sync: TestPool failure on windows-amd64-2016

[josharian]

Noticed on build.golang.org.

https://build.golang.org/log/a3f357b132ef8cb703e42085a50c8c4499e64301

##### sync -cpu=10
--- FAIL: TestPool (0.00s)
	pool_test.go:29: got "b"; want a
FAIL
FAIL	sync	0.412s

First showed up after CL 42090, although that seems unlikely to be the cause.

cc @valyala @dvyukov

[josharian]

@dlespiau

[bradfitz]

/cc @aclements for log history greppin'.

[dlespiau]

It seems unlikely to be caused by CL 42090 indeed. That (SSE) instruction isn't generated by the compiler and not present in any of the .s files in the go project (well, apart from the testdata file checking its correctness).

[dvyukov]

Perhaps the goroutine was rescheduled to another P (due to preemption?).
runtime.GOMAXPROCS(1) should with against that.

[bradfitz]

Also openbsd-386:
https://build.golang.org/log/71a13d246b73925bd56923c0a706a95cbaf74e74
and others

[bradfitz]

@aclements, this started happening pretty frequently. Do you know what changed?

[gopherbot]

CL https://golang.org/cl/42770 mentions this issue.

[josharian]

The only recent sync.Pool change I can think of is CL 40913.

[bradfitz]

That one seems safe.

[josharian]

Oh, also CL 40918.