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  • Cached data accessed by reference?

    - by arthurdent510
    I am running into an odd problem, and this is the only thing I can think of. I'm storing a list in cache, and I am randomly losing items from my list as users use the site. I have a class that is called that either goes to cache and returns the list from there, or if the cache is over a certain time frame old, it goes to the database and refreshes the cache. So when I pull the data from cache, this is what it looks like.... results = (List<Software>)cache["software"]; And then I return results and do some processing, filter for security, and eventually it winds up on the screen. For each Software record, there can be multiple resources attached to it, and based on how the security goes they may see some, all, or none of the records. So in the security check it will remove some of those resources from the software record. So my question is.... when I return my results list, is it a reference directly to the cache object? So when I remove a resource from the software object, it is really removing from cache as well? If that is the case, is there any way to not return it as a reference? Thanks!

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  • Error handling approach on PHP

    - by Industrial
    Hi everybody, We have a web server that we're about to launch a number of applications onto. They will all share database and memcached servers, but each application has it's own mySQL database and all memcached keys per application, is prefixed. Possible scenario: If a memcached server in our cluster goes boom, we want someone (operative system admin) to be automatically contacted by email/iphone push notification or in any other appropriate way. If we we're about to install 150 identical applications for our customers on our servers, and a memcached server dies - all 150 applications will individually find this out and contact our system admin, which most certainly is going to think about getting a new job where he or she isn't about to be woken up by getting 150 messages sent 4:15 in the morning. Possible solution: One idea is to set up an external server for error handling that gets a $_POST or cURL request sent, and handles storage of the error message depending on the seriousness of the actual error message. It would of course check upon receiving the error call, that if the same memcached server have already been reported as offline, there would be no need to spam the system admin with additional reminders... The questions: What's a good approach on how to handle errors? How does the big guys in the industry handle this? Thanks!

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  • How to get a checkout-able revision info from subversion?

    - by zhongshu
    I want to check a svn url and to get the latest revision, then checkout it, I don't want to use HEAD because I will compare the latest revision to others. so I use "svn info" to get the "Last Changed Rev" for the url like this: D:\Project>svn info svn://.../branches/.../path Path: ... URL: svn://.../branches/.../path Repository Root: svn://yt-file-srv/ Repository UUID: 9ed5ffd7-7585-a14e-96b2-4aab7121bb21 Revision: 2400 Node Kind: directory Last Changed Author: xxx Last Changed Rev: 2396 Last Changed Date: 2010-03-12 09:31:52 +0800 but, I found the 2396 revision is not checkout-able, because this path is in a branch copied from trunk, and the 2396 is the revision modified in the trunk. so when I use svn checkout -r 2396, I will get a workcopy for the path in the trunk, then I can not do checkin for the branch. D:\Project>svn checkout svn://.../branches/.../path -r 2396 workcopy ..... ..... D:\Project>svn info workcopy Path: workcopy URL: svn://.../trunk/.../path Repository Root: svn://yt-file-srv/ Repository UUID: 9ed5ffd7-7585-a14e-96b2-4aab7121bb21 Revision: 2396 Node Kind: directory Schedule: normal Last Changed Author: xxx Last Changed Rev: 2396 Last Changed Date: 2010-03-12 09:31:52 +0800 So, my question is how to get a checkout-able revision for the branch path, for this example, I want to get 2397 (because 2397 is the revision which copy occur). And I know "svn log" can get the info, but "svn log" output maybe very long and parse it will be difficult than "svn info". I just want know which revision is the latest checkout-able revision for the path.

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  • Booking logic and architecture, database sync: Hotels, tennis courts reservation system ...

    - by coulix
    Hello Stackers, Imagine that you want to design a tennis booking system. You have 5 tennis clubs as partenrs with no online api allowing you to check on their side if a court is booked or not: You have to build this part as well. Every time a booking is done on their side you want it to be know by our system. Probably using a POST request form tennis partner to our server. Every time a booking is done on our website, we want to push the booking to their system. The difficulty is that their system need to be online and accessible from outside. Ip may change, we have to use a dns updater. In case their system is not available we still accept the booking and fallback to an async email with 'i confirm booking/reject booking' link sent to the club. I find the whole process quite complex and was wondering about the way online hotel booking system and hotel were working. Do they all have their data open and online ? The good thing is that the data will grow large and fits nicely to some no SQL ;) like couch db

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  • Callers block until getFoo() has a value ready?

    - by Sean Owen
    I have a Java Thread which exposes a property which other threads want to access: class MyThread extends Thread { private Foo foo; ... Foo getFoo() { return foo; } ... public void run() { ... foo = makeTheFoo(); ... } } The problem is that it takes some short time from the time this runs until foo is available. Callers may call getFoo() before this and get a null. I'd rather they simply block, wait, and get the value once initialization has occurred. (foo is never changed afterwards.) It will be a matter of milliseconds until it's ready, so I'm comfortable with this approach. Now, I can make this happen with wait() and notifyAll() and there's a 95% chance I'll do it right. But I'm wondering how you all would do it; is there a primitive in java.util.concurrent that would do this, that I've missed? Or, how would you structure it? Yes, make foo volatile. Yes, synchronize on an internal lock Object and put the check in a while loop until it's not null. Am I missing anything?

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  • NVelocity (or Velocity) as a stand-alone formula evaluator

    - by dana
    I am using NVelocity in my application to generate html emails. My application has an event-driven model, where saving and/or updating of objects causes these emails to be sent out. Each event can trigger zero, one or multiple multiple emails. I want to be able to configure which emails get sent out at run-time without having to modify code. I was thinking I could leverage the NVelocity #if() directive to do this. Here is my idea... Step 1) Prior to email sending, the administrator must configure a formula for NVelocity to evaluate. For example: $User.FirstName == "Jack" Step 2) When an object is saved or created, build an NVelocity template in memory based on the input formula. For example: String formula = GetFormulaFromDB(); // $User.FirstName == "Jack" String templ = "#if( " + formula + ") 1 #else 0 #end"; Step 3) Execute the NVelocity engine in memory against the template. Check the results to see if we have to send the email: String result = VelocityMerge(templ); // utility function if( result.Trim() == "1" ) { SendEmail(); } I know this is not exactly what NVelocity was intended to do, but I think it just might work :) One of the benefits of doing things this way is that the same syntax can be used for the formula as is used inside the template. Does anybody have any words of caution or suggestions? Is there a way to execute the #if() directive without jumping through hoops like I have above? Is there a recommended way to validate the formula syntax ahead of time? Thanks.

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  • Concurrent connections in C# socket

    - by Chu Mai
    There are three apps run at the same time, 2 clients and 1 server. The whole system should function as following: The client sends an serialized object to server then server receives that object as a stream, finally the another client get that stream from server and deserialize it. This is the sender: TcpClient tcpClient = new TcpClient(); tcpClient.Connect("127.0.0.1", 8888); Stream stream = tcpClient.GetStream(); BinaryFormatter binaryFormatter = new BinaryFormatter(); binaryFormatter.Serialize(stream, event); // Event is the sending object tcpClient.Close(); Server code: TcpListener listener = new TcpListener(IPAddress.Parse("127.0.0.1"), 8888); listener.Start(); Console.WriteLine("Server is running at localhost port 8888 "); while (true) { Socket socket = listener.AcceptSocket(); try { Stream stream = new NetworkStream(socket); // Typically there should be something to write the stream // But I don't knwo exactly what should the stream write } catch (Exception e) { Console.WriteLine("Exception: " + e.Message); Console.WriteLine("Disconnected: {0}", socket.RemoteEndPoint); } } The receiver: TcpClient client = new TcpClient(); // Connect the client to the localhost with port 8888 client.Connect("127.0.0.1", 8888); Stream stream = client.GetStream(); Console.WriteLine(stream); when I run only the sender and server, and check the server, server receives correctly the data. The problem is when I run the receiver, everything is just disconnected. So where is my problem ? Could anyone point me out ? Thanks

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  • Android Bluetooth syncing

    - by Darryl
    I am connecting to a bluetooth enabled camera, and I am able to connect using the methods found in the BluetoothChat example. I need to send commands to the camera. The issue is that I also need to get a response BACK from the camera after I send the command in the first place. So basically I need to write a command and receive a response. However, the thing is that the commands sometimes don't generate a response. Even the documentation on the camera says that you "have to send the sync command as many as 25 times on power up before you will get a response." So I cannot just write a command and wait for a response, as the "read" function blocks the thread. If I have the read function in another thread, like the bluetooth chat example, there seems to be sync issues, i.e., if I issue a write command, how can I know that it is reading if that is happening in another thread? I did set a global variable to check for, but this seems "iffy" at best. So basically I need to write to the bluetooth and then attempt to read from it. However, I need to let that read timeout and if I haven't received a response, I need to write again until I get a response (or until it's tried a set number of times). I don't need the read function to be going all the time in the background. Any ideas? Thanks in advance for your time.

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  • How to color or highlight line when user click the checkbox in jQuery?

    - by Rohit
    I am implementing the highlight procedure of line . If the user click the checkbox it will highlight whole line by yellow. User can make as this any number of line. So it is possible to highlight the whole line when user click the checkbox? Please check my picture I select all text when I click the checkbox (because you will understand my problem) I am trying here in this fiddle <div> <button id="next">next </button> <button id ="previous">previous </button> </div> Checked rows: <span id="checkedRows"></span> <div id="content"> <div id="left"> <div class='cb'> <input type="checkbox" /> </div> </div> <div id="realTimeContents" class="left realtimeContend_h"></div> </div>

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  • Is this feasbile with GIS?

    - by Gnu Engineer
    I'm just getting myself to familiarize with GIS but i like to know before hand if the following is feasible with current GIS apps/tools... I get the point for an address by geocoding. Easy part. Now if the point falls within a boundary (may be a city/county/state) then i need to get the data (any id/flag) associated with the boundary. Based on the id/flag i then apply some business logic. My question is... How do i define the boundary? What tools should i use for it? How can i store the boundary definition in database in order to check if the point falls within it? This has to be done in the back end and not in visual maps as we don't intend to show/use maps. How do i associate my custom data (id/flag) with the above boundary definition? Hope i'm having right assumption on capabilities of GIS. Most of examples what i see is around people trying to show maps with data which is exactly not what i'm looking for. Also please suggest me some tools/books on this.

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  • Show only div of the product hovering in category grid with jQuery

    - by Dane
    On Magento, I'm trying to get avalable attributes per product in a new div (show/ hide onmouseover) as soon as I hover a product. Unfortunately, my jQuery code opens every div with the same name. I think, I need to do it with jQuery(this) but I tried it in a 1000 different ways, and it won't work. Maybe, somebody here can help me with a better code. jQuery(function() { jQuery('.slideDiv').hide().data('over', false); jQuery('#hover').hover(function() { jQuery('.slideDiv').fadeIn(); }, function() { // Check if mouse did not go over .dialog before hiding it again var timeOut = setTimeout(function() { if (!jQuery('.slideDiv').data('over')) { jQuery('.slideDiv').fadeOut(); clearTimeout(timeOut); } }, 100); }); // Set data for filtering on mouse events for #hover-here jQuery('.slideDiv').hover(function() { jQuery(this).data('over', true); }, function() { jQuery(this).fadeOut().data('over', false); }); }); The PHP just prints the attributes needed. <a href="#" id="hover">Custom Attributes</a> <div class="slideDiv"> <?php $attrs = $_product->getTypeInstance(true)->getConfigurableAttributesAsArray($_product); foreach($attrs as $attr) { if(0 == strcmp("shoe_size", $attr['attribute_code'])) { $options = $attr['values']; print "Größen:<br />"; foreach($options as $option) { print "{$option['store_label']}<br />"; } } } ?> </div> I added the script to [new link] http://jsfiddle.net/xsxfr/47/ so you can see there, that it is not working like this right now :(.

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  • Efficient mapping of game entity positions in Java

    - by byte
    In Java (Swing), say I've got a 2D game where I have various types of entities on the screen, such as a player, bad guys, powerups, etc. When the player moves across the screen, in order to do efficient checking of what is in the immediate vicinity of the player, I would think I'd want indexed access to the things that are near the character based on their position. For example, if player 'P' steps onto element 'E' in the following example... | | | | | | | | | |P| | | | |E| | | | | | | | | ... would be to do something like: if(player.getPosition().x == entity.getPosition().x && entity.getPosition.y == thing.getPosition().y) { //do something } And thats fine, but that implies that the entities hold their positions, and therefor if I had MANY entities on the screen I would have to loop through all possible entities available and check each ones position against the player position. This seems really inefficient especially if you start getting tons of entities. So, I would suspect I'd want some sort of map like Map<Point, Entity> map = new HashMap<Point, Entity>(); And store my point information there, so that I could access these entities in constant time. The only problem with that approach is that, if I want to move an entity to a different point on the screen, I'd have to search through the values of the HashMap for the entity I want to move (inefficient since I dont know its Point position ahead of time), and then once I've found it remove it from the HashMap, and re-insert it with the new position information. Any suggestions or advice on what sort of data structure / storage format I ought to be using here in order to have efficient access to Entities based on their position, as well as Position's based on the Entity?

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  • How do I compare two PropertyInfos or methods reliably?

    - by Rob Ashton
    Same for methods too: I am given two instances of PropertyInfo or methods which have been extracted from the class they sit on via GetProperty or GetMember etc, (or from a MemberExpression maybe). I want to determine if they are in fact referring to the same Property or the same Method so (propertyOne == propertyTwo) or (methodOne == methodTwo) Clearly that isn't going to actually work, you might be looking at the same property, but it might have been extracted from different levels of the class hierarchy (in which case generally, propertyOne != propertyTwo) Of course, I could look at DeclaringType, and re-request the property, but this starts getting a bit confusing when you start thinking about Properties/Methods declared on interfaces and implemented on classes Properties/Methods declared on a base class (virtually) and overridden on derived classes Properties/Methods declared on a base class, overridden with 'new' (in IL world this is nothing special iirc) At the end of the day, I just want to be able to do an intelligent equality check between two properties or two methods, I'm 80% sure that the above bullet points don't cover all of the edge cases, and while I could just sit down, write a bunch of tests and start playing about, I'm well aware that my low level knowledge of how these concepts are actually implemented is not excellent, and I'm hoping this is an already answered topic and I just suck at searching. The best answer would give me a couple of methods that achieve the above, explaining what edge cases have been taken care of and why :-)

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  • Find window with specific text for a Process

    - by Axarydax
    Hello, I'm trying to find if a window with specific has been open by a Process. That process spawns multiple windows, and I need to check them all. I have no trouble finding the process, with foreach (Process p in Process.GetProcesses()) { if (p.MainModule.FileName.ToLower().EndsWith("foo.exe")) FindChildWindowWithText(p); //do work the problem is what to do next. I cannot use Process' MainWindowText, because it changes with whichever window is activated. Then I've tried to use Windows function EnumChildWindows and GetWindowText, but I am not sure if I'm passing a correct handle to EnumChildWindows. The EnumChildWindows works as expected when passed MainWindowHandle, but of course the MainWindowHandle changes with active window. So I passed Process.Handle, but I get different handles and different results when switching the app's windows. (I understand that EnumChildWindows returns handles to not only windows, but controls in .net speak, that's no problem if I could get the caption of the window too) Maybe I am doing this the wrong way and I need a different approach - again, my problem is as simple as finding a window with text that matches specific regular expression. So I would probably need a function that enumerates all windows, that are visible in the taskbar or so. Thanks

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  • Performing centralized authorization for multiple applications

    - by Vaibhav
    Here's a question that I have been wrestling with for a while. We have a situation wherein we have a number of applications that we have created. These have grown organically over a period of time. All of these applications have permissions code built into them that controls access to various parts of the application depending on whether the currently logged in user has the necessary permissions or not. Alongside these applications is a utility application which allows an administrator to map users to permissions for all applications - the way it works is that every application has code which reads this external database of the said utility application to check if the currently logged in user has the necessary permission or not. Now, the question is this. Should the user-permissions mapping information reside in and be owned by the applications themselves, or is it okay to have this information reside within an external entity/DB (as in this case the utility application's database). Part of me thinks that application permissions are very specific to the application context itself, so shouldn't be separated from the application itself. But I am not sure. Any comments?

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  • How can I load an external jQuery gallery/slideshow into a div

    - by DanTransformer
    Ive got a jQuery navigation menu loading external content into my #main div, which works fine when the content is static, but the site im working on contains jQuery galleries/slideshows which id like to call into the div. The problem im having is when the gallery is loaded, the images all appear but the jQuery functionality does not work. Any help appreciated. here is the javascript im using... $(document).ready(function() { // Check for hash value in URL var hash = window.location.hash.substr(1); var href = $('#accordion ul li a').each(function(){ var href = $(this).attr('href'); if(hash==href.substr(0,href.length-5)){ var toLoad = hash+'.html #main'; $('#main').load(toLoad) } }); $('#accordion ul li a').click(function(){ var toLoad = $(this).attr('href')+' #main'; $('#main').hide('fast',loadContent); $('#load').remove(); $('#wrapper').append('<span id="load">LOADING...</span>'); $('#load').fadeIn('normal'); window.location.hash = $(this).attr('href').substr(0,$(this).attr('href').length-5); function loadContent() { $('#main').load(toLoad,'',showNewContent()) } function showNewContent() { $('#main').show('normal',hideLoader()); } function hideLoader() { $('#load').fadeOut('normal'); } return false; }); });

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  • How to add additional condition to the JOIN generated by include?

    - by KandadaBoggu
    I want to add additional criteria to the LEFT OUTER JOIN generated by the :include option in ActiveRecord finder. class Post has_many :comments end class Comment belongs_to :post has_many :comment_votes end class CommentVote belongs_to :comment end Now lets say I want to find last 10 posts with their associated comments and the up comment votes. Post.find.all(:limit => 10, :order => "created_at DESC", :include => [{:comments => :comment_votes]) I cant add the condition to check for up votes as it will ignore the posts without the up votes. So the condition has to go the ON clause of the JOIN generated for the comment_votes. I am wishing for a syntax such as: Post.find.all(:limit => 10, :order => "created_at DESC", :include => [{:comments => [:comment_votes, :on => "comment_votes.vote > 0"]) Have you faced such problems before? Did you managed to solve the problem using the current finder? I hope to hear some interesting ideas from the community. PS: I can write a join SQL to get the expected result and stitch the results together. I want to make sure there is no other alternative before going down that path.

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  • pthread_create followed by pthread_detach still results in possibly lost error in Valgrind.

    - by alesplin
    I'm having a problem with Valgrind telling me I have some memory possible lost: ==23205== 544 bytes in 2 blocks are possibly lost in loss record 156 of 265 ==23205== at 0x6022879: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==23205== by 0x540E209: allocate_dtv (in /lib/ld-2.12.1.so) ==23205== by 0x540E91D: _dl_allocate_tls (in /lib/ld-2.12.1.so) ==23205== by 0x623068D: pthread_create@@GLIBC_2.2.5 (in /lib/libpthread-2.12.1.so) ==23205== by 0x758D66: MTPCreateThreadPool (MTP.c:290) ==23205== by 0x405787: main (MServer.c:317) The code that creates these threads (MTPCreateThreadPool) basically gets an index into a block of waiting pthread_t slots, and creates a thread with that. TI becomes a pointer to a struct that has a thread index and a pthread_t. (simplified/sanitized): for (tindex = 0; tindex < NumThreads; tindex++) { int rc; TI = &TP->ThreadInfo[tindex]; TI->ThreadID = tindex; rc = pthread_create(&TI->ThreadHandle,NULL,MTPHandleRequestsLoop,TI); /* check for non-success that I've omitted */ pthread_detach(&TI->ThreadHandle); } Then we have a function MTPDestroyThreadPool that loops through all the threads we created and cancels them (since the MTPHandleRequestsLoop doesn't exit). for (tindex = 0; tindex < NumThreads; tindex++) { pthread_cancel(TP->ThreadInfo[tindex].ThreadHandle); } I've read elsewhere (including other questions here on SO) that detaching a thread explicitly would prevent this possibly lost error, but it clearly isn't. Any thoughts?

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  • Can Boost Program_options separate comma separated argument values

    - by lrm
    If my command line is: > prog --mylist=a,b,c Can Boost's program_options be setup to see three distinct argument values for the mylist argument? I have configured program_options as: namespace po = boost::program_options; po::options_description opts("blah") opts.add_options() ("mylist", std::vector<std::string>>()->multitoken, "description"); po::variables_map vm; po::store(po::parse_command_line(argc, argv, opts), vm); po::notify(vm); When I check the value of the mylist argument, I see one value as a,b,c. I'd like to see three distinct values, split on comma. This works fine if I specify the command line as: > prog --mylist=a b c or > prog --mylist=a --mylist=b --mylist=c Is there a way to configure program_options so that it sees a,b,c as three values that should each be inserted into the vector, rather than one? I am using boost 1.41, g++ 4.5.0 20100520, and have enabled c++0x experimental extensions.

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  • Execute files included in Resource folder

    - by Sumeet Pujari
    In WPF application where I have included some files in resources, I want to execute them on a button click. How do I specify a path in Process.Start(). private void button1_Click_2(object sender, RoutedEventArgs e) { Process.Start("test.txt"); } Or is there any other way? private void button1_Click_2(object sender, RoutedEventArgs e) { string path = System.IO.Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location) + @"\test.txt"; if (File.Exists(path)) { Process.Start(new ProcessStartInfo(path)); } else { MessageBox.Show("No file found"+path); } I added a message box and it showed No files found. :( EDIT: I Tried to check the path after publishing and this what i got. No File Found With a Path - C:\Users\Administrator\AppData\Local\Apps\2.0... test.txt Before I published the Application I got a path which id No File Found at ..project..\bin\Debug\test.txt which is obvious since my Resource file not included there its Under a Resource Folder and not Debug when i add a test file in debug it open without any problem. Can someone Help throwing some light on this case. EDIT: I want to open a file from Resource directory @ C:\Users\Administrator\Documents\Visual Studio 2010\Projects\FastFix\FastFix\Resources Which would be included in my project when i am going to publish it is going to run as a standalone application without installation.

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  • Page URL and database organization.

    - by shurik2533
    I want that its name would be the page address. For example, if page has heading "Some Page", than its address should be http://somesite/some_page/. "some_page"-name generated by system automatically. "some_page" - is the unique identifier of page. The problem in that the user in the future can enter a name which already exists that will cause an error. It is necessary to find an optimum variant of the decision of a problem for great volumes of the data. I have solved a problem as follows: The page identifier in a database is the name of page and a suffix which is by default equal to zero. At page addition there is a check on existence. If such page does not exist, the suffix is equal 0 and its name is "some_page", if page is exist, than - search for the maximum number of a suffix and suffix=suffix+1 and page name become "some_page_1". For this I create in a database the compound key from fields "suffix" and "pageName": Table Pages suffix|pageName |pageTitle 0 |some_page |Some Page 1 |some_page |Some Page 0 |other_page|Other Page Addition of pages occurs through stored procedure: CREATE PROCEDURE addPage (pageNameVal VARCHAR(100), pageTitleVal VARCHAR(100)) BEGIN DECLARE v INT DEFAULT 0; SELECT MAX(suffix) FROM pages WHERE pageName=pageNameVal INTO v; IF v >= 0 THEN SET v = v + 1; ELSE SET v = 0; END IF; INSERT INTO pages (suffix, pageName) VALUES (pageNameVal, v, pageTitleVal); END; Whether there are more the best decisions?

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  • Is this a safe way to release resources in Java?

    - by palto
    Usually when code needs some resource that needs to be released I see it done like this: InputStream in = null; try{ in = new FileInputStream("myfile.txt"); doSomethingWithStream(in); }finally{ if(in != null){ in.close(); } } What I don't like is that you have to initialize the variable to null and after that set it to another value and in the finally block check if the resource was initialized by checking if it is null. If it is not null, it needs to be released. I know I'm nitpicking, but I feel like this could be done cleaner. What I would like to do is this: InputStream in = new FileInputStream("myfile.txt"); try{ doSomethingWithStream(in); }finally{ in.close(); } To my eyes this looks almost as safe as the previous one. If resource initialization fails and it throws an exception, there's nothing to be done(since I didn't get the resource) so it doesn't have to be inside the try block. The only thing I'm worried is if there is some way(I'm not Java certified) that an exception or error can be thrown between operations? Even simpler example: Inputstream in = new FileInputStream("myfile.txt"); in.close(); Is there any way the stream would be left open that a try-finally block would prevent?

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  • Java's Swing Threading

    - by nevets1219
    My understanding is that if I start up another thread to perform some actions, I would need to SwingUtilities.invokeAndWait or SwingUtilities.invokeLater to update the GUI while I'm in said thread. Please correct me if I'm wrong. What I'm trying to accomplish is relatively straightforward: when the user clicks submit, I want to (before performing any actions) disable the submit button, perform the action, and at the end of the action re-enable the button. My method to perform the action updates the GUI directly (displays results) when it gets the results back. This action basically queries a server and gets some results back. What I have so far is: boolean isRunning = false; synchronized handleButtonClick() { if ( isRunning == false ) { button.setEnabled( false ); isRunning = true; doAction(); } } doAction() { new Thread() { try { doAction(); // Concern A } catch ( ... ) { displayStackTrace( ... ); // Concern B } finally { SwingUtilities.invokeLater ( /* simple Runnable to enable button */ ); isRunning = false; } } } For both of my concerns above, do I would have to use SwingUtilities.invokeAndWait since they both will update the GUI? All GUI updates revolve around updating JTextPane. Do I need to in my thread check if I'm on EDT and if so I can call my code (regardless of whether it updates the GUI or not) and NOT use SwingUtilities.invokeAndWait?

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  • Collision Handling in Javascript - Particles Get Stuck

    - by Conner Ruhl
    I am trying to recreate this, and I have been fairly successful. I am having issues with the collision handling though. Although the collision handling seems to work, it has very strange behavior. Here is what I have so far. This is the code that handles collisions: var dx = particle2.getX() - particle1.getX(); var dy = particle2.getY() - particle1.getY(); var angle = Math.atan2(dy, dx); var newP2X = particle1.getX() + (particle1.getRadius() + particle2.getRadius()) * Math.cos(angle); var newP2Y = particle1.getY() + (particle1.getRadius() + particle2.getRadius()) * Math.sin(angle); particle2.setX(newP2X); particle2.setY(newP2Y); var p1Vxi = particle1.getVx(); var p1Vyi = particle1.getVy(); var p1Mass = particle1.getMass(); var p2Vxi = particle2.getVx(); var p2Vyi = particle2.getVy(); var p2Mass = particle2.getMass(); var vxf = (p1Mass * p1Vxi + p2Mass * p2Vxi) / (p1Mass + p2Mass); var vyf = (p1Mass * p1Vyi + p2Mass * p2Vyi) / (p1Mass + p2Mass); particle1.setVx(vxf); particle1.setVy(vyf); particle2.setVx(vxf); particle2.setVy(vyf); EDIT: I have tried to change it to inelastic collisions like suggested, but for some reason the balls collide erratically. Check it out here. Any help is much appreciated!

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  • Help! I'm a Haskell Newbie

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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