Re: panic: invalid memory address or nil pointer dereference / throw: panic during gc

Dmitry Vyukov

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Nov 15, 2012, 1:00:19 AM11/15/12

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On Thursday, November 15, 2012 2:20:55 AM UTC+4, S.Çağlar Onur wrote:

Hello,

I was playing with a dummy tool to find my duplicated jpg files in my iPhoto library and I observed the following problem. It looks like compiled binary works couple of times before throwing a panic. The problem is reproducible on my machine (memory issues?). I tried searching the group archives and open issues at code.google.com/p/go but couldn't find something related.

This is a go-1.0.3 on top of OSX 10.8.2
[caglar@Zangetsu:~/Projects/github/godup] go build dup.go
[caglar@Zangetsu:~/Projects/github/godup] ./dup 
[caglar@Zangetsu:~/Projects/github/godup] ./dup 
CONFLICT between /Users/caglar/Pictures/iPhoto Library/Masters/2012/09/26/20120926-140126/IMG_0601.JPG and /Users/caglar/Pictures/iPhoto Library/Masters/2012/09/29/20120929-235343/IMG_0780.JPG
[caglar@Zangetsu:~/Projects/github/godup] ./dup 
CONFLICT between /Users/caglar/Pictures/iPhoto Library/Masters/2012/09/26/20120926-140126/IMG_0601.JPG and /Users/caglar/Pictures/iPhoto Library/Masters/2012/09/29/20120929-235343/IMG_0780.JPG
[caglar@Zangetsu:~/Projects/github/godup] ./dup 
panic: invalid memory address or nil pointer dereference
throw: panic during gc
[signal 0xb code=0x1 addr=0x0 pc=0x9045]

Hi,

Is it 32 or 64 bit?

It looks like http://code.google.com/p/go/issues/detail?id=3798

S.Çağlar Onur

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Nov 15, 2012, 2:41:54 PM11/15/12

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Hi Dmitry,

It is 64 bit. If I understand correctly changing map[uint64]string to map[string]string should resolve this problem because of uint64's alignment issue, right?

Best,

S.Çağlar Onur

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Nov 15, 2012, 2:48:00 PM11/15/12

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Hi,

I just tried changing the map but didn't help (unless I made a mistake), please see http://10ur.org/panic_2.txt

Best,

Dmitry Vyukov

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Nov 15, 2012, 2:52:45 PM11/15/12

to S.Çağlar Onur, golang-nuts

Humm... then perhaps you have a data race in the code, that badly corrupts memory. If you are on tip, then you may to run under race detector (go test/run -race).

S.Çağlar Onur

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Nov 15, 2012, 3:54:18 PM11/15/12

to Dmitry Vyukov, golang-nuts

Hi Dmitry,

Thanks for the tip about the tip, I wasn't aware of that race detector. So I switched to that (I was using release) and it looks like I've a race due to map operations not being atomic.

[caglar@Zangetsu:~/Projects/github/godup] go run -race dup2.go

==================

WARNING: DATA RACE

Read by goroutine 3:

main.hasher()

/Users/caglar/Projects/github/godup/dup2.go:47 +0x46b

Previous write by goroutine 2:

main.hasher()

/Users/caglar/Projects/github/godup/dup2.go:52 +0x5ff

Goroutine 3 (running) created at:

main.main()

/Users/caglar/Projects/github/godup/dup2.go:67 +0x162

runtime.main()

/Users/caglar/Downloads/go/src/pkg/runtime/proc.c:248 +0x91

Goroutine 2 (finished) created at:

main.main()

/Users/caglar/Projects/github/godup/dup2.go:67 +0x162

runtime.main()

/Users/caglar/Downloads/go/src/pkg/runtime/proc.c:248 +0x91

==================

Thanks!

--
S.Çağlar Onur <cag...@10ur.org>

Dmitry Vyukov

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Nov 16, 2012, 3:22:46 AM11/16/12

to S.Çağlar Onur, golang-nuts

On Fri, Nov 16, 2012 at 12:54 AM, S.Çağlar Onur <cag...@10ur.org> wrote:

Hi Dmitry,

Thanks for the tip about the tip, I wasn't aware of that race detector. So I switched to that (I was using release) and it looks like I've a race due to map operations not being atomic.

[caglar@Zangetsu:~/Projects/github/godup] go run -race dup2.go
==================
WARNING: DATA RACE
Read by goroutine 3:
main.hasher()
/Users/caglar/Projects/github/godup/dup2.go:47 +0x46b

Previous write by goroutine 2:
main.hasher()
/Users/caglar/Projects/github/godup/dup2.go:52 +0x5ff

Goroutine 3 (running) created at:
main.main()

/Users/caglar/Projects/github/godup/dup2.go:67 +0x162
runtime.main()
/Users/caglar/Downloads/go/src/pkg/runtime/proc.c:248 +0x91

Goroutine 2 (finished) created at:

main.main()
/Users/caglar/Projects/github/godup/dup2.go:67 +0x162
runtime.main()
/Users/caglar/Downloads/go/src/pkg/runtime/proc.c:248 +0x91

==================

Thanks!

Great!

Map operations were never intended to be atomic. You need to protect maps with channels/mutexes.

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