Duplicate of #16272

Merged into #16354.

Dup of #16272
On Jul 14, 2016 6:14 PM, "Joe Toscano" notifications@github.com wrote:

This wasn't happening on my machine before I installed the macOS beta.
Kind of regretting it now! 😁

What version of Go are you using?
go version go1.6.2 darwin/amd64
2.

What operating system and processor architecture are you using?
macOS Sierra beta2 (macOS 10.12 16A238m)
on amd64
3.

What did you do?
Compiled and ran the following small program:

package main

import (
"fmt"
"time"
)

func main() {
i := 0
for {
i++
fmt.Printf("Sleeping, pass #%d... ", i)
time.Sleep(time.Millisecond * 50)
fmt.Printf("done.\n")
}
}

What did you expect to see?
A practically infinite number of loop iterations.
2.

What did you see instead?
Output for a few seconds, then nothing, because time.Sleep() fails to
return after a few iterations of the loop.
Using a debugger (https://github.com/derekparker/delve), I'm able to
interrupt the program and grab a stack trace when it freezes, and it's
always exactly the same:

0 0x0000000000056c43 in runtime.mach_semaphore_timedwait
at /usr/local/go/src/runtime/sys_darwin_amd64.s:421
1 0x0000000000026d0b in runtime.semasleep1
at /usr/local/go/src/runtime/os1_darwin.go:412
2 0x000000000004b250 in runtime.semasleep.func1
at /usr/local/go/src/runtime/os1_darwin.go:439
3 0x0000000000053597 in runtime.systemstack
at /usr/local/go/src/runtime/asm_amd64.s:291
4 0x000000000002d390 in runtime.startTheWorldWithSema
at /usr/local/go/src/runtime/proc.go:986
5 0x0000000000183600 in (nil)
at ?:-1

I get the same result if the for loop is moved into a separate goroutine,
or if the sleep duration is varied.

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