def __init__(self,
device,
adapters=(),
device_builder=None,
control_server=None):
super(Simulation, self).__init__()
self._device_builder = device_builder
self._device = device
self._adapters = AdapterCollection(*adapters)
self._speed = 1.0 # Multiplier for delta t
self._cycle_delay = 0.1 # Target time between cycles
self._start_time = None # Real time when the simulation started
self._cycles = 0 # Number of cycles processed
self._runtime = 0.0 # Total simulation time processed
self._running = False
self._started = False
self._stop_commanded = False
# Constructing the control server must be deferred until the end,
# because the construction is not complete at this point
self._control_server = None # Just initialize to None and use property setter afterwards
self.control_server = control_server
self.log.debug(
'Created simulation. Device type: %s, Protocol(s): %s, Possible setups for '
'switching: %s, Control server: %s', device.__class__.__name__,
', '.join(self._adapters.protocols),
', '.join(device_builder.setups.keys())
if device_builder else None, control_server)
def test_set_device(self):
adapter = DummyAdapter(protocol="foo")
adapter.interface = MagicMock()
collection = AdapterCollection(adapter)
collection.set_device("test")
self.assertEqual(adapter.interface.device, "test")
def __init__(self, device, adapters=(), device_builder=None, control_server=None):
super(Simulation, self).__init__()
self._device_builder = device_builder
self._device = device
self._adapters = AdapterCollection(*adapters)
self._speed = 1.0 # Multiplier for delta t
self._cycle_delay = 0.1 # Target time between cycles
self._start_time = None # Real time when the simulation started
self._cycles = 0 # Number of cycles processed
self._runtime = 0.0 # Total simulation time processed
self._running = False
self._started = False
self._stop_commanded = False
# Constructing the control server must be deferred until the end,
# because the construction is not complete at this point
self._control_server = None # Just initialize to None and use property setter afterwards
self._control_server_thread = None
self.control_server = control_server
self.log.debug(
'Created simulation. Device type: %s, Protocol(s): %s, Possible setups for '
'switching: %s, Control server: %s', device.__class__.__name__,
', '.join(self._adapters.protocols),
', '.join(device_builder.setups.keys()) if device_builder else None,
control_server)
def test_configuration(self):
collection = AdapterCollection(
DummyAdapter("protocol_a", options={
"bar": 2,
"foo": 3
}),
DummyAdapter("protocol_b", options={
"bar": True,
"foo": False
}),
)
self.assertDictEqual(
collection.configuration(),
{
"protocol_a": {
"bar": 2,
"foo": 3
},
"protocol_b": {
"bar": True,
"foo": False
},
},
)
self.assertDictEqual(
collection.configuration("protocol_a"),
{
"protocol_a": {
"bar": 2,
"foo": 3
},
},
)
self.assertDictEqual(
collection.configuration("protocol_b"),
{
"protocol_b": {
"bar": True,
"foo": False
},
},
)
def test_remove_adapter(self):
collection = AdapterCollection(DummyAdapter("foo"))
self.assertSetEqual(set(collection.protocols), {"foo"})
self.assertRaises(RuntimeError, collection.remove_adapter, "bar")
assertRaisesNothing(self, collection.remove_adapter, "foo")
self.assertEqual(len(collection.protocols), 0)
def test_remove_adapter(self):
collection = AdapterCollection(DummyAdapter('foo'))
self.assertSetEqual(set(collection.protocols), {'foo'})
self.assertRaises(RuntimeError, collection.remove_adapter, 'bar')
assertRaisesNothing(self, collection.remove_adapter, 'foo')
self.assertEqual(len(collection.protocols), 0)
def test_configuration(self):
collection = AdapterCollection(
DummyAdapter('protocol_a', options={'bar': 2, 'foo': 3}),
DummyAdapter('protocol_b', options={'bar': True, 'foo': False}))
self.assertDictEqual(collection.configuration(),
{
'protocol_a': {'bar': 2, 'foo': 3},
'protocol_b': {'bar': True,
'foo': False}
})
self.assertDictEqual(collection.configuration('protocol_a'),
{
'protocol_a': {'bar': 2, 'foo': 3},
})
self.assertDictEqual(collection.configuration('protocol_b'),
{
'protocol_b': {'bar': True, 'foo': False},
})
def test_add_adapter(self):
collection = AdapterCollection()
self.assertEqual(len(collection.protocols), 0)
assertRaisesNothing(self, collection.add_adapter, DummyAdapter('foo'))
self.assertEqual(len(collection.protocols), 1)
self.assertSetEqual(set(collection.protocols), {'foo'})
assertRaisesNothing(self, collection.add_adapter, DummyAdapter('bar'))
self.assertEqual(len(collection.protocols), 2)
self.assertSetEqual(set(collection.protocols), {'foo', 'bar'})
self.assertRaises(RuntimeError, collection.add_adapter, DummyAdapter('bar'))
def test_add_adapter(self):
collection = AdapterCollection()
self.assertEqual(len(collection.protocols), 0)
assertRaisesNothing(self, collection.add_adapter, DummyAdapter("foo"))
self.assertEqual(len(collection.protocols), 1)
self.assertSetEqual(set(collection.protocols), {"foo"})
assertRaisesNothing(self, collection.add_adapter, DummyAdapter("bar"))
self.assertEqual(len(collection.protocols), 2)
self.assertSetEqual(set(collection.protocols), {"foo", "bar"})
self.assertRaises(RuntimeError, collection.add_adapter,
DummyAdapter("bar"))
class Simulation(object):
"""
The Simulation class controls certain aspects of a device simulation,
the most important one being time.
Once :meth:`start` is called, the process-method of the device
is called in regular intervals. The time between these calls is
influenced by the cycle_delay property. Because of the way some
network protocols work, the actual processing time can be
longer or shorter, so cycle_delay should be seen as a guideline
rather than a guaranteed parameter.
In the simplest case, the actual time-delta between two cycles
is passed to the simulated device so that it can update its internal
state according to the elapsed time. It is however possible to set
a simulation speed, which serves as a multiplier for this time.
If the speed is set to 2 and 0.1 seconds pass between two cycles,
the simulation is asked to simulate 0.2 seconds, and so on. Speed 0
effectively stops all time dependent calculations in the
simulated device.
Another possibility to pause the simulation is the pause-method. After
calling it, all processing in the device is suspended, while the communication
adapters continue to work. This can be used to simulate that a device is "hanging".
The simulation can be continued using the resume-method.
A number of status properties provide information about the simulation.
The total uptime (in actually elapsed time) can be obtained through the
uptime-property, whereas the runtime-property contains the simulated time.
The cycles-property indicates the total number of simulation cycles, which
does not increase when the simulation is paused.
Finally, the simulation can be stopped entirely with the stop-method.
All functionality except for the start-method can be made available to remote
computers via a :class:`ControlServer`-instance. The way to expose device and simulation
is to pass a 'host:port'-string as the control_server argument,
which will construct the control server. Simulation will try to start the
control server using the start_server method.
:param device: The simulated device.
:param adapters: Adapters which expose the simulated device.
:param device_builder: :class:`~lewis.core.devices.DeviceBuilder` instance to enable setup-
switching at runtime.
:param control_server: 'host:port'-string to construct control server or None.
"""
def __init__(self,
device,
adapters=(),
device_builder=None,
control_server=None):
super(Simulation, self).__init__()
self._device_builder = device_builder
self._device = device
self._adapters = AdapterCollection(*adapters)
self._speed = 1.0 # Multiplier for delta t
self._cycle_delay = 0.1 # Target time between cycles
self._start_time = None # Real time when the simulation started
self._cycles = 0 # Number of cycles processed
self._runtime = 0.0 # Total simulation time processed
self._running = False
self._started = False
self._stop_commanded = False
# Constructing the control server must be deferred until the end,
# because the construction is not complete at this point
self._control_server = None # Just initialize to None and use property setter afterwards
self.control_server = control_server
self.log.debug(
'Created simulation. Device type: %s, Protocol(s): %s, Possible setups for '
'switching: %s, Control server: %s', device.__class__.__name__,
', '.join(self._adapters.protocols),
', '.join(device_builder.setups.keys())
if device_builder else None, control_server)
def _create_control_server(self, control_server):
if control_server is None:
return None
return ControlServer(
{
'device':
ExposedObject(self._device,
exclude_inherited=True,
lock=self._adapters.device_lock),
'simulation':
ExposedObject(self,
exclude=('start', 'control_server', 'log'),
exclude_inherited=True),
'interface':
ExposedObject(self._adapters,
exclude=('device_lock', 'add_adapter',
'remove_adapter', 'handle', 'log'),
exclude_inherited=True)
}, control_server)
@property
def setups(self):
"""
A list of setups that are available. Use :meth:`switch_setup` to
change the setup.
"""
return list(self._device_builder.setups.keys()
) if self._device_builder is not None else []
def switch_setup(self, new_setup):
"""
This method switches the setup, which means that it replaces the currently
simulated device with a new device, as defined by the setup.
If any error occurs during setup switching it is logged and re-raised.
:param new_setup: Name of the new setup to load.
"""
try:
self._device = self._device_builder.create_device(new_setup)
self._adapters.set_device(self._device)
self.log.info('Switched setup to \'%s\'', new_setup)
except Exception as e:
self.log.error(
'Caught an error while trying to switch setups. Setup not switched, '
'simulation continues: %s', e)
raise
def start(self):
"""
Starts the simulation.
"""
self.log.info('Starting simulation')
self._running = True
self._started = True
self._stop_commanded = False
if self._control_server is not None:
self._control_server.start_server()
self._adapters.connect()
self._start_time = datetime.now()
delta = 0.0
while not self._stop_commanded:
delta = self._process_cycle(delta)
self._running = False
self._started = False
self._adapters.disconnect()
def _process_cycle(self, delta):
"""
Processes one cycle, which consists of one simulation cycle and processing
of control server commands. The method measures how long all this takes
and returns the elapsed time in seconds.
:param delta: Elapsed time in last cycle, passed to simulation.
:return: Elapsed time in this cycle.
"""
start = datetime.now()
self._process_simulation_cycle(delta)
delta = seconds_since(start)
return delta
def _process_simulation_cycle(self, delta):
"""
If the simulation is not paused, the device's process-method is
called with the supplied delta, multiplied by the simulation speed.
If the simulation is paused, the process sleeps for the duration
of one cycle_delay.
:param delta: Time delta passed to simulation.
"""
self.log.debug('Cycle, dt=%s', delta)
sleep(self._cycle_delay)
if self._running:
delta_simulation = delta * self._speed
with self._adapters.device_lock:
self._device.process(delta_simulation)
if self._control_server:
self._control_server.process()
self._cycles += 1
self._runtime += delta_simulation
@property
def cycle_delay(self):
"""
Desired time between simulation cycles, this can not be negative.
Use 0 for highest possible processing rate.
"""
return self._cycle_delay
@cycle_delay.setter
def cycle_delay(self, delay):
if delay < 0.0:
raise ValueError('Cycle delay can not be negative.')
self._cycle_delay = delay
self.log.info('Changed cycle delay to %s', self._cycle_delay)
@property
def cycles(self):
"""
Simulation cycles processed since start has been called.
"""
return self._cycles
@property
def uptime(self):
"""
Elapsed time in seconds since the simulation has been started.
"""
if not self._started:
return 0.0
return seconds_since(self._start_time)
@property
def speed(self):
"""
Simulation speed. Actual elapsed time is multiplied with this property
to determine simulated time. Values greater than 1 increase the simulation
speed, values between 1 and 0 decrease it. A speed of 0 effectively pauses
the simulation.
"""
return self._speed
@speed.setter
def speed(self, new_speed):
if new_speed < 0:
raise ValueError('Speed can not be negative.')
self._speed = new_speed
self.log.info('Changed speed to %s', self._speed)
@property
def runtime(self):
"""
The accumulated simulation time. Whenever speed is different from 1, this
progresses at a different rate than uptime.
"""
return self._runtime
def set_device_parameters(self, parameters):
"""
Set multiple parameters of the simulated device "simultaneously". The passed
parameter is assumed to be device parameter/value dict.
The method only allows to set existing attributes. If there are invalid
attribute names, the attributes are not updated, instead a RuntimeError
is raised. The same happens if any of the parameters are methods, which
can not be updated with this mechanisms.
:param parameters: Dict of device attribute/values to update the device.
"""
invalid_parameters = set(parameters.keys()) - set(
x for x in dir(self._device)
if not callable(getattr(self._device, x)))
if invalid_parameters:
raise RuntimeError(
'The following parameters do not exist in the device or are methods: {}.'
'Parameters not updated.'.format(invalid_parameters))
with self._adapters.device_lock:
for name, value in parameters.items():
setattr(self._device, name, value)
self.log.debug('Updated device parameters: %s', parameters)
def pause(self):
"""
Pause the simulation. Can only be called after start has been called.
"""
if not self._running:
raise RuntimeError('Can only pause a running simulation.')
self.log.info('Pausing simulation')
self._running = False
def resume(self):
"""
Resume a paused simulation. Can only be called after start
and pause have been called.
"""
if not self._started or self._running:
raise RuntimeError('Can only resume a paused simulation.')
self.log.info('Resuming simulation')
self._running = True
def stop(self):
"""
Stops the simulation entirely.
"""
self.log.warning('Stopping simulation')
self._stop_commanded = True
@property
def is_started(self):
"""
This property is true if the simulation has been started.
"""
return self._started
@property
def is_paused(self):
"""
True if the simulation is paused (implies that the simulation has been started).
"""
return self._started and not self._running
@property
def control_server(self):
"""
ControlServer-instance that exposes the object to remote machines. Can only
be set before start has been called or on a running simulation if no
control server was previously present. If the server is not running, it will be started
after it has been set.
"""
return self._control_server
@control_server.setter
def control_server(self, control_server):
if self.is_started and self._control_server:
raise RuntimeError(
'Can not replace control server while simulation is running.')
self._control_server = self._create_control_server(control_server)
if self.is_started and self._control_server is not None:
self._control_server.start_server()
def test_connect_disconnect_connected(self):
collection = AdapterCollection(DummyAdapter("foo", running=False),
DummyAdapter("bar", running=False))
# no arguments connects everything
collection.connect()
self.assertDictEqual(collection.is_connected(), {
"bar": True,
"foo": True
})
self.assertTrue(collection.is_connected("bar"))
self.assertTrue(collection.is_connected("foo"))
collection.disconnect()
self.assertDictEqual(collection.is_connected(), {
"bar": False,
"foo": False
})
self.assertFalse(collection.is_connected("bar"))
self.assertFalse(collection.is_connected("foo"))
collection.connect("foo")
self.assertDictEqual(collection.is_connected(), {
"bar": False,
"foo": True
})
self.assertFalse(collection.is_connected("bar"))
self.assertTrue(collection.is_connected("foo"))
self.assertRaises(RuntimeError, collection.connect, "baz")
self.assertRaises(RuntimeError, collection.disconnect, "baz")
collection.disconnect() # Clean up so that the test does not hang
class Simulation(object):
"""
The Simulation class controls certain aspects of a device simulation,
the most important one being time.
Once :meth:`start` is called, the process-method of the device
is called in regular intervals. The time between these calls is
influenced by the cycle_delay property. Because of the way some
network protocols work, the actual processing time can be
longer or shorter, so cycle_delay should be seen as a guideline
rather than a guaranteed parameter.
In the simplest case, the actual time-delta between two cycles
is passed to the simulated device so that it can update its internal
state according to the elapsed time. It is however possible to set
a simulation speed, which serves as a multiplier for this time.
If the speed is set to 2 and 0.1 seconds pass between two cycles,
the simulation is asked to simulate 0.2 seconds, and so on. Speed 0
effectively stops all time dependent calculations in the
simulated device.
Another possibility to pause the simulation is the pause-method. After
calling it, all processing in the device is suspended, while the communication
adapters continue to work. This can be used to simulate that a device is "hanging".
The simulation can be continued using the resume-method.
A number of status properties provide information about the simulation.
The total uptime (in actually elapsed time) can be obtained through the
uptime-property, whereas the runtime-property contains the simulated time.
The cycles-property indicates the total number of simulation cycles, which
does not increase when the simulation is paused.
Finally, the simulation can be stopped entirely with the stop-method.
All functionality except for the start-method can be made available to remote
computers via a :class:`ControlServer`-instance. The way to expose device and simulation
is to pass a 'host:port'-string as the control_server argument,
which will construct the control server. Simulation will try to start the
control server using the start_server method.
:param device: The simulated device.
:param adapters: Adapters which expose the simulated device.
:param device_builder: :class:`~lewis.core.devices.DeviceBuilder` instance to enable setup-
switching at runtime.
:param control_server: 'host:port'-string to construct control server or None.
"""
def __init__(self, device, adapters=(), device_builder=None, control_server=None):
super(Simulation, self).__init__()
self._device_builder = device_builder
self._device = device
self._adapters = AdapterCollection(*adapters)
self._speed = 1.0 # Multiplier for delta t
self._cycle_delay = 0.1 # Target time between cycles
self._start_time = None # Real time when the simulation started
self._cycles = 0 # Number of cycles processed
self._runtime = 0.0 # Total simulation time processed
self._running = False
self._started = False
self._stop_commanded = False
# Constructing the control server must be deferred until the end,
# because the construction is not complete at this point
self._control_server = None # Just initialize to None and use property setter afterwards
self._control_server_thread = None
self.control_server = control_server
self.log.debug(
'Created simulation. Device type: %s, Protocol(s): %s, Possible setups for '
'switching: %s, Control server: %s', device.__class__.__name__,
', '.join(self._adapters.protocols),
', '.join(device_builder.setups.keys()) if device_builder else None,
control_server)
def _create_control_server(self, control_server):
if control_server is None:
return None
return ControlServer({
'device': ExposedObject(
self._device,
exclude_inherited=True,
lock=self._adapters.device_lock
),
'simulation': ExposedObject(
self,
exclude=('start', 'control_server', 'log'),
exclude_inherited=True
),
'interface': ExposedObject(
self._adapters,
exclude=('device_lock', 'add_adapter', 'remove_adapter', 'handle', 'log'),
exclude_inherited=True
)},
control_server)
@property
def setups(self):
"""
A list of setups that are available. Use :meth:`switch_setup` to
change the setup.
"""
return list(self._device_builder.setups.keys()) if self._device_builder is not None else []
def switch_setup(self, new_setup):
"""
This method switches the setup, which means that it replaces the currently
simulated device with a new device, as defined by the setup.
If any error occurs during setup switching it is logged and re-raised.
:param new_setup: Name of the new setup to load.
"""
try:
self._device = self._device_builder.create_device(new_setup)
self._adapters.set_device(self._device)
self.log.info('Switched setup to \'%s\'', new_setup)
except Exception as e:
self.log.error(
'Caught an error while trying to switch setups. Setup not switched, '
'simulation continues: %s', e)
raise
def start(self):
"""
Starts the simulation.
"""
self.log.info('Starting simulation')
self._running = True
self._started = True
self._stop_commanded = False
self._start_control_server()
self._adapters.connect()
self._start_time = datetime.now()
delta = 0.0
while not self._stop_commanded:
delta = self._process_cycle(delta)
self._running = False
self._started = False
self.log.info('Simulation has ended.')
def _start_control_server(self):
if self._control_server is not None and self._control_server_thread is None:
def control_server_loop():
self._control_server.start_server()
while not self._stop_commanded:
self._control_server.process(blocking=True)
self.log.info('Stopped processing control server commands, ending thread.')
self._control_server_thread = Thread(target=control_server_loop)
self._control_server_thread.start()
def _stop_control_server(self):
if self._control_server_thread is not None:
self._control_server_thread.join(timeout=1.0)
self._control_server_thread = None
def _process_cycle(self, delta):
"""
Processes one cycle, which consists of one simulation cycle and processing
of control server commands. The method measures how long all this takes
and returns the elapsed time in seconds.
:param delta: Elapsed time in last cycle, passed to simulation.
:return: Elapsed time in this cycle.
"""
start = datetime.now()
self._process_simulation_cycle(delta)
delta = seconds_since(start)
return delta
def _process_simulation_cycle(self, delta):
"""
If the simulation is not paused, the device's process-method is
called with the supplied delta, multiplied by the simulation speed.
If the simulation is paused, the process sleeps for the duration
of one cycle_delay.
:param delta: Time delta passed to simulation.
"""
self.log.debug('Cycle, dt=%s', delta)
sleep(self._cycle_delay)
if self._running:
delta_simulation = delta * self._speed
with self._adapters.device_lock:
self._device.process(delta_simulation)
self._cycles += 1
self._runtime += delta_simulation
@property
def cycle_delay(self):
"""
Desired time between simulation cycles, this can not be negative.
Use 0 for highest possible processing rate.
"""
return self._cycle_delay
@cycle_delay.setter
def cycle_delay(self, delay):
if delay < 0.0:
raise ValueError('Cycle delay can not be negative.')
self._cycle_delay = delay
self.log.info('Changed cycle delay to %s', self._cycle_delay)
@property
def cycles(self):
"""
Simulation cycles processed since start has been called.
"""
return self._cycles
@property
def uptime(self):
"""
Elapsed time in seconds since the simulation has been started.
"""
if not self._started:
return 0.0
return seconds_since(self._start_time)
@property
def speed(self):
"""
Simulation speed. Actual elapsed time is multiplied with this property
to determine simulated time. Values greater than 1 increase the simulation
speed, values between 1 and 0 decrease it. A speed of 0 effectively pauses
the simulation.
"""
return self._speed
@speed.setter
def speed(self, new_speed):
if new_speed < 0:
raise ValueError('Speed can not be negative.')
self._speed = new_speed
self.log.info('Changed speed to %s', self._speed)
@property
def runtime(self):
"""
The accumulated simulation time. Whenever speed is different from 1, this
progresses at a different rate than uptime.
"""
return self._runtime
def set_device_parameters(self, parameters):
"""
Set multiple parameters of the simulated device "simultaneously". The passed
parameter is assumed to be device parameter/value dict.
The method only allows to set existing attributes. If there are invalid
attribute names, the attributes are not updated, instead a RuntimeError
is raised. The same happens if any of the parameters are methods, which
can not be updated with this mechanisms.
:param parameters: Dict of device attribute/values to update the device.
"""
invalid_parameters = set(parameters.keys()) - set(
x for x in dir(self._device) if not callable(getattr(self._device, x)))
if invalid_parameters:
raise RuntimeError(
'The following parameters do not exist in the device or are methods: {}.'
'Parameters not updated.'.format(invalid_parameters))
with self._adapters.device_lock:
for name, value in parameters.items():
setattr(self._device, name, value)
self.log.debug('Updated device parameters: %s', parameters)
def pause(self):
"""
Pause the simulation. Can only be called after start has been called.
"""
if not self._running:
raise RuntimeError('Can only pause a running simulation.')
self.log.info('Pausing simulation')
self._running = False
def resume(self):
"""
Resume a paused simulation. Can only be called after start
and pause have been called.
"""
if not self._started or self._running:
raise RuntimeError('Can only resume a paused simulation.')
self.log.info('Resuming simulation')
self._running = True
def stop(self):
"""
Stops the simulation entirely.
"""
if self.is_started:
self.log.warning('Stopping simulation')
self._stop_commanded = True
self._stop_control_server()
self._adapters.disconnect()
@property
def is_started(self):
"""
This property is true if the simulation has been started.
"""
return self._started
@property
def is_paused(self):
"""
True if the simulation is paused (implies that the simulation has been started).
"""
return self._started and not self._running
@property
def control_server(self):
"""
ControlServer-instance that exposes the object to remote machines. Can only
be set before start has been called or on a running simulation if no
control server was previously present. If the server is not running, it will be started
after it has been set.
"""
return self._control_server
@control_server.setter
def control_server(self, control_server):
if self.is_started and self._control_server:
raise RuntimeError('Can not replace control server while simulation is running.')
self._control_server = self._create_control_server(control_server)
if self.is_started and self._control_server is not None:
self._control_server.start_server()
def test_connect_disconnect_connected(self):
collection = AdapterCollection(
DummyAdapter('foo', running=False), DummyAdapter('bar', running=False))
# no arguments connects everything
collection.connect()
self.assertDictEqual(collection.is_connected(), {'bar': True, 'foo': True})
self.assertTrue(collection.is_connected('bar'))
self.assertTrue(collection.is_connected('foo'))
collection.disconnect()
self.assertDictEqual(collection.is_connected(), {'bar': False, 'foo': False})
self.assertFalse(collection.is_connected('bar'))
self.assertFalse(collection.is_connected('foo'))
collection.connect('foo')
self.assertDictEqual(collection.is_connected(), {'bar': False, 'foo': True})
self.assertFalse(collection.is_connected('bar'))
self.assertTrue(collection.is_connected('foo'))
self.assertRaises(RuntimeError, collection.connect, 'baz')
self.assertRaises(RuntimeError, collection.disconnect, 'baz')
collection.disconnect() # Clean up so that the test does not hang