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• Reverse massive text file in Java

  - by DanJanson

  What would be the best approach to reverse a large text file that is uploaded asynchronously to a servlet that reverses this file in a scalable and efficient way? text file can be massive (gigabytes long) can assume mulitple server/clustered environment to do this in a distributed manner. open source libraries are encouraged to consider I was thinking of using Java NIO to treat file as an array on disk (so that I don't have to treat the file as a string buffer in memory). Also, I am thinking of using MapReduce to break up the file and process it in separate machines. Any input is appreciated. Thanks. Daniel

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• How do I implement something like pointers in javascript?

  - by Shaun

  I know that javascript doesn't have pointers in terms of a variable referring to a place in memory but what I have is a number of variables which are subject to change and dependent on each other. For example: Center (x,y) = (offsetLeft + width/scale , offsetTop + height/scale) As of now I have rewritten the equation in terms of each individual variable and after any changes I call the appropriate update function. For example: If scale changes, then then the center, height, and width stay the same. So I call updateoffset() { offsetLeft = centerx - width/scale; offsetTop = centery - height/scale; } Is this the easiest way to update each of these variables when any of them changes?

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• How to integrate an open source C program instead of calling its executable through a system call?

  - by ihamer

  I have an executable (fossil scm) that is being invoked by my program externally through ::CreateProcess windows call. The stdout and stderr are then captured. Since the source code for fossil is available, I would prefer to create a static library out of it and issue calls directly. Currently, communication to fossil is done through the command line parameters, and the communication back is through the process return code, stdout and stderr. Fossil writes to stdout/err through printf and fprintf calls. What is the best way to solve this with minimum alteration of fossil source? Is there a reliable and cross-platform way to intercept stdout/err and send it into a memory buffer?

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• how to open many files simultaneously for reading in c

  - by monkeyking

  I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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• How to implement a mailing system with Rails that sends emails in the background

  - by Tam

  I want to implement a reliable mailing system with Ruby on Rails that sends emails in the background as sending email sometimes takes like 10 seconds or more so I don't want the user to wait. Some ideas I thought of: 1- Write to a table in DB a have a background process that go over and send email (concern: potential many reads/writes to DB slows down my application) 2- Messaging Queue background process / Rake task (concern: if server crashes queued mails will be lost also might eat up a lot of memory if many emails) I was wondering if you a know of a good solution that provides a balance between reliability and performance.

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• How do I do a join in ActiveRecord after records have been returned?

  - by Russ Bradberry

  I am using ActiveRecord in Rails 3 to pull data from two different tables in two different databases. These databases can not join on each other, but I have the need to do a simple join after-the-fact. I would like to preserve the relation so that I can chain it down the line. here is a simplified version of what I am doing browsers = Browser.all # <-- this is fairly small and can reside in memory events = Event.where(:row_date=>Date.today).select(:name, :browser_id) So as you can see, I want to join browsers in on the events relation, where browser_id should equal browsers.name. events is a relation and I can still add clauses to it down the line, so I dont want to run the query on the db just yet. How would I accomplish this?

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• Ruby: Read large data from stdout and stderr of an external process on Windows

  - by BinaryMuse

  Greetings, all, I need to run a potentially long-running process from Ruby on Windows and subsequently capture and parse the data from the external process's standard output and error. A large amount of data can be sent to each, but I am only necessarily interested in one line at a time (not capturing and storing the whole of the output). After a bit of research, I found that the Open3 class would take care of executing the process and giving me IO objects connected to the process's standard output and error (via popen3). Open3.popen3("external-program.bat") do |stdin, out, err, thread| # Step3.profit() ? end However, I'm not sure how to continually read from both streams without blocking the program. Since calling IO#readlines on out or err when a lot of data has been sent results in a memory allocation error, I'm trying to continuously check both streams for available input, but not having much luck with any of my implementations. Thanks in advance for any advice!

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• Whats the problem with int *p=23;

  - by piemesons

  Yesterday in my interview I was asked this question. (At that time I was highly pressurized by so many abrupt questions). int *p; *p=23; printf('%d',*p); Is there any problem with this code? I explained him that you are trying to assign value to a pointer to whom memory is not allocated. But the way he reacted, it was like I am wrong. Although I got the job but after that he said Mohit think about this question again. I don't know what he was trying to say. Please let me know is there any problem in my answer?

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• Public static variables and Android activity life cycle management

  - by jsstp24n5

  According to the documentation the Android OS can kill the activity at the rear of the backstack. So, say for example I have an app and open the Main Activity (let's call it Activity A). In this public activity class I declare and initialize a public static variable (let's call it "foo"). In Activity A's onCreate() method I then change the value of "foo." From Activity A the user starts another activity within my app called Activity B. Variable "foo" is used in Activity B. Activity B is then paused after the user navigates to some other activities in other apps. Eventually, after a memory shortage occurs, Activity A then Activity B can be killed. After the user navigates back to my app it restarts (actually "recreates") activity B. What happens: 1) Will variable "foo" at this point have the value that was set to it when Activity A's onCreate() method ran? 2) Variable "foo" does not exist? 3) Variable "foo" exists and but is now the initialized value and not the value set in Activity A's onCreate() method?

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• Django: Gracefully restart nginx + fastcgi sites to reflect code changes?

  - by Bartek

  Hi, Common situation: I have a client on my server who may update some of the code in his python project. He can ssh into his shell and pull from his repository and all is fine -- but the code is stored in memory (as far as I know) so I need to actually kill the fastcgi process and restart it to have the code change. I know I can gracefully restart fcgi but I don't want to have to manually do this. I want my client to update the code, and within 5 minutes or whatever, to have the new code running under the fcgi process. Thanks

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• How to store the result of a JSP in a string?

  - by Spines

  I want to store the result of a JSP in a string. For example, I want to be able to call a function like: String result = ProcessJsp("/jspfile.jsp"); Also, this must be rather efficient. Making a url request to the jsp and then storing it would definitely be too slow. How could I do this? Here are my thoughts on how to do this, though I'm not sure if it would work, and I'm hoping there is something simpler: Do RequestDispatcher("/jspfile.jsp").include(hreq, hresp), but instead of putting the real HttpResponse object in there, you put your own where the getWriter() method returns something that writes to your String or a memory buffer, etc.

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• what kind of credentials/prerequisites do you need to be a professional penetration tester ?

  - by dfafa

  does it take more than knowing Bt4 ? are there any one that just runs a scanner and no real labor involved ? would you be expected to be able to code your own exploits without having to dl from milw0rm and discover entry into a system by yourself, in other words, do you have to think outside the box even when there's so many tools that makes the job a lot easier ? would you ever be expected to be able to write your own scanners, exploits and etc ? i am also curious how people are able to write long pages of hex address, that magically causes some type of memory overflow...how are people guessing at the hex values for game hacks for instance ? are certification important ? what about formal school education ? I am a CS major.

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• In C, would !~b ever be faster than b == 0xff ?

  - by James Morris

  From a long time ago I have a memory which has stuck with me that says comparisons against zero are faster than any other value (ahem Z80). In some C code I'm writing I want to skip values which have all their bits set. Currently the type of these values is char but may change. I have two different alternatives to perform the test: if (!~b) /* skip */ and if (b == 0xff) /* skip */ Apart from the latter making the assumption that b is an 8bit char whereas the former does not, would the former ever be faster due to the old compare to zero optimization trick, or are the CPUs of today way beyond this kind of thing?

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• Which Ipod touch generation should I buy? 2nd or 3rd?

  - by kukabunga

  I want to create games for Iphone/Ipod touch. Unfortunately I don't have a lot of money so I can buy only one device. Ipod is cheaper than Iphone, so I decided to bought Ipod touch. But I am afraid of buying 3rd generation - because it has more memory, more faster CPU, etc. And I think if I post my app on appstore - people with 2nd generation Ipod might have trouble with my app (because I was testing it on 3rd generation). But on the other hand - I am planning to create 3d/cpu demanding game - and it would be easy for me to implement it on device with more calculation power... What should I do in this situation? Any advice is appreciate.

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• CPU Usage relative to number of users? - ASP.Net Application

  - by soldieraman

  My Asp.net application uses 25-30% of the CPU on a test server which has 600 MB Ram on it. I can see the asp_wb process taking that much percentage of CPU. This is when I am testing using one user. How many users can the server afford then without falling over? Is there a relationship between the CPU Usage and number of user aka if there are 2 users my application will sky rocket to 60% of memory usage? Or does/Should/How does the server handle this?

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• Render asp.net repeater as-and-when chunks of html is ready (streaming)

  - by sash

  The problem is to render huge reports. Basically we have lots of data that get rendered in html reports (mostly using repeater or gridview). As it so happens, the data started out small and now we have tons of it. There are lots of such reports already built so total rewrite is not an option. Heck, the business is not even letting us page the data. Now server memory is shooting up each time we try to render some reports. So the question is - is there some way we can bind data to repeater and have it stream html to browser as and when chunks are ready? That way we hope to not bring all that data into app server at once. I'm thinking we'll use a datareader or something to get parts of data and render it to browser. Any pointers, links, ideas?

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• double fork using vfork

  - by Oren S

  HI I am writing a part of a server which should dispatch some other child processes. Because I want to wait on some of the processes, and dispatch others without waiting for completion, I use double fork for the second kind of processes (thus avoiding the zombie processes). Problem is, my server holds a lot of memory, so forking takes a long time (even the copy-on-write fork used in Linux which copies only the paging tables) I want to replace the fork() with vfork(), and it's easy for the second fork (as it only calls execve() in the child), but I couldn't find any way I can replace the first one. Does anyone know how I can do that? Thanks! The server is a linux (RH5U4), written in C++.

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• Why MSSQL keeps throwing me Exceptions?

  - by Augusto Càzares

  I have my project in .NET that uses a db in MSSQL Server,i'm using LINQ , sometimes when the projec throws me an exception (Constraint) in a part of the project this same error keeps showing in other part of the project when i do another thing with the db, like when i do an insertion and i had before an exception on delete the insertion throws me the delete exeption, and it remainds this way until i close and open again the project, my major problem is when this happen in my online project, this error in my project causes me problems in the project i'm testing online (i use the same db). I don't know if this exception is on the memory or something but its have been causing me a lot of headechs.

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• just-in-time list

  - by intuited

  I'd like to know if there is a class available, either in the standard library or in pypi, that fits this description. The constructor would take an iterator. It would implement the container protocol (ie _getitem_, _len_, etc), so that slices, length, etc., would work. In doing so, it would iterate and retain just enough values from its constructor argument to provide whatever information was requested. So if jitlist[6] was requested, it would call self.source.next() 7 times, save those elements in its list, and return the last one. This would allow downstream code to use it as a list, but avoid unnecessarily instantiating a list for cases where list functionality was not needed, and avoid allocating memory for the entire list if only a few members ended up being requested. It seems like a pretty easy one to write, but it also seems useful enough that it's likely that someone would have already made it available in a module.

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• Clojure closures and GC

  - by Ralph

  It is my understanding that the default ClassLoader used in Java (and thus, Clojure) holds on to pointers to any anonymous classes created, and thus, onto lambdas and closures. These are never garbage collected, and so represent a "memory leak". There is some investigation going on for Java 7 or 8 to adding an anonymous ClassLoader that will not retain references to these functions. In the mean time how are people dealing with writing long-running applications in languages like Clojure and Scala, that encourage the use of these constructs? Is there any possibility that Clojure could provide its own anonymous ClassLoader, extending the system one, but not holding onto created classes?

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• C++ initializing constants and inheritance

  - by pingvinus

  I want to initialize constant in child-class, instead of base class. And use it to get rid of dynamic memory allocation (I know array sizes already, and there will be a few child-classes with different constants). So I try: class A { public: const int x; A() : x(0) {} A(int x) : x(x) {} void f() { double y[this->x]; } }; class B : A { B() : A(2) {} }; Pretty simple, but compiler says: error C2057: expected constant expression How can I say to compiler, that it is really a constant?

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• Parsing a text file with a fixed format in Java

  - by EugeneP

  Suppose I know a text file format, say, each line contains 4 fields like this: firstword secondword thirdword fourthword firstword2 secondword2 thirdword2 fourthword2 ... and I need to read it fully into memory I can use this approach: open a text file while not EOF read line by line split each line by a space create a new object with four fields extracted from each line add this object to a Set Ok, but is there anything better, a special 3-rd party Java library? So that we could define the structure of each text line beforehand and parse the file with some function thirdpartylib.setInputTextFileFormat("format.xml"); thirdpartylib.parse(Set, "pathToFile") ?

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• Storing CLLocationCoordinates2D in NSMutableArray

  - by Amarsh

  After some searching, I got the following solution : ref: http://stackoverflow.com/questions/1392909/nsmutablearray-addobject-with-mallocd-struct CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D)); new_coordinate->latitude = latitude; new_coordinate->longitude = longitude; [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]]; free(new_coordinate); And access it as: CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes]; However, someone claims that there is a memory leak here? Can anyone suggest me where is the leak and how to fix it. Further, is there a better way of storing a list of CLLocationCoordinate2D in NSMutableArray? Please give sample code since I am an Objective C newbie.

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• Direct video card access

  - by icemanind

  Guys, I am trying to write a class in C# that can be used as a direct replacement for the C# Bitmap class. What I want to do instead though is perform all graphic functions done on the bitmap using the power of the video card. From what I understand, functions such as DrawLine or DrawArc or DrawText are primitive functions that use simple cpu math algorithms to perform the job. I, instead, want to use the graphics card cpu and memory to do these and other advanced functions, such as skinning a bitmap (applying a texture) and true transparancy. My problem is, in C#, how do I access direct video functions? Is there a library or something I need?

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• Entity Framework ObjectContext Life-cycle

  - by Leonardo

  Hello, I'm developing a web application using asp.net 4.0 with Entity Framework. In my apllication I have a page DataEntry.aspx wich has 3 web user control.Each user control manage an entity and use a repository class to access data. The final user before save all the changes can add or remove entity in memory. My question is: how can i share the ObjectContext between the repositories? Basically I need a ObjectContext for the entire session working of DataEntry.aspx. How can I achive this? Thank you

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