Source file test/stackobj.go

     1  // run
     2  
     3  // Copyright 2018 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  type HeapObj [8]int64
    15  
    16  type StkObj struct {
    17  	h *HeapObj
    18  }
    19  
    20  var n int
    21  var c int = -1
    22  
    23  func gc() {
    24  	// encourage heap object to be collected, and have its finalizer run.
    25  	runtime.GC()
    26  	runtime.GC()
    27  	runtime.GC()
    28  	n++
    29  }
    30  
    31  func main() {
    32  	f()
    33  	gc() // prior to stack objects, heap object is not collected until here
    34  	if c < 0 {
    35  		panic("heap object never collected")
    36  	}
    37  	if c != 1 {
    38  		panic(fmt.Sprintf("expected collection at phase 1, got phase %d", c))
    39  	}
    40  }
    41  
    42  func f() {
    43  	var s StkObj
    44  	s.h = new(HeapObj)
    45  	runtime.SetFinalizer(s.h, func(h *HeapObj) {
    46  		// Remember at what phase the heap object was collected.
    47  		c = n
    48  	})
    49  	g(&s)
    50  	gc()
    51  }
    52  
    53  func g(s *StkObj) {
    54  	gc() // heap object is still live here
    55  	runtime.KeepAlive(s)
    56  	gc() // heap object should be collected here
    57  }
    58  

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