span context: set the default recorded flag to 0, and fix default trace options bug

[wsabransky]

Closes #298 .

Currently, the default trace option for a new trace context is to set enabled to true. This causes all samplers applied to be ignored here. We should keep the parent sampling decision if it is true, but ignore it if false. A parent shouldn't be able to force a downstream service to not sample.

Also fixes bug described here.

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[wsabransky]

I signed it!

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[songy23]

Please rebase and fix lint.

[benley]

Please rebase and fix lint.

The lint error appears to be wholly unrelated to this PR, in a file not touched. Do you want it fixed in this change?

[songy23]

The lint error appears to be wholly unrelated to this PR, in a file not touched. Do you want it fixed in this change?

I see, For some reason lint didn't fail on my local machine. For now please ignore the error and just rebase against master.

[c24t]

I looked into the same issue in #482. There's another problem here: multiple Tracers can set the sampling ("enabled") bit on the shared default TraceOptions. See #482 (review).

Note that we still set the tracing bit in get_tracer based on the sampler, and the default sampler always samples:

opencensus-python/opencensus/trace/tracer.py

Lines 79 to 89 in f669aa9

	def get_tracer(self):
	"""Return a tracer according to the sampling decision."""
	sampled = self.should_sample()
	if sampled:
	self.span_context.trace_options.set_enabled(True)
	return context_tracer.ContextTracer(
	exporter=self.exporter,
	span_context=self.span_context)
	else:
	return noop_tracer.NoopTracer()

)

This might be the behavior you want, but to merge this PR we also need a test to show that the old behavior is broken. E.g. that the tracer used to sample even while using the AlwaysOffSampler.

[c24t]

If you add the test to show that the old behavior was wrong we can merge this.

[bogdandrutu]

@wsabransky any chance we can get some tests :)

[wsabransky]

@bogdandrutu @c24t Sorry about the delay, I'll add some tests today.

[wsabransky]

@c24t @bogdandrutu Okay, apparently there were already tests that cover this case, but they weren't included by the test runner because of how they were named.

Additionally, a scoping problem was causing the default trace options to be overwritten at runtime in some cases.

[wsabransky]

@c24t any chance we could get this merged?

[c24t]

@wsabransky it looks like this change breaks a jaeger integration test. I may have time to check it out later, but it can't merge as-is.

[wsabransky]

@c24t looks like it was just a fixture that needed to be updated to reflect the new behavior in this PR. I've made the change.

[c24t]

Thanks @wsabransky!