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• ACL architechture for a Software As a service in Sprgin 3.0

  - by geoaxis

  I am making a software as a service using Spring 3.0 (Spring MVC, Spring Security, Spring Roo, Hibernate) I have to come up with a flexible access control list mechanism.I have three different kinds of users System (who can do any thing to the system, includes admin and internal daemons) Operations (who can add and delete users, organizations, and do maintenance work on behalf of users and organizations) End Users (they belong to one or more organization, for each organization, the user can have one or more roles, like being organization admin, or organization read-only member) (role like orgadmin can also add users for that organization) Now my question is, how should i model the entity of User? If I just take the End User, it can belong to one or more organizations, so each user can contain a set of references to its organizations. But how do we model the users role for each organization, So for example User UX belongs to organizations og1, og2 and og3, and for og1 he is both orgadmin, and org-read-only-user, where as for og2 he is only orgadmin and for og3 he is only org-read-only-user I have the possibility of making each user belong to one organization alone, but that's making the system bounded and I don't like that idea (although i would still satisfy the requirement) If you have a better extensible ACL architecture, please suggest it. Since its a software as a service, one would expect that alot of different organizations would be part if the same system. I had one concern that it is not a good idea to keep og1 and og2 data on the same DB (if og1 decides to spawn a 100 reports on the system, og2 should not suffer) But that is some thing advanced for now and is not directly related to ACL but to the physical distribution of data and setup of services based on those ACLs This is a community Wiki question, please correct any thing which you wish to do so. Thanks

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• Sorting out POCO, Repository Pattern, Unit of Work, and ORM

  - by CoffeeAddict

  I'm reading a crapload on all these subjects: POCO Repository Pattern Unit of work Using an ORM mapper ok I see the basic definitions of each in books, etc. but I can't visualize this all together. Meaning an example structure (DL, BL, PL). So what, you have your DL objects that contain your CRUD methods, then your BL objects which are "mapped" using an ORM back to your DL objects? What about DTOs...they're your DL objects right? I'm confused. Can anyone really explain all this together or send me example code? I'm just trying to put this together. I am determining whether to go LINQ to SQL or EF 4 (not sure about NHibrernate yet). Just not getting the concepts as in physical layers and code layers here and what each type of object contains (just properties for DTOs, and CRUDs for your core DL classes that match the table fields???). I just need some guidance here. I'm reading Fowler's books and starting to read Evans but just not all there yet.

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• Thoughts on GoGrid vs EC2

  - by Jason

  I am currently hosting my SaaS application at GoGrid (Microsoft stack). Here's what I have: Database Server - physical box, 12 GB RAM, 2 X Quad Core CPU (2.13 GHz Xeon E5506) 2 Web / App servers - cloud servers, 2 GB RAM, 2 VCPUs 300 GB monthly bandwidth I am paying around $900 / month for this. My web / app servers are busting at the seams and need to be upgraded to 4 GB of RAM. I also need a firewall, and GoGrid just added this service for an additional $200. After the upgrade, I will be paying around $1,400. I started looking at Amazon EC2, specifically this config: Database server - "High Memory Double Extra Large Instance" - 34 GB RAM, 13 EC2 compute units 2 Web / App servers - "Large Instance" - 7.5 GB RAM, 4 EC2 compute units If I go with 1 year reserved instances, my upfront cost would be $4,500 and my monthly would be $700. This comes to $1,075 / month when amortized. Amazon also includes a firewall for free. Here are my questions: Do any of you have experience running a database (especially SQL Server) on an EC2 instance? How did it perform compared to a dedicated machine? One of my major concerns is with disk I/O. Amazon's description of a compute unit is fairly vague. Any ideas on how the CPU performance on the database servers would compare? I am hoping that the Amazon solution will provide significantly better performance than my current or even improved GoGrid setup. Having a virtual database server would also be nice in terms of availability. Right now I would be in serious trouble if I had any hardware issues. Thanks for any insight...

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• Django Development Environment Setup Questions

  - by Ross Peoples

  Hello, I'm trying to set up a good development environment for a Django project that I will be working on from two different physical locations. I have two Mac machines, one at home and one at work that I do most of my development on. I currently host a Ubuntu virtual machine on one of the machines to host the Django environemnt, install DropBox on it, and edit source code from my Mac. When I save the code file, the changes get synced over DropBox to the Ubuntu VM and the Django development server automatically restarts because of the change. This method has worked well in the past, but I am starting to use DropBox for a lot of other things now and don't want all of that to be downloaded on every virtual machine I use. Plus, I want to start using Eclipse + PyDev to be able to debug code and have code completion. Currently, I use TextEdit which is great, but doesn't support debugging or completion. So what are my options? I thought about setting up a Parallels VM on a thumb drive that has my entire environment on it (Eclipse included), but that has its own problems. Any other thoughts?

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• Varchar columns: Nullable or not.

  - by NYSystemsAnalyst

  The database development standards in our organization state the varchar fields should not allow null values. They should have a default value of an empty string (""). I know this makes querying and concatenation easier, but today, one of my coworkers questioned me about why that standard only existed for varchar types an not other datatypes (int, datetime, etc). I would like to know if others consider this to be a valid, defensible standard, or if varchar should be treated the same as fields of other data types? I believe this standard is valid for the following reason: I believe that an empty string and null values, though technically different, are conceptually the same. An empty, zero length string is a string that does not exist. It has no value. However, a numeric value of 0 is not the same as NULL. For example, if a field called OutstandingBalance has a value of 0, it means there are $0.00 remaining. However, if the same field is NULL, that means the value is unknown. On the other hand, a field called CustomerName with a value of "" is basically the same as a value of NULL because both represent the non-existence of the name. I read somewhere that an analogy for an empty string vs. NULL is that of a blank CD vs. no CD. However, I believe this to be a false analogy because a blank CD still phyically exists and still has physical data space that does not have any meaningful data written to it. Basically, I believe a blank CD is the equivalent of a string of blank spaces (" "), not an empty string. Therefore, I believe a string of blank spaces to be an actual value separate from NULL, but an empty string to be the absense of value conceptually equivalent to NULL. Please let me know if my beliefs regarding variable length strings are valid, or please enlighten me if they are not. I have read several blogs / arguments regarding this subject, but still do not see a true conceptual difference between NULLs and empty strings.

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• Delphi Pascal / Windows API - Small problem with SetFilePointerEx and parameter FILE_END

  - by SuicideClutchX2

  I know I am about to be slapped by at least one person who was helping me with this API. Alright I have been able to use SetFilePointerEx just fine, when setting the position only. SetFilePointerEx(PD,512,@PositionVar,FILE_BEGIN); SetFilePointerEx(PD,0,@PositionVar,FILE_CURRENT); Both work, I can set positions and even check my current one. But when I set FILE_END as per the documentation no matter what the second parameter is and whether or not i provide a pointer for the third parameter it fails even on a valid handle that many other operations are able to use without fail. For Example: SetFailed := SetFilePointerEx(PD,0,@PositionVar,FILE_END); SetFailed := SetFilePointerEx(PD,0,nil,FILE_END); Whatever I put it fails. I am working with a handle to a physical disk and it most definitely has an end. SetFilePointer works just fine its just a little more trouble than I would like. Its not the end of the world, but whats happening.

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• NASM - Load code from USB Drive

  - by new123456

  Hola, Would any assembly gurus know the argument (register dl) that signifies the first USB drive? I'm working through a couple of NASM tutorials, and would like to get a physical boot (I can get a clean one with qemu). This is the section of code that loads the "kernel" data from disk: loadkernel: mov si, LMSG ;; 'Loading kernel',13,10,0 call prints ;; ex puts() mov dl, 0x00 ;; The disk to load from mov ah, 0x02 ;; Read operation mov al, 0x01 ;; Sectors to read mov ch, 0x00 ;; Track mov cl, 0x02 ;; Sector mov dh, 0x00 ;; Head mov bx, 0x2000 ;; Buffer end mov es, bx mov bx, 0x0000 ;; Buffer start int 0x13 jc loadkernel mov ax, 0x2000 mov ds, ax jmp 0x2000:0x00 If it makes any difference, I'm running a stock Dell Inspiron 15 BIOS. Apparently, the correct value for me is 0x80. The BIOS loads the hard drives and labels them starting at 0x80 according to this answer. My particular BIOS decides to load the USB drive up as the first, for some reason, so I can boot from there.

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• Determining what action an NPC will take, when it is partially random but influenced by preferences?

  - by lala

  I want to make characters in a game perform actions that are partially random but also influenced by preferences. For instance, if a character feels angry they have a higher chance of yelling than telling a joke. So I'm thinking about how to determine which action the character will take. Here are the ideas that have come to me. Solution #1: Iterate over every possible action. For each action do a random roll, then add the preference value to that random number. The action with the highest value is the one the character takes. Solution #2: Assign a range of numbers to an action, with more likely actions having a wider range. So, if the random roll returns anywhere from 1-5, the character will tell a joke. If it returns 6-75, they will yell. And so on. Solution #3: Group all the actions and make a branching tree. Will they take a friendly action or a hostile action? The random roll (with preference values added) says hostile. Will they make a physical attack or verbal? The random roll says verbal. Keep going down the line until you reach the action. Solution #1 is the simplest, but hardly efficient. I think Solution #3 is a little more complicated, but isn't it more efficient? Does anyone have any more insight into this particular problem? Is #3 the best solution? Is there a better solution?

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• Event feed implementation - will it scale?

  - by SlappyTheFish

  Situation: I am currently designing a feed system for a social website whereby each user has a feed of their friends' activities. I have two possible methods how to generate the feeds and I would like to ask which is best in terms of ability to scale. Events from all users are collected in one central database table, event_log. Users are paired as friends in the table friends. The RDBMS we are using is MySQL. Standard method: When a user requests their feed page, the system generates the feed by inner joining event_log with friends. The result is then cached and set to timeout after 5 minutes. Scaling is achieved by varying this timeout. Hypothesised method: A task runs in the background and for each new, unprocessed item in event_log, it creates entries in the database table user_feed pairing that event with all of the users who are friends with the user who initiated the event. One table row pairs one event with one user. The problems with the standard method are well known – what if a lot of people's caches expire at the same time? The solution also does not scale well – the brief is for feeds to update as close to real-time as possible The hypothesised solution in my eyes seems much better; all processing is done offline so no user waits for a page to generate and there are no joins so database tables can be sharded across physical machines. However, if a user has 100,000 friends and creates 20 events in one session, then that results in inserting 2,000,000 rows into the database. Question: The question boils down to two points: Is this worst-case scenario mentioned above problematic, i.e. does table size have an impact on MySQL performance and are there any issues with this mass inserting of data for each event? Is there anything else I have missed?

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• ASP.NET web form Routing issue via UNC Path

  - by Slash

  I create a IIS 7.0 website via UNC path to load .aspx to dynamic compile files and runs. however, it's running perfect. I always use IIS URL Rewrite module 2 to rewrite my site URL n' its perfect, too. Today, I wanna use System.Web.Routing to implement url rewrite but I encountered difficulties... When I wrote code in Global.asax: System.Web.Routing.RouteTable.Routes.MapPageRoute("TEST", "AAA/{prop}", "~/BBB/CCC.aspx"); And it just CANNOT reDirect to /BBB/CCC.aspx When I type the URL(like: xx.xx.xx.xx/BBB/CCC.aspx) in browser directly, it runs normally that I want. (so it proof CCC.aspx is in right path.) thus, I copy all of the code and open VS2010 running with IIS 7.5 Express locally, it works perfect! e.g: in browser URL I type xx.xx.xx.xx/AAA/1234, it will turn to page xx.xx.xx.xx/BBB/CCC.aspx (Works perfect!) Why??? help me plz. thanks. Update: I think I should consider not UNC path to make it error! when I move all code to physical disk and setup IIS 7.0 to monitor this Folder, it still not works! But the same code run in VS2010 + IIS 7.5 Express it works!? so strange!

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• Serializing and deserializing a map with key as string

  - by Grace K

  Hi! I am intending to serialize and deserialize a hashmap whose key is a string. From Josh Bloch's Effective Java, I understand the following. P.222 "For example, consider the case of a harsh table. The physical representation is a sequence of hash buckets containing key-value entries. Which bucket an entry is placed in is a function of the hash code of the key, which is not, in general guaranteed to be the same from JVM implementation to JVM implementation. In fact, it isn't even guranteed to be the same from run to run on the same JVM implementation. Therefore accepting the default serialized form for a hash table would constitute a serious bug. Serializing and deserializing the hash table could yield an object whose invariants were seriously corrupt." My questions are: 1) In general, would overriding the equals and hashcode of the key class of the map resolve this issue and the map can be correctly restored? 2) If my key is a String and the String class is already overriding the hashCode() method, would I still have problem described above. (I am seeing a bug which makes me think this is probably still a problem even though the key is String with overriding hashCode.) 3)Previously, I get around this issue by serializing an array of entries (key, value) and when deserializing I would reconstruct the map. I am wondering if there is a better approach. 4) If the answers to question 1 and 2 are that I still can't be guaranteed. Could someone explain why? If the hashCodes are the same would they go to the same buckets across JVMs? Thanks, Grace

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• Update SQL Server 2000 to SQL Server 2008: Benefits please?

  - by Ciaran Archer

  Hi there I'm looking for the benefits of upgrading from SQL Server 2000 to 2008. I was wondering: What database features can we leverage with 2008 that we can't now? What new TSQL features can we look forward to using? What performance benefits can we expect to see? What else will make management go for it? And the converse: What problems can we expect to encounter? What other problems have people found when migrating? Why fix something that isn't (technically) broken? We work in a Java shop, so any .NET / CLR stuff won't rock our world. We also use Eclipse as our main development so any integration with Visual Studio won't be a plus. We do use SQL Server Management Studio however. Some background: Our main database machine is a 32bit Dell Intel Xeon MP CPU 2.0GHz, 40MB of RAM with Physical Address Extension running Windows Server 2003 Enterprise Edition. We will not be changing our hardware. Our databases in total are under a TB with some having more than 200 tables. But they are busy and during busy times we see 60-80% CPU utilisation. Apart form the fact that SQL Server 2000 is coming close to end of life, why should we upgrade? Any and all contributions are appreciated!

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• Advice needed: cold backup for SQL Server 2008 Express?

  - by Mikey Cee

  What are my options for achieving a cold backup server for SQL Server Express instance running a single database? I have an SQL Server 2008 Express instance in production that currently represents a single point of failure for my application. I have a second physical box sitting at the installation that is currently doing nothing. I want to somehow replicate my database in near real time (a little bit of data loss is acceptable) to the second box. The database is very small and resources are utilized very lightly. In the case that the production server dies, I would manually reconfigure my application to point to the backup server instead. Although Express doesn't support log shipping, I am thinking that I could manually script a poor man's version of it, where I use batch files to take the logs and copy them across the network and apply them to the second server at 5 minute intervals. Does anyone have any advice on whether this is technically achievable, or if there is a better way to do what I am trying to do? Note that I want to avoid having to pay for the full version of SQL Server and configure mirroring as I think it is an overkill for this application. I understand that other DB platforms may present suitable options (eg. a MySQL Cluster), but for the purposes of this discussion, let's assume we have to stick to SQL Server.

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• Does the "Supporting Multiple Screens" document contradict itself?

  - by Neil Traft

  In the Supporting Multiple Screens document in the Android Dev Guide, some example screen configurations are given. One of them states that the small-ldpi designation is given to QVGA (240x320) screens with a physical size of 2.6"-3.0". According to this DPI calculator, a 2.8" QVGA display equates to 143 dpi. However, further down the page the document explicitly states that all screens over 140 dpi are considered "medium" density. So which is it, ldpi or mdpi? Is this a mistake? Does anyone know what the HTC Tattoo or similar device actually reports? I don't have access to any devices like this. Also, with the recent publishing of this document, I'm glad to see we finally have an explicit statement of the exact DPI ranges of the three density categories. But why haven't we been given the same for the small, medium, and large screen size categories? I'd like to know the exact ranges for all these. Thanks in advance for your help!

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• looking to streamline my RSS feed mashup

  - by Mark Cejas

  Hello crafty developers, I have aggregated RSS feeds from various sources with RSSowl, fetching directly from the social mention API. The RSS feeds are categorized into the following major categories: blogs, news, twitter, Q&A and social networking sites. Each major category is nested with a common group of RSS feeds that represent a particular client/brand ontology. Merging these feeds into the RSSowl reader application, allows me to conduct and save refined search queries (from the aggregated data) into a single file - that I can then tag and further segment for analysis. This scheme is utilized for my own research needs and has helped me considerably. However, I find this RSS mashup scheme kinda clumsy, it requires quite a bit of time to initially organize all of the feeds and I would like to be able to do further natural language processing to the data as well as eventually be able to rank the collected list of URL's into some order of media prominence - right I don't want to pay the ridiculous radian6 web analytics fees, when my intuition is telling me that with a bit of 'elbow grease' I can maybe leverage some available resources online to develop a functional low scale web mining application and get some good intelligence from it. I am now starting to learn a little about computer science - my background is in physical science/statistics so is my thinking in the right track? So, I guess I am imagining an application that allows me to query in a refined manner. A manner that allows me to search for keyword combinations, applying AND/OR operators, selectively focus my queries into particular sources - like a collection of blogs or twitter, or social networking communities, then save the results of my queries into a structured format that can then be manipulated and explored. Am I dreaming? I just had to get all of this out. any bit of advice and insight would be hugely appreciated. my best, Mark

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• sql server mdf file database attachment

  - by jnsohnumr

  hello all i'm having a bear of a time getting visual studio 2010 (ultimate i think) to properly attach to my database. it was moved from original spot to #MYAPP#/#MYAPP#.Web/App_Data/#MDF_FILE#.mdf. I have three instances of sql server running on this machine. i have tried to replace the old mdf file with my new one and cannot get the connectionstring right for it. what i'm really wanting to do is to just open some DB instance, run a DB create script. Then I can have a DB that was generated via my edmx (generate database from model) in silverlight business application (c#) right now, when i go to server explorer in VS, choose add new connection, choose MS SQL Server Database FIle (SqlClient), choose my file location (app_data directory), use windows authentication, and hit the Test Connection button I get the following error: Unable to open the physical file "". Operating system error 5: "5(Access Denied.)". An attempt to attach to an auto-named database for file"" failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share. The mdf file was created on the same machine by connecting to (local) on the sql server management studio, getting a new query, pasting in the SQL from the generated ddl file, adding a CREATE DATABASE [NcrCarDatabase]; GO before the pasted SQL, and executing the query. I then disconnected from the DB in management studio, closed management studio, navigated to the DATA directory for that instance, and copying the mdf and ldf files to my application's app_data folder. I am then trying to connect to the same file inside visual studio. I hope that gives more clarity to my problems :). Connection string is: Data Source=.\SQLEXPRESS;AttachDbFilename=C:\SourceCode\NcrCarDatabase\NcrCarDatabase.Web\App_Data\NcrCarDatabase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True

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• Nhibernate - getting single column from other table

  - by Muhammad Akhtar

  I have following tables Employee: ID,CompanyID,Name //CompanyID is foriegn key of Company Table Company: CompanyID, Name I want to map this to the following class: public class Employee { public virtual Int ID { get; set; } public virtual Int CompanyID { get; set; } public virtual string Name { get; set; } public virtual string CompanyName { get; set; } protected Employee() { } } here is my xml class <class name="Employee" table="Employee" lazy="true"> <id name="Id" type="Int32" column="Id"> <generator class="native" /> </id> <property name="CompanyID" column="CompanyID" type="Int32" not-null="false"/> <property name="Name" column="Name" type="String" length="100" not-null="false"/> What I need to add in xml class to map CompanyName in my result? here is my code... public ArrayList getTest() { ISession session = NHibernateHelper.GetCurrentSession(); string query = "select Employee.*,(Company.Name)CompanyName from Employee inner join Employee on Employee.CompanyID = Company.CompanyID"; ArrayList document = (ArrayList)session.CreateSQLQuery(query, "Employee", typeof(Document)).List(); return document; } but in the returned result, I am getting CompanyName is null is result set and other columns are fine. Note:In DB, tables don't physical relation Please suggest my solution ------ Thanks

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• How to download a file from a UNC mapped share via IIS and ASP

  - by helgeg

  I am writing an ASP application that will serve files to clients through the browser. The files are located on a file server that is available from the machine IIS is running on via a UNC path (\server\some\path). I want to use something like the code below to serve the file. Serving files that are local to the machine IIS is running on is working well with this method, my trouble is being able to serve files from the UNC mapped share: //Set the appropriate ContentType. Response.ContentType = "Application/pdf"; //Get the physical path to the file. string FilePath = MapPath("acrobat.pdf"); //Write the file directly to the HTTP content output stream. Response.WriteFile(FilePath); Response.End(); My question is how I can specify a UNC path for the file name. Also, to access the file share I need to connect with a specific username/password. I would appreciate some pointers on how I can achieve this (either using the approach above or by other means).

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• Distinct or group by on some columns but not others

  - by Nazadus

  I have a view that I'm trying to filter with something similar to DISTINCT on some columns but not others. I have a view like this: Name LastName Zip Street1 HouseholdID (may not be unique because it may have multiple addresses -- think of it in the logical sense as grouping persons but not physical locations; If you lookup HouseholdID 4130, you may get two rows.. or more, because the person may have mutiple mailing locations) City State I need to pull all those columns but filter on LastName,Zip, and Street1. Here's the fun part: The filter is arbitrary -- meaning I don't care which one of the duplicates goes away. This is for a mail out type thing and the other information is not used for any other reason than than to look up a specific person if needed (I have no idea why). So.. given one of the records, you can easily figure out the removed ones. As it stands now, my Sql-Fu fails me and I'm filtering in C# which is incredibly slow and is pretty much a foreach that starts with an empty list and adds the row in if the combined last name, zip, and street aren't are not in the list. I feel like I'm missing a simple / basic part of SQL that I should be understanding.

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• ASP.NET MVC 2.0 + Implementation of a IRouteHandler goes not fire

  - by Peter

  Can anybody please help me with this as I have no idea why public IHttpHandler GetHttpHandler(RequestContext requestContext) is not executing. In my Global.asax.cs I have public class MvcApplication : System.Web.HttpApplication { public static void RegisterRoutes(RouteCollection routes) { routes.IgnoreRoute("{resource}.axd/{*pathInfo}"); routes.MapRoute( "Default", // Route name "{controller}/{action}/{id}", // URL with parameters new { controller = "Home", action = "Index", id = "" } // Parameter defaults ); routes.Add("ImageRoutes", new Route("Images/{filename}", new CustomRouteHandler())); } protected void Application_Start() { RegisterRoutes(RouteTable.Routes); } } //CustomRouteHandler implementation is below public class CustomRouteHandler : IRouteHandler { public IHttpHandler GetHttpHandler(RequestContext requestContext) { // IF I SET A BREAK POINT HERE IT DOES NOT HIT FOR SOME REASON. string filename = requestContext.RouteData.Values["filename"] as string; if (string.IsNullOrEmpty(filename)) { // return a 404 HttpHandler here } else { requestContext.HttpContext.Response.Clear(); requestContext.HttpContext.Response.ContentType = GetContentType(requestContext.HttpContext.Request.Url.ToString()); // find physical path to image here. string filepath = requestContext.HttpContext.Server.MapPath("~/logo.jpg"); requestContext.HttpContext.Response.WriteFile(filepath); requestContext.HttpContext.Response.End(); } return null; } } Can any body tell me what I'm missing here. Simply public IHttpHandler GetHttpHandler(RequestContext requestContext) does not fire. I havn't change anything in the web.config either. What I'm missing here? Please help.

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• Are programming languages and methods inefficient? (assembler and C knowledge needed)

  - by b-gen-jack-o-neill

  Hi, for a long time, I am thinking and studying output of C language compiler in assembler form, as well as CPU architecture. I know this may be silly to you, but it seems to me that something is very ineffective. Please, don´t be angry if I am wrong, and there is some reason I do not see for all these principles. I will be very glad if you tell me why is it designed this way. I actually truly believe I am wrong, I know the genius minds of people which get PCs together knew a reason to do so. What exactly, do you ask? I´ll tell you right away, I use C as a example: 1: Stack local scope memory allocation: So, typical local memory allocation uses stack. Just copy esp to ebp and than allocate all the memory via ebp. OK, I would understand this if you explicitly need allocate RAM by default stack values, but if I do understand it correctly, modern OS use paging as a translation layer between application and physical RAM, when address you desire is further translated before reaching actual RAM byte. So why don´t just say 0x00000000 is int a,0x00000004 is int b and so? And access them just by mov 0x00000000,#10? Because you wont actually access memory blocks 0x00000000 and 0x00000004 but those your OS set the paging tables to. Actually, since memory allocation by ebp and esp use indirect addressing, "my" way would be even faster. 2: Variable allocation duplicity: When you run application, Loader load its code into RAM. When you create variable, or string, compiler generates code that pushes these values on the top o stack when created in main. So there is actual instruction for do so, and that actual number in memory. So, there are 2 entries of the same value in RAM. One in form of instruction, second in form of actual bytes in the RAM. But why? Why not to just when declaring variable count at which memory block it would be, than when used, just insert this memory location?

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• How is external memory, internal memory, and cache organized?

  - by goldenmean

  Consider a system as follows:= A hardware board having say ARM Cortex-A8 and Neon Vector coprocessor, and Embedded Linux OS running on Cortex-A8. On this environment, if there is some application - say, a video decoder is executing - then: How is it decided that which buffers would be in external memory, which ones would be allocated in internal SRAM, etc. When one says calloc/malloc on such system/code, the pointer returned is from which memory: internal or external? Can a user make buffers to be allocated to the memories of his choice (internal/external)? In ARM architectures, there is another memory called as Tightly coupled memory (TCM). What is that and how can user enable and use it? Can I declare buffers in this memory? Do I need to see the memory map (if any) of the hardware board to understand about all these different physical memories present in a typical hardware board? How much of a role does the OS play in distinguishing these different memories? Sorry for multiple questions, but i think they all are interlinked.

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• User to kernel mode big picture?

  - by fsdfa

  I've to implement a char device, a LKM. I know some basics about OS, but I feel I don't have the big picture. In a C programm, when I call a syscall what I think it happens is that the CPU is changed to ring0, then goes to the syscall vector and jumps to a kernel memmory space function that handle it. (I think that it does int 0x80 and in eax is the offset of the syscall vector, not sure). Then, I'm in the syscall itself, but I guess that for the kernel is the same process that was before, only that it is in kernel mode, I mean the current PCB is the process that called the syscall. So far... so good?, correct me if something is wrong. Others questions... how can I write/read in process memory?. If in the syscall handler I refer to address, say, 0xbfffffff. What it means that address? physical one? Some virtual kernel one?

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• "No keyboard for id 0"?

  - by Mellon

  I am new in Android app. development, now I have encountered a strange problem with the Menu button. Here is the thing: I have two activities, "ActivityOne" and "ActivityTwo", where "ActivityTwo" is the child Activity of "ActivityOne". In both activity, I have defined the menu button options like following: @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); MenuItem insertMenuItem = menu.add(0, INSERT_ID, 0, R.string.menu_insert); insertMenuItem.setIcon(R.drawable.ic_menu_add); MenuItem settingMenuItem = menu.add(0, SETTING_ID, 0, R.string.menu_setting); settingMenuItem.setIcon(R.drawable.ic_menu_settings); MenuItem aboutMenuItem = menu.add(0, ABOUT_ID, 0, R.string.menu_about); aboutMenuItem.setIcon(R.drawable.ic_menu_about); logPrinter.println("creating menu options..."); return true; } @Override public boolean onMenuItemSelected(int featureId, MenuItem item) { switch(item.getItemId()) { case INSERT_ID: doInsert(); return true; case SETTING_ID: return true; case ABOUT_ID: showAbout(); return true; } return super.onMenuItemSelected(featureId, item); } In "ActivityOne", when I click the physical Menu button, there is no menu options pop up from screen bottom, when I checked the LogCat console, there are two warning messages, which are "No keyboard for id 0" and "Using default keyMap:/system/usr/keychars/qwerty.kcm.bin" . BUT, in "ActivityTwo", the menu button works fine, it shows me those menu options I defined. Why the menu button does not work in "ActivityOne" ?? What does the warning msg mean???

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• maximum memory which malloc can allocate!

  - by Vikas

  I was trying to figure out how much memory I can malloc to maximum extent on my machine (1 Gb RAM 160 Gb HD Windows platform). I read that maximum memory malloc can allocate is limited to physical memory.(on heap) Also when a program exceeds consumption of memory to a certain level, the computer stops working because other applications do not get enough memory that they require. So to confirm,I wrote a small program in C, int main(){ int *p; while(1){ p=(int *)malloc(4); if(!p)break; } } Hoping that there would be a time when memory allocation will fail and loop will be breaked. But my computer hanged as It was an infinite loop. I waited for about an hour and finally I had to forcely shut down my computer. Some questions: Does malloc allocate memory from HD also? What was the reason for above behaviour? Why didn't loop breaked at any point of time.? Why wasn't there any allocation failure?

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