go race data detection when setting up handlers for nats-streaming

Question

For a nats-streaming subscription the handler needs to look like this

handler := func(ms *stan.Msg){}

I created the following function in an attempt to take the their handler and then call my own to process the message returned.

func (t *T) Subscribe(sub Subscription, h ...message.Handler) (stan.Subscription, error) {
    process := func(ms *stan.Msg) {         
        for i := range h {
            h[i](ms)
        }
    }

    return t.subscribe(sub, process)
}

With go test -race I get a data warning race condition around the area where I loop over/call my handlers. I am Looking for some suggestions on how I can improve this to remove that race warning.

== race detection output

==================
WARNING: DATA RACE
Read at 0x00c4201f8040 by goroutine 82:
  github.com/MyTest/nats/v3_test.TestDurability.func2()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:399 +0x4d
  github.com/MyTest/nats/v3.(*T).Subscribe.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:222 +0x2a0
  github.com/nats-io/go-nats-streaming.(*conn).processMsg()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/stan.go:464 +0x41c
  github.com/nats-io/go-nats-streaming.(*conn).(github.com/nats-io/go-nats-streaming.processMsg)-fm()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x4b
  github.com/nats-io/go-nats.(*Conn).waitForMsgs()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:1564 +0x1eb

Previous write at 0x00c4201f8040 by goroutine 81:
  github.com/MyTest/nats/v3_test.TestDurability.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:383 +0xe7
  github.com/MyTest/nats/v3.(*T).Subscribe.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:222 +0x2a0
  github.com/nats-io/go-nats-streaming.(*conn).processMsg()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/stan.go:464 +0x41c
  github.com/nats-io/go-nats-streaming.(*conn).(github.com/nats-io/go-nats-streaming.processMsg)-fm()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x4b
  github.com/nats-io/go-nats.(*Conn).waitForMsgs()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:1564 +0x1eb

Goroutine 82 (running) created at:
  github.com/nats-io/go-nats.(*Conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2238 +0x3f8
  github.com/nats-io/go-nats.(*Conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2155 +0x7e
  github.com/nats-io/go-nats-streaming.(*conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x59e
  github.com/nats-io/go-nats-streaming.(*conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:185 +0xb0
  github.com/MyTest/nats/v3.(*T).subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:279 +0x1be
  github.com/MyTest/nats/v3.(*T).Subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:226 +0x1f7
  github.com/MyTest/nats/v3_test.TestDurability()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:398 +0xa1a
  testing.tRunner()
      /usr/lib64/golang/src/testing/testing.go:746 +0x16c

Goroutine 81 (finished) created at:
  github.com/nats-io/go-nats.(*Conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2238 +0x3f8
  github.com/nats-io/go-nats.(*Conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2155 +0x7e
  github.com/nats-io/go-nats-streaming.(*conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x59e
  github.com/nats-io/go-nats-streaming.(*conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:185 +0xb0
  github.com/MyTest/nats/v3.(*T).subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:279 +0x1be
  github.com/MyTest/nats/v3.(*T).Subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:226 +0x1f7
  github.com/MyTest/nats/v3_test.TestDurability()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:382 +0x606
  testing.tRunner()
      /usr/lib64/golang/src/testing/testing.go:746 +0x16c
==================
==================
WARNING: DATA RACE
Read at 0x00c4201f0000 by goroutine 82:
  runtime.growslice()
      /usr/lib64/golang/src/runtime/slice.go:82 +0x0
  github.com/MyTest/nats/v3_test.TestDurability.func2()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:399 +0x166
  github.com/MyTest/nats/v3.(*T).Subscribe.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:222 +0x2a0
  github.com/nats-io/go-nats-streaming.(*conn).processMsg()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/stan.go:464 +0x41c
  github.com/nats-io/go-nats-streaming.(*conn).(github.com/nats-io/go-nats-streaming.processMsg)-fm()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x4b
  github.com/nats-io/go-nats.(*Conn).waitForMsgs()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:1564 +0x1eb

Previous write at 0x00c4201f0000 by goroutine 81:
  github.com/MyTest/nats/v3_test.TestDurability.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:383 +0xb2
  github.com/MyTest/nats/v3.(*T).Subscribe.func1()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:222 +0x2a0
  github.com/nats-io/go-nats-streaming.(*conn).processMsg()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/stan.go:464 +0x41c
  github.com/nats-io/go-nats-streaming.(*conn).(github.com/nats-io/go-nats-streaming.processMsg)-fm()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x4b
  github.com/nats-io/go-nats.(*Conn).waitForMsgs()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:1564 +0x1eb

Goroutine 82 (running) created at:
  github.com/nats-io/go-nats.(*Conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2238 +0x3f8
  github.com/nats-io/go-nats.(*Conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2155 +0x7e
  github.com/nats-io/go-nats-streaming.(*conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x59e
  github.com/nats-io/go-nats-streaming.(*conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:185 +0xb0
  github.com/MyTest/nats/v3.(*T).subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:279 +0x1be
  github.com/MyTest/nats/v3.(*T).Subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:226 +0x1f7
  github.com/MyTest/nats/v3_test.TestDurability()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:398 +0xa1a
  testing.tRunner()
      /usr/lib64/golang/src/testing/testing.go:746 +0x16c

Goroutine 81 (finished) created at:
  github.com/nats-io/go-nats.(*Conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2238 +0x3f8
  github.com/nats-io/go-nats.(*Conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats/nats.go:2155 +0x7e
  github.com/nats-io/go-nats-streaming.(*conn).subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:217 +0x59e
  github.com/nats-io/go-nats-streaming.(*conn).Subscribe()
      /home/chadit/Projects/src/github.com/nats-io/go-nats-streaming/sub.go:185 +0xb0
  github.com/MyTest/nats/v3.(*T).subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:279 +0x1be
  github.com/MyTest/nats/v3.(*T).Subscribe()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats.go:226 +0x1f7
  github.com/MyTest/nats/v3_test.TestDurability()
      /home/chadit/Projects/src/github.com/MyTest/nats/v3/nats_test.go:382 +0x606
  testing.tRunner()
      /usr/lib64/golang/src/testing/testing.go:746 +0x16c
==================
--- FAIL: TestDurability (1.01s)
    testing.go:699: race detected during execution of test
FAIL
exit status 1

link to project https://github.com/chadit/MessageQueueExamples/tree/master/nats-streaming/nats

The race involves testing code. Are you by any chance setting a global handler in your test code? If so, you'll want a mutex around it. It's hard to tell without the test code or filenames/line numbers. — Marc, Dec 29 '17 at 12:43
@Marc thank you that was it, put mutex around the test handler and it is now passing. — Chadit, Dec 29 '17 at 13:58

go race data detection when setting up handlers for nats-streaming

0 Answers0