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  • Map element position in data file to class property

    - by Augusto
    I need to read/write files, following a format provided by a third party specification. The specification itself is pretty simple: it says the position and the size of the data that will be saved in the file. For example: Position Size Description -------------------------------------------------- 0001 10 Device serial number 0011 02 Hour 0013 02 Minute 0015 02 Second 0017 02 Day 0019 02 Month 0021 02 Year The list is very long, it has about 400 elements. But lots of them can be combined. For example, hour, minute, second, day, month and year can be combined in a single DateTime object. I've splitted the elements into about 4 categories, and created separeted classes for holding the data. So, instead of a big structure representing the data, I have some smaller classes. I've also created different classes for reading and writing the data. The problem is: how to map the positions in the file to the objects properties, so that I don't need to repeat the values in the reading/writing class? I could use some custom attributes and retrieve them via reflection. But since the code will be running on devices with small memory and processor, it would be nice to find another way. My current read code looks like this: public void Read() { DataFile dataFile = new DataFile(); // the arguments are: position, size dataFile.SerialNumber = ReadLong(1, 10); //... } Any ideas on this one? Thanks!

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  • How do php apps identify a user after the session has timed out?

    - by Bill Zimmerman
    I am trying to understand how PHP apps check to see if a user is logged in. I am specifically looking at mediawiki's code to try to help me understand, but these cases should be fairly common in all php apps. From what I gather, the main cases are: A user just logged in or was created, every time they visit the page PHP knows its them by checking data common to the $_SESSION variable and the cookie. A user had the 'remember me' option checked on the login page a long time ago. They have a cookie on there computer with a tokenID, which is checked with a token on the server to authenticate them. In this case, there is no session variable, because the time between accesses could be weeks. My question is, what happens when a user is logged in, but the PHP session times out and he wants to access a page? I would have assumed that there is no easy way for the server to know who the person is - and that they would have to be redirected to the login page. However, mediawiki does just that. I've verified that the session files are deleted after X minutes, but when I hit refresh in mediawiki, it knows which user I am, and the 'token' variable is not included in the cookie.

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  • Moving a ASP.NET application to the cloud

    - by user102533
    I am new to cloud computing, so please bear with me here. I have an existing ASP.NET application with SQL Server 2008 hosted on a Virtual Private Server. Here's what it briefly does: The front end accepts user's requests and adds them to a DB table A Windows Service running in the background picks up the request, processes it and sets a flag. The Windows Services also creates a file for the user to download. User downloads file I'd like to move this web application with the service to the cloud. The architecture I envision is that I'll have 1 Web server in which I will install the front end and the windows service. I'll also have a cloud files server for file storage. The windows service should somehow create a file and transfer it to the cloud file server (I assume this is possible?) My questions: Does the architecture look like I am going in the right direction? I know Amazon has been providing cloud services for a long time. If I want to do minimal changes to my application, should I go with Amazon, Rackspace, Azure or some other provider? I understand that I would not only pay for file storage and web server but also for the bandwidth of users downloading the file and the windows servic uploading the file to the cloud server. Can I assume these costs are negligible? Should I go with VPS + Cloud Files combination to begin with? Any other thoughts/suggestions?

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  • How to pull UIImages from NSData from a socket.

    - by Jus' Wondrin'
    Hey all! I'm using ASyncSocket to move some UIImages from one device over to another. Essentially, on one device I have: NSMutableData *data = UIImageJPEGRepresentation(image, 0.1); if(isRunning){ [sock writeData:data withTimeout:-1 tag:0]; } So a new image will be added to the socket every so often (like a webcam). Then, on the other device, I am calling: [listenSocket readDataWithTimeout:1 tag:0]; which will respond with: - (void)onSocket:(AsyncSocket *)sock didReadData:(NSData *)data withTag:(long)tag { [responseData appendData:data]; [listenSocket readDataWithTimeout:1 tag:0]; } Essentially, what I want to be able to do is have an NSTimer going which will call @selector(PullImages): -(void) PullImages { In here, I want to be able to pull images out of ResponseData. How do I do that? There might not be a complete image yet, there might be multiple images, there might be one and a half images! I want to parse the NSData into each existing image! } Any assistance? Thanks in advance!

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  • Hibernate : Opinions in Composite PK vs Surrogate PK

    - by Albert Kam
    As i understand it, whenever i use @Id and @GeneratedValue on a Long field inside JPA/Hibernate entity, i'm actually using a surrogate key, and i think this is a very nice way to define a primary key considering my not-so-good experiences in using composite primary keys, where : there are more than 1 business-value-columns combination that become a unique PK the composite pk values get duplicated across the table details cannot change the business value inside that composite PK I know hibernate can support both types of PK, but im left wondering by my previous chats with experienced colleagues where they said that composite PK is easier to deal with when doing complex SQL queries and stored procedure processes. They went on saying that when using surrogate keys will complicate things when doing joining and there are several condition when it's impossible to do some stuffs when using surrogate keys. Although im sorry i cant explain the detail here since i was not clear enough when they explain it. Maybe i'll put more details next time. Im currently trying to do a project, and want to try out surrogate keys, since it's not getting duplicated across tables, and we can change the business-column values. And when the need for some business value combination uniqueness, i can use something like : @Table(name="MY_TABLE", uniqueConstraints={ @UniqueConstraint(columnNames={"FIRST_NAME", "LAST_NAME"}) // name + lastName combination must be unique But im still in doubt because of the previous discussion about the composite key. Could you share your experiences in this matter ? Thank you !

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  • What's a good way of building up a String where you specific start and end locations?

    - by Michael Campbell
    (java 1.5) I have a need to build up a String, in pieces. I'm given a set of (sub)strings, each with a start and end point of where they belong in the final string. Was wondering if there were some canonical way of doing this. This isn't homework, and I can use any licensable OSS, such as jakarta commons-lang StringUtils etc. My company has a solution using a CharBuffer, and I'm content to leave it as is (and add some unit tests, of which there are none (?!)) but the code is fairly hideous and I would like something easier to read. As I said this isn't homework, and I don't need a complete solution, just some pointers to libraries or java classes that might give me some insight. The String.Format didn't seem QUITE right... I would have to honor inputs too long and too short, etc. Substrings would be overlaid in the order they appear (in case of overlap). As an example of input, I might have something like: String:start:end FO:0:3 (string shorter than field) BAR:4:5 (String larger than field) BLEH:5:9 (String overlays previous field) I'd want to end up with FO BBLEH 01234567890

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  • Using "Object.create" instead of "new"

    - by Graham King
    Javascript 1.9.3 / ECMAScript 5 introduces Object.create, which Douglas Crockford amongst others has been advocating for a long time. How do I replace new in the code below with Object.create? var UserA = function(nameParam) { this.id = MY_GLOBAL.nextId(); this.name = nameParam; } UserA.prototype.sayHello = function() { console.log('Hello '+ this.name); } var bob = new UserA('bob'); bob.sayHello(); (Assume MY_GLOBAL.nextId exists). The best I can come up with is: var userB = { init: function(nameParam) { this.id = MY_GLOBAL.nextId(); this.name = nameParam; }, sayHello: function() { console.log('Hello '+ this.name); } }; var bob = Object.create(userB); bob.init('Bob'); bob.sayHello(); There doesn't seem to be any advantage, so I think I'm not getting it. I'm probably being too neo-classical. How should I use Object.create to create user 'bob'?

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  • Source of UIView Implicit Animation delay?

    - by iPhoneToucher
    I have a block of UIView animation code that looks like this: [UIView beginAnimations:@"pushView" context:nil]; [UIView setAnimationDelay:0]; [UIView setAnimationDuration:.5]; [UIView setAnimationDelegate:self]; [UIView setAnimationWillStartSelector:@selector(animationWillStart)]; view.frame = CGRectMake(0, 0, 320, 416); [UIView commitAnimations]; The code basically mimics the animation of a ModalView presentation and is tied to a button on my interface. When the button is pressed, I get a long (.5 sec) delay (on iPod Touch...twice as fast on iPhone 3GS) before the animationWillStart: actually gets called. My app has lots going on besides this, but I've timed various points of my code and the delay definitely occurs at this block. In other words, a timestamp immediately before this code block and a timestamp when animationWillStart: gets called shows a .5 sec difference. I'm not too experienced with Core Animation and I'm just trying to figure out what the cause of the delay is...Memory use is stable when the animation starts and CoreAnimation FPS seems to be fine in Instruments. The view that gets animated does have upwards of 20 total subviews, but if that were the issue wouldn't it cause choppiness after the animation starts, rather than before? Any ideas?

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  • What's a good way of building up a String given specific start and end locations?

    - by Michael Campbell
    (java 1.5) I have a need to build up a String, in pieces. I'm given a set of (sub)strings, each with a start and end point of where they belong in the final string. Was wondering if there were some canonical way of doing this. This isn't homework, and I can use any licensable OSS, such as jakarta commons-lang StringUtils etc. My company has a solution using a CharBuffer, and I'm content to leave it as is (and add some unit tests, of which there are none (?!)) but the code is fairly hideous and I would like something easier to read. As I said this isn't homework, and I don't need a complete solution, just some pointers to libraries or java classes that might give me some insight. The String.Format didn't seem QUITE right... I would have to honor inputs too long and too short, etc. Substrings would be overlaid in the order they appear (in case of overlap). As an example of input, I might have something like: String:start:end FO:0:3 (string shorter than field) BAR:4:5 (String larger than field) BLEH:5:9 (String overlays previous field) I'd want to end up with FO BBLEH 01234567890

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  • Name Values in Excel Object model

    - by mcoolbeth
    I am using VSTO to create an Excel add-in. My plan is to persist objects inside of excel workbooks by serializing them to strings and assigning those strings to be the values of names in the workbook. However, when I call the API function to add the new name, I get a mysterious exception from the COM library. More precisely, I am calling _app.ActiveWorkbook.Names.Add(name, value, true, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing); where name = "an_object" and value = "TestTemplate|'Sheet1'!$A$1| 1Cube=(0,1):(1,2)| 2EntryNumber=(1,1):(2,2)| 3Description=(2,1):(3,2)| 4Group=(4,1):(5,2)| 5Repost=(3,1):(4,2)| 6Debit=(13,3):(16,4)| 7Credit=(13,2):(16,3)|Company=(6,1):(7,2)|Company Partner=(7,1):(8,2)|Time Monthly=(8,1):(9,2)|Currency=(9,1):(10,2)|Version=(10,1):(11,2)|Department=(13,0):(16,1)|Account=(13,1):(16,2)|" A hypothesis is that the value string does not qualify as a string that can be stored in a name (illegal characters, too long, etc) but I cannot find any documentation about what the restrictions are. Does anyone know what is going wrong here? The error message, in case anyone wants it, is Exception from HRESULT: 0x800A03EC Thanks alot.

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  • Playing a .TS file on iOS

    - by Jonathan Grynspan
    We're working with some hardware that produces files in the .TS format, and we'd like to play them on an iOS device. (The files are internally consistent with what iOS supports--MPEG-4 video, AAC audio.) We've been investigating three options so far: Roll our own integrated HTTP Live Streaming server and serve up a faux M3U8 playlist from within the app. This... doesn't seem to want to play nice, and we've had mixed luck actually getting the .TS files to play on devices. Unwrap the MPEG-4 and AAC data from the TS file and re-wrap it as MP4. This, I'm told, is exceedingly difficult to do, and I haven't found anything useful online that could shed light on how to do it. We've got code in the pipeline to do it but it won't be ready until long after we need it. If we could do it, I could easily subclass NSURLProtocol and have it working within a matter of hours minutes. Use FFmpeg to implement option #2. FFmpeg seems like a possible solution but it isn't configured to build for iOS and I don't have the background to get it working (whereas the rest of our engineers don't have the Apple background needed.) I think #2 is our best bet, but as I don't know the ins and outs of MPEG-2 TS and MPEG-4, I don't have the ability to put it together myself. Does anybody have any insight into this problem? Perhaps some experience playing local TS files on iOS, or some tips on converting from TS to MP4?

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  • ObjectDataSource.Select with Parameters Time Out

    - by MasterMax1313
    I'm using an ObjectDataSource with a 2008 ReportViewer control and Linq to CSV. The ODS has two parameters (the SQL is spelled out in an XSD file with a table adapter). The Reportviewer takes a very long time to render the output after a button is clicked to generate the report. That's my first problem. Even though it works (most of the time), the processing time worries me, and subsequent requests don't seem to be changing the results shown on the screen. The next issue is that when I go to export the ODS to CSV I'm getting a time out exception on the select method of the ODS (shown below). This works for ODS without parameters, but it seems like now that I've added parameters that it doesn't want to cooperate. I'm fresh out of ideas, any thoughts? <asp:ObjectDataSource ID="obsGetDataAllCustomers" runat="server" SelectMethod="GetDataAllCustomers" TypeName="my.myAdapter.AllCustomers" OldValuesParameterFormatString="original_{0}" > <SelectParameters> <asp:ControlParameter ControlID="StartDate" Name="Start" PropertyName="Text" Type="DateTime" /> <asp:ControlParameter ControlID="EndDate" Name="_End" PropertyName="Text" Type="DateTime" /> </SelectParameters> </asp:ObjectDataSource> After button click to view report - rvAllCustomers.LocalReport.Refresh() Export to CSV (adding the items returned to a list which is then processed by working code) - For Each dr As DataRow In CType(obs.Select(), DataView).Table.Rows l.Add(New FullOrderOutput(dr)) Next

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  • Good patterns for loose coupling in Java?

    - by Eye of Hell
    Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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  • Rails model relations depending on count of nested relations

    - by Lowgain
    I am putting together a messaging system for a rails app I am working on. I am building it in a similar fashion to facebook's system, so messages are grouped into threads, etc. My related models are: MsgThread - main container of a thread Message - each message/reply in thread Recipience - ties to user to define which users should subscribe to this thread Read - determines whether or not a user has read a specific message My relationships look like class User < ActiveRecord::Base #stuff... has_many :msg_threads, :foreign_key => 'originator_id' #threads the user has started has_many :recipiences has_many :subscribed_threads, :through => :recipiences, :source => :msg_thread #threads the user is subscribed to end class MsgThread < ActiveRecord::Base has_many :messages has_many :recipiences belongs_to :originator, :class_name => "User", :foreign_key => "originator_id" end class Recipience < ActiveRecord::Base belongs_to :user belongs_to :msg_thread end class Message < ActiveRecord::Base belongs_to :msg_thread belongs_to :author, :class_name => "User", :foreign_key => "author_id" end class Read < ActiveRecord::Base belongs_to :user belongs_to :message end I'd like to create a new selector in the user sort of like: has_many :updated_threads, :through => :recipiencies, :source => :msg_thread, :conditions => {THREAD CONTAINS MESSAGES WHICH ARE UNREAD (have no 'read' models tying a user to a message)} I was thinking of either writing a long condition with multiple joins, or possibly writing giving the model an updated_threads method to return this, but I'd like to see if there is an easier way first. Any ideas? Also, if there is something fundamentally wrong with my structure for this functionality let me know! Thanks!!

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  • Python script, runs well, but not perfectly, debugging help.

    - by S1syphus
    What it does (sort of)... or is meant to, the script reads from a csv file that contains information on sound files and create a play list exactly 60 minutes long. An example csv, contains: their title, duration (in seconds), minium total time to be played (in minutes) An example is: Soundfoo,120,10 Soundbar,30,6 Sounddev,60,20 Soundrandom,15,8 The script works out the minimum instances of plays, take 'Soundfoo' for example, the length of each sample is 120 seconds and the minimum time to be played is 10 minutes, so basic maths 10*60/120 gives the number of instances the song is to be played, in this case 5. It is meant to take minimum number of instances and spread out equally from each other; so there will never be a period where for example Soundbar is played twice in a row. Then if the minium instances of each song has been used, and there is still time with in the 60 min, how is it possible to tell it to go back and fill the time by selecting each sound and including it till the 60 min is filled while remaining sparsely populated. Heres the issue(s)! The script fails to calculate the actual time require to play all the sounds in a file and the total time of the playlist, the thing is tho it doesn't get it wrong all the time maybe 3/5 times, even if I run it on the same csv file it will give me different answers. Here is the file I shall run the script on e for sake of ease to see the issue: Sound1,60,10 Sound2,60,10 Sound3,60,10 Sound4,60,10 Sound5,60,10 Sound6,60,10 I'll do it three times and post the results: 1 Required playtime in minutes: 60 Actual time in minutes to play all required ads: 62 Total playtime in minutes: 62.0 2 Required playtime in minutes: 60 Actual time in minutes to play all required ads: 71 Total playtime in minutes: 71.0 3 Required playtime in minutes: 60 Actual time in minutes to play all required ads: 60 Total playtime in minutes: 60.0 Relevant Code: pastebin.com/demkBXk6 And finally... in context: http://pastebin.com/demkBXk6 If you made it down to here, thanks for staying and reading, kudos.

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  • session regeneration in tomcat ?

    - by shrini1000
    Hi, I am using Spring security to secure my Java web application which is deployed in tomcat. I found out that it is vulnerable to session fixation attacks because tomcat does not create a new session upon successful log in. On debugging some more, here's what I found. For the following code (which is supposed to create a new session - pl. note, it's just a snippet and not full code): HttpSession session = request.getSession(false); session.invalidate(); session = request.getSession(true); // we now have a new session I thought a new session will be created, but tomcat simply uses the same session that got invalidated and hence the session id does not change. I searched online and found a solution which uses a 'valve' - http://marvinsmutterings.blogspot.com/2010/02/fixing-session-fixation-in-liferay-on.html but could not get it to work because it's looking for a jboss logging class and when I add it to lib, I get a reflection exception and the server doesn't start up. I'm using tomcat 5.5.28. Will be glad to have any pointers. Pl. let me know if you need more details, since I don't want to make this post too long. Sincere thanks!

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  • iPhone OpenGL and NSTimer issues

    - by Kyle
    I have an NSTimer that runs at 60hz. With an OpenGL scene loaded and rendering, my game can get 60fps, solid, all day long.. Then if I go and recompile the app, or reload it, it will get 40fps. Same resources loaded. I've been running into this problem for years, and I just want to know why. It's crazy, and I want to know if I should just abandon this stupid Timer. Conditions are not different on my 3GS between loads. It will just get 40fps sometimes. Obviously the clockrate is not different between loads, so the performance figures should be constant given a constant scene. Here is a log of my framerates: A good load: :-) FrameRate: 61 FrameRate: 61 FrameRate: 61 FrameRate: 60 FrameRate: 60 FrameRate: 61 FrameRate: 60 FrameRate: 60 FrameRate: 61 FrameRate: 60 FrameRate: 61 Now, I'll go ahead and do nothing, recompile, and run: FrameRate: 43 FrameRate: 50 FrameRate: 45 FrameRate: 48 FrameRate: 40 FrameRate: 45 FrameRate: 42 FrameRate: 41 FrameRate: 42 FrameRate: 44 FrameRate: 41 FrameRate: 46 ^- Massive difference visually. What the flying heck could cause this? SAME area of the scene, SAME camera setup. No variables are different.

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  • Approximate string matching with a letter confusion matrix?

    - by zigglenaut
    I'm trying to model a phonetic recognizer that has to isolate instances of words (strings of phones) out of a long stream of phones that doesn't have gaps between each word. The stream of phones may have been poorly recognized, with letter substitutions/insertions/deletions, so I will have to do approximate string matching. However, I want the matching to be phonetically-motivated, e.g. "m" and "n" are phonetically similar, so the substitution cost of "m" for "n" should be small, compared to say, "m" and "k". So, if I'm searching for [mein] "main", it would match the letter sequence [meim] "maim" with, say, cost 0.1, whereas it would match the letter sequence [meik] "make" with, say, cost 0.7. Similarly, there are differing costs for inserting or deleting each letter. I can supply a confusion matrix that, for each letter pair (x,y), gives the cost of substituting x with y, where x and y are any letter or the empty string. I know that there are tools available that do approximate matching such as agrep, but as far as I can tell, they do not take a confusion matrix as input. That is, the cost of any insertion/substitution/deletion = 1. My question is, are there any open-source tools already available that can do approximate matching with confusion matrices, and if not, what is a good algorithm that I can implement to accomplish this?

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  • ExternalInterface

    - by Jesse
    Hey, so I'm having a bunch of trouble getting ExternalInterface to work, which is odd, because I use it somewhat often. I'm hoping it's something I just missed because I've been looking at it too long. The flash_ready function is correctly returning the objectID, and as far as I can tell, everything else is in order. Unfortunately, when I run it, I get an error (varying by browser) telling me that basically document.getElementById(<movename>).test() is not a valid method. Here's the code: javascript: function flash_ready(i){ document.getElementById(i).test('success!'); } Embed Html (Generated): <script type="text/javascript"> swfobject.embedSWF("/chainmaille/includes/media/flash/upload_image.swf", "/chainmaille/includes/media/flash/upload_image", "500", "50", "9.0.0","expressInstall.swf", {}, {allowScriptAccess:'always', wmode:'transparent'},{id:'uploader_flash',name:'uploader_flash'}); </script> <object type="application/x-shockwave-flash" id="uploader_flash" name="uploader_flash" data="/chainmaille/includes/media/flash/upload_image.swf" width="500" height="50"><param name="allowScriptAccess" value="always"><param name="wmode" value="transparent"></object> AS3 : package com.jesseditson.uploader { import flash.display.MovieClip; import flash.external.ExternalInterface; import flash.system.Security; public class UI extends MovieClip { // Initialization: public function UI() { Security.allowDomain('*'); ExternalInterface.addCallback("test", test); var jscommand:String = "flash_ready('"+ExternalInterface.objectID+"');"; var url:URLRequest = new URLRequest("javascript:" + jscommand + " void(0);"); navigateToURL(url, "_self"); } public function test(t){ trace(t); } } } Swfobject is being included via google code, and the flash embeds just fine, so that's not the problem. I've got a very similar setup working on another server, but can't seem to get it working on this one. It's a Hostgator shared server. Could it be the server's fault? Anybody see any obvious syntax problems? Thanks in advance!

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  • setInterval alternative

    - by spyder
    Hi folks, In my app I am polling the webserver for messages every second and displaying them in the frontend. I use setInterval to achieve this. However as long as the user stays on that page the client keeps polling the server with requests even if there is no data. The server does give an indication when no more messages are being generated by setting a variable. I thought of using this variable to clearInterval and stop the timer but that didn't work. What else can I use in this situation? I am using jquery and django. Here is my code: jquery: var refresh = setInterval( function () { var toLoad = '/myMonitor'+' #content'; $('#content').load(toLoad).show(); }, 1000); // refresh every 1000 milliseconds }); html: div id=content is here I can access the django variable for completion in html with each refresh. How can I set clearInterval if at all ? Note: stack overflow does not let me put is &gt &lt so html is incomplete Thanks

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  • Does overloading Grails static 'mapping' property to bolt on database objects violate DRY?

    - by mikesalera
    Does Grails static 'mapping' property in Domain classes violate DRY? Let's take a look at the canonical domain class: class Book {      Long id      String title      String isbn      Date published      Author author      static mapping = {             id generator:'hilo', params:[table:'hi_value',column:'next_value',max_lo:100]      } } or: class Book { ...         static mapping = {             id( generator:'sequence', params:[sequence_name: "book_seq"] )     } } And let us say, continuing this thought, that I have my Grails application working with HSQLDB or MySQL, but the IT department says I must use a commercial software package (written by a large corp in Redwood Shores, Calif.). Does this change make my web application nobbled in development and test environments? MySQL supports autoincrement on a primary key column but does support sequence objects, for example. Is there a cleaner way to implement this sort of 'only when in production mode' without loading up the domain class?

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  • Optimizing MySQL update query

    - by Jernej Jerin
    This is currently my MySQL UPDATE query, which is called from program written in Java: String query = "UPDATE maxday SET DatePressureREL = (SELECT Date FROM ws3600 WHERE PressureREL = (SELECT MAX" + "(PressureREL) FROM ws3600 WHERE Date >= '" + Date + "') AND Date >= '" + Date + "' ORDER BY Date DESC LIMIT 1), " + "PressureREL = (SELECT PressureREL FROM ws3600 WHERE PressureREL = (SELECT MAX(PressureREL) FROM ws3600 " + "WHERE Date >= '" + Date + "') AND Date >= '" + Date + "' ORDER BY Date DESC LIMIT 1), ..."; try { s.execute(query); } catch (SQLException e) { System.out.println("SQL error"); } catch(Exception e) { e.printStackTrace(); } Let me explain first, what does it do. I have two tables, first is ws3600, which holds columns (Date, PressureREL, TemperatureOUT, Dewpoint, ...). Then I have second table, called maxday, which holds columns like DatePressureREL, PressureREL, DateTemperatureOUT, TemperatureOUT,... Now as you can see from an example, I update each column, the question is, is there a faster way? I am asking this, because I am calling MAX twice, first to find the Date for that value and secondly to find the actual value. Now I know that I could write like that: SELECT Date, PressureREL FROM ws3600 WHERE PressureREL = (SELECT MAX(PressureREL) FROM ws3600 WHERE Date >= '" + Date + "') AND Date >= '" + Date + "' ORDER BY Date DESC LIMIT 1 That way I get the Date of the max and the max value at the same time and then update with those values the data in maxday table. But the problem of this solution is, that I have to execute many queries, which as I understand takes alot more time compared to executing one long mysql query because of overhead in sending each query to the server. If there is no better way, which solution beetwen this two should I choose. The first, which only takes one query but is very unoptimized or the second which is beter in terms of optimization, but needs alot more queries which probably means that the preformance gain is lost because of overhead in sending each query to the server?

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  • Is there a way to do 'correct' arithmetical rounding in .NET? / C#

    - by Markus
    I'm trying to round a number to it's first decimal place and, considering the different MidpointRounding options, that seems to work well. A problem arises though when that number has sunsequent decimal places that would arithmetically affect the rounding. An example: With 0.1, 0.11..0.19 and 0.141..0.44 it works: Math.Round(0.1, 1) == 0.1 Math.Round(0.11, 1) == 0.1 Math.Round(0.14, 1) == 0.1 Math.Round(0.15, 1) == 0.2 Math.Round(0.141, 1) == 0.1 But with 0.141..0.149 it always returns 0.1, although 0.146..0.149 should round to 0.2: Math.Round(0.145, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.AwayFromZero) == 0.1 Math.Round(0.146, 1, MidpointRounding.ToEven) == 0.1 Math.Round(0.146M, 1, MidpointRounding.ToEven) == 0.1M Math.Round(0.146M, 1, MidpointRounding.AwayFromZero) == 0.1M I tried to come up with a function that addresses this problem, and it works well for this case, but of course it glamorously fails if you try to round i.e. 0.144449 to it's first decimal digit (which should be 0.2, but results 0.1.) (That doesn't work with Math.Round() either.) private double round(double value, int digit) { // basically the old "add 0.5, then truncate to integer" trick double fix = 0.5D/( Math.Pow(10D, digit+1) )*( value = 0 ? 1D : -1D ); double fixedValue = value + fix; // 'truncate to integer' - shift left, round, shift right return Math.Round(fixedValue * Math.Pow(10D, digit)) / Math.Pow(10D, digit); } I assume a solution would be to enumerate all digits, find the first value larger than 4 and then round up, or else round down. Problem 1: That seems idiotic, Problem 2: I have no idea how to enumerate the digits without a gazillion of multiplications and subtractios. Long story short: What is the best way to do that?

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  • "do it all" page structure and things to watch out for?

    - by Andrew Heath
    I'm still getting my feet wet in PHP (my 1st language) and I've reached the competency level where I can code one page that handles all sorts of different related requests. They generally have a structure like this: (psuedo code) <?php include 'include/functions.php'; IF authorized IF submit (add data) ELSE IF update (update data) ELSE IF list (show special data) ELSE IF tab switch (show new area) ELSE display vanilla (show default) ELSE "must be registered/logged-in" ?> <HTML> // snip <?php echo $output; ?> // snip </HTML> and it all works nicely, and quite quickly which is cool. But I'm still sorta feeling my way in the dark... and would like some input from the pros regarding this type of page design... is it a good long-term structure? (it seems easily expanded...) are there security risks particular to this design? are there corners I should avoid painting myself into? Just curious about what lies ahead, really...

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  • Python MD5 Hash Faster Calculation

    - by balgan
    Hi everyone. I will try my best to explain my problem and my line of thought on how I think I can solve it. I use this code for root, dirs, files in os.walk(downloaddir): for infile in files: f = open(os.path.join(root,infile),'rb') filehash = hashlib.md5() while True: data = f.read(10240) if len(data) == 0: break filehash.update(data) print "FILENAME: " , infile print "FILE HASH: " , filehash.hexdigest() and using start = time.time() elapsed = time.time() - start I measure how long it takes to calculate an hash. Pointing my code to a file with 653megs this is the result: root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.624 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.373 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.540 Ok now 12 seconds +- on a 653mb file, my problem is I intend to use this code on a program that will run through multiple files, some of them might be 4/5/6Gb and it will take wayy longer to calculate. What am wondering is if there is a faster way for me to calculate the hash of the file? Maybe by doing some multithreading? I used a another script to check the use of the CPU second by second and I see that my code is only using 1 out of my 2 CPUs and only at 25% max, any way I can change this? Thank you all in advance for the given help.

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