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106 lines
3.5 KiB
106 lines
3.5 KiB
5 years ago
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import time
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import threading
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try:
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from greenlet import getcurrent as get_ident
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except ImportError:
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try:
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from thread import get_ident
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except ImportError:
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from _thread import get_ident
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class CameraEvent(object):
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"""An Event-like class that signals all active clients when a new frame is
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available.
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"""
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def __init__(self):
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self.events = {}
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def wait(self):
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"""Invoked from each client's thread to wait for the next frame."""
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ident = get_ident()
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if ident not in self.events:
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# this is a new client
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# add an entry for it in the self.events dict
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# each entry has two elements, a threading.Event() and a timestamp
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self.events[ident] = [threading.Event(), time.time()]
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return self.events[ident][0].wait()
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def set(self):
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"""Invoked by the camera thread when a new frame is available."""
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now = time.time()
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remove = None
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for ident, event in self.events.items():
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if not event[0].isSet():
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# if this client's event is not set, then set it
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# also update the last set timestamp to now
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event[0].set()
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event[1] = now
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else:
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# if the client's event is already set, it means the client
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# did not process a previous frame
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# if the event stays set for more than 5 seconds, then assume
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# the client is gone and remove it
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if now - event[1] > 5:
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remove = ident
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if remove:
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del self.events[remove]
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def clear(self):
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"""Invoked from each client's thread after a frame was processed."""
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self.events[get_ident()][0].clear()
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class BaseCamera(object):
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thread = None # background thread that reads frames from camera
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frame = None # current frame is stored here by background thread
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last_access = 0 # time of last client access to the camera
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event = CameraEvent()
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def __init__(self):
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"""Start the background camera thread if it isn't running yet."""
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if BaseCamera.thread is None:
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BaseCamera.last_access = time.time()
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# start background frame thread
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BaseCamera.thread = threading.Thread(target=self._thread)
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BaseCamera.thread.start()
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# wait until frames are available
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while self.get_frame() is None:
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time.sleep(0)
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def get_frame(self):
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"""Return the current camera frame."""
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BaseCamera.last_access = time.time()
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# wait for a signal from the camera thread
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BaseCamera.event.wait()
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BaseCamera.event.clear()
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return BaseCamera.frame
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@staticmethod
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def frames():
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""""Generator that returns frames from the camera."""
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raise RuntimeError('Must be implemented by subclasses.')
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@classmethod
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def _thread(cls):
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"""Camera background thread."""
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print('Starting camera thread.')
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frames_iterator = cls.frames()
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for frame in frames_iterator:
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BaseCamera.frame = frame
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BaseCamera.event.set() # send signal to clients
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time.sleep(0)
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# if there hasn't been any clients asking for frames in
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# the last 10 seconds then stop the thread
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if time.time() - BaseCamera.last_access > 10:
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frames_iterator.close()
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print('Stopping camera thread due to inactivity.')
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break
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BaseCamera.thread = None
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