ReportEvent() race condition

[cfchou]

CircuitBreaker.ReportEvent() checks Circuit.open without acquiring a lock. It's possible to run into data race when other goroutines running for example CircuitBreaker.setOpen().

This problem can be observed by running the test I add with package quick:

(Checkout #346dd5d and increase -quickchecks if not seeing race condition.)

go test -race github.com/cfchou/hystrix-go/hystrix -test.v -test.run ^TestReportEventMultiThreaded$ -quickchecks 50
...
==================
WARNING: DATA RACE
Write at 0x00c420106dd0 by goroutine 81:
  github.com/cfchou/hystrix-go/hystrix.(*CircuitBreaker).setOpen()
      /Users/cfchou/Project/gopath/src/github.com/cfchou/hystrix-go/hystrix/circuit.go:150 +0x1c9
  github.com/cfchou/hystrix-go/hystrix.(*CircuitBreaker).IsOpen()
      /Users/cfchou/Project/gopath/src/github.com/cfchou/hystrix-go/hystrix/circuit.go:108 +0x21e
  github.com/cfchou/hystrix-go/hystrix.TestReportEvent.func1.1()
      /Users/cfchou/Project/gopath/src/github.com/cfchou/hystrix-go/hystrix/circuit_test.go:137 +0x2bd

Previous read at 0x00c420106dd0 by goroutine 64:
  github.com/cfchou/hystrix-go/hystrix.(*CircuitBreaker).ReportEvent()
      /Users/cfchou/Project/gopath/src/github.com/cfchou/hystrix-go/hystrix/circuit.go:173 +0x393
  github.com/cfchou/hystrix-go/hystrix.TestReportEvent.func1.1()
      /Users/cfchou/Project/gopath/src/github.com/cfchou/hystrix-go/hystrix/circuit_test.go:131 +0x170
...

[afex]

thanks very much for the fix and test!