创建池时,请使用initializer和initargs参数,以便在所有子进程中定义全局变量。
例如:
from multiprocessing import Pool, Lock
from time import sleep
def do_job(i):
"The greater i is, the shorter the function waits before returning."
with lock:
sleep(1-(i/10.))
return i
def init_child(lock_):
global lock
lock = lock_
def main():
lock = Lock()
poolsize = 4
with Pool(poolsize, initializer=init_child, initargs=(lock,)) as pool:
results = pool.imap_unordered(do_job, range(poolsize))
print(list(results))
if __name__ == "__main__":
main()
该代码将按升序(提交作业的顺序)打印数字0-3,因为它使用了锁。注释掉该with lock:
行以查看它以降序打印出数字。
此解决方案在Windows和UNIX上均适用。但是,由于进程可以在unix系统上派生,因此unix只需要在模块范围内声明全局变量。子进程将获取父级内存的副本,其中包括仍有效的锁对象。因此,并不是严格要求初始化程序,但是它可以帮助记录代码的预期工作方式。当多处理能够通过派生创建流程时,以下内容也将起作用。
from multiprocessing import Pool, Lock
from time import sleep
lock = Lock()
def do_job(i):
"The greater i is, the shorter the function waits before returning."
with lock:
sleep(1-(i/10.))
return i
def main():
poolsize = 4
with Pool(poolsize) as pool:
results = pool.imap_unordered(do_job, range(poolsize))
print(list(results))
if __name__ == "__main__":
main()