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  • What is the best practice for using lock within inherited classes

    - by JDMX
    I want to know if one class is inheriting from another, is it better to have the classes share a lock object that is defined at the base class or to have a lock object defined at each inheritance level. A very simple example of a lock object on each level of the class public class Foo { private object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { private object thisLock2 = new object(); public int DoubleValue { get { lock( thisLock2 ) { return base.Value * 2; } } set { lock( thisLock2 ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { private object thisLock6 = new object(); public int TripleDoubleValue { get { lock( thisLock6 ) { return base.DoubleValue * 3; } } set { lock( thisLock6 ) { base.DoubleValue = value / 3; } } } } A very simple example of a shared lock object public class Foo { protected object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { public int DoubleValue { get { lock( thisLock ) { return base.Value * 2; } } set { lock( thisLock ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { public int TripleDoubleValue { get { lock( thisLock ) { return base.DoubleValue * 3; } } set { lock( thisLock ) { base.DoubleValue = value / 3; } } } } Which example is the preferred way to manage locking within an inherited class?

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  • What is considered a long execution time?

    - by stjowa
    I am trying to figure out just how "efficient" my server-side code is. Using start and end microtime(true) values, I am able to calculate the time it took my script to run. I am getting times from .3 - .5 seconds. These scripts do a number of database queries to return different values to the user. What is considered an efficient execution time for PHP scripts that will be run online for a website? Note: I know it depends on exactly what is being done, but just consider this a standard script that reads from a database and returns values to the user. Also, I look at Google and see them search the internet in .15 seconds and I feel like my script is crap. Thanks.

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  • effective retrieve for a voting system in PHP and MySQL

    - by Adnan
    Hello, I have a system where registered users can vote up/vote down comment for a picture. Something very similar to SO's voting system. I store the votes in a table with values as such; vote_id | vote_comment_id | vote_user_id | vote_date | vote_type Now I have few a question concerned the speed and efficiency for the following; PROB: Once a user opens the picture page with comments I need, if that user has already voted UP/DOWN a comment to show it like; "you voted up" or "you voted down" next to the comment (in SO it the vote image is highlighted) MY POSSIBLE SOL: Right now when I open a picture page for each comment I loop thru, I loop thru my table of votes as well and check if a user has voted and show the status (I compare the vote_user_id with the user's session). How efficient is this? Anyone have a better approach to tackle this kind of problem?

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  • Debugging strategy to find the cause of bad_alloc

    - by SalamiArmi
    I have a fairly serious bug in my program - occasional calls to new() throw a bad_alloc. From the documentation I can find on bad_alloc, it seems to be thrown for these reasons: When the computer runs out of memory (which definitely isn't happening, I have 4GB of RAM, program throws bad_alloc when using less than 5MB (checked in taskmanager) with nothing serious running in the background). If the memory becomes too fragmented to allocate new blocks (which, again, is unlikely - the largest sized block I ever allocate would be about 1KB, and that doesn't get done more than 100 times before the crash occurs). Based on these descriptions, I don't really have anywhere in which a bad_alloc could be thrown. However, the application I am running runs more than one thread, which could possibly be contributing to the problem. By testing all of the objects on a single thread, everything seems to be working smoothly. The only other thing that I can think of that is going on here could be some kind of race-condition caused by calling new() in more than one place at the same time, but I've tried adding mutexes to prevent that behaviour to no effect. Because the program is several hundred lines and I have no idea where the problem actually lies, I'm not sure of what, if any, code snippets to post. Instead, I was wondering if there were any tools that will help me test for this kind of thing, or if there are any general strategies that can help me with this problem. I'm using Microsoft Visual Studio 2008, with Poco for threading.

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  • Normalize or Denormalize in high traffic websites

    - by Inam Jameel
    what is the best practice for database design for high traffic websites like this one stackoverflow? should one must use normalize database for record keeping or normalized technique or combination of both? is it sensible to design normalize database as main database for record keeping to reduce redundancy and at the same time maintain another denormalized form of database for fast searching? or main database should be denormalize and one can make normalized views in the application level for fast database operations? or beside above mentioned approach? what is the best practice of designing high traffic websites???

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  • GAE modeling relationship options

    - by Sway
    Hi there, I need to model the following situation and I can't seem to find a consistent example on how to do it "correctly" for the google app engine. Suppose I've got a simple situation like the following: [Company] 1 ----- M [Stare] A company has one to many stores. Each store has an address made up of a address line 1, city, state, country, postcode etc. Ok. Lets say we need to create say an "Audit". An Audit is for a company and can be across one to many stares. So something like: [Audit] 1 ------ 1 [Company] 1 ------ M [Store] Now we need to query all of the "audits" based on the Store "addresses" in order to send the "Auditors" to the right locations. There seem to be numerous articles like this one: http://code.google.com/appengine/articles/modeling.html Which give examples of creating a "ContactCompany" model class. However they also say that you should use this kind of relationship only when you "really need to" and with "care" for performance. I've also read - frequently - that you should denormalize as much as possible thereby moving all of the "query-able" data into the Audit class. So what would you suggest as the best way to solve this? I've seen that there is an Expando class but I'm not sure if that is the "best" option for this. Any help or thoughts on this would be totally appreciated. Thanks in advance, Matt

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  • Signals and threads - good or bad design decision?

    - by Jens
    I have to write a program that performs highly computationally intensive calculations. The program might run for several days. The calculation can be separated easily in different threads without the need of shared data. I want a GUI or a web service that informs me of the current status. My current design uses BOOST::signals2 and BOOST::thread. It compiles and so far works as expected. If a thread finished one iteration and new data is available it calls a signal which is connected to a slot in the GUI class. My question(s): Is this combination of signals and threads a wise idea? I another forum somebody advised someone else not to "go down this road". Are there potential deadly pitfalls nearby that I failed to see? Is my expectation realistic that it will be "easy" to use my GUI class to provide a web interface or a QT, a VTK or a whatever window? Is there a more clever alternative (like other boost libs) that I overlooked? following code compiles with g++ -Wall -o main -lboost_thread-mt <filename>.cpp code follows: #include <boost/signals2.hpp> #include <boost/thread.hpp> #include <boost/bind.hpp> #include <iostream> #include <iterator> #include <string> using std::cout; using std::cerr; using std::string; /** * Called when a CalcThread finished a new bunch of data. */ boost::signals2::signal<void(string)> signal_new_data; /** * The whole data will be stored here. */ class DataCollector { typedef boost::mutex::scoped_lock scoped_lock; boost::mutex mutex; public: /** * Called by CalcThreads call the to store their data. */ void push(const string &s, const string &caller_name) { scoped_lock lock(mutex); _data.push_back(s); signal_new_data(caller_name); } /** * Output everything collected so far to std::out. */ void out() { typedef std::vector<string>::const_iterator iter; for (iter i = _data.begin(); i != _data.end(); ++i) cout << " " << *i << "\n"; } private: std::vector<string> _data; }; /** * Several of those can calculate stuff. * No data sharing needed. */ struct CalcThread { CalcThread(string name, DataCollector &datcol) : _name(name), _datcol(datcol) { } /** * Expensive algorithms will be implemented here. * @param num_results how many data sets are to be calculated by this thread. */ void operator()(int num_results) { for (int i = 1; i <= num_results; ++i) { std::stringstream s; s << "["; if (i == num_results) s << "LAST "; s << "DATA " << i << " from thread " << _name << "]"; _datcol.push(s.str(), _name); } } private: string _name; DataCollector &_datcol; }; /** * Maybe some VTK or QT or both will be used someday. */ class GuiClass { public: GuiClass(DataCollector &datcol) : _datcol(datcol) { } /** * If the GUI wants to present or at least count the data collected so far. * @param caller_name is the name of the thread whose data is new. */ void slot_data_changed(string caller_name) const { cout << "GuiClass knows: new data from " << caller_name << std::endl; } private: DataCollector & _datcol; }; int main() { DataCollector datcol; GuiClass mc(datcol); signal_new_data.connect(boost::bind(&GuiClass::slot_data_changed, &mc, _1)); CalcThread r1("A", datcol), r2("B", datcol), r3("C", datcol), r4("D", datcol), r5("E", datcol); boost::thread t1(r1, 3); boost::thread t2(r2, 1); boost::thread t3(r3, 2); boost::thread t4(r4, 2); boost::thread t5(r5, 3); t1.join(); t2.join(); t3.join(); t4.join(); t5.join(); datcol.out(); cout << "\nDone" << std::endl; return 0; }

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  • j2ee deployment error

    - by Rajesh
    hi im new to j2ee.. the problem is while deploying a particular project i'm getting deployment error like "module has not been deployed".. but i'm able to deploy other projects... the error shown is as follows In-place deployment at F:\onlineexam_1\build\web deploy?path=F:\onlineexam_1\build\web&name=onlineexam_1&force=true failed on GlassFish v3 Domain F:\onlineexam_1\nbproject\build-impl.xml:577: The module has not been deployed. BUILD FAILED (total time: 3 seconds) pls assist me to overcome this problem Thnx in advance Raj

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  • Looking for exercises to learn SQL, using the Northwind database

    - by MedicineMan
    I am trying to become more familiar with SQL by writing queries against the Northwind database. I am looking for some exercises that would help me to learn SQL and features of SQL Server. It is important that the exercises have solutions, and in complicated cases, it would be great if there was an explanation for the query. Thanks for the answers so far but I still have not found what I am looking for: Is there any free resource, available online, without registration, that I can find a list of these exercises?

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  • How-to limit feature functionality

    - by ph0enix
    Are there any standard or "best practice" ways of limiting feature functionality for a particular application? Example: We have a product with a variety of features, and our customers can pick and choose which features they would like to use, and the cost of the product varies based on which features they are actually using. In the past, we have distributed along with our software installer an encrypted license file that contains information about the customer, as well as the collection of features that they have enabled. In code, we read from the license file and enable the functionality according to the license file. This seems to work fine, except there a few disadvantages: Upgrading users with new functionality can be sort of a pain If a particular feature shows up in multiple places throughout the application, a developer might not realize that this feature should be licensed, and forget to check the license file before granting functionality to the user If the license file becomes corrupted, deleted, moved, renamed, etc. the application will not run We're getting ready to roll out a new set of features, and I was just curious what others in the community have done to tackle this problem?

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  • Best practice? iphone: sync data

    - by Andy Jacobs
    So i'm working on a project where there is data visualization. My ultimate goal is that i have a set of data shipped with the download of the iphone app. But i want it connected to a backend, that if the iphone has a connection with the internet. it can sync the changes from the backend. The syncing is no problem or the connection between the backend & the iphone. But what should i use as data storage on my iphone? what is the best way. my data is purely text and doesn't have to be secure. But it's main feature should be updating certain parts of data ( adding and deleting are not so important ) so what is the easiest (read: least time consuming development ) or the best way? sqlite? plist? ..?

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  • Best practice in this situation?

    - by Steve
    My Delphi program relies heavily on Outlook automation. Outlook versions prior to 2007-SP2 tend to get stuck in memory due to badly written addins and badly written Outlook code. If Outlook is stuck, calling CreateOleObject('Outlook.Application') or GetActiveObject ... doesn't return and keeps my application hanging till Outlook.exe is closed in the task manager. I've thought of a solution, but I'm unsure whether it's good practice or not. I'd start Outlook with CreateOleObject in a separate thread, wait 10 seconds in my main thread and if Outlook hangs (CreateOleObject doesn't return), offer the user to kill the Outlook.exe process from my program. But since I don't want to force the user to kill the Outlook.exe proccess, as an alternative I also need a way to kill the new thread in my program which keeps hanging now. My questions are: a, Is this good practice b, How can I terminate a hanging thread in Delphi without leaking memory? Is there a way?

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  • Rails: find by day of week with timestamp

    - by Sleepycat
    I need to grab the records for same day of the week for the preceeding X days of the week. There must be a better way to do it than this: Transaction.find_by_sql "select * from transactions where EXTRACT(DOW from date) = 1 and organisation_id = 4 order by date desc limit 7" It gets me what I need but is Postgres specific and not very "Rails-y". Date is a timestamp. Anyone got suggestions?

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  • Including libraries in project. Best practise.

    - by mridang
    Hi guys, I'm writing a Python open-source app. My app uses some open source Python libraries. These libraries in turn use other open-source libraries. I intend to release my code at Sourceforge or Google Code but do I need to include the sources of the other libraries? Is this a good practice? ...or should I simply write this information into a README file informing the use about the other required libraries. I've placed all these libraries into a libs sub folder in my source directory. When checking my code into SVN, should I use something called svn:externals to link to other sources? Is there a way to dynamically update my libraries to the latest version or is this something I have to do manually when I release a new version. My sincerest apologies if my question sounds vague but I'm pretty lost in this matter and I don't know what to Google for. Thanks all.

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  • Programming tips for writing document editors?

    - by Tesserex
    I'm asking this because I'm in the process of writing two such editors for my Mega Man engine, one a tileset editor, and another a level editor. When I say document editor, I mean the superset application type for things like image editors and text editors. All of these share things like toolbars, menu options, and in the case of image editors, and my apps, tool panes. We all know there's tons of advice out there for interface design in these apps, but I'm wondering about programming advice. Specifically, I'm doubting my code designs with the following things: Many menu options toggle various behaviors. What's the proper way to reliably tie the checked state of the option with the status of the behavior? Sometimes it's more complicated, like options being disabled when there's no document loaded. More and more consensus seems to be against using MDI, but how should I control tool panes? For example, I can't figure out how to get the panels to minimize and maximize along with the main window, like Photoshop does. When tool panels are responsible for a particular part of the document, who actually owns that thing? The main window, or the panel class? How do you do communication between the tool panels and the main window? Currently mine is all event based but it seems like there could be a better way. This seems to be a common class of gui application, but I've never seen specific pointers on code design for them. Could you please offer whatever advice or experience you have for writing them?

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  • In Ruby, how to implement global behaviour?

    - by Gordon McAllister
    Hi all, I want to implement the concept of a Workspace. This is a global concept - all other code will interact with one instance of this Workspace. The Workspace will be responsible for maintaining the current system state (i.e. interacting with the system model, persisting the system state etc) So what's the best design strategy for my Workspace, bearing in mind this will have to be testable (using RSpec now, but happy to look at alternatives). Having read thru some open source projects out there and I've seen 3 strategies. None of which I can identify as "the best practice". They are: Include the singleton class. But how testable is this? Will the global state of Workspace change between tests? Implemented all behaviour as class methods. Again how do you test this? Implemented all behaviour as module methods. Not sure about this one at all! Which is best? Or is there another way? Thanks, Gordon

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  • What is your strategy to avoid dynamic typing errors in Python (NoneType has no attribute x)?

    - by Koen Bok
    Python is one of my favorite languages, but I really have a love/hate relationship with it's dynamicness. Apart from the advantages, it often results in me forgetting to check a type, trying to call an attribute and getting the NoneType (or any other) has no attribute x error. A lot of them are pretty harmless but if not handled correctly they can bring down your entire app/process/etc. Over time I got better predicting where these could pop up and adding explicit type checking, but because I'm only human I miss one occasionally and then some end-user finds it. So I'm interested in your strategy to avoid these. Do you use type-checking decorators? Maybe special object wrappers? Please share...

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  • CSS selectors : should I make my CSS easier to read or optimise the speed

    - by Laurent Bourgault-Roy
    As I was working on a small website, I decided to use the PageSpeed extension to check if their was some improvement I could do to make the site load faster. However I was quite surprise when it told me that my use of CSS selector was "inefficient". I was always told that you should keep the usage of the class attribute in the HTML to a minimum, but if I understand correctly what PageSpeed tell me, it's much more efficient for the browser to match directly against a class name. It make sense to me, but it also mean that I need to put more CSS classes in my HTML. It make my .css file harder to read. I usually tend to mark my CSS like this : #mainContent p.productDescription em.priceTag { ... } Which make it easy to read : I know this will affect the main content and that it affect something in a paragraph tag (so I wont start to put all sort of layout code in it) that describe a product and its something that need emphasis. However it seem I should rewrite it as .priceTag { ... } Which remove all context information about the style. And if I want to use differently formatted price tag (for example, one in a list on the sidebar and one in a paragraph), I need to use something like that .paragraphPriceTag { ... } .listPriceTag { ... } Which really annoy me since I seem to duplicate the semantic of the HTML in my classes. And that mean I can't put common style in an unqualified .priceTag { ... } and thus I need to replicate the style in both CSS rule, making it harder to make change. (Altough for that I could use multiple class selector, but IE6 dont support them) I believe making code harder to read for the sake of speed has never been really considered a very good practice . Except where it is critical, of course. This is why people use PHP/Ruby/C# etc. instead of C/assembly to code their site. It's easier to write and debug. So I was wondering if I should stick with few CSS classes and complex selector or if I should go the optimisation route and remove my fancy CSS selectors for the sake of speed? Does PageSpeed make over the top recommandation? On most modern computer, will it even make a difference?

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  • Debugging NSoperation BAD ACCESS within graphics context

    - by Joe
    I tried everything to debug this one but I can't get to the bottom of it. This code lives in a subclass of NSOperation which is processed from a queue: (borders is an ivar NSArray containing 5 UIimage objects) NSMutableArray *images = [[NSMutableArray alloc] init]; for (unsigned i = 0; i < 5; i++) { CGSize size = CGSizeMake(60, 60); UIGraphicsBeginImageContext(size); CGPoint thumbPoint = CGPointMake(6, 6); [controller.image drawAtPoint:thumbPoint]; CGPoint borderPoint = CGPointMake(0, 0); [[borders objectAtIndex:i] drawAtPoint:borderPoint]; [images addObject:UIGraphicsGetImageFromCurrentImageContext()]; UIGraphicsEndImageContext(); } [images release]; The code works fine most of the time but when I push the iphone by access subviews and pressing lots of buttons on the UI I either get this exception which is trapped by the operation: Exception Load view: *** -[NSCFArray insertObject:atIndex:]: attempt to insert nil or I get this: Program received signal: “EXC_BAD_ACCESS”. The exception is caused because UIGraphicsGetImageFromCurrentImageContext() return nil. I don't know how to debug the EXC_BAD_ACCESS but I'm guessing that this error (in fact both of these errors) is caused by low memory. The debugger stops at the line: [controller.image drawAtPoint:thumbPoint]; As I mentioned I've trapped the exception so I can live with that but the EXC_BAD_ACCESS is more serious. IF this is memory related how can I tell and is it possible to increase the memory available to NSOperation?

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  • Is there a way to avoid debugger?

    - by Gabriel Šcerbák
    I don't like debugging in a debugger, because I think it is often below the abstraction layer of the programming language and it is often not reproducible. I favor usign unit tests when possible and I think they are a good way, but it is not always that easy to implement them. Do you know about any other alternative approaches to avoid the use of debugger?

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