python 设置未来状态

Question

设置未来的状态来传递参数是不好的做法吗？具体使用 future.q = q 之类的东西在回调

中使用 q

from threading import Thread
from threading import RLock
from threading import current_thread
from concurrent.futures import Future
import time
import random

class NonBlockingQueue:

    def __init__(self, max_size):
        self.max_size = max_size
        self.q = []
        self.q_waiting_puts = []
        self.q_waiting_gets = []
        self.lock = RLock()

    def enqueue(self, item):

            future = None
            with self.lock:
                curr_size = len(self.q)

                # queue is full so create a future for a put
                # request
                if curr_size == self.max_size:
                    future = Future()
                    self.q_waiting_puts.append(future)

                else:
                    self.q.append(item)

                    # remember to resolve a pending future for
                    # a get request
                    if len(self.q_waiting_gets) != 0:
                        future_get = self.q_waiting_gets.pop(0)
                        future_get.set_result(self.q.pop(0))

            return future


    def retry_enqueue(future):
        print("\nCallback invoked by thread {0}".format(current_thread().getName()))
        item = future.item
        q = future.q
        new_future = q.enqueue(item)

        if new_future is not None:
            new_future.item = item
            new_future.q = q
            new_future.add_done_callback(retry_enqueue)
        else:
            print("\n{0} successfully added on a retry".format(item))



### MAIN CODE
def producer_thread(q):
    item = 1
    while 1:
        future = q.enqueue(item)
        if future is not None:
            future.item = item
            future.q = q
            future.add_done_callback(retry_enqueue)

        item += 1

        # slow down the producer
        time.sleep(random.randint(1, 3))

Answer 1

像这样传递参数不是一个好主意。

原因是将来（没有双关语），他们可能会禁止在 Future 对象上设置自定义属性，这会破坏您的代码。

更好的解决方案是使用 functools.partial 或 lambda 将额外参数传递给回调。

首先，接受 q 作为 retry_enqueue 函数中的参数：


def retry_enqueue(future, q): # accept 'q' argument
    ...

使用 functools.partial 的示例：

import functools

future.add_done_callback(functools.partial(retry_enqueue, q=q))

使用 lambda 的示例：

future.add_done_callback(lambda future: retry_enqueue(future, q))

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