先上有问题的代码：

import multiprocessing
import time
import cv2
import os

def run(ts):
    img = cv2.imread(r'E:\untitled2\Company\hccr\example\rotate.jpg')
    cv2.imwrite(os.path.join(root, 'img_{}.jpg'.format(ts)), img)
    print("end")

if __name__ == "__main__":
    t1 = time.time()
    pool = multiprocessing.Pool(processes=4)
    root = r'G:\check\ocr\hccr\data\hwdb1\trainPart1_segments'
    for i in range(3):
        pool.apply_async(run, args=(i, ))  

    pool.close()
    pool.join()   
    print("Sub-process(es) done.")
    print('cost:{}'.format(time.time() - t1))

执行后会发现，图片并没有被保存。问题出在run()函数这里，需要把要保存的根路径加到函数的参数中，def run(root, ts): ...., 在pool.apply_async(run, args(=(i,))中需要将args中加入root参数，应为pool.apply_async(run, args(=(root, i,)), 运行成功。

完整代码：

import multiprocessing
import time
import cv2
import os

def run(root, ts):  #****************改动*****************
    img = cv2.imread(r'E:\untitled2\Company\hccr\example\rotate.jpg')
    cv2.imwrite(os.path.join(root, 'img_{}.jpg'.format(ts)), img)
    print("end")

if __name__ == "__main__":
    t1 = time.time()
    pool = multiprocessing.Pool(processes=4)
    root = r'G:\check\ocr\hccr\data\hwdb1\trainPart1_segments'
    for i in range(3):
        pool.apply_async(run, args=(root, i, ))   #****************改动*****************

    pool.close()
    pool.join()  
    print("Sub-process(es) done.")
    print('cost:{}'.format(time.time() - t1))