python - 多处理中的管理器字典

Question

这是一个简单的多处理代码:

from multiprocessing import Process, Manager

manager = Manager()
d = manager.dict()

def f():
    d[1].append(4)
    print d

if __name__ == '__main__':
    d[1] = []
    p = Process(target=f)
    p.start()
    p.join()

我得到的输出是:

{1: []}

为什么我没有得到 {1: [4]} 作为输出？

Answer 1

这是你写的:

# from here code executes in main process and all child processes
# every process makes all these imports
from multiprocessing import Process, Manager

# every process creates own 'manager' and 'd'
manager = Manager() 
# BTW, Manager is also child process, and 
# in its initialization it creates new Manager, and new Manager
# creates new and new and new
# Did you checked how many python processes were in your system? - a lot!
d = manager.dict()

def f():
    # 'd' - is that 'd', that is defined in globals in this, current process 
    d[1].append(4)
    print d

if __name__ == '__main__':
# from here code executes ONLY in main process 
    d[1] = []
    p = Process(target=f)
    p.start()
    p.join()

这是你应该写的:

from multiprocessing import Process, Manager
def f(d):
    d[1] = d[1] + [4]
    print d

if __name__ == '__main__':
    manager = Manager() # create only 1 mgr
    d = manager.dict() # create only 1 dict
    d[1] = []
    p = Process(target=f,args=(d,)) # say to 'f', in which 'd' it should append
    p.start()
    p.join()