Can I use a goldmark.Markdown from multiple goroutines?

[karlmcguire]

I've read all the documentation and haven't seen any mention of concurrency safety or the relative "cheapness" of producing a goldmark.Markdown for individual goroutines...

[karelbilek]

I have done a simple test by changing DoTestCases and it seems like it's working fine.

// DoTestCases runs a set of test cases.
func DoTestCases(m goldmark.Markdown, cases []MarkdownTestCase, t TestingT, opts ...parser.ParseOption) {
	var wg sync.WaitGroup
	for _, testCase := range cases {
		testCase := testCase
		wg.Add(1)
		go func() {
			defer wg.Done()
			DoTestCase(m, testCase, t, opts...)
		}()
	}
	wg.Wait()
}

and go test ./... shows no error.

that's however not a guarantee.

And I should not commit that either, as the concurrency bugs would still be hard to replicate/debug if they actually happened. Maybe a separate test?

But I think it's all concurrency safe, looking at the code.

[karelbilek]

So it's not trivially broken. :D But not sure how much has @yuin thought about concurrency either

[moorereason]

Also, use go test -race ./... to enable the race detector.

[karelbilek]

In a dumb way we can use the fuzz tests to check this too, but... not sure. As most of the fuzzer inputs are not markdown and are garbage (naturally), it will probably parse them as a single text block without much work :)

[karelbilek]

@moorereason tried that too now, thx. Also no bugs.

[karelbilek]

I tried this dumb fuzzing, not sure if I do it correctly, but again if there is something super broken it would catch it if I'm not wrong.

// Fuzz runs automated fuzzing against goldmark.
func Fuzz(data []byte) int {

	var b bytes.Buffer
	if err := markdown.Convert(data, &b); err != nil {
		return 0
	}
	correct := b.String()

	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go func() {
			var newb bytes.Buffer

			defer wg.Done()
			err := markdown.Convert(data, &newb)
			if err != nil {
				panic("foo")
			}

			second := newb.String()
			if correct != second {
				panic("incorrect")
			}
		}()
	}
	wg.Wait()

	return 1
}

It seems like it's working and not panicking. 🤷

[yuin]

Yes, you can use goldmark.Markdown with multiple goroutines.