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python线程池ThreadPoolExecutor与进程池ProcessPoolExecutor

 python中ThreadPoolExecutor(线程池)与ProcessPoolExecutor(进程池)都是concurrent.futures模块下的,主线程(或进程)中可以获取某一个线程(进程)执行的状态或者某一个任务执行的状态及返回值。

通过submit返回的是一个future对象,它是一个未来可期的对象,通过它可以获悉线程的状态

 

ThreadPoolExecutor(线程池)

 

通过submit函数提交执行的函数到线程池中,done()判断线程执行的状态:

1 import time 2 from concurrent.futures import ThreadPoolExecutor 3 4 def get_thread_time(times): 5 time.sleep(times) 6 return times 7 8 # 创建线程池 指定最大容纳数量为4 9 executor = ThreadPoolExecutor(max_workers=4)10 # 通过submit提交执行的函数到线程池中11 task1 = executor.submit(get_thread_time, (1))12 task2 = executor.submit(get_thread_time, (2))13 task3 = executor.submit(get_thread_time, (3))14 task4 = executor.submit(get_thread_time, (4))15 print("task1:{} ".format(task1.done()))16 print("task2:{}".format(task2.done()))17 print("task3:{} ".format(task3.done()))18 print("task4:{}".format(task4.done()))19 time.sleep(2.5)20 print("after 3s {}".format("-"*20))21 22 done_map = {23 "task1":task1.done(),24 "task2":task2.done(),25 "task3":task3.done(),26 "task4":task4.done()27 }28 # 2.5秒之后,线程的执行状态29 for task_name,done in done_map.items():30 if done:31 print("{}:completed".format(task_name))

result:

task1:False task2:Falsetask3:False task4:Falseafter 3s --------------------task1:completedtask2:completed

初始状态4个task都是未完成状态,2.5秒后task1和task2执行完成,task3和task由于是sleep(3) sleep(4)所以仍然是未完成的sleep状态

通过wait()判断线程执行的状态:

wait(fs, timeout=None, return_when=ALL_COMPLETED),wait接受3个参数,fs表示执行的task序列;timeout表示等待的最长时间,超过这个时间即使线程未执行完成也将返回;return_when表示wait返回结果的条件,默认为ALL_COMPLETED全部执行完成再返回:

1 import time 2 from concurrent.futures import ( 3 ThreadPoolExecutor, wait 4 ) 5 6 7 def get_thread_time(times): 8 time.sleep(times) 9 return times10 11 12 start = time.time()13 executor = ThreadPoolExecutor(max_workers=4)14 task_list = [executor.submit(get_thread_time, times) for times in [1, 2, 3, 4]]15 i = 116 for task in task_list:17 print("task{}:{}".format(i, task))18 i += 119 print(wait(task_list, timeout=2.5))

wait在2.5秒后返回线程的状态,result:

task1:<Future at 0x7ff3c885f208 state=running>task2:<Future at 0x7ff3c885fb00 state=running>task3:<Future at 0x7ff3c764b2b0 state=running>task4:<Future at 0x7ff3c764b9b0 state=running>DoneAndNotDoneFutures(done={<Future at 0x7ff3c885f208 state=finished returned int>, <Future at 0x7ff3c885fb00 state=finished returned int>}, not_done={<Future at 0x7ff3c764b2b0 state=running>, <Future at 0x7ff3c764b9b0 state=running>})

可以看到在timeout 2.5时,task1和task2执行完毕,task3和task4仍在执行中

通过map返回线程的执行结果:

1 import time 2 from concurrent.futures import ThreadPoolExecutor 3 4 5 def get_thread_time(times): 6 time.sleep(times) 7 return times 8 9 10 start = time.time()11 executor = ThreadPoolExecutor(max_workers=4)12 13 i = 114 for result in executor.map(get_thread_time,[2,3,1,4]):15 print("task{}:{}".format(i, result))16 i += 1

 

map(fn, *iterables, timeout=None),第一个参数fn是线程执行的函数;第二个参数接受一个可迭代对象;第三个参数timeout跟wait()的timeout一样,但由于map是返回线程执行的结果,如果timeout小于线程执行时间会抛异常TimeoutError。

import timefrom concurrent.futures import ThreadPoolExecutordef get_thread_time(times): time.sleep(times) return timesstart = time.time()executor = ThreadPoolExecutor(max_workers=4)i = 1for result in executor.map(get_thread_time,[2,3,1,4]): print("task{}:{}".format(i, result)) i += 1

map的返回是有序的,它会根据第二个参数的顺序返回执行的结果:

task1:2task2:3task3:1task4:4

 

as_completed返回线程执行结果:

1 import time 2 from collections import OrderedDict 3 from concurrent.futures import ( 4 ThreadPoolExecutor, as_completed 5 ) 6 7 8 def get_thread_time(times): 9 time.sleep(times)10 return times11 12 13 start = time.time()14 executor = ThreadPoolExecutor(max_workers=4)15 task_list = [executor.submit(get_thread_time, times) for times in [2, 3, 1, 4]]16 task_to_time = OrderedDict(zip(["task1", "task2", "task3", "task4"],[2, 3, 1, 4]))17 task_map = OrderedDict(zip(task_list, ["task1", "task2", "task3", "task4"]))18 19 for result in as_completed(task_list):20 task_name = task_map.get(result)21 print("{}:{}".format(task_name,task_to_time.get(task_name)))

task1、task2、task3、task4的等待时间分别为2s、3s、1s、4s,通过as_completed返回执行完的线程结果,as_completed(fs, timeout=None)接受2个参数,第一个是执行的线程列表,第二个参数timeout与map的timeout一样,当timeout小于线程执行时间会抛异常TimeoutError。

task3:1task1:2task2:3task4:4

通过执行结果可以看出,as_completed返回的顺序是线程执行结束的顺序,最先执行结束的线程最早返回。

 

ProcessPoolExecutor

对于频繁的cpu操作,由于GIL锁的原因,多个线程只能用一个cpu,这时多进程的执行效率要比多线程高。

线程池操作斐波拉切:

1 import time 2 from concurrent.futures import ThreadPoolExecutor 3 4 5 def fib(n): 6 if n < 3: 7 return 1 8 return fib(n - 1) + fib(n - 2) 9 10 11 start_time = time.time()12 executor = ThreadPoolExecutor(max_workers=4)13 task_list = [executor.submit(fib, n) for n in range(3, 35)]14 thread_results = [task.result() for task in as_completed(task_list)]15 print(thread_results)16 print("ThreadPoolExecutor time is: {}".format(time.time() - start_time))

result:

[8, 5, 3, 2, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 10946, 46368, 6765, 28657, 17711, 75025, 121393, 196418, 317811, 514229, 832040, 1346269, 2178309, 3524578, 5702887]ThreadPoolExecutor time is: 4.998981237411499

 

进程池操作斐波拉切:

1 import time 2 from concurrent.futures import ProcessPoolExecutor 3 4 5 def fib(n): 6 if n < 3: 7 return 1 8 return fib(n - 1) + fib(n - 2) 9 10 11 start_time = time.time()12 executor = ProcessPoolExecutor(max_workers=4)13 task_list = [executor.submit(fib, n) for n in range(3, 35)]14 process_results = [task.result() for task in as_completed(task_list)]15 print(process_results)16 print("ProcessPoolExecutor time is: {}".format(time.time() - start_time))

result:

[2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 75025, 28657, 46368, 196418, 121393, 317811, 514229, 832040, 1346269, 2178309, 3524578, 5702887]ProcessPoolExecutor time is: 3.3585257530212402

可以看出,对于频繁cpu操作进程是优于线程的,3.3s<4.9s

ProcessPoolExecutor在使用上和ThreadPoolExecutor大致是一样的,它们在futures中的方法也是相同的,但是对于map()方法ProcessPoolExecutor会多一个参数chunksize(ThreadPoolExecutor中这个参数没有任何作用),chunksize将迭代对象切成块,将其作为分开的任务提交给pool,对于很大的iterables,设置较大chunksize可以提高性能。