在python中的进程之间共享/使用对象

Question

I am trying to use an object (of class Event) between two processes. The main process creates the object (self.event) and passes it to the new process as args. The new process will call the inject() method of the Event() in foo1() and again the main process will call restore when foo2() is called.

from multiprocessing import Process, Queue
class Event:
    def __init__(self):
        print('init')
        self.i = None
    def inject(self):
        print(self.i)
        self.i = 100
        print(self.i)
    def restore(self):
        print(self.i)


class Test:
    def __init__(self):
        self.event = Event()
    def foo1(self):
        p1 = Process(target=self.foo1_target, args=(self.event,))
        p1.start()
        p1.join()
    def foo1_target(self, event):
        event.inject()
    def foo2(self):
        self.event.restore()


t = Test()
t.foo1()
t.foo2()

When I run t.foo1(), it prints

None

100

When I run t.foo2(), it prints

None

My understanding is that t.foo2() should print 100. I am not able to understand why it prints None. Also, how do I use Event object between main process and new process ?

Answer 1

I was able to achieve that using Semaphores and Threads from threading. :

from threading import Semaphore, Thread
class Event:
    def __init__(self):
        print('init')
        self.i = None
        self.sem = Semaphore(0)

    def inject(self):0
        print(self.i)
        self.i = 100
        print(self.i)
        self.sem.release()

    def restore(self):
        self.sem.acquire()
        print(self.i, "finished")



class Test:
    def __init__(self):
        self.event = Event() 
    def foo1(self):
        p1 = Thread(target=self.foo1_target, args=())
        p1.start()
        p1.join()
    def foo1_target(self):
        self.event.inject()

    def foo2(self):
        self.event.restore()



if __name__ == '__main__':
    t = Test()
    t.foo1()
    t.foo2()

output

init
None
100
100 finished