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| 1 | +// run |
| 2 | + |
| 3 | +// Copyright 2015 The Go Authors. All rights reserved. |
| 4 | +// Use of this source code is governed by a BSD-style |
| 5 | +// license that can be found in the LICENSE file. |
| 6 | + |
| 7 | +package main |
| 8 | + |
| 9 | +import ( |
| 10 | + "fmt" |
| 11 | + "runtime" |
| 12 | +) |
| 13 | + |
| 14 | +const N = 100000 |
| 15 | + |
| 16 | +func main() { |
| 17 | + // Allocate more Ps than processors. This raises |
| 18 | + // the chance that we get interrupted by the OS |
| 19 | + // in exactly the right (wrong!) place. |
| 20 | + p := runtime.NumCPU() |
| 21 | + runtime.GOMAXPROCS(2 * p) |
| 22 | + |
| 23 | + // Allocate some pointers. |
| 24 | + ptrs := make([]*int, p) |
| 25 | + for i := 0; i < p; i++ { |
| 26 | + ptrs[i] = new(int) |
| 27 | + } |
| 28 | + |
| 29 | + // Arena where we read and write pointers like crazy. |
| 30 | + collider := make([]*int, p) |
| 31 | + |
| 32 | + done := make(chan struct{}, 2*p) |
| 33 | + |
| 34 | + // Start writers. They alternately write a pointer |
| 35 | + // and nil to a slot in the collider. |
| 36 | + for i := 0; i < p; i++ { |
| 37 | + i := i |
| 38 | + go func() { |
| 39 | + for j := 0; j < N; j++ { |
| 40 | + // Write a pointer using memmove. |
| 41 | + copy(collider[i:i+1], ptrs[i:i+1]) |
| 42 | + // Write nil using memclr. |
| 43 | + // (This is a magic loop that gets lowered to memclr.) |
| 44 | + r := collider[i : i+1] |
| 45 | + for k := range r { |
| 46 | + r[k] = nil |
| 47 | + } |
| 48 | + } |
| 49 | + done <- struct{}{} |
| 50 | + }() |
| 51 | + } |
| 52 | + // Start readers. They read pointers from slots |
| 53 | + // and make sure they are valid. |
| 54 | + for i := 0; i < p; i++ { |
| 55 | + i := i |
| 56 | + go func() { |
| 57 | + for j := 0; j < N; j++ { |
| 58 | + var ptr [1]*int |
| 59 | + copy(ptr[:], collider[i:i+1]) |
| 60 | + if ptr[0] != nil && ptr[0] != ptrs[i] { |
| 61 | + panic(fmt.Sprintf("bad pointer read %p!", ptr[0])) |
| 62 | + } |
| 63 | + } |
| 64 | + done <- struct{}{} |
| 65 | + }() |
| 66 | + } |
| 67 | + for i := 0; i < 2*p; i++ { |
| 68 | + <-done |
| 69 | + } |
| 70 | +} |
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