python - 在装饰器中运行多处理

Question

我想更新有关装饰器内部多处理的问题(我之前的问题在我看来已经死了:))。我偶然发现了这个问题，不幸的是我不知道如何解决这个问题。为了我的应用程序的需要，我必须在装饰器中使用多处理但是......当我在装饰器中使用多处理时我得到错误: Can't pickle <function run_testcase at 0x00000000027789C8>: it's not found as __main__.run_testcase .另一方面，当我像普通函数一样调用我的多处理函数时 wrapper(function,*arg)有用。这非常棘手，但我不知道我做错了什么。我几乎可以得出结论，这是 python 错误 :)。也许有人知道这个问题的解决方法，但语法相同。我在 Windows 上运行这段代码(不幸的是)。

上一个问题:Using multiprocessing inside decorator generates error: can't pickle function...it's not found as

模拟这个错误最简单的代码:

from multiprocessing import Process,Event

class ExtProcess(Process):
    def __init__(self, event,*args,**kwargs):
        self.event=event
        Process.__init__(self,*args,**kwargs)

    def run(self):
        Process.run(self)
        self.event.set()

class PythonHelper(object):

    @staticmethod
    def run_in_parallel(*functions):
        event=Event()
        processes=dict()
        for function in functions:
            fname=function[0]
            try:fargs=function[1]
            except:fargs=list()
            try:fproc=function[2]
            except:fproc=1
            for i in range(fproc):
                process=ExtProcess(event,target=fname,args=fargs)
                process.start()
                processes[process.pid]=process
        event.wait()
        for process in processes.values():
            process.terminate()
        for process in processes.values():
            process.join()

class Recorder(object):
    def capture(self):
        while True:print("recording")

from z_helper import PythonHelper
from z_recorder import Recorder

def wrapper(fname,*args):
    try:
        PythonHelper.run_in_parallel([fname,args],[Recorder().capture])
        print("success")
    except Exception as e:
        print("failure: {}".format(e))

from z_wrapper import wrapper
from functools import wraps

class Report(object):
    @staticmethod
    def debug(fname):
        @wraps(fname)
        def function(*args):
            wrapper(fname,args)
        return function

执行:

from z_report import Report
import time

class Test(object):
    @Report.debug
    def print_x(self,x):
        for index,data in enumerate(range(x)):
            print(index,data); time.sleep(1)

if __name__=="__main__":
    Test().print_x(10)

我在之前的版本中添加了@wraps

我的回溯:

Traceback (most recent call last):
  File "C:\Interpreters\Python32\lib\pickle.py", line 679, in save_global
    klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'run_testcase'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\EskyTests\w_Logger.py", line 19, in <module>
    logger.run_logger()
  File "C:\EskyTests\w_Logger.py", line 14, in run_logger
    self.run_testcase()
  File "C:\EskyTests\w_Decorators.py", line 14, in wrapper
    PythonHelper.run_in_parallel([function,args],[recorder.capture])
  File "C:\EskyTests\w_PythonHelper.py", line 25, in run_in_parallel
    process.start()
  File "C:\Interpreters\Python32\lib\multiprocessing\process.py", line 130, in start
    self._popen = Popen(self)
  File "C:\Interpreters\Python32\lib\multiprocessing\forking.py", line 267, in __init__
    dump(process_obj, to_child, HIGHEST_PROTOCOL)
  File "C:\Interpreters\Python32\lib\multiprocessing\forking.py", line 190, in dump
    ForkingPickler(file, protocol).dump(obj)
  File "C:\Interpreters\Python32\lib\pickle.py", line 237, in dump
    self.save(obj)
  File "C:\Interpreters\Python32\lib\pickle.py", line 344, in save
    self.save_reduce(obj=obj, *rv)
  File "C:\Interpreters\Python32\lib\pickle.py", line 432, in save_reduce
    save(state)
  File "C:\Interpreters\Python32\lib\pickle.py", line 299, in save
    f(self, obj) # Call unbound method with explicit self
  File "C:\Interpreters\Python32\lib\pickle.py", line 623, in save_dict
    self._batch_setitems(obj.items())
  File "C:\Interpreters\Python32\lib\pickle.py", line 656, in _batch_setitems
    save(v)
  File "C:\Interpreters\Python32\lib\pickle.py", line 299, in save
    f(self, obj) # Call unbound method with explicit self
  File "C:\Interpreters\Python32\lib\pickle.py", line 683, in save_global
    (obj, module, name))
_pickle.PicklingError: Can't pickle <function run_testcase at 0x00000000027725C8>: it's not found as __main__.run_testcase

Answer 1

multiprocessing 模块通过调用 pickler 在其从属进程中“调用”函数。这是因为它必须通过它创建的 IPC 接口(interface)将函数的名称 发送到从属进程。 pickler 找出要使用的正确名称并将其发送出去，然后在另一侧 unpickler 将名称转换回函数。

当一个函数是一个类成员时，没有帮助就不能正确地 pickle。对于 @staticmethod 成员来说情况更糟，因为它们具有类型 function 而不是类型 instancemethod，这会愚弄 pickler。您可以在不使用 multiprocessing 的情况下很容易地看到这一点:

import pickle

class Klass(object):
    @staticmethod
    def func():
        print 'func()'
    def __init__(self):
        print 'Klass()'

obj = Klass()
obj.func()
print pickle.dumps(obj.func)

产生:

Klass()
func()
Traceback (most recent call last):
 ...
pickle.PicklingError: Can't pickle <function func at 0x8017e17d0>: it's not found as __main__.func

当您尝试 pickle 像 obj.__init__ 这样的常规非静态方法时，问题就更清楚了，因为 pickler 然后意识到它确实是一个实例方法:

TypeError: can't pickle instancemethod objects

然而，一切并没有丢失。您只需要添加一个间接级别。您可以提供一个在 target 进程中创建实例绑定(bind)的普通函数，向它发送至少两个参数:(pickle-able)类 instance 和功能。为了完整性，我还添加了调用函数时要使用的任何参数。然后在目标进程中调用这个普通函数，它调用类的成员函数:

def call_name(instance, name, *args = (), **kwargs = None):
    "helper function for multiprocessing: call instance.getattr(name)"
    if kwargs is None:
        kwargs = {}
    getattr(instance, name)(*args, **kwargs)

现在而不是(这是从您的链接帖子中复制的):

PythonHelper.run_in_parallel([self.run_testcase],[recorder.capture])

你会做这样的事情(你可能想对调用顺序大惊小怪):

PythonHelper.run_in_parallel([call_name, (self, 'run_testcase')],
    [recorder.capture])

(注意:这都是未经测试的，可能会有各种错误)。

---

更新

我使用了您发布的新代码并进行了试用。

首先，我必须修复 z_report.py 中的缩进(取消所有 class Report 的缩进)。

完成后，运行它会出现与您显示的错误完全不同的错误:

Process ExtProcess-1:
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/tmp/t/marcin/z_helper.py", line 9, in run
    Process.run(self)
  File "/usr/local/lib/python2.7/multiprocessing/process.py", line 114, in run
recording
[infinite spew of "recording" messages]

修复没完没了的“录音”消息:

diff --git a/z_recorder.py b/z_recorder.py
index 6163a87..a482268 100644
--- a/z_recorder.py
+++ b/z_recorder.py
@@ -1,4 +1,6 @@
+import time
 class Recorder(object):
     def capture(self):
-        while True:print("recording")
-
+        while True:
+            print("recording")
+            time.sleep(5)

剩下的一个问题是:print_x 的错误参数:

TypeError: print_x() takes exactly 2 arguments (1 given)

此时 Python 实际上为您做了所有正确的事情，只是 z_wrapper.wrapper 有点过分热心:

diff --git a/z_wrapper.py b/z_wrapper.py
index a0c32bf..abb1299 100644
--- a/z_wrapper.py
+++ b/z_wrapper.py
@@ -1,7 +1,7 @@
 from z_helper import PythonHelper
 from z_recorder import Recorder

-def wrapper(fname,*args):
+def wrapper(fname,args):
     try:
         PythonHelper.run_in_parallel([fname,args],[Recorder().capture])
         print("success")

这里的问题是，当您到达 z_wrapper.wrapper 时，函数参数已全部捆绑到一个元组中。 z_report.Report.debug 已经有:

    def function(*args):

因此这两个参数，在本例中是 main.Test 的实例和值 10，已被制成一个元组。您只希望 z_wrapper.wrapper 将该(单个)元组传递给 PythonHelper.run_in_parallel，以提供参数。如果您添加另一个 *args，该元组将被包装到另一个元组中(这次是一个元素)。 (您可以通过在 z_wrapper.wrapper 中添加 print "args:", args 来查看。)