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ianlancetaylor opened this issue Jan 4, 2018 · 1 comment
Closed

encoding/gob: race on idToType #23328

ianlancetaylor opened this issue Jan 4, 2018 · 1 comment
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Go1.10

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@ianlancetaylor
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On current master, this program sometimes fails when using the race detector:

package main

import (
	"bytes"
	"encoding/gob"
	"fmt"
	"sync"
)

type S0 struct {
	I int
}

type S1 struct {
	I int
}

type S2 struct {
	I int
}

type S3 struct {
	I int
}

type S4 struct {
	I int
}

type S5 struct {
	I int
}

type S6 struct {
	I int
}

type S7 struct {
	I int
}

type S8 struct {
	I int
}

type S9 struct {
	I int
}

func main() {
	c := make(chan bool)
	var wg sync.WaitGroup
	for i := 0; i < 10; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			var buf bytes.Buffer
			var x interface{}
			switch i {
			case 0:
				x = &S0{0}
			case 1:
				x = &S1{1}
			case 2:
				x = &S2{2}
			case 3:
				x = &S3{3}
			case 4:
				x = &S4{4}
			case 5:
				x = &S5{5}
			case 6:
				x = &S6{6}
			case 7:
				x = &S7{7}
			case 8:
				x = &S8{8}
			case 9:
				x = &S9{9}
			default:
				panic(i)
			}
			enc := gob.NewEncoder(&buf)
			dec := gob.NewDecoder(&buf)
			<-c
			if err := enc.Encode(x); err != nil {
				fmt.Println(err)
			}
			if err := enc.Encode(x); err != nil {
				fmt.Println(err)
			}
			m := make(map[string]string)
			// This call to Decode is expected to fail.
			dec.Decode(&m)
		}(i)
	}
	close(c)
	wg.Wait()
}

Sample failure:

==================
WARNING: DATA RACE
Write at 0x00c4200961e0 by goroutine 7:
  runtime.mapassign_fast32()
      /home/iant/go/src/runtime/hashmap_fast.go:350 +0x0
  encoding/gob.setTypeId()
      /home/iant/go/src/encoding/gob/type.go:186 +0xf8
  encoding/gob.newStructType()
      /home/iant/go/src/encoding/gob/type.go:429 +0xb6
  encoding/gob.newTypeObject()
      /home/iant/go/src/encoding/gob/type.go:522 +0xd36
  encoding/gob.getType()
      /home/iant/go/src/encoding/gob/type.go:598 +0x112
  encoding/gob.getBaseType()
      /home/iant/go/src/encoding/gob/type.go:585 +0x94
  encoding/gob.buildTypeInfo()
      /home/iant/go/src/encoding/gob/type.go:715 +0x106
  encoding/gob.getTypeInfo()
      /home/iant/go/src/encoding/gob/type.go:702 +0xed
  encoding/gob.(*Encoder).sendActualType()
      /home/iant/go/src/encoding/gob/encoder.go:96 +0xcb
  encoding/gob.(*Encoder).sendType()
      /home/iant/go/src/encoding/gob/encoder.go:168 +0x116
  encoding/gob.(*Encoder).sendTypeDescriptor()
      /home/iant/go/src/encoding/gob/encoder.go:190 +0x166
  encoding/gob.(*Encoder).EncodeValue()
      /home/iant/go/src/encoding/gob/encoder.go:243 +0x52c
  encoding/gob.(*Encoder).Encode()
      /home/iant/go/src/encoding/gob/encoder.go:175 +0x72
  main.main.func1()
      /home/iant/foo8.go:86 +0x1d8

Previous read at 0x00c4200961e0 by goroutine 13:
  runtime.mapaccess1_fast32()
      /home/iant/go/src/runtime/hashmap_fast.go:12 +0x0
  encoding/gob.(*Decoder).typeString()
      /home/iant/go/src/encoding/gob/decode.go:1041 +0x76
  encoding/gob.(*Decoder).compileSingle()
      /home/iant/go/src/encoding/gob/decode.go:1056 +0x563
  encoding/gob.(*Decoder).compileDec()
      /home/iant/go/src/encoding/gob/decode.go:1088 +0x132
  encoding/gob.(*Decoder).getDecEnginePtr()
      /home/iant/go/src/encoding/gob/decode.go:1145 +0x23b
  encoding/gob.(*Decoder).decodeValue()
      /home/iant/go/src/encoding/gob/decode.go:1190 +0x10b
  encoding/gob.(*Decoder).DecodeValue()
      /home/iant/go/src/encoding/gob/decoder.go:212 +0x1cb
  encoding/gob.(*Decoder).Decode()
      /home/iant/go/src/encoding/gob/decoder.go:187 +0x1c9
  main.main.func1()
      /home/iant/foo8.go:94 +0x371

Goroutine 7 (running) created at:
  main.main()
      /home/iant/foo8.go:55 +0xd9

Goroutine 13 (finished) created at:
  main.main()
      /home/iant/foo8.go:55 +0xd9
==================
Found 1 data race(s)
exit status 66

This is not a new failure but it's probably simple to fix.
@ianlancetaylor ianlancetaylor added the NeedsFix The path to resolution is known, but the work has not been done. label Jan 4, 2018
@ianlancetaylor ianlancetaylor added this to the Go1.10 milestone Jan 4, 2018
@gopherbot
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Change https://golang.org/cl/86075 mentions this issue: encoding/gob: avoid race on idToType

@golang golang locked and limited conversation to collaborators Jan 4, 2019
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