sync: do not unnecessarily keep alive functions wrapped by Once(Func|Value|Values)
The function passed to OnceFunc/OnceValue/OnceValues may transitively
keep more allocations alive. As the passed function is guaranteed to be
called at most once, it is safe to drop it after the first call is
complete. This avoids keeping the passed function (and anything it
transitively references) alive until the returned function is GCed.
Change-Id: I2faf397b481d2f693ab3aea8e2981b02adbc7a21
Reviewed-on: https://go-review.googlesource.com/c/go/+/481515
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: qiulaidongfeng <
2645477756@qq.com>