1、Process类
from multiprocessing import Process def func(name): print('hello', name) if __name__ == '__main__': p = Process(target=func, args=('bob',)) p.start() p.join()
2、上下文和开始方法
开始方法
import multiprocessing as mp def foo(q): q.put('hello') if __name__ == '__main__': mp.set_start_method('spawn') q = mp.Queue() p = mp.Process(target=foo, args=(q,)) p.start() print(q.get()) p.join()
上下文
import multiprocessing as mp def foo(q): q.put('hello') if __name__ == '__main__': ctx = mp.get_context('spawn') q = ctx.Queue() p = ctx.Process(target=foo, args=(q,)) p.start() print(q.get()) p.join()
3、进程间交换对象
Queues
from multiprocessing import Process, Queue def func(q): q.put([42, None, 'hello']) if __name__ == '__main__': q = Queue() p = Process(target=func, args=(q,)) p.start() print(q.get()) # prints "[42, None, 'hello']" p.join()
Pipes
from multiprocessing import Process, Pipe def func(conn): conn.send([42, None, 'hello']) conn.close() if __name__ == '__main__': parent_conn, child_conn = Pipe() p = Process(target=func, args=(child_conn,)) p.start() print(parent_conn.recv()) # prints "[42, None, 'hello']" p.join()
4、进程间同步
例如你可以使用一个锁来确保只有一个进程打印到标准输出
from multiprocessing import Process, Lock def func(lock, i): lock.acquire() try: print('hello world', i) finally: lock.release() if __name__ == '__main__': lock = Lock() for num in range(10): Process(target=func, args=(lock, num)).start()
5、进程间共享状态
Shared memory
使用 Value 或 Array，数据可以存储在一个共享内存映射 。例如，下面的代码
from multiprocessing import Process, Value, Array def f(n, a): n.value = 3.1415927 for i in range(len(a)): a[i] = -a[i] if __name__ == '__main__': num = Value('d', 0.0) arr = Array('i', range(10)) p = Process(target=f, args=(num, arr)) p.start() p.join() print(num.value) print(arr[:])
参数' d '表示双精度浮点数，参数“i”表示一个带符号整数。这些共享对象将进程和线程安全的。
Server process
通过 Manager() ，返回一个管理器对象，用以控制持有Python对象的服务进程，并允许其他进程使用代理来操作它们。
通过 Manager() 返回的管理器对象支持的类型有：list, dict, Namespace, Lock, RLock, Semaphore, BoundedSemaphore, Condition, Event, Barrier, Queue, Value and Array.
from multiprocessing import Process, Manager def f(d, l): d[1] = '1' d['2'] = 2 d[0.25] = None l.reverse() if __name__ == '__main__': with Manager() as manager: d = manager.dict() l = manager.list(range(10)) p = Process(target=f, args=(d, l)) p.start() p.join() print(d) print(l)
服务进程管理器比使用共享内存对象更加灵活，因为他们可以支持任意的对象类型。同样，一个管理器可以在不同的电脑通过网络共享的过程。然而，他们慢于使用共享内存。
6、使用进程池
from multiprocessing import Pool from time import sleep def f(x): return x*x if __name__ == '__main__': # start 4 worker processes with Pool(processes=4) as pool: # print "[0, 1, 4,..., 81]" print(pool.map(f, range(10))) # print same numbers in arbitrary order for i in pool.imap_unordered(f, range(10)): print(i) # evaluate "f(10)" asynchronously res = pool.apply_async(f, [10]) print(res.get(timeout=1)) # prints "100" # make worker sleep for 10 secs res = pool.apply_async(sleep, [10]) print(res.get(timeout=1)) # raises multiprocessing.TimeoutError # exiting the 'with'-block has stopped the pool
