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• waiting for 2 different events in a single thread

  - by João Portela

  component A (in C++) - is blocked waiting for alarm signals (not relevant) and IO signals (1 udp socket). has one handler for each of these. component B (java) - has to receive the same information the component A udp socket receives. periodicaly gives instructions that should be sent through component A udp socket. How to join both components? it is strongly desirable that: the changes to attach component B to component A are minimal (its not my code and it is not very pleasent to mess with). the time taken by the new operations (usually communicating with component B) interfere very little with the usual processing time of component A - this means that if the operations are going to take a "some" time I would rather use a thread or something to do them. note: since component A receives udp packets more frequently that it has component B instructions to forward, if necessary, it can only forward the instructions (when available) from the IO handler. my initial ideia was to develop a component C (in C++) that would sit inside the component A code (is this called an adapter?) that when instanciated starts the java process and makes the necessary connections (that not so little overhead in the initialization is not a problem). It would have 2 stacks, one for the data to give component B (lets call it Bstack) and for the data to give component A (lets call it Astack). It would sit on its thread (lets call it new-thread) waiting for data to be available in Bstack to send it over udp, and listen on the udp socket to put data on the Astack. This means that the changes to component A are only: when it receives a new UDP packet put it on the Bstack, and if there is something on the Astack sent it over its UDP socket (I decided for this because this socket would only be used in the main thread). One of the problems is that I don't know how to wait for both of these events at the same time using only one thread. so my questions are: Do I really need to use the main thread to send the data over component A socket or can I do it from the new-thread? (I think the answer is no, but I'm not sure about race conditions on sockets) how to I wait for both events? boost::condition_variable or something similar seems the solution in the case of the stack and boost::asio::io_service io_service.run() seems like the thing to use for the socket. Is there any other alternative solution for this problem that I'm not aware of? Thanks for reading this long text but I really wanted you to understand the problem.

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• Is OOP based on any branch of mathematics?

  - by ektrules

  I know relational databases are based on set-theory, functional programming is based on lambda calculus, logic programming is based on logic (of course :)), and now that I think of it; I'm not sure if imperative and generic programming is based on any particular branch of mathematics either.

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• Python shortcuts

  - by lyrae

  Python is filled with little neat shortcuts. For example: self.data = map(lambda x: list(x), data) and (although not so pretty) tuple(t[0] for t in self.result if t[0] != 'mysql' and t[0] != 'information_schema') among countless others. In the irc channel, they said "too many to know them all". I think we should list some here, as i love using these shortcuts to shorten & refctor my code. I'm sure this would benefit many.

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• Rails: three most recent records by unique belongs_to associated record

  - by Dennis Collective

  class User has_many :comments end class Comment belongs_to :user named_scope :recent, :order => 'comments.created_at DESC' named_scope :limit, lambda { |limit| {:limit => limit}} named_scope :by_unique_users end what would I put in the :by_unique_users so that I can do Comment.recent.by_unique_users.limit(3), and only get one comment per user on sqlite named_scope :by_unique_user, :group = "user_id" works, but makes it freak out on postgres, which is deployed on production PGError: ERROR: column "comments.id" must appear in the GROUP BY clause or be used in an aggregate function

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• Dealing with &rest-parameters in common lisp

  - by Patrick

  I want define a functions that accepts &rest - parameters and delegates them to another function. (html "blah" "foo" baz) = "blahfoobaz" I did not find a better way than this one: (defun html (&rest values) (concatenate 'string "" (reduce #'(lambda(a b) (concatenate 'string a b)) values :initial-value "") "")) But this looks somewhat glumbsy to me, since line 4 does no more than concatenating the &rest parameter "values". I tried (concatenate 'string "" (values-list values) "") but this does not seem to work (SBCL). Could someone give me an advice? Kind regards

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• Is there any standard delete functor?

  - by FredOverflow

  I am looking for a functor that deletes its argument: template<class T> struct delete_functor { void operator()(T* p) { delete p; } }; Is there something like this in std, tr1 or boost?

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• Calendar control GUI C++ library

  - by Dmitriy

  Who knows a good component for a "calendar control" (NOT date/time picker)? "Calendar control" means something like Mozilla Sunbird: Requirements to the control: - C++; - Day/Week/Month view; - Support of several calendars; - Without MFC dependences; Nice to have: - Open source; - Cross plathform; - Free; - Minimum external dependences (boost etc are fine);

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• small & readable scheme interpreter in C++ ?

  - by anon

  Anyone know of a good / small scheme interpreter in C++? Perferably something < 2000 LOC, with a simple garbage collectro (either compacting or mark & sweep), no need to support all of R5RS, just basics of if/lambda/set!/cons/car/cdr and some basic operations. Thanks!

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• Is there any documentation for the Cassandra Erlang interface?

  - by Zubair

  I have looked everywhere, and to use Cassandra from Erlang you end up having to download (amongst others): boost thrift : and then you have generate the erlang library by hand, and then copy lib files and beams files. Once you have the whole thing working there is absolutely zero documentation anywhere. If anyone could show me some user friendly documentation it would be much appreciated.

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• Debugging with cgdb -- want to debug only my code

  - by rkbang

  Hello all, I am using standard template libraries along with boost. I want to debug code using cgdb. But I just want to debug my code while doing next and step in cgdb, like right now it enters the code in other libraries whereas I want it should just return or step into the code which I have coded and wrote down. Is there any way to make this happen.

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• Python - Differences between elements of a list

  - by psihodelia

  Given a list of numbers how to find differences between every (i)-th and (i+1)-th of its elements? Should one better use lambda or maybe lists comprehension?

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• Approaching Java from a Ruby perspective

  - by Travis

  There are plenty of resources available to a Java developer for getting a jump-start into Ruby/Rails development. The reverse doesn't appear to be true. What resources would you suggest for getting up-to-date on the current state of java technologies? How about learning how to approach DRY (don't repeat yourself) without the use of metaprogramming? Or how to approach various scenarios where a ruby developer is used to passing in a function (proc/lambda/block) as an argument (callbacks, etc)?

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• Any PHP MVC framework planning to use 5.3 features?

  - by alexandrul

  I would like to get started with PHP, and 5.3 release seems to bring many nice features (namespaces, lambda functions, and many others). I have found some MVC frameworks, and some of them support only PHP 5: PHP Frameworks PHP MVC Frameworks Model–view–controller on Wikipedia but can anyone recommend one of those MVC frameworks that plans to actively use PHP 5.3 features, not just being compatible with PHP 5.3? Update Results so far: Zend Framework 2.0 (in development) Lithium (in development, based on CakePHP) Symfony (in development) FLOW3 (in development, alpha)

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• How to set configuration properties in VS once and for all?

  - by atch

  In VS 2010RC I have to specify configuration properties and specifically included path every time I'm creating new project. Is there a way to do it just once for all future projects? I'm asking this for a reason that I'm starting to use Boost libraries and I have to specify all those paths every time I'm creating project which is bit tedious.

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• Are incremental Macro definition possible?

  - by Davorak

  I often find the following type of incremental definition useful: (define (foo) (display "bar")) (foo) ;prints bar (define foo (let ((bar foo)) (lambda () (display "foo") (bar)))) (foo) ;prints foobar How do I preform this type of incremental definition with macros? I could not get let-syntax to provide the same functionality. Currently I use plt scheme, but would like to see answers in different lisp implementations as well.

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• Compilation error with C++ templates. Is there any easy way to understand them?

  - by Naveen

  While working with the C++ templates (most of the time using STL or boost) I run into the compilation errors that are miles long. I find it hard to figure out what compiler is trying to tell me. Is there any quick reference guide or a tool which can convert this error into something more understandable to humans?

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• What should my teacher talk about in my Advanced C++ class? [advice needed]

  - by Goose Bumper

  My teacher for Advanced C++ has opened the class up for students to suggest whatever topics we want. What are some good advanced C++ topics to know? We've already covered: template metaprogramming the STL (obviously) introduction to the boost libraries Please give reasons for suggestions as well.

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• Free JVM profilers for websites

  - by 2Real

  I'm looking for a JVM profiler (preferably open source) so I can look at the heap and cpu usage of my personal website. I've used Lambda Probe, and I like it because it provides a web interface for my remote Unix computer that has no display. I was wondering what else is available Thanks,

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• Is there any cross-platform threading library in C/C++?

  - by NumberFour

  Hello, I'm looking for some easy to use cross-platform threading library written in C/C++. What's your opinion on boost::thread or Pthreads? Does Pthreads run only on POSIX compliant systems? What about the threading support in the Qt library? Thanks for any hints.

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• Compare versions as strings

  - by Dmitriy

  Comparing version numbers as strings is not so easy... "1.0.0.9" "1.0.0.10", but it's not correct. Obvious way to do it properly is parse these strings, convert to numbers and compare as numbers. Is it other way to do it more "elegant"? For example, boost::string_algo...

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• Sorting a 2 dimensional array on multiple columns

  - by Anon

  I need to sort a 2 dimensional array of doubles on multiple columns using either C or C++. Could someone point me to the algorithm that I should use or an existing library (perhaps boost?) that has this functionality? I have a feeling that writing a recursive function may be the way to go but I am too lazy to write out the algorithm or implement it myself if it has been done elsewhere. :-) Thanks

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• Python Logging across multiple classes and files; how to configure so as to be easily disabled?

  - by mellort

  Currently, I have osmething like this in all of my classes: # Import logging to log information import logging # Set up the logger LOG_FILENAME = 'log.txt' logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG) This works well, and I get the output I want, but I would really like to have all this sort of information in one place, and be able to just do something like import myLogger and then start logging, and then hopefully be able to just go into that file and turn off logging when I need an extra performance boost. Thanks in advance

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• Find out the number of digits of min/max values of an integral type at compile time

  - by Checkers

  Is there a way to find out the number of digits of min/max values of an integral type at compile time so that it's suitable to be placed as a template parameter? Ideally, there will be an existing solution in, for example, Boost MPL. Failing that I'm looking for some pointers for a hand-coded solution.

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• how to made a "admin-only" for in html page (not view.py),has this method :user.is_superuser ??

  - by zjm1126

  in views.py: @user_passes_test(lambda u: u.is_superuser) def h_view(request): return render_to_response('mytest/news.html',context_instance=RequestContext(request)) but i want to show this page when admin login,and my now page is : <li id="tab_mytest"><a href="{% url mytest_list %}" class="{% block mytest_css_name %}{% endblock %}">{% trans "mytest" %}</a></li> how to change it, has this method :user.is_superuser ?? thanks

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• Is incremental Macro definition possible?

  - by Davorak

  I often find the following type of incremental definition useful: (define (foo) (display "bar")) (foo) ;prints bar (define foo (let ((bar foo)) (lambda () (display "foo") (bar)))) (foo) ;prints foobar How do I preform this type of incremental definition with macros? I could not get let-syntax to provide the same functionality. Currently I use plt scheme, but would like to see answers in different lisp implementations as well.

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