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Avoid reference cycle between Node and ParameterService #490

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merged 4 commits into from
Jan 7, 2020
Merged

Avoid reference cycle between Node and ParameterService #490

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23fccd3
Avoid reference cycle between Node and ParameterService
ivanpauno Jan 6, 2020
69d3a62
Address peer review comments
ivanpauno Jan 6, 2020
d41fc53
Raise error if weak reference is invalid
ivanpauno Jan 6, 2020
ab994d1
Use ReferenceError instead of RuntimeError
ivanpauno Jan 6, 2020
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28 changes: 21 additions & 7 deletions rclpy/rclpy/parameter_service.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,8 @@
# See the License for the specific language governing permissions and
# limitations under the License.

import weakref

from rcl_interfaces.msg import ParameterDescriptor
from rcl_interfaces.msg import SetParametersResult
from rcl_interfaces.srv import DescribeParameters, GetParameters, GetParameterTypes
Expand All @@ -25,7 +27,7 @@
class ParameterService:

def __init__(self, node):
self._node = node
self._node_weak_ref = weakref.ref(node)
nodename = node.get_name()

describe_parameters_service_name = \
Expand Down Expand Up @@ -64,28 +66,32 @@ def __init__(self, node):
)

def _describe_parameters_callback(self, request, response):
node = self._get_node()
for name in request.names:
try:
descriptor = self._node.describe_parameter(name)
descriptor = node.describe_parameter(name)
except ParameterNotDeclaredException:
descriptor = ParameterDescriptor()
response.descriptors.append(descriptor)
return response

def _get_parameters_callback(self, request, response):
node = self._get_node()
for name in request.names:
p = self._node.get_parameter_or(name)
p = node.get_parameter_or(name)
response.values.append(p.get_parameter_value())
return response

def _get_parameter_types_callback(self, request, response):
node = self._get_node()
for name in request.names:
response.types.append(self._node.get_parameter_or(name).type_)
response.types.append(node.get_parameter_or(name).type_)
return response

def _list_parameters_callback(self, request, response):
names_with_prefixes = []
for name in self._node._parameters.keys():
node = self._get_node()
for name in node._parameters.keys():
if PARAMETER_SEPARATOR_STRING in name:
names_with_prefixes.append(name)
continue
Expand Down Expand Up @@ -125,10 +131,11 @@ def _list_parameters_callback(self, request, response):
return response

def _set_parameters_callback(self, request, response):
node = self._get_node()
for p in request.parameters:
param = Parameter.from_parameter_msg(p)
try:
result = self._node.set_parameters_atomically([param])
result = node.set_parameters_atomically([param])
except ParameterNotDeclaredException as e:
result = SetParametersResult(
successful=False,
Expand All @@ -138,12 +145,19 @@ def _set_parameters_callback(self, request, response):
return response

def _set_parameters_atomically_callback(self, request, response):
node = self._get_node()
try:
response.result = self._node.set_parameters_atomically([
response.result = node.set_parameters_atomically([
Parameter.from_parameter_msg(p) for p in request.parameters])
except ParameterNotDeclaredException as e:
response.result = SetParametersResult(
successful=False,
reason=str(e)
)
return response

def _get_node(self):
node = self._node_weak_ref()
if node is None:
raise RuntimeError('Expected valid node weak reference')
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Should this be a ValueError instead (or what is the reason to choose RuntimeError)?

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AFAIU, ValueError is used when an argument passed by the user is not of the appropiate value. There's not "argument" involved here, just an attribute of the object being invalid.

RuntimeError is the choice when the error doesn't fall in any of the other categories (link), and I don't think there is a more appropiate standard error.
I also can create a custom error if that sounds better.

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I was mostly wondering because RuntimeError is treated differently by the command line tools - they suppress the stacktrace and only show the exception string. Not sure if that is intended in this case.

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It sounds like ReferenceError is what we want here.

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It sounds like ReferenceError is what we want here.

Sounds like the right option! Updated the PR.

I was mostly wondering because RuntimeError is treated differently by the command line tools - they suppress the stacktrace and only show the exception string. Not sure if that is intended in this case.

A little off-topic:
I have observed this, and find that behavior strange. Why do the command line tools do that?

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Some kind of error messages don't warrant to show a stacktrace to the user. And in those cases we use RuntimeError.

return node