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  • File Encrypt/Decrypt under load?

    - by chopps
    I found an interesting article about encrypting and decrypting files but since it uses a file.dat to store the key this will run into problems when theres alot of users on the site dealing with alot of files. http://www.codeproject.com/KB/security/VernamEncryption.aspx?display=Print Should a new file be created every time a file needs decrypting or would there be a better way to do this? UPDATE: Here is what im using to avoid the locking problems. using (Mutex FileLock = new Mutex(true, System.Guid.NewGuid().ToString())) { try { FileLock.WaitOne(); using (FileStream fs = new FileStream(keyFile, FileMode.Open)) { keyBytes = new byte[fs.Length]; fs.Read(keyBytes, 0, keyBytes.Length); } } catch (Exception ex) { EventLog.LogEvent(ex); } finally { FileLock.ReleaseMutex(); } } I tested it on 1000 TIFFs doing both encryption and decryption without any errors.

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  • Devise and cancan gems: has_many association

    - by tiktak
    I use devise and cancan gems and have simple model association: user has_many subscriptions, subscription belongs_to :user. Have following SubscriptionsController: class SubscriptionsController < ApplicationController load_and_authorize_resource :user load_and_authorize_resource :subscription, through: :user before_filter :authenticate_user! def index @subscriptions = @user.subscriptions.paginate(:page => params[:page]).order(:created_at) end #other actions end And Cancan Ability.rb: class Ability include CanCan::Ability def initialize(user) user ||=User.new can [:index, :show], [Edition, Kind] if user.admin? can :manage, :all elsif user.id can [:read, :create, :destroy, :pay], Subscription, user_id: user.id can [:delete_from_cart, :add_to_cart, :cart], User, id: user.id end end end The problem is that i cannot use subscriptions actions as a user but can as a admin. And have no problems with UsersController. When i delete following lines from SubscriptionsController: load_and_authorize_resource :user load_and_authorize_resource :subscription, through: :user before_filter :authenticate_user! Have no problems at all. So the issue in these lines or in Ability.rb. Any suggestions?

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  • What to see in India as a developer and student

    - by lasseespeholt
    Hi, I'm planning a trip to India around July-August. And I want to hear Indian developers or developers traveled to India if there are something interesting to see in India (around Bombay) for developers in general. Maybe a conference etc. I have looked at http://www.conferencealerts.com/computing.htm I have studied computer science in a year now but have been a spare time and independent developer for some years now. Furthermore, I have tried finding summer courses but that is properly too late now and computer science summer courses is hard to find in India. Best regards, Lasse Espeholt

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  • Should class IOException in Java have been an unchecked RuntimeException?

    - by Derek Mahar
    Do you agree that the designers of Java class java.io.IOException should have made it an unchecked run-time exception derived from java.lang.RuntimeException instead of a checked exception derived only from java.lang.Exception? I think that class IOException should have been an unchecked exception because there is little that an application can do to resolve problems like file system errors. However, in When You Can't Throw An Exception, Elliotte Rusty Harold claims that most I/O errors are transient and so you can retry an I/O operation several times before giving up: For instance, an IOComparator might not take an I/O error lying down, but — because many I/O problems are transient — you can retry a few times, as shown in Listing 7: Is this generally the case? Can a Java application correct I/O errors or wait for the system to recover? If so, then it is reasonable for IOException to be checked, but if it is not the case, then IOException should be unchecked so that business logic can delegate handling of this exception to a separate system error handler.

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  • What is it about Fibonacci numbers?

    - by Ian Bishop
    Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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  • What are some useful SQL statements that should be known by all developers who may touch the Back en

    - by Jian Lin
    What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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  • Making of a "Babbelbox" where you can speak to for partys

    - by Spidfire
    Ive got a project to make for a party, its called in holland a "Babbelbox". its a computer with a webcam and microphone that can be used to make a kind of video log of everyone who wants to say something about the party. But the problem is that i dont know where to start. ive made a kind of video show system in c but i cant save any data to a good format so it wont jam my harddisk in one hour full. Requirements: Record video + audio Recoding has to start after pressing a button Good compression over the recorded videos (would be even better if it can to be read by final cut pro or premiere pro) Light wight programm would be nice but i could scale up the computer power

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  • CUDA driver installation on a laptop with nVidia NVS140M card

    - by stanigator
    I'm trying to first figure out if my computer contains a CUDA-enabled card. It has an nVidia NVS 140M card, but I can't seem to figure out if it is the 128 MB version or 256 MB version. On the laptop purchase receipt, I found out that I ordered the 128 MB version, but the control panel description of the card said otherwise as shown below: When I ran the CUDA driver from nVidia's site, it cannot find a hardware compatible with CUDA (even though the product series is CUDA-enabled, the card does not have 256 MB minimum of memory to do so). What would be your recommendations in this case with trying to use CUDA on this computer (I'm not sure if nothing can be done at this point)? Thanks in advance.

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  • Singletons and other design issues

    - by Ahmed Saleh
    I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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  • manage.py runserver not working

    - by Dan Appleyard
    I am new to django and python in general, so pardon me for any simple mistakes I may be doing. I am trying to setup my first django project on my local windows vista machine. I have created the project successfully with no problems. The issue I am coming across is when my settings.py has values for my database keys, the manage.py runserver command is failing. If I have values in settings before I run the command, as soon as I run it I get errors. If I have already run the command and the server is running, as soon as I edit the settings file with values, the errors show up in my still open command prompt. The inner most exception seems to "Error loading MySQLdb module: No module named MYSQLdb". If I leave the settings.py blank, the command executes with no problems. Any advice would be greatly appreciated! Thanks

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  • Help debugging Apache, Passenger and Rails problem

    - by Matt Dressel
    We have an environment running that uses Apache, Passenger and rails. The system is handling most request normally, yet certain requests do not make it to the rails application. For instance, a request to /books is successful, but /books/1 hits apache and passenger, but does not even make it to rails. We set the apache log level to debug and the passenger log level to 3 so that we could monitor all incoming requests. We could see each request coming through and even the /books/1 request is being handled by passenger. But it never gets to rails. Is there any way to determine where the request goes between Passenger and rails or where debugging information might live? Has anyone ever seen any problems with passenger spawning or queuing? We have spawning set to conservative. Also, we have had some permission/ownership problems in the past, so I am not ruling this out yet. Thanks in advance

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  • Cuda program results are always zero in HW, correct in EMU??

    - by Orion Nebula
    Hi all! I am having a weird problem .. I have written a CUDA code which executes correctly in emulation and all results show up.. however, when executed on hardware "G210" .. the results in the result memory are always 0 I am passing two vectors to the kernel, one with random variables the other is initialized to zero, the code copies the first vector to shared memory, does some swapping and other operations and then writes back the results on the second vector (the one with the initial 0's) I am using double precision, the -arch sm13 flag is used, all memory allocation also use sizeof(double) .. I have checked if the kernel is invoked, it does .. so no problems here .. the cudaMemCpy has no problems .. what could be the problem .. :( why would it work in emulation but not on HW I am quite confused .. any ideas?

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  • Is it possible to do have Capistrano do a checkout over a reverse SSH tunnel?

    - by James A. Rosen
    I am developing an application that resides on a public host but whose source I must keep in a Git repository behind a corporate firewall. I'm getting very tired of the slowness of deploying via scp (copying the whole repository and shipping it over SSH on each deploy) and would like to have the remote host simply do a git pull to update. The problem is that the firewall prohibits incoming SSH connections. Would it be possible for me to set up an SSH tunnel from my computer to the deployment computer and use my repository as the source for the git pull? After all, git is distributed, so my copy is just as valid a repository as the central one. If this is possible, what would the tunnel command and the Capistrano configuration be? I think the tunnel will look something like ssh -R something:deployserver.com:something [email protected]

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  • Managing StringBuilder Resources in C#

    - by Jim Fell
    Hello. My C# (.NET 2.0) application has a StringBuilder variable with a capacity of 2.5MB. Obviously, I do not want to copy such a large buffer to a larger buffer space every time it fills. By that point, there is so much data in the buffer anyways, removing the older data is a viable option. Can anyone see any obvious problems with how I'm doing this (i.e. am I introducing more performance problems than I'm solving), or does it look okay? tText_c = new StringBuilder(2500000, 2500000); private void AppendToText(string text) { if (tText_c.Length * 100 / tText_c.Capacity > 95) { tText_c.Remove(0, tText_c.Length / 2); } tText_c.Append(text); } Thanks.

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  • Programming language for fast calculations with big integers

    - by sub
    I'm doing Project Euler problems at the moment and I can solve most of them using my own programming language which uses direct C++ integers (so they are bound to 2^32 on my machine). However, at times there are problems which require me to work with very high numbers, I can't do that with native integers. So I implemented a BigInt library in my language which unfortunately gets extremely slow at times. Is there a programming language suitable for very efficient handling of big numbers? I mean that I want to do the things I could do in other programming languages with it (variables, loops, etc.), but in a faster way. If you have got tips for workarounds of the 2^32 limit in my language/C++/other languages, please tell me too!

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  • Efficient algorithm to distribute work?

    - by Zwei Steinen
    It's a bit complicated to explain but here we go. We have problems like this (code is pseudo-code, and is only for illustrating the problem. Sorry it's in java. If you don't understand, I'd be glad to explain.). class Problem { final Set<Integer> allSectionIds = { 1,2,4,6,7,8,10 }; final Data data = //Some data } And a subproblem is: class SubProblem { final Set<Integer> targetedSectionIds; final Data data; SubProblem(Set<Integer> targetedSectionsIds, Data data){ this.targetedSectionIds = targetedSectionIds; this.data = data; } } Work will look like this, then. class Work implements Runnable { final Set<Section> subSections; final Data data; final Result result; Work(Set<Section> subSections, Data data) { this.sections = SubSections; this.data = data; } @Override public void run(){ for(Section section : subSections){ result.addUp(compute(data, section)); } } } Now we have instances of 'Worker', that have their own state sections I have. class Worker implements ExecutorService { final Map<Integer,Section> sectionsIHave; { sectionsIHave = {1:section1, 5:section5, 8:section8 }; } final ExecutorService executor = //some executor. @Override public void execute(SubProblem problem){ Set<Section> sectionsNeeded = fetchSections(problem.targetedSectionIds); super.execute(new Work(sectionsNeeded, problem.data); } } phew. So, we have a lot of Problems and Workers are constantly asking for more SubProblems. My task is to break up Problems into SubProblem and give it to them. The difficulty is however, that I have to later collect all the results for the SubProblems and merge (reduce) them into a Result for the whole Problem. This is however, costly, so I want to give the workers "chunks" that are as big as possible (has as many targetedSections as possible). It doesn't have to be perfect (mathematically as efficient as possible or something). I mean, I guess that it is impossible to have a perfect solution, because you can't predict how long each computation will take, etc.. But is there a good heuristic solution for this? Or maybe some resources I can read up before I go into designing? Any advice is highly appreciated!

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  • What are some useful SQL statements / usage patterns that should be known by all developers who may

    - by Jian Lin
    What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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  • How to Create VBA Add-In with Shared Codes for All Excels?

    - by StanFish
    I'm writing VBA codes for multiple Excel spreadsheets, which will be shared with others from time to time. At some point I find there are lots of duplications in my works. So I want to find a way to share codes in a sort of Excel add-in, like the .xla file. But when I tried to save the Excel file containing shared codes as .xla file, I got some problems: The file cannot be edit anymore after I save it in the default add-in folder If I move the .xls file to a folder other than the add-in folder, and open it directly - I cannot use its classes - which creates problems for sharing the codes Any ideas to create add-ins in a flexible and powerful way please? Thanks a lot for the help

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  • How I can I get my home network's IP address from a shell script?

    - by Steven Stewart-Gallus
    I have an account at a server at school, and a home computer that I need to work with sometimes. I have exchanged keys, and now only have one problem. While my school account has a name associated with it, "account_name@school", my home network does not. My plan is to have a script that every hour retrieves my home network's IP address, ssh'es into my school account and updates my ssh config file storing my home network's IP address. How can I retrieve my home computer's IP address from a shell script? P.S. Is this a sensible plan?

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  • Communication via internet in Java

    - by Stuart
    What I mean is like servers on video games. You can run an application and it will set up a server on your computer with an IP and a port. For example, how would you make an application where one host application sets up a thing where it has an IP and a port, and another computer that has access to the internet as well can type in the IP and port and it would be able to communicate with the host? I mean simple communication, like sending a boolean or String. And would there be any security problems that would be needed to fix?

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  • C++ networking simple send and receive

    - by Wallter
    I'm trying to link 10 computers together, the program i would like to write would have one 'control' computer. From what I've looked up this computer would take all the packets sent over the network and do a echo with them... right? The other computers would need to be able to send information (then echoed to the others) to the 'control' ... is there a easy! or simple way to do this? From what I've seen i want a non-blocking socket? I have looked into sockets and such but for an armature programmer like me, this seems like a daunting task :) I'm kind-of looking for an easy class implication that has a send() and an event driven recv(). I'm not going to be sending that much information over the network.

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  • ClickOnce deployment with VS2008 - prerequisites not installing on Windows 7 (only)

    - by dataft
    I have a VS2008 clickonce application with a custom prerequiste, which I install with the bootstrapper. When deployed online, the prerequisite is downloaded and installed fine. No problems. When deployed via CD to a Windows XP machine, also fine as above. No problems. However, when deployed via CD to a Windows 7 machine: the prerequisite is downloaded - good then the user is asked for permission to the run the file - good then the installation of the prerequiste is just SKIPPED - bad and the ClickOnce application installation begins without the prerequisite - bad Has anyone encountered this weird behaviour? I cannot find a solution anywhere.

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