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  • Why is my GUI unresponsive while a SwingWorker thread runs?

    - by Starchy
    Hello, I have a SwingWorker thread with an IOBound task which is totally locking up the interface while it runs. Swapping out the normal workload for a counter loop has the same result. The SwingWorker looks basically like this: public class BackupWorker extends SwingWorker<String, String> { private static String uname = null; private static String pass = null; private static String filename = null; static String status = null; BackupWorker (String uname, String pass, String filename) { this.uname = uname; this.pass = pass; this.filename = filename; } @Override protected String doInBackground() throws Exception { BackupObject bak = newBackupObject(uname,pass,filename); return "Done!"; } } The code that kicks it off lives in a class that extends JFrame: public void actionPerformed(ActionEvent event) { String cmd = event.getActionCommand(); if (BACKUP.equals(cmd)) { SwingUtilities.invokeLater(new Runnable() { public void run() { final StatusFrame statusFrame = new StatusFrame(); statusFrame.setVisible(true); SwingUtilities.invokeLater(new Runnable() { public void run () { statusFrame.beginBackup(uname,pass,filename); } }); } }); } } Here's the interesting part of StatusFrame: public void beginBackup(final String uname, final String pass, final String filename) { worker = new BackupWorker(uname, pass, filename); worker.execute(); try { System.out.println(worker.get()); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } } So far as I can see, everything "long-running" is handled by the worker, and everything that touches the GUI on the EDT. Have I tangled things up somewhere, or am I expecting too much of SwingWorker?

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  • Error setting env thru subprocess.call to run a python script on a remote linux machine

    - by John Smith
    I am running a python script on a windows machine to invoke another python script on a remote linux machine. I am using subprocess.call with ssh to do this, like below: subprocess.call('ssh -i <identify file> username@hostname python <script_on_linux_machine>') and this works fine. However, if I want to set some environment variables, like below: subprocess.call('ssh -i <identify file> username@hostname python <script_on_linux_machine>', env={key1:value1}) it fails. I get the following error: ssh_connect: getnameinfo failed ssh: connect to host <hostname> port 22: Operation not permitted 255 I've tried splitting the ssh commands into list and passing. Didn't help. I've tried to run other 'local'(windows) commands thru subprocess.call() and tried setting the env. It works fine. I've tried to run other commands(such as ls) on the remote linux machine. Again, subprocess.call() works fine, as long as I don't try to set the environment. What am I doing wrong? Would I be able to set the environment for a python script on a remote machine? Any help will be appreciated.

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  • Is there a way to easily convert a series of tarballs of a source tree into a git repository?

    - by Hotei
    I'm new to git and I have a moderately large number of weekly tarballs from a long running project. Each tarball has on average a few hundred files in it. I'm looking for a git strategy that will allow me to add the expanded contents of each tarball to a new git repository, starting from version 1.001 and going through version 1.650. As of this stage of the project 99.5% of tarball(n) is just a copy of version(n-1) - in other words, a perfect candidate for git. The desired end result is to have only the master branch remaining at the end of the process. I think I know git well enough to do this "by hand". As I understand it there is no possibility of a merge conflict since there will be no opportunity to change the master before the next version is added and committed. A shell script is my first guess, but I'm not sure how well bash will like it when git checkout branch_n gets processed while bash is executing in branch_n-1. For the purposes of this project the host environment is Ubuntu 10.4, resources available are 8 Gig RAM, 500 Gig Disk space free and 4 CPU processor at 3.ghz . I don't need someone else to solve the problem but I could use a nudge in the right direction as to how a git expert would approach it. Any advice from someone who's "been there done that" would be appreciated. Hotei PS: I have looked at site's suggested "related questions" and found nothing relevant.

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  • EC2 persistence of machine

    - by Seagull
    I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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  • JBoss Clustered Service that sends emails from txt file

    - by michael lucas
    I need a little push in the right direction. Here's my problem: I have to create an ultra-reliable service that sends email messages to clients whose addresses are stored in txt file on FTP server. Single txt file may contain unlimited number of entries. Most often the file contains about 300,000 entries. Service exposes interface with just two simple methods: TaskHandle sendEmails(String ftpFilePath); ProcessStatus checkProcessStatus(TaskHandle taskHandle); Method sendEmails() returns TaskHandle by which we can ask for ProcessStatus. For such a service to be reliable clustering is necessary. Processing single txt file might take a long time. Restarting one node in a cluster should have no impact on sending emails. We use JBoss AS 4.2.0 which comes with a nice HASingletonController that ensure one instance of service is running at given time. But once a fail-over happens, the second service should continue work from where the first one stopped. How can I share state between nodes in a cluster in such a way that leaves no possibility of sending some emails twice?

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  • Linq to sql Repository pattern , Some doubts

    - by MindlessProgrammer
    I am using repository pattern with linq to sql, I am using a repository class per table. I want to know , am i doing at good/standard way, ContactRepository Contact GetByID() Contact GetAll() COntactTagRepository List<ContactTag> Get(long contactID) List<ContactTag> GetAll() List<ContactTagDetail> GetAllDetails() class ContactTagDetail { public Contact Contact {get;set;} public ContactTag COntactTag {get;set;} } When i need a contact i call method in contactrepository, same for contacttag but when i need contact and tags together i call GetDetais() in ContactTag repository its not returning the COntactTag entity generated by the orm insted its returning ContactTagDetail entity conatining both COntact and COntactTag generated by the orm, i know i can simple call GetAll in COntactTag repository and can access Contact.ContactTag but as its linq to sql it will there is no option to Deferred Load in query level, so whenever i need a entity with a related entity i create a projection class Another doubt is where i really need to right the method i can do it in both contact & ContactTag repostitory like In contact repository GetALlWithTags() or something but i am doing it in in COntactTag repository Whats your suggestions ?

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  • Looking for pros/cons of using GWT or JSF

    - by cliff.meyers
    I'm a long time Java developer who has been building UI with Adobe Flex for the past few years. I'm looking to broaden my repertoire with a RIA technology that runs in a plain-old browser, no plug-ins required. I've read a lot about GWT but don't know much about JSF, especially given the varying implementations. Below are some criteria that are important to me as a developer. I'm hoping that the community might be able to tell me about the strengths and weaknesses of GWT and JSF in each: Layout: is it declarative, programmatic or a mix of both? Control library: how rich is the available control library? How easy is it to extend or write custom controls that "play nice" with the built-ins? Javascript: how much of it do I need to write in order to be successful with the framework? Cross-browser: assuming I'm not writing a lot of my own HTML and JS, do the frameworks function equally well in all modern browsers? Tooling: is a rapid edit/refresh cycle available? How easy is it to debug the client and server code? Bookmarking / Browser Navigation: this is a common problem in Flex; does the framework play nicely with these? I would love to hear any other important pros / cons I might not have covered. Thanks!

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  • How can I force a ListView with a custom panel to re-measure when the ListView width goes below the

    - by Scott Whitlock
    Sorry for the long winded question (I'm including background here). If you just want the question, go to the end. I have a ListView with a custom Panel implementation that I'm using to implement something similar to a WrapPanel, but not quite. I'm overriding the MeasureOverride and ArrangeOverride methods in the custom panel. If I do the naive implementation of a WrapPanel in the MeasureOverride method it doesn't work when the ListView is resized. Let's say the custom panel does a measure and the constraint is a width of 100 and let's say I have 3 items that are 40 wide each. The naive approach is to return a size of 80,80 but when I resize the window that the ListView is in, down to say 75, it just turns on the horizontal scrollbar and never calls measure or arrange again (it does keep measuring and arranging if the width is greater than 80). To get around this, I hard coded the measurement to only have a width of the widest item. Then in the arrange, it gives me more space than I asked for and I use as much horizontal space as I can before wrapping. If I resize the window smaller than the smallest item in the ListView, then it turns on the scrollbar, which is great. Unfortunately this is causing a big problem when I have one of these ListViews with a custom panel nested inside of another one. The outside one works ok, but I can't get the inside one to "take as much as it needs". It always sizes to the smallest item, and the only way around it is to set the MinWidth to be something greater than zero. Anyway, stepping back for a second, I think the real way to fix this is to go back to the Naive implementation of the WrapPanel but force it to re-measure when the ListView width goes below the Size I previously returned as a measurement. That should solve my problem with the nested one. So, that's my question: I have a ListView with a custom panel If I return a measurement width on the panel and the ListView is resized to less than that width, it stops calling MeasureOverride How can I get it to continue calling MeasureOverride?

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  • Using the contents of an array to set individual pixels in a Quartz bitmap context

    - by Magic Bullet Dave
    I have an array that contains the RGB colour values for each pixel in a 320 x 180 display. I would like to be able to set individual pixel values in the a bitmap context of the same size offscreen then display the bitmap context in a view. It appears that I have to create 1x1 rects and either put a stroke on them or a line of length 1 at the point in question. Is that correct? I'm looking for a very efficient way of getting the array data onto the graphics context as you can imagine this is going to be an image buffer that cycles at 25 frames per second and drawing in this way seems inefficient. I guess the other question is should I use OPENGL ES instead? Thoughts/best practice would be much appreciated. Regards Dave OK, have come a short way, but can't make the final hurdle and I am not sure why this isn't working: - (void) displayContentsOfArray1UsingBitmap: (CGContextRef)context { long bitmapData[WIDTH * HEIGHT]; // Build bitmap int i, j, h; for (i = 0; i < WIDTH; i++) { for (j = 0; j < HEIGHT; j++) { h = frameBuffer01[i][j]; bitmapData[i * j] = h; } } // Blit the bitmap to the context CGDataProviderRef providerRef = CGDataProviderCreateWithData(NULL, bitmapData,4 * WIDTH * HEIGHT, NULL); CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); CGImageRef imageRef = CGImageCreate(WIDTH, HEIGHT, 8, 32, WIDTH * 4, colorSpaceRef, kCGImageAlphaFirst, providerRef, NULL, YES, kCGRenderingIntentDefault); CGContextDrawImage(context, CGRectMake(0.0, HEIGHT, WIDTH, HEIGHT), imageRef); CGImageRelease(imageRef); CGColorSpaceRelease(colorSpaceRef); CGDataProviderRelease(providerRef); }

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  • Question regarding ip checksum code

    - by looktt
    unsigned short /* this function generates header checksums */ csum (unsigned short *buf, int nwords) { unsigned long sum; for (sum = 0; nwords > 0; nwords--) // add words(16bits) together sum += *buf++; sum = (sum >> 16) + (sum & 0xffff); //add carry over sum += (sum >> 16); //what does this step do??? add possible left-over //byte? But isn't it already added in the loop (if //any)? return ((unsigned short) ~sum); } I assume nwords in the number of 16bits word, not 8bits byte (if there are odd byte, nword is rounded to next large), is it correct? The line sum = (sum 16) + (sum & 0xffff) is to add carry over to make 16bit complement sum += (sum 16); What's the purpose of this step? Add left-over byte? How? Thanks!

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  • Clearly defined Rails routing problem - undefined method for Nil:NilClass

    - by sscirrus
    Guys and girls, I have been working on this problem for a while but still no joy. This is my second question within this general area, because the last question was getting too long and this is now more well-defined. Summary of the Problem: I am loading a page for my customers and I get error: undefined method 'name' for Nil:NilClass My Code #Link on views/users/show.html.erb: <%= link_to "Customer Account", :action => "home", :controller => "customers", :id => @user.user_type_id %> #Regular Route: map.connect 'customers/home/:id', :controller => 'customers', :action => 'home' #Rake Routes, first entry: /customers/home/:id :controller=>:"customers", :action=>"home" #Customers Controller: def home render :layout => 'home' @customer = Customer.find(params[:id]) @user = @current_user_session.user flash[:error] = "Customer not found" and return unless @customer @jobs = @customer.jobs end #views/customers/home.html.erb: <%= @customer.name %> I have absolutely no idea why this seemingly clear sequence of events is resulting in a NilClass. Search the console for Customer.find(2) returns the correct customer. What is this noob missing? Thank you very much.

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  • ProtoInclude for fields ?

    - by Big
    I have a simple object [ProtoContract] public class DataChangedEventArgs<T> : EventArgs { private readonly object key; private readonly T data; private readonly DataChangeType changeType; ///<summary> /// Key to identify the data item ///</summary> public object Key { get { return key; } } [ProtoMember(2, IsRequired = true)] public T Data { get { return data; } } [ProtoMember(3, IsRequired = true)] public DataChangeType ChangeType { get { return changeType; } } and I have a problem with the key. Its type is object, but it can be either int, long or string. I would intuitively use a ProtoInclude attribute to say "expect these types" but unfortunately they are class only attribute. Does anybody has any idea how I could work around this ? For background, the public object Key is here for historical reasons (and all over the place) so I would very much like to avoid the mother of all refactorings ;-) Any chance I could get this to Serialize, even force it to Serialize as a string ?

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  • New Rails deployment half working...not sure why?

    - by Meltemi
    I'm in the final stages of going round trip through the entire Rails cycle: development - test - production (on an external server). I'm very close...but seeing some errors with the production version and don't know enough about Rails' "magic" to troubleshoot it yet... all seems well and I can load my app by going to www.mydomain.com/rails and it seems to work...I can interact with my app and create new objects in my database. However, when I go to www.mydomain.com/rails/ (difference is the trailing slash) i get a webpage that just says "Index from public" on it?!? I don't know where that's coming from? index.html is long removed from public. this may or may not be related to why I can't access, say, the first record in one of my classes by calling its controller like so: www.mydomain.com/rails/mycontroller/1 . and yes, there are records in the database. anyway, something's askew. it works fine on development box. but, only half working on production server. anyone know what might be causing this? this app is running on the server box (not development) Installed Passenger on server to serve app via Apache modified my httpd.conf with Passenger's stuff (headache but finally got it to respond) loaded schema into the production database: rake db:schema:load RAILS_ENV=production

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  • C#: Wrong answer when finding "cool" numbers.

    - by user300484
    Hello you all! In my application, a "cool" number is a number that is both a square and a cube, like for example: 64 = 8^2 and 64 = 4^3. My application is supposed to find the number of "cool numbers" between a range given by the user. I wrote my code and the application runs fine, but it is giving me the wrong answer. Can you help me here please? for example: IMPUT 1 100 OUTPUT 1 using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace ConsoleApplication1 { class Program { static void Main(string[] args) { double a = Convert.ToDouble(Console.ReadLine()); // first number in the range double b = Convert.ToDouble(Console.ReadLine()); // second number in the range long x = 0; for (double i = a; i <= b; i++) { double cube = 1.0 / 3.0; double cuad = 1.0 / 2.0; double crt = Math.Pow(i, cube); // cube root double sqrt = Math.Pow(i, cuad); // square root if ((crt * 10) % 10 == 0 || (sqrt * 10) % 10 == 0) // condition to determine if it is a cool number. x++; } Console.WriteLine(x); Console.ReadLine(); } } }

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  • Cannot run Python script on Windows with output redirected??

    - by Wai Yip Tung
    This is running on Windows 7 (64 bit), Python 2.6 with Win32 Extensions for Python. I have a simple script that just print "hello world". I can launch it with python hello.py. In this case I can redirect the output to a file. But if I run it by just typing hello.py on the command line and redirect the output, I get an exception. C:> python hello.py hello world C:> python hello.py >output C:> type output hello world C:> hello.py hello world C:> hello.py >output close failed in file object destructor: Error in sys.excepthook: Original exception was: I think I first get this error after upgrading to Windows 7. I remember it should work in XP. I have seen people talking about this bug python-Bugs-1012692 | Can't pipe input to a python program. But that was long time ago. And it does not mention any solution. Have anyone experienced this? Anyone can help?

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  • substitution cypher with different alphabet length

    - by seanizer
    I would like to implement a simple substitution cypher to mask private ids in URLs I know how my IDs will look like (combination of upperchase ascii, digits and underscore), and they will be rather long, as they are composed keys. I would like to use a longer alphabet to shorten the resulting codes (I'd like to use upper and lower case ascii letters, digits and nothing else). So my incoming alphabet would be [A-Z0-9_] (37 chars) and my outgoing alphabet would be [A-Za-z0-9] (62 chars) so a compression of almost 50% would be available. let's say my URLs look like this: /my/page/GFZHFFFZFZTFZTF_24_F34 and I want them to look like this instead: /my/page/Ft32zfegZFV5 Obviously both arrays would be shuffled to bring some random order in. This does not have to be secure. if someone figures it out: fine, but I don't want the scheme to be obvious. My desired solution would be to convert the string to an integer representation of radix 37, convert the radix to 62 and use the second alphabet to write out that number. is there any sample code available that does something similar? Integer.parseInt ( http://java.sun.com/javase/6/docs/api/java/lang/Integer.html#parseInt%28java.lang.String,%20int%29 ) has some similar logic, but it is hard-coded to use standard digit behavior Any hints? I am using java to implement this but code or pseudo-code in any other language is of course also helpful

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  • Javascript library: to obfuscate or not to obfuscate - that is the question

    - by morpheous
    I need to write a GUI related javascript library. It will give my website a bit of an edge (in terms of functionality I can offer) - up until my competitors play with it long enough to figure out how to write it by themselves. I can accept the fact that it will be emulated over time - thats par for the course (its part of business). However, what I cannot bear, is the idea of effectively, simply handing over all the hard work that would have gone into the library to my competitors, by using plain javascript that anyone can download and use. It is an established fact that no none in the industry I am "attacking" has this functionality, so the value of such a library is undeniable and is not up for discussion (i.e. thats not what I'm asking here). What I am seeking to find out are the pros and cons of obfuscating a javascript library, so that I can come to a final decision. Two of my biggest concerns are debugging, and subtle errors that may be introduced by the obfuscator. I would like to know: How can I manage those risks (being able to debug faulty code, ensuring/minimizing against obfuscation errors) Are there any good quality industry standard obfuscators you can recommend (preferably something you use yourself). What are your experiences of using obfuscated code in a production environment?

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  • When I include only the jQuery 1.4 Library, I get an exception, why?

    - by codeninja
    I keep getting this error all over the place where I only have jquery 1.3 or 1.4 included. "setting a property that has only a getter" and a long list of warnings in the Firefox Error Console. What's going on? I can't find any information on this issue =/ <!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-US"> <head> <title>Demo</title> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <link rel="shortcut icon" href="images/favicon.ico"> <link rel="stylesheet" href="css/common.css" type="text/css" /> <link rel="stylesheet" href="css/modules.css" type="text/css" /> <script type="text/javascript" src="js/jquery-1.4.2.min.js"></script> </head> Just some Warning snippets: Warning: reference to undefined property a[++e] Source File: /js/jquery-1.4.2.min.js Line: 30 Warning: reference to undefined property a[0] Source File: /js/jquery-1.4.2.min.js Line: 30 Warning: function oa does not always return a value Source File: /js/jquery-1.4.2.min.js Line: 18, Column: 165 Source Code: th;n<r;n++){j=d[n];a.currentTarget=j.elem;a.data=j.handleObj.data;a.handleObj=j.handleObj;if(j.handleObj.origHandler.apply(j.elem,e)===false){b=false;break}}return b}}function pa(a,b){return"live."+(a&&a!=="*"?a+".":"")+b.replace(/\./g,"`").replace(/ /g,

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  • PHP Regex to match lines with all-caps with occaisional hyphens.

    - by Yaaqov
    I'm trying to to convert an existing PHP Regular Expression match case to apply to a slightly different style of document. Here's the original style of the document: **FOODS - TYPE A** ___________________________________ **PRODUCT** 1) Mi Pueblito Queso Fresco Authentic Mexican Style Fresh Cheese; 2) La Fe String Cheese **CODE** Sell by date going back to February 1, 2009 And the successfully-running PHP Regex match code that only returns "true" if the line is surrounded by asterisks, and stores each side of the "-" as $m[1] and $m[2], respectively. if ( preg_match('#^\*\*([^-]+)(?:-(.*))?\*\*$#', $line, $m) ) { // only for **header - subheader** $m[2] is set. if ( isset($m[2]) ) { return array(TYPE_HEADER, array(trim($m[1]), trim($m[2]))); } else { return array(TYPE_KEY, array($m[1])); } } So, for line 1: $m[1] = "FOODS" AND $m[2] = "TYPE A"; Line 2 would be skipped; Line 3: $m[1] = "PRODUCT", etc. The question: How would I re-write the above regex match if the headers did not have the asterisks, but still was all-caps, and was at least 4 characters long? For example: FOODS - TYPE A ___________________________________ PRODUCT 1) Mi Pueblito Queso Fresco Authentic Mexican Style Fresh Cheese; 2) La Fe String Cheese CODE Sell by date going back to February 1, 2009 Thank you.

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  • PHP/MySQL - Working with two databases, one shared and one local to an instance of application

    - by Extrakun
    The situation: Using a off-the-shelf PHP application, I have to add in a new module for extra functionality. Today, it is made known that eventually four different instances of the application are to be deployed, but the data from the new functionality is to be shared among those 4 instances. Each instance should still have their own database for users, content and etc. So the data for the new functionality goes into a 'shared' database. The data for the application (user login, content, uploads) go into a 'local' database To make things more complex, the new module I am writing will fetch data from the local DB and the shared DB at the same time. A re-write of the base application will take too long. I only have control over the new module which I am writing. The ideal solution: Is there a way to encapsulate 2 databases into one name using MySQL? I do not wish to switch DB connections or specifically name the DB to query from inside my SQL statements. The application uses a DB wrapper, so I am able to change it somehow so I can invisibly attempt to read/write to two different DB. What is the best way to handle this problem?

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  • PHP in Wordpress Posts - Is this okay?

    - by Thomas
    I've been working with some long lists of information and I've come up with a good way to post it in various formats on my wordpress blog posts. I installed the exec-PHP plugin, which allows you to run php in posts. I then created a new table (NEWTABLE) in my wordpress database and filled that table with names, scores, and other stuff. I was then able to use some pretty simple code to display the information in a wordpress post. Below is an example, but you could really do whatever you wanted. My question is - is there a problem with doing this? with security? or memory? I could just type out all the information in each post, but this is really much nicer. Any thoughts are appreciated. <?php $theResult = mysql_query("SELECT * FROM NEWTABLE WHERE Score < 100 ORDER BY LastName"); while($row = mysql_fetch_array($theResult)) { echo $row['FirstName']; echo " " . $row['LastName']; echo " " . $row['Score']; echo "<br />"; } ?>

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  • Looking for combinations of server and embedded database engines

    - by codeelegance
    I'm redesigning an application that will be run as both a single user and multiuser application. It is a .NET 2.0 application. I'm looking for server and embedded databases that work well together. I want to deploy the embedded database in the single user setup and of course, the server in the multiuser setup. Past releases have been based on MSDE but in the past year we've been having a lot of install issues: new installs hanging and leaving the system in an unknown state, upgrades disconnecting the database, etc. I migrated the application to SQL Server 2005 and the install is more reliable (as long as a user doesn't try to install over a broken MSDE installation). Since next year's release will be a complete redesign I figured now's the best time to address the database issue as well. The database has been abstracted from the rest of the application so I just need to choose which database(s) to use and write an implementation for each one. So far I've considered: SQL Server/ SQL Server Compact Edition Firebird (same DB engine is available in two different server modes and an embedded dll) Each has its own merits but I'm also interested in any other suggestions. This is a fairly simple program and its data requirements are simple as well. I don't expect it to strain whatever database I eventually choose. So easy configuration and deployment hold more weight than performance.

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  • Thread-safe data structure design

    - by Inso Reiges
    Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of "exists" call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? EDIT: I have a better example. Suppose that element retrieval returns either a reference or a pointer to the stored element and not it's copy. How can a caller be protected to safely use this pointer\reference after the call returns? If you think that not returning copies is a problem, then think about deep copies, i.e. objects that should also copy another objects they point to internally. Thank you.

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  • Python Ephem / Datetime calculation

    - by dassouki
    the output should process the first date as "day" and second as "night". I've been playing with this for a few hours now and can't figure out what I'm doing wrong. Any ideas? Edit I assume that the problem is due to my date comparison implementation Output: $ python time_of_day.py * should be day: event date: 2010/4/6 16:00:59 prev rising: 2010/4/6 09:24:24 prev setting: 2010/4/5 23:33:03 next rise: 2010/4/7 09:22:27 next set: 2010/4/6 23:34:27 day * should be night: event date: 2010/4/6 00:01:00 prev rising: 2010/4/5 09:26:22 prev setting: 2010/4/5 23:33:03 next rise: 2010/4/6 09:24:24 next set: 2010/4/6 23:34:27 day time_of_day.py import datetime import ephem # install from http://pypi.python.org/pypi/pyephem/ #event_time is just a date time corresponding to an sql timestamp def type_of_light(latitude, longitude, event_time, utc_time, horizon): o = ephem.Observer() o.lat, o.long, o.date, o.horizon = latitude, longitude, event_time, horizon print "event date ", o.date print "prev rising: ", o.previous_rising(ephem.Sun()) print "prev setting: ", o.previous_setting(ephem.Sun()) print "next rise: ", o.next_rising(ephem.Sun()) print "next set: ", o.next_setting(ephem.Sun()) if o.previous_rising(ephem.Sun()) <= o.date <= o.next_setting(ephem.Sun()): return "day" elif o.previous_setting(ephem.Sun()) <= o.date <= o.next_rising(ephem.Sun()): return "night" else: return "error" print "should be day: ", type_of_light('45.959','-66.6405','2010/4/6 16:01','-4', '-6') print "should be night: ", type_of_light('45.959','-66.6405','2010/4/6 00:01','-4', '-6')

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  • Consulting a Prolog Source Code from within a VS2008 Solution File

    - by Joshua Green
    I have a Prolog file (Hanoi.pl) containing the code for solving the Hanoi Towers puzzle: hanoi( N ):- move( N, left, middle, right ). move( 0, _, _, _ ):- !. move( N, A, B, C ):- M is N-1, move( M, A, C, B ), inform( A, B ), move( M, C, B, A ). inform( X, Y ):- write( 'move a disk from ' ), write( X ), write( ' to ' ), writeln( Y ). I also have a C++ file written in VS2008 IDE: #include <iostream> #include <string> #include <stdio.h> #include <stdlib.h> using namespace std; #include "SWI-cpp.h" #include "SWI-Prolog.h" predicate_t phanoi; term_t t0; int main(int argc, char** argv) { long n = 5; int rval; if ( !PL_initialise(1, argv) ) PL_halt(1); PL_put_integer( t0, n ); phanoi = PL_predicate( "hanoi", 1, NULL ); rval = PL_call_predicate( NULL, PL_Q_NORMAL, phanoi, t0 ); system( "PAUSE" ); } How can I consult my Prolog source code (Hanoi.pl) from within my C++ code? Not from the Command Prompt - from the code, something like include or consult or compile? It is located in the same folder as my cpp file. Thanks,

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