RuntimeError: 
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

This probably means that you are not using fork to start your

        in the main module:

multiprocessing的使用在Linux和mac中直接使用即可，但是在window中不太一樣

python-2.7-docs-html/library/multiprocessing.html#multiprocessing-programming

簡而言之，需要在p=Process()前加上 
if __name__ == ‘__main__’:
      p = Process(...

Safe importing of main module

    Make sure that the main module can be safely imported by a new Python interpreter without causing unintended side effects (such a starting a new process).

    For example, under Windows running the following module would fail with a RuntimeError:

    from multiprocessing import Process

    def foo():
        print 'hello'

    p = Process(target=foo)
    p.start()

    Instead one should protect the “entry point” of the program by using if __name__ == '__main__': as follows:

    from multiprocessing import Process, freeze_support

    def foo():
        print 'hello'

    if __name__ == '__main__':
        freeze_support()
        p = Process(target=foo)
        p.start()

    (The freeze_support() line can be omitted if the program will be run normally instead of frozen.)

    This allows the newly spawned Python interpreter to safely import the module and then run the module’s foo() function.

from multiprocessing import Process
#window不可以用fork()，但是可以用multiprocessing，可以跨平臺使用
import time

def test():
	print("hello")

if __name__=='__main__':
	#freeze__support()
	p=Process(target=test)
	p.start()
#所有的程序結束後，程式才結束