当两个线程同时调用一个生成器的next方法时就会引发“generator already executing”异常。

解决方法：加锁。

如下代码所示：

import threading

class threadsafe_generator:
    """Takes an generator and makes it thread-safe by
    serializing call to the `next` method of given generator.
    """
    def __init__(self, gen):
        self.gen = gen
        self.lock = threading.Lock()

    def __iter__(self):
        return self.next()

    def next(self):
        with self.lock:
            return self.gen.next()


# 定义我们的生成器
def all_keywords():
    for row in csv.reader(open('companies.csv')):
        if row[0]:
           yield row[0]


# 将其转换为线程安全的
keywords = threadsafe_generator(all_keywords())
# 然后在线程中就可以随意地使用keywords.next()而不必担心"generator already executing"异常了。