--- /dev/null
+// run
+
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+ "fmt"
+ "runtime"
+)
+
+const N = 100000
+
+func main() {
+ // Allocate more Ps than processors. This raises
+ // the chance that we get interrupted by the OS
+ // in exactly the right (wrong!) place.
+ p := runtime.NumCPU()
+ runtime.GOMAXPROCS(2 * p)
+
+ // Allocate some pointers.
+ ptrs := make([]*int, p)
+ for i := 0; i < p; i++ {
+ ptrs[i] = new(int)
+ }
+
+ // Arena where we read and write pointers like crazy.
+ collider := make([]*int, p)
+
+ done := make(chan struct{}, 2*p)
+
+ // Start writers. They alternately write a pointer
+ // and nil to a slot in the collider.
+ for i := 0; i < p; i++ {
+ i := i
+ go func() {
+ for j := 0; j < N; j++ {
+ // Write a pointer using memmove.
+ copy(collider[i:i+1], ptrs[i:i+1])
+ // Write nil using memclr.
+ // (This is a magic loop that gets lowered to memclr.)
+ r := collider[i : i+1]
+ for k := range r {
+ r[k] = nil
+ }
+ }
+ done <- struct{}{}
+ }()
+ }
+ // Start readers. They read pointers from slots
+ // and make sure they are valid.
+ for i := 0; i < p; i++ {
+ i := i
+ go func() {
+ for j := 0; j < N; j++ {
+ var ptr [1]*int
+ copy(ptr[:], collider[i:i+1])
+ if ptr[0] != nil && ptr[0] != ptrs[i] {
+ panic(fmt.Sprintf("bad pointer read %p!", ptr[0]))
+ }
+ }
+ done <- struct{}{}
+ }()
+ }
+ for i := 0; i < 2*p; i++ {
+ <-done
+ }
+}