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Add Trace.wrap decorator #30

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Merged
elijahandrews merged 13 commits into from
Aug 3, 2016
Merged

Add Trace.wrap decorator #30

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9bf2df8
First pass on make Span usable as a function decorator
elijahandrews Jul 29, 2016
c9c2bef
Clean up test_decorator_exception by using assert_raises
elijahandrews Aug 1, 2016
845eddc
Add tracer.trace_function
elijahandrews Aug 2, 2016
9564ccb
Remove decorator from Span
elijahandrews Aug 3, 2016
f30c4e0
Tracer.trace_function -> Tracer.wrap, add more wrap tests
elijahandrews Aug 3, 2016
6fa5c74
Remove unused import from span
elijahandrews Aug 3, 2016
78968d9
Remove unused import from span tests
elijahandrews Aug 3, 2016
089021d
Merge branch 'master' into elijah/decorator
elijahandrews Aug 3, 2016
c73e1b3
Include module name in default span name when wrapping functions
elijahandrews Aug 3, 2016
44d4f72
Fix typo in test_tracer_wrap_span_nesting comment
elijahandrews Aug 3, 2016
8faed3b
Add docs for tracer.wrap
elijahandrews Aug 3, 2016
ff0fbef
Add test for setting tags within wrapped function
elijahandrews Aug 3, 2016
a582a89
Make sure that we can pass args to function wrapped with trace.wrap
elijahandrews Aug 3, 2016
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49 changes: 48 additions & 1 deletion ddtrace/tracer.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@

import functools
import logging
import threading

Expand Down Expand Up @@ -63,6 +63,53 @@ def configure(self, enabled=None, hostname=None, port=None, sampler=None):
if sampler is not None:
self.sampler = sampler

def wrap(self, name=None, service=None, resource=None, span_type=None):
"""A decorator used to trace an entire function.

:param str name: the name of the operation being traced. If not set,
defaults to the fully qualified function name.
:param str service: the name of the service being traced. If not set,
it will inherit the service from it's parent.
:param str resource: an optional name of the resource being tracked.
:param str span_type: an optional operation type.

>>> @tracer.wrap('my.wrapped.function', service='my.service')
def run():
return 'run'
>>> @tracer.wrap() # name will default to 'execute' if unset
def execute():
return 'executed'

You can access the parent span using `tracer.current_span()` to set
tags:

>>> @tracer.wrap()
def execute():
span = tracer.current_span()
span.set_tag('a', 'b')

You can also create more spans within a traced function. These spans
will be children of the decorator's span:

>>> @tracer.wrap('parent')
def parent_function():
with tracer.trace('child'):
pass
"""

def wrap_decorator(func):
if name is None:
span_name = '{}.{}'.format(func.__module__, func.__name__)
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@elijahandrews elijahandrews Aug 3, 2016

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It's worth discussing whether we want to include the module name as well as the function name here.

Including the module name is good because we can tell exactly which function is being traced.

Including the module name is bad because we may get really long span names, and our interface doesn't display these well at this time.

I'm learning towards including the module name.

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@elijahandrews elijahandrews Aug 3, 2016

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(comment got buried so reposting):

It's worth discussing whether we want to include the module name as well as the function name here.

Including the module name is good because we can tell exactly which function is being traced.

Including the module name is bad because we may get really long span names, and our interface doesn't display these well at this time.

I'm learning towards including the module name.

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@clutchski clutchski Aug 3, 2016

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i really want to nudge people towards short spans. datalayer.metrics.query.spidly._parse_spidly will make me slightly insane. i guess its' ok though.

else:
span_name = name

@functools.wraps(func)
def func_wrapper(*args, **kwargs):
with self.trace(span_name, service=service, resource=resource, span_type=span_type):
func(*args, **kwargs)
return func_wrapper
return wrap_decorator

def trace(self, name, service=None, resource=None, span_type=None):
"""Return a span that will trace an operation called `name`.

Expand Down
104 changes: 103 additions & 1 deletion tests/test_tracer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@

import time

from nose.tools import eq_
from nose.tools import assert_raises, eq_

from ddtrace.tracer import Tracer

Expand Down Expand Up @@ -77,6 +77,108 @@ def _make_cake():
for s in spans:
assert s.trace_id != make.trace_id

def test_tracer_wrap():
writer = DummyWriter()
tracer = Tracer()
tracer.writer = writer

@tracer.wrap('decorated_function', service='s', resource='r',
span_type='t')
def f(tag_name, tag_value):
# make sure we can still set tags
span = tracer.current_span()
span.set_tag(tag_name, tag_value)
f('a', 'b')

spans = writer.pop()
eq_(len(spans), 1)
s = spans[0]
eq_(s.name, 'decorated_function')
eq_(s.service, 's')
eq_(s.resource, 'r')
eq_(s.span_type, 't')
eq_(s.to_dict()['meta']['a'], 'b')

def test_tracer_wrap_default_name():
writer = DummyWriter()
tracer = Tracer()
tracer.writer = writer

@tracer.wrap()
def f():
pass
f()

eq_(writer.spans[0].name, 'tests.test_tracer.f')

def test_tracer_wrap_exception():
writer = DummyWriter()
tracer = Tracer()
tracer.writer = writer

@tracer.wrap()
def f():
raise Exception('bim')

assert_raises(Exception, f)

eq_(len(writer.spans), 1)
eq_(writer.spans[0].error, 1)

def test_tracer_wrap_multiple_calls():
# Make sure that we create a new span each time the function is called
writer = DummyWriter()
tracer = Tracer()
tracer.writer = writer

@tracer.wrap()
def f():
pass
f()
f()

spans = writer.pop()
eq_(len(spans), 2)
assert spans[0].span_id != spans[1].span_id

def test_tracer_wrap_span_nesting():
# Make sure that nested spans have the correct parents
writer = DummyWriter()
tracer = Tracer()
tracer.writer = writer

@tracer.wrap('inner')
def inner():
pass
@tracer.wrap('outer')
def outer():
with tracer.trace('mid'):
inner()
outer()

spans = writer.pop()
eq_(len(spans), 3)

# sift through the list so we're not dependent on span ordering within the
# writer
for span in spans:
if span.name == 'outer':
outer_span = span
elif span.name == 'mid':
mid_span = span
elif span.name == 'inner':
inner_span = span
else:
assert False, 'unknown span found' # should never get here

assert outer_span
assert mid_span
assert inner_span

eq_(outer_span.parent_id, None)
eq_(mid_span.parent_id, outer_span.span_id)
eq_(inner_span.parent_id, mid_span.span_id)

def test_tracer_disabled():
# add some dummy tracing code.
writer = DummyWriter()
Expand Down