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>