python 并行计算 pathos模块简介

2023-05-16

pathos模块

1、pathos自身的多进程方法（pathos.multiprocessing.ProcessPool、pathos.multiprocessing.ProcessingPool、pathos.pools.ProcessPool）

2、映射multiprocess模块的多进程方法（pathos.multiprocessing.Pool）

3、映射pp模块的多进程方法1（pathos.pools.ParallelPool、pathos.pp.ParallelPool、pathos.pp.ParallelPythonPool、pathos.parallel.ParallelPythonPool、pathos.parallel.ParallelPool）

4、映射pp模块的多进程方法2（pathos.pp.pp模块）

5、映射python内置map函数的方法（pathos.serial.SerialPool、pathos.pools.SerialPool）

实例（pathos模块）

（1）pathos.multiprocessing.ProcessPool()，pipe方法

（2）pathos.multiprocessing.ProcessPool()，apipe方法

（3）pathos.multiprocessing.ProcessPool()，map方法

（4）pathos.multiprocessing.ProcessPool()，imap方法

（5）pathos.multiprocessing.ProcessPool()，uimap方法

（6）pathos.multiprocessing.ProcessPool()，amap方法

（7）pathos.pp.ParallelPool()，pipe方法

（8）pathos.pp.ParallelPool()，apipe方法

（9）pathos.pp.ParallelPool()，map方法

（10）pathos.pp.ParallelPool()，amap方法

（11）pathos.pp.ParallelPool()，imap方法

（12）pathos.pp.ParallelPool()，uimap方法

pathos模块

pathos是一个较为综合性的模块，既能多进程，也能多线程。其主要采用进程池/线程池方法。

pathos本身有一套进程池方法，同时也集成了multiprocess、pp模块的进程池方法。

1、pathos自身的多进程方法（pathos.multiprocessing.ProcessPool、pathos.multiprocessing.ProcessingPool、pathos.pools.ProcessPool）

（1）建立进程池

pathos.multiprocessing.ProcessPool(*args, **kwds) #建立pathos的进程池（pathos.multiprocessing.ProcessPool实例）。

pathos.multiprocessing.ProcessingPool(*args, **kwds) #同上。

pathos.pools.ProcessPool(*args, **kwds) #同上。

nodes：workers的数量。如果不指定nodes，则自动检测processors的数量（即ncpus）。
ncpus：worker processors的数量。
servers：worker servers的列表。
scheduler：相应的scheduler。
workdir：用于scratch calculations/files的$WORKDIR。
scatter：如为True，表示采用scatter-gatter（默认为worker-pool）。
source：如为False，表示尽可能少使用TemporaryFiles。
timeout：等待scheduler返回值的时间。

同样也有几个进程池通用的方法：

XXX.close() #关闭进程池，关闭后不能往pool中增加新的子进程，然后可以调用join()函数等待已有子进程执行完毕。XXX为进程池。

XXX.join() #等待进程池中的子进程执行完毕。需在close()函数后调用。XXX为进程池。

def f(a, b = value):
    pass

pool = pathos.multiprocessing.Pool() 
pool.map(f, a_seq, b_seq)
pool.close()
pool.join()

（2）创建子进程

（a）单个子进程可通过pipe方法创建：

XXX.pipe(f, *args, **kwds) #采用阻塞方式（非并行）提交一个任务，阻塞直到返回结果为止。XXX为进程池实例。

XXX.apipe(f, *args, **kwds) #异步（并行）提交一个任务到队列（queue）中，返回ApplyResult实例（其get方法可获得任务返回值，但get方法是阻塞的，应在所有子进程添加完后再调用）。XXX为进程池实例。

f(*args,**kwds)为子进程对应的活动。

（b）如果子进程有返回值，且返回值需要集中处理，则建议采用map方式（子进程活动允许多个参数）：

XXX.map(f, *args, **kwds) #采用阻塞方式按顺序运行一批任务，返回结果组成的list。func(iterable1[i], iterable2[i], ...)为子进程对应的活动。XXX为进程池实例。

XXX.amap(f, *args, **kwds) #XXX.map()的异步（并行）版本，返回MapResult实例（其具有get()方法，获取结果组成的list）。XXX为进程池实例。

def f(a, b): #map方法允许多个参数
    pass

pool = pathos.multiprocessing.Pool() 
result = pool.map_async(f, (a0, a1, ...), (b0, b1, ...)).get()
pool.close()
pool.join()

（c）如果内存不够用，也可采用imap迭代器方式：

XXX.imap(f, *args, **kwds) #XXX.map()的非阻塞、按顺序迭代器版本，返回迭代器实例。XXX为进程池实例。

XXX.uimap(f, *args, **kwds) #XXX.imap()的无序版本（不会按照调用顺序返回，而是按照结束顺序返回），返回迭代器实例。XXX为进程池实例。

def f(a, b): 
    pass

pool = pathos.multiprocessing.Pool() 
result = pool.uimap(f, a_seq, b_seq)
pool.close()
pool.join()

for item in result:
    pass

2、映射multiprocess模块的多进程方法（pathos.multiprocessing.Pool）

（1）建立进程池

pathos.multiprocessing.Pool(processes=None, initializer=None, initargs=(), maxtasksperchild=None, context=None) #建立multiprocess的进程池。

processes ：使用的工作进程的数量，如果processes是None那么使用 os.cpu_count()返回的数量。
initializer：如果initializer不是None，那么每一个工作进程在开始的时候会调用initializer(*initargs)。
maxtasksperchild：工作进程退出之前可以完成的任务数，完成后用一个新的工作进程来替代原进程，来让闲置的资源被释放。maxtasksperchild默认是None，意味着只要Pool存在工作进程就会一直存活。
context: 用在制定工作进程启动时的上下文，一般使用 multiprocess.Pool() 或者一个context对象的Pool()方法来创建一个池，两种方法都适当的设置了context。

（2）创建子进程

该进程池对应的创建子进程方法与multiprocess.Pool()（也即multiprocessing.Pool()）完全相同。

3、映射pp模块的多进程方法1（pathos.pools.ParallelPool、pathos.pp.ParallelPool、pathos.pp.ParallelPythonPool、pathos.parallel.ParallelPythonPool、pathos.parallel.ParallelPool）

（1）建立进程池

pathos.pp.ParallelPool(*args, **kwds) #建立映射pp模块方法的进程池，返回pathos.parallel.ParallelPool实例。注意，建立的进程池的方法与pp模块完全不同。

pathos.pp.ParallelPythonPool(*args, **kwds) #等价pathos.pp.ParallelPool()。

pathos.pools.ParallelPool(*args, **kwds) #等价pathos.pp.ParallelPool()。

pathos.parallel.ParallelPool(*args, **kwds) #等价pathos.pp.ParallelPool()。

pathos.parallel.ParallelPythonPool(*args, **kwds) #等价pathos.pp.ParallelPool()。

nodes：workers的数量。如果不指定nodes，则自动检测processors的数量（即ncpus）。
ncpus：worker processors的数量。
servers：worker servers的列表。
scheduler：相应的scheduler。
workdir：用于scratch calculations/files的$WORKDIR。
scatter：如为True，表示采用scatter-gatter（默认为worker-pool）。
source：如为False，表示尽可能少使用TemporaryFiles。
timeout：等待scheduler返回值的时间。

（2）创建子进程

该进程池对应的创建子进程方法与pathos.multiprocessing.ProcessPool()完全相同（与pp模块完全不同）。

注意，multiprocessing.Pipe()或multiprocess.Pipe()建立的管道对象无法传入子进程（可能是pickle错误）。但是，ParallelPool进程池中，子进程print函数可以直接输出到标准输出，因此也不必通过管道将信息传递到主进程了。但是，子进程print输出的格式经常出现异常，最好还是通过返回值在主进程输出。

而且，amap方法是个特例。amap方法中，如果子进程有print语句，会导致返回结果不对，只包含最后一个子进程返回值的tuple，而不是所有子进程的返回值组成完整list，原因暂不清楚。因此，amap方法中，子进程需要输出的内容只能通过返回值在主进程输出。

4、映射pp模块的多进程方法2（pathos.pp.pp模块）

该方法实质就是pp模块。

5、映射python内置map函数的方法（pathos.serial.SerialPool、pathos.pools.SerialPool）

该类方法实际是串行（非并行），不做具体介绍。

SerialPool建立的进程池实际只能用pipe、map、imap方法（均是阻塞的），不能使用apipe、amap、uimap方法。

实例（pathos模块）

（1）pathos.multiprocessing.ProcessPool()，pipe方法

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    res = []
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    for i in var:
        res.append(p.pipe(f, i, c_conn, t0))

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，所有子进程都是逐个执行的。

 output:
factorial of 4: start@1.11s
factorial of 4: finish@2.61s, res = 24
factorial of 8: start@2.61s
factorial of 8: finish@6.12s, res = 40320
factorial of 12: start@6.12s
factorial of 12: finish@11.62s, res = 479001600
factorial of 20: start@11.63s
factorial of 20: finish@21.13s, res = 2432902008176640000
factorial of 16: start@21.15s
factorial of 16: finish@28.65s, res = 20922789888000
factorial of (4, 8, 12, 20, 16)@28.73s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（2）pathos.multiprocessing.ProcessPool()，apipe方法

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    res = []
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    for i in var:
        res.append(p.apipe(f, i, c_conn, t0))
    for i in range(len(res)):
        res[i] = res[i].get()

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：

output:
factorial of 4: start@1.10s
factorial of 8: start@1.18s
factorial of 12: start@1.19s
factorial of 20: start@1.25s
factorial of 4: finish@2.60s, res = 24
factorial of 16: start@2.61s
factorial of 8: finish@4.69s, res = 40320
factorial of 12: finish@6.69s, res = 479001600
factorial of 16: finish@10.11s, res = 20922789888000
factorial of 20: finish@10.75s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@10.85s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（3）pathos.multiprocessing.ProcessPool()，map方法

注意，实例将multiprocessing.Pipe()创建的连接作为参数传递给子进程，pickle出错，改为multiprocess.Pipe()创建连接即可解决。

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    conn_s = [c_conn] * len(var)
    t0_s = [t0] * len(var)
    res = p.map(f, var, conn_s, t0_s)

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。

output:
factorial of 4: start@1.15s
factorial of 8: start@1.15s
factorial of 12: start@1.19s
factorial of 20: start@1.26s
factorial of 4: finish@2.65s, res = 24
factorial of 16: start@2.65s
factorial of 8: finish@4.66s, res = 40320
factorial of 12: finish@6.70s, res = 479001600
factorial of 16: finish@10.15s, res = 20922789888000
factorial of 20: finish@10.76s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@10.91s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（4）pathos.multiprocessing.ProcessPool()，imap方法

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    conn_s = [c_conn] * len(var)
    t0_s = [t0] * len(var)
    res = list(p.imap(f, var, conn_s, t0_s))

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。

output:
factorial of 4: start@1.27s
factorial of 8: start@1.29s
factorial of 12: start@1.30s
factorial of 20: start@1.38s
factorial of 4: finish@2.77s, res = 24
factorial of 16: start@2.77s
factorial of 8: finish@4.79s, res = 40320
factorial of 12: finish@6.81s, res = 479001600
factorial of 16: finish@10.27s, res = 20922789888000
factorial of 20: finish@10.89s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@11.01s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（5）pathos.multiprocessing.ProcessPool()，uimap方法

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    conn_s = [c_conn] * len(var)
    t0_s = [t0] * len(var)
    res = list(p.uimap(f, var, conn_s, t0_s))

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。而且，第5个进程的返回值排在第4个进程的返回值之前。

output:
factorial of 4: start@1.03s
factorial of 8: start@1.08s
factorial of 12: start@1.10s
factorial of 20: start@1.15s
factorial of 4: finish@2.53s, res = 24
factorial of 16: start@2.53s
factorial of 8: finish@4.58s, res = 40320
factorial of 12: finish@6.60s, res = 479001600
factorial of 16: finish@10.03s, res = 20922789888000
factorial of 20: finish@10.66s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@10.78s: [24, 40320, 479001600, 20922789888000, 2432902008176640000]

（6）pathos.multiprocessing.ProcessPool()，amap方法

import pathos
import multiprocess
import time

def f(x, conn, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    conn.send('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    conn.send('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.multiprocessing.ProcessPool()
    p_conn, c_conn = multiprocess.Pipe()
    t0 = time.time()
    conn_s = [c_conn] * len(var)
    t0_s = [t0] * len(var)
    res = p.amap(f, var, conn_s, t0_s).get()

    print('output:')
    while p_conn.poll():
        print(p_conn.recv())
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。

output:
factorial of 4: start@1.04s
factorial of 8: start@1.07s
factorial of 12: start@1.12s
factorial of 20: start@1.13s
factorial of 4: finish@2.54s, res = 24
factorial of 16: start@2.54s
factorial of 8: finish@4.58s, res = 40320
factorial of 12: finish@6.62s, res = 479001600
factorial of 16: finish@10.04s, res = 20922789888000
factorial of 20: finish@10.64s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@10.76s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（7）pathos.pp.ParallelPool()，pipe方法

注意，multiprocessing.Pipe()或multiprocess.Pipe()产生的管道对象无法传入子进程（可能是pickle错误）。但是，pathos.pp.ParallelPool()进程池中，子进程print函数可以直接输出到标准输出，因此也不必通过管道将信息传递到主进程了。

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    print('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    print('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    res = []
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    for i in var:
        res.append(p.pipe(f, i, t0))
        
    print('output:')
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，所有子进程都是逐个执行的。

factorial of 4: start@0.12s
factorial of 4: finish@1.62s, res = 24
factorial of 8: start@1.80s
factorial of 8: finish@5.30s, res = 40320
factorial of 12: start@5.46s
factorial of 12: finish@10.96s, res = 479001600
factorial of 20: start@11.16s
factorial of 20: finish@20.66s, res = 2432902008176640000
factorial of 16: start@20.94s
factorial of 16: finish@28.44s, res = 20922789888000
output:
factorial of (4, 8, 12, 20, 16)@28.67s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（8）pathos.pp.ParallelPool()，apipe方法

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    print('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    print('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    res = []
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    for i in var:
        res.append(p.apipe(f, i, t0))
        
    print('output:')
    for i in range(len(res)):
        res[i] = res[i].get()
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。

output:
factorial of 4: start@0.20s
factorial of 4: finish@1.70s, res = 24
 factorial of 8: start@0.21s
factorial of 8: finish@3.71s, res = 40320
 factorial of 12: start@0.13s
factorial of 12: finish@5.63s, res = 479001600
 factorial of 20: start@0.18s
factorial of 20: finish@9.68s, res = 2432902008176640000
factorial of 16: start@1.70s
factorial of 16: finish@9.20s, res = 20922789888000
 factorial of (4, 8, 12, 20, 16)@9.72s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（9）pathos.pp.ParallelPool()，map方法

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    print('factorial of %d: start@%.2fs' % (x0, t))
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    print('factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans))
    return ans

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    res= p.map(f, var, [t0] * 5)
        
    print('output:')
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，所有子进程都是逐个执行的。

factorial of 4: start@0.14s
factorial of 4: finish@1.64s, res = 24
factorial of 8: start@1.74s
factorial of 8: finish@5.24s, res = 40320
factorial of 12: start@5.35s
factorial of 12: finish@10.85s, res = 479001600
factorial of 20: start@11.01s
factorial of 20: finish@20.51s, res = 2432902008176640000
factorial of 16: start@20.66s
factorial of 16: finish@28.16s, res = 20922789888000
 output:
factorial of (4, 8, 12, 20, 16)@28.51s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（10）pathos.pp.ParallelPool()，amap方法

注意：amap方法中，如果子进程有print语句，会导致返回结果是只包含最后一个子进程返回值的tuple，而不是所有子进程的返回值组成完整list，原因暂不清楚。因此，amap方法中，子进程需要输出的内容只能通过返回值在主进程输出。

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    msg1 = 'factorial of %d: start@%.2fs' % (x0, t)
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    msg2 = 'factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans)
    return (ans, msg1, msg2)

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    ret = p.amap(f, var, [t0] * 5).get()
    res = [item[0] for item in ret]
        
    print('output:')
    for item in ret:
        print(item[1])
        print(item[2])
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，第一批次4个子进程几乎同时开启；当一个子进程结束后，马上开启第5个子进程。

output:
factorial of 4: start@0.16s
factorial of 4: finish@1.66s, res = 24
factorial of 8: start@0.18s
factorial of 8: finish@3.68s, res = 40320
factorial of 12: start@0.19s
factorial of 12: finish@5.69s, res = 479001600
factorial of 20: start@0.14s
factorial of 20: finish@9.64s, res = 2432902008176640000
factorial of 16: start@1.66s
factorial of 16: finish@9.16s, res = 20922789888000
factorial of (4, 8, 12, 20, 16)@9.72s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（11）pathos.pp.ParallelPool()，imap方法

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    msg1 = 'factorial of %d: start@%.2fs' % (x0, t)
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    msg2 = 'factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans)
    return (ans, msg1, msg2)

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    ret = list(p.imap(f, var, [t0] * 5))
    res = [item[0] for item in ret]
        
    print('output:')
    for item in ret:
        print(item[1])
        print(item[2])
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

结果：可以看出，所有子进程都是逐个执行的。

output:
factorial of 4: start@0.17s
factorial of 4: finish@1.67s, res = 24
factorial of 8: start@1.67s
factorial of 8: finish@5.17s, res = 40320
factorial of 12: start@5.17s
factorial of 12: finish@10.67s, res = 479001600
factorial of 20: start@10.67s
factorial of 20: finish@20.17s, res = 2432902008176640000
factorial of 16: start@20.17s
factorial of 16: finish@27.67s, res = 20922789888000
factorial of (4, 8, 12, 20, 16)@28.41s: [24, 40320, 479001600, 2432902008176640000, 20922789888000]

（12）pathos.pp.ParallelPool()，uimap方法

import pathos
import time

def f(x, t0):
    ans = 1
    x0 = x
    t = time.time() - t0
    msg1 = 'factorial of %d: start@%.2fs' % (x0, t)
    while x > 1:
        ans *= x
        time.sleep(0.5)
        x -= 1
    t = time.time() - t0
    msg2 = 'factorial of %d: finish@%.2fs, res = %d' %(x0, t, ans)
    return (ans, msg1, msg2)

def main():
    var = (4, 8, 12, 20, 16)
    p = pathos.pp.ParallelPool()
    t0 = time.time()
    ret = list(p.uimap(f, var, [t0] * 5))
    res = [item[0] for item in ret]
        
    print('output:')
    for item in ret:
        print(item[1])
        print(item[2])
    t = time.time() - t0
    print('factorial of %s@%.2fs: %s' % (var, t, res))

if __name__ == '__main__':
    main()

output:
factorial of 4: start@0.26s
factorial of 4: finish@1.76s, res = 24
factorial of 8: start@0.29s
factorial of 8: finish@3.79s, res = 40320
factorial of 12: start@0.25s
factorial of 12: finish@5.75s, res = 479001600
factorial of 16: start@1.77s
factorial of 16: finish@9.28s, res = 20922789888000
factorial of 20: start@0.31s
factorial of 20: finish@9.81s, res = 2432902008176640000
factorial of (4, 8, 12, 20, 16)@10.24s: [24, 40320, 479001600, 20922789888000, 2432902008176640000]

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