python - 如何从python中的线程池中获取结果？

Question

我在这里搜索了如何在 python 中进行线程化，但到目前为止我还没有得到我需要的答案。 我对 Queue 和 Threading python 类不是很熟悉，因此这里提供的一些答案对我来说毫无意义。

我想创建一个线程池，我可以提供不同的任务，当所有线程都结束时，获取结果值并处理它们。 到目前为止，我已经尝试过这样做，但我无法得到结果。我写的代码是:

from threading import Thread
from Queue import Queue

class Worker(Thread):
    """Thread executing tasks from a given tasks queue"""
    def __init__(self, tasks):
        Thread.__init__(self)
        self.tasks = tasks
        self.daemon = True
        self.result = None
        self.start()
    def run(self):
        while True:
            func, args, kargs = self.tasks.get()
            try:
                self.result = func(*args, **kargs)
            except Exception, e:
                print e
            self.tasks.task_done()
    def get_result(self):
        return self.result

class ThreadPool:
    """Pool of threads consuming tasks from a queue"""
    def __init__(self, num_threads):
        self.tasks = Queue(num_threads)
        self.results = []
        for _ in range(num_threads):
            w = Worker(self.tasks)
            self.results.append(w.get_result())
    def add_task(self, func, *args, **kargs):
        """Add a task to the queue"""
        self.tasks.put((func, args, kargs))
    def wait_completion(self):
        """Wait for completion of all the tasks in the queue"""
        self.tasks.join()
    def get_results(self):
        return self.results

def foo(word, number):
    print word*number
    return number

words = ['hello', 'world', 'test', 'word', 'another test']
numbers = [1,2,3,4,5]
pool = ThreadPool(5)
for i in range(0, len(words)):
    pool.add_task(foo, words[i], numbers[i])

pool.wait_completion()
results = pool.get_results()
print results

输出打印带有单词给定乘以给定数字的字符串，但结果列表充满了 None 值，所以我应该把 func 的返回值放在哪里。

或者简单的方法是创建一个列表，在其中填充队列并添加字典或一些变量以将结果作为参数存储到我的函数中，然后在将任务添加到队列后将此结果参数添加到结果列表:

def foo(word, number, r):
    print word*number
    r[(word,number)] = number
    return number

words = ['hello', 'world', 'test', 'word', 'another test']
numbers = [1,2,3,4,5]
pool = ThreadPool(5)
results = []
for i in range(0, len(words)):
    r = {}
    pool.add_task(foo, words[i], numbers[i], r)
    results.append(r)
print results

Answer 1

在 Python 3.x 中，您可以使用 concurrent.futures.ThreadPoolExecutor这样做，而不是自己动手。

Python 2.x 实际上有一个你也可以使用的内置线程池，its just not well documented :

from multiprocessing.pool import ThreadPool

def foo(word, number):
    print (word * number)
    r[(word,number)] = number
    return number

words = ['hello', 'world', 'test', 'word', 'another test']
numbers = [1,2,3,4,5]
pool = ThreadPool(5)
results = []
for i in range(0, len(words)):
    results.append(pool.apply_async(foo, args=(words[i], numbers[i])))

pool.close()
pool.join()
results = [r.get() for r in results]
print results

或者(使用 map 而不是 apply_async):

from multiprocessing.pool import ThreadPool

def foo(word, number):
    print word*number
    return number

def starfoo(args):
    """ 

    We need this because map only supports calling functions with one arg. 
    We need to pass two args, so we use this little wrapper function to
    expand a zipped list of all our arguments.
    
    """    
    return foo(*args)

words = ['hello', 'world', 'test', 'word', 'another test']
numbers = [1,2,3,4,5]
pool = ThreadPool(5)
# We need to zip together the two lists because map only supports calling functions
# with one argument. In Python 3.3+, you can use starmap instead.
results = pool.map(starfoo, zip(words, numbers))
print results

pool.close()
pool.join()