Passing instance method issues in a process pool

1, a number of processes, parameters to the instance method, successive runs without problems, the code is as follows:

Import Multiprocessingclass MyClass (object):    def calc (self,num):        print ' The number is ', numif __name__ = = ' __ main__ ':    mc = MyClass ()    ths = [multiprocessing. Process (target = Mc.calc,args = (i,)) for I in a range (3)] for    th in ths:        Th.start ()

Operation Result:

The number is  0the number was  1the number is  2

2, put in the process pool together concurrency

Import Multiprocessingclass MyClass (object):    def calc (self,num):        print ' The number is ', numif __name__ = = ' __ main__ ':    mc = MyClass ()    pool = multiprocessing. Pool (processes = 3)    Pool.apply_async (Mc.calc, (3,))    Pool.apply_async (Mc.calc, (4,))    Pool.apply_ Async (Mc.calc, (5,))    pool.close ()    pool.join ()    print ' end! '

Operation Result:

end!

Only the final result is printed, and the instance method passed in is not running at all!!!

3, the solution is as follows:

Import Multiprocessingimport copy_regimport typesdef _reduce_method (m):    if M.im_self is None:        return GetAttr, ( M.im_class, M.im_func.func_name)    else:        return getattr, (m.im_self, M.im_func.func_name) Copy_reg.pickle ( Types. Methodtype, _reduce_method) class MyClass (object):    def calc (self,num):        print ' The number is ', numif __name__ = = ' __main__ ':    mc = MyClass ()    pool = multiprocessing. Pool (processes = 3)    Pool.apply_async (Mc.calc, (3,))    Pool.apply_async (Mc.calc, (4,))    Pool.apply_async ( Mc.calc, (5,))    pool.close ()    pool.join ()    print ' end! '

Operation Result:

The number is  4the number was  3the number is  5end!

When an instance method is used in the process pool of a child process, the program actually calls multiprocessing. Pipe to serialize data. python2.7, Multiprocessing.pipe is implemented using C language and is immediately called

Pickle_dumps, instead of calling Forkingpickler, the instance method passed in does not work.

However, if you use Copy_reg to register an instance method, it is unlikely that it will become possible.

After the python3.0 version, the instance method can be serialized normally, no need to use Copy_reg.

Detailed instructions can also be consulted:

http://stackoverflow.com/questions/27318290/ Why-can-i-pass-an-instance-method-to-multiprocessing-process-but-not-a-multipro

　　

　　

　　

　　

　　

Passing instance method issues in a process pool