Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
On Feb 11, 2007, at 7:29 PM, Manuel Vazquez Acosta wrote: My scenario is akin a consumer-producer with shared buffer. Consumers pull items from the buffer whilst producers put items in the buffer. The buffer is an OOBTree along with an IOBTree which gives serial numbers to the keys of the OOBTree. I'm not sure if this is a match, but if you follow Chris' suggestions (which I recommend generally) then you might want to look at zc.queue: http://cheeseshop.python.org/pypi/zc.queue/ . Gary ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
Hi Gary, Although the shared buffer indeed has a queue-like interface there's a catch for my needs. I need that pull method to retrieve the item in the head and to move the head forward, and not to remove the item from the buffer. Just like zc.queue I need a single copy of a item in the queue, but I also need this uniqueness over the time, so that any item which has being consumed already, does not get back to buffer. Thanks for your advice, I haven't seen zc.queue, so you comments are really an improvement to my knowledge. Besides I'm going to take a peek at zc.queue and compare it with my own implementation. Thanks and best regards, Manuel. Gary Poster wrote: On Feb 11, 2007, at 7:29 PM, Manuel Vazquez Acosta wrote: My scenario is akin a consumer-producer with shared buffer. Consumers pull items from the buffer whilst producers put items in the buffer. The buffer is an OOBTree along with an IOBTree which gives serial numbers to the keys of the OOBTree. I'm not sure if this is a match, but if you follow Chris' suggestions (which I recommend generally) then you might want to look at zc.queue: http://cheeseshop.python.org/pypi/zc.queue/ . Gary ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
On Feb 12, 2007, at 10:01 AM, Manuel Vazquez Acosta wrote: Hi Gary, Although the shared buffer indeed has a queue-like interface there's a catch for my needs. I need that pull method to retrieve the item in the head and to move the head forward, and not to remove the item from the buffer. Just like zc.queue I need a single copy of a item in the queue, but I also need this uniqueness over the time, so that any item which has being consumed already, does not get back to buffer. Ah, OK. FWIW, you could get the same functionality with a wrapper around a zc.queue pretty easily, of course, with at least a couple of variants off the top of my head (both involving an additional data structure that you maintain, and supplying your own `put` and `pull` that wrap the zc.queue methods, either with composition or inheritance). If, instead, you move to a multi-threaded model following the same approach you outlined before (sequential int keys, IIUC) you'll need to be careful of write conflict errors. Gary ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
On Sun, Feb 11, 2007 at 07:29:58PM -0500, Manuel Vazquez Acosta wrote: The other question is about compiling ZODB without using the out-of-the-box distutils installation procedure. I'm also playing with Zope and Plone, so I have several instances on the same machine. I think installing with distutils may cause conflicts with the Zope instances. Am I right? If so, then how should I install ZODB side-by-side the consumer-producer application? This sounds like a job for zc.buildout. Marius Gedminas -- Special bonus feature: absolutely nowhere in RetchMail's code is there an arbitrary 3-second sleep(). Wow! What other mail retriever can say that? (Hint: not fetchmail.) -- http://open.nit.ca/wiki/index.php?page=RetchMail signature.asc Description: Digital signature ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
Manuel Vazquez Acosta wrote at 2007-2-11 19:29 -0500: ... I have read that each thread should have its own connection to the DB. However, in my case, each thread should be aware of what is actually in the DB at all times. So I wonder if I can shared the connection between those threads as long as I take the means to protect it (i.e RLock). You might be able to do that -- but you would loose almost all benefits of the ZODB: an earlier discussion with Jim and Jeremy indicated that not only writes would need such locking but reads as well I think, you should forget about using the same ZODB connection in different threads... -- Dieter ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Threads, ZODB, and how to install ZODB without distutils
Chris, Thanks for your response. I will try the locking first and the see if I can implement a transaction manager of my own. I will read about virtualizing Python, I'm a debian user :)) Thanks and best regards, Manuel. Chris McDonough wrote: On Feb 11, 2007, at 7:29 PM, Manuel Vazquez Acosta wrote: Hi all, I'm writing a small application for which I want to use ZODB's persistence machinery. I have a couple of question, though. I have read that each thread should have its own connection to the DB. However, in my case, each thread should be aware of what is actually in the DB at all times. So I wonder if I can shared the connection between those threads as long as I take the means to protect it (i.e RLock). I am not certain, actually. The mechanism for doing this is in there. The interfaces.py file states: Synchronization --- A Connection instance is not thread-safe. It is designed to support a thread model where each thread has its own transaction. If an application has more than one thread that uses the connection or the transaction the connection is registered with, the application should provide locking. And it goes on to talk about the sync=False parameter vaguely. But the story doesnt really end there... there is also the capability to register a different transaction manager at DB open time.. the default one assumes one transaction per thread. I'd need to dig through all this code to reunderstand it, but it looks possible. My scenario is akin a consumer-producer with shared buffer. Consumers pull items from the buffer whilst producers put items in the buffer. The buffer is an OOBTree along with an IOBTree which gives serial numbers to the keys of the OOBTree. The typical way to do this using one-connection-per-thread and a threaded txn manager would be to call transaction.commit() when mutating the shared data structures. To detect changes to the objects provided by a connection (due to other threads committing during the connection's transaction), you can connection.sync(). Zope calls transaction.begin() at the beginning of a request and either transaction.abort() (on failure) or transaction.commit() (on success) at its termination. It never needs to do an explict connection.sync() because it never wants to do a dirty read (each request has its own connection and sees its connection data as canonical for the duration of its existence). Zope handles conflicts by retrying the request. But Zope has it easy because the web has natural transaction boundaries that don't always exist in GUI apps or other apps with a different request/response cycle. The other question is about compiling ZODB without using the out-of-the-box distutils installation procedure. I'm also playing with Zope and Plone, so I have several instances on the same machine. I think installing with distutils may cause conflicts with the Zope instances. Am I right? If so, then how should I install ZODB side-by-side the consumer-producer application? The easiest thing to do here is to install a separate Python instance for each project. Alternately if you're on UNIX, you can use virtual python (http://peak.telecommunity.com/dist/virtual-python.py) which makes a tree of symlinks that acts like a new Python instance but has its own site packages directory in which distutils stuff is installed. If you're on Windows, I believe Zope/Plone ship with their own copy of Python on that platform, so installing to the system python shouldnt create a conflict. - C ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
