线程池很慢，速度和seri相同

Question

我正在努力加快计算速度，以便进行广泛的实时目标检测，并对其进行计算。你知道吗

我用OpenCV和线程池，生产者和消费者的视频捕获。但是执行速度和串行的一样。你知道吗

如何提高执行速度？你知道吗

if __name__ == "__main__":
    video_name = '2016-11-18_07-30-01.h264'

    cap = cv2.VideoCapture(video_name)

    det = detector.CarDetector()
    car_tracker = Sort_Algorithm.Sort()
    ped_tracker = Sort_Algorithm.Sort()
    df_region, df_line = load_filter()
    region = Region(df_region)
    distance = compute_max_polygon_diagonal(df_region) * 0.1
    region_buffered = region.buffer(distance)

    threadn = cv2.getNumberOfCPUs()
    pool = ThreadPool(processes = 2)
    pending = deque()
    threaded_mode = True
    lock = threading.Lock()
    while True:
        while len(pending) > 0 and pending[0].ready():
            res = pending.popleft().get()
            cv2.imshow('video ', res)

        if  len(pending) < threadn:
            ret, frame = cap.read()
            if threaded_mode:
                t1 = time.time()
                H = [-2.01134074616, -16.6502442427, -1314.05715739, -3.35391526592, -22.3546973012, 2683.63584335,
                     -0.00130731963137, -0.0396207582264, 1]
                matrix = np.reshape(H, (3, 3))
                dst = cv2.warpPerspective(frame.copy(), matrix, (frame.shape[1], frame.shape[0]))
                task = pool.apply_async(pipeline, (lock, frame.copy(),car_tracker, ped_tracker,df_region,region_buffered, df_line, det, dst, matrix))

                cv2.imshow('dst', dst)
            else:
                task = DummyTask(pipeline,(lock, frame.copy(),car_tracker, ped_tracker,df_region, region_buffered, df_line, det, dst, matrix))

            pending.append(task)
        ch = cv2.waitKey(1)
        if ch == ord(' '):
            threaded_mode = not threaded_mode
        if ch == 27:
            break

管道规范：

def pipeline(lock, img, car_tracker, ped_tracker, df_region, region_buffered, df_line, det, dst, H):
    lock.acquire()
    global point_lists
    global df_car_lists
    global frame_idx
    global counter
    global  data_peds
    global  data_cars
    global  genera_data_pd_cars
    global  genera_data_pd_peds

    car_box, ped_box = det.get_localization(img)
    car_detections = car_tracker.update(np.array(car_box))
    ped_detections = ped_tracker.update(np.array(ped_box))
    saved_region = df_region.values
    saved_region = np.delete(saved_region, 2, 1)
    frame_idx+=1
    cv2.warpPerspective(np.array(df_line, dtype=np.float32), H, (df_line.shape[1], df_line.shape[0]))

    cv2.polylines(dst, np.int32([[saved_region]]), False, color=(255, 0, 0))
    cv2.polylines(dst, np.int32([np.array(df_line, dtype=np.float32)]), False, color=(255, 0, 0))

    for trk in car_detections:
        trk = trk.astype(np.int32)
        helpers.draw_box_label(img, trk, trk[4])  # Draw the bounding boxes on the

    for other in ped_detections:
            other = other.astype(np.int32)
            helpers.draw_box_label(img, other, other[4])  # Draw the bounding boxes on the

    for trk in car_detections:
        trk = trk.astype(np.int32)
        p = np.array([[((trk[1] + trk[3]) / 2,  (trk[0] + trk[2]) / 2)]], dtype=np.float32)
        center_pt = cv2.perspectiveTransform(p, H)
        ptx = center_pt.T.item(0)
        pty = center_pt.T.item(1)
        df_cars = compute(trk[4], ptx, pty, frame_idx, df_region, region_buffered, df_line)
        genera_data_pd_cars = genera_data_pd_cars.append(df_cars)
        for other in ped_detections:
            other = other.astype(np.int32)
            p = np.array([[((other[1] + other[3]) / 2, (other[0] + other[2]) / 2)]], dtype=np.float32)
            center_pt = cv2.perspectiveTransform(p, H)
            ptx = center_pt.T.item(0)
            pty = center_pt.T.item(1)
            df_peds = compute(other[4], ptx, pty, frame_idx, df_region, region_buffered, df_line)
            genera_data_pd_peds = genera_data_pd_cars.append(df_peds)
            query = "is_in_region == True and is_in_region_now == True"
            df_peds = genera_data_pd_peds.query(query)
            query = " is_in_region == True"
            df_cars = genera_data_pd_cars.query(query)
            if len(df_cars)> 1 and len(df_peds) > 1:

                df_car_in_t_range_ped = select_slice(df_cars, df_peds)
                df_ped_in_t_range_car = select_slice(df_peds, df_cars)
                t_abs_crossing_car = df_cars['t_abs_at_crossing'].iloc[0]
                t_abs_crossing_ped = df_peds['t_abs_at_crossing'].iloc[0]

                dt_crossing = t_abs_crossing_car - t_abs_crossing_ped

                is_able_to_pass_before_ped = \
                    ((df_car_in_t_range_ped['t_abs_at_crossing_estimated'] -
                      t_abs_crossing_ped) > 0).any()

                behavior = Behavior(  # is_passed_before_ped
                    dt_crossing < 0,
                    # is_able_to_stop
                    df_car_in_t_range_ped['is_able_to_halt'].any(),
                    # is_too_fast
                    df_car_in_t_range_ped['is_too_fast'].any(),
                    # is_close_enough
                    df_car_in_t_range_ped['is_close_enough'].any(),
                    # is_able_to_pass_before_ped
                    is_able_to_pass_before_ped)

                interaction = Interaction(trk[4], other[4])
                interaction = interaction.assess_behavior(behavior)
                code, res, msg = interaction.code, interaction.res, interaction.msg
                print(msg)
                genera_data_pd_cars = genera_data_pd_cars.iloc[0:0]
                genera_data_pd_peds = genera_data_pd_peds.iloc[0:0]
    lock.release()
    return img

Answer 1

线程不是在cpython中并行执行的。尝试改用ProcessPoolExecutor。你知道吗

Answer 2

python中用于CPU受限任务的多线程受到GIL的限制，有效地使单线程一次运行。你知道吗

当然，如果为CPU受限的任务启动多个线程，性能甚至会下降，因为内核和python解释器管理这些线程的开销都很大。你知道吗

内核想要调度这些线程，而python想要限制这些线程同时运行，这会导致大量的上下文切换，从而降低性能。你知道吗

如果在线程中只使用numpy，那么就可以了，因为numpy不受GIL的影响，因为它使用原子操作，但是我不确定OpenCV是否也是这样。你知道吗

python中的线程不适用于计算任务。你知道吗

这是python线程的典型问题，请考虑使用multiprocessing并且有很多关于这个主题的文章，您可能想检查其中的一些。你知道吗