issue27695.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  // Make sure return values are always scanned, when
     8  // calling methods (+functions, TODO) with reflect.
     9  
    10  package main
    11  
    12  import (
    13  	"reflect"
    14  	"runtime/debug"
    15  	"sync"
    16  )
    17  
    18  func main() {
    19  	debug.SetGCPercent(1) // run GC frequently
    20  	var wg sync.WaitGroup
    21  	for i := 0; i < 20; i++ {
    22  		wg.Add(1)
    23  		go func() {
    24  			defer wg.Done()
    25  			for i := 0; i < 2000; i++ {
    26  				_test()
    27  			}
    28  		}()
    29  	}
    30  	wg.Wait()
    31  }
    32  
    33  type Stt struct {
    34  	Data interface{}
    35  }
    36  
    37  type My struct {
    38  	b byte
    39  }
    40  
    41  func (this *My) Run(rawData []byte) (Stt, error) {
    42  	var data string = "hello"
    43  	stt := Stt{
    44  		Data: data,
    45  	}
    46  	return stt, nil
    47  }
    48  
    49  func _test() (interface{}, error) {
    50  	f := reflect.ValueOf(&My{}).MethodByName("Run")
    51  	if method, ok := f.Interface().(func([]byte) (Stt, error)); ok {
    52  		s, e := method(nil)
    53  		// The bug in issue27695 happens here, during the return
    54  		// from the above call (at the end of reflect.callMethod
    55  		// when preparing to return). The result value that
    56  		// is assigned to s was not being scanned if GC happens
    57  		// to occur there.
    58  		i := interface{}(s)
    59  		return i, e
    60  	}
    61  	return nil, nil
    62  }
    63
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