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  • What is optimal hardware configuration for heavy load LAMP application

    - by Piotr Kochanski
    I need to run Linux-Apache-PHP-MySQL application (Moodle e-learning platform) for a large number of concurrent users - I am aiming 5000 users. By concurrent I mean that 5000 people should be able to work with the application at the same time. "Work" means not only do database reads but writes as well. The application is not very typical, since it is doing a lot of inserts/updates on the database, so caching techniques are not helping to much. We are using InnoDB storage engine. In addition application is not written with performance in mind. For instance one Apache thread usually occupies about 30-50 MB of RAM. I would be greatful for information what hardware is needed to build scalable configuration that is able to handle this kind of load. We are using right now two HP DLG 380 with two 4 core processors which are able to handle much lower load (typically 300-500 concurrent users). Is it reasonable to invest in this kind of boxes and build cluster using them or is it better to go with some more high-end hardware? I am particularly curious how many and how powerful servers are needed (number of processors/cores, size of RAM) what network equipment should be used (what kind of switches, network cards) any other hardware, like particular disc storage solutions, etc, that are needed Another thing is how to put together everything, that is what is the most optimal architecture. Clustering with MySQL is rather hard (people are complaining about MySQL Cluster, even here on Stackoverflow).

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  • Readonly SiteMapNodes in ASP.Net MVC?

    - by BenN
    I'm using MVCSiteMap as a SiteMapProvider for my MVC site. I have a node set up like so.... <mvcSiteMapNode key="1" title="Product" controller="Product" action="Display" isDynamic="true" dynamicParameters="id"> <mvcSiteMapNode key="11" title="More Details" controller="Product" action="MoreDetails" isDynamic="true" dynamicParameters="id" /> </mvcSiteMapNode> ...Which means I can go to ~/Product/Display/12 and get a correct sitemap node for product id 12 (in this case just Product. And I can go to ~/Product/MoreDetails/12 and get the sitemap path for the MoreDetails (Product - More Details). The problem is that the link back to Product in this sitemap doesn't work - it skips the id off the end, instead linking to ~/Product/Display/. Which sucks. I've discovered I can edit the Title of a node using SiteMap.CurrentNode.Title = "My New Title"; But... SiteMap.CurrentNode.ParentNode.Url = "http://www.google.com"; Doesn't set the Url for the parent node; it gets the default link described before. Any ideas how I can set the URL of a SiteMapNode?

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  • How do I make the following interaction with mySQL more efficient?

    - by Travis
    I've got an array that contains combinations of unique MySql IDs: For example: [ [1,10,11], [2,10], [3,10,12], [3,12,13,20], [4,12] ] In total there are a couple hundred different combinations of IDs. Some of these combinations are "valid" and some are not. For example, [1,10,11] may be a valid combination, whereas [3,10,12] may be invalid. Combinations are valid or invalid depending on how the data is arranged in the database. Currently I am using a SELECT statement to determine whether or not a specific combination of IDs is valid. It looks something like this: SELECT id1 FROM table WHERE id2 IN ($combination) GROUP BY id1 HAVING COUNT(distinct id2) = $number ...where $combination is one possible combination of IDs (eg 1,10,11) and $number is the number of IDs in that combination (in this case, 3). An invalid combination will return 0 rows. A valid combination will return 1 or more rows. However, to solve the entire set of possible combinations means looping a couple hundred SELECT statements, which I would rather not be doing. I am wondering: Are there any tricks for making this more efficient? Is it possible to submit the entire dataset to mySQL in one go, and have mySQL iterate through it? Any suggestions would be much appreciated. Thanks in advance!

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  • My 3D object (opengl es) is disappearing behind the iPhone camera view

    - by KLC
    I have an augmented reality iPhone app that I am converting from Core Animation to OpenGL ES 1.1. I have added code that has been modified from the Apple OpenGL template. My problem is that my 3D object , when translating along the negative Z-axis (away from the user), appears to disappear into the camera view, until its completely gone. I have experimented with several solutions, but to no avail. What I have determined: Using the 3D icosahedron from Jeff Lamarche's blog here, the object starts it at 0,0,0 and then translates with decreasing z coordinates. By the time the z value reaches -2.0f, the object is gone. It appears as if it is disappearing behind the camera view. This is how I set my frustrum & viewport (unchanged from Apple's code) glMatrixMode(GL_PROJECTION); size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0); //Grab the size of the screen CGRect rect = self.bounds; glFrustumf(-size, size, -size / (rect.size.width / rect.size.height), size / (rect.size.width / rect.size.height), zNear, zFar); glViewport(0, 0, rect.size.width, rect.size.height); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); What I have tried: The camera view is the main view and several other views are added to it as subviews, including the openGLView. I have commented those views out for test purposes. I have applied CATransforms to move the openGLView in the z direction -500 and +500, and done the same to the camera view. I have also changed the zFar in the above code to 1.0f, and it still disappears at z position of -2.0, which doesn't make sense (shouldn't it disappear at z=1.0?) My experimentation has got me more confused than when I started ( which usually means I am missing a key piece, but I can't figure out what). Thanks for your help.

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  • How can I extract a string between matching braces in Perl?

    - by Srilesh
    My input file is as below : HEADER {ABC|*|DEF {GHI 0 1 0} {{Points {}}}} {ABC|*|DEF {GHI 0 2 0} {{Points {}}}} {ABC|*|XYZ:abc:def {GHI 0 22 0} {{Points {{F1 1.1} {F2 1.2} {F3 1.3} {F4 1.4}}}}} {ABC|*|XYZ:ghi:jkl {JKL 0 372 0} {{Points {}}}} {ABC|*|XYZ:mno:pqr {GHI 0 34 0} {{Points {}}}} { ABC|*|XYZ:abc:pqr {GHI 0 68 0} {{Points {{F1 11.11} {F2 12.10} {F3 14.11} {F4 16.23}}}} } TRAILER I want to extract the file into an array as below : $array[0] = "{ABC|*|DEF {GHI 0 1 0} {{Points {}}}}" $array[1] = "{ABC|*|DEF {GHI 0 2 0} {{Points {}}}}" $array[2] = "{ABC|*|XYZ:abc:def {GHI 0 22 0} {{Points {{F1 1.1} {F2 1.2} {F3 1.3} {F4 1.4}}}}}" .. .. $array[5] = "{ ABC|*|XYZ:abc:pqr {GHI 0 68 0} {{Points {{F1 11.11} {F2 12.10} {F3 14.11} {F4 16.23}}}} }" Which means, I need to match the first opening curly brace with its closing curly brace and extract the string in between. I have checked the below link, but this doesnt apply to my question. http://stackoverflow.com/questions/413071/regex-to-get-string-between-curly-braces-i-want-whats-between-the-curly-braces I am trying but would really help if someone can assist me with their expertise ... Thanks Sri ...

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  • Free Memory Occupied by Std List, Vector, Map etc

    - by Graviton
    Coming from a C# background, I have only vaguest idea on memory management on C++-- all I know is that I would have to free the memory manually. As a result my C++ code is written in such a way that objects of the type std::vector, std::list, std::map are freely instantiated, used, but not freed. I didn't realize this point until I am almost done with my programs, now my code is consisted of the following kinds of patterns: struct Point_2 { double x; double y; }; struct Point_3 { double x; double y; double z; }; list<list<Point_2>> Computation::ComputationJob(list<Point_3> pts3D, vector<Point_2> vectors) { map<Point_2, double> pt2DMap=ConstructPointMap(pts3D); vector<Point_2> vectorList = ConstructVectors(vectors); list<list<Point_2>> faceList2D=ConstructPoints(vectorList , pt2DMap); return faceList2D; } My question is, must I free every.single.one of the list usage ( in the above example, this means that I would have to free pt2DMap, vectorList and faceList2D)? That would be very tedious! I might just as well rewrite my Computation class so that it is less prone to memory leak. Any idea how to fix this?

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  • Where can I find a list of all possible messages that an XmlException can contain?

    - by Rahul
    I'm writing an XML code editor and I want to display syntax errors in the user interface. Because my code editor is strongly constrained to a particular problem domain and audience, I want to rewrite certain XMLException messages to be more meaningful for users. For instance, an exception message like this: '"' is an unexpected token. The expected token is '='. Line 30, position 35 .. is very technical and not very informative to my audience. Instead, I'd like to rewrite it and other messages to something else. For completeness' sake that means I need to build up a dictionary of existing messages mapped to the new message I would like to display instead. To accomplish that I'm going to need a list of all possible messages XMLException can contain. Is there such a list somewhere? Or can I find out the possible messages through inspection of objects in C#? Edit: specifically, I am using XmlDocument.LoadXml to parse a string into an XmlDocument, and that method throws an XmlException when there are syntax errors. So specifically, my question is where I can find a list of messages applied to XmlException by XmlDocument.LoadXml. The discussion about there potentially being a limitless variation of actual strings in the Message property of XmlException is moot.

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  • error on connecting to the server : socket io is not defined

    - by max
    i know there's been couple of question about the same problem , i've already check them . i have very simple node.js chat app i have a server running on 8000 port and it works fine my client pages are html , they are running on apache and i'm using socket.io to connect them to the server and it works fine on the local host but when i upload the app on the server i keep on getting this error in the firebug io is not defined var socket = io.connect('http://atenak.com:8000/'); or sometimes it doesn't show that but when i try to broadcast message from cliend i get this error : socket is undefined socket.emit('msg', { data: msg , user:'max' }); the only difference is i've changed the localhost with atenak.com ! here is my html code var socket = io.connect('http://atenak.com:8000/'); var user = 'jack'; socket.on('newmsg', function (data) { if(data.user == user ) { $('#container').html(data.data); } }); function brodcast(){ var msg = $('#fild').val(); socket.emit('msg', { data: msg , user:'max' }); } </script> </head> <body> <div id="container"> </div> <input id="fild" type="text"> <input name="" type="button" onClick="brodcast();"> </body> i have included the sockt.io.js and server is running ok which means socket.io is installed on the server here is the live page http://atenak.com/client.html

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  • Rails rspec expects Admin::PostsController, which is there.

    - by berkes
    I have a file app/controllers/admin/posts_controller.rb class Admin::PostsController < ApplicationController layout 'admin' # GET /admin/posts def index @pposts = Post.paginate :page => params[:page], :order => 'created_at DESC' end # ...Many more standard CRUD/REST methods... end And an rspec test spec/controllers/admin/posts_controller_spec.rb require 'spec_helper' describe Admin::PostsController do describe "GET 'index'" do it "should be successful" do get 'index' response.should be_success end end #...many more test for all CRUD/REST methods end However, running that spec throws an error. I have no idea what that error means, nor how to start solving it. /home/...../active_support/dependencies.rb:492:in `load_missing_constant': Expected /home/...../app/controllers/admin/posts_controller.rb to define Admin::PostsController (LoadError) I may have it all set up wrong, or may be doing something really silly, but all I want is my CRUD actions on /admin, with separate before filters and a separate layout. And to test these controllers. EDIT ZOMG, made a terrible copy-paste error into this SO posting. The controller was PostsController, not the PagesController that I pasted into there. Problem still stands, as my code is correct, just the SO post, here was wrong.

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  • Is there a way to prevent Maven Test from rebuilding the database?

    - by Christopher W. Allen-Poole
    I've recently been asked to, effectively, sell my department on unit testing. I can't tell you how excited this makes me, but I do have one concern. We're using JUnit with Spring and Maven, and this means that each time mvn test is called, it rebuilds the database. Obviously, we can't integrate that with our production server -- it would kill valuable data. How do I prevent the rebuilding without telling maven to skip testing? The best I could figure was to assign the script to operate in a test database (line breaks added for readability): mvn test -Ddbunit.schema=<database>test -Djdbc.url=jdbc:mysql://localhost/<database>test? createDatabaseIfNotExist=true&amp; useUnicode=true&amp;characterEncoding=utf-8 I can't help but think there must be a better way. I'm especially interested in learning if there is an easy way to tell Maven to only run tests on particular classes without building anything else? mvn -Dtest=<test-name> test still rebuilds the database. ======= update ======= Bit of egg on my face here. I didn't realize that I was using the same variable in two places, meaning that the POM was using a "skip.test" variable for both rebuilding the database and for running the tests...

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  • How can we change views in a UISplitViewController other than using the popover and selecting?

    - by wolverine
    I have done a sample app with UISplitViewController studying the example they have provided. I have created three detailviews and have configured them to change by the default means. Either using the left/master view in landscape AND using the popover in the portrait orientation. Now I am trying to move to another view(previous/next) from the currentView by using left/right swipe in each view. For that, what I did was just created a function in the RootViewController. I copy-pasted the same code as that of the tablerow selection used by the popover from the RootViewController. I am calling this function from my current view's controller and is passing the respective index of the view(to be displayed next) from the current view. Function is being called but nothing is happening. Plz help me OR is anyother way to do it other than this complex step? I am giving the function that I used to change the view. - (void) rearrangeViews:(int)viewRow { UIViewController <SubstitutableDetailViewController> *detailViewController = nil; if (viewRow == 0) { DetailViewController *newDetailViewController = [[DetailViewController alloc] initWithNibName:@"DetailView" bundle:nil]; detailViewController = newDetailViewController; } if (viewRow == 1) { SecondDetailViewController *newDetailViewController = [[SecondDetailViewController alloc] initWithNibName:@"SecondDetailView" bundle:nil]; detailViewController = newDetailViewController; } if (viewRow == 2) { ThirdDetailViewController *newDetailViewController = [[ThirdDetailViewController alloc] initWithNibName:@"ThirdDetailView" bundle:nil]; detailViewController = newDetailViewController; } // Update the split view controller's view controllers array. NSArray *viewControllers = [[NSArray alloc] initWithObjects:self.navigationController, detailViewController, nil]; splitViewController.viewControllers = viewControllers; [viewControllers release]; if (rootPopoverButtonItem != nil) { [detailViewController showRootPopoverButtonItem:self.rootPopoverButtonItem]; } [detailViewController release]; }

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  • Registry remotley hacked win 7 need help tracking the perp

    - by user577229
    I was writing some .VBS code at thhe office that would allow certain file extensions to be downloaded without a warning dialog on a w7x32 system. The system I was writing this on is in a lab on a segmented subnet. All web access is via a proxy server. The only means of accessing my machine is via the internet or from within the labs MSFT AD domain. While writing and testing my code I found a message of sorts. Upon refresing the registry to verify my code changed a dword, instead the message HELLO was written and visible in regedit where the dword value wass called for. I took a screen shot and proceeded to edit my code. This same weird behavior occurred last time I was writing registry code except on another internal server. I understand that remote registry access exists for windows systems. I will block this immediately once I return to the office. What I want to know is, can I trace who made this connection? How would I do this? I suspect the cause of this is the cause of other "odd" behaviors I'm experiencing at work such as losing control of my input director master control for over an hour and unchanged code that all of a sudden fails for no logical region. These failures occur at funny times, whenver I'm about to give a demonstration of my test code. I know this sounds crazy however knowledge of the registry component makes this believable. Once the registry can be accessed, the entire system is compromised. Any help or sanity checking is appreciated.

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  • How do I render *parts* of a svg file?

    - by Fake Code Monkey Rashid
    Hello good people! :) I want to render parts of a svg file by name but for the life of me I cannot figure out how to do so (using python + gtk). Here's the svg file in question: http://david.bellot.free.fr/svg-cards/files/SVG-cards-2.0.1.tar.gz On his site, David, says: You can draw a card either by rendering the file onto a pixmap and clipping each card manually or by using the card's name through a DOM interface. All cards are embedded into a SVG group. I don't know what he means by a DOM interface. I have done some searching and the best result I found that seems to fit what I want to do is: QSvgRenderer *renderer = new QSvgRenderer(QLatin1String("SvgCardDeck.svg")); QGraphicsSvgItem *black = new QGraphicsSvgItem(); QGraphicsSvgItem *red = new QGraphicsSvgItem(); black->setSharedRenderer(renderer); black->setElementId(QLatin1String("black_joker")); red->setSharedRenderer(renderer); red->setElementId(QLatin1String("red_joker")); Notice however that it is for Qt and is not even written in python. This is what I have so far: #!/usr/bin/env python from __future__ import absolute_import import cairo import gtk import rsvg from xml import xpath from xml.dom import minidom window = gtk.Window() window.set_title("Foo") window.set_size_request(256, 256) window.set_property("resizable", False) window.set_position(gtk.WIN_POS_CENTER) window.connect("destroy", gtk.main_quit) window.show() document = minidom.parse("cards.svg") element = xpath.Evaluate("//*[@id='1_club']", document)[0] xml = element.toxml() svg = rsvg.Handle() svg.write(xml) pixbuf = svg.get_pixbuf() image = gtk.Image() image.set_from_pixbuf(pixbuf) image.show() window.add(image) gtk.main() It doesn't work, of course. What am I missing?

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  • Naming multi-instance performance counters in .NET

    - by Roger Lipscombe
    Most multiple instance performance counters in Windows seem to automatically(?) have a #n on the end if there's more than one instance with the same name. For example: if, in Perfmon, you look under the Process category, you'll see: ... dwm explorer explorer#1 ... I have two explorer.exe processes, so the second counter has #1 appended to its name. When I attempt to do this in a .NET application: I can create the category, and register the instance (using the PerformanceCounterCategory.Create that takes a CounterCreationDataCollection). I can open the counter for write and write to it. When I open the counter a second time, it opens the same counter. This means that I have two applications fighting over the counters. The documentation for PerformanceCounter.InstanceName states that # is not allowed in the name. So: how do I have multiple-instance performance counters that are actually multiple instance? And where the second (and subsequent) instances get #n appended to the name? That is: I know that I can put the process ID (e.g.) on the instance name. This works, but has the unfortunate side effect that restarting the process results in a new PID, and Perfmon continues monitoring the old counter.

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  • NSOperation for animation loop causes strange scrolling behaviour

    - by Tricky
    Hi, I've created an animation loop which I run as an operation in order to keep the rest of my interface responsive. Whilst almost there, there is still one remaining issue. My UIScrollViews don't seem to be reliably picking up when a user touch ends. What this means is, for example, if a user drags down on a scroll view, when they lift their fingers the scrollview doesn't bounce back into place and the scrollbar remains visible. As if the finger hasn't left the screen. It takes another tap on the scrollview for it to snap to its correct position and the scrollbar to fade away... Here's the loop I created in a subclassed NSOperation: (void)main { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; _displayLink = [[CADisplayLink displayLinkWithTarget: self selector: @selector(animationLoop:)] retain]; [_displayLink setFrameInterval: 1.0f]; [_displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode: NSRunLoopCommonModes]; while (![self isCancelled]) { NSAutoreleasePool *loopPool = [[NSAutoreleasePool alloc] init]; [runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]]; [loopPool drain]; } [_displayLink invalidate]; [pool release]; } DOes anyone have any idea what might be going on here, and even better how to fix it... Thanks!

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  • Speedup writing C programs using a subset of the Python syntax

    - by psihodelia
    I am constantly trying to optimize my time. Writing a C code takes a lot of time and requires much more keyboard touches than say writing a Python program. However, in order to speed up the time required to create a C program, one can automatize many things. I'd like to write my programs using smth. like Python but with C semantics. It means, all keywords are C keywords, but syntax is optimized. For example, this C code: #include "dsplib.h" #include "coeffs.h" #define MODULENAME "dsplib" #define NUM_SAMPLES 320 typedef float t_Vec; typedef struct s_Inter { char *pc_Name; struct s_Inter *px_Next; }t_Inter; typedef struct s_DspLibControl { t_Vec f_Y; }t_DspLibControl; void v_DspLibName(void) { printf("Module: %s", MODULENAME); printf("\n"); } int v_DspLibInitInterControl(t_DspLibControl *px_Con) { int y; px_Con->f_Y = 0.0; for(int i=0;i<10;i++) { y += i * i; } return y; } in optimized pythonized version can look like: include dsplib, coeffs define MODULENAME="dsplib", NUM_SAMPLES=320 typedef float t_Vec typedef struct s_Inter: char *pc_Name struct s_Inter *px_Next t_Inter typedef struct s_DspLibControl: t_Vec f_Y t_DspLibControl v_DspLibName(): printf("Module: %s", MODULENAME); printf("\n") int v_DspLibInitInterControl(t_DspLibControl *px_Con): int y px_Con->f_Y = 0.0 for int i=0;i<10;i++: y += i * i return y My question is: Do you know any VIM script, which allows to translate an original pythonized C code into a standard C code? For example, one is writing a C code but uses pythonized syntax, once she decides to translate pythonized blocks into standard C, she selects such blocks and press some key. And she doesn't save such pythonized code of course, VIM translates it into standard C.

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  • Getting exception when trying to monkey patch pymongo.connection._Pool

    - by Creotiv
    I use pymongo 1.9 on Ubuntu 10.10 with python 2.6.6 When i trying to monkey patch pymongo.connection._Pool i'm getting error on connection: AutoReconnect: could not find master/primary But when i change _Pool class in pymongo.connection module, it work pretty fine. Even if i copy _Pool implementation from pymongo.connection module and will try to monkey patch by the same code, it still giving same exception. I need to remove threading.local from _Pool class, because i use gevent and i need to implement Pool for all mongo connections(for all threads). I use this code: import pymongo class GPool: """A simple connection pool. Uses thread-local socket per thread. By calling return_socket() a thread can return a socket to the pool. Right now the pool size is capped at 10 sockets - we can expose this as a parameter later, if needed. """ # Non thread-locals __slots__ = ["sockets", "socket_factory", "pool_size","sock"] #sock = None def __init__(self, socket_factory): self.pool_size = 10 if not hasattr(self,"sock"): self.sock = None self.socket_factory = socket_factory if not hasattr(self, "sockets"): self.sockets = [] def socket(self): # we store the pid here to avoid issues with fork / # multiprocessing - see # test.test_connection:TestConnection.test_fork for an example # of what could go wrong otherwise pid = os.getpid() if self.sock is not None and self.sock[0] == pid: return self.sock[1] try: self.sock = (pid, self.sockets.pop()) except IndexError: self.sock = (pid, self.socket_factory()) return self.sock[1] def return_socket(self): if self.sock is not None and self.sock[0] == os.getpid(): # There's a race condition here, but we deliberately # ignore it. It means that if the pool_size is 10 we # might actually keep slightly more than that. if len(self.sockets) < self.pool_size: self.sockets.append(self.sock[1]) else: self.sock[1].close() self.sock = None pymongo.connection._Pool = GPool

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  • Use AJAX to reload captcha

    - by arik-so
    Hello! This question may have been asked already - but unfortunately, I could not find any satisfactory answers. I will just ask it for my concrete case and ask the admins not to delete the question for at least a few days so I can try it out... I have a page. It uses a captcha. Like so: <?php session_start(); // the captcha saves the md5 into the session ?> <img src="captcha.php" onclick="this.src = this.src" /> That was my first code. It did not work, because the browser condsidered it useless to reload an image if the source is the same. My current solution is to pass a get parameter: onclick="this.src = 'captcha.php?randomNumber='+ranNum" The JavaScript variable var ranNum is generated randomly every time the onclick event fires. It works fine, still, I don't like the possibility, if the - though improbable - case of two numbers being the same twice in a row. Although the random number varies between -50,000 and 50,000 - I still do not like it. And I don't think the method is right. I would like to know the 'righter' method, by means of AJAX. I know it's possible. I hope you know how it's possible ^^ In that case, please show me. Thanks in advance! By the way - if I spell cap(t)cha differently, never mind, the reference to the PHP file is right in my code: I use randomImage.php

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  • Is it possible to store pointers in shared memory without using offsets?

    - by Joseph Garvin
    When using shared memory, each process may mmap the shared region into a different area of their address space. This means that when storing pointers within the shared region, you need to store them as offsets of the start of the shared region. Unfortunately, this complicates use of atomic instructions (e.g. if you're trying to write a lock free algorithm). For example, say you have a bunch of reference counted nodes in shared memory, created by a single writer. The writer periodically atomically updates a pointer 'p' to point to a valid node with positive reference count. Readers want to atomically write to 'p' because it points to the beginning of a node (a struct) whose first element is a reference count. Since p always points to a valid node, incrementing the ref count is safe, and makes it safe to dereference 'p' and access other members. However, this all only works when everything is in the same address space. If the nodes and the 'p' pointer are stored in shared memory, then clients suffer a race condition: x = read p y = x + offset Increment refcount at y During step 2, p may change and x may no longer point to a valid node. The only workaround I can think of is somehow forcing all processes to agree on where to map the shared memory, so that real pointers rather than offsets can be stored in the mmap'd region. Is there any way to do that? I see MAP_FIXED in the mmap documentation, but I don't know how I could pick an address that would be safe.

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  • Why are virtual methods considered early bound?

    - by AspOnMyNet
    One definition of binding is that it is the act of replacing function names with memory addresses. a) Thus I assume early binding means function calls are replaced with memory addresses during compilation process, while with late binding this replacement happens during runtime? b) Why are virtual methods also considered early bound (thus the target method is found at compile time, and code is created that will call this method)? As far as I know, with virtual methods the call to actual method is resolved only during runtime and not compile time?! thanx EDIT: 1) A a=new A(); a.M(); As far as I know, it is not known at compile time where on the heap (thus at which memory address ) will instance a be created during runtime. Now, with early binding the function calls are replaced with memory addresses during compilation process. But how can compiler replace function call with memory address, if it doesn’t know where on the heap will object a be created during runtime ( here I’m assuming the address of method a.M will also be at same memory location as a )? 2) v-table calls are neither early nor late bound. Instead there's an offset into a table of function pointers. The offset is fixed at compile time, but which table the function pointer is chosen from depends on the runtime type of the object (the object contains a hidden pointer to its v-table), so the final function address is found at runtime. But assuming the object of type T is created via reflection ( thus app doesn’t even know of existence of type T ), then how can at compile time exist an entry point for that type of object?

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  • Temporary users table or legitimate users table?

    - by John
    I have a freelance web application that lets users register for events. In my database, I have a t_events_applicants table with the column t_events_applications.user_id with a foreign key constraint linked to the t_users.user_id column. So this means only users who have registered with my web application can register for my web application's events. My client would now like to allow non-registered users, users who do not have an entry in my t_user table, to register for events. These non-registered users only need to provide their name and email address to register for events. Should I create a t_temporary_user table with columns name and email and then remove the t_events_applicants.user_id fk constraint? Or should I add un-registered users to the t_user table and then add a column called t_user.type where type can be 'registered' or 'non-registered'? How do I decide which approach to go with? A lot of times, I hesitate with either approach. I ask myself, "What if at a later time, a temporary user is allowed to become a fully registered user? Then maybe I should have only a t_user table. But then I also don't feel good about storing a lot of temporary users in t_user."

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  • Python Regular Expressions: Capture lookahead value (capturing text without consuming it)

    - by Lattyware
    I wish to use regular expressions to split words into groups of (vowels, not_vowels, more_vowels), using a marker to ensure every word begins and ends with a vowel. import re MARKER = "~" VOWELS = {"a", "e", "i", "o", "u", MARKER} word = "dog" if word[0] not in VOWELS: word = MARKER+word if word[-1] not in VOWELS: word += MARKER re.findall("([%]+)([^%]+)([%]+)".replace("%", "".join(VOWELS)), word) In this example we get: [('~', 'd', 'o')] The issue is that I wish the matches to overlap - the last set of vowels should become the first set of the next match. This appears possible with lookaheads, if we replace the regex as follows: re.findall("([%]+)([^%]+)(?=[%]+)".replace("%", "".join(VOWELS)), word) We get: [('~', 'd'), ('o', 'g')] Which means we are matching what I want. However, it now doesn't return the last set of vowels. The output I want is: [('~', 'd', 'o'), ('o', 'g', '~')] I feel this should be possible (if the regex can check for the second set of vowels, I see no reason it can't return them), but I can't find any way of doing it beyond the brute force method, looping through the results after I have them and appending the first character of the next match to the last match, and the last character of the string to the last match. Is there a better way in which I can do this? The two things that would work would be capturing the lookahead value, or not consuming the text on a match, while capturing the value - I can't find any way of doing either.

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  • Can I stop the dbml designer from adding a connection string to the dbml file?

    - by drs9222
    We have a custom function AppSettings.GetConnectionString() which is always called to determine the connection string that should be used. How this function works is unimportant to the discussion. It suffices to say that it returns a connection string and I have to use it. I want my LINQ to SQL DataContext to use this so I removed all connection string informatin from the dbml file and created a partial class with a default constructor like this: public partial class SampleDataContext { public SampleDataContext() : base(AppSettings.GetConnectionString()) { } } This works fine until I use the designer to drag and drop a table into the diagram. The act of dragging a table into the diagram will do several unwanted things: A settings file will be created A app.config file will be created My dbml file will have the connection string embedded in it All of this is done before I even save the file! When I save the diagram the designer file is recreated and it will contain its own default constructor which uses the wrong connection string. Of course this means my DataContext now has two default constructors and I can't build anymore! I can undo all of these bad things but it is annoying. I have to manually remove the connection string and the new files after each change! Is there anyway I can stop the designer from making these changes without asking? EDIT The requirement to use the AppSettings.GetConnectionString() method was imposed on me rather late in the game. I used to use something very similar to what it generates for me. There are quite a few places that call the default constructor. I am aware that change them all to create the data context in another way (using a different constructor, static method, factory, ect..). That kind of change would only be slightly annoying since it would only have to be done once. However, I feel, that it is sidestepping the real issue. The dbml file and configuration files would still contain an incorrect, if unused, connection string which at best could confuse other developers.

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  • Handling data update/freshness issue in web-app in general (or GWT specifically)

    - by edwin.nathaniel
    In general, how do you guys handle user update/data freshness interaction with the user (UI issue) in web-apps? For example: Multi-users web-app (like project management) Login to a "virtual" space People can update project names, etc How to handle a situation such that: user-A and user-B load a project with title "Project StackOverflow" user-B updates the title to "Project StackExchange" user-A updates the title after user-B update operation to "Project Basecamp" The question I'm asking is from the user perspective (UI) and not about transactional operation. What do most people do in this situation? What would you do after user-B updates the title in user-A screen/view? What happened when user-A tries to update the title after user-B finished his/her update operation? do you inform user-A that the title has changed and he/she has to reload the page? do you go ahead and change the title and let user-B has old data? Do you do some sort of application-level "locking" mechanism? (if someone is updating, nobody else can?) Or fix the application workflow? (who has the access to be able to change things, etc). What would be the simplest solution, but at the same time not annoy the user with more dialog/warning messages. I've encountered this particular problem frequently in a GWT app specifically where domain models are being passed around and refreshing the whole app/client-side isn't the optimal solution in my mind (since it means the whole "loading"/initialization phase must be executed again in this specific environment). Maybe the answer is to stay away from GWT? :) Love to hear options, solutions, and advises from you guys. Thanks

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  • Which of these is better practice?

    - by Fletcher Moore
    You have a sequence of functions to execute. Case A: They do not depend on each other. Which of these is better? function main() { a(); b(); c(); } or function main() { a(); } function a() { ... b(); } function b() { ... c(); } Case B: They do depend on successful completion of the previous. function main() { if (a()) if (b()) c(); } or function main() { if (!a()) return false; if (!b()) return false; c(); } or function main() { a(); } function a() { ... // maybe return false b(); } funtion b() { ... // maybe return false c(); } Better, of course, means more maintainable and easier to follow.

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