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  • concurrent doubly-linked list (1 writer, n-readers)

    - by Arne
    Hi guys, I am back in the field of programming for my Diploma-thesis now and stumbled over the following issue: I need to implement a thread-safe doubly-linked list for one thread writing the list at any position (delete, insert, mutate node data) and one to many threads traversing and reading the list. I am well aware that mutexes can be used to serialize access to the list, still I presume that a naive lock around any write operation will be less than optimal. I am wondering whether there are better variants. (I am well aware that 'optimal' has not much of a practical meaning as long as no exact measure/profiling are available but this is an academic thesis after all..) I am very gratefull for code-samples as well as references to academic granted these have at least a tiny bit of practical relevance. Thanks at lot

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  • What does the R function `poly` really do?

    - by merlin2011
    I have read through the manual page ?poly (which I admit I did not completely comphrehend) and also read the description of the function in book Introduction to Statistical Learning. My current understanding is that a call to poly(horsepower, 2) should be equivalent to writing horsepower + I(horsepower^2). However, this seems to be contradicted by the output of the following code. library(ISLR) summary(lm(mpg~poly(horsepower,2), data=Auto))$coef summary(lm(mpg~horsepower+I(horsepower^2), data=Auto))$coef Output: Estimate Std. Error t value Pr(>|t|) (Intercept) 23.44592 0.2209163 106.13030 2.752212e-289 poly(horsepower, 2)1 -120.13774 4.3739206 -27.46683 4.169400e-93 poly(horsepower, 2)2 44.08953 4.3739206 10.08009 2.196340e-21 Estimate Std. Error t value Pr(>|t|) (Intercept) 56.900099702 1.8004268063 31.60367 1.740911e-109 horsepower -0.466189630 0.0311246171 -14.97816 2.289429e-40 I(horsepower^2) 0.001230536 0.0001220759 10.08009 2.196340e-21 My question is, why does the output not match, and what is poly really doing?

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  • bash—Better way to store variable between runs?

    - by shardbearer
    I've made a bash script which I run every hour with crontab, and I need to store one variable so that I can access it the next time I run it. The script changes the variable every time it runs, so I can't hardcode it in. Right now I am writing it to a txt file and then reading it back. Is there a better way to do it than this? And the way I am reading the txt file is something I found on here, I don't understand it, and it's kinda clunky. Is there not a built in command for this? Anyway, here's the applicable code, with some of the variables changed to make it easier to read. while read x; do var=$x done < var.txt # Do some stuff, change var to a new value echo $var > var.txt The variable is only a single integer, so the text file feels overkill.

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  • JUnit - Testing a method that in turn invokes a few more methods

    - by stratwine
    Hi, This is my doubt on what we regard as a "unit" while unit-testing. say I have a method like this, public String myBigMethod() { String resultOne = moduleOneObject.someOperation(); String resultTwo = moduleTwoObject.someOtherOperation(resultOne); return resultTwo; } ( I have unit-tests written for someOperation() and someOtherOperation() seperately ) and this myBigMethod() kinda integrates ModuleOne and ModuleTwo by using them as above, then, is the method "myBigMethod()" still considered as a "unit" ? Should I be writing a test for this "myBigMethod()" ? Say I have written a test for myBigMethod()... If testSomeOperation() fails, it would also result in testMyBigMethod() to fail... Now testMyBigMethod()'s failure might show a not-so-correct-location of the bug. One-Cause causing two tests to fail doesn't look so good to me. But donno if there's any better way...? Is there ? Thanks !

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  • Pulling .live() functionality out of jQuery

    - by Daniel
    I am writing a Firefox Add-On that currently is depending on jQuery for the following things: Selectors Animations A special .live("focus") hail-mary event-catching maneuver that happens to work with jQuery 1.4.2 (but not 1.4.4) jQuery isn't well suited for functioning inside XUL, and it's a miracle we've gotten this far with it. We're trying to remove the jQuery requirements, the first two are easy (animations are simple, and we can use .querySelector() instead of jQuery), but the .live has proven impossible to do on our own. I've tried reading the source code, but I haven't been able to piece it apart. What is the jQuery .live function doing? There's clearly a lot more going on than document.addEventListener("focus"/"focusin",function_to_pick_apart_events). What else is going on here?

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  • Constructors + Dependency Injection

    - by Sunny
    If I am writing up a class with more than 1 constructor parameter like: class A{ public A(Dependency1 d1, Dependency2 d2, ...){} } I usually create a "argument holder"-type of class like: class AArgs{ public Dependency1 d1 { get; private set; } public Dependency2 d2 { get; private set; } ... } and then: class A{ public A(AArgs args){} } Typically, using a DI-container I can configure the constructor for dependencies & resolve them & so there is minimum impact when the constructors need to change. Is this considered an anti-pattern and/or any arguments against doing this?

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  • Ruby: Streaming large AWS S3 object freezes

    - by Peter
    Hi, I am using the ruby aws/s3 library to retrieve files from Amazon S3. I stream an object and write it to file as per the documentation (with debug every 100 chunks to confirm progress) This works for small files, but randomly freezes downloading large (150MB) files on VPS Ubuntu. Fetching the same files (150MB) from my mac on a much slower connection works just fine. When it hangs there is no error thrown and the last line of debug output is the 'Finished chunk'. I've seen it write between 100 and 10,000 chunks before freezing. Anyone come across this or have ideas on what the cause might be? Thanks The code that hangs: i=1 open(local_file, 'w') do |f| AWS::S3::S3Object.value(key, @s3_bucket) do |chunk| puts("Writing chunk #{i}") f.write chunk.read_body puts("Finished chunk #{i}") i=i+1 end end

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  • Read options from file

    - by Devel
    I would like to write a function which will read values from a text file and write them to variables. For example my file is: mysql_server localhost mysql_user root mysql_passworg pospaz mysql_database testgenerator log log.txt username admin password abcd and I have the same variables as the first word in the line. So how to make the function read data from file and do sth like this: char *mysql_server = localhost; char *mysql_user = root; ... I have no idea even how to start writing it...

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  • Can I get parameter names/values procedurally from the currently executing function?

    - by Pwninstein
    I would like to do something like this: public MyFunction(int integerParameter, string stringParameter){ //Do this: LogParameters(); //Instead of this: //Log.Debug("integerParameter: " + integerParameter + // ", stringParameter: " + stringParameter); } public LogParameters(){ //Look up 1 level in the call stack (if possible), //Programmatically loop through the function's parameters/values //and log them to a file (with the function name as well). //If I can pass a MethodInfo instead of analyzing the call stack, great. } I'm not even sure what I want to do is possible, but it would be very nice to be able to automatically output parameter names/values at runtime to a file without explicitly writing the code to log them. Thanks!

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  • Calculate time taken by each cpp file to compile in VS2005?

    - by Rajiv Podar
    Hi Guys, I am writing a tool which can be used to make the matrix for the current performance of the project. For that I required to get the time taken by each file to get compiled. I tried with the following option but didn't succeed :( Tools-Options-Proejcts & Solutions - VC++ Project Settings - Build Timing- Yes From the above option I am able to get the whole time taken to build the solution but my problem is to get for each one. I am using VS2005 So anyone is having any idea then pls revert back ASAP....

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  • How to check for a file's authenticity ?

    - by Ale_x
    Let's say I write a game application. I want the level of the player to be stored in an external file. How can I prevent a hacker from writing and modifying the file to put another level ? I want the file to be modified by my application only. I can sign the file's content with a key, but then this key will be stored in the application, therefore it would be possible for a hacker to decompile the binary and find the key. Is there any way to do this ?

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  • Have my UIPickerView having the same behavior than the keyboard.

    - by camilo
    Hi. So I have a UITableView where one of its rows is a UITextView. When the user is writing something to UITextView (using the keyboard) the user can scroll the tableview and select another cell. Everything works. When the user selects another cell, a datePicker appears, and the user can select a given date. I want the user to be able to scroll the tableView the same way like when the keyboard is on the screen. The problem here is that when I scroll with the picker, the table bounces back to the previous position (with some cells hidden by the picker). I assume that this happens because I add the picker to the main window, as a subview... but I'm honestly not sure... Where (and how) should I add my picker so that it "appears" where the keyboard appears? Not sure I was clear... Thanks a lot.

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  • Delete files in C# that windows does not want me to delete?

    - by user315881
    At my company, we are writing a script to take care of simple tasks that we usually would do by hand. I am using c# to delete profiles in c:\documents and settings\, except a few. These will simply be left alone. The problem is that even with code that sets the files to normal and marks the admin user as an owner, they won't delete. They say that the quick launch folder has access denied. I am using a recursive permissions change method and I know that it works. Same thing with file attributes. Why won't it work? How do I fix this?

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  • Best approach to store username & password

    - by Zerotoinfinite
    Hi All, I have created a site in asp.net 3.5 & my query is this that I have only 2 or 3 login Id (user) who can login to my website, then what would be the better way to save the login details. What I know I am writing below, please let me know which would be the correct approach to achieve this also if their is any nice approach to get this done: 1: to save username and password in web.config file 2: to create a text file in directory and modify it 3: To use form authentication Please let me know the approach I can use to solve it. thanks in advance P.S. : I have to create only 2-3 users, or in future may be 1-2 more, that's it.

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  • Methods of sending web-generated config files to servers and restarting services.

    - by JPG
    Hi, We're writing a web-based tool to configure our services provided by multiple servers. This includes interfaces configuration, dhcp configs etc. etc. Having configs in database and views that generate proper output, how to send it/make it available for servers? I'm thinking about sending it through scp and invoking reload command to services through ssh. I'm also thinking about using Func to do all the job, as this is Python tool and will seemingly integrate with python-based (django) config tool. Any other proposals?

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  • Why can't i call Contains method from my array?

    - by xbnevan
    Arrrg!I am running into what i feel is a dumb issue with a simple script i'm writing in powershell. I am invoking a sql command that is calling a stored proc, with the results i put it a array. The results look something like this: Status ProcessStartTime ProcessEndTime ------ ---------------- -------------- Expired May 22 2010 8:31PM May 22 2010 8:32PM What i'm trying to do is if($s.Contains("Expired")) , report failed. Simple...? :( Problem i'm running into is it looks like Contains method is not being loaded as i get an error like this: Method invocation failed because [System.Object[]] doesn't contain a method named 'Contains'. At line:1 char:12 + $s.Contains <<<< ("Expired") + CategoryInfo : InvalidOperation: (Contains:String) [], RuntimeException + FullyQualifiedErrorId : MethodNotFound So, what can i do to stop powershell from unrolling it to string? Actual ps script below - $s = @(Invoke-Sqlcmd -Query "USE DB GO exec Monitor_TEST_ps 'EXPORT_RUN',NULL,20 " ` -ServerInstance "testdb002\testdb_002") if ($s.Contains("Expired")) { Write-Host "Expired found, FAIL." } else { Write-Host "Not found, OK." }

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  • Design cache mechanism

    - by Delashmate
    Hi All, I got assignment to write design for cache mechanism, This is my first time writing a design document, Our program display images for doctors, and we wan't to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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  • Constructors in Inner classes (implementing Interfaces)

    - by thepandaatemyface
    Hi, How would I go about writing a constructor for an inner class which is implementing an interface? I know I could make a whole new class, but I figure there's got to be a way to do something along the line of this: JButton b = new JButton(new AbstractAction() { public AbstractAction() { super("This is a button"); } public void actionPerformed(ActionEvent e) { System.out.println("button clicked"); } }); When I enter this it doesn't recognize the AbstractAction method as a constructor (compiler asks for return type). Anyone have an idea? Thanks

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  • How to switch data pins on/off on parallel port?

    - by Matt
    I want to simply switch certain data pins on and off, so that they can control a set of relays. I'm not asking about the hardware bit (should be easy), but I don't know where to begin writing the software. I don't want a high level library that can send bytes to a device - I literally want to switch on/off certain pins. I'm running Linux and I want to do this in Java, so would I just need a library? It would be nice if the library has good documentation and is easy to use, but if not then a short example code will help me get started.

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  • Silently binding a variable instance to a class in C++?

    - by gct
    So I've got a plugin-based system I'm writing. Users can create a child class of a Plugin class and then it will be loaded at runtime and integrated with the rest of the system. When a Plugin is run from the system, it's run in the context of a group of plugins, which I call a Session. My problem is that inside the user plugins, two streaming classes called pf_ostream and pf_istream can be used to read/write data to the system. I'd like to bind the plugin instance's session variable to pf_ostream and pf_istream somehow so that when the user instantiates those classes, it's already bound to the session for them (basically I don't want them to see the session internals) I could just do this with a macro, wrapping a call to the constructor like: #define MAKE_OSTREAM = pf_ostream_int(this->session) But I thought there might be a better way. I looked at using a nested class inside Plugin wrapping pf_ostream but it appears nested classes don't get access to the enclosing classes variables in a closure sort of way. Does anyone know of a neat way to do this?

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  • Speedup C++ code

    - by Werner
    Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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  • how to sort an existing table in greasemonkey ?

    - by user570512
    i'm writing a greasemonkey user.js for a page with a table in it. (table is 100 rows by 18 columns.) now what i want to do is to make it sortable on column. and also have it run in both chrome and firefox. all searches for answers sofar resulted in suggestions to use jquery/dojo or something alike. can i be done without any external code? after all it's just a matter of replacing the row's in a different order, right? or is that a silly thing to say? the thing is that i'm already using dojo for some query needs but since i want it to run in both firefox and chrome, i just copy paste the whole dojo thing in my script.. also, most of the solutions i found sofar seem to be more for use when building a table. not for altering an existing one. any help is appreciated.

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  • What's some simple F# code that generates the .tail IL instruction?

    - by kld2010
    I'd like to see the .tail IL instruction, but the simple recursive functions using tail calls that I've been writing are apparently optimized into loops. I'm actually guessing on this, as I'm not entirely sure what a loop looks like in Reflector. I definitely don't see any .tail opcodes though. I have "Generate tail calls" checked in my project's properties. I've also tried both Debug and Release builds in Reflector. The code I used is from Programming F# by Chris Smith, page 190: let factorial x = // Keep track of both x and an accumulator value (acc) let rec tailRecursiveFactorial x acc = if x <= 1 then acc else tailRecursiveFactorial (x - 1) (acc * x) tailRecursiveFactorial x 1 Can anyone suggest some simple F# code which will indeed generate .tail?

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  • Rails: What's the suggested approach to retrieve xml from an outside source

    - by Syrahn
    Rails newbie (though long time programmer) here. I'm writing an test app that retrieves data from several outside sources (think Twitter, RSS feeds, etc.) and under certain circumstances, it stores that data in a db (or presents it to the user). The data model and the views are trivial. What I'm having difficulty with is making the actual xml HTTP call to the outside source and deserialize the xml response so I can query/use it in my controller/helper. What library/gem should I use to accomplish this? I tried looking this up around the net, but only came up with some article from 2006 which, knowing how fast Rails has developed, might well be completely deprecated. Your help is much appreciated.

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  • C++ operator[] syntax.

    - by Lanissum
    Just a quick syntax question. I'm writing a map class (for school). If I define the following operator overload: template<typename Key, typename Val> class Map {... Val* operator[](Key k); What happens when a user writes: Map<int,int> myMap; map[10] = 3; Doing something like that will only overwrite a temporary copy of the [null] pointer at Key k. Is it even possible to do: map[10] = 3; printf("%i\n", map[10]); with the same operator overload?

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