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• [java] Efficiency of while(true) ServerSocket Listen

  - by Submerged

  I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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• Does it take time to deallocate memory?

  - by jm1234567890

  I have a C++ program which, during execution, will allocate about 3-8Gb of memory to store a hash table (I use tr1/unordered_map) and various other data structures. However, at the end of execution, there will be a long pause before returning to shell. For example, at the very end of my main function I have std::cout << "End of execution" << endl; But the execution of my program will go something like $ ./program do stuff... End of execution [long pause of maybe 2 min] $ -- returns to shell Is this expected behavior or am I doing something wrong? I'm guessing that the program is deallocating the memory at the end. But, commercial applications which use large amounts of memory (such as photoshop) do not exhibit this pause when you close the application. Please advise :)

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• optional local variables in rails partial templates: how do I get out of the (defined? foo) mess?

  - by brahn

  I've been a bad kid and used the following syntax in my partial templates to set default values for local variables if a value wasn't explicitly defined in the :locals hash when rendering the partial -- <% foo = default_value unless (defined? foo) %> This seemed to work fine until recently, when (for no reason I could discern) non-passed variables started behaving as if they had been defined to nil (rather than undefined). As has been pointed by various helpful people on SO, http://api.rubyonrails.org/classes/ActionView/Base.html says not to use defined? foo and instead to use local_assigns.has_key? :foo I'm trying to amend my ways, but that means changing a lot of templates. Can/should I just charge ahead and make this change in all the templates? Is there any trickiness I need to watch for? How diligently do I need to test each one?

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• Is there any simple way to test two PNGs for equality?

  - by Mason Wheeler

  I've got a bunch of PNG images, and I'm looking for a way to identify duplicates. By duplicates I mean, specifically, two PNG files whose uncompressed image data are identical, not necessarily whose files are identical. This means I can't do something simple like compare CRC hash values. I figure this can actually be done reliably since PNGs use lossless compression, but I'm worried about speed. I know I can winnow things down a little by testing for equal dimensions first, but when it comes time to actually compare the images against each other, is there any way to do it reasonably efficiently? (ie. faster than the "double-for-loop checking pixel values against each other" brute-force method?)

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• Confused by Perl grep function

  - by titaniumdecoy

  I don't understand the last line of this function from Programming Perl 3e. Here's how you might write a function that does a kind of set intersection by returning a list of keys occurring in all the hashes passed to it: @common = inter( \%foo, \%bar, \%joe ); sub inter { my %seen; for my $href (@_) { while (my $k = each %$href) { $seen{$k}++; } } return grep { $seen{$_} == @_ } keys %seen; } I understand that %seen is a hash which maps each key to the number of times it was encountered in any of the hashes provided to the function.

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• ZooKeeper and RabbitMQ/Qpid together - overkill or a good combination?

  - by Chris Sears

  Greetings, I'm evaluating some components for a multi-data center distributed system. We're going to be using message queues (via either RabbitMQ or Qpid) so agents can make asynchronous requests to other agents without worrying about addressing, routing, load balancing or retransmission. In many cases, the agents will be interacting with components that were not designed for highly concurrent access, so locking and cross-agent coordination will be needed to avoid race conditions. Also, we'd like the system to automatically respond to agent or data center failures. With the above use cases in mind, ZooKeeper seemed like it might be a good fit. But I'm wondering if trying to use both ZK and message queuing is overkill. It seems like what Zookeeper does could be accomplished by my own cluster manager using AMQP messaging, but that would be hard to get really right. On the other hand, I've seen some examples where ZooKeeper was used to implement message queuing, but I think RabbitMQ/Qpid are a more natural fit for that. Has anyone out there used a combination like this? Thanks in advance, -Chris

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• How can I make Rails 3 router to localize url's using localization files?

  - by edgerunner

  What I'd like to be able to do is: in config/routes.rb resources :posts in config/locale/en.yml en: resources: posts: "posts" new: "new" edit: "edit" in config/locale/tr.yml tr: resources: posts: "yazilar" new: "yeni" edit: "duzenle" and get I18n.locale = :en edit_post_path(3) #=> /posts/3/edit I18n.locale = :tr edit_post_path(3) #=> /yazilar/3/duzenle I'd also like rails to match any of these routes anytime and pass the associated locale in the params hash such that when I navigate to /yazilar , the request should be routed to the posts#index action. Any simple way of doing that?

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• Filesystem synchronization library?

  - by IsaacB

  Hi, I've got 10 GB of files to back up daily to another site. The client is way out in the country so bandwidth is an issue. Does anyone know of any existing software or libraries out there that help with keeping a folder with its files synchronized across a slow link, that is it only sends files across if they have changed? Some kind of hash checking would be nice, too, to at least confirm the two sides are the same. I don't mind paying some money for it, seeing as how it might take me several weeks to a month to implement something decent on my own. I just don't want to re-invent the wheel, here. BTW it is a windows shop (they have an in house windows IT guy) so windows is preferred. I also have 10 GB of SQL Server 2000 databases to go across. Is the SQL server replication mode reliable? Thanks!

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• Perl XML::Simple XMLout function

  - by Jeremey

  I pass in the following XML to XMLin: <root foo="bar" foo2="bar2"> <pizzas> <pizza>Pepperoni</pizza> </pizzas> </root> I then edit part of the root element via hash array. I don't care about the pizza, but i do need that XML to come back out exactly as it was. However, I get the following from XMLout: <root foo="bar" foo2="bar2"> <pizzas pizza="Pepperoni"</pizzas> </root> Thoughts?

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• NLB and Host Header Value

  - by Hafeez

  Background: We are using MOSS 2007 in farm configuration, 2 WFE, 1 Indexer and SQL Server. MS NLB is used for load balancing. Host header value mapped to Virtual IP of Cluster in DNS, is used while creating the web applications in MOSS and all are sharing port 80. Problem: When client tries to access the web application that are configured with host header values. Both of WFEs Hangs for 5 minutes, they stop responding to ping and browser shows 'Page not found'. In the Application Log on the WFE, this error is registered "provider: TCP Provider, error: 0 - The semaphore timeout period has expired". Interestingly, the web application with no host header value and hosted on different ports is working correctly. Any clue to solve this problem will be helpful. Thks. Hafeez

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• MAD method compression function

  - by Jacques

  I ran across the question below in an old exam. My answers just feels a bit short and inadequate. Any extra ideas I can look into or reasons I have overlooked would be great. Thanx Consider the MAD method compression function, mapping an object with hash code i to element [(3i + 7)mod9027]mod6000 of the 6000-element bucket array. Explain why this is a poor choice of compression function, and how it could be improved. I basically just say that the function could be improved by changing the value for p (or 9027) to an prime number and choosing an other constant for a (or 3) could also help.

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• What is the most efficient Java Collections library?

  - by dehmann

  What is the most efficient Java Collections library? A few years ago, I did a lot of Java and had the impression back then that trove is the best (most efficient) Java Collections implementation. But when I read the answers to the question "Most useful free Java libraries?" I noticed that trove is hardly mentioned. So which Java Collections library is best now? UPDATE: To clarify, I mostly want to know what library to use when I have to store millions of entries in a hash table etc. (need a small runtime and memory footprint).

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• Prototype.js: How can i return an array without all the methods Prototypes extends Array with?

  - by Morten

  Hi! Is there a way to return a new version of an array/hash that does not contain all the methods/functions that prototype extends the array object with? Example: var myArray = $A(); myArray['test'] = '1'; myArray['test2'] = '2'; var myVariableToPassToAjax = myArray; If I debug myVariableToPassToAjax it looks like this: Array ( [test] = 1 [test2] = 2 [each] = function each(iterator, context) { .......... .......... } ...and all the other extended array functions ); Is there a way to solve this? :-/ Morten

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• Rails: translations for table's column.

  - by Andrew

  In rails application I have two models: Food and Drink. Both food and drink have a name, which has to be stored in two languages. How do I better realize translations for theese tables? First solution I realized was to replace name column with name_en and name_ru. Another solution is to encode with YAML hash like { :en => 'eng', :ru => 'rus' } and store yaml as a name. What would you recommend, assuming content is not static? Maybe there's good article?

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• Server authorization with MD5 and SQL.

  - by Charles

  I currently have a SQL database of passwords stored in MD5. The server needs to generate a unique key, then sends to the client. In the client, it will use the key as a salt then hash together with the password and send back to the server. The only problem is that the the SQL DB has the passwords in MD5 already. Therefore for this to work, I would have to MD5 the password client side, then MD5 it again with the salt. Am I doing this wrong, because it doesn't seem like a proper solution. Any information is appreciated.

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• Hadoop on windows server

  - by Luca Martinetti

  Hello, I'm thinking about using hadoop to process large text files on my existing windows 2003 servers (about 10 quad core machines with 16gb of RAM) The questions are: Is there any good tutorial on how to configure an hadoop cluster on windows? What are the requirements? java + cygwin + sshd ? Anything else? HDFS, does it play nice on windows? I'd like to use hadoop in streaming mode. Any advice, tool or trick to develop my own mapper / reducers in c#? What do you use for submitting and monitoring the jobs? Thanks

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• Getting clusters of rows close together in time

  - by Mike

  I have a table basically like so ID | ItemID | Start | End | --------------------------------------------------------------- 1 234 10/20/09 8:34:22 10/20/09 8:35:10 2 274 10/20/09 8:35:30 10/20/09 8:36:27 3 272 10/21/09 12:15:00 10/21/09 12:17:00 4 112 10/21/09 12:20:14 10/21/09 12:21:21 5 15 10/21/09 12:22:39 10/21/09 12:24:15 There are two "clusters" of entries here, 1-2 and 3-5 separated by a gap in time, specifically 30 minutes is what I'm interested in. What I would like is the first and last rows of the cluster of entries. This is fairly easy to achieve by retrieving all the rows and looping through them in order of start time, but I'd like to have it in SQL if possible. I'm using SQL Server 2008, thanks.

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• jQuery .animate chains, callbacks, and .stop(true, true)

  - by JKS

  So I have a animation chain (.animate().animate().animate()), and on the last .animate(), there is a callback to do some clean-up. The animation is triggered by the hash in the address changing (#page1, #page2, etc.) -- so when the user changes the history state rapidly, if there is a currently executing animation, it needs to stop so they don't queue up. The problem is, if I add a .stop(true, true), it appears only to jump to end of the currently running animation -- and executes only its callback, if there is one. What I need is for it to jump to the end of all of the chained animations, and fire all of the callbacks (well, really just the last one). Is this possible somehow? Huge thanks.

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• Out of memory error while using clusterdata in MATLAB

  - by Hossein

  Hi, I am trying to cluster a Matrix (size: 20057x2).: T = clusterdata(X,cutoff); but I get this error: ??? Error using == pdistmex Out of memory. Type HELP MEMORY for your options. Error in == pdist at 211 Y = pdistmex(X',dist,additionalArg); Error in == linkage at 139 Z = linkagemex(Y,method,pdistArg); Error in == clusterdata at 88 Z = linkage(X,linkageargs{1},pdistargs); Error in == kmeansTest at 2 T = clusterdata(X,1); can someone help me. I have 4GB of ram, but think that the problem is from somewhere else..

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• MYSQL KEY-VALUE PAIR Viability

  - by Amit

  Hi, I am new to mysql and I am looking for some answers to the follwoing questions: a) Can mysql community server can be leveraged for a key-value pair type database.?? b) Which mysql engine is best suited for a key-value pair type database ?? c) Is Mysql cluster a must for horizontal scaling of key-value based datastore or can it be acheived using MySQL replication?? d) Are there any docs or whitepapers for best practices when implementiing a kv datastore on mysql?? e) Are there any known big implementations other that friendfeed doing kv pair using MYSQL?? Would really appreciate some advise from all you Mysql gurus out there !! Thanks In Advance, Amit

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• What's the best general programming book to review basic development concepts?

  - by Charles S.

  I'm looking for for a programming book that reviews basic concepts like implementing linked lists, stacks, queues, hash tables, tree traversals, search algorithms, etc. etc. Basically, I'm looking for a review of everything I learned in college but have forgotten. I prefer something written in the last few years that includes at least a decent amount of code in object-oriented languages. This is to study for job interview questions but I already have the "solving interview questions" books. I'm looking for something with a little more depth and explanation. Any good recommendations?

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• Windows/.NET Load Distribution & Balancing

  - by andrewbadera

  Hi all, Is there a vetted Windows-friendly, or even .NET-native, load-distributing/load-balancing utility out there along the lines of HA Proxy? We have a .NET stack product, and the one piece that we step out of the stack is for load-balancing. We need something with configurable rules for distribution -- perhaps subdomain-driven -- that NLB alone doesn't seem to offer. If it integrates directly with .NET, or offers an exposed API callable by webservices, so much the better! Thanks in advance! Clarification: we need to logically part over boxes. This is not just a cluster/failover/replication scenario.

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• Cherrypicking versus Rebasing

  - by Lakshman Prasad

  The following is a scenario I commonly face: You have a set of commits on master or design, that I want to put on top of production branch. I tend to create a new branch with the base as production cherry-pick these commits on it and merge it to production Then when I merge master to production, I face merge conflicts because even tho the changes are same, but are registered as a different commit because of cherry-pick. I have found some workarounds to deal with this, all of which are laborious and can be termed "hacks". Altho' I haven't done too much rebasing, I believe that too creates a new commit hash. Should I be using rebasing where I am cherrypicking. What other advantages does that have over this.

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• How to call a Thor task multiple times?

  - by deepak

  Thor like Rake (and Make) has task management. If I call a task multiple times, it will effectively call the task only once. How can I call a task multiple times? I tried modifying the @_invocations hash, but that did not work: require 'csv' require './config/environment' class MisReport < Thor desc "all", "generate mysql and postgres mis" def all generate("pg_mis_report", "pg") generate("mysql_mis_report", "mysql") end desc "generate", "generate mis report" def generate(file_name = "mis_report_#{Time.now.to_s(:number)}", connection = "postgres") if connection == "pg" puts "== postgres database" ActiveRecord::Base.establish_connection :development_mysql else puts "== mysql database" ActiveRecord::Base.establish_connection :development end # generate MIS puts puts "mis file is at: #{file_path}" end end

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• OpenID and Authlogic - login and password?

  - by skrat

  How can I get rid of validation messages telling me that: Login is too short (minimum is 3 characters) Login should use only letters, numbers, spaces, and .-_@ please. Password is too short (minimum is 4 characters) Password confirmation is too short (minimum is 4 characters) this happens even before map_openid_registration is called, thus not giving me any chance to fill login with something from returned registration Hash. I would like to have OpenID auto-registration (on login) without requiring user to supply login/password. I also won't make this fields "not required" or "not validated", since I still need them with old school login/password registration. Thank you

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