摘要：和類(lèi)是高級(jí)類(lèi)，大部分情況下只要學(xué)會(huì)使用即可，無(wú)需關(guān)注其實(shí)現(xiàn)細(xì)節(jié)。類(lèi)與類(lèi)十分相似，只不過(guò)一個(gè)是處理進(jìn)程，一個(gè)是處理線(xiàn)程，可根據(jù)實(shí)際需要選擇。示例運(yùn)行結(jié)果不同機(jī)器運(yùn)行結(jié)果可能不同。

該模塊主要特色在于ThreadPoolExecutor 和 ProcessPoolExecutor 類(lèi)，這兩個(gè)類(lèi)都繼承自concurrent.futures._base.Executor類(lèi)，它們實(shí)現(xiàn)的接口能分別在不同的線(xiàn)程或進(jìn)程中執(zhí)行可調(diào)用的對(duì)象，它們都在內(nèi)部維護(hù)著一個(gè)工作線(xiàn)程或者進(jìn)程池。

ThreadPoolExecutor 和 ProcessPoolExecutor 類(lèi)是高級(jí)類(lèi)，大部分情況下只要學(xué)會(huì)使用即可，無(wú)需關(guān)注其實(shí)現(xiàn)細(xì)節(jié)。

####ProcessPoolExecutor 類(lèi)

>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.

初始化可以指定一個(gè)最大進(jìn)程數(shù)作為其參數(shù) max_workers 的值，該值一般無(wú)需指定，默認(rèn)為當(dāng)前運(yùn)行機(jī)器的核心數(shù)，可以由os.cpu_count()獲取；類(lèi)中含有方法：

map()方法，與python內(nèi)置方法map() 功能類(lèi)似，也就是映射，參數(shù)為：

一個(gè)可調(diào)用函數(shù) fn

一個(gè)迭代器 iterables

超時(shí)時(shí)長(zhǎng) timeout

塊數(shù)chuncksize 如果大于1, 迭代器會(huì)被分塊處理

---->> 該函數(shù)有一個(gè)特性：其返回結(jié)果與調(diào)用開(kāi)始的順序是一致的；在調(diào)用過(guò)程中不會(huì)產(chǎn)生阻塞，也就是說(shuō)可能前者被調(diào)用執(zhí)行結(jié)束之前，后者被調(diào)用已經(jīng)執(zhí)行結(jié)束了。

如果一定要獲取到所有結(jié)果后再處理，可以選擇采用submit()方法和futures.as_completed函數(shù)結(jié)合使用。

shutdown()方法，清理所有與當(dāng)前執(zhí)行器（executor)相關(guān)的資源

submit() 方法，提交一個(gè)可調(diào)用對(duì)象給fn使用

從concurrent.futures._base.Executor繼承了__enter__() 和 __exit__()方法，這意味著ProcessPoolExecutor 對(duì)象可以用于with 語(yǔ)句。

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

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.

與ProcessPoolExecutor 類(lèi)十分相似，只不過(guò)一個(gè)是處理進(jìn)程，一個(gè)是處理線(xiàn)程，可根據(jù)實(shí)際需要選擇。

from time import sleep, strftime
from concurrent import futures


def 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*10


def main():
    display("Script starting")
    executor = futures.ThreadPoolExecutor(max_workers=3)
    results = executor.map(loiter, range(5))
    display("results:", results)
    display("Waiting for individual results:")
    for i, result in enumerate(results):
        display("result {} : {}".format(i, result))


if __name__ == "__main__":
    main()

運(yùn)行結(jié)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: .result_iterator at 0x00000246DB21BC50>
[20:32:12]Waiting for individual 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

不同機(jī)器運(yùn)行結(jié)果可能不同。

示例中設(shè)置max_workers=3，所以代碼一開(kāi)始運(yùn)行，則有三個(gè)對(duì)象（0,1,2）被執(zhí)行l(wèi)oiter() 操作; 三秒后，對(duì)象0運(yùn)行結(jié)束，得到結(jié)果result 0之后，對(duì)象3才開(kāi)始被執(zhí)行，同理，對(duì)象4的執(zhí)行時(shí)間在對(duì)象1執(zhí)行結(jié)果result 1打印結(jié)束之后。