runtime/trace: rename "Span" with "Region"
"Span" is a commonly used term in many distributed tracing systems (Dapper, OpenCensus, OpenTracing, ...). They use it to refer to a period of time, not necessarily tied into execution of underlying processor, thread, or goroutine, unlike the "Span" of runtime/trace package. Since distributed tracing and go runtime execution tracing are already similar enough to cause confusion, this CL attempts to avoid using the same word if possible. "Region" is being used in a certain tracing system to refer to a code region which is pretty close to what runtime/trace.Span currently refers to. So, replace that. https://software.intel.com/en-us/itc-user-and-reference-guide-defining-and-recording-functions-or-regions This CL also tweaks APIs a bit based on jbd and heschi's comments: NewContext -> NewTask and it now returns a Task object that exports End method. StartSpan -> StartRegion and it now returns a Region object that exports End method. Also, changed WithSpan to WithRegion and it now takes func() with no context. Another thought is to get rid of WithRegion. It is a nice concept but in practice, it seems problematic (a lot of code churn, and polluting stack trace). Already, the tracing concept is very low level, and we hope this API to be used with great care. Recommended usage will be defer trace.StartRegion(ctx, "someRegion").End() Left old APIs untouched in this CL. Once the usage of them are cleaned up, they will be removed in a separate CL. Change-Id: I73880635e437f3aad51314331a035dd1459b9f3a Reviewed-on: https://go-review.googlesource.com/108296 Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: JBD <jbd@google.com>
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