Python中运行并行任务技巧

示例

标准线程多进程，生产者/消费者示例：
Worker越多,问题越大

# -*- coding: utf8 -*-

import os

import time

import Queue

import threading

from PIL import Image
def create_thumbnail(filename, size=(128, 128)):

    try:

        fp, fmt = filename.rsplit('.', 1)

        im = Image.open(filename)

        im.thumbnail(size, Image.ANTIALIAS)

        im.save((fp + '_'+'x'.join(str(i) for i in size) + '.'+fmt), im.format)

        return '%s thumbnail success!' % filename

    except Exception:

        return '%s thumbnail failed!' % filename


def get_image_paths(folder):

    return [os.path.join(folder, f) for f in os.listdir(folder) if 'png' in f]


class Consumer(threading.Thread):

    def __init__(self, queue):

        threading.Thread.__init__(self)

        self._queue = queue
    def run(self):

        while True:

            content = self._queue.get()

            if isinstance(content, str) and content == 'quit':

                break

            respone = create_thumbnail(content)

        print 'Bye bye!'


def Producer():

    filenames = get_image_paths('images')

    queue = Queue.Queue()

    worker_threads = build_worker_pool(queue, 4)

    start_time = time.time()
    for filename in filenames:

        queue.put(filename)

    for worker in worker_threads:

        queue.put('quit')

    for worker in worker_threads:

        worker.join()
    print time.time() - start_time


def build_worker_pool(queue, size):

    workers = []

    for _ in range(size):

        worker = Consumer(queue)

        worker.start()

        workers.append(worker)

    return workers


if __name__ == '__main__':

    Producer()

map

Map能够处理集合按顺序遍历，最终将调用产生的结果保存在一个简单的集合当中。

# -*- coding: utf8 -*-

import os

import time

from multiprocessing import Pool

from PIL import Image
def create_thumbnail(filename, size=(128, 128)):

    try:

        fp, fmt = filename.rsplit('.', 1)

        im = Image.open(filename)

        im.thumbnail(size, Image.ANTIALIAS)

        im.save((fp + '_'+'x'.join(str(i) for i in size) + '.'+fmt), im.format)

        return '%s thumbnail success!' % filename

    except Exception:

        return '%s thumbnail failed!' % filename


def get_image_paths(folder):

    return [os.path.join(folder, f) for f in os.listdir(folder) if 'png' in f]


def main():

    filenames = get_image_paths('images')

    start_time = time.time()

    

    pool = Pool(4)

    pool.map(create_thumbnail, filenames)

    pool.close()

    pool.join()
    print time.time() - start_time


if __name__ == '__main__':

    main()