Re: Read-write lock for Python
On Fri, Apr 29, 2011 at 12:38 AM, Ryan Kelly r...@rfk.id.au wrote: On Thu, 2011-04-28 at 07:02 -0700, Geoff Bache wrote: Hi all, I currently find myself needing a Python read-write lock. I note that there is none in the standard library, but googling python read-write lock quickly produced 6 different competing examples, including two languishing patch proposals for the standard library. I can always pick a random one and hope for the best, but I was hoping someone here might have a tip for one that has been used and debugged and is likely to work. I wrote and have used the SHLock class in threading2 which should do what you need. Don't know about likely to work but if it doesn't, I'd like to hear about it so I can fix it :-) That's good enough for me :) Thanks, I'll give it a try. /Geoff -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
Geoff Bache wrote: Hi all, I currently find myself needing a Python read-write lock. I note that there is none in the standard library, but googling python read-write lock quickly produced 6 different competing examples, including two languishing patch proposals for the standard library. I can always pick a random one and hope for the best, but I was hoping someone here might have a tip for one that has been used and debugged and is likely to work. Regards, Geoff Bache What about http://docs.python.org/library/threading.html#lock-objects ? JM -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant jeanmic...@sequans.com wrote: Geoff Bache wrote: Hi all, I currently find myself needing a Python read-write lock. I note that there is none in the standard library, but googling python read-write lock quickly produced 6 different competing examples, including two languishing patch proposals for the standard library. I can always pick a random one and hope for the best, but I was hoping someone here might have a tip for one that has been used and debugged and is likely to work. Regards, Geoff Bache What about http://docs.python.org/library/threading.html#lock-objects Those aren't read-write locks. They are basic locks, which don't distinguish between readers and writers. I need to be able to lock between reader and writer operations, without readers locking each other out. /Geoff -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
On Thu, 28 Apr 2011 19:14:45 +0200 Geoff Bache geoff.ba...@gmail.com wrote: On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant jeanmic...@sequans.com wrote: What about http://docs.python.org/library/threading.html#lock-objects Those aren't read-write locks. They are basic locks, which don't distinguish between readers and writers. I need to be able to lock between reader and writer operations, without readers locking each other out. There really isn't any such thing as read-write locks. In fact, the term locks without any further explanation is pretty loose in any case. You can use the above method to implement your own locking scheme. However, that only works if your application is a single, multi-threaded app. Is that the case? When I saw your original question I thought that you needed something inter-process. If so then you need another scheme. I think you have to first clarify your requirements and ask again. I have gleaned a little more information from your above response, you don't require readers to be locked out during an update if I understand the requirement. There is still a lot of information missing. For example: - What is being read and written? Files? - Is this a single multi-threaded app or multiple processes? - if multiple processes, can they be counted on to cooperate? - Do update requests need to be queued or is random availability OK? Now, don't just answer the above questions. Try to start with that and think about what other requirements you have. The more information you give us, the better the answer will be. You may even find that locking is not the actual answer you need. People do have a tendency to offer solutions when they think they are asking questions. Don't pre-suppose the answer. http://www.catb.org/~esr/faqs/smart-questions.html is always a good read in these situations. -- D'Arcy J.M. Cain da...@druid.net | Democracy is three wolves http://www.druid.net/darcy/| and a sheep voting on +1 416 425 1212 (DoD#0082)(eNTP) | what's for dinner. -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
On Thu, Apr 28, 2011 at 7:53 PM, D'Arcy J.M. Cain da...@druid.net wrote: On Thu, 28 Apr 2011 19:14:45 +0200 Geoff Bache geoff.ba...@gmail.com wrote: On Thu, Apr 28, 2011 at 4:28 PM, Jean-Michel Pichavant jeanmic...@sequans.com wrote: What about http://docs.python.org/library/threading.html#lock-objects Those aren't read-write locks. They are basic locks, which don't distinguish between readers and writers. I need to be able to lock between reader and writer operations, without readers locking each other out. There really isn't any such thing as read-write locks. Did you google it? I even provided the exact search terms to use in my initial posting. It takes you straight to two standard library patch proposals and four other solutions, all labelled this way (sometimes reader-writer locks admittedly). That doesn't happen if it isn't a standard problem. I'm not looking for general advice on how to solve some specific problem. I'm asking if anyone knows anything about the relative merits of the above 6 solutions. Regards, Geoff Bache -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
Geoff Bache geoff.ba...@gmail.com writes: I currently find myself needing a Python read-write lock. Please tell us what you mean by “read-write lock”. I note that there is none in the standard library, but googling python read-write lock quickly produced 6 different competing examples, including two languishing patch proposals for the standard library. That's probably because the term isn't well defined. What is your definition? -- \ “If you can't beat them, arrange to have them beaten.” —George | `\Carlin | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Read-write lock for Python
On Thu, 2011-04-28 at 07:02 -0700, Geoff Bache wrote: Hi all, I currently find myself needing a Python read-write lock. I note that there is none in the standard library, but googling python read-write lock quickly produced 6 different competing examples, including two languishing patch proposals for the standard library. I can always pick a random one and hope for the best, but I was hoping someone here might have a tip for one that has been used and debugged and is likely to work. I wrote and have used the SHLock class in threading2 which should do what you need. Don't know about likely to work but if it doesn't, I'd like to hear about it so I can fix it :-) `pip install threading2` Cheers, Ryan -- Ryan Kelly http://www.rfk.id.au | This message is digitally signed. Please visit r...@rfk.id.au| http://www.rfk.id.au/ramblings/gpg/ for details signature.asc Description: This is a digitally signed message part -- http://mail.python.org/mailman/listinfo/python-list
