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Articles indexed Monday June 14 2010

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  • How do I avoid a race condition in my Rails app?

    - by Cathal
    Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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  • Modbus driver: C vs Java

    - by cpf
    Hi stackoverflow, I am soon going to start a project where I'm required to program a Modbus driver. My initial approach was to want to do it in Java, however my boss has had contact with a company that has experience in Modbus, and they said C is the better language to approach Modbus. So my boss pretty much demanded it to be in C. My C knowledge is not really big, so it would require me to learn enough to get the Modbus driver working in proper and stable order. So, my question to you stackoverflow people with some experience in Modbus: how important could the choice of C vs Java be? The modbus site seems to have Java libraries, if C was so superior to Java in every way, why would they have those libraries? Would it be useful to learn C properly for the advantages that might give?

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  • how to use ggplot conditional on data

    - by Andreas
    I asked this question and it seams ggplot2 currently has a bug with empty data.frames. Therefore I am trying to check if the dataframe is empty, before I make the plot. But what ever I come up with, it gets really ugly, and doesn't work. So I am asking for your help. example data: SOdata <- structure(list(id = 10:55, one = c(7L, 8L, 7L, NA, 7L, 8L, 5L, 7L, 7L, 8L, NA, 10L, 8L, NA, NA, NA, NA, 6L, 5L, 6L, 8L, 4L, 7L, 6L, 9L, 7L, 5L, 6L, 7L, 6L, 5L, 8L, 8L, 7L, 7L, 6L, 6L, 8L, 6L, 8L, 8L, 7L, 7L, 5L, 5L, 8L), two = c(7L, NA, 8L, NA, 10L, 10L, 8L, 9L, 4L, 10L, NA, 10L, 9L, NA, NA, NA, NA, 7L, 8L, 9L, 10L, 9L, 8L, 8L, 8L, 8L, 8L, 9L, 10L, 8L, 8L, 8L, 10L, 9L, 10L, 8L, 9L, 10L, 8L, 8L, 7L, 10L, 8L, 9L, 7L, 9L), three = c(7L, 10L, 7L, NA, 10L, 10L, NA, 10L, NA, NA, NA, NA, 10L, NA, NA, 4L, NA, 7L, 7L, 4L, 10L, 10L, 7L, 4L, 7L, NA, 10L, 4L, 7L, 7L, 7L, 10L, 10L, 7L, 10L, 4L, 10L, 10L, 10L, 4L, 10L, 10L, 10L, 10L, 7L, 10L), four = c(7L, 10L, 4L, NA, 10L, 7L, NA, 7L, NA, NA, NA, NA, 10L, NA, NA, 4L, NA, 10L, 10L, 7L, 10L, 10L, 7L, 7L, 7L, NA, 10L, 7L, 4L, 10L, 4L, 7L, 10L, 2L, 10L, 4L, 12L, 4L, 7L, 10L, 10L, 12L, 12L, 4L, 7L, 10L), five = c(7L, NA, 6L, NA, 8L, 8L, 7L, NA, 9L, NA, NA, NA, 9L, NA, NA, NA, NA, 7L, 8L, NA, NA, 7L, 7L, 4L, NA, NA, NA, NA, 5L, 6L, 5L, 7L, 7L, 6L, 9L, NA, 10L, 7L, 8L, 5L, 7L, 10L, 7L, 4L, 5L, 10L), six = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("2010-05-25", "2010-05-27", "2010-06-07"), class = "factor"), seven = c(0.777777777777778, 0.833333333333333, 0.333333333333333, 0.888888888888889, 0.5, 0.888888888888889, 0.777777777777778, 0.722222222222222, 0.277777777777778, 0.611111111111111, 0.722222222222222, 1, 0.888888888888889, 0.722222222222222, 0.555555555555556, NA, 0, 0.666666666666667, 0.666666666666667, 0.833333333333333, 0.833333333333333, 0.833333333333333, 0.833333333333333, 0.722222222222222, 0.833333333333333, 0.888888888888889, 0.666666666666667, 1, 0.777777777777778, 0.722222222222222, 0.5, 0.833333333333333, 0.722222222222222, 0.388888888888889, 0.722222222222222, 1, 0.611111111111111, 0.777777777777778, 0.722222222222222, 0.944444444444444, 0.555555555555556, 0.666666666666667, 0.722222222222222, 0.444444444444444, 0.333333333333333, 0.777777777777778), eight = c(0.666666666666667, 0.333333333333333, 0.833333333333333, 0.666666666666667, 1, 1, 0.833333333333333, 0.166666666666667, 0.833333333333333, 0.833333333333333, 1, 1, 0.666666666666667, 0.666666666666667, 0.333333333333333, 0.5, 0, 0.666666666666667, 0.5, 1, 0.666666666666667, 0.5, 0.666666666666667, 0.666666666666667, 0.666666666666667, 0.333333333333333, 0.333333333333333, 1, 0.666666666666667, 0.833333333333333, 0.666666666666667, 0.666666666666667, 0.5, 0, 0.833333333333333, 1, 0.666666666666667, 0.5, 0.666666666666667, 0.666666666666667, 0.5, 1, 0.833333333333333, 0.666666666666667, 0.833333333333333, 0.666666666666667), nine = c(0.307692307692308, NA, 0.461538461538462, 0.538461538461538, 1, 0.769230769230769, 0.538461538461538, 0.692307692307692, 0, 0.153846153846154, 0.769230769230769, NA, 0.461538461538462, NA, NA, NA, NA, 0, 0.615384615384615, 0.615384615384615, 0.769230769230769, 0.384615384615385, 0.846153846153846, 0.923076923076923, 0.615384615384615, 0.692307692307692, 0.0769230769230769, 0.846153846153846, 0.384615384615385, 0.384615384615385, 0.461538461538462, 0.384615384615385, 0.461538461538462, NA, 0.923076923076923, 0.692307692307692, 0.615384615384615, 0.615384615384615, 0.769230769230769, 0.0769230769230769, 0.230769230769231, 0.692307692307692, 0.769230769230769, 0.230769230769231, 0.769230769230769, 0.615384615384615), ten = c(0.875, 0.625, 0.375, 0.75, 0.75, 0.75, 0.625, 0.875, 1, 0.125, 1, NA, 0.625, 0.75, 0.75, 0.375, NA, 0.625, 0.5, 0.75, 0.875, 0.625, 0.875, 0.75, 0.625, 0.875, 0.5, 0.75, 0, 0.5, 0.875, 1, 0.75, 0.125, 0.5, 0.5, 0.5, 0.625, 0.375, 0.625, 0.625, 0.75, 0.875, 0.375, 0, 0.875), elleven = c(1, 0.8, 0.7, 0.9, 0, 1, 0.9, 0.5, 0, 0.8, 0.8, NA, 0.8, NA, NA, 0.8, NA, 0.4, 0.8, 0.5, 1, 0.4, 0.5, 0.9, 0.8, 1, 0.8, 0.5, 0.3, 0.9, 0.2, 1, 0.8, 0.1, 1, 0.8, 0.5, 0.2, 0.7, 0.8, 1, 0.9, 0.6, 0.8, 0.2, 1), twelve = c(0.666666666666667, NA, 0.133333333333333, 1, 1, 0.8, 0.4, 0.733333333333333, NA, 0.933333333333333, NA, NA, 0.6, 0.533333333333333, NA, 0.533333333333333, NA, 0, 0.6, 0.533333333333333, 0.733333333333333, 0.6, 0.733333333333333, 0.666666666666667, 0.533333333333333, 0.733333333333333, 0.466666666666667, 0.733333333333333, 1, 0.733333333333333, 0.666666666666667, 0.533333333333333, NA, 0.533333333333333, 0.6, 0.866666666666667, 0.466666666666667, 0.533333333333333, 0.333333333333333, 0.6, 0.6, 0.866666666666667, 0.666666666666667, 0.6, 0.6, 0.533333333333333)), .Names = c("id", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "elleven", "twelve"), class = "data.frame", row.names = c(NA, -46L)) And the plot iqr <- function(x, ...) { qs <- quantile(as.numeric(x), c(0.25, 0.5, 0.75), na.rm = T) names(qs) <- c("ymin", "y", "ymax") qs } magic <- function(y, ...) { high <- median(SOdata[[y]], na.rm=T)+1.5*sd(SOdata[[y]],na.rm=T) low <- median(SOdata[[y]], na.rm=T)-1.5*sd(SOdata[[y]],na.rm=T) ggplot(SOdata, aes_string(x="six", y=y))+ stat_summary(fun.data="iqr", geom="crossbar", fill="grey", alpha=0.3)+ geom_point(data = SOdata[SOdata[[y]] > high,], position=position_jitter(w=0.1, h=0),col="green", alpha=0.5)+ geom_point(data = SOdata[SOdata[[y]] < low,], position=position_jitter(w=0.1, h=0),col="red", alpha=0.5)+ stat_summary(fun.y=median, geom="point",shape=18 ,size=4, col="orange") } for (i in names(SOdata)[-c(1,7)]) { p<- magic(i) ggsave(paste("magig_plot_",i,".png",sep=""), plot=p, height=3.5, width=5.5) } The problem is that sometimes in the call to geom_point the subset returns an empty dataframe, which sometimes (!) causes ggplot2 to plot all the data instead of none of the data. geom_point(data = SOdata[SOdata[[y]] > high,], position=position_jitter(w=0.1, h=0),col="green", alpha=0.5)+ This is kindda of important to me, and I am really stuck trying to find a solution. Any help that will get me started is much appreciated. Thanks in advance.

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  • How to specify character encoding for Ant Task parameters in Java

    - by räph
    I'm writing an ANT task in Java. In my build.xml I specify parameters, which should be read from my java class. Problems occur, when I use special characters, like german umlauts (Ö,Ä,Ü) in these parameters. In my java task they appear as ?-characters (using System.out.print). All my files are encoded as UTF-8. and my build.xml has the corresponding declaration: <?xml version="1.0" encoding="UTF-8" ?> For the details of writing the task: I do it according to http://ant.apache.org/manual/develop.html (especially Point 5 nested elements). I have nested elements in my task like: <parameter name="test" value="ÖÄÜtest"/> and a java method: public void addConfiguredParameter(Parameter prop) { System.out.println(prop.getValue()); //prints ???test } to read the parameter values.

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  • onbeforeunload in safari does not run code server side

    - by Deepa
    On browser close or F5, I have to perform some code on server side For this I have a button. On click of that button which has onclientclick and onclick functions written. I also wrote an event on window.onbeforeunload which does a button.click(). window.onbeforeunload=function(e) { button.click() } My problem is that this runs the code of the client side click function of the button, however server side code does not get executed. This happens only when i close the browser. When I do F5 it works perfectly. Also this happens only on Safari. In FF and mozila it works perfectly . How can i

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  • tinyMCE automatically parses links

    - by gong
    hello, I use tinyMCE like: $usetinymce="tinyMCE.init({ entity_encoding : \"raw\", elements : \"text,newstext\", mode : \"exact\", theme: \"advanced\", theme_advanced_buttons1 : \"bold,italic,underline,strikethrough,separator,\" + \"justifyleft,justifycenter,justifyright,justifyfull,formatselect,\" + \"bullist,numlist,outdent,indent\", theme_advanced_buttons2 : \"link,unlink,anchor,image,separator,\" +\"undo,redo,cleanup,code,separator,sub,sup,charmap\", theme_advanced_buttons3 : \"\" });"; If I insert a link the it appears like: www.111.gr/ How is this extra \ added? I also did a print_r($_POST) and still appears. any help

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  • showing loading image still shows "browser loading image" icon

    - by ooo
    i have this code running to load my images all asynch and show a ajax loading image until the real image is downloaded. $('img.loadable-image').css('background', 'transparent url(/images/ajax-loader1.gif) no-repeat center center') $('img.loadable-image').load(function() { $(this).css('background', ''); }); this works in that it shows my ajax loading icon until the images is downloaded but it also shows the background as well here is a screenshot of what i get: as you can see on the left, you see the little ajax loader but also see the missing image square around it. any suggestions?

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  • process running on login: can't find in AD or login batch scripts

    - by tombull89
    Hallo, I'm trying to deploy some classroom control software (NetSupport School) to some of the machines on our network but for some reason when you log off and restart the computer any user who logs on ends up re-installing the software while logging on. I spent two hours on the phone to the complanys support and we eventually nailed it down to most likely a setting in Active Directory or in the login.bat (drive mapping and settings) but we can't find anything in those that would say "run this installer at logon". Is there anywhere else on the system that would set something like this? Server 2003/XP. Ta!

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  • Apache: VirtualHost *:80 -- mixing * ports and non-* ports with a NameVirtualHost address is not sup

    - by user45761
    Hi, when i add the line below to /etc/apache2/apache2.conf I get the error belower when i restart apache: Include /usr/share/doc/apache2.2-common/examples/apache2/extra/httpd-vhosts.conf [Mon Jun 14 12:16:47 2010] [error] VirtualHost *:80 -- mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results [Mon Jun 14 12:16:47 2010] [warn] NameVirtualHost *:80 has no VirtualHosts This is my httpd-vhosts.conf file: # # Use name-based virtual hosting. # NameVirtualHost *:80 # # VirtualHost example: # Almost any Apache directive may go into a VirtualHost container. # The first VirtualHost section is used for all requests that do not # match a ServerName or ServerAlias in any <VirtualHost> block. <VirtualHost *:80> ServerName tirengarfio.com DocumentRoot /var/www/rs3 <Directory /var/www/rs3> AllowOverride All Options MultiViews Indexes SymLinksIfOwnerMatch Allow from All </Directory> Alias /sf /var/www/rs3/lib/vendor/symfony/data/web/sf <Directory "/var/www/rs3/lib/vendor/symfony/data/web/sf"> AllowOverride All Allow from All </Directory> </VirtualHost> Any idea? Regards Javi

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  • Apache2 and logrotate: delaycompress needed?

    - by j0nes
    Hello, I am currently looking at the file size of my Apache logs as they became huge. In my logrotate conf, I have delaycompress enabled. Does Apache really need this (as the logrotate documentation says that some programs still write in the old file) or is it safe to disable delaycompress? Best regards, Jonas

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  • WPF Ignoring ProgressBar Style

    - by Nidonocu
    Following a problem in WPF 4 where the default ProgressBar template has an off-white highlight applied causing it to dull the foreground colour, I decided to extract the template and manually edit the values to white. After doing this, I put the template as a style in App.xaml for global use and the Visual Studio designer began to use it right away. However, when I run my app, the default style is still being applied: I then tried setting the style specifically using a key, then even having it as an inline style and finally as a inline template without a wrapping style for the specific progress bar and it is still ignored. What's going wrong? Current Code for progress bar: <ProgressBar Grid.Column="1" Grid.Row="2" Height="15" Width="355" Margin="0,0,0,7" IsIndeterminate="{Binding ProgressState, FallbackValue=False}" Visibility="{Binding ProgressVisibility, FallbackValue=Collapsed}" Value="{Binding ProgressValue, Mode=OneWay, FallbackValue=100}" Foreground="{Binding ProgressColor,FallbackValue=Red}"> <ProgressBar.Template> <ControlTemplate> <Grid Name="TemplateRoot" SnapsToDevicePixels="True"> <Rectangle RadiusX="2" RadiusY="2" Fill="{TemplateBinding Panel.Background}" /> ...

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  • Editline with non-blocking input.

    - by Sasun Hambardzumyan
    I use editline library in my program, for user commands input in shell. But becides shell, program have a gui interface, so I need to run editline's readline() function in separate thread, because it blocks until Enter pressed. Is there a way to use readline() function without blocking, so I could avoid separate thread usage?

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  • excluding a column in csv file with regex

    - by JPro
    Is there any way to exclude/delete/replace one field from a csv file with some regexp in notepad++? I have a csv file with some data like this: '1','data1','data2','data3','data4','data5','data6','data7','data8','data9', 'data10','data11','data12','data13','data14','data15','data16','data17','data18', 'data19','data20','data21','data22','data23','\'data24 with some commas, here and there and some "double quotes", and fullstops.','data25','data26' The only problem I am facing is with data24 WHERE I encounter \' and then "" and some wild characters like , and .. This is particularly fixed at 24 field. For the purpose of clarity, I have entered a newline here. But the entire text above is in juts one line. Any ideas on how to solve? Thanks.

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  • Nhibernate.Bytecode.Castle Trust Level on IIS

    - by jack london
    Trying to deploy the wcf service, depended on nhibernate. And getting the following exception On Reflection activator. [SecurityException: That assembly does not allow partially trusted callers.] System.Security.CodeAccessSecurityEngine.ThrowSecurityException(Assembly asm, PermissionSet granted, PermissionSet refused, RuntimeMethodHandle rmh, SecurityAction action, Object demand, IPermission permThatFailed) +150 System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) +0 System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) +86 System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) +230 System.Activator.CreateInstance(Type type, Boolean nonPublic) +67 NHibernate.Bytecode.ActivatorObjectsFactory.CreateInstance(Type type) +8 NHibernate.Driver.ReflectionBasedDriver.CreateConnection() +28 NHibernate.Connection.DriverConnectionProvider.GetConnection() +56 NHibernate.Tool.hbm2ddl.SchemaExport.Execute(Action`1 scriptAction, Boolean export, Boolean justDrop) +376 in IIS configuration service's trust level is Full-trust also application's web config's trust level is full. how could i make this service in working state?

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  • What algorithm should I use for encrypting and embedding a password for an application?

    - by vfclists
    What algorithm should I use for encrypting and embedding a password for an application? It obviously is not bullet proof, but it should be good enough to thwart someone scanning the database with a hex editor, or make it hard for someone who has the skills to use a debugger to trace the code to work out, either by scanning for the encrypted password, or using a debugger to run through the decryption code. Object Pascal would be nice. /vfclists

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  • Adding Transparency/alpha to Embedded Font

    - by Shubhra Bhushan
    Hi guys, I have embedded a font type in my application. Its working fine inside a text area. Now i need to add 60% transparency to it. In fact I need multiple transparency levels. Like - 60 % transparency for TextARea 70% for WindowShade Header etc. How do I add alpha values to it?

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  • Are static members of a generic class tied to the specific instance?

    - by mafutrct
    This is more of a documentation than a real question. I noticed the principle it is not described on SO yet (did I miss it?), so here goes: Imagine a generic class that contains a static member: class Foo<T> { public static int member; } Is there a new instance of the member for each specific class, or is there only a single instance for all Foo-type classes? It can easily be verified by code like this: Foo<int>.member = 1; Foo<string>.member = 2; Console.WriteLine (Foo<int>.member); What is the result, and where is this behavior documented?

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  • Qt training tips and tricks

    - by 0xDEAD BEEF
    I have just arrived at new company and have never worked with Qt before, but my task is to learn Qt in 2 weeks, so i can give training to others. So i got 2 weeks to learn Qt and prepare for 2 weeks long Qt training. I am so dead! Please point out some common mistakes, tricks, styles so i can make that training a bit better! Thank you!

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  • iphone - navigation controller - move to first view from last view without traversing all intermedia

    - by satyam
    i'm working on iphone app which will show 4 buttons in first view. on click of a button, it will load a new view with navigation controller. this navigation controller view allows to travel upto 11 sub views. in 11th sub view, i've a reset button. on click of reset button, i've to go back to navigation controllers first view without traversing all the 11 views? is it possible to achieve it? if yes how? if no, what can be the solution?

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  • Validators are not working anymore in Zend Framework?

    - by Pavel Dubinin
    Eariler I happily used the following code for creating form elements (inside Zend_Form descendant): //Set for options $this->setOptions(array( 'elements' => array( 'title' => array( 'type' => 'text', 'options' => array( 'required' => true, 'label' => 'Title', 'filters' => array('StringTrim'), 'validators' => array( array('StringLength', false, array('minLength'=>1, 'maxLength'=>50)), ), ) ) )); But now I've noticed that validators are not working.. I suspect this might be due to zend updates.. Does anyone face this problem?

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