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  • Segmentation Fault

    - by Biranchi
    Hi All, I have the following piece of code for getting the hostname and IP address, #include <stdlib.h> #include <stdio.h> #include <netdb.h> /* This is the header file needed for gethostbyname() */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> int main(int argc, char *argv[]) { struct hostent *he; if (argc!=2){ printf("Usage: %s <hostname>\n",argv[0]); exit(-1); } if ((he=gethostbyname(argv[1]))==NULL){ printf("gethostbyname() error\n"); exit(-1); } printf("Hostname : %s\n",he->h_name); /* prints the hostname */ printf("IP Address: %s\n",inet_ntoa(*((struct in_addr *)he->h_addr))); /* prints IP address */ } but i am getting a warning and segmentation fault as host.c: In function ‘main’: host.c:24: warning: format ‘%s’ expects type ‘char *’, but argument 2 has type ‘int’ What is the error in the code ?? Thanks

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  • Method returns an IDisposable - Should I dispose of the result, even if it's not assigned to anythin

    - by mjd79
    This seems like a fairly straightforward question, but I couldn't find this particular use-case after some searching around. Suppose I have a simple method that, say, determines if a file is opened by some process. I can do this (not 100% correctly, but fairly well) with this: public bool IsOpen(string fileName) { try { File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None); } catch { // if an exception is thrown, the file must be opened by some other process return true; } } (obviously this isn't the best or even correct way to determine this - File.Open throws a number of different exceptions, all with different meanings, but it works for this example) Now the File.Open call returns a FileStream, and FileStream implements IDisposable. Normally we'd want to wrap the usage of any FileStream instantiations in a using block to make sure they're disposed of properly. But what happens in the case where we don't actually assign the return value to anything? Is it still necessary to dispose of the FileStream, like so: try { using (File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); { /* nop */ } } catch { return true; } Should I create a FileStream instance and dispose of that? try { using (FileStream fs = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.None)); } ... Or are these totally unnecessary? Can we simply call File.Open and not assign it to anything (first code example), and let the GC dispose of it right away?

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  • Design for fastest page download

    - by mexxican
    I have a file with millions of URLs/IPs and have to write a program to download the pages really fast. The connection rate should be at least 6000/s and file download speed at least 2000 with avg. 15kb file size. The network bandwidth is 1 Gbps. My approach so far has been: Creating 600 socket threads with each having 60 sockets and using WSAEventSelect to wait for data to read. As soon as a file download is complete, add that memory address(of the downloaded file) to a pipeline( a simple vector ) and fire another request. When the total download is more than 50Mb among all socket threads, write all the files downloaded to the disk and free the memory. So far, this approach has been not very successful with the rate at which I could hit not shooting beyond 2900 connections/s and downloaded data rate even less. Can somebody suggest an alternative approach which could give me better stats. Also I am working windows server 2008 machine with 8 Gig of memory. Also, do we need to hack the kernel so as we could use more threads and memory. Currently I can create a max. of 1500 threads and memory usage not going beyond 2 gigs [ which technically should be much more as this is a 64-bit machine ]. And IOCP is out of question as I have no experience in that so far and have to fix this application today. Thanks Guys!

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  • Live clock javascript starts from my custom time

    - by newworroo
    I was trying to create a live/dynamic clock is based on my custom time instead of system time. There are many scripts, but I couldn't find the clock starts from my custom time. Here is an example that I'm trying to modify. The problem is the seconds doesn't change, and it looks like I need to use ajax. Is there any way to do it without ajax? If not, help me to do it using ajax!!! The reason I don't like ajax method is that another page should be called and refreshed, so it will eat server ram. ex) http://www.javascriptkit.com/script/cut2.shtml Before: <script> function show(){ var Digital=new Date() var hours=Digital.getHours() var minutes=Digital.getMinutes() var seconds=Digital.getSeconds() ... ... After: <script> function show(){ var Digital=new Date() var hours=<?php echo $hr; ?>; var minutes=<?php echo $min; ?>; var seconds=<?php echo $sec; ?>; ... ...

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  • Fastest reliable way for Clojure (Java) and Ruby apps to communicate

    - by jkndrkn
    Hi There, We have cloud-hosted (RackSpace cloud) Ruby and Java apps that will interact as follows: Ruby app sends a request to Java app. Request consists of map structure containing strings, integers, other maps, and lists (analogous to JSON). Java app analyzes data and sends reply to Ruby App. We are interested in evaluating both messaging formats (JSON, Buffer Protocols, Thrift, etc.) as well as message transmission channels/techniques (sockets, message queues, RPC, REST, SOAP, etc.) Our criteria: Short round-trip time. Low round-trip-time standard deviation. (We understand that garbage collection pauses and network usage spikes can affect this value). High availability. Scalability (we may want to have multiple instances of Ruby and Java app exchanging point-to-point messages in the future). Ease of debugging and profiling. Good documentation and community support. Bonus points for Clojure support. What combination of message format and transmission method would you recommend? Why? I've gathered here some materials we have already collected for review: Comparison of various java serialization options Comparison of Thrift and Protocol Buffers (old) Comparison of various data interchange formats Comparison of Thrift and Protocol Buffers Fallacies of Protocol Buffers RPC features Discussion of RPC in the context of AMQP (Message-Queueing) Comparison of RPC and message-passing in distributed systems (pdf) Criticism of RPC from perspective of message-passing fan Overview of Avro from Ruby programmer perspective

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  • Setting up a NAS with Citrix XenServer

    - by JasonBrown
    Just a quick query on anyone whos worked with XenServer, I want to setup a NAS at home but with virtualization (I've looked into VMWare Server and KVM, I quite like KVM!) but I was told about XenServer 5.5. I have comomodity hardware (ASUS board, dual core 2.66Ghz CPU with 8Gb RAM), I need to setup a fileserver to house about 2-3Tb worth of data (big chunky video - not porn!). Need to run Linux (preferably CentOS) but also run Windows virtualised for testing. I was thinking of going the XenServer route, however I want to be able to offer a VM access to the 2-3Tb of HDDs (5 HDD drives) directly so it can do its thing (maybe using FreeNAS). Would this be possible with XenServer? Or will I have to do more work - and another box - to offer this? My goals are to use FreeNAS (ZFS!) for the filesserver, CentOS for SVN and aother bits we need to use (LAMP Stack), Windows for our win32 testing all on one box. I see this iSCSI target bits and get scared.

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  • finding long repeated substrings in a massive string

    - by Will
    I naively imagined that I could build a suffix trie where I keep a visit-count for each node, and then the deepest nodes with counts greater than one are the result set I'm looking for. I have a really really long string (hundreds of megabytes). I have about 1 GB of RAM. This is why building a suffix trie with counting data is too inefficient space-wise to work for me. To quote Wikipedia's Suffix tree: storing a string's suffix tree typically requires significantly more space than storing the string itself. The large amount of information in each edge and node makes the suffix tree very expensive, consuming about ten to twenty times the memory size of the source text in good implementations. The suffix array reduces this requirement to a factor of four, and researchers have continued to find smaller indexing structures. And that was wikipedia's comments on the tree, not trie. How can I find long repeated sequences in such a large amount of data, and in a reasonable amount of time (e.g. less than an hour on a modern desktop machine)? (Some wikipedia links to avoid people posting them as the 'answer': Algorithms on strings and especially Longest repeated substring problem ;-) )

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  • log activity. intrusion detection. user event notification ( interraction ). messaging

    - by Julian Davchev
    Have three questions that I somehow find related so I put them in same place. Currently building relatively large LAMP system - making use of messaging(activeMQ) , memcache and other goodies. I wonder if there are best practices or nice tips and tricks on howto implement those. System is user aware - meaning all actions done can be bind to particular logged user. 1. How to log all actions/activities of users? So that stats/graphics might be extracted later for analysing. At best that will include all url calls, post data etc etc. Meaning tons of inserts. I am thinking sending messages to activeMQ and later cron dumping in DB and cron analysing might be good idea here. Since using Zend Framework I guess I may use some request plugin so I don't have to make the log() call all over the code. 2.How to log stuff so may be used for intrusion detection? I know most things might be done on http level using apache mods for example but there are also specific cases like (5 failed login attempts in a row (leads to captcha) etc etc..) This also would include tons of inserts. Here I guess direct usage of memcache might be best approach as data don't seem vital to be permanantly persisted. Not sure if cannot use data from point 1. 3.System will notify users of some events. Like need approval , something broke..whatever.Some events will need feedback(action) from user, others are just informational. Wonder if there is common solutions for needs like this. Example: Based on occuring event(s) user will be notifed (user inbox for example) what happend. There will be link or something to lead him to details of thingy that happend and take action accordingly. Those seem trivial at first look but problem I see if coding it directly is becoming really fast hard to maintain.

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  • How to break out from nested doseqs

    - by fizbin
    Hi, I have a question regarding nested doseq loops. In the start function, once I find an answer I set the atom to true, so that the outer loop validation with :while fails. However it seems that it doesn't break it, and the loops keep on going. What's wrong with it? I am also quite confused with the usage of atoms, refs, agents (Why do they have different names for the update functions when then the mechanism is almost the same?) etc. Is it okay to use an atom in this situation as a flag? Obviously I need a a variable like object to store a state. (def pentagonal-list (map (fn [a] (/ (* a (dec (* 3 a))) 2)) (iterate inc 1))) (def found (atom false)) (defn pentagonal? [a] (let [y (/ (inc (Math/sqrt (inc (* 24 a)))) 6) x (mod (* 10 y) 10)] (if (zero? x) true false))) (defn both-pent? [a b] (let [sum (+ b a) diff (- a b)] (if (and (pentagonal? sum) (pentagonal? diff)) true false))) (defn start [] (doseq [x pentagonal-list :while (false? @found)] (doseq [y pentagonal-list :while (<= y x)] (if (both-pent? x y) (do (reset! found true) (println (- x y)))))))

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  • PHP shell_exec() - Run directly, or perform a cron (bash/php) and include MySQL layer?

    - by Jimbo
    Sorry if the title is vague - I wasn't quite sure how to word it! What I'm Doing I'm running a Linux command to output data into a variable, parse the data, and output it as an array. Array values will be displayed on a page using PHP, and this PHP page output is requested via AJAX every 10 seconds so, in effect, the data will be retrieved and displayed/updated every 10 seconds. There could be as many as 10,000 characters being parsed on every request, although this is usually much lower. Alternative Idea I want to know if there is a better* alternative method of retrieving this data every 10 seconds, as multiple users (<10) will be having this command executed automatically for them. A cronjob running on the server could execute either bash or php (which is faster?) to grab the data and store it in a MySQL database. Then, any AJAX calls to the PHP output would return values in the MySQL database rather than making a direct call to execute server code every 10 seconds. Why? I know there are security concerns with running execs directly from PHP, and (I hope this isn't micro-optimisation) I'm worried about CPU usage on the server. The server is running a sempron processor. Yes, they do still exist. Having this only execute when the user is on the page (idea #1) means that the server isn't running code that doesn't need to be run. However, is this slow and insecure? Just in case the type of linux command may be of assistance in determining it's efficiency: shell_exec("transmission-remote $host:$port --auth $username:$password -l"); I'm hoping that there are differences in efficiency and level of security with the two methods I have outlined above, and that this isn't just micro-micro-optimisation. If there are alternative methods that are better*, I'd love to learn about these! :)

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  • C# Linq Select Problem in Method Chain.

    - by Gnought
    Note that the _src inherit IQueryable<U> and V inherit new(); I wrote the following statement, there is no syntax error. IQueryable<V> a = from s in _src where (s.Right - 1 == s.Left) select new V(); But if i re-wrote it as follows, the Visual Studio editor complains an error in the "Select" IQueryable<V> d = _src.Where(s => s.Right - 1 == s.Left).Select(s=> new V()); The Error is: The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly. Candidates are: System.Collections.Generic.IEnumerable<V> Select<U,V>(this System.Collections.Generic.IEnumerable<U>, System.Func<U,V>) (in class Enumerable) System.Linq.IQueryable<V> Select<U,V>(this System.Linq.IQueryable<U>, System.Linq.Expressions.Expression<System.Func<U,V>>) (in class Queryable) Could anyone explain this phenomenon, and what the solution is to fix the error?

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  • [PHP/MySQL] How to create text diff web app

    - by Adam Kiss
    Hello, idea I would like to create a little app for myself to store ideas (the thing is - I want it to do MY WAY) database I'm thinking going simple: id - unique id of revision in database text_id - identification number of text rev_id - number of revision flags - various purposes - expl. later title - self expl. desc - description text - self expl . flags - if I (i.e.) add flag rb;65, instead of storing whole text, I just said, that whenever I ask for latest revision, I go again in DB and check revision 65 Question: Is this setup the best? Is it better to store the diff, or whole text (i know, place is cheap...)? Does that revision flag make sense (wouldn't it be better to just copy text - more disk space, but less db and php processing. php I'm thinking, that I'll go with PEAR here. Although main point is to open-edit-save, possiblity to view revisions can't be that hard to program and can be life-saver in certain situations (good ideas got deleted, saving wrong version, etc...). However, I've never used PEAR in a long-time or full-project relationship, however, brief encounters in my previous experience left rather bad feeling - as I remember, it was too difficult to implement, slow and humongous to play with, so I don't know, if there's anything better. why? Although there are bazillions of various time/project/idea management tools, everything lacks something for me, whether it's sharing with users, syncing on more PCs, time-tracking, project management... And I believe, that this text diff webapp will be for internal use with various different tools later. So if you know any good and nice-UI-having project management app with support for text-heavy usage, just let me know, so I'll save my time for something better than redesigning the weel.

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  • PHP include taking too long

    - by wxiiir
    I have a php file with around 100mb which is full of arrays (only arrays). I've made a script that includes this file (for processing), first it exhausted the default Xampp 128mb memory limit, i've raised it to 1024mb but it just takes forever and doesn't do anything. I'm sure the problem is being created by the sheer size of the file because i've tried removing all lines of code and just leaving the include and an echo for me to know when it finishes executing, and it does the same thing (which is taking forever), i've also tried to run the 100mb file in separate and same thing again. A 10mb file is taking forever as well but a similar 1mb file is almost instantly read and executed so the problem must be more than just the file size. I was avoiding using c++ for a simple project as this and would rather not to as php is easier for me and the task that will be executed doesn't need to benefit from the added speed that it would have if it had been done in c++ but if i have no luck in solving this problem i guess i'll have to. EDIT Reasons for not using a database: 1-Whoever made it didn't used a database and it will be pretty hard to store this in an organized database if i'm not able to do something with it first, like just reading it, copying parts from it or putting in memory or something. 2-I don't have experience working with databases as pretty much all stuff i've ever done in php didn't needed large amounts of stored data, 50kb at best, if i was thinking about a big project or huge chunks of data as this one, i definitely would, but i didn't made this mess to start with and now i have to undo it. 3-The logic for having to store a small portion of data like 10mb in hard drive when now every computer has pretty much enough ram to fit the whole OS in it is pretty much incomprehensible unless someone gives a good explanation about it, if i had to access a lot of said files simultaneously i would understand but like i said, this is a simple project, this is the only file that will be accessed at a given time this isn't even to make some kind of website, it's to run a few times and be done with it.

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  • Developers: How does BitLocker affect performance?

    - by Chris
    I'm an ASP.NET / C# developer. I use VS2010 all the time. I am thinking of enabling BitLocker on my laptop to protect the contents, but I am concerned about performance degradation. Developers who use IDEs like Visual Studio are working on lots and lots of files at once. More than the usual office worker, I would think. So I was curious if there are other developers out there who develop with BitLocker enabled. How has the performance been? Is it noticeable? If so, is it bad? My laptop is a 2.53GHz Core 2 Duo with 4GB RAM and an Intel X25-M G2 SSD. It's pretty snappy but I want it to stay that way. If I hear some bad stories about BitLocker, I'll keep doing what I am doing now, which is keeping stuff RAR'ed with a password when I am not actively working on it, and then SDeleting it when I am done (but it's such a pain).

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  • How security of the systems might be improved using database procedures?

    - by Centurion
    The usage of Oracle PL/SQL procedures for controlling access to data often emphasized in PL/SQL books and other sources as being more secure approach. I'v seen several systems where all business logic related with data is performed through packages, procedures and functions, so application code becomes quite "dumb" and is only responsible for visualization part. I even heard some devs call such approaches and driving architects as database nazi :) because all logic code resides in database. I do know about DB procedure performance benefits, but now I'm interested in a "better security" when using thick client model. I assume such design mostly used when Oracle (and maybe MS SQL Server) databases are used. I do agree such approach improves security but only if there are not much users and every system user has a database account, so we might control and monitor data access through standard database user security. However, how such approach could increase the security for an average web system where thick clients are used: for example one database user with DML grants on all tables, and other users are handled using "users" and"user_rights" tables? We could use DB procedures, save usernames into context use that for filtering but vulnerability resides at the root - if the main database account is compromised than nothing will help. Of course in a real system we might consider at least several main users (for example frontend_db_user, backend_db_user).

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  • IS operator behaving a bit strangely

    - by flockofcode
    1) According to my book, IS operator can check whether expression E (E is type) can be converted to the target type only if E is either a reference conversion, boxing or unboxing. Since in the following example IS doesn’t check for either of the three types of conversion, the code shouldn’t work, but it does: int i=100; if (i is long) //returns true, indicating that conversion is possible l = i; 2) a) B b; A a = new A(); if (a is B) b = (B)a; int i = b.l; class A { public int l = 100; } class B:A { } The above code always causes compile time error “Use of unassigned variable”. If condition a is B evaluates to false, then b won’t be assigned a value, but if condition is true, then it will. And thus by allowing such a code compiler would have no way of knowing whether the usage of b in code following the if statement is valid or not ( due to not knowing whether a is b evaluates to true or false) , but why should it know that? Intsead why couldn’t runtime handle this? b) But if instead we’re dealing with non reference types, then compiler doesn’t complain, even though the code is identical.Why? int i = 100; long l; if (i is long) l = i; thank you

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  • My method is too specific. How can I make it more generic?

    - by EricBoersma
    I have a class, the outline of which is basically listed below. import org.apache.commons.math.stat.Frequency; public class WebUsageLog { private Collection<LogLine> logLines; private Collection<Date> dates; WebUsageLog() { this.logLines = new ArrayList<LogLine>(); this.dates = new ArrayList<Date>(); } SortedMap<Double, String> getFrequencyOfVisitedSites() { SortedMap<Double, String> frequencyMap = new TreeMap<Double, String>(Collections.reverseOrder()); //we reverse order to sort from the highest percentage to the lowest. Collection<String> domains = new HashSet<String>(); Frequency freq = new Frequency(); for (LogLine line : this.logLines) { freq.addValue(line.getVisitedDomain()); domains.add(line.getVisitedDomain()); } for (String domain : domains) { frequencyMap.put(freq.getPct(domain), domain); } return frequencyMap; } } The intention of this application is to allow our Human Resources folks to be able to view Web Usage Logs we send to them. However, I'm sure that over time, I'd like to be able to offer the option to view not only the frequency of visited sites, but also other members of LogLine (things like the frequency of assigned categories, accessed types [text/html, img/jpeg, etc...] filter verdicts, and so on). Ideally, I'd like to avoid writing individual methods for compilation of data for each of those types, and they could each end up looking nearly identical to the getFrequencyOfVisitedSites() method. So, my question is twofold: first, can you see anywhere where this method should be improved, from a mechanical standpoint? And secondly, how would you make this method more generic, so that it might be able to handle an arbitrary set of data?

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  • How to optimize this simple function which translates input bits into words?

    - by psihodelia
    I have written a function which reads an input buffer of bytes and produces an output buffer of words where every word can be either 0x0081 for each ON bit of the input buffer or 0x007F for each OFF bit. The length of the input buffer is given. Both arrays have enough physical place. I also have about 2Kbyte free RAM which I can use for lookup tables or so. Now, I found that this function is my bottleneck in a real time application. It will be called very frequently. Can you please suggest a way how to optimize this function? I see one possibility could be to use only one buffer and do in-place substitution. void inline BitsToWords(int8 *pc_BufIn, int16 *pw_BufOut, int32 BufInLen) { int32 i,j,z=0; for(i=0; i<BufInLen; i++) { for(j=0; j<8; j++, z++) { pw_BufOut[z] = ( ((pc_BufIn[i] >> (7-j))&0x01) == 1? 0x0081: 0x007f ); } } } Please do not offer any compiler specific or CPU/Hardware specific optimization, because it is a multi-platform project.

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  • C/C++ Bit Array or Bit Vector

    - by MovieYoda
    Hi, I am learning C/C++ programming & have encountered the usage of 'Bit arrays' or 'Bit Vectors'. Am not able to understand their purpose? here are my doubts - Are they used as boolean flags? Can one use int arrays instead? (more memory of course, but..) What's this concept of Bit-Masking? If bit-masking is simple bit operations to get an appropriate flag, how do one program for them? is it not difficult to do this operation in head to see what the flag would be, as apposed to decimal numbers? I am looking for applications, so that I can understand better. for Eg - Q. You are given a file containing integers in the range (1 to 1 million). There are some duplicates and hence some numbers are missing. Find the fastest way of finding missing numbers? For the above question, I have read solutions telling me to use bit arrays. How would one store each integer in a bit?

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  • A basic load test question

    - by user236131
    I have a very basic load test question. I am running a load test using VSTS 2008 and I have test rig with controller + 10 agents. This load test is against a SharePoint farm I have. My goal of the load test is to find out the resource utilization on web+app+db tiers of my farm for any given load scenario. An example of a load scenario is Usage profile: Average collaboration (as defined by SCCP) User Load: 500 (using step load pattern=a step of 50 every 2 mins and a warm up time of 2mins for every step) Think time: 0 Load duration: 8hrs Now, the question is: Is it fair to expect that metrics like Requests/sec, %processor time on web front end / App / DB, Test/sec, and etc become flat or enter a steady state at one point in time during the load test. Like I said, the goal is not to create a bottleneck but to only measure the utilization of resources by the above load profile. I am asking this question because I see something different. At one point in the load test, requests/sec becomes more or less flat. But processor utilization on the web/DB servers keeps increasing. After digging through the data a bit, I see that "tests running" counter also steadily increased over time. So, if I run the load test for more than 8hrs, %processor may go up further. This way, I don't know what to consider as the load excreted by the load profile. What does this "tests running" counter really signify? How is this different from tests/sec? Another question is: how can I find out why "tests running" counter shows an increase overtime? Thanks for your time

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  • Memory increases with Java UDP Server

    - by Trevor
    I have a simple UDP server that creates a new thread for processing incoming data. While testing it by sending about 100 packets/second I notice that it's memory usage continues to increase. Is there any leak evident from my code below? Here is the code for the server. public class UDPServer { public static void main(String[] args) { UDPServer server = new UDPServer(15001); server.start(); } private int port; public UDPServer(int port) { this.port = port; } public void start() { try { DatagramSocket ss = new DatagramSocket(this.port); while(true) { byte[] data = new byte[1412]; DatagramPacket receivePacket = new DatagramPacket(data, data.length); ss.receive(receivePacket); new DataHandler(receivePacket.getData()).start(); } } catch (IOException e) { e.printStackTrace(); } } } Here is the code for the new thread that processes the data. For now, the run() method doesn't do anything. public class DataHandler extends Thread { private byte[] data; public DataHandler(byte[] data) { this.data = data; } @Override public void run() { System.out.println("run"); } }

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  • Coding the R-ight way - avoiding the for loop

    - by mropa
    I am going through one of my .R files and by cleaning it up a little bit I am trying to get more familiar with writing the code the r-ight way. As a beginner, one of my favorite starting points is to get rid of the for() loops and try to transform the expression into a functional programming form. So here is the scenario: I am assembling a bunch of data.frames into a list for later usage. dataList <- list (dataA, dataB, dataC, dataD, dataE ) Now I like to take a look at each data.frame's column names and substitute certain character strings. Eg I like to substitute each "foo" and "bar" with "baz". At the moment I am getting the job done with a for() loop which looks a bit awkward. colnames(dataList[[1]]) [1] "foo" "code" "lp15" "bar" "lh15" colnames(dataList[[2]]) [1] "a" "code" "lp50" "ls50" "foo" matchVec <- c("foo", "bar") for (i in seq(dataList)) { for (j in seq(matchVec)) { colnames (dataList[[i]])[grep(pattern=matchVec[j], x=colnames (dataList[[i]]))] <- c("baz") } } Since I am working here with a list I thought about the lapply function. My attempts handling the job with the lapply function all seem to look alright but only at first sight. If I write f <- function(i, xList) { gsub(pattern=c("foo"), replacement=c("baz"), x=colnames(xList[[i]])) } lapply(seq(dataList), f, xList=dataList) the last line prints out almost what I am looking for. However, if i take another look at the actual names of the data.frames in dataList: lapply (dataList, colnames) I see that no changes have been made to the initial character strings. So how can I rewrite the for() loop and transform it into a functional programming form? And how do I substitute both strings, "foo" and "bar", in an efficient way? Since the gsub() function takes as its pattern argument only a character vector of length one.

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  • CPU overheating because of Delphi IDE

    - by Altar
    I am using Delphi 7 but I have trialed the Delphi 2005 - 2010 versions. In all these new versions my CPU utilization is 50% (one core is 100%, the other is "relaxed") when Delphi IDE is visible on screen. It doesn't happen when the IDE is minimized. My computer is overheating because of this. Any hints why this happens? It looks like if I want to upgrade to Delphi 2010, I need to upgrade my cooling system first. And I am a bit lazy about that, especially that I want to discahrge my computer and buy a new one (in the next 6 months) - probably I will have to buy a Win 7 license too. Edit: My CPU is AMD Dual Core 4600+. 4GB RAM Overheating means that temperature of the HDDs is raising because the CPU. Edit: Comming to a possible solution I just deleted all HKCU/CodeGear key and let started Delphi as "new". Guess what? The CPU utilization is 0%. I will investigate more.

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  • Python, web log data mining for frequent patterns

    - by descent
    Hello! I need to develop a tool for web log data mining. Having many sequences of urls, requested in a particular user session (retrieved from web-application logs), I need to figure out the patterns of usage and groups (clusters) of users of the website. I am new to Data Mining, and now examining Google a lot. Found some useful info, i.e. querying Frequent Pattern Mining in Web Log Data seems to point to almost exactly similar studies. So my questions are: Are there any python-based tools that do what I need or at least smth similar? Can Orange toolkit be of any help? Can reading the book Programming Collective Intelligence be of any help? What to Google for, what to read, which relatively simple algorithms to use best? I am very limited in time (to around a week), so any help would be extremely precious. What I need is to point me into the right direction and the advice of how to accomplish the task in the shortest time. Thanks in advance!

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  • Holding variables in memory, C++

    - by b-gen-jack-o-neill
    Today something strange came to my mind. When I want to hold some string in C (C++) the old way, without using string header, I just create array and store that string into it. But, I read that any variable definition in C in local scope of function ends up in pushing these values onto the stack. So, the string is actually 2* bigger than needed. Because first, the push instructions are located in memory, but then when they are executed (pushed onto the stack) another "copy" of the string is created. First the push instructions, than the stack space is used for one string. So, why is it this way? Why doesn't compiler just add the string (or other variables) to the program instead of creating them once again when executed? Yes, I know you cannot just have some data inside program block, but it could just be attached to the end of the program, with some jump instruction before. And than, we would just point to these data? Because they are stored in RAM when the program is executed. Thanks.

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