python之如果我在 python 中使用多处理但我的函数不返回任何内容，我是否需要调用 get()

我想利用 python 的多处理模块来并行化这个简单的例子:

import numpy as np 
import h5py 
import os 
import matplotlib.pyplot as plt 
from multiprocessing import Pool 
 
def load_array(path, variable): 
    try: 
        return np.array(h5py.File(path, "r").get(variable)) 
    except: 
        raise FileNotFoundError("Corrupted file: {}".format(path)) 
 
def mat2img(rootdir, save_path, variable): 
 
    fig = plt.figure() 
 
    print("Processing " + rootdir) 
 
    for subdir, dirs, files in os.walk(rootdir): 
        for file in files: 
            arr = load_array(os.path.join(subdir, file), variable).T 
 
            fig.subplots_adjust(top=1, bottom=0, right=1, left=0) 
            plt.pcolormesh(np.arange(0, arr.shape[1]), np.arange(0, arr.shape[0]), arr, cmap="jet") 
            plt.axis("off") 
            plt.savefig(os.path.join(save_path, subdir.split(os.path.sep)[-1], file + ".jpg")) 
            plt.clf() 
 
if __name__ == '__main__': 
 
    with Pool(processes=3) as pool: 
        pool.apply_async(mat2img, ("O:\\data1", "O:\\spectrograms", "spectrum")) 
        pool.apply_async(mat2img, ("O:\\data2", "O:\\spectrograms", "spectrum")) 
        pool.apply_async(mat2img, ("O:\\data3", "O:\\spectrograms", "spectrum")) 

然而，这没有任何作用，就好像 apply_async 没有调用任何函数一样。来自documentation我看到每个 apply_async 都分配给了某个变量 res。即使我的函数不返回任何内容，我是否也需要做同样的事情？如果是这样，该变量 res 包含什么，调用 get() 会得到什么？我哪里做错了？

请您参考如下方法:

您使用 appy_async 安排您的工作。然后你必须等到他们完成。如果您不等待，他们甚至都不会开始。

with Pool(processes=3) as pool: 
    pool.apply_async(mat2img, ("O:\\data1", "O:\\spectrograms", "spectrum")) 
    pool.apply_async(mat2img, ("O:\\data2", "O:\\spectrograms", "spectrum")) 
    pool.apply_async(mat2img, ("O:\\data3", "O:\\spectrograms", "spectrum")) 
    pool.close()  # Do not accept any more jobs. 
    pool.join(timeout=1000)  # Wait until all async jobs complete. 

或者，您可以.get() 确保每个作业完成:

with Pool(processes=3) as pool: 
    # Schedule the jobs. 
    jobs = [pool.apply_async(mat2img, (dest, "O:\\spectrograms", "spectrum")) 
            for dest in ("O:\\data1", "O:\\data2", "O:\\data3")] 
    # Wait for the jobs to complete. 
    for job in jobs: 
        job.get(timeout=100) 

正如@AndreaCorbellini 正确指出的那样，如果您的作业没有返回您关心的任何结果，您可以执行 job.wait() 而不是 job.get()。