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  • Why not allow mutation of the this binding?

    - by gnucom
    Hi Everyone, I'm building a interpreter/compiler for a school project (well now its turning into a hobby project) and an instructor warned me not to allow mutation of the 'this' binding (he said it was gross and made a huge deal about it) but I never learned why this is so... dangerous or bad. I'm very curious about why this is so bad. I figured this sort of feature could be useful in some way or another. I'm wondering if anyone familiar with building languages can tell me what sort of problems mutation on the 'this' binding can cause, and if they know of any cool or useful tricks that one could do if it actually was allowed. Do any languages that you're aware of allow mutation of 'this'? Thanks,

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  • accelerating Wheel - psychtoolbox in matlab

    - by ariel
    Hi I am trying to write a code that will show an acceleration wheel. as long as the user press 'a' the wheel should accelerate counterclock wize. the thing is that it turn in the right direction but it doesn't accelerate. This is the code I am using . PTB-3 windows XP. img=imread('c:\images.jpg'); [yimg,ximg,z]=size(img); rot_spd = 1; larrow = KbName('a'); % modify this for Windows rarrow = KbName('b'); [w,rect]=Screen('OpenWindow',0,[0 0 0]); sx = 400; % desired x-size of image (pixels) sy = yimg*sx/ximg; % desired y-size--keep proportional t = Screen('MakeTexture',w,img); bdown=0; th = 0; % initial rotation angle (degrees) HideCursor while(~any(bdown)) % exit loop if mouse button is pressed [x,y,bdown]=GetMouse; [keyisdown,secs,keycode] = KbCheck; if(keycode(larrow)) th = th - rot_spd-1; % accelerate counterclockwise th end if(keycode(rarrow)) th = th + rot_spd+1; % accelerate clockwise th end destrect=[x-sx/2,y-sy/2,x+sx/2,y+sy/2]; Screen('DrawTexture',w,t,[],destrect,th); Screen('Flip',w); end Screen('Close',w) ShowCursor If anyone has an odea why it doesn't accelerate I'd appriciate it very much. Ariel

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  • Linux Kernel - Red/Black Trees

    - by CodeRanger
    I'm trying to implement a red/black tree in Linux per task_struct using code from linux/rbtree.h. I can get a red/black tree inserting properly in a standalone space in the kernel such as a module but when I try to get the same code to function with the rb_root declared in either task_struct or task_struct-files_struct, I get a SEGFAULT everytime I try an insert. Here's some code: In task_struct I create a rb_root struct for my tree (not a pointer). In init_task.h, macro INIT_TASK(tsk), I set this equal to RB_ROOT. To do an insert, I use this code: rb_insert(&(current-fd_tree), &rbnode); This is where the issue occurs. My insert command is the standard insert that is documented in all RBTree documentation for the kernel: int my_insert(struct rb_root *root, struct mytype *data) { struct rb_node **new = &(root->rb_node), *parent = NULL; /* Figure out where to put new node */ while (*new) { struct mytype *this = container_of(*new, struct mytype, node); int result = strcmp(data->keystring, this->keystring); parent = *new; if (result < 0) new = &((*new)->rb_left); else if (result > 0) new = &((*new)->rb_right); else return FALSE; } /* Add new node and rebalance tree. */ rb_link_node(&data->node, parent, new); rb_insert_color(&data->node, root); return TRUE; } Is there something I'm missing? Some reason this would work fine if I made a tree root outside of task_struct? If I make rb_root inside of a module this insert works fine. But once I put the actual tree root in the task_struct or even in the task_struct-files_struct, I get a SEGFAULT. Can a root node not be added in these structs? Any tips are greatly appreciated. I've tried nearly everything I can think of.

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  • Timing the Linux Kernel boot-time optimisation

    - by CVS-2600Hertz-wordpress-com
    I am trying to optimise the boot-up time of linux on an embedded device (not PC) Currently to profile the boot-up sequence, I have enabled the timing info on printk logs. Is this the most optimum way? If not, how do i profile the boot-up sequence (with timing) with minimum overhead? PS: I have a terminal (of the device) over a serial-connection & I use TeraTerm over windows-XP to access it.

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  • Reference for proper handling of PID file on Unix

    - by bignose
    Where can I find a well-respected reference that details the proper handling of PID files on Unix? On Unix operating systems, it is common practice to “lock” a program (often a daemon) by use of a special lock file: the PID file. This is a file in a predictable location, often ‘/var/run/foo.pid’. The program is supposed to check when it starts up whether the PID file exists and, if the file does exist, exit with an error. So it's a kind of advisory, collaborative locking mechanism. The file contains a single line of text, being the numeric process ID (hence the name “PID file”) of the process that currently holds the lock; this allows an easy way to automate sending a signal to the process that holds the lock. What I can't find is a good reference on expected or “best practice” behaviour for handling PID files. There are various nuances: how to actually lock the file (don't bother? use the kernel? what about platform incompatibilities?), handling stale locks (silently delete them? when to check?), when exactly to acquire and release the lock, and so forth. Where can I find a respected, most-authoritative reference (ideally on the level of W. Richard Stevens) for this small topic?

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  • Orientation change event in Browser on Palm webOS

    - by organicveggie
    I'm working on a web application where I'm trying to capture when the user rotates the screen. Fundamentally, I want to know if the user is browsing in portrait mode or landscape mode. The iPhone/iPad and Android browsers send a resize event when the screen orientation changes. Unfortunately, the browser in webOS doesn't seem to send that notification. Any advice on how to detect in the browser any changes in orientation on Palm webOS? Thanks.

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  • Bad File descriptor

    - by Luke
    Does anyone see a problem with this, its not working saying bad file descriptor not sure why? pipe(pipefd[0]); if ((opid = fork()) == 0) { dup2(pipefd[0][1],1);/*send to output*/ close(pipefd[0][0]); close(pipefd[0][1]); execlp("ls","ls","-al",NULL); } if((cpid = fork())==0){ dup2(pipefd[0][1],0);/*read from input*/ close(pipefd[0][0]); close(pipefd[1][1]); execlp("grep","grep",".bak",NULL); } close(pipefd[0][0]); close(pipefd[0][1]);

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  • What language has the longest "Hello world" program?

    - by Kip
    In most scripting languages, a "Hello world!" application is very short: print "Hello world" In C++, it is a little more complicated, requiring at least 46 non-whitespace characters: #include <cstdio> int main() { puts("Hello world"); } Java, at 75 non-whitespace characters, is even more verbose: class A { public static void main(String[] args) { System.out.print("Hello world"); } } Are there any languages that require even more non-whitespace characters than Java? Which language requires the most? Notes: I'm asking about the length of the shortest possible "hello world" application in a given language. A newline after "Hello world" is not required. I'm not counting whitespace, but I know there is some language that uses only whitespace characters. If you use that one you can count the whitespace characters.

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  • Cartesian product in Scheme

    - by John Retallack
    I've been trying to do a function that returns the Cartesian Product of n sets,in Dr Scheme,the sets are given as a list of lists,I've been stuck at this all day,I would like a few guidelines as where to start,I've wrote a pice of code but it dosen't work. (define cart-n(?(l) (if (null? l) '(()) (map (?(lst) (cons (car ( car(l))) lst)) (cart-n (cdr l) )))))

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  • Forking with Pipes

    - by Luke
    Hello I have tried to do fork() and piping in main and it works perfectly fine but when I try to implement it in a function for some reason I don't get any output, this is my code: void cmd(int **pipefd,int count,int type, int last); int main(int argc, char *argv[]) { int pipefd[3][2]; int i, total_cmds = 3,count = 0; int in = 1; for(i = 0; i < total_cmds;i++){ pipe(pipefd[count++]); cmd(pipefd,count,i,0); } /*Last Command*/ cmd(pipefd,count,i,1); exit(EXIT_SUCCESS); } void cmd(int **pipefd,int count,int type, int last){ int child_pid,i,i2; if ((child_pid = fork()) == 0) { if(count == 1){ dup2(pipefd[count-1][1],1); /*first command*/ } else if(last!=0){ dup2(pipefd[count - 2][0],0); /*middle commands*/ dup2(pipefd[count - 1][1],1); } else if(last == 1){ dup2(pipefd[count - 1][0],0); /*last command*/ } for(i = 0; i < count;i++){/*close pipes*/ for(i2 = 0; i2 < 2;i2++){ close(pipefd[i][i2]); }} if(type == 0){ execlp("ls","ls","-al",NULL); } else if(type == 1){ execlp("grep","grep",".bak",NULL); } else if(type==2){ execl("/usr/bin/wc","wc",NULL); } else if(type ==3){ execl("/usr/bin/wc","wc","-l",NULL); } perror("exec"); exit(EXIT_FAILURE); } else if (child_pid < 0) { perror("fork"); exit(EXIT_FAILURE); } } I checked the file descriptors and it is opening the right ones, not sure what the problem could be..

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  • Data Transfer Objects VS Domain/ActiveRecord Entities in the View in RoR

    - by leypascua
    I'm coming from a .NET background, where it is a practice to not bind domain/entity models directly to the view in not-so-basic CRUD-ish applications where the view does not directly project entity fields as-is. I'm wondering what's the practice in RoR, where the default persistence mechanism is ActiveRecord. I would assert that presentation-related info should not be leaked to the entities, not sure though if this is how real RoR heads would do it. If DTOs/model per view is the approach, how will you do it in Rails? Your thoughts? EDIT: Some examples: - A view shows a list of invoices, with the number of unique items in one column. - A list of credit card accounts, where possibly fraudulent transactions were executed. For that, the UI needs to show this row in red. For both scenarios, The lists don't show all of the fields of the entities, just a few to show in the list (like invoice #, transaction date, name of the account, the amount of the transaction) For the invoice example, The invoice entity doesn't have a field "No. of line items" mapped on it. The database has not been denormalized for perf reasons and it will be computed during query time using aggregate functions. For the credit card accounts example, surely the card transaction entity doesn't have a "Show-in-red" or "IsFraudulent" invariant. Yes it may be a business rule, but for this example, that is a presentation concern, so I would like to keep it out of my domain model.

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  • Filter items from a feed using words in a text file, with Yahoo Pipes

    - by pufferfish
    I have a pipe that filters an RSS feed and removes any item that contains "stopwords" that I've chosen. Currently I've manually created a filter for each stopword in the pipe editor, but the more logical way is to read these from a file. I've figured out how to read the stopwords out of the text file, but how do I apply the filter operator to the feed, once for every stopword? The documentation states explicitly that operators can't be applied within the loop construct, but hopefully I'm missing something here.

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  • Receiving broadcast messages

    - by Prasad
    Hi, I'm trying to receive broadcast messages using C# code in an ISDN network with BRI interface at my end. I see the packets sent to the broadcast ip address (239.255.255.255) on some ports using Comm View tool. But when I try to listen to this IP address, it says the address is not in a valid context. But when I send broadcast messages to 255.255.255.255 on a port, I can receive those messages with the below code.. What could be the problem with this ip address - 239.255.255.255 ? The code I use to listen to broadcast messages is.. UdpClient udp = new UdpClient(); IPEndPoint receiveEndPoint = new IPEndPoint(IPAddress.Any, 8013); // If I use IPAddress.Parse("239.255.255.255") to listen to, // it says "the address is not in a valid // context." udp.Client.Bind(receiveEndPoint); udp.BeginReceive(_Callback, udp); static private void _Callback(IAsyncResult iar) { try { UdpClient client = (UdpClient)iar.AsyncState; client.BeginReceive(_Callback, client); IPEndPoint ipRemote = new IPEndPoint(IPAddress.Any, 8013); byte[] rgb = client.EndReceive(iar, ref ipRemote); Console.WriteLine("Received {0} bytes: \"{1}\"", rgb.Length.ToString(), Encoding.UTF8.GetString(rgb)); } catch (ObjectDisposedException) { Console.WriteLine("closing listening socket"); } catch (Exception exc) { Console.WriteLine("Listening socket error: \"" + exc.Message + "\""); } } There are packets sent to the broadcast ipaddress (239.255.255.255) which I can see in Commview tool, but can't receive them from the code... Can anybody help me out please? Thanking you in advance, Prasad Kancharla.

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  • NVIDIA CUDA SDK Examples Compilation Unsupported Architecture 'computer_20'

    - by Andrew Bolster
    On compilation of the CUDA SDK, I'm getting a nvcc fatal : Unsupported gpu architecture 'compute_20' My toolkit is 2.3 and on a shared system (i.e cant really upgrade) and the driver version is also 2.3, running on 4 Tesla C1060s If it helps, the problem is being called in radixsort. It appears that a few people online have had this problem but i havent found anywhere that actually gives a solution.

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  • Get Taskbar's Battery and PhoneSignal indicators icons and draw into a picturebox (C#/WindowsMobile)

    - by Christian Almeida
    Hi, Is there any way to get taskbar's battery and phonesignal indicators icons and then draw into a picturebox or something? Why do I need this? I need all screen space available, so all forms are maximized and they cover up the windowsmobile taskbar. But, I have to display information about battery e phone signal strength in just a couple of forms. I know how to get their values (like systeminformation.phonesignalstrength), but what I want is the "current icon", so I don't need to worry about their values. It's just a visual information for the user. In last case, if this is not possible, how to get those icons from windowsmobile shell, so I'll draw them by my self, treating each differente status/values that they assume. (This is what I don't want to do!) Thanks in advance and sorry for my poor english.

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  • Auto switching databases from a rails app gracefully from the ApplicationController?

    - by Zaqintosh
    I've seen this post a few times, but haven't really found the answer to this specific question. I'd like to run a rails application that based on the detected request.host (imagine I have two subdomains points to the same rails app and server ip address: myapp1.domain.com and myapp2.domain.com). I'm trying to have myapp1 use the default "production" database, and myapp2 requests always use the alternative remote database. Here is an example of what I tried to do in Application controller that did not work: class ApplicationController < ActionController::Base helper :all before_filter :use_alternate_db private def use_alternate_db if request.host == 'myapp1.domain.com' regular_db elsif request.host == 'myapp2.domain.com' alternate_db end end def regular_db ActiveRecord::Base.establish_connection :production end def alternate_db ActiveRecord::Base.establish_connection( :adapter => 'mysql', :host => '...', :username => '...', :password => '...', :database => 'alternatedb' ) end end The problem is when it switches databases using this method, all connections (including valid sessions across the different subdomains get interrupted...). All examples online have people controlling database connectivity at the model level, but this would involve adding code all over my application. Is there some way to globally switch database connections on a per-request basis in the manner I'm suggesting above WITHOUT having to inject code all over my application? The added complexity here is I'm using Heroku as a hosting provider, so I have no control at the apache / rails application server level. I have looked at solutions like dbcharmer and magicmodels, but none seem to show examples of doing it in the manner that I'm trying to. Thanks for any help!

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  • How do I trap the ENTER key in WM 6.1 using C++

    - by Rob King
    Hi,Our barcode scanner application is written in C++ eMbedded V 4.00 and works well on the Motorola MC50 WM5 where the ENTER key is interpreted as an IDOK. We are moving the app to the MC55 with WM6.1 and the ENTER key does not translate to an IDOK. I'm of the impression we will have to programatically trap the key entry (or the value passed on via DataWedge). I have made several attempts to implement either a HOTKEY or something via an Accelerator Table but have been unable to interpret the Microsoft on-line descriptions. If there is a simpler answer that would be good news. If not, a more specific example than the MS samples would be greatly appreciated. Thanks in advance.

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  • Enable real fixed positioning on Samsung Android browsers

    - by Mr. Shiny and New ??
    The Android browser, since 2.2, supports fixed positioning, at least under certain circumstances such as when scaling is turned off. I have a simple HTML file with no JS, but the fixed positioning on three Samsung phones I've tried is simply wrong. Instead of true fixed positioning, the header scrolls out of view then pops back into place after the scrolling is done. This doesn't happen on the Android SDK emulator for any configuration I've tested (2.2, 2.3, 2.3 x86, 4.0.4). It also doesn't happen when using the WebView in an app on the Samsung phones: in those cases the positioning works as expected. Is there a way to make the Samsung Android "stock" browser use real fixed positioning? I've tested: 1. Samsung Galaxy 551, Android 2.2 2. Samsung Galaxy S, Android 2.3 3. Samsung Galaxy S II, Android 2.3 Sample code: <html> <head> <meta name="viewport" content="initial-scale=1.0,maximum-scale=1.0,user-scalable=no,width=device-width,height=device-height"> <style> h1 { position: fixed; top: 0; left: 0; height: 32px; background-color: #CDCDCD; color: black; font-size: 32px; line-height: 32px; padding: 2px; width: 100%; margin: 0;} p { margin-top: 36px; } </style> </head> <body> <h1>Header</h1> <p>Long text goes here</p> </body> </html> The expected behaviour is that the grey header fills the top of the screen and stays put no matter how much you scroll. On Samsung Android browsers it seems to scroll out of view then pop back into place once the scrolling is done, as if the fixed-positioning is being simulated using Javascript, which it isn't. Edit Judging by the comments and "answers" it seems that maybe I wasn't clear on what I need. I am looking for a meta tag or css rule/hack or javascript toggle which turns off Samsung's broken fixed-positioning and turns on the Android browser's working fixed-positioning. I am not looking for a Javascript solution that adds broken fixed-positioning to a browser that has no support whatsoever; the Samsung fixed-positioning does that already, it just looks stupid.

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  • Pocket IE has some maximum width for textboxes?

    - by eidylon
    I have a page running on WinMo 6.1 Pocket IE. It seems I cannot make a textbox wider than 219 pixels, is this the case? I've tried width="100%" width="300px" style="width: 100%;" style="width: 300px;" columns="50" but no matter what I do, the textbox will not grow beyond 219 pixels wide, which looks kinda dorky on a 320x screen. Does pIE really limit the width of a textbox???

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  • touchesBegin & touchesMove Xcode Obj C Question

    - by AndrewDK
    So I have my app working good when you press and drag along. I also have UIButtons set to Touch Down in Interface Builder. As well when you drag you need to drag from the outside of the UIButton. You cannot click on the UIButton and drag to the other. TOUCHES MOVED: Code: -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [[event touchesForView:self.view] anyObject]; CGPoint location = [touch locationInView:touch.view]; if(CGRectContainsPoint(oneButton.frame, location)) { if (!oneButton.isHighlighted){ [self oneFunction]; [oneButton setHighlighted:YES]; } }else { [oneButton setHighlighted:NO]; } // if(CGRectContainsPoint(twoButton.frame, location)) { if (!twoButton.isHighlighted){ [self twoFunction]; [twoButton setHighlighted:YES]; } }else { [twoButton setHighlighted:NO]; } } TOUCHES BEGAN: Code: - (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [[event touchesForView:self.view] anyObject]; CGPoint location = [touch locationInView:touch.view]; if(CGRectContainsPoint(oneButton.frame, location)) { [self oneFunction]; [oneButton setHighlighted:YES]; } if(CGRectContainsPoint(twoButton.frame, location)) { [self twoFunction]; [twoButton setHighlighted:YES]; } } I want to be able to click on any of the button fire the function & also be able to drag from one button on to the other and fire that function. So basically just being able to click on a button and slide your finger over and activate the other button without having to press and slide from outside of the button. I think I'm close, need a bit of help. Hope thats clear enough. Thanks.

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  • Managing Cisco programatically; Telnet vs SNMP?

    - by MikeHerrera
    I was recently approached by a network-engineer, co-worker who would like to offload his minor network admin duties to a junior-level helpdesk tech. The specific location in need of management acts as an ISP for tenants on its single-site property, so there's a lot of small adjustments being made on a daily basis. I am thinking it would be helpful to write him a winform app to manage the 32 Cisco devices, on-site. I'd like to initially provide functionality which could modify access control lists, port VLAN assignments, and bandwidth limitations per VLAN... adding more to the list as its deemed valuable. My initial thought was to emulate a telnet session with the network device; utilizing my network-engineer's familiarity with the command-line / IOS interaction. Minimal time would be required to learn Cisco IOS conventions, myself. Though while searching for solutions, it appears that most people favor SNMP. That, or, their specific circumstances pushed them in the direction of SNMP. I wanted to know if I've overlooked an obvious benefit of SNMP. Should I be using SNMP? Why or why not?

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  • What are your recommended tools and frameworks for network development on Linux?

    - by Vivek Sharma
    What are your favourite network-tools, which you use to troubleshoot or design (as in conceptualize) your network-application code. Ethereal/Wireshark Nmap any particular simulators (e.g. ns) any special purpose sniffer any particular frameworks, (e.g. iptables) I am looking at must have, and good/advantage to have tools/framework in ones profile/skill set. I think Wireshark and Nmap are must haves.

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