tree 08389eb643928a9092308c100dcb5e933bf85f5a
parent cd1fc871568e9947e84377f82c8d7a4882a07067
author Joe Tsai <joetsai@digital-static.net> 1675286582 -0800
committer Joseph Tsai <joetsai@digital-static.net> 1675462940 +0000

log: reduce lock contention

Logger.Log methods are called in a highly concurrent manner in many servers.
Acquiring a lock in each method call results in high lock contention,
especially since each lock covers a non-trivial amount of work
(e.g., formatting the header and outputting to the writer).

Changes made:
* Modify the Logger to use atomics so that the header formatting
  can be moved out of the critical lock section.
  Acquiring the flags does not occur in the same critical section
  as outputting to the underlying writer, so this introduces
  a very slight consistency instability where concurrently calling
  multiple Logger.Output along with Logger.SetFlags may cause
  the older flags to be used by some ongoing Logger.Output calls
  even after Logger.SetFlags has returned.
* Use a sync.Pool to buffer the intermediate buffer.
  This approach is identical to how fmt does it,
  with the same max cap mitigation for #23199.
* Only protect outputting to the underlying writer with a lock
  to ensure serialized ordering of output.

Performance:
	name           old time/op  new time/op  delta
	Concurrent-24  19.9µs ± 2%   8.3µs ± 1%  -58.37%  (p=0.000 n=10+10)

Updates #19438

Change-Id: I091beb7431d8661976a6c01cdb0d145e37fe3d22
Reviewed-on: https://go-review.googlesource.com/c/go/+/464344
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>