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• Assistance with Lua functions

  - by Josh

  As noted before, I'm relatively new to lua, but again, I learn quick. The last time I got help here, it helped me immensely, and I was able to write a better script. Now I've come to another question that I think will make my life a bit easier. I have no clue what I'm doing with functions, but I'm hoping there is a way to do what I want to do here. Below, you'll see an example of code I have to do to strip down some unneeded elements. Yeah, I realize it's not efficient in the least, so if anyone else has a better idea of how to make it much more efficient, I'm all ears. What I would like to do is create a function with it so that I can strip down whatever variable with a simple call of it (like stripdown(winds)). I appreciate any help that is offered, and any lessons given. Thanks! winds = string.gsub(winds,"%b<>","") winds = string.gsub(winds,"%c"," ") winds = string.gsub(winds," "," ") winds = string.gsub(winds," "," ") winds = string.gsub(winds,"^%s*(.-)%s*$", "%1)") winds = string.gsub(winds,"&nbsp;","") winds = string.gsub(winds,"/ ", "(") Josh

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• In Ruby, why does a method invocation not be able to be treated as a unit when "do" and "end" is use

  - by Jian Lin

  The following question is related to http://stackoverflow.com/questions/2127836/ruby-print-inject-do-syntax The question is, can we insist on using DO and END and make it work with puts or p? This works: a = [1,2,3,4] b = a.inject do |sum, x| sum + x end puts b # prints out 10 so, is it correct to say, inject is a class method of the Array class, which takes a block of code, and then returns a number. If so, then it should be no different from calling a function and getting back a return value: b = foo(3) puts b or b = circle.getRadius() puts b In the above two cases, we can directly say puts foo(3) puts circle.getRadius() so, there is no way to make it work directly by using the following 2 ways: a = [1,2,3,4] puts a.inject do |sum, x| sum + x end but it gives ch01q2.rb:7:in `inject': no block given (LocalJumpError) from ch01q2.rb:4:in `each' from ch01q2.rb:4:in `inject' from ch01q2.rb:4 grouping the method call using ( ) doesn't work either: a = [1,2,3,4] puts (a.inject do |sum, x| sum + x end) and this gives: ch01q3.rb:4: syntax error, unexpected kDO_BLOCK, expecting ')' puts (a.inject do |sum, x| ^ ch01q3.rb:4: syntax error, unexpected '|', expecting '=' puts (a.inject do |sum, x| ^ ch01q3.rb:6: syntax error, unexpected kEND, expecting $end end) ^ finally, the following version works: a = [1,2,3,4] puts a.inject { |sum, x| sum + x } but why doesn't the grouping of the method invocation using ( ) work? What if a programmer insists that he uses do and end, can it be made to work directly with p or puts, without an extra temporary variable?

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• VS2010 Implement Generic Interface expansion doesn't use specified type

  - by TJB

  Using the release version of Visual Studio 2010 I think there's a difference in the "Implement Interface" expansion from VS2008 If I speicify an interface and implement it in a class as so: public interface IRepository<T> where T : IModel { T Get<T>(int id); void Update<T>(); int Add<T>(T item); } public class MockRepository : IRepository<MockUser> { // ... } Then use the "Implement Interface" expansion and get this: public class MockRepository : IRepository<MockUser> { public T Get<T>(int id) { throw new NotImplementedException(); } public void Update<T>() { throw new NotImplementedException(); } public int Add<T>(T item) { throw new NotImplementedException(); } } Instead of what I expected public class MockRepository : IRepository<MockUser> { public MockUser Get<MockUser>(int id) { throw new NotImplementedException(); } public void Update<MockUser>() { throw new NotImplementedException(); } public int Add<MockUser>(MockUser item) { throw new NotImplementedException(); } } The IDE uses the type variable name from the generic interface definition T instead of the specified concrete type MockUser. Is this a bug? Or is something new just for VS2010 / .Net 4.0?

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• Inject App Settings using Windsor

  - by Damian Powell

  How can I inject the value of an appSettings entry (from app.config or web.config) into a service using the Windsor container? If I wanted to inject the value of a Windsor property into a service, I would do something like this: <properties> <importantIntegerProperty>666</importantIntegerProperty> </properties> <component id="myComponent" service="MyApp.IService, MyApp" type="MyApp.Service, MyApp" > <parameters> <importantInteger>#{importantIntegerProperty}</importantInteger> </parameters> </component> However, what I'd really like to do is take the value represented by #{importantIntegerProperty} from an app settings variable which might be defined like this: <appSettings> <add key="importantInteger" value="666"/> </appSettings> EDIT: To clarify; I realise that this is not natively possible with Windsor and the David Hayden article that sliderhouserules refers to is actually about his own (David Hayden's) IoC container, not Windsor. I'm surely not the first person to have this problem so what I'd like to know is how have other people solved this issue?

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• trying to read a delimited text file from resources - but it wont run

  - by Bigfatty

  I'm having a problem where instead of reading a text file from the location string, I changed it to read the text file from the resource location and it messes up my program. I've also used the insert snippet method to get most of this code, so it is safe to say I don't know what is going on. Could some one please help? 'reads the text out of a delimited text file and puts the words and hints into to separate arrays ' this works and made the program run ' Dim filename As String = Application.StartupPath + "\ProggramingList.txt" 'this dosnt work and brings back a Illegal characters in path error. dim filename as string = My.Resources.GamesList Dim fields As String() 'my text files are delimited Dim delimiter As String = "," Using parser As New TextFieldParser(filename) parser.SetDelimiters(delimiter) While Not parser.EndOfData ' Read in the fields for the current line fields = parser.ReadFields() ' Add code here to use data in fields variable. 'put the result into two arrays (the fields are the arrays im talking about). one holds the words, and one holds the corresponding hint Programingwords(counter) = Strings.UCase(fields(0)) counter += 1 'this is where the hint is at Programingwords(counter) = (fields(1)) counter += 1 End While End Using

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• CakePHP: Custom Function in bootstrap that uses $ajax->link not working

  - by nekko

  Hello I have two questions: (1) Is it best practice to create global custom functions in the bootstrap file? Is there a better place to store them? (2) I am unable use the following line of code in my custom function located in my bootstrap.php file: $url = $ajax->link ( 'Delete', array ('controller' => 'events', 'action' => 'delete', 22 ), array ('update' => 'event' ), 'Do you want to delete this event?' ); echo $url; I receive the following error: Notice (8): Undefined variable: ajax [APP\config\bootstrap.php, line 271] Code } function testAjax () { $url = $ajax->link ( 'Delete', array ('controller' => 'events', 'action' => 'delete', 22 ), array ('update' => 'event' ), 'Do you want to delete this event?' ); testAjax - APP\config\bootstrap.php, line 271 include - APP\views\event\queue.ctp, line 19 View::_render() - CORE\cake\libs\view\view.php, line 649 View::render() - CORE\cake\libs\view\view.php, line 372 Controller::render() - CORE\cake\libs\controller\controller.php, line 766 Dispatcher::_invoke() - CORE\cake\dispatcher.php, line 211 Dispatcher::dispatch() - CORE\cake\dispatcher.php, line 181 [main] - APP\webroot\index.php, line 91 However it works as intended if I place that same code in my view: <a onclick=" event.returnValue = false; return false;" id="link1656170149" href="/shout/events/delete/22">Delete</a> Please help :) Thanks in advance!!

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• confusing fork system call

  - by benjamin button

  Hi, i was just checking the behaviour of fork system call and i found it very confusing. i saw in a website that Unix will make an exact copy of the parent's address space and give it to the child. Therefore, the parent and child processes have separate address spaces #include <stdio.h> #include <sys/types.h> int main(void) { pid_t pid; char y='Y'; char *ptr; ptr=&y; pid = fork(); if (pid == 0) { y='Z'; printf(" *** Child process ***\n"); printf(" Address is %p\n",ptr); printf(" char value is %c\n",y); sleep(5); } else { sleep(5); printf("\n ***parent process ***\n",&y); printf(" Address is %p\n",ptr); printf(" char value is %c\n",y); } } the output of the above program is : *** Child process *** Address is 69002894 char value is Z ***parent process *** Address is 69002894 char value is Y so from the above mentioned statement it seems that child and parent have separet address spaces.this is the reason why char value is printed separately and why am i seeing the address of the variable as same in both child and parent processes.? Please help me understand this!

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• How to asynchronously read to std::string using Boost::asio?

  - by SpyBot

  Hello. I'm learning Boost::asio and all that async stuff. How can I asynchronously read to variable user_ of type std::string? Boost::asio::buffer(user_) works only with async_write(), but not with async_read(). It works with vector, so what is the reason for it not to work with string? Is there another way to do that besides declaring char user_[max_len] and using Boost::asio::buffer(user_, max_len)? Also, what's the point of inheriting from boost::enable_shared_from_this<Connection> and using shared_from_this() instead of this in async_read() and async_write()? I've seen that a lot in the examples. Here is a part of my code: class Connection { public: Connection(tcp::acceptor &acceptor) : acceptor_(acceptor), socket_(acceptor.get_io_service(), tcp::v4()) { } void start() { acceptor_.get_io_service().post( boost::bind(&Connection::start_accept, this)); } private: void start_accept() { acceptor_.async_accept(socket_, boost::bind(&Connection::handle_accept, this, placeholders::error)); } void handle_accept(const boost::system::error_code& err) { if (err) { disconnect(); } else { async_read(socket_, boost::asio::buffer(user_), boost::bind(&Connection::handle_user_read, this, placeholders::error, placeholders::bytes_transferred)); } } void handle_user_read(const boost::system::error_code& err, std::size_t bytes_transferred) { if ( err or (bytes_transferred != sizeof(user_)) ) { disconnect(); } else { ... } } ... void disconnect() { socket_.shutdown(tcp::socket::shutdown_both); socket_.close(); socket_.open(tcp::v4()); start_accept(); } tcp::acceptor &acceptor_; tcp::socket socket_; std::string user_; std::string pass_; ... };

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• Some Async Socket Code - Help with Garbage Collection?

  - by divinci

  Hi all, I think this question is really about my understanding of Garbage collection and variable references. But I will go ahead and throw out some code for you to look at. // Please note do not use this code for async sockets, just to highlight my question // SocketTransport // This is a simple wrapper class that is used as the 'state' object // when performing Async Socket Reads/Writes public class SocketTransport { public Socket Socket; public byte[] Buffer; public SocketTransport(Socket socket, byte[] buffer) { this.Socket = socket; this.Buffer = buffer; } } // Entry point - creates a SocketTransport, then passes it as the state // object when Asyncly reading from the socket. public void ReadOne(Socket socket) { SocketTransport socketTransport_One = new SocketTransport(socket, new byte[10]); socketTransport_One.Socket.BeginRecieve ( socketTransport_One.Buffer, // Buffer to store data 0, // Buffer offset 10, // Read Length SocketFlags.None // SocketFlags new AsyncCallback(OnReadOne), // Callback when BeginRead completes socketTransport_One // 'state' object to pass to Callback. ); } public void OnReadOne(IAsyncResult ar) { SocketTransport socketTransport_One = ar.asyncState as SocketTransport; ProcessReadOneBuffer(socketTransport_One.Buffer); // Do processing // New Read // Create another! SocketTransport (what happens to first one?) SocketTransport socketTransport_Two = new SocketTransport(socket, new byte[10]); socketTransport_Two.Socket.BeginRecieve ( socketTransport_One.Buffer, 0, 10, SocketFlags.None new AsyncCallback(OnReadTwo), socketTransport_Two ); } public void OnReadTwo(IAsyncResult ar) { SocketTransport socketTransport_Two = ar.asyncState as SocketTransport; .............. So my question is: The first SocketTransport to be created (socketTransport_One) has a strong reference to a Socket object (lets call is ~SocketA~). Once the async read is completed, a new SocketTransport object is created (socketTransport_Two) also with a strong reference to ~SocketA~. Q1. Will socketTransport_One be collected by the garbage collector when method OnReadOne exits? Even though it still contains a strong reference to ~SocketA~ Thanks all!

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• JSF/Seam - call one component method for many radio groups

  - by purecharger

  I've got the following jsf page: <h:form> <ui:repeat value="#{list.categories}" var="cat"> <h:selectOneRadio id="sel1Rad" value="#{list.choose}" layout="pageDirection"> <f:selectItems value="#{list.names}"/> </h:selectOneRadio> </ui:repeat> <h:commandButton id="submit" action="#{list.submit}" value="Submit"/> </h:form> And a component named list. The variable cat is injected to the component, used by the method list.getNames(). What I am trying to have happen is to have list.choose() be called for each radio group. I'm not sure if this is possible with Seam. Going by the booking example distributed with Seam, there is a distinct separate method for each selectOneRadio or selectOneMenu group. Since I have an unknown number of categories, I can't / don't want to define a method for each possible choice. When I submit the form, all my choices are sent in the POST, I just don't know the correct way to tell Seam how to dispatch them to my component. Any help is appreciated!

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• Protecting an Application's Memory From Tampering

  - by Changeling

  We are adding AES 256 bit encryption to our server and client applications for encrypting the TCP/IP traffic containing sensitive information. We will be rotating the keys daily. Because of that, the keys will be stored in memory with the applications. Key distribution process: Each server and client will have a list of initial Key Encryption Key's (KEK) by day If the client has just started up or the server has just started up, the client will request the daily key from the server using the initial key. The server will respond with the daily key, encrypted with the initial key. The daily key is a randomly generated set of alphanumeric characters. We are using AES 256 bit encryption. All subsequent communications will be encrypted using that daily key. Nightly, the client will request the new daily key from the server using the current daily key as the current KEK. After the client gets the new key, the new daily key will replace the old daily key. Is it possible for another bad application to gain access to this memory illegally or is this protected in Windows? The key will not be written to a file, only stored in a variable in memory. If an application can access the memory illegally, how can you protect the memory from tampering? We are using C++ and XP (Vista/7 may be an option in the future so I don't know if that changes the answer).

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• Performing calculations by subsets of data in R

  - by Vivi

  I want to perform calculations for each company number in the column PERMNO of my data frame, the summary of which can be seen here: > summary(companydataRETS) PERMNO RET Min. :10000 Min. :-0.971698 1st Qu.:32716 1st Qu.:-0.011905 Median :61735 Median : 0.000000 Mean :56788 Mean : 0.000799 3rd Qu.:80280 3rd Qu.: 0.010989 Max. :93436 Max. :19.000000 My solution so far was to create a variable with all possible company numbers compns <- companydataRETS[!duplicated(companydataRETS[,"PERMNO"]),"PERMNO"] And then use a foreach loop using parallel computing which calls my function get.rho() which in turn perform the desired calculations rhos <- foreach (i=1:length(compns), .combine=rbind) %dopar% get.rho(subset(companydataRETS[,"RET"],companydataRETS$PERMNO == compns[i])) I tested it for a subset of my data and it all works. The problem is that I have 72 million observations, and even after leaving the computer working overnight, it still didn't finish. I am new in R, so I imagine my code structure can be improved upon and there is a better (quicker, less computationally intensive) way to perform this same task (perhaps using apply or with, both of which I don't understand). Any suggestions?

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• Why does C++ not allow multiple types in one auto statement?

  - by Walter

  The 2011 C++ standard introduced the new keyword auto, which can be used for defining variables instead of a type, i.e. auto p=make_pair(1,2.5); // pair<int,double> auto i=std::begin(c), end=std::end(c); // decltype(std::begin(c)) In the second line, i and end are of the same type, referred to as auto. The standard does not allow auto i=std::begin(container), e=std::end(container), x=*i; when x would be of different type. My question: why does the standard not allow this last line? It could be allowed by interpreting auto not as representing some to-be-decuded type, but as indicating that the type of any variable declared auto shall be deduced from its assigned value. Is there any good reason for the C++11 standard to not follow this approach? There is actually a use case for this, namely in the initialisation statement of for loops: for(auto i=std::begin(c), end=std::end(c), x=*i; i!=end; ++i, x+=*i) { ... } when the scope of the variables i, end, and x is limited to the for loop. AFAIK, this cannot be achieved in C++ unless those variables have a common type. Is this correct? (ugly tricks of putting all types inside a struct excluded) There may also be use cases in some variadic template applications.

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• nhibernate fluent repository pattern insert problem

  - by voam

  I am trying to use Fluent NHibernate and the repository pattern. I would like my business layer to not be knowledgeable of the data persistence layer. Ideally I would pass in an initialized domain object to the insert method of the repository and all would be well. Where I run into problems is if the object being passed in has a child object. For example say I want to insert an a new order for a customer, and the customer is a property of the order object. I would like to do something like this: Customer c = new Customer; c.CustomerId = 1; Order o = new Order; o.Customer = c; repository.InsertOrder(o); The problem is that using NHiberate the CustomerId field is only privately settable so I can not set it directly like this. so what I have ended up doing is have my repository have an interface of Order InsertOrder(int customerId) where all the foreign keys get passed in as parameters. Somehow this just doesn't seem right. The other approach was to use the NHibernate session variable to load a customer object in my business model and then have the order passed in to the repository but this defeats my persistence ignorance ideal. Should I throw this persistence ignorance out the window or am I missing something here? Thanks

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• Creating Mobile Cross-Platform Scripting Solution

  - by Aplomb

  I am having the dream to design a Mobile cross-platform scripting solution to achieve Developer only need to code once by scripting language(it's possible be Javascript or others need further investigation), then the solution will be able to generate the installation files for multiple mobile platforms like J2me, Android, Symbian, BlackBerry, Palm, Windows Mobile/Phone, iPhone, etc. Using the scripting language, developer can code with unified platform API. And other extension frameworks under scripting language, like, 1. 2D UI framework Most probably using for Mobile Applications, the UI style will compete with native UI framework and no longer every application in particular platform looks similar. 2. 3D UI framework Provide the platforms who has 3D capability can represent their Mobile Application with more fashion 3D style which will be much more abstractive. 3. Variable game engine Developers can can use it for easily and high-quality build games. 4. etc This Mobile solution is providing three points, 1. Cross-Platform 2. Scripting 3. Middleware So guys, what do you think about this idea, is it good for Developers? is it profitable? where is the better direction for this idea?

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• Insert HTML on Radio Label on Formtastic

  - by Adrian Matteo

  I have a form that has a radio button on it (Formtastic), and It works just fine with the :collection I'm passing. The problem is I want some part of the text to be affected by some CSS, but the :collection attribute does not let me put in HTML. Here's my code: = subscription.input :plan_type_id, :as => :radio, :label => false, :wrapper_html => {:class => "plan_type"}, :collection => { @plans[:premium_yearly][:description]+number_to_currency(@plans[:premium_yearly][:amount], :precision => 2) => @plans[:premium_yearly][:value], @plans[:premium_monthly][:description]+number_to_currency(@plans[:premium_monthly][:amount], :precision => 2) => @plans[:premium_monthly][:value] } Has you may may see, I build the label I want to show with my @plans variable and the :collection attribute. Is there any way I can modify the way it renders the label, I want to put some css to some part of the label. I want something like this: = subscription.input :plan_type_id, :as => :radio, :label => false, :wrapper_html => {:class => "plan_type"}, :collection => { @plans[:premium_yearly][:description]+'<b>'+number_to_currency(@plans[:premium_yearly][:amount], :precision => 2)+'<\\b>' => @plans[:premium_yearly][:value], @plans[:premium_monthly][:description]+'<b>'+number_to_currency(@plans[:premium_monthly][:amount], :precision => 2)+'<\\b>' => @plans[:premium_monthly][:value] } Thanks in advanced.

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• Problems Using memset and memcpy

  - by user306557

  So I am trying to create a Memory Management System. In order to do this I have a set amount of space (allocated by malloc) and then I have a function myMalloc which will essentially return a pointer to the space allocated. Since we will then try and free it, we are trying to set a header of the allocated space to be the size of the allocated space, using memset. memset(memPtr,sizeBytes,sizeof(int)); We then need to be able to read this so we can see the size of it. We are attempting to do this by using memcpy and getting the first sizeof(int) bytes into a variable. For testing purposes we are just trying to do memset and then immediately get the size back. I've included the entire method below so that you can see all declarations. Any help would be greatly appreciated! Thanks! void* FirstFit::memMalloc(int sizeBytes){ node* listPtr = freelist; void* memPtr; // Cycle through each node in freelist while(listPtr != NULL) { if(listPtr->size >= sizeBytes) { // We found our space // This is where the new memory allocation begins memPtr = listPtr->head; memset(memPtr,sizeBytes,sizeof(int)); void *size; memcpy(size, memPtr, sizeof(memPtr)); // Now let's shrink freelist listPtr->size = listPtr->size - sizeBytes; int *temp = (int*)listPtr->head + (sizeBytes*sizeof(int)); listPtr->head = (int*) temp; return memPtr; } listPtr = listPtr->next; }

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• Store variables during loop and use in it another template

  - by krisvandenbergh

  Is there a way to store a variable/param during a for-each loop in a sort of array, and use it in another template, namely <xsl:template match="Foundation.Core.Classifier.feature">. All the classname values that appear during the for-each should be stored. How would you implement that in XSLT? Here's my current code. <xsl:for-each select="Foundation.Core.Class"> <xsl:for-each select="Foundation.Core.ModelElement.name"> <xsl:param name="classname"> <xsl:value-of select="Foundation.Core.ModelElement.name"/> </xsl:param> </xsl:for-each> <xsl:apply-templates select="Foundation.Core.Classifier.feature" /> </xsl:for-each> Here's the template in which the classname parameters should be used. <xsl:template match="Foundation.Core.Classifier.feature"> <xsl:for-each select="Foundation.Core.Attribute"> <owl:DatatypeProperty rdf:ID="{Foundation.Core.ModelElement.name}"> <rdfs:domain rdf:resource="$classname" /> </owl:DatatypeProperty> </xsl:for-each> </xsl:template> The input file can be found at http://krisvandenbergh.be/uml_pricing.xml

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• clojure: ExceptionInInitializerError in Namespace.<init> loading from a non-default classpath

  - by Charles Duffy

  In attempting to load an AOT-compiled class from a non-default classpath, I receive the following exception: Traceback (innermost last): File "test.jy", line 10, in ? at clojure.lang.Namespace.<init>(Namespace.java:34) at clojure.lang.Namespace.findOrCreate(Namespace.java:176) at clojure.lang.Var.internPrivate(Var.java:149) at aot_demo.JavaClass.<clinit>(Unknown Source) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:247) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) java.lang.ExceptionInInitializerError: java.lang.ExceptionInInitializerError I'm able to reproduce this with the following trivial project.clj: (defproject aot-demo "0.1.0-SNAPSHOT" :dependencies [[org.clojure/clojure "1.3.0"]] :aot [aot-demo.core]) ...and src/aot_demo/core.clj defined as follows: (ns aot-demo.core (:gen-class :name aot_demo.JavaClass :methods [#^{:static true} [lower [java.lang.String] java.lang.String]])) (defn -lower [str] (.toLower str)) The following Jython script is then sufficient to trigger the bug: #!/usr/bin/jython import java.lang.Class import java.net.URLClassLoader import java.net.URL import os cl = java.net.URLClassLoader( [java.net.URL('file://%s/target/aot-demo-0.1.0-SNAPSHOT-standalone.jar' % (os.getcwd()))]) java.lang.Class.forName('aot_demo.JavaClass', True, cl) However, the exception does not occur if the test script is started with the uberjar already in the CLASSPATH variable. What's going on here? I'm trying to write a plugin for the BaseX database in Clojure; the above accurately represents how their plugin-loading mechanism works for the purpose of providing a SSCE for this problem.

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• Understanding Symbols In Ruby

  - by Kezzer

  Despite reading this article, I'm still confused as to the representation of the data in memory when it comes to using symbols. If a symbol, two of them contained in different objects, exist in the same memory location, then how is it that they contain different values? I'd have expected the same memory location to contain the same value. As a quote from the link: Unlike strings, symbols of the same name are initialized and exist in memory only once during a session of ruby I just don't understand how it manages to differentiate the values contained in the same memory location. EDIT So let's consider the example: patient1 = { :ruby => "red" } patient2 = { :ruby => "programming" } patient1.each_key {|key| puts key.object_id.to_s} 3918094 patient2.each_key {|key| puts key.object_id.to_s} 3918094 patient1 and patient2 are both hashes, that's fine. :ruby however is a symbol. If we were to output the following: patient1.each_key {|key| puts key.to_s} Then what will be output? "red", or "programming"? FURTHER EDIT I'm still really quite confused. I'm thinking a symbol is a pointer to a value. Let's forget hashes for a second. The questions I have are; can you assign a value to a symbol? Is a symbol just a pointer to a variable with a value in it? If symbols are global, does that mean a symbol always points to one thing?

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• BackgroundWorker and instance variables

  - by Alastair Pitts

  One thing that's always confused me is how a BackgroundWorker seems to have thread-safe access to the instance variables of the surrounding class. Given a basic class: public class BackgroundProcessor { public List<int> Items { get; private set; } public BackgroundProcessor(IEnumerable<int> items) { Items = new List<int>(items); } public void DoWork() { BackgroundWorker worker = new BackgroundWorker(); worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted); worker.DoWork += new DoWorkEventHandler(worker_DoWork); worker.RunWorkerAsync(); } void worker_DoWork(object sender, DoWorkEventArgs e) { var processor = new ProcessingClass(); processor.Process(this.Points); //Accessing the instance variable } void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { //Stuff goes here } } Am I erroneous in my assumption the the call to processor.Process(this.Points); is a thread-safe call? How don't I get a cross-thread access violation? I'm sure it's obvious, but it always has confused me.

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• How to make Web Storage persistent in Cordova using JS?

  - by ett

  I have a small quiz app, which is a cross-platform mobile app, that I plan for it to run on Android, iOS, and WP8. I want to store a local highscore, where it will keep track how many points the user had, and if he/she does better than the already stored highscore, update the current highscore. Though, I want the highscore to be persistent, what I mean is, every time the user opens the app I want the last highscore to be present and it to be compared with the new quiz score. Meaning, I don't want the highscore to be deleted after each time the app is closed. I also want for the first time when the app is ran, the highscore to be set to 0, so obviously the first time the user finishes the quiz gets a new highscore. I have those codes so far: scoredb.js // Wait for device API libraries to load document.addEventListener("deviceready", initScoreDB, false); // Device APIs are available function initScoreDB() { window.localStorage.setItem("score", 0); highscore = window.localStorage.getItem("score"); } main.js var correct = 0; var highscore; // In between I have some code that keeps incrementing // correct variable for each correct answer. if (correct > highscore) { window.localStorage.setItem("score", correct); highscore = correct; } It does seem to work okay once the app is started. I did the quiz three times, in the simulator, and it keeps the score as it should. Though, each time I open the app, highscore is reseted to 0. I guess it is due to the fact that I call initScoreDB when the device is ready, and I initialize the score to 0 there and give that value to highscore. Can someone help me to initialize the score to 0 only when the app is ran for the first time, and all the other times to keep the latest highscore as the current highscore and compare it each time with the score that is achieved when the quiz is finished. If someone can help me, I would be glad.

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• C# parameters by reference and .net garbage collection

  - by Yarko

  I have been trying to figure out the intricacies of the .NET garbage collection system and I have a question related to C# reference parameters. If I understand correctly, variables defined in a method are stored on the stack and are not affected by garbage collection. So, in this example: public class Test { public Test() { } public int DoIt() { int t = 7; Increment(ref t); return t; } private int Increment(ref int p) { p++; } } the return value of DoIt() will be 8. Since the location of t is on the stack, then that memory cannot be garbage collected or compacted and the reference variable in Increment() will always point to the proper contents of t. However, suppose we have: public class Test { private int t = 7; public Test() { } public int DoIt() { Increment(ref t); return t; } private int Increment(ref int p) { p++; } } Now, t is stored on the heap as it is a value of a specific instance of my class. Isn't this possibly a problem if I pass this value as a reference parameter? If I pass t as a reference parameter, p will point to the current location of t. However, if the garbage collector moves this object during a compact, won't that mess up the reference to t in Increment()? Or does the garbage collector update even references created by passing reference parameters? Do I have to worry about this at all? The only mention of worrying about memory being compacted on MSDN (that I can find) is in relation to passing managed references to unmanaged code. Hopefully that's because I don't have to worry about any managed references in managed code. :)

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• Why doesn't 'Q' unify in this PROLOG program

  - by inspectorG4dget

  Hello SO, I am writing a PROLOG program in which the variable of interest (Q) refuses to unify. I have gotten around this with a hacky solution (include a write statement). But there has to be a way to make this unify, but for the love of me, I am not able to figure it out. I'd really appreciate any help. Thanks in advance. Here is my code (I have annotated wherever I have excluded code for brevity) :- use_module(library(bounds)). :- use_module(library(lists)). solve([17],Q,_,_,_):- write(Q). %this is the hacky workaround solve(L,Q,1,3,2) :- jump(L,Q,N,1,3,2,R), solve(N,R,S,D,M), member([S|[D|[M|[]]]],[[1, 3, 2], [1, 9, 4], [2, 10, 5] this list contains 76 items - all of which are lists of length 3. I have omitted them here for the sake of brevity]). % there are about 75 other definitions for solve, all of which are structured exactly the same. The only difference is that the numbers in the input parameters will be different in each definition jump(L,Q,N,S,D,M,R):- member(S,L), not(member(D,L)), member(M,L), delete(L,S,X), delete(X,M,Y), append(Y,[D],N), append(Q,[[S,D]],R). cross_sol(Q) :- solve([5,9,10,11,17,24],[],S,D,M), member([S,D,M], [ I have edited out this list here for the sake of brevity. It is the same list found in the definition of solve ]). For some reason, Q does not unify. Please help!

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• Why slim reader/writer exclusive lock outperformance the shared one?

  - by Jichao

  I have tested the performance of slim reader/writer lock under windows 7 using the codefrom Windows Via C/C++. The result surprised me that the exclusive lock out performance the shared one. Here are the code and the result. unsigned int __stdcall slim_reader_writer_exclusive(void *arg) { //SRWLOCK srwLock; //InitializeSRWLock(&srwLock); for (int i = 0; i < 1000000; ++i) { AcquireSRWLockExclusive(&srwLock); g_value = 0; ReleaseSRWLockExclusive(&srwLock); } _endthreadex(0); return 0; } unsigned int __stdcall slim_reader_writer_shared(void *arg) { int b; for (int i = 0; i < 1000000; ++i) { AcquireSRWLockShared(&srwLock); //b = g_value; g_value = 0; ReleaseSRWLockShared(&srwLock); } _endthreadex(0); return 0; } g_value is a global int volatile variable. Could you kindly explain why this could happen?

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