Python中并发future模块的介绍（代码）

百变鹏仔 2小时前 #Python

文章标签模块

本篇文章给大家带来的内容是关于python中并发future模块的介绍（代码），有一定的参考价值，有需要的朋友可以参考一下，希望对你有所帮助。

concurrent.futures模块

该模块主要特色在于ThreadPoolExecutor 和 ProcessPoolExecutor 类，这两个类都继承自concurrent.futures._base.Executor类，它们实现的接口能分别在不同的线程或进程中执行可调用的对象，它们都在内部维护着一个工作线程或者进程池。

ThreadPoolExecutor 和 ProcessPoolExecutor 类是高级类，大部分情况下只要学会使用即可，无需关注其实现细节。

####ProcessPoolExecutor 类

>class ThreadPoolExecutor(concurrent.futures._base.Executor)>|  This is an abstract base class for concrete asynchronous executors.>|  Method resolution order:>|      ThreadPoolExecutor |      concurrent.futures._base.Executor |      builtins.object | |  Methods defined here: | |  init(self, max_workers=None, thread_name_prefix='') |      Initializes a new ThreadPoolExecutor instance. | |      Args: |          max_workers: The maximum number of threads that can be used to |              execute the given calls. |          thread_name_prefix: An optional name prefix to give our threads. | |  shutdown(self, wait=True) |      Clean-up the resources associated with the Executor. | |      It is safe to call this method several times. Otherwise, no other |      methods can be called after this one. | |      Args: |          wait: If True then shutdown will not return until all running |              futures have finished executing and the resources used by the |              executor have been reclaimed. | |  submit(self, fn, *args, **kwargs) |      Submits a callable to be executed with the given arguments. | |      Schedules the callable to be executed as fn(*args, **kwargs) and returns |      a Future instance representing the execution of the callable. | |      Returns: |          A Future representing the given call. | |  ---------------------------------------------------------------------- |  Methods inherited from concurrent.futures._base.Executor: | |  enter(self) | |  exit(self, exc_type, exc_val, exc_tb) | |  map(self, fn, *iterables, timeout=None, chunksize=1) |      Returns an iterator equivalent to map(fn, iter). | |      Args: |          fn: A callable that will take as many arguments as there are |              passed iterables. |          timeout: The maximum number of seconds to wait. If None, then there |              is no limit on the wait time. |          chunksize: The size of the chunks the iterable will be broken into |              before being passed to a child process. This argument is only |              used by ProcessPoolExecutor; it is ignored by |              ThreadPoolExecutor. | |      Returns: |          An iterator equivalent to: map(func, *iterables) but the calls may |          be evaluated out-of-order. | |      Raises: |          TimeoutError: If the entire result iterator could not be generated |              before the given timeout. |          Exception: If fn(*args) raises for any values.

初始化可以指定一个最大进程数作为其参数 max_workers 的值，该值一般无需指定，默认为当前运行机器的核心数，可以由os.cpu_count()获取；类中含有方法：

立即学习“Python免费学习笔记（深入）”；

map()方法，与python内置方法map() 功能类似，也就是映射，参数为：

一个可调用函数 fn
一个迭代器 iterables
超时时长 timeout
块数chuncksize 如果大于1, 迭代器会被分块处理

---->> 该函数有一个特性：其返回结果与调用开始的顺序是一致的；在调用过程中不会产生阻塞，也就是说可能前者被调用执行结束之前，后者被调用已经执行结束了。

如果一定要获取到所有结果后再处理，可以选择采用submit()方法和futures.as_completed函数结合使用。

shutdown()方法，清理所有与当前执行器（executor)相关的资源
submit() 方法，提交一个可调用对象给fn使用
从concurrent.futures._base.Executor继承了__enter__() 和 __exit__()方法，这意味着ProcessPoolExecutor 对象可以用于with 语句。

from concurrent import futureswith futures.ProcessPoolExecutor(max_works=3) as executor:     executor.map()

ThreadPoolExecutor类

class ThreadPoolExecutor(concurrent.futures._base.Executor) |  This is an abstract base class for concrete asynchronous executors. | |  Method resolution order: |      ThreadPoolExecutor |      concurrent.futures._base.Executor |      builtins.object | |  Methods defined here: | |  init(self, max_workers=None, thread_name_prefix='') |      Initializes a new ThreadPoolExecutor instance. | |      Args: |          max_workers: The maximum number of threads that can be used to |              execute the given calls. |          thread_name_prefix: An optional name prefix to give our threads. | |  shutdown(self, wait=True) |      Clean-up the resources associated with the Executor. | |      It is safe to call this method several times. Otherwise, no other |      methods can be called after this one. | |      Args: |          wait: If True then shutdown will not return until all running |              futures have finished executing and the resources used by the |              executor have been reclaimed. | |  submit(self, fn, *args, **kwargs) |      Submits a callable to be executed with the given arguments. | |      Schedules the callable to be executed as fn(*args, **kwargs) and returns |      a Future instance representing the execution of the callable. | |      Returns: |          A Future representing the given call. | |  ---------------------------------------------------------------------- |  Methods inherited from concurrent.futures._base.Executor: | |  enter(self) | |  exit(self, exc_type, exc_val, exc_tb) | |  map(self, fn, *iterables, timeout=None, chunksize=1) |      Returns an iterator equivalent to map(fn, iter). | |      Args: |          fn: A callable that will take as many arguments as there are |              passed iterables. |          timeout: The maximum number of seconds to wait. If None, then there |              is no limit on the wait time. |          chunksize: The size of the chunks the iterable will be broken into |              before being passed to a child process. This argument is only |              used by ProcessPoolExecutor; it is ignored by |              ThreadPoolExecutor. | |      Returns: |          An iterator equivalent to: map(func, *iterables) but the calls may |          be evaluated out-of-order. | |      Raises: |          TimeoutError: If the entire result iterator could not be generated |              before the given timeout. |          Exception: If fn(*args) raises for any values.

与ProcessPoolExecutor 类十分相似，只不过一个是处理进程，一个是处理线程，可根据实际需要选择。

示例

from time import sleep, strftimefrom concurrent import futuresdef display(*args):    print(strftime('[%H:%M:%S]'), end="")    print(*args)def loiter(n):    msg = '{}loiter({}): doing nothing for {}s'    display(msg.format('	'*n, n, n))    sleep(n)    msg = '{}loiter({}): done.'    display(msg.format('	'*n, n))    return n*10def main():    display('Script starting')    executor = futures.ThreadPoolExecutor(max_workers=3)    results = executor.map(loiter, range(5))    display('results:', results)    display('Waiting for inpidual results:')    for i, result in enumerate(results):        display('result {} : {}'.format(i, result))if __name__ == '__main__':    main()

运行结果：

[20:32:12]Script starting[20:32:12]loiter(0): doing nothing for 0s[20:32:12]loiter(0): done.[20:32:12]      loiter(1): doing nothing for 1s[20:32:12]              loiter(2): doing nothing for 2s[20:32:12]results: <generator object Executor.map.<locals>.result_iterator at 0x00000246DB21BC50>[20:32:12]Waiting for inpidual results:[20:32:12]                      loiter(3): doing nothing for 3s[20:32:12]result 0 : 0[20:32:13]      loiter(1): done.[20:32:13]                              loiter(4): doing nothing for 4s[20:32:13]result 1 : 10[20:32:14]              loiter(2): done.[20:32:14]result 2 : 20[20:32:15]                      loiter(3): done.[20:32:15]result 3 : 30[20:32:17]                              loiter(4): done.[20:32:17]result 4 : 40

不同机器运行结果可能不同。

示例中设置max_workers=3，所以代码一开始运行，则有三个对象（0,1,2）被执行loiter() 操作; 三秒后，对象0运行结束，得到结果result 0之后，对象3才开始被执行，同理，对象4的执行时间在对象1执行结果result 1打印结束之后。

文章推荐

Python中并发future模块的介绍（代码）

concurrent.futures模块

ThreadPoolExecutor类

示例

python时间戳怎么获得？

当前时间如何获取？

如何格式化时间？

如何让Python继承多个类？

python中if条件语句是什么？