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• How can I improve my real-time behavior in multi-threaded app using pthreads and condition variables

  - by WilliamKF

  I have a multi-threaded application that is using pthreads. I have a mutex() lock and condition variables(). There are two threads, one thread is producing data for the second thread, a worker, which is trying to process the produced data in a real time fashion such that one chuck is processed as close to the elapsing of a fixed time period as possible. This works pretty well, however, occasionally when the producer thread releases the condition upon which the worker is waiting, a delay of up to almost a whole second is seen before the worker thread gets control and executes again. I know this because right before the producer releases the condition upon which the worker is waiting, it does a chuck of processing for the worker if it is time to process another chuck, then immediately upon receiving the condition in the worker thread, it also does a chuck of processing if it is time to process another chuck. In this later case, I am seeing that I am late processing the chuck many times. I'd like to eliminate this lost efficiency and do what I can to keep the chucks ticking away as close to possible to the desired frequency. Is there anything I can do to reduce the delay between the release condition from the producer and the detection that that condition is released such that the worker resumes processing? For example, would it help for the producer to call something to force itself to be context switched out? Bottom line is the worker has to wait each time it asks the producer to create work for itself so that the producer can muck with the worker's data structures before telling the worker it is ready to run in parallel again. This period of exclusive access by the producer is meant to be short, but during this period, I am also checking for real-time work to be done by the producer on behalf of the worker while the producer has exclusive access. Somehow my hand off back to running in parallel again results in significant delay occasionally that I would like to avoid. Please suggest how this might be best accomplished.

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• Multimedia files written over WAN are getting truncated

  - by Dean

  I use the windows Multimedia API to create .wav files. 1. Open file with mmsioOpen 2. Creates WAVE,frm and data chunks using mmioCreateChunk 3. Write audio data using mmioWrite 4. Ascend out of the chunks using mmioAscend 5. Close file using mmioClose The file is being written into a temporary location, so after it has been closed it gets copied to another location using the CopyFile. This program is written in C++ and works great until the file it is writing resides over a WAN in a different city or country. The end result is a wav file that should be 20-30 seconds long ends up being 4 secodns long. It is always the last bit that is missing, so when you play it back it just stops before then of the recording. I initially thought that maybe I was copying the file too soon so as a test I put in a pause of 30 seconds after closing the file using Sleep(30000), but this made no difference to either it being truncated or by how much. I have modified the program to write to a file in parrallel using CreateFile and WriteFile, and the result is the same, so it is not an issue specifically with the mmio API's. Does anyone have any ideas why this is happening and if there is a work-around to it? I suspect that I may end up having the temporary location on the local drive, but this is quite a big change to the application as well as existing deployments. thanks for everyones time Dean

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• rails search nested set (categories and sub categories)

  - by bob

  Hello, I am using the http://github.com/collectiveidea/awesome_nested_set awesome nested set plugin and currently, if I choose a sub category as my category_id for an item, I can not search by its parent. Category.parent Category.Child I choose Category.child as the category that my item is in. So now my item has category_id of 4 stored in it. If I go to a page in my rails application, lets say teh Category page and I am on the Category.parent's page, I want to show products that have category_id's of all the descendants as well. So ideally i want to have a find method that can take into account the descendants. You can get the descendants of a root by calling root.descendants (a built in plugin method). How would I go about making it so I can query a find that gets the descendants of a root instead of what its doing now which is binging up nothing unless the product had a specific category_id of the Category.parent. I hope I am being clear here. I either need to figure out a way to create a find method or named_scope that can query and return an array of objects that have id's corresponding tot he descendants of a root OR if I have any other options, what are they? I thought about creating a field in my products table like parent_id which can keep track of the parent so i can then create two named scopes one finding the parent stuff and one finding the child stuff and chaining them. I know I can create a named scope for each child and chain them together for multiple children but this seems a very tedious process and also, if you add more children, you would need to specify more named scopes.

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• Encoding issue - 2nd band of ISO-8859-1 values do not get encoded?

  - by bstack

  Hello, I want to send the pound sign character i.e. '£' encoded as ISO-8859-1 across the wire. I perform this by doing the following: var _encoding = Encoding.GetEncoding("iso-8859-1"); var _requestContent = _encoding.GetBytes(requestContent); var _request = (HttpWebRequest)WebRequest.Create(target); _request.Headers[HttpRequestHeader.ContentEncoding] = _encoding.WebName; _request.Method = "POST"; _request.ContentType = "application/x-www-form-urlencoded; charset=iso-8859-1"; _request.ContentLength = _requestContent.Length; _requestStream = _request.GetRequestStream(); _requestStream.Write(_requestContent, 0, _requestContent.Length); _requestStream.Flush(); _requestStream.Close(); When I put a breakpoint at the target, I expect to receive the following: '%a3', however I receive '%u00a3' instead. ISO-8859-1 is divided into 2 groups of characters: (ref: http://en.wikipedia.org/wiki/ISO_8859-1) The lower range 20 to 7E - is where all characters seem to be encoded correctly The higher range A0 to FF - is where all characters seem to encode to their Unicode equivalent value As '£' is in higher range A0 to FF, it gets encoded to %u00a3. In fact when I use the first few characters of the higher range A0 to FF i.e. '¡¢£¤¥¦§¨©ª«¬®', I get '%u00a1%u00a2%u00a3%u00a4%u00a5%u00a6%u00a7%u00a8%u00a9%u00aa%u00ab%u00ac%u00ae'. This behaviour is consistent. The question I have is why do characters in the higher range A0 to FF get encoded to their unicode value - and not to their equivalent ISO-8859-1 value? Help would be greatly appreciated... Billy

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• iPhone UI addSubview causing concurrency exception

  - by Eli

  This is really odd... I run my app, and while it is opening and the views are constructing I get: Collection <CALayerArray: 0x124650> was mutated while being enumerated. The code trace goes through the following: main UIApplicationMain -[UIApplication _run] CFRunLoopRunInMode CFRunLoopRunSpecific _UIApplicationHandleEvent -[UIApplication sendEvent:] -[UIApplication handleEvent:withNewEvent:] -[UIApplication _runWithURL:sourceBundleID:] -[UIApplication _performInitilizationWithURL:sourceBundleID:] -[AppDelegate applicationDidFinishLaunching:] +[Controller initializeController] //This is my own function [window addSubview: pauseMenuController.view] //This is the last point of my code it goes through -[UIView(Hierarchy) addSubview:] -[UIView(Internal) _addSubview:positioned:relativeTo:] -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:] -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] _NSFastEnumerationMutationHandler objc_exception_throw I've run the game lots and lots and lots of times and I've never seen this, then suddenly it popped up. The weird thing is that I'm not creating any other threads (that I know of) until after this code all gets called. It'll be easier for me to debug this if someone can give me some explanation of what might be getting modified while it's being accessed in a UIView. Does it have something to do with adding something to the view while it's already adding something, maybe? Any ideas?

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• Designing a fluid Javascript interface to hide callback asynchrony

  - by Anurag

  How would I design an API to hide the asynchronous nature of AJAX and HTTP requests, or basically delay it to provide a fluid interface. To show an example from Twitter's new Anywhere API: // get @ded's first 20 statuses, filter only the tweets that // mention photography, and render each into an HTML element T.User.find('ded').timeline().first(20).filter(filterer).each(function(status) { $('div#tweets').append('<p>' + status.text + '</p>'); }); function filterer(status) { return status.text.match(/photography/); } vs this (asynchronous nature of each call is clearly visible) T.User.find('ded', function(user) { user.timeline(function(statuses) { statuses.first(20).filter(filterer).each(function(status) { $('div#tweets').append('<p>' + status.text + '</p>'); }); }); }); It finds the user, gets their tweet timeline, filters only the first 20 tweets, applies a custom filter, and ultimately uses the callback function to process each tweet. I am guessing that a well designed API like this should work like a query builder (think ORMs) where each function call builds the query (HTTP URL in this case), until it hits a looping function such as each/map/etc., the HTTP call is made and the passed in function becomes the callback. An easy development route would be to make each AJAX call synchronous, but that's probably not the best solution. I am interested in figuring out a way to make it asynchronous, and still hide the asynchronous nature of AJAX.

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• ASP.NET MVC Image refreshing

  - by user295541

  Hi, I have an Employee object which has an image property. Image class contains image metadata as image caption, and image file name. If I upload a new image for an employee on async way without full post back the new image is not appeared on the page. I use GUID to name the image file to avoid the page caching. I do the image modifying the following way: ctrEmployee employee = Repository.Get(PassedItemID); if (employee.ctrImage != null) { string fullFileName = serverFolder + employee.ctrImage.FileName; FileInfo TheFile = new FileInfo(fullFileName); if (TheFile.Exists) { TheFile.Delete(); } fileName = Guid.NewGuid() + ".jpg"; employee.ctrImage.FileName = fileName; } resizedBmp.Save(string.Format("{0}{1}", serverFolder, fileName), System.Drawing.Imaging.ImageFormat.Jpeg); Repository.Edit<ctrEmployee>(employee); ImageID = employee.Image.Value; return PartialView(UserControlPaths.Thumbnail, new ThumbnailDataModel(employee.Image.Value, 150, 150)); The partial view has an image tag which gets the saved image url string which is a GUID. Anybody has an idea what I do wrong?

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• Improve Efficiency for This Text Processing Code

  - by johnv

  I am writing a program that counts the number of words in a text file which is already in lowercase and separated by spaces. I want to use a dictionary and only count the word IF it's within the dictionary. The problem is the dictionary is quite large (~100,000 words) and each text document has also ~50,000 words. As such, the codes that I wrote below gets very slow (takes about 15 sec to process one document on a quad i7 machine). I'm wondering if there's something wrong with my coding and if the efficiency of the program can be improved. Thanks so much for your help. Code below: public static string WordCount(string countInput) { string[] keywords = ReadDic(); /* read dictionary txt file*/ /*then reads the main text file*/ Dictionary<string, int> dict = ReadFile(countInput).Split(' ') .Select(c => c) .Where(c => keywords.Contains(c)) .GroupBy(c => c) .Select(g => new { word = g.Key, count = g.Count() }) .OrderBy(g => g.word) .ToDictionary(d => d.word, d => d.count); int s = dict.Sum(e => e.Value); string k = s.ToString(); return k; }

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• how to make a explorer like logic in Obj C for iphone

  - by Ekra

  Hi friends, To make the query simple first we can take example:- If we open the explorer in our Windows desktop how it shows us the tree. As we keep on clicking the tree it get expanded and shows the file in it. The same way I want to show a explorer which gets expanded as the user clicks on it(I want to get the business logic the UI is simple). The information of the explorer i.e. which folder has what files come in a XML format to me. I have 2 options of getting the XML either I can get the whole XML at one query(but I guess this might slow the application if the XML is quite big). OR I can get the XML for every list like first only the root structure then if user clicks on any folder in root I can get the list(the files or folders inside that folder) of that particular folder. Now the question is What would be the approach to implement both the method and which would be the best. Should I need to create some dictionary to maintain the link of the files like which file is inside what. I am not able to get as how I would be able to link all the files. Any hint or direction would be highly appreciated. Thanks in advance

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• How to perform two-way data binding of controls in a user control inside a FormView

  - by Sandor Drieënhuizen

  I'm trying to perform two-way data binding on the controls in my user control, which is hosted inside a FormView template. FormView: <asp:ObjectDataSource runat="server" ID="ObjectDataSource" TypeName="WebApplication1.Data" SelectMethod="GetItem" UpdateMethod="UpdateItem"> </asp:ObjectDataSource> <asp:FormView runat="server" ID="FormView" DataSourceID="ObjectDataSource"> <ItemTemplate> <uc:WebUserControl1 runat="server"></uc:WebUserControl1> </ItemTemplate> <EditItemTemplate> <uc:WebUserControl1 runat="server"></uc:WebUserControl1> </EditItemTemplate> </asp:FormView> User control: <%@ Control Language="C#" ... %> <asp:TextBox runat="server" ID="TitleTextBox" Text='<%# Bind("Title") %>'> </asp:TextBox> The binding works fine when the FormView is in View mode but when I switch to Edit mode, upon calling UpdateItem on the FormView, the bindings are lost. I know this because the FormView tries to call an update method on the ObjectDataSource that does not have an argument called 'Title'. I tried to solve this by implementing IBindableTemplate to load the controls that are inside my user control, directly into the templates (just like I had entered them declaratively like in the code above). However, when calling UpdateItem in edit mode, the container that gets passed into the ExtractValues method of the template, does not contain the TextBox anymore. It did in view mode! I have found some questions on SO that relate to this problem but they are rather dated and they don't provide any answers that helped me solve this problem. How do you think I could solve this problem? It seems to be such a simple requirement but apparently it's more like opening a can of worms...

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• String length differs from Javascript to Java code

  - by François P.

  I've got a JSP page with a piece of Javascript validation code which limits to a certain amount of characters on submit. I'm using a <textarea> so I can't simply use a length attribute like in a <input type="text">. I use document.getElementById("text").value.length to get the string length. I'm running Firefox 3.0 on Windows (but I've tested this behavior with IE 6 also). The form gets submitted to a J2EE servlet. In my Java servlet the string length of the parameter is larger than 2000! I've noticed that this can easily be reproduced by adding carriage returns in the <textarea>. I've used Firebug to assert the length of the <textare> and it really is 2000 characters long. On the Java side though, the carriage returns get converted to UNIX style (\r\n, instead of \n), thus the string length differs! Am I missing something obvious here or what ? If not, how would you reliably (cross-platform / browser) make sure that the <textarea> is limited.

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• python / sqlite - database locked despite large timeouts

  - by Chris Phillips

  Hi, I'm sure I'm missing something pretty obvious, but I can't for the life of me stop my pysqlite scripts crashing out with a database is locked error. I have two scripts, one to load data into the database, and one to read data out, but both will frequently, and instantly, crash depending on what the other is doing with the database at any given time. I've got the timeout on both scripts set to 30 seconds: cx = sqlite.connect("database.sql", timeout=30.0) and think I can see some evidence of the timeouts in that i get what appears to be a timing stamp (e.g 0.12343827e-06 0.1 - and how do I stop that being printed?) dumped occasionally in the middle of my curses formatted output screen, but no delay that ever gets remotely near the 30 second timeout, but still one of the other keeps crashing again and again from this. I'm running RHEL5.4 on a 64 bit 4 cpu HS21 IBM blade, and have heard some mention about issues about multi-threading and am not sure if this might be relevant. Packages in use are sqlite-3.3.6-5 and python-sqlite-1.1.7-1.2.1, and upgrading to newer versions outside of RedHat's official provisions is not a great option for me. Possible, but not desirable due to the environment in general. I have had autocommit=1 on previously on both scripts, but have since disabled on both, and am now cx.commit()ing on the inserting script and not committing on the select script. Ultimately as I only ever have one script actually making any modifications, I don't really see why this locking should ever ever happen. I have noticed that this is significantly worse over time when the database has gotten larger. It was recently at 13mb with 3 equal sized tables, which was about 1 day's worth of data. creating a new file has significantly improved this, which seems understandable, but the timeout ultimately just doesn't seem to be being obeyed. Any pointers very much appreciated. Thanks Chris

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• cakephp: Custom Authentication Object authenticate not called

  - by Kristoffer Darj

  The method authenticate in a Custom Authentication Object is never called. Is this a glicth or am I missing something? I don't get anything in the log, I'm just redirected to users/login (or the one I specified) CakeVersion: 2.4.1 <?php //My custom Auth Class //Path: app/Controller/Component/Auth/HashAuthenticate.php App::uses('BaseAuthenticate', 'Controller/Component/Auth'); class HashAuthenticate extends BaseAuthenticate { public function authenticate(CakeRequest $request, CakeResponse $response) { //Seems to not be called CakeLog::write('authenticate'); debug($this); die('gaah'); } } If I add the method getUser() (or unauthenticated() ), those gets called however so at least I know that cake finds the class and so on. It just skips the authenticate-method. The AppController looks like this class AppController extends Controller { public $helpers = array('Html', 'Form', 'Session'); public $components = array('Auth' => array( 'authenticate' => array('Hash'), 'authorize' => array('Controller'), ) ); } I found a similar question here: CakePHP 2.x custom "Authentication adapter &quot;LdapAuthorize&quot; was not found but there the issue was typos.

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• How is jQuery so fast?

  - by ClarkeyBoy

  Hey, I have a rather large application which, on the admin frontend, takes a few seconds to load a page because of all the pageviews that it has to load into objects before displaying anything. Its a bit complex to explain how the system works, but a few of my other questions explains the system in great detail. The main difference between what they say and the current system is that the customer frontend no longer loads all the pageviews into objects when a customer first views the page - it simply adds the pageview to the database and creates an object in an unsynchronised list... to put it simply, when a customer views a page it no longer loads all the pageviews into objects; but the admin frontend still does. I have been working on some admin tools on the customer frontend recently, so if an administrator clicks the description of an item in the catalogue then the right hand column will display statistics and available actions for the selected item. To do this the page which gets loaded (through $('action-container').load(bla bla bla);) into the right hand column has to loop through ALL the pageviews - this ultimately means that ALL the pageviews are loaded into objects if they haven't been already. For some reason this loads really REALLY fast. The difference in speed is only like a second on my dev site, but the live site has thousands of pageviews so the difference is quite big... So my question is: why is it that the admin frontend loads so slowly while using $(bla).load(bla); is so fast? I mean whatever method jQuery uses, can't browsers use this method too and load pages super-fast? Obviously not as someone would've done that by now - but I am interested to know just why the difference is so big... is it just my system or is there a major difference in speed between the browser getting a page and jQuery getting a page? Do other people experience the same kind of differences? Thanks in advance, Regards, Richard

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• Sysdeo Tomcat DevLoader - Hot deploy of java class causes whole application to restart

  - by Gala101

  Hi, I am using sysdeo tomcat plugin 3.2.1 with eclipse 3.5.1 (Galileo) and tomcat 5.5.23 on windows XP. I can get tomcat plugin working in eclipse, and have extracted devloader.zip into [tomcat]\server\classes. I have also updated the context and now it has this entry: <Context path="/myapp1" reloadable="true" docBase="F:\Work\eclipse_workspace\myapp1" workDir="F:\Work\eclipse_workspace\myapp1\work" > <Logger className="org.apache.catalina.logger.SystemOutLogger" verbosity="4" timestamp="true"/> <Loader className="org.apache.catalina.loader.DevLoader" reloadable="true" debug="1" useSystemClassLoaderAsParent="false" /> </Context> I have activated devloader (in Project Properties Tomcat Devloader Classpath) and have 'checked' all my classes and jars, I haven't 'checked' commons-loggin.jar jsp-api.jar, servlet-api.jar. So on launching tomcat via the plugin, I can get it running with devloader as shown in eclipse console view [DevLoader] Starting DevLoader [DevLoader] projectdir=F:\Work\eclipse_workspace\myapp1 [DevLoader] added file:/F:/Work/eclipse_workspace/myapp1/WEB-INF/classes/ [DevLoader] added file:/F:/Work/eclipse_workspace/myapp1/WEB-INF/lib/activation.jar However, if I even add a single System.out.println into any java file and save it, the whole application gets reloaded (takes ~80 sec) which is as good as stopping/starting tomcat itself. I've tried adding -Xdebug in JAVA_OPTS in the catalina.bat but no luck :( Can you please guide where I may be doing it wrong.. Please note that I can 'redeploy' the whole application on tomcat but that's not what I need, I am looking to be able to make small changes in java classes 'on-the-fly' while coding/debugging without having to wait for complete app restart. Another annoyance is that restarting tomcat/application causes the session/debug progress to be lost.. Can you please guide me how to go about it. PS: I am not using any ant/maven scripts explicitly, just relying on eclipse to do the build for me (which it does).

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• Keymap issues with NX from Mac OS X Lion

  - by Andy

  I tried to answer the question from Mark: Keymap issues with NX from Mac OS X Lion to Ubuntu However, it is locked so I figured I would post a new question / answer. I have been trying to answer this for a few days now because I have no issues when connecting through NX Client (technically OpenNX) to FreeNX server from an iMac (with Lion), but if I try to connect with a Macbook Pro I get horrible keyboard binding issues. The fix that is working for me is to go into: ~/.nx/config/HOST.nxs and change: <option key="Current keyboard" value="false"/> <option key="Custom keyboard layout" value="empty"/> <option key="Grab keyboard" value="false"/> I have tried this on three NX Servers and all are fixed. Hope it helps or gets you closer. Always check in the ~/.nx/temp/ for the sshlog and see if --keyboard="empty/empty" instead of "pc105/en" because the Mac is really pc104. 9:05:35: startsession --session="HOST" --type="unix-gnome" --cache="8M" --images="32M" --link="adsl" --geometry="2556\ x1396" --screeninfo="2560x1440x32+render" --keyboard="empty/empty" --backingstore="1" --encryption="1" --composite="1" --\ shmem="1" --shpix="1" --streaming="1" --samba="0" --cups="0" --nodelay="1" --defer="0" --client="macosx" --media="0" --st\ rict="0" --aux="1"

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• C++ from SpeakHere in iPhone app

  - by niklassaers

  Hi guys, I've made a template app where I've grabbed the recording part of the SpeakHere example and removed the file handling part, but I'm struggeling to get the C++ part of the app working right. As soon as it enters the C++ class, it gets syntax errors. If I don't import the header files from C++ (and then of course don't use the code) into my Objective C classes, all works fine. I cannot see the difference between how I'm doing it and the example is doing it. Can you see the difference? I've posted the entire code here: http://github.com/niklassaers/testFFT The build errors I get are: testFFT/CAStreamBasicDescription.h:91:0 testFFT/CAStreamBasicDescription.h:91: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAStreamBasicDescription' testFFT/CAStreamBasicDescription.h:298:0 testFFT/CAStreamBasicDescription.h:298: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token testFFT/CAStreamBasicDescription.h:299:0 testFFT/CAStreamBasicDescription.h:299: error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token testFFT/CAStreamBasicDescription.h:301:0 testFFT/CAStreamBasicDescription.h:301: error: expected '=', ',', ';', 'asm' or '__attribute__' before '!=' token testFFT/CAStreamBasicDescription.h:302:0 testFFT/CAStreamBasicDescription.h:302: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<=' token testFFT/CAStreamBasicDescription.h:303:0 testFFT/CAStreamBasicDescription.h:303: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>=' token testFFT/CAStreamBasicDescription.h:304:0 testFFT/CAStreamBasicDescription.h:304: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>' token testFFT/CAStreamBasicDescription.h:307:0 testFFT/CAStreamBasicDescription.h:307: error: expected ';', ',' or ')' before '&' token testFFT/CAXException.h:65:0 testFFT/CAXException.h:65: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAX4CCString' testFFT/CAXException.h:87:0 testFFT/CAXException.h:87: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAXException' testFFT/AQRecorder.h:59:0 testFFT/AQRecorder.h:59: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'AQRecorder' testFFT/RecorderLink.h:57:0 testFFT/RecorderLink.h:57: error: expected specifier-qualifier-list before 'AQRecorder' testFFT/RecorderLink.h:62:0 testFFT/RecorderLink.h:62: error: expected specifier-qualifier-list before 'AQRecorder' Any idea what's going on here? Cheers Nik

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• function's return address is different from its supposed value, buffer overflow,

  - by ultrajohn

  Good day everyone! I’m trying to understand how buffer overflow works. I’m doing this for my project in a computer security course I’m taking. Right now, I’m in the process of determining the address of the function’s return address which I’m supposed to change to perform a buffer overflow attack. I’ve written a simple program based from an example I’ve read in the internet. What this program does is it creates an integer pointer that will be made to point to the address of the function return address in the stack. To do this, (granted I understand how a function/program variables get organized in the stack), I add 8 to the buffer variable’ address and set it as the value of ret. I’m not doing anything here that would change the address contained in the location of func’s return address. here's the program: Output of the program when gets excecuted: As you can see, I’m printing the address of the variables buffer and ret. I’ve added an additional statement printing the value of the ret variable (supposed location of func return address, so this should print the address of the next instruction which will get executed after func returns from execution). Here is the dump which shows the supposed address of the instruction to be executed after func returns. (Underlined in green) As you can see, that value is way different from the value printed contained in the variable ret. My question is, why are they different? (of course in the assumption that what I’ve done are all right). Else, what have I done wrong? Is my understanding of the program’s runtime stack wrong? Please, help me understand this. My project is due nextweek and I’ve barely touched it yet. I’m sorry if I’m being demanding, I badly need your help.

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• Mercurial: a few questions all related to .hgignore

  - by WizardOfOdds

  I've been working for a long time with a .hgignore file that was fine and recently added one new type of files to ignore. When running "hg status", I noticed this: M .hgignore So Mercurial considers the .hgignore to be a file that needs to be tracked (if it's a the root of the project). Now I've read various docs but my points weren't specifically adressed so here are some very detailed questions which hopefully can help me figure this out (it would be great is someone answering could quote and address these three points [even with a simply yes/no answer for each question]): Should .hgignore be at the root of the project? (I guess it should, seen that a developer can potentially be working on several projects which would all have different .hgignore requirements) Can .hgignore be ignored be Mercurial? If it can be ignored, should .hgignore be ignored by Mercurial (which is different than the previous question) In the case where .hgignore should not be ignored, can't some really bad thing happens if you suddenly rollback way earlier, when a really old and incomplete .hgignore was used? I think I saw weird things happening with certain per-user IDE project files (I'm not saying all IDEs project files are per-user only, but some definitely are) that were supposed to be ignored, but then the user rolls back to an old version, where an old .hgignore gets used, and then suddenly files supposed to be ignored are committed because the old .hgignore didn't exclude these.

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• Android: How to get a custom view to redraw partially?

  - by Peterdk

  I have a custom view that fills my entire screen. (A piano keyboard) When a user touches the key, it would cause a invalidate() to be called and the whole keyboard gets redrawn to show the new state with a touched key. Currently the view is very simple, but I plan to add a bit more nice graphics. Since the whole keyboard is dynamically rendered this would make redrawing the entire keyboard more expensive. So I thought, let's look into partial redrawing. Now I call invalidate(Rect dirty) with the correct dirty region. I set my onDraw(Canvas canvas) method to only draw the keys in the dirty region if I do indeed want a partial redraw. This results in those keys being drawn, but the rest of the keyboard is totally black/not drawn at all. Am I wrong in expecting that calling invalidate(Rect dirty) would "cache" the current canvas, and only "allows" drawing in the dirty region? Is there any way I can achieve what I want? (A way to "cache" the canvas and only redraw the dirty area?"

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• NAudio playback wont stop successfully

  - by Kurru

  Hi When using NAudio to playback an mp3 [in the console], I cant figure out how to stop the playback. When I call waveout.Stop() the code just stops running and waveout.Dispose() never gets called. Is it something to do with the function callback? I dont know how to fix that if it is. static string MP3 = @"song.mp3"; static WaveOut waveout; static WaveStream playback; static void Main(string[] args) { waveout = new WaveOut(WaveCallbackInfo.FunctionCallback()); playback = OpenMp3Stream(MP3); waveout.Init(playback); waveout.Play(); Console.WriteLine("Started"); Thread.Sleep(2 * 1000); Console.WriteLine("Ending"); if (waveout.PlaybackState != PlaybackState.Stopped) waveout.Stop(); Console.WriteLine("Stopped"); waveout.Dispose(); Console.WriteLine("1st dispose"); playback.Dispose(); Console.WriteLine("2nd dispose"); } private static WaveChannel32 OpenMp3Stream(string fileName) { WaveChannel32 inputStream; WaveStream mp3Reader = new Mp3FileReader(fileName); WaveStream pcmStream = WaveFormatConversionStream.CreatePcmStream(mp3Reader); WaveStream blockAlignedStream = new BlockAlignReductionStream(pcmStream); inputStream = new WaveChannel32(blockAlignedStream); return inputStream; }

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• glitchy stuttery iphone game loop

  - by Adam

  This is a problem I've been trying to solve for a few days now, and I've looked at the various solutions on stackoverflow and nothing has really seemed to work for me. I'm making an iPhone game with OpenGLES graphics and accelerometer input, at this point it's very simple, but the rendering is already pretty bad... it stutters and seems to jump back or forward in time. It doesn't happen a lot, but it happens enough to be a problem. I mean, who wants to play a game where a bullet gets magically transported into the player, and then it's game over? No one. I've tried using NSTimer for the game loop, I've tried using a separate thread (with a frame rate and continuously) I've tried using different frame rates, from 30FPS to 60FPS (It seems to have a max frame rate around 45FPS, but no problems at 30FPS) I've tried using timeIntervalSince1970 and CFGetAbsoluteTime to measure loop time, with no noticeable diffence Anyone have any ideas on what is the best way to get this looking better? One of the posts I've read suggested running the simulation at a fixed frame rate and then just render as fast as possible, does that seem like a good idea?

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• How to set focus to a brand new TextBox which was created as a result of a databinding in WPF?

  - by Mike

  Hi everyone, I have a WPF ItemsControl that is bound to an ObservableCollection. The XAML: <ItemsControl Name="mItemsControl"> <ItemsControl.ItemTemplate> <DataTemplate> <TextBox Text="{Binding Mode=OneWay}"></TextBox> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> The codebehind: private ObservableCollection<string> mCollection = new ObservableCollection<string>(); public MainWindow() { InitializeComponent(); this.mCollection.Add("Test1"); this.mCollection.Add("Test2"); this.mItemsControl.ItemsSource = this.mCollection; } private void Button_Click(object sender, RoutedEventArgs e) { this.mCollection.Add("new item!"); } When I click a button, it adds a new string to the databound ObservableCollection which triggers a new TextBox to appear. I want to give this new textbox focus. I've tried this technique from a related StackOverflow question but it always sets focus to the textbox before the newly created one. private void Button_Click(object sender, RoutedEventArgs e) { this.mCollection.Add("new item!"); // MoveFocus takes a TraversalRequest as its argument. TraversalRequest request = new TraversalRequest(FocusNavigationDirection.Previous); // Gets the element with keyboard focus. UIElement elementWithFocus = Keyboard.FocusedElement as UIElement; // Change keyboard focus. if (elementWithFocus != null) { elementWithFocus.MoveFocus(request); } } My need seems simple enough, but it's almost like the new textbox doesn't really exist until a slight delay after something is added to the ObservableCollection. Any ideas of what would work? Thanks! -Mike

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• Query on simple C++ threadpool implementation

  - by ticketman

  Stackoverflow has been a tremendous help to me and I'd to give something back to the community. I have been implementing a simple threadpool using the tinythread C++ portable thread library, using what I have learnt from Stackoverflow. I am new to thread programming, so not that comfortable with mutexes, etc. I have a question best asked after presenting the code (which runs quite well under Linux): // ThreadPool.h class ThreadPool { public: ThreadPool(); ~ThreadPool(); // Creates a pool of threads and gets them ready to be used void CreateThreads(int numOfThreads); // Assigns a job to a thread in the pool, but doesn't start the job // Each SubmitJob call will use up one thread of the pool. // This operation can only be undone by calling StartJobs and // then waiting for the jobs to complete. On completion, // new jobs may be submitted. void SubmitJob( void (*workFunc)(void *), void *workData ); // Begins execution of all the jobs in the pool. void StartJobs(); // Waits until all jobs have completed. // The wait will block the caller. // On completion, new jobs may be submitted. void WaitForJobsToComplete(); private: enum typeOfWorkEnum { e_work, e_quit }; class ThreadData { public: bool ready; // thread has been created and is ready for work bool haveWorkToDo; typeOfWorkEnum typeOfWork; // Pointer to the work function each thread has to call. void (*workFunc)(void *); // Pointer to work data void *workData; ThreadData() : ready(false), haveWorkToDo(false) { }; }; struct ThreadArgStruct { ThreadPool *threadPoolInstance; int threadId; }; // Data for each thread ThreadData *m_ThreadData; ThreadPool(ThreadPool const&); // copy ctor hidden ThreadPool& operator=(ThreadPool const&); // assign op. hidden // Static function that provides the function pointer that a thread can call // By including the ThreadPool instance in the void * parameter, // we can use it to access other data and methods in the ThreadPool instance. static void ThreadFuncWrapper(void *arg) { ThreadArgStruct *threadArg = static_cast<ThreadArgStruct *>(arg); threadArg->threadPoolInstance->ThreadFunc(threadArg->threadId); } // The function each thread calls void ThreadFunc( int threadId ); // Called by the thread pool destructor void DestroyThreadPool(); // Total number of threads available // (fixed on creation of thread pool) int m_numOfThreads; int m_NumOfThreadsDoingWork; int m_NumOfThreadsGivenJobs; // List of threads std::vector<tthread::thread *> m_ThreadList; // Condition variable to signal each thread has been created and executing tthread::mutex m_ThreadReady_mutex; tthread::condition_variable m_ThreadReady_condvar; // Condition variable to signal each thread to start work tthread::mutex m_WorkToDo_mutex; tthread::condition_variable m_WorkToDo_condvar; // Condition variable to signal the main thread that // all threads in the pool have completed their work tthread::mutex m_WorkCompleted_mutex; tthread::condition_variable m_WorkCompleted_condvar; }; cpp file: // // ThreadPool.cpp // #include "ThreadPool.h" // This is the thread function for each thread. // All threads remain in this function until // they are asked to quit, which only happens // when terminating the thread pool. void ThreadPool::ThreadFunc( int threadId ) { ThreadData *myThreadData = &m_ThreadData[threadId]; std::cout << "Hello world: Thread " << threadId << std::endl; // Signal that this thread is ready m_ThreadReady_mutex.lock(); myThreadData->ready = true; m_ThreadReady_condvar.notify_one(); // notify the main thread m_ThreadReady_mutex.unlock(); while(true) { //tthread::lock_guard<tthread::mutex> guard(m); m_WorkToDo_mutex.lock(); while(!myThreadData->haveWorkToDo) // check for work to do m_WorkToDo_condvar.wait(m_WorkToDo_mutex); // if no work, wait here myThreadData->haveWorkToDo = false; // need to do this before unlocking the mutex m_WorkToDo_mutex.unlock(); // Do the work switch(myThreadData->typeOfWork) { case e_work: std::cout << "Thread " << threadId << ": Woken with work to do\n"; // Do work myThreadData->workFunc(myThreadData->workData); std::cout << "#Thread " << threadId << ": Work is completed\n"; break; case e_quit: std::cout << "Thread " << threadId << ": Asked to quit\n"; return; // ends the thread } // Now to signal the main thread that my work is completed m_WorkCompleted_mutex.lock(); m_NumOfThreadsDoingWork--; // Unsure if this 'if' would make the program more efficient // if(NumOfThreadsDoingWork == 0) m_WorkCompleted_condvar.notify_one(); // notify the main thread m_WorkCompleted_mutex.unlock(); } } ThreadPool::ThreadPool() { m_numOfThreads = 0; m_NumOfThreadsDoingWork = 0; m_NumOfThreadsGivenJobs = 0; } ThreadPool::~ThreadPool() { if(m_numOfThreads) { DestroyThreadPool(); delete [] m_ThreadData; } } void ThreadPool::CreateThreads(int numOfThreads) { // Check a thread pool has already been created if(m_numOfThreads > 0) return; m_NumOfThreadsGivenJobs = 0; m_NumOfThreadsDoingWork = 0; m_numOfThreads = numOfThreads; m_ThreadData = new ThreadData[m_numOfThreads]; ThreadArgStruct threadArg; for(int i=0; i<m_numOfThreads; ++i) { threadArg.threadId = i; threadArg.threadPoolInstance = this; // Creates the thread and save in a list so we can destroy it later m_ThreadList.push_back( new tthread::thread( ThreadFuncWrapper, (void *)&threadArg ) ); // It takes a little time for a thread to get established. // Best wait until it gets established before creating the next thread. m_ThreadReady_mutex.lock(); while(!m_ThreadData[i].ready) // Check if thread is ready m_ThreadReady_condvar.wait(m_ThreadReady_mutex); // If not, wait here m_ThreadReady_mutex.unlock(); } } // Adds a job to the batch, but doesn't start the job void ThreadPool::SubmitJob(void (*workFunc)(void *), void *workData) { // Check that the thread pool has been created if(!m_numOfThreads) return; if(m_NumOfThreadsGivenJobs >= m_numOfThreads) return; m_ThreadData[m_NumOfThreadsGivenJobs].workFunc = workFunc; m_ThreadData[m_NumOfThreadsGivenJobs].workData = workData; std::cout << "Submitted job " << m_NumOfThreadsGivenJobs << std::endl; m_NumOfThreadsGivenJobs++; } void ThreadPool::StartJobs() { // Check that the thread pool has been created // and some jobs have been assigned if(!m_numOfThreads || !m_NumOfThreadsGivenJobs) return; // Set 'haveworkToDo' flag for all threads m_WorkToDo_mutex.lock(); for(int i=0; i<m_NumOfThreadsGivenJobs; ++i) m_ThreadData[i].haveWorkToDo = true; m_NumOfThreadsDoingWork = m_NumOfThreadsGivenJobs; // Reset this counter so we can resubmit jobs later m_NumOfThreadsGivenJobs = 0; // Notify all threads they have work to do m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); } void ThreadPool::WaitForJobsToComplete() { // Check that a thread pool has been created if(!m_numOfThreads) return; m_WorkCompleted_mutex.lock(); while(m_NumOfThreadsDoingWork > 0) // Check if all threads have completed their work m_WorkCompleted_condvar.wait(m_WorkCompleted_mutex); // If not, wait here m_WorkCompleted_mutex.unlock(); } void ThreadPool::DestroyThreadPool() { std::cout << "Ask threads to quit\n"; m_WorkToDo_mutex.lock(); for(int i=0; i<m_numOfThreads; ++i) { m_ThreadData[i].haveWorkToDo = true; m_ThreadData[i].typeOfWork = e_quit; } m_WorkToDo_condvar.notify_all(); m_WorkToDo_mutex.unlock(); // As each thread terminates, catch them here for(int i=0; i<m_numOfThreads; ++i) { tthread::thread *t = m_ThreadList[i]; // Wait for thread to complete t->join(); } m_numOfThreads = 0; } Example of usage: (this calculates pi-squared/6) struct CalculationDataStruct { int inputVal; double outputVal; }; void LongCalculation( void *theSums ) { CalculationDataStruct *sums = (CalculationDataStruct *)theSums; int terms = sums->inputVal; double sum; for(int i=1; i<terms; i++) sum += 1.0/( double(i)*double(i) ); sums->outputVal = sum; } int main(int argc, char** argv) { int numThreads = 10; // Create pool ThreadPool threadPool; threadPool.CreateThreads(numThreads); // Create thread workspace CalculationDataStruct sums[numThreads]; // Set up jobs for(int i=0; i<numThreads; i++) { sums[i].inputVal = 3000*(i+1); threadPool.SubmitJob(LongCalculation, &sums[i]); } // Run the jobs threadPool.StartJobs(); threadPool.WaitForJobsToComplete(); // Print results for(int i=0; i<numThreads; i++) std::cout << "Sum of " << sums[i].inputVal << " terms is " << sums[i].outputVal << std::endl; return 0; } Question: In the ThreadPool::ThreadFunc method, would better performance be obtained if the following if statement if(NumOfThreadsDoingWork == 0) was included? Also, I'd be grateful of criticisms and ways to improve the code. At the same time, I hope the code is of use to others.

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• Can't get MySQL source query to work using Python mysqldb module

  - by Chris

  I have the following lines of code: sql = "source C:\\My Dropbox\\workspace\\projects\\hosted_inv\\create_site_db.sql" cursor.execute (sql) When I execute my program, I get the following error: Error 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'source C:\My Dropbox\workspace\projects\hosted_inv\create_site_db.sql' at line 1 Now I can copy and past the following into mysql as a query: source C:\\My Dropbox\\workspace\\projects\\hosted_inv\\create_site_db.sql And it works perfect. When I check the query log for the query executed by my script, it shows that my query was the following: source C:\\My Dropbox\\workspace\\projects\\hosted_inv\\create_site_db.sql However, when I manually paste it in and execute, the entire create_site_db.sql gets expanded in the query log and it shows all the sql queries in that file. Am I missing something here on how mysqldb does queries? Am I running into a limitation. My goal is to run a sql script to create the schema structure, but I don't want to have to call mysql in a shell process to source the sql file. Any thoughts? Thanks!

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