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Newsgroups: comp.lang.python
Date: Thu, 19 Jul 2012 08:08:49 -0700 (PDT)
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Subject: Re: reloading code and multiprocessing
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Xref: csiph.com comp.lang.python:25629

andrea crotti=E6=96=BC 2012=E5=B9=B47=E6=9C=8819=E6=97=A5=E6=98=9F=E6=9C=9F=
=E5=9B=9BUTC+8=E4=B8=8B=E5=8D=886=E6=99=8215=E5=88=8611=E7=A7=92=E5=AF=AB=
=E9=81=93=EF=BC=9A
> We need to be able to reload code on a live system.  This live system
> has a daemon process always running but it runs many subprocesses with
> multiprocessing, and the subprocesses might have a short life...
>=20
> Now I found a way to reload the code successfully, as you can see from
> this testcase:
>=20
>=20
> def func():
>     from . import a
>     print(a.ret())
>=20
>=20
> class TestMultiProc(unittest.TestCase):
>     def setUp(self):
>         open(path.join(cur_dir, &#39;a.py&#39;), &#39;w&#39;).write(old_a=
)
>=20
>     def tearDown(self):
>         remove(path.join(cur_dir, &#39;a.py&#39;))
>=20
>     def test_reloading(self):
>         &quot;&quot;&quot;Starting a new process gives a different result
>         &quot;&quot;&quot;
>         p1 =3D Process(target=3Dfunc)
>         p2 =3D Process(target=3Dfunc)
>         p1.start()
>         res =3D p1.join()
>         open(path.join(cur_dir, &#39;a.py&#39;), &#39;w&#39;).write(new_a=
)
>         remove(path.join(cur_dir, &#39;a.pyc&#39;))
>=20
>         p2.start()
>         res =3D p2.join()
>=20
>=20
> As long as I import the code in the function and make sure to remove the
> &quot;pyc&quot; files everything seems to work..
> Are there any possible problems which I&#39;m not seeing in this approach=
 or
> it&#39;s safe?
>=20
> Any other better ways otherwise?

If a byte code interpreter is embedded in the executable, then the program=
=20
can obtain or reload code objects in the run time.

In C/C++, unless one can swap some DLL safely or spawn in another process w=
ith=20
new executables obtained from other places, or a script interpreter is embe=
dded, otherwise it's not easy for an instance in C/C++ to get new methods d=
ynamically.

or=20