issue45045.go

     1  // run
     2  
     3  // Copyright 2021 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  	"reflect"
    11  	"runtime"
    12  	"unsafe"
    13  )
    14  
    15  func k(c chan string, val string) string {
    16  	b := make([]byte, 1000)
    17  	runtime.SetFinalizer(&b[0], func(*byte) {
    18  		c <- val
    19  	})
    20  	var s string
    21  	h := (*reflect.StringHeader)(unsafe.Pointer(&s))
    22  	h.Data = uintptr(unsafe.Pointer(&b[0]))
    23  	h.Len = len(b)
    24  	return s
    25  }
    26  
    27  func main() {
    28  	{
    29  		c := make(chan string, 2)
    30  		m := make(map[string]int)
    31  		m[k(c, "first")] = 0
    32  		m[k(c, "second")] = 0
    33  		runtime.GC()
    34  		if s := <-c; s != "first" {
    35  			panic("map[string], second key did not retain.")
    36  		}
    37  		runtime.KeepAlive(m)
    38  	}
    39  
    40  	{
    41  		c := make(chan string, 2)
    42  		m := make(map[[2]string]int)
    43  		m[[2]string{k(c, "first")}] = 0
    44  		m[[2]string{k(c, "second")}] = 0
    45  		runtime.GC()
    46  		if s := <-c; s != "first" {
    47  			panic("map[[2]string], second key did not retain.")
    48  		}
    49  		runtime.KeepAlive(m)
    50  	}
    51  }
    52
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