Mailman 3 December 2007 - python-uk

Minimalistic software transactional memory
by Michael Sparks Dec. 21, 2007

Dec. 21, 2007

I've just posted this message on comp.lang.python fishing for comments, but I'll post it here in case there's any feedback this way :-) (apologies for any dupes people get - I don't *think* python-uk & pyconuk are strict subsets) I'm interested in writing a simple, minimalistic, non persistent (at this stage) software transactional memory (STM) module. The idea being it should be possible to write such a beast in a way that can be made threadsafe fair easily. For those who don't know, STM is a really fancy way of saying variables with version control (as far as I can tell :-) designed to enable threadsafe shared data. I'm starting with the caveat here that the following code is almost certainly not threadsafe (not put any real thought into that as yet), and I'm interested in any feedback on the following: * Does the API look simple enough? * Are there any glaring mistakes in the code ? (It's always harder to see your own bugs) * What key areas appear least threadsafe, and any general suggestions around that. If I get no feedback I hope this is of interest. Since these things get archived, if you're reading this a month, 6 months, a year or more from now, I'll still be interested in feedback... OK, API. First of all we need to initialise the store: S = Store() We then want to get a value from the store such that we can use the value, and do stuff with it: greeting = S.using("hello") Access the value: print repr(greeting.value) Update the value: greeting.set("Hello World") Commit the value back to the store: greeting.commit() If you have concurrent updates of the same value, the following exception gets thrown: ConcurrentUpdate cf: >>> S = Store() >>> greeting = S.using("hello") >>> par = S.using("hello") >>> greeting.set("Hello World") >>> par.set("Woo") >>> greeting.commit() >>> par.commit() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 12, in commit File "<stdin>", line 11, in set __main__.ConcurrentUpdate That's pretty much the simplest API I can come up with. (I've tried a few others but didn't really like them) The way this works is we have a Store that manages Values. (perhaps a better name may be variables to avoid clashing with pythons parlance of labels and values?) Anyhow, you can ask the store for Value, which it will give you. The Value knows what it's called and where it's from, so when you tell it to commit, it can try to do so. The little detail here is you get a copy of the Value not the stored Value. (This is to avoid accidental concurrent update of the same actual object) As a result, Store looks like this: class Store(object): def __init__(self): self.store = {} def get(self, key): return self.store[key].clone() def set(self, key, value): if not (self.store[key].version > value.version): self.store[key] = Value(value.version+1, value.value, self, key) value.version= value.version+1 else: raise ConcurrentUpdate def using(self, key): try: return self.get(key) except KeyError: self.store[key] = Value(0, None,self,key) return self.get(key) def dump(self): for k in self.store: print k, ":", self.store[k] You'll note that the set method is the greatest candidate for any possible race hazard here - though I can see a possible boundary issue in "using". (I think :-) Otherwise I think the above code is relatively straightforward. You'll note that this API allows this: greeting.set("Hello") greeting.commit() greeting.set("Hello World") greeting.commit() greeting.set("Hello World. Game") greeting.commit() greeting.set("Hello World. Game Over") greeting.commit() The other class is value that looks like this: class Value(object): def __init__(self, version, value,store,key): self.version = version self.value = value self.store = store self.key = key def __repr__(self): return "Value"+repr((self.version,self.value,self.store,self.key)) def set(self, value): self.value = value def commit(self): self.store.set(self.key, self) def clone(self): return Value(self.version, self.value,self.store,self.key) To me this looks like a pretty complete minimalistic thing, which does seem to work OK, but I'm interested in the three points I mention above - if anyone is willing to comment - specifcally: * Does the API look simple enough? * Are there any glaring mistakes in the code ? (It's always harder to see your own bugs) * What key areas appear least threadsafe, and any general suggestions around that. Full code below. Many thanks for any comments in advance, Michael -- Michael Sparks, Kamaelia Project Lead http://kamaelia.sourceforge.net/Developers/ http://yeoldeclue.com/blog #!/usr/bin/python class ConcurrentUpdate(Exception): pass class Value(object): def __init__(self, version, value,store,key): self.version = version self.value = value self.store = store self.key = key def __repr__(self): return "Value"+repr((self.version,self.value)) def set(self, value): self.value = value def commit(self): self.store.set(self.key, self) def clone(self): return Value(self.version, self.value,self.store,self.key) class Store(object): def __init__(self): self.store = {} def get(self, key): return self.store[key].clone() def set(self, key, value): if not (self.store[key].version > value.version): self.store[key] = Value(value.version+1, value.value, self, key) value.version= value.version+1 else: raise ConcurrentUpdate def using(self, key): try: return self.get(key) except KeyError: self.store[key] = Value(0, None,self,key) return self.get(key) def dump(self): for k in self.store: print k, ":", self.store[k] S = Store() greeting = S.using("hello") print repr(greeting.value) greeting.set("Hello World") greeting.commit() # ------------------------------------------------------ print greeting S.dump() # ------------------------------------------------------ par = S.using("hello") par.set("Woo") par.commit() # ------------------------------------------------------ print greeting S.dump() # ------------------------------------------------------ greeting.set("Woo") greeting.commit() print repr(greeting), repr(greeting.value) S.dump()

2 7

Cambridge & East Anglia Pub Meeting, 8th *Jan*, not Feb
by Tony Ibbs Dec. 20, 2007

Dec. 20, 2007

Apologies -- the next Cambridge & East Anglian Python group meeting will be on the 8th *January* 2008. The other details were right, though: Carlton Arms at 8pm. Tony Ibbs / Tibs

1 0

Cambridge & East Anglia Pub Meeting, 8th Feb
by Tony Ibbs Dec. 20, 2007

Dec. 20, 2007

The next meeting of the Cambridge & East Anglia Python group will be at 8pm on Tuesday 8th February 2008 at the Carlton Arms (http://www.thecarltonarms.co.uk/). Meetings after that will be on the first Tuesday of each month, same time, same place. Tony Ibbs / Tibs -- tibs(a)tibsnjoan.co.uk http://www.pyconuk.org/community/Cambridge_and_East_of_England http://groups.google.com/group/campug

1 0

DJANGO/Python Developer positions (Contract/Permanent)
by james tarin Dec. 14, 2007

Dec. 14, 2007

Hi There, I'm hoping it is OK to post this message to this list, as I have seen Job ads here before: We are currently expanding our in-house team to take forward the development of an exciting Web 2.0 business networking platform and have both permanent and contract opportunities for django/python developers. We are a small team which is working on a functionally complex Web 2.0networking platform and are looking for talented developers to play an important role in this innovative project. Comfortable working with others and able to talk to non-technical staff, this is an opportunity for your creative side. The people we're looking for will have experience in requirements analysis, design, coding and unit testing of scalable, distributed, fault-tolerant applications in Web environments. You will also need the following: - Development experience using Python and preferably DJANGO - Experience of at least one other OO language such as Java or C++ - Hands-on knowledge of relational databases (preferably PostgreSQL) - Basic LINUX system administration skills - Experience of working with Subversion or other source control systems If you are in need of a new challenge then give me (James) a ring on 01865 339395 or mail me at spam*at*meltwaterventures.com

1 0

Re: [python-uk] Python and Linux Vacancies
by Rakesh Thakrar Dec. 10, 2007

Dec. 10, 2007

Hi Mike, Thanks for getting back to me. Could you please send me your CV with your contact details? Regards Rakesh -----Original Message----- From: python-uk-bounces(a)python.org [mailto:python-uk-bounces@python.org] On Behalf Of Mike Ross Sent: Monday, December 10, 2007 9:20 AM To: UK Python Users Subject: Re: [python-uk] Python and Linux Vacancies Hi Rakesh, Can you provide me with more details on the Python vacancies in Central and South London? What are the full job descriptions and which companies are recruiting? Regards, Mike Ross. > Hi All, > > > > I am looking for a number of Permanent Python Developers for clients > based in Central London, South London and Bristol. > > > > I am also looking for a Linux enthusiasts (graduates welcome to apply) > for an innovative software company in Cambridge. > > > > If you are interested in finding out more please do not hesitate to > contact me. > > > > Regards > > Rakesh > > > > ___________________ > Rakesh Thakrar > Manager > Microcom > Recruitment Division > Tel: 0845 389 2322 > Mob: 079 7094 3227 > Fax: 0845 389 2392 > www.microcom-recruitment.com <http://www.microcom-recruitment.com> > Unit F > The Chase > Foxholes Business Park > John Tate Road > Hertford > SG13 7NN > > Permanent and Contract IT Recruitment Specialists > > ____________________________________ > > ************************************************************ > The views expressed in this e-mail are not necessarily the views of > European Recruitment Network Ltd, its directors, officers or employees > make no representation or accept any liability for its accuracy or > completeness unless expressly stated to the contrary. > This e-mail, and any attachments are strictly confidential and intended > for the addressee(s) only. > The content may also contain legal, professional or other privileged > information. Unless expressly stated to the contrary, no contracts may > be concluded on behalf of European Recruitment Network Ltd by means of > e-mail communication. You may report the matter by calling us on 0845 > 389 2322. > Please ensure you have adequate virus protection before you open or > detach any documents from this transmission. European Network > Recruitment Ltd does not accept any liability for viruses. > > European Recruitment Network Ltd is registered in England: Company > number: > 5651508. > Registered Office: Greener House, 66-68 Haymarket, London, SW1Y 4RF > > ************************************************************ > > > > _______________________________________________ > python-uk mailing list > python-uk(a)python.org > http://mail.python.org/mailman/listinfo/python-uk > _______________________________________________ python-uk mailing list python-uk(a)python.org http://mail.python.org/mailman/listinfo/python-uk

1 0

Python and Linux Vacancies
by Rakesh Thakrar Dec. 10, 2007

Dec. 10, 2007

Hi All, I am looking for a number of Permanent Python Developers for clients based in Central London, South London and Bristol. I am also looking for a Linux enthusiasts (graduates welcome to apply) for an innovative software company in Cambridge. If you are interested in finding out more please do not hesitate to contact me. Regards Rakesh ___________________ Rakesh Thakrar Manager Microcom Recruitment Division Tel: 0845 389 2322 Mob: 079 7094 3227 Fax: 0845 389 2392 www.microcom-recruitment.com <http://www.microcom-recruitment.com> Unit F The Chase Foxholes Business Park John Tate Road Hertford SG13 7NN Permanent and Contract IT Recruitment Specialists ____________________________________ ************************************************************ The views expressed in this e-mail are not necessarily the views of European Recruitment Network Ltd, its directors, officers or employees make no representation or accept any liability for its accuracy or completeness unless expressly stated to the contrary. This e-mail, and any attachments are strictly confidential and intended for the addressee(s) only. The content may also contain legal, professional or other privileged information. Unless expressly stated to the contrary, no contracts may be concluded on behalf of European Recruitment Network Ltd by means of e-mail communication. You may report the matter by calling us on 0845 389 2322. Please ensure you have adequate virus protection before you open or detach any documents from this transmission. European Network Recruitment Ltd does not accept any liability for viruses. European Recruitment Network Ltd is registered in England: Company number: 5651508. Registered Office: Greener House, 66-68 Haymarket, London, SW1Y 4RF ************************************************************

2 1

Forwarding an Agency python request
by Michael Grazebrook Dec. 6, 2007

Dec. 6, 2007

I know it's an agency, and know nothing about the agency, but since at least one person at last night's meeting was looking for work I hope it's OK to forward the following spam: ------ From othon.vroulakis(a)it-skillfinder.co.uk A leading investment bank, located in Central London, is currently looking for Python developers to join their team. The ideal candidate will have great technical skills as well as a proven financial background (ideally in credit derivatives). Duration of contract: 6 months extendable with the choice of working permanently for the employer. Excellent rates guaranteed. Start date: ASAP but could wait for the right person. Othon Vroulakis IT- Skillfinder 20 St Dunstan's Hill London EC3R 8HY www.it-skillfinder.co.uk Direct Line: +44 (0)20 7256 3538 Switchboard: +44 (0)20 7256 3550 Fax: +44(0)20 7256 3551

1 0

Anyone alive
by andy Dec. 6, 2007

Dec. 6, 2007

Hi all At the risk of being flamed, I just wanted to see if this list was still active. I've been a subscriber for a few days now and there have been no posts. Andy -- "If they can get you asking the wrong questions, they don't have to worry about the answers." - Thomas Pynchon, "Gravity's Rainbow"

5 5

Re: [python-uk] Anyone alive?
by Alexander Harrowell Dec. 5, 2007

Dec. 5, 2007

I'm sure many have seen this: http://xkcd.com/353/

2 1

Re: [python-uk] Anyone alive (Out of office)
by Pierre DeWet Dec. 5, 2007

Dec. 5, 2007

I will be out of the office until Monday 10 December. If your request is urgent, please contact the helpdesk at: helpdesk(a)bitc.org.uk, alternatively, please dial: 0207 566 8771 Cheers Pierre

1 0