added video_threaded.py sample

samples/python2/video_threaded.py

+import numpy as np
+import cv2
+
+from Queue import Queue
+from threading import Thread
+from collections import deque
+
+class Worker(Thread):
+    def __init__(self, tasks):
+        Thread.__init__(self)
+        self.tasks = tasks
+        self.daemon = True
+        self.start()
+    
+    def run(self):
+        while True:
+            func, args, kargs = self.tasks.get()
+            try: func(*args, **kargs)
+            except Exception, e: print e
+            self.tasks.task_done()
+
+class ThreadPool:
+    def __init__(self, num_threads):
+        self.tasks = Queue(num_threads)
+        for _ in range(num_threads): Worker(self.tasks)
+
+    def add_task(self, func, *args, **kargs):
+        self.tasks.put((func, args, kargs))
+
+    def wait_completion(self):
+        self.tasks.join()
+
+if __name__ == '__main__':
+    results = deque()
+
+    def process_frame(i, frame):
+        global results
+        res = cv2.medianBlur(frame, 15)
+        results.append((i, res))
+    
+    pool = ThreadPool(4)
+    cap = cv2.VideoCapture(0)
+    frame_count = 0
+    last_frame = None
+    last_count = -1
+    while True:
+        ret, frame = cap.read()
+        pool.add_task(process_frame, frame_count, frame.copy())
+        frame_count += 1
+        while len(results) > 0:
+            i, frame = results.popleft()
+            if i > last_count:
+                last_count, last_frame = i, frame
+        if last_frame is not None:
+            cv2.imshow('res', last_frame)
+        if cv2.waitKey(1) == 27:
+            break
+
+    pool.wait_completion()
+
+
+
+