[rclpy] Create a package with an example showing how guard conditions work

rclpy/guard_conditions/examples_rclpy_guard_conditions/trigger_guard_condition.py

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+# Copyright 2020 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import rclpy
+
+
+def main(args=None):
+
+    rclpy.init(args=args)
+    node = rclpy.create_node('demo_guard_condition')
+    executor = rclpy.executors.SingleThreadedExecutor()
+    executor.add_node(node)
+
+    def guard_condition_callback():
+        rclpy.shutdown()
+        node.get_logger().info('guard callback called shutdown')
+
+    def timer_callback():
+        guard_condition.trigger()
+        node.get_logger().info('timer callback triggered guard condition')
+
+    node.create_timer(timer_period_sec=2, callback=timer_callback)
+    guard_condition = node.create_guard_condition(guard_condition_callback)
+
+    while rclpy.ok():
+        # First loop: `spin_once` waits for timer to be ready, then calls
+        #   the timer's callback, which triggers the guard condition.
+        # Second loop: The guard condition is ready so it's callback is
+        #   called. The callback calls shutdown, so the loop doesn't run
+        #   again and the program exits.
+        node.get_logger().info("waiting for 'spin_once' to finish...")
+        executor.spin_once()
+        node.get_logger().info("...'spin_once' finished!\n")
+
+
+if __name__ == '__main__':
+    main()

rclpy/guard_conditions/package.xml

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+<?xml version="1.0"?>
+<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
+<package format="3">
+  <name>examples_rclpy_guard_conditions</name>
+  <version>0.9.2</version>
+  <description>Examples of using guard conditions.</description>
+  <maintainer email="audrow@openrobotics.org">Audrow Nash</maintainer>
+  <license>Apache License 2.0</license>
+
+  <exec_depend>rclpy</exec_depend>
+
+  <test_depend>ament_copyright</test_depend>
+  <test_depend>ament_flake8</test_depend>
+  <test_depend>ament_pep257</test_depend>
+  <test_depend>python3-pytest</test_depend>
+
+  <export>
+    <build_type>ament_python</build_type>
+  </export>
+</package>

rclpy/guard_conditions/setup.cfg

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+[develop]
+script-dir=$base/lib/examples_rclpy_guard_conditions
+[install]
+install-scripts=$base/lib/examples_rclpy_guard_conditions

rclpy/guard_conditions/setup.py

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+from setuptools import setup
+
+package_name = 'examples_rclpy_guard_conditions'
+
+setup(
+    name=package_name,
+    version='0.9.2',
+    packages=[package_name],
+    data_files=[
+        ('share/ament_index/resource_index/packages', ['resource/' + package_name]),
+        ('share/' + package_name, ['package.xml']),
+    ],
+    install_requires=['setuptools'],
+    zip_safe=True,
+    maintainer='Audrow Nash',
+    maintainer_email='audrow@openrobotics.com',
+    keywords=['ROS'],
+    classifiers=[
+        'Intended Audience :: Developers',
+        'License :: OSI Approved :: Apache Software License',
+        'Programming Language :: Python',
+        'Topic :: Software Development',
+    ],
+    description='Examples of using guard conditions.',
+    license='Apache License, Version 2.0',
+    tests_require=['pytest'],
+    entry_points={
+        'console_scripts': [
+            'trigger_guard_condition = '
+            'examples_rclpy_guard_conditions.trigger_guard_condition:main'
+        ],
+    },
+)

rclpy/guard_conditions/test/test_copyright.py

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+# Copyright 2015 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ament_copyright.main import main
+import pytest
+
+
+@pytest.mark.copyright
+@pytest.mark.linter
+def test_copyright():
+    rc = main(argv=['.', 'test'])
+    assert rc == 0, 'Found errors'

rclpy/guard_conditions/test/test_flake8.py

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+# Copyright 2017 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ament_flake8.main import main_with_errors
+import pytest
+
+
+@pytest.mark.flake8
+@pytest.mark.linter
+def test_flake8():
+    rc, errors = main_with_errors(argv=[])
+    assert rc == 0, \
+        'Found %d code style errors / warnings:\n' % len(errors) + \
+        '\n'.join(errors)

rclpy/guard_conditions/test/test_pep257.py

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+# Copyright 2015 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ament_pep257.main import main
+import pytest
+
+
+@pytest.mark.linter
+@pytest.mark.pep257
+def test_pep257():
+    rc = main(argv=['.', 'test'])
+    assert rc == 0, 'Found code style errors / warnings'