????? 標(biāo)準(zhǔn)庫 multiprocessing 支持使用類似于 threading 的用法來創(chuàng)建管理線程，并且避免了 GIL 問題。

13.4.1 創(chuàng)建線程

from multiprocessing import Process
import os

def f(name):
    print('module name:', __name__)
    print('parent process:', os.getppid())  
    print('process id:', os.getpid())
    print('hello', name)

if __name__ == '__main__':
    p = Process(target = f, args = ('bob',))
    p.start()
    p.join()

????? multiprocessing 還提供了 Pool 對象支持?jǐn)?shù)據(jù)的并行操作。下面的代碼并發(fā)計算二維數(shù)組每行的平均值。

from multiprocessing import Pool
from statistics import mean

def f(x):
    return mean(x)

if __name__ == '__main__':
    x = [list(range(10)), list(range(20, 30)), list(range(50, 60)), list(range(80, 90))]
    with Pool(5) as p:
        print(p.map(f, x))

13.4.2 進(jìn)程間數(shù)據(jù)交換

????? 使用 Queue 對象在進(jìn)程間交換數(shù)據(jù)。

import multiprocessing as mp

def foo(q):
    q.put('hello world!')

if __name__ == '__main__':
    mp.set_start_method('spawn')
    q = mp.Queue()
    p = mp.Process(target = foo, args = (q,))
    p.start()
    p.join()
    print(q.get())

????? 也可以使用上下文對象 context 的 Queue 對象實(shí)現(xiàn)進(jìn)程間的數(shù)據(jù)交換。

import multiprocessing as mp
def foo(q):
    q.put('hello world')


if __name__ == '__main__':
    
    ctx = mp.get_context('spawn')
    q = ctx.Queue()
    p = ctx.Process(target = foo, args = (q,))
    p.start()
    p.join()
    print(q.get())

????? 使用管道實(shí)現(xiàn)數(shù)據(jù)交換。

from multiprocessing import Process, Pipe

def f(conn):
    conn.send('hello world')    # 向管道中發(fā)送數(shù)據(jù)
    conn.close()

if __name__ == '__main__':
    parent_conn, child_conn = Pipe()    # 創(chuàng)建管道對象
    p = Process(target = f, args = (child_conn,))   # 將管道的一方作為參數(shù)傳遞給子進(jìn)程
    p.start()
    print(parent_conn.recv())  # 通過管道的另一方接收數(shù)據(jù)
    p.join()

????? 使用共享內(nèi)存實(shí)現(xiàn)進(jìn)程間數(shù)據(jù)交換。

from multiprocessing import Process, Value, Array

def f(n, a):
    n.value = 3.1415927
    for i in range(len(a)):
        a[i] = a[i] * a[i]

if __name__ == '__main__':
    num = Value('d', 0.0)   # 實(shí)型
    arr = Array('i', range(10)) # 整數(shù)型
    p = Process(target = f, args = (num, arr))
    p.start()
    p.join()
    print(num.value)
    print(arr[:])

????? 使用Manager 對象實(shí)現(xiàn)進(jìn)程間數(shù)據(jù)交換。
????? Manager 對象控制一個擁有 list、dict、Lock、RLock、Semaphore、BoundeSemaphore、Condition、Event、Barrier、Queue、Value、Array、Namespace 等對象的服務(wù)端進(jìn)程，允許其他進(jìn)程訪問這些對象。

from multiprocessing import Process, Manager

def f(d, l, t):
    d['name'] = 'dfg'
    d['age'] = 38
    d['sex'] = 'Male'
    d['affiliation'] = 'SDIBT'
    l.reverse()
    t.value = 3

if __name__ == '__main__':
    with Manager() as manager:
        d = manager.dict()
        l = manager.list(range(10))
        t = manager.Value('i', 0)
        p = Process(target = f, args = (d, l, t))
        p.start()
        p.join()
        for item in d.items():
            print(item)
        print(l)
        print(t.value)

13.4.3 進(jìn)程同步

????? 使用 Lock 對象實(shí)現(xiàn)進(jìn)程同步。

from multiprocessing import Process, Lock

def f(l, i):
    l.acquire()
    try:
        print('hello world', i)
    finally:
        l.release()

if __name__ == '__main__':
    lock = Lock()
    for num in range(10):
        Process(target = f, args = (lock, num)).start()

????? 使用 Event 對象實(shí)現(xiàn)進(jìn)程同步。

from multiprocessing import Process, Event

def f(e, i):
    if e.is_set():
        e.wait()
        print('hello world', i)
        e.clear()
    else :
        e.set()

if __name__ == '__main__':
    e = Event()
    for num in range(10):
        Process(target = f, args = (e, num)).start()