goroutine safety guarantees for jaeger + opentracing-go

[Hechen Gao]

Hi jaeger community,

I have a question about the goroutine safety guarantees for jaeger + opentracing-go.

In my code I am using jaeger and set jaeger tracer as global tracer for opentracing-go API. And I have a following code block.

func xyz(ctx context.Context, ...) {

    span, spanctx := opentracing.StartSpanFromContext(ctx, "xyz")

    defer span.Finish()

    span.LogFields(

        log.String("event", "soft error"),

        log.String("type", "cache timeout"),

        log.Int("waited.millis", 1500))

    ...

    go taskProcess(spanctx, ...)

}

func taskProcess(ctx context.Context, ...) {

span, spanctx := opentracing.StartSpanFromContext(ctx, "taskProcess")

        defer span.Finish()

        ...

}

I am passing the span context to a goroutine function, and start a new span from that context. I am wondering if this is safe to do.

Looking forward to your reply.

Best regards

[Yuri Shkuro]

Good question. Yes, it is safe to do so, but I often seen people get burned by the fact that if the original context comes from an RPC framework it might contain a deadline, which doesn't work great when you transfer said context to a goroutine. Also, the context might get cancelled once the RPC is completed. So you might want to do this in teh goroutine

1. create a new child span from the original context
2. create a new Background context for the goroutine
3. save the span to the next context

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[Yuri Shkuro]

So basically add this to your example: 

func taskProcess(ctx context.Context, ...) {

callerSpan := opentracing.SpanFromContext(ctx)

ctx = opentracing.ContextWithSpan(Background(), callerSpan)

// now ctx is independent of the caller but has access to its span

span, spanctx := opentracing.StartSpanFromContext(ctx, "taskProcess")

        defer span.Finish()

        ...

}

On Tue, Feb 13, 2018 at 2:59 PM, Hechen Gao <zere...@gmail.com> wrote:

I see, could you please add a more specific example? I feel this would be very useful to add in opentracing and jaeger doc.

Best regards,

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