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• Isolating read and write in multithreaded

  - by the_lotus

  Hi In a multithreaded application. I have a bunch of function that loop through a collection to read the information. I also have a bunch of function that modifies that same collection. I’m looking for a way to isolate all the read and the write together. I don’t want a write to be done while a read is in progress. I was thinking of using SyncLock on the collection object but this will block multiple read trying to work in parallel.

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• grouping objects to achieve a similar mean property for all groups

  - by cytochrome

  I have a collection of objects, each of which has a numerical 'weight'. I would like to create groups of these objects such that each group has approximately the same arithmetic mean of object weights. The groups won't necessarily have the same number of members, but the size of groups will be within one of each other. In terms of numbers, there will be between 50 and 100 objects and the maximum group size will be about 5. Is this a well-known type of problem? It seems a bit like a knapsack or partition problem. Are efficient algorithms known to solve it? As a first step, I created a python script that achieves very crude equivalence of mean weights by sorting the objects by weight, subgrouping these objects, and then distributing a member of each subgroup to one of the final groups. I am comfortable programming in python, so if existing packages or modules exist to achieve part of this functionality, I'd appreciate hearing about them. Thank you for your help and suggestions.

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• How do I use python wx:Config to access the Windows registry?

  - by GreenAsJade

  I've read http://wxpython.org/docs/api/wx.ConfigBase-class.html I've done some basic things like the appended. What I can see is that Config.Create() returns me some sort of configuration object, which has information about python in it. But clearly that's not what I'm looking for: I seem to be missing the magic to say "give me a Config that is the Windows Registry"... Thanks! GaJ import wx from wx import Config app=wx.App(False) config=Config.Create() config.HasGroup("HKEY_CURRENT_USER") False config.GetFirstEntry() (0, u'', -1) config.GetFirstGroup() (1, u'PythonCore', 1) config.GetNextGroup(1) (0, u'', -1) config.GetNumberOfGroups() 1 config.GetPath() u'' config.HasEntry("PythonCore") False config.GetFirstGroup() (1, u'PythonCore', 1)

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• c# how to get keydown and button click to do the same thing??

  - by myax

  I am new to C#.I am learning to make a calculator just like ms windows calculator.the buttons work when i click it, but I want the numpad to work too. Suppose the user types '0', it should be the same as if he clicked the 0 button on my gui. here is my button click event for 0. private void button0_Click(object sender, EventArgs e) { checkifequa(); textBox1.Text = textBox1.Text + "0"; } how do i get the keydown to work?

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• C++: static function member shared between threads, can block all?

  - by mhambra

  Hi all, I have a class, which has static function defined to work with C-style extern C { static void callback(foo bar) { } }. // static is defined in header. Three objects (each in separate pthread) are instantiated from this class, each of them has own loop (in class constructor), which can receive the callback. The pointer to function is passed as: x = init_function(h, queue_id, &callback, NULL); while(1) { loop_function(x); } So each thread has the same pointer to &callback. Callback function can block for minutes. Each thread object, excluding the one which got the blocking callback, can call callback again. If the callback function exists only once, then any thread attempting to callback will also block. This would give me an undesired bug, circa is interesting to ask: can anything in C++ become acting this way? Maybe, due to extern { } or some pointer usage?

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• Using jQuery, how do I way attach a string array as a http parameter to a http request?

  - by predhme

  I have a spring controller with a request mapping as follows @RequestMapping("/downloadSelected") public void downloadSelected(@RequestParam String[] ids) { // retrieve the file and write it to the http response outputstream } I have an html table of objects which for every row has a checkbox with the id of the object as the value. When they submit, I have a jQuery callback to serialize all ids. I want to stick those ids into an http request parameter called, "ids" so that I can grab them easily. I figured I could do the following var ids = $("#downloadall").serializeArray(); Then I would need to take each of the ids and add them to a request param called ids. But is there a "standard" way to do this? Like using jQuery?

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• Django - Expression based model constraints

  - by rtmie

  Is it possible to set an expression based constraint on a django model object, e.g. If I want to impose a constraint where an owner can have only one widget of a given type that is not in an expired state, but can have as many others as long as they are expired. Obviously I can do this by overriding the save method, but I am wondering if it can be done by setting constraints, e.g. some derivative of the unique_together constraint WIDGET_STATE_CHOICES = ( ('NEW', 'NEW'), ('ACTIVE', 'ACTIVE'), ('EXPIRED', 'EXPIRED') ) class MyWidget(models.Model): owner = models.CharField(max_length=64) widget_type = models.CharField(max_length = 10) widget_state = models.CharField(max_length = 10, choices = WIDGET_STATE_CHOICES) #I'd like to be able to do something like class Meta: unique_together = (("owner","widget_type","widget_state" != 'EXPIRED')

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• So I dynamically load a jar at runtime how do I use it?

  - by justinhj

  So question 194698 shows how to load a jar file at runtime and you can load individual named classes and get a Class object. Now my problem is I want to be able to cast those Classes to the types they really are, but I can't because I can't use an import since the whole point is to load it at runtime rather than compile time. It seems like the way to go is to use reflection to discover the functions and field names, but that seems brittle since the API in the jar files could change and the code won't break until it is run. Is there a better way?

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• How can I apply indexer to Dictionary VALUES (C#3.0)

  - by Newbie

  I have done a program string[] arrExposureValues = stock.ExposureCollection[dt] .Values.ToArray(); for(int i=0;i<arrExposureValues .length;i++) Console.WriteLine(arrExposureValues[i]); Nothing wrong and works fine. But is it possible to do something like the below for(int i=0;i<stock.ExposureCollection[dt].Count;i++) Console.WriteLine(stock.ExposureCollection[dt].Values[i]); This is just for my sake of knowledge (Basically trying to accomplish the same in one line). Note: ExposureCollection is a dictionary object Dictionary<DateTime, Dictionary<string, string>> First of all I have the doubt if it is at all possible! I am using C#3.0. Thanks.

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• How to make TObjectDictionary.Values accessible as property?

  - by Holgerwa

  I have an object like this: TMyObj = class private FObjList: TObjectDictionary <integer, TMyObject>; public constructor Create; destructor Destroy; // How to access Values correctly? Something similar to this not working code property Values: TValueCollection read FObjList.Values write FObjList.Values; end; var MyObj: TMyObj; To access the values of FObjList, I'd like to write: for tmpObject in MyObj.Values do ... How do I need to declare the property "Values" so that MyObj.Values behaves exactly as if I would access MyObj.FObjList.Values?

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• Make the Enter key act like the submit button

  - by Michael Quiles

  How can I make it where some one presses the enter key on my form it will submit this code ? Ive tried the ligtning bolt events etc... but I can't seem to figure it out. private void xTripSubmitButton_Click(object sender, EventArgs e) { // Calculates the numbers from the input and output boxes/labels Miles = double.Parse(this.xTripDestinationTextBox.Text); Mpg = double.Parse(this.xTripMpgTextBox.Text); Price = double.Parse(this.xTripPricepgTextBox.Text); Output = Miles / Mpg; Coutput = Output * Price; //displays a message and the result for the numbers the user inputs this.xTripOutputLabel.Text = "Total gallons you would use: " + Output.ToString("0") + Environment.NewLine + "Total amount it will cost you: " + Coutput.ToString("C"); }

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• Java vs C# - AddActionListener vs event subscription

  - by S.O.

  Very simple question from one somewhat new to Java: when adding an event handler (or whatever it is called in Java) to a Control, MUST it be an object? I mean, in C# I can do control.event += System.eventHandler(methodThatHandlesEvent) Sure, that's because we have delegate types in C#, but I was wondering if I can choose which method would be called when an event is raised in Java? I mean, in Java I can have something like control.AddActionListener(objectWhichClassImplementsActionListener) And then I have the stupid actionPerformed method in this class, which is the only method that is called. I know, there are more kinds of listeners, but I can't have a "ActionListenerHandler" class in which I implement several actionPerformed methods that can be assigned to different controls?

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• How to set a predefined value in a form in Rails

  - by marco

  So I just got started in Rails, and I'm trying to create an Object (a book_loan in my case) with a Form. The thing is that I get to this form by clicking on a book, so I pass the book_id as a parameter, like localhost:3000/loans/new?id=1. Now I don't want the user to be able to set the book id field in the form, since I already know the id. So my question is how to set the value in the form. I have been trying things like: <% form_for(@loan) do |f| %> <%= f.error_messages %> ... <%= @loan.book_id = params[:id] %> <%= f.submit 'Create' %> <% end %> without any success. Does anybody have a hint for me?

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• Makefile: expand dependencies

  - by Danyel

  First off, the title is very generic because there are just tons of ways of how to possibly solve this. However, I'm looking for a clean and neat way. Situation: I have two equal object files foo.o and foo-pi.o, the latter of which is position-independent (compiled with -fPIC). Both depend on foo.h and bar.h. Problem: How do I, without code duplication, declare dependency of all foo*.o to bar.h? Solutions so far: $(shell bash -c 'echo -ne foo{-pi,}.o'}: bar.h $(addsuffix .o, $(addprefix fo, o-pi o)): bar.h The first solution is not portable on systems that don't support bash, the second is a dirty solution since I could not figure out how to use empty strings in addprefix.

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• Separating data from the UI code with Linq to SQL entities

  - by Sir Psycho

  If it's important to keep data access 'away' from business and presentation layers, what alternatives or approaches can I take so that my LINQ to SQL entities can stay in the data access layer? So far I seem to be simply duplicating the classes produced by sqlmetal, and passing those object around instead simply to keep the two layers appart. For example, I have a table in my DB called Books. If a user is creating a new book via the UI, the Book class generated by sqlmetal seems like a perfect fit although I'm tightly coupling my design by doing so.

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• Windows Service Fails on Launch

  - by Jeff

  I'm trying to write a windows service. It installs fine, but fails when I run it with the following exception. I've searched for the string "MyNewProgramService", but I can't find any conversions that would throw this error. I've also added try/catch blocks to a bunch of code with custom exception handling without finding where this exception is occuring. I'm thinking it's somewhere in the auto-generated configuartion/setup code. Any ideas? Event Type: Error Event Source: MyNewProgram Event Category: None Event ID: 0 Date: 4/15/2010 Time: 12:48:34 PM User: N/A Computer: 20F7KF1 Description: Service cannot be started. System.InvalidCastException: Conversion from string "MyNewProgramService" to type 'Integer' is not valid. ---> System.FormatException: Input string was not in a correct format. at Microsoft.VisualBasic.CompilerServices.Conversions.ParseDouble(String Value, NumberFormatInfo NumberFormat) at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value) --- End of inner exception stack trace --- at Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value) at TaskManagerFailureHandlerService.MyNewProgramService.OnStart(String[] args) at System.ServiceProcess.ServiceBase.ServiceQueuedMainCallback(Object state)

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• Problem with anonymouse delegate within foreach

  - by geting

  public Form1() { InitializeComponent(); Collection<Test> tests = new Collection<Test>(); tests.Add(new Test("test1")); tests.Add(new Test("test2")); foreach (Test test in tests) { Button button = new Button(); button.Text = test.name; button.Click+=new EventHandler((object obj, EventArgs arg)=>{ this.CreateTest(test); }); this.flowLayoutPanel1.Controls.Add(button); } } public void CreateTest(Test test) { MessageBox.Show(test.name); } } when i click the button witch text is 'test1', the messagebox will show 'test2',but my expect is 'test1'. So ,would anyone please tell me why or what`s wrong with my code.

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• Timeout Expire on INSERT Query

  - by Sachin Gaur

  I am trying to insert a row in a table using simple INSERT Query in a transaction. It works fine in SQL Server but I am not able to insert the data using my business object. I am calling a SELECT query using the Command as: Using cm As New SqlCommand With cm .Connection = tr.Connection .Transaction = tr .CommandType = CommandType.Text .CommandText = Some Select Query .ExecuteScalar() '' Do something .CommandText = Insert Query .ExecuteNonQuery() End With End Using I am getting the Timeout period expired error at ".ExecuteNonQuery()" line. Any other DML query is running perfectly fine at this point. Can anyone tell me the reason?

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• Python sqlite3 and concurrency

  - by RexE

  I have a Python program that uses the "threading" module. Once every second, my program starts a new thread that fetches some data from the web, and stores this data to my hard drive. I would like to use sqlite3 to store these results, but I can't get it to work. The issue seems to be about the following line: conn = sqlite3.connect("mydatabase.db") If I put this line of code inside each thread, I get an OperationalError telling me that the database file is locked. I guess this means that another thread has mydatabase.db open through a sqlite3 connection and has locked it. If I put this line of code in the main program and pass the connection object (conn) to each thread, I get a ProgrammingError, saying that SQLite objects created in a thread can only be used in that same thread. Previously I was storing all my results in CSV files, and did not have any of these file-locking issues. Hopefully this will be possible with sqlite. Any ideas?

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• SQLAlchemy - loading user by username

  - by keithjgrant

  Just diving into pylons here, and am trying to get my head around the basics of SQLALchemy. I have figured out how to load a record by id: user_q = session.query(model.User) user = user_q.get(user_id) But how do I query by a specific field (i.e. username)? I assume there is a quick way to do it with the model rather than hand-building the query. I think it has something with the add_column() function on the query object, but I can't quite figure out how to use it. I've been trying stuff like this, but obviously it doesn't work: user_q = meta.Session.query(model.User).add_column('username'=user_name) user = user_q.get()

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• Can I use MFC objects in STL containers?

  - by Jesse Stimpson

  The following code doesn't compile for me in MSVC2005: std::vector<CMenu> vec(10); CMenu is an MFC menu object (such as a context menu). Through some testing I learned that CMenu does not have a public copy constructor. To do what I wanted to do, I needed to use a dynamic array. CMenu* menus = new CMenu[10]; // ... delete [] menus; Of course, now I've lost all the benefits of using an STL container. Do I have any other options?

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• Explicit constructor still has default values even though a default constructor is not invoked.

  - by Phoenix

  According to my understanding a default constructor initializes the state of the object to default values, so if i provide an explicit no-arg public constructor like this then how are the values of d and e still getting initialized to zero because in this case the default constructor is not invoked. public class B extends A{ private int d; private int e; public B() { System.out.println(d); System.out.println(e); } } EDIT:: The only thing default constructor does is call to super() then how come if i have a explicitly mentioned a constructor here and A has a protected variable say c which is initialized to 17 in its constructor. Should I not be explicitly calling super() to be able to see that change since I'm using my own constructor ? Why is B still getting the value of 17 through inheritance ?

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• scala xml rewrite rule (or, simple pattern help)

  - by williamstw

  I'm missing some fairly simple syntax I gather. I'm trying to rewrite an element label to something else and keep everything else intact. object htmlRule extends RewriteRule { override def transform(n: Node): Seq[Node] = n match { case Elem(prefix, "document", attribs, scope, child@_*) => Elem(prefix, "html", attribs, scope, child) case other => other } } Now, I ask for an explanation of two things: 1) What exactly does "child@_*" mean in plain English? 2) How can I capture the value of "child@_*" and just let it pass right through to the new element? Currently, I get the following error, which makes sense. [error] found : Seq[scala.xml.Node] [error] required: scala.xml.Node [error] Elem(prefix, "html", attribs, scope, child) I'm not wedded to this either, so if there's a better way to simply change the element name of a specific node, let's here it... Thanks, --tim

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• Ignoring "Content is not allowed in trailing section" SAXException

  - by Paul J. Lucas

  I'm using Java's DocumentBuilder.parse(InputStream) to parse an XML document. Occasionally, I get malformed XML documents in that there is extra junk after the final > that causes a SAXException: Content is not allowed in trailing section. (In the cases I've seen, the junk is simply one or more null bytes.) I don't care what's after the final >. Is there an easy way to parse an entire XML document in Java and have it ignore any trailing junk? Note that by "ignore" I don't simply mean to catch and ignore the exception: I mean to ignore the trailing junk, throw no exception, and to return the Document object since the XML up to an including the final > is valid.

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• returning values from function or method multiple times by only calling the class once

  - by Sokhrat Sikar

  I have a members.php file that shows my websites members. I echo members name by using foreach method. A method of Members class returns an array, then I use foreach loop in the members.php file to echo the members. I am trying to aovid writing php code in my members.php file. Is there a way to avoid using foreach inside members.php file? For example, is it possible to return value from a method couple of times? (by only calling the object once). Just like how we normally call the functions? This question doesn't make sense, but I am just trying to see if there is a away around this issue?

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