callctx: race condition

[jjkoh95]

callctx.SetHeaders is not concurrent safe.
I'm not sure if this is by design or potentially a bug.
It should be explicit in the comment section if it is designed to be non-concurrent safe.

Environment details

• Programming language: Go
• OS: Debian GNU/Linux 12 (bookworm)
• Language runtime version: go version go1.22.0 linux/amd64
• Package version: github.com/googleapis/gax-go/v2 v2.12.0

Steps to reproduce

// go run --race main.go
func main() {
	// first call to search places
	cctx := callctx.SetHeaders(context.Background(), "x-goog-fieldmask", "*")
	// for each place, get place details...
	for i := 0; i < 3; i++ {
		go func(ctx context.Context) {
			ctx = callctx.SetHeaders(ctx, "x-goog-fieldmask", "*")
			m := callctx.HeadersFromContext(ctx)
			fmt.Println(m)
		}(cctx)
	}

	fmt.Scanln()
}

---

For more information, I'm using this to search places in Google Maps, then foreach place, I do parallel calls to retrieve place details where I naively reused the same context and hit this error.

[noahdietz]

Hey @jjkoh95 thanks for this, especially the repro! We will take a look and get back to you, apologies for the friction

[noahdietz]

We found the issue and are fixing it! We definitely want this to be concurrent safe

[noahdietz]

Fix is in, release will be cut on Monday and I will close this. Thanks for the report, it's really appreciated!