works around both of these issues by using a single global subscription, which collects events into a per-thread Array.
Thanks to lots of advice from @matthewd