Python线程和多处理

Question

This is my code:

from threading import Thread
from multiprocessing import Process

def foo(x, y):
    x += 5
    y.append(5)

if __name__ == '__main__':
    x = 0
    y = []

    thread = Thread(target=foo, args=(x, y,))
    thread.start()
    thread.join()

    print 'Value of x is: ' + str(x)
    print 'Value of y is: ' + str(y)

When i run this code, the result is:

Value of x is: 0
Value of y is: [5]

When i change the Thread into Process, the result is:

Value of x is: 0
Value of y is: []

Why the +5 for x doesn't work while the append for y works?

And, why when i use Process both +5 and append don't work?

Answer 1

I suggest you to read tutorial before asking basic questions as it will save everyone's time including yours.

In short, when you use Thread , the main thread and launched thread share the same memory space but the x in function foo is another internal x but not the same x outside. So you just change the internal x but not the x outside. Further, actually y is also an internal y , but you are changing what it points to but not itself. You can confirm this by change y.append(5) to y = [0] to see will the outside y change.

And, when you use Process , the main thread and launched process hold totally separate memory space.