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  • GAE update different fields of the same entity

    - by bach
    Hi, UserA and UserB are changing objectA.filedA objectA.filedB respectively and at the same time. Because they are not changing the same field one might think that there are no overlaps. Is that true? or the implementation of pm.makePersistnace() actually override the whole object... good to know...

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  • How to write my own global lock / unlock functions for PostgreSQL

    - by rafalmag
    I have postgresql (in perlu) function getTravelTime(integer, timestamp), which tries to select data for specified ID and timestamp. If there are no data or if data is old, it downloads them from external server (downloading time ~300ms). Multiple process use this database and this function. There is an error when two process do not find data and download them and try to do an insert to travel_time table (id and timestamp pair have to be unique). I thought about locks. Locking whole table would block all processes and allow only one to proceed. I need to lock only on id and timestamp. pg_advisory_lock seems to lock only in "current session". But my processes uses their own sessions. I tried to write my own lock/unlock functions. Am I doing it right? I use active waiting, how can I omit this? Maybe there is a way to use pg_advisory_lock() as global lock? My code: CREATE TABLE travel_time_locks ( id_key integer NOT NULL, time_key timestamp without time zone NOT NULL, UNIQUE (id_key, time_key) ); ------------ -- Function: mylock(integer, timestamp) DROP FUNCTION IF EXISTS mylock(integer, timestamp) CASCADE; -- Usage: SELECT mylock(1, '2010-03-28T19:45'); -- function tries to do a global lock similar to pg_advisory_lock(key, key) CREATE OR REPLACE FUNCTION mylock(id_input integer, time_input timestamp) RETURNS void AS $BODY$ DECLARE rows int; BEGIN LOOP BEGIN -- active waiting here !!!! :( INSERT INTO travel_time_locks (id_key, time_key) VALUES (id_input, time_input); EXCEPTION WHEN unique_violation THEN CONTINUE; END; EXIT; END LOOP; END; $BODY$ LANGUAGE 'plpgsql' VOLATILE COST 1; ------------ -- Function: myunlock(integer, timestamp) DROP FUNCTION IF EXISTS myunlock(integer, timestamp) CASCADE; -- Usage: SELECT myunlock(1, '2010-03-28T19:45'); -- function tries to do a global unlock similar to pg_advisory_unlock(key, key) CREATE OR REPLACE FUNCTION myunlock(id_input integer, time_input timestamp) RETURNS integer AS $BODY$ DECLARE BEGIN DELETE FROM ONLY travel_time_locks WHERE id_key=id_input AND time_key=time_input; RETURN 1; END; $BODY$ LANGUAGE 'plpgsql' VOLATILE COST 1;

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  • How to infer the type of a derived class in base class?

    - by enzi
    I want to create a method that allows me to change arbitrary properties of classes that derive from my base class, the result should look like this: SetPropertyValue("size.height", 50); – where size is a property of my derived class and height is a property of size. I'm almost done with my implementation but there's one final obstacle that I want to solve before moving on, to describe this I will first have to explain my implementation a bit: Properties that can be modified are decorated with an attribute There's a method in my base class that searches for all derived classes and their decorated properties For each property I generate a "property modifier", a class that contains 2 delegates: one to set and one to get the value of the property. Property Modifiers are stored in a dictionary, with the name of the property as key In my base class, there is another dictionary that contains all property-modifier-dictionaries, with the Type of the respective class as key. What the SetPropertyValue method does is this: Get the correct property-modifier-dictionary, using the concrete type of the derived class (<- yet to solve) Get the property modifier of the property to change (e.g. of the property size) Use the get or set delegate to modify the property's value Some example code to clarify further: private static Dictionary<RuntimeTypeHandle, object> EditableTypes; //property-modifier-dictionary protected void SetPropertyValue<T>(EditablePropertyMap<T> map, string property, object value) { var property = map[property]; // get the property modifier property.Set((T)this, value); // use the set delegate (encapsulated in a method) } In the above code, T is the Type of the actual (derived) class. I need this type for the get/set delegates. The problem is how to get the EditablePropertyMap<T> when I don't know what T is. My current (ugly) solution is to pass the map in an overriden virtual method in the derived class: public override void SetPropertyValue(string property, object value) { base.SetPropertyValue((EditablePropertyMap<ExampleType>)EditableTypes[typeof(ExampleType)], property, value); } What this does is: get the correct dictionary containing the property modifiers of this class using the class's type, cast it to the appropiate type and pass it to the SetPropertyValue method. I want to get rid of the SetPropertyValue method in my derived class (since there are a lot of derived classes), but don't know yet how to accomplish that. I cannot just make a virtual GetEditablePropertyMap<T> method because I cannot infer a concrete type for T then. I also cannot acces my dictionary directly with a type and retrieve an EditablePropertyMap<T> from it because I cannot cast to it from object in the base class, since again I do not know T. I found some neat tricks to infere types (e.g. by adding a dummy T parameter), but cannot apply them to my specific problem. I'd highly appreciate any suggestions you may have for me.

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  • Ruby: Alter class static method in a code block

    - by Phuong Nguy?n
    Given the Thread class with it current method. Now inside a test, I want to do this: def test_alter_current_thread Thread.current = a_stubbed_method # do something that involve the work of Thread.current Thread.current = default_thread_current end Basically, I want to alter the method of a class inside a test method and recover it after that. I know it sound complex for another language, like Java & C# (in Java, only powerful mock framework can do it). But it's ruby and I hope such nasty stuff would be available

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  • writing boot sector code

    - by JGC
    hi I want to write a code which put something in bootsector but when I run the assembly 8086 code which does this purpose, nothing happens. does any one know what can I do or does any one has code (in any language) which answer my need?

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  • Realtime MySQL search results on an advanced search page

    - by Andrew Heath
    I'm a hobbyist, and started learning PHP last September solely to build a hobby website that I had always wished and dreamed another more competent person might make. I enjoy programming, but I have little free time and enjoy a wide range of other interests and activities. I feel learning PHP alone can probably allow me to create 98% of the desired features for my site, but that last 2% is awfully appealing: The most powerful tool of the site is an advanced search page that picks through a 1000+ record game scenario database. Users can data-mine to tremendous depths - this advanced page has upwards of 50 different potential variables. It's designed to allow the hardcore user to search on almost any possible combination of data in our database and it works well. Those who aren't interested in wading through the sea of options may use the Basic Search, which is comprised of the most popular parts of the Advanced search. Because the advanced search is so comprehensive, and because the database is rather small (less than 1,200 potential hits maximum), with each variable you choose to include the likelihood of getting any qualifying results at all drops dramatically. In my fantasy land where I can wield AJAX as if it were Excalibur, my users would have a realtime Total Results counter in the corner of their screen as they used this page, which would automatically update its query structure and report how many results will be displayed with the addition of each variable. In this way it would be effortless to know just how many variables are enough, and when you've gone and added one that zeroes out the results set. A somewhat similar implementation, at least visually, would be the Subtotal sidebar when building a new custom computer on IBuyPower.com For those of you actually still reading this, my question is really rather simple: Given the time & ability constraints outlined above, would I be able to learn just enough AJAX (or whatever) needed to pull this one feature off without too much trouble? would I be able to more or less drop-in a pre-written code snippet and tweak to fit? or should I consider opening my code up to a trusted & capable individual in the future for this implementation? (assuming I can find one...) Thank you.

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  • What is the use of mysql_rollback() function in PHP?

    - by OM The Eternity
    What is the use of mysql_rollback() function in PHP? How is it used? please explain me with some example, PS: Please Do not give me link to the php.net or, mysql site, I dont need AUTHOR language to understand it, I need the Developer way to understand... I hope u understand... Thanks in advance. UPDATE if i have Updated something in a tanle can i Reset the previous value using this function?

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  • How do I rename a process on Linux?

    - by jemfinch
    I'm using Python, for what it's worth, but will accept answers in any applicable language. I've tried writing to /proc/$pid/cmdline, but that's a readonly file. I've tried assigning a new string to sys.argv[0], but that has no perceptible impact. Are there any other possibilities? My program is executing processes via os.system (equivalent to system(3)) so a general, *NIX-based solution using an additional spawning process would be fine.

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  • Why was this T-SQL Syntax never implemented?

    - by ChrisA
    Why did they never let us do this sort of thing: Create Proc RunParameterisedSelect @tableName varchar(100), @columnName varchar(100), @value varchar(100) as select * from @tableName where @columnName = @value You can use @value as a parameter, obviously, and you can achieve the whole thing with dynamic SQL, but creating it is invariably a pain. So why didn't they make it part of the language in some way, rather than forcing you to EXEC(@sql)?

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  • Bpm audio detection Library

    - by user58815
    I'm looking for a library that simplify tempo/bpm audio detection. Something similar to this http://adionsoft.net/bpm/ , but to use on *NIX machines. Any language, but preference goes to php, perl, python.

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  • Nested function in C

    - by Sachin Chourasiya
    Can we have a nested function in C? What is the use of nested functions? If they exist in C does there implementation differes from compiler to compiler. Are nested functions allowed in any other language? If yes then what is there significance?

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  • Standard library function in R for finding the mode?

    - by Nick
    In statistical language R, mean() and median() are standard functions which do what you'd expect. mode() tells you the internal storage mode of the R object, not the value that occurs the most in its argument. But surely there is a standard library function that implements mode for a vector (or list).

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  • How to animate line-drawing in iPhone development?

    - by david
    I have been searching around, but there seems no good answer for this simple question. So I am asking again: how to animate line-drawing in iphone dev? Basically what I want is something like this: @implementation MyUIView - (void) triggerLineDrawing: (CGPathRef) path { ... // animate line drawing here } Can it be done?

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  • Multiple Inheritance Debates II: according to Stroutroup

    - by asksuperuser
    I know very well about the traditional arguments about why Interface Inheritance is prefered to multiple inheritance, there has been already a post here : http://stackoverflow.com/questions/191691/should-c-include-multiple-inheritance But according to Stroutroup the real reason why Microsoft and Sun decided to get rid off multiple inheritance is that they have vested interest to do so: instead of putting features in the languages, they put in frameworks so that people then become tied to their platform instead of people having the same capability at a language standard level. What do you think ?

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  • Well tested C/C++ lock free queue?

    - by uj
    I am looking for a well-tested, publicly available C/C++ implementation of a lock free queue. I need at least multiple-producers/single-consumer functionality. Multiple-consumers is even better, if exists. I'm targetting VC's _Interlocked... intrinsics, though anything which is straight forward to port would be fine. Could anyone give any pointers?

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  • Use Shakespeare-text and external file

    - by Adam
    How can I convert the below example to use an external file instead of the embedded lazy text quasi quotes? {-# LANGUAGE QuasiQuotes, OverloadedStrings #-} import Text.Shakespeare.Text import qualified Data.Text.Lazy.IO as TLIO import Data.Text (Text) import Control.Monad (forM_) data Item = Item { itemName :: Text , itemQty :: Int } items :: [Item] items = [ Item "apples" 5 , Item "bananas" 10 ] main :: IO () main = forM_ items $ \item -> TLIO.putStrLn [lt|You have #{show $ itemQty item} #{itemName item}.|] This is from the yesod online book.

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  • How to extract the data from a website using java?

    - by giri
    Hi I am familier with java programming language I like to extract the data from a website and store it to my database running on my machine.Is that possible in java.If so which API I should use. For example the are number of schools listed on a website How can I extract that data and store it to my database using java.

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  • DATA command hangs

    - by Tharban
    Hello, what can i do, if a Mailserver accepts a connection but does not return any data? The default javax.mail implementation just hangs indefinitley. Event setting the smtp.timeout does not help - it still hangs. I even tried to set a custom SocketFactory to set the sotimeouts and solinger directly, but it still hangs. Somehow the socket does get kept alive? But how? Thx for any ideas! Ciao, Nils

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  • What can you do in C without "std" includes? Are they part of "C," or just libraries?

    - by Chris Cooper
    I apologize if this is a subjective or repeated question. It's sort of awkward to search for, so I wasn't sure what terms to include. What I'd like to know is what the basic foundation tools/functions are in C when you don't include standard libraries like stdio and stdlib. What could I do if there's no printf(), fopen(), etc? Also, are those libraries technically part of the "C" language, or are they just very useful and effectively essential libraries?

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