encoding/gob: avoid filling userTypeCache at init time
Doing this work at init time does make the first encode or decode call
slightly faster, but the cost is still paid upfront.
However, not all programs which directly or indirectly import
encoding/gob end up encoding or decoding any values.
For example, a program might only be run with the -help flag,
or it might only use gob encoding when a specific mode is enabled.
Moreover, any work done at init time needs to happen sequentially and
before the main function can start, blocking the entire program.
Using benchinit, we see a moderate saving at init time:
goos: linux
goarch: amd64
cpu: AMD Ryzen 7 PRO 5850U with Radeon Graphics
│ old │ new │
│ sec/op │ sec/op vs base │
EncodingGob 188.9µ ± 0% 175.4µ ± 0% -7.15% (p=0.000 n=10)
│ old │ new │
│ B/op │ B/op vs base │
EncodingGob 39.78Ki ± 0% 38.46Ki ± 0% -3.32% (p=0.000 n=10)
│ old │ new │
│ allocs/op │ allocs/op vs base │
EncodingGob 668.0 ± 0% 652.0 ± 0% -2.40% (p=0.000 n=10)
Change-Id: I75a5df18c9b1d02566e5885a966360d8a525913a
Reviewed-on: https://go-review.googlesource.com/c/go/+/479396 Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Rob Pike <r@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>