[ZODB-Dev] Re: Deadlock in ZODB/DB.py?

[Christian Zagrodnick]

On 09.10.2006, at 17:40, Tres Seaver wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
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> Christian Zagrodnick wrote:
>> Hi there,
>>
>> the DB.open method makes me wonder how it works
>> (http://svn.zope.org/ZODB/trunk/src/ZODB/DB.py?rev=69551&view=auto)
>>
>> It locks with self._a() and calls self._connectionMap which locks  
>> too. I
>> cannot imagine a way this could possibly work.
>>
>> I guess the lock should be released before the _connectionMap call?
>>
>> Interestingly both all the tests pass and ZODB works...
>
> Note the following in the __init__()::
>
>         # Allocate lock.
>         x = threading.RLock()
>         self._a = x.acquire
>         self._r = x.release
>
> The lock is a "reentrant" lock[1], which means that subsequent locks
> from within the same thread do not deadlock;  instead, they increment
> the lock count.
>
> [1] http://docs.python.org/lib/module-threading.html#l2h-3418


Right. *removing blindfold* This explains something :)  Thanks for  
the note.


Actually I came to that lock while investigating Ape for ZODB 3.6  
where it in some way actually *did* lock. But I'll investigate that  
later.


-- 
Christian Zagrodnick

gocept gmbh & co. kg  ·  forsterstrasse 29 · 06112 halle/saale
www.gocept.com · fon. +49 345 12298894 · fax. +49 345 12298891




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