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• Reading from a database located in the Program Files folder using ODBC

  - by Dabblernl

  We have an application that stores its database files in a subfolder of the Program Files directory. These files are redirected to the VirtualStore in Vista and Windows 7. We represent data from the database using Microsoft DataReports (VB6). So far so good. But we now want to use Crystal Reports XI to represent data from the database. Our idea is to NOT pass this data to CR from our program, but to have CR retreive it from the database using a a system DSN through ODBC. In this way we hope to present our users with more flexibility in designing their own reports. What we do want to ensure though is that these system DSNs are configured correctly when the user installs our program or when the program calls the Crystal Report. Is there a smart way to do this using System variables for instance, instead of having to write a routine that checks for OS-version, whether UAC is enabled on the OS, whether the write restrictions on the Program Files folder have been lifted, etc and then adapts he System DSN to point to either the C:\Program Files\OurApp\Data folder, or the C:\Users\User\AppData\VirtualStore\Program Files\OurApp\Data folder? Suggestions for an entirely different approach are welcome too!

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• Designing DAOs around a JSON API for iPhone Development

  - by Bob Spryn

  So I've been trying to design a clean way of grabbing data for my models in iPhone land. All the data for my application is coming from JSON API's. So right now when a VC needs some models, it does the JSON call itself (asynch) and when it receives the data, it builds the models. It works, but I'm trying to think of a cleaner method whereby the DAO's retrieve the information for me and return the models, all in an async manner. My initial thought is build a protocol for my DAOs, such that the VC would instantiate a DAO and make itself the delegate. When you requested data [DAOinstance getAllUsers] the DAO would do all the network request stuff, and then when it had the data, it would call a method on its delegate (the VC) to pass the data. So I think that's a cool solution, but realized that if I needed to use the same DAO for different purposes in the same VC, my delegate method would have to branch logic depending on which DAO instance initiated the request. So my second thought was to be able to pass 'handler' selectors to the DAO object a la typical javascript patterns. So instead of an official protocol, I would say something like [DAOinstance getAllUsersWithSelector:"TheHandlerFunctionOnMyVC:"] Then when the DAO completed its network activities, it would call the passed selector on the VC, and pass the data back. So am I headed in the wrong direction entirely here? Seems like maybe an ok way to go. Any pointers or articles on designing this kind of data layer would be sweet. Thanks! Bob

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• Redirect uploaded files to another server, using nginx

  - by Serg ikS

  I am creating a web service of scheduled posts to some soc. network.Need help dealing with file uploads under high traffic. Process overview: User uploads files to SomeServer (not mine). SomeServer then responds with a JSON string. My web app should store that JSON response. Opt. 1 — Save, cURL POST, delete tmp The stupid way I made it work: User uploads files to MyWebApp; MyWebApp cURL's the file further to SomeServer, getting the response. Opt.2 — JS magic The smart way it could be perfect: User uploads the file directly to SomeServer, from within an iFrame; MyWebApp gets the response through JavaScript. But this is(?) impossible due to the 'Same Origin Policy', isn't it? Opt. 3 — nginx proxying? The better way for a production server: User uploads files to MyWebApp; nginx intercepts the file uploads and sends them directly to the SomeServer; JSON response is also intercepted by nginx and processed by MyWebApp. Does this make any sense, and what would be the nginx config for, say, /fileupload Location to proxy it to SomeServer ?

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• problem loading texture with transparency with OpenGL ES and Android

  - by Evan Kimia

  Im trying to load an image that has background transparency that will be layered over another texture. When i try and load it, all i get is a white screen. The texture is 512 by 512, and its saved in photoshop as a 24 bit PNG (standard PNG specs in the Photoshop Save for Web and Devices config window). Any idea why its not showing? The texture without transparency shows without a problem. Here is my loadTextures method: public void loadGLTexture(GL10 gl, Context context) { //Get the texture from the Android resource directory Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.m1); Bitmap normalScheduleLines = BitmapFactory.decodeResource(context.getResources(), R.drawable.m1n); //Generate texture pointers... gl.glGenTextures(3, textures, 0); //...and bind it to our array gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[1]); //Create Nearest Filtered Texture gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR_MIPMAP_NEAREST); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR); gl.glTexParameterf(GL11.GL_TEXTURE_2D, GL11.GL_GENERATE_MIPMAP, GL11.GL_TRUE); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE); GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0); bitmap.recycle(); //Bind our normal schedule bus map lines gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]); //Create Nearest Filtered Texture gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR_MIPMAP_NEAREST); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR); gl.glTexParameterf(GL11.GL_TEXTURE_2D, GL11.GL_GENERATE_MIPMAP, GL11.GL_TRUE); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_CLAMP_TO_EDGE); gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_CLAMP_TO_EDGE); GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, GL10.GL_RGBA, normalScheduleLines, 0); normalScheduleLines.recycle(); }

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• MySQL query pulling from two tables, display in correct fields

  - by Matt Nathanson

  I'm trying to select all fields in two separate tables as long as they're sharing a common ID. //mysql query $result = mysql_query("SELECT * FROM project, links WHERE project.id = links.id and project.id = $clientID") //displaying the link if ($row['url'] != null){ echo "<div class='clientsection' id='links'>Links</div>"; echo "<a class='clientlink' id='link1' href='" . $row['url'] . "'>" . $row['name'] . "</a>"; } else { echo "<a class='clientlink' id='link1' href='" . $row['url'] . "' style='display:none;'>" . $row['name'] . "</a>"; }; As you can see, my tables are "projects", and "links" Each is sharing a common field "id" for reference. It looks as though where both links.id and project.id are equal, it outputs anything, but when there is no links.id associated with a given $clientID the container relative to the $clientID doesn't display at all. Essentially I'm using this to add links dynamically to a specific client in this CMS and if there are no links, I want the container to show up anyway. Hopefully I've expressed myself clearly, any pointers in the right direction are appreciated. Thanks!

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• Helping Rails Newbies identify version-specific information on web pages

  - by corprew

  I am trying to help some people getting started programming on rails identify which version that advice found on web pages corresponds to, and am seeking advice and/or guides on how to do it so they don't have to rely on me and/or waste time trying outdated advice. Narrative: I am helping some people get up to speed on rails development, and their stock response to running into problems is searching google for advice. They're using 2.3.5 and thinking of moving to 3. The problem they're running into is that there's a lot of advice out there specific to older rails versions (2.2 for example being popular) that isn't identified. I can usually figure out when the pages are old pretty easily, but they can't (yet.) It seems like random web page authors don't identify which version they're using when they're using the current version, and not all pages are dated. This seems to be a general problem that will get worse -- current unadorned advice is usually 2.3.5 and older unadorned advice is 2.2.x at this point, but people are moving / will be moving to version 3 over the next while and newbies will be stuck looking at a bunch of deprecated/incompatible 2.3.x advice without realizing which version it is. Any advice / pointers / telltales?

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• Ajax heavy JS apps using excessive amounts of memory over time.

  - by Shane Reustle

  I seem to have some pretty large memory leaks in an app that I am working on. The app itself is not very complex. Every 15 seconds, the page requests approx 40kb of JSON from the server, and draws a table on the page using it. It is cheaper to draw the table over because the data is usually always new. I am attaching a few events to the table, approx 5 per line, 30 lines in the table. I used jQuery's .html() method to put the new html into the container and overwrite the existing. I do this specifically so that jQuery's special cleanup functions go in and attempt to detach all events on the elements in the element that it is overwriting. I then also delete the large variables of html once they are sent to the DOM using delete my_var. I have checked for circular references and attached events that are never cleared a few times, but never REALLY dug into it. I was wondering if someone could give me a few pointers on how to optimize a very heavy app like this. I just picked up "High Performance Javascript" by Nicholas Zakas, but didn't have much time to get into it yet. To give an idea on how much memory this is using, after 4~ hours, it is using about 420,000k on chrome, and much more on Firefox or IE. Thanks!

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• Rolling back file moves, folder deletes and mysql queries

  - by Workoholic

  This has been bugging me all day and there is no end in sight. When the user of my php application adds a new update and something goes wrong, I need to be able to undo a complex batch of mixed commands. They can be mysql update and insert queries, file deletes and folder renaming and creations. I can track the status of all insert commands and undo them if an error is thrown. But how do I do this with the update statements? Is there a smart way (some design pattern?) to keep track of such changes both in the file structure and the database? My database tables are MyISAM. It would be easy to just convert everything to InnoDB, so that I can use transactions. That way I would only have to deal with the file and folder operations. Unfortunately, I cannot assume that all clients have InnoDB support. It would also require me to convert many tables in my database to InnoDB, which I am hesitant to do.

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• Ranking/ weighing search result

  - by biso

  I am trying to build an application that has a smart adaptive search engine (lets say for cars). If I search for for 4x4 then the DB will return all the 4x4 cars I have (100 cars) - but as time goes by and I start checking out cars, liking them, commenting on them, etc the order of the search result should be the different. That means 1 month later when searching for 4x4, I should get the same result set ordered differently as per my previous interaction with the site. If I was mainly liking and commenting on German cars, BMW should be on the top and Land cruiser should be further down. This ranking should be based on attributes that I captureduring user interaction (eg: car origin, user age, user location, car type[4x4, coupe, hatchback], price range). So for each car result I get, I will be weighing it based on how well it is performing on the 5 attributes above. I intend to use the DB just as a repository and do the ranking and the thinking on the server. My question is, what kind of algorithm should I be using to weigh/rank my search result? Thanks.

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• gcc, strict-aliasing, and horror stories

  - by Joseph Quinsey

  In http://stackoverflow.com/questions/2906365/gcc-strict-aliasing-and-casting-through-a-union I asked whether anyone had encountered problems with union punning through pointers. So far, the answer seems to be No. This question is broader: do you have any horror stories about gcc and strict-aliasing? Background: Quoting from AndreyT's answer in http://stackoverflow.com/questions/2771023/c99-strict-aliasing-rules-in-c-gcc/2771041#2771041: "Strict aliasing rules are rooted in parts of the standard that were present in C and C++ since the beginning of [standardized] times. The clause that prohibits accessing object of one type through a lvalue of another type is present in C89/90 (6.3) as well as in C++98 (3.10/15). ... It is just that not all compilers wanted (or dared) to enforce it or rely on it." Well, gcc is now daring to do so, with its -fstrict-aliasing switch. And this has caused some problems. See, for example, the excellent article http://davmac.wordpress.com/2009/10/ about a Mysql bug, and the equally excellent discussion in http://cellperformance.beyond3d.com/articles/2006/06/understanding-strict-aliasing.html. Some other less-relevant links: http://stackoverflow.com/questions/1225741/performance-impact-of-fno-strict-aliasing http://stackoverflow.com/questions/754929/strict-aliasing http://stackoverflow.com/questions/262379/when-is-char-safe-for-strict-pointer-aliasing http://stackoverflow.com/questions/725138/how-to-detect-strict-aliasing-at-compile-time So to repeat, do you have a horror story of your own? Problems not indicated by -Wstrict-aliasing would, of course, be preferred. And other C compilers are also welcome.

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• Good guidelines for developing an ecommerce application

  - by kaciula

  I'm making an ecommerce application on Android and, as it is my first serious project, I'm trying to figure out beforehand the best approach to do this. The application talks to a web service (magento api, meaning soap or xml rpc unfortunately) and gets all the content on the phone (product categories, product details, user credentials etc.). I think it should do lazy loading or something like that. So, I was thinking to keep the user credentials in a custom Object which will be kept in a SharedPreferences so that every Activity cand easily access it. I'll use a couple of ListViews to show the content and AsyncTask to fetch the data needed. Should I keep all the data in memory in objects or should I use some sort of cache or a local database? Also, I'm planning to use a HashMap with SoftReferences to hold the bitmaps I am downloading. But wouldn't this eat a lot of memory? How cand all the activities have access to all these objects (ecommerce basket etc.)? I'm thinking of passing them using Intents but this doesn't seem right to me. Can SharedPreferences be used for a lot of objects and are there any concurrency issues? Any pointers would be really appreciated. What are some good guidelines? What classes should I look into? Do you know of any resources on the Internet for me to check out?

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• Where to post code for open source usage?

  - by Douglas

  I've been working for a few weeks now with the Google Maps API v3, and have done a good bit of development for the map I've been creating. Some of the things I've done have had to be done to add usability where there previously was not any, at least not that I could find online. Essentially, I made a list of what had to be done, searched all over the web for the ways to do what I needed, and found that some were not(at the time) possible(in the "grab an example off the web" sense). Thus, in my working on this map, I have created a number of very useful tools, which I would like to share with the development community. Is there anywhere I could use as a hub, apart from my portfolio ( http://dougglover.com ), to allow people to view and recycle my work? I know how hard it can be to need to do something, and be unable to find the solution elsewhere, and I don't think that if something has been done before, it should necessarily need to be written again and again. Hence open source code, right? Firstly, I was considering coming on here and asking a question, and then just answering it. Problem there is I assume that would just look like a big reputation grab. If not, please let me know and I'll go ahead and do that so people here can see it. Other suggestions appreciated. Some stuff I've made: A (new and improved) LatLng generator Works quicker, generates LatLng based on position of a draggable marker Allows searching for an address to place the marker on/near the desired location(much better than having to scroll to your location all the way from Siberia) Since it's a draggable marker, double-clicking zooms in, instead of creating a new LatLng marker like the one I was originally using The ability to create entirely custom "Smart Paths" Plot LatLng points on the map which connect to each other just like they do using the actual Google Maps Using Dijkstra's algorithm with Javascript, the routing is intelligent and always gives the shortest possible route, using the points provided Simple, easy to read multi-dimensional array system allows for easily adding new points to the grid Any suggestions, etc. appreciated.

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• Django Database design -- Is this a good stragety for overriding defaults

  - by rh0dium

  Hi SO's I have a question on good database design practices and I would like to leverage you guys for pointers. The project started out simple. Hey we have a bunch of questions we want answered for every project (no problem) Which turned into... Hey we have so many questions can we group them into sections (yup we can do that) Which lead into.. Can we weight these questions and I don't really want some of these questions for my project (Yes but we are getting difficult) And then I'm thinking they will want to have each section have it's own weight.. Requirements So there's the requirements - For n number of project Allow a admin member the ability select the questions for a project Allow the admin member to re-weigh or use the default weights for the questions Allow the admin member to re-weight the sections Allow team members to answer the questions. So here is what I came up with. Please feel free to comment and provide better examples models.py from django.db import models from django.contrib.sites.models import Site from django.conf import settings class Section(models.Model): """ This describes the various sections for a checklist: """ name = models.CharField(max_length=64) description = models.TextField() class Question(models.Model): """ This simply provides a simple way to list out the questions. """ question = models.CharField(max_length=255) answer_type = models.CharField(max_length=16) description = models.TextField() section = models.ForeignKey(Section) class ProjectQuestion(models.Model): """ These are the questions relevant to the project """ question = models.ForeignKey(Question) answer = models.CharField(max_length=255) required = models.BooleanField(default=True) weight = models.FloatField(default = XXX) class Project(models.Model): """ Here is where we want to gather our questions """ questions = models.ManyToManyField(ProjectQuestion) Immediate questions: - When I start a project - any ideas on how to "pre-populate" the questions (and ultimately the weights) for the project? - Is there a generally accepted method for doing this process that I am missing? Basically the idea that you refer to the questions overide your own default weight, and store the answer? - It appears that a good chuck of the work will be done in the views and that a lot of checking will need to occur there? Is that OK? Again - feel free to give me better strategies!! Thanks

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• Looking for a fast, compact, streamable, multi-language, strongly typed serialization format

  - by sanity

  I'm currently using JSON (compressed via gzip) in my Java project, in which I need to store a large number of objects (hundreds of millions) on disk. I have one JSON object per line, and disallow linebreaks within the JSON object. This way I can stream the data off disk line-by-line without having to read the entire file at once. It turns out that parsing the JSON code (using http://www.json.org/java/) is a bigger overhead than either pulling the raw data off disk, or decompressing it (which I do on the fly). Ideally what I'd like is a strongly-typed serialization format, where I can specify "this object field is a list of strings" (for example), and because the system knows what to expect, it can deserialize it quickly. I can also specify the format just by giving someone else its "type". It would also need to be cross-platform. I use Java, but work with people using PHP, Python, and other languages. So, to recap, it should be: Strongly typed Streamable (ie. read a file bit by bit without having to load it all into RAM at once) Cross platform (including Java and PHP) Fast Free (as in speech) Any pointers?

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• URL with no query parameters - How to distinguish.

  - by Broken Link

  Env: .NET 1.1 I got into this situation. Where I need to give a URL that someone could redirect them to our page. When they redirect they also need to tell us, what message I need to display on the page. Initially I thought of something like this. http://example.com/a.aspx?reason=100 http://example.com/a.aspx?reason=101 ... http://example.com/a.aspx?reason=115 So when we get this url based on 'reason' we can display different message. But the problem turns out to be that they can not send any query parameters at all. They want 15 difference URL's since they can't send query params. It doesn't make any sense to me to created 15 pages just to display a message. Any smart ideas,that have one URL and pass the 'reason' thru some means? EDIT: Options I'm thinking based on Answers Try HttpRequest.PathInfo or Second option I was thinking was to have a httphanlder read read the path like this - HttpContext.Request.Path based on path act. Ofcourse I will have some 15 entries like this in web.config. <add verb="*" path="reason1.ashx" type="WebApplication1.Class1, WebApplication1" /> <add verb="*" path="reason2.ashx" type="WebApplication1.Class1, WebApplication1" /> Does that look clean?

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• What makes this "declarator invalid"? C++

  - by nieldw

  I have Vertex template in vertex.h. From my graph.h: 20 template<class edgeDecor, class vertexDecor, bool dir> 21 class Vertex; which I use in my Graph template. I've used the Vertex template successfully throughout my Graph, return pointers to Vertices, etc. Now for the first time I am trying to declare and instantiate a Vertex object, and gcc is telling me that my 'declarator' is 'invalid'. How can this be? 81 template<class edgeDecor, class vertexDecor, bool dir> 82 Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const 83 { 84 /* Construct new Graph with apropriate decorators */ 85 Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); 86 span.E.reserve(this->E.size()); 87 88 typename Vertex<edgeDecor,int,dir> v = new Vertex(INT_MAX); 89 span.V = new vector<Vertex<edgeDecor,int,dir> >(this->V.size,v); 90 }; And gcc is saying: graph.h: In member function ‘Graph<edgeDecor, int, dir> Graph<edgeDecor, vertexDecor, dir>::Dijkstra(Vertex<edgeDecor, vertexDecor, dir>, bool) const’: graph.h:88: error: invalid declarator before ‘v’ graph.h:89: error: ‘v’ was not declared in this scope I know this is probably another noob question, but I'll appreciate any help.

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• Why do compiled Haskell libraries see invalid static FFI storage?

  - by John Millikin

  I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. Given the following three modules: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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• Reflecting over classes in .NET produces methods only differing by a modifier

  - by mrjoltcola

  I'm a bit boggled by something, I hope the CLR gearheads can help. Apparently my gears aren't big enough. I have a reflector utility that generates assembly stubs for Cola for .NET, and I find classes have methods that only differ by a modifier, such as virtual. Example below, from Oracle.DataAccess.dll, method GetType(): class OracleTypeException : System.SystemException { virtual string ToString (); virtual System.Exception GetBaseException (); virtual void set_Source (string value); virtual void GetObjectData (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context); virtual System.Type GetType (); // here virtual bool Equals (object obj); virtual int32 GetHashCode (); System.Type GetType (); // and here } What is this? I have not been able to reproduce this with C# and it causes trouble for Cola as it thinks GetType() is a redefinition, since the signature is identical. My method reflector starts like this: static void DisplayMethod(MethodInfo m) { if ( // Filter out things Cola cannot yet import, like generics, pointers, etc. m.IsGenericMethodDefinition || m.ContainsGenericParameters || m.ReturnType.IsGenericType || !m.ReturnType.IsPublic || m.ReturnType.IsArray || m.ReturnType.IsPointer || m.ReturnType.IsByRef || m.ReturnType.IsPointer || m.ReturnType.IsMarshalByRef || m.ReturnType.IsImport ) return; // generate stub signature // [snipped] }

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• How to start writing out an existing AudioQueue in response to an event?

  - by Halle

  Hello, I am writing a class that opens an AudioQueue and analyzes its characteristics, and then under certain conditions can begin or end writing out a file from that AudioQueue that is already instantiated. This is my code (entirely based on SpeakHere) that opens the AudioQueue without writing anything out to tmp: void AQRecorder::StartListen() { int i, bufferByteSize; UInt32 size; try { SetupAudioFormat(kAudioFormatLinearPCM); XThrowIfError(AudioQueueNewInput(&mRecordFormat, MyInputBufferHandler, this, NULL, NULL, 0, &mQueue), "AudioQueueNewInput failed"); mRecordPacket = 0; size = sizeof(mRecordFormat); XThrowIfError(AudioQueueGetProperty(mQueue, kAudioQueueProperty_StreamDescription, &mRecordFormat, &size), "couldn't get queue's format"); bufferByteSize = ComputeRecordBufferSize(&mRecordFormat, kBufferDurationSeconds); for (i = 0; i < kNumberRecordBuffers; ++i) { XThrowIfError(AudioQueueAllocateBuffer(mQueue, bufferByteSize, &mBuffers[i]), "AudioQueueAllocateBuffer failed"); XThrowIfError(AudioQueueEnqueueBuffer(mQueue, mBuffers[i], 0, NULL), "AudioQueueEnqueueBuffer failed"); } mIsRunning = true; XThrowIfError(AudioQueueStart(mQueue, NULL), "AudioQueueStart failed"); } catch (CAXException &e) { char buf[256]; fprintf(stderr, "Error: %s (%s)\n", e.mOperation, e.FormatError(buf)); } catch (...) { fprintf(stderr, "An unknown error occurred\n"); } } But I'm a little unclear on how to write a function that will tell this queue "from now until the stop signal, start writing out this queue to tmp as a file". I understand how to tell an AudioQueue to write out as a file at the time that it's created, how to set files format, etc, but not how to tell it to start and stop midstream. Much appreciative of any pointers, thanks.

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• Getting a handle on GIS math, where do I start?

  - by Joshua

  I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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• Best practices, PHP, tracking millions of impressions per day.

  - by John

  What do I have to do to make 20k mysql inserts per second possible (during peak hours around 1k/sec during slower times)? I've been doing some research and I've seen the "INSERT DELAYED" suggestion, writing to a flat file, "fopen(file,'a')", and then running a chron job to dump the "needed" data into mysql, etc. I've also heard you need multiple servers and "load balancers" which I've never heard of, to make something like this work. I've also been looking at these "cloud server" thing-a-ma-jigs, and their automatic scalability, but not sure about what's actually scalable. The application is just a tracker script, so if I have 100 websites that get 3 million page loads a day, there will be around 300 million inserts a day. The data will be ran through a script that will run every 15-30 minutes which will normalize the data and insert it into another mysql table. How do the big dogs do it? How do the little dogs do it? I can't afford a huge server anymore so any intuitive ways, if there are multiple ways of going at it, you smart people can think of.. please let me know :)

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Please help with passing multidimensional arrays

  - by nn

  Hi, I'm writing a simple test program to pass multidimensional arrays. I've been struggling to get the signature of the callee function. void p(int (*s)[100], int n) { ... } In the code I have: int s1[10][100], s2[10][1000]; p(s1, 100); This code appears to work, but it's not what I intended. I want to the function p to be oblivious whether the range of values is 100 or 1000, but it should know there are 10 pointers. I tried as a first attempt: void p(int (*s)[10], int n) // n = # elements in the range of the array and also: void p(int **s, int n) // n = # of elements in the range of the array But to no avail can I seem to get this correct. I don't want to hardcode the 100 or 1000, but instead pass it in, but there will always be 10 arrays. Obviously, I want to avoid having to declare the function: void p(int *s1, int *s2, int *s3, ..., int *s10, int n) FYI, I'm looking at the answers to a similar question but still confused.

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• Recycle Freed Objects

  - by uray

  suppose I need to allocate and delete object on heap frequently (of arbitrary size), is there any performance benefit if instead of deleting those objects, I will return it back to some "pool" to be reused later? would it give benefit by reduce heap allocation/deallocation?, or it will be slower compared to memory allocator performance, since the "pool" need to manage a dynamic collection of pointers. my use case: suppose I create a queue container based on linked list, and each node of that list are allocated on the heap, so every call to push() and pop() will allocate and deallocate that node: ` template <typename T> struct QueueNode { QueueNode<T>* next; T object; } template <typename T> class Queue { void push(T object) { QueueNode<T>* newNode = QueueNodePool<T>::get(); //get recycled node if(!newNode) { newNode = new QueueNode<T>(object); } // push newNode routine here.. } T pop() { //pop routine here... QueueNodePool<T>::store(unusedNode); //recycle node return unusedNode->object; } } `

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• Working with complex objects in Prevayler commands

  - by alexantd

  The demos included in the Prevayler distribution show how to pass in a couple strings (or something simple like that) into a command constructor in order to create or update an object. The problem is that I have an object called MyObject that has a lot of fields. If I had to pass all of them into the CreateMyObject command manually, it would be a pain. So an alternative I thought of is to pass my business object itself into the command, but to hang onto a clone of it (keeping in mind that I can't store the BO directly in the command). Of course after executing this command, I would need to make sure to dispose of the original copy that I passed in. public class CreateMyObject implements TransactionWithQuery { private MyObject object; public CreateMyObject(MyObject business_obj) { this.object = (MyObject) business_obj.clone(); } public Object executeAndQuery(...) throws Exception { ... } } The Prevayler wiki says: Transactions can't carry direct object references (pointers) to business objects. This has become known as the baptism problem because it's a common beginner pitfall. Direct object references don't work because once a transaction has been serialized to the journal and then deserialized for execution its object references no longer refer to the intended objects - - any objects they may have referred to at first will have been copied by the serialization process! Therefore, a transaction must carry some kind of string or numeric identifiers for any objects it wants to refer to, and it must look up the objects when it is executed. I think by cloning the passed-in object I will be getting around the "direct object pointer" problem, but I still don't know whether or not this is a good idea...

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