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testing: race in outputting to the root io.Writer #18741

dsnet opened this issue Jan 22, 2017 · 1 comment


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commented Jan 22, 2017

Using Go1.7.4.

Consider the following test:

func Test(t *testing.T) {
	var wg sync.WaitGroup
	defer wg.Wait()
	for i := 0; i < 100; i++ {
		go func(i int) {
			defer wg.Done()
			t.Run(fmt.Sprintf("LongLongLongLongName%d", i), func(t *testing.T) {})

On some invocations, I see something like:

=== RUN   Test/LongLongLongLongName48
=== RUN   Test/LongLon=== RUN   Test/LongLongLongLongName50
=== RUN   Test/LongLongLongLongName51

In testing.go, we directly write "=== RUN %s\n" directly to the root's io.Writer (which is os.Stdout). Although it is safe to concurrently write to os.Stdout, the results can sometimes be non-sensical.

Instead, we should acquire the root's lock before writing.

@dsnet dsnet added this to the Go1.9 milestone Jan 22, 2017

@dsnet dsnet added the NeedsFix label Jan 22, 2017


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commented Jan 24, 2017

CL mentions this issue.

@gopherbot gopherbot closed this in 7f31971 Feb 1, 2017

@golang golang locked and limited conversation to collaborators Feb 1, 2018

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