зеркало из https://github.com/CryptoPro/go.git
80 строки
2.1 KiB
Go
80 строки
2.1 KiB
Go
// run
|
|
|
|
// Copyright 2016 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.
|
|
|
|
// Previously, cmd/compile would rewrite
|
|
//
|
|
// check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
|
|
//
|
|
// to
|
|
//
|
|
// var autotmp_1 uintptr = testMeth(1).Pointer()
|
|
// var autotmp_2 uintptr = testMeth(2).Pointer()
|
|
// check(unsafe.Pointer(autotmp_1), unsafe.Pointer(autotmp_2))
|
|
//
|
|
// However, that means autotmp_1 is the only reference to the int
|
|
// variable containing the value "1", but it's not a pointer type,
|
|
// so it was at risk of being garbage collected by the evaluation of
|
|
// testMeth(2).Pointer(), even though package unsafe's documentation
|
|
// says the original code was allowed.
|
|
//
|
|
// Now cmd/compile rewrites it to
|
|
//
|
|
// var autotmp_1 unsafe.Pointer = unsafe.Pointer(testMeth(1).Pointer())
|
|
// var autotmp_2 unsafe.Pointer = unsafe.Pointer(testMeth(2).Pointer())
|
|
// check(autotmp_1, autotmp_2)
|
|
//
|
|
// to ensure the pointed-to variables are visible to the GC.
|
|
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"reflect"
|
|
"runtime"
|
|
"unsafe"
|
|
)
|
|
|
|
func main() {
|
|
// Test all the different ways we can invoke reflect.Value.Pointer.
|
|
|
|
// Direct method invocation.
|
|
check(unsafe.Pointer(testMeth(1).Pointer()), unsafe.Pointer(testMeth(2).Pointer()))
|
|
|
|
// Invocation via method expression.
|
|
check(unsafe.Pointer(reflect.Value.Pointer(testMeth(1))), unsafe.Pointer(reflect.Value.Pointer(testMeth(2))))
|
|
|
|
// Invocation via interface.
|
|
check(unsafe.Pointer(testInter(1).Pointer()), unsafe.Pointer(testInter(2).Pointer()))
|
|
|
|
// Invocation via method value.
|
|
check(unsafe.Pointer(testFunc(1)()), unsafe.Pointer(testFunc(2)()))
|
|
}
|
|
|
|
func check(p, q unsafe.Pointer) {
|
|
a, b := *(*int)(p), *(*int)(q)
|
|
if a != 1 || b != 2 {
|
|
fmt.Printf("got %v, %v; expected 1, 2\n", a, b)
|
|
}
|
|
}
|
|
|
|
func testMeth(x int) reflect.Value {
|
|
// Force GC to run.
|
|
runtime.GC()
|
|
return reflect.ValueOf(&x)
|
|
}
|
|
|
|
type Pointerer interface {
|
|
Pointer() uintptr
|
|
}
|
|
|
|
func testInter(x int) Pointerer {
|
|
return testMeth(x)
|
|
}
|
|
|
|
func testFunc(x int) func() uintptr {
|
|
return testMeth(x).Pointer
|
|
}
|