如下，但执行的时候并没有返回任何参数

Question

p=Pool(20)with open(temp_path,'r') as f:for line in f.readlines():p.apply_async(execute_monitor_sql,args=(type,)) --其中execute_monitor_sql函数会返回一个执行结果。我需要将这些结果汇总到一个参数p.close()p.join()

Answer 1

共享变量的方法。

没有办法直接实现你的需求，但是，你可以用共享变量的方法实现，比如：

def worker(procnum, return_dict):

'''worker function'''

print str(procnum) + ' represent!'

return_dict[procnum] = procnumif __name__ == '__main__':

manager = Manager()

return_dict = manager.dict()

jobs = []    for i in range(5):

p = multiprocessing.Process(target=worker, args=(i,return_dict))
jobs.append(p)

p.start()    for proc in jobs:

proc.join()    print return_dict.values()

Answer 2

交换数据一般用queue吧。

17.2.1.3. Exchanging objects between processes

multiprocessing supports two types of communication
channel between processes:

Queues

The Queue
class is a near clone of queue.Queue. For example:

from multiprocessing import Process, Queue

def f(q):
q.put([42, None, 'hello'])

if __name__ == '__main__':
q = Queue()
p = Process(target=f, args=(q,))
p.start()
print(q.get()) # prints "[42, None, 'hello']"
p.join()

Queues are thread and process safe.

Pipes

The Pipe() function returns a pair of connection objects
connected by a pipe which by default is duplex (two-way). For example:

from multiprocessing import Process, Pipe

def f(conn):
conn.send([42, None, 'hello'])
conn.close()

if __name__ == '__main__':
parent_conn, child_conn = Pipe()
p = Process(target=f, args=(child_conn,))
p.start()
print(parent_conn.recv()) # prints "[42, None, 'hello']"
p.join()

The two connection objects returned by Pipe()
represent the two ends of the pipe. Each connection object has send()
and recv()
methods (among others). Note that data in a pipe may become corrupted if two
processes (or threads) try to read from or write to the same end of the
pipe at the same time. Of course there is no risk of corruption from processes
using different ends of the pipe at the same time.