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  • Perl : package using problem.

    - by pavun_cool
    Hi All.. Normally when I am writing the perl program . I used to include following package . use strict ; use warnings ; use Data::Dumper ; Now , I want like this, I will not include all this package for every program . for that I will have these all package in my own package. like following. my_packages.pm package my_packages ; { use strict ; use warnings ; use Data::Dumper; } 1; So, that if I add my_packages.pm in perl program , it needs have all above packages . Actually I have done this experimentation . But I am not able get this things . which means when I am using my_packages . I am not able get the functionality of "use strict, use warnings , use Data::Dumper ". Someone help me out of this problem.....

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  • NSPredicate as a constraint solver?

    - by Felixyz
    I'm working on a project which includes some slightly more complex dynamic layout of interface elements than what I'm used to. I always feel stupid writing complex code that checks if so-and-so is close to such-and-such and in that case move it x% in some direction, etc. That's just not how programming should be done. Programming should be as declarative as possible! Precisely because what I'm going to do is fairly simple, I thought it would be a good opportunity to try something new, and I thought of using NSPredicate as a simple constraints solver. I've only used NSPredicate for very simple tasks so far, but I know that it capable of much more. Are there any ideas, experiences, examples, warnings, insights that could be useful here? I'll give a very simple example so there will be something concrete to answer. How could I use NSPredicate to solve the following constraints: viewB.xmid = (viewB.leftEdge + viewB.width) / 2 viewB.xmid = max(300, viewA.rightEdge + 20 + viewB.width/2) ("viewB should be horizontally centered on coordinate 300, unless its left edge gets within 20 pixels of viewB's right edge, in which case viewA's left edge should stay fixed at 20 pixels to the right of viewB's right edge and viewA's horizontal center get pushed to the right.") viewA.rightEdge and viewB.width can vary, and those are the 'input variables'. EDIT: Any solution would probably have to use the NSExpression method -(id)expressionValueWithObject:(id)object context:(NSMutableDictionary *)context. This answer is relevant.

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  • NSFetchedResultsController: changing predicate not working?

    - by icerelic
    Hi, I'm writing an app with two tables on one screen. The left table is a list of folders and the right table shows a list of files. When tapped on a row on the left, the right table will display the files belonging to that folder. I'm using Core Data for storage. When the selection of folder changes, the fetch predicate of the right table's NSFetchedResultsController will change and perform a new fetch, then reload the table data. I used the following code snippet: NSPredicate *predicate = [NSPredicate predicateWithFormat:@"list = %@",self.list]; [fetchedResultsController.fetchRequest setPredicate:predicate]; NSError *error = nil; if (![[self fetchedResultsController] performFetch:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } [table reloadData]; However the fetch results are still the same. I've NSLog'ed "predicate" before and after the fetch, and they were correct with updated information. The fetch results stay the same as initial fetch (when view is loaded). I'm not very familiar with the way Core Data fetches objects (is there a caching system?), but I've done similar things before(changing predicates, re-fetching data, and refreshing table) with single table views and everything went well. If someone could gave me a hint I would be very appreciated. Thanks in advance.

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  • How to distinguish between two different UDP clients on the same IP address?

    - by Ricket
    I'm writing a UDP server, which is a first for me; I've only done a bit of TCP communications. And I'm having trouble figuring out exactly how to distinguish which user is which, since UDP deals only with packets rather than connections and I therefore cannot tell exactly who I'm communicating with. Here is pseudocode of my current server loop: DatagramPacket p; socket.receive(p); // now p contains the user's IP and port, and the data int key = getKey(p); if(key == 0) { // connection request key = makeKey(p); clients.add(key, p.ip); send(p.ip, p.port, key); // give the user his key } else { // user has a key // verify key belongs to that IP address // lookup the user's session data based on the key // react to the packet in the context of the session } When designing this, I kept in mind these points: Multiple users may exist on the same IP address, due to the presence of routers, therefore users must have a separate identification key. Packets can be spoofed, so the key should be checked against its original IP address and ignored if a different IP tries to use the key. The outbound port on the client side might change among packets. Is that third assumption correct, or can I simply assume that one user = one IP+port combination? Is this commonly done, or should I continue to create a special key like I am currently doing? I'm not completely clear on how TCP negotiates a connection so if you think I should model it off of TCP then please link me to a good tutorial or something on TCP's SYN/SYNACK/ACK mess. Also note, I do have a provision to resend a key, if an IP sends a 0 and that IP already has a pending key; I omitted it to keep the snippet simple. I understand that UDP is not guaranteed to arrive, and I plan to add reliability to the main packet handling code later as well.

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  • Java: Reading images and displaying as an ImageIcon

    - by 11helen
    I'm writing an application which reads and displays images as ImageIcons (within a JLabel), the application needs to be able to support jpegs and bitmaps. For jpegs I find that passing the filename directly to the ImageIcon constructor works fine (even for displaying two large jpegs), however if I use ImageIO.read to get the image and then pass the image to the ImageIcon constructor, I get an OutOfMemoryError( Java Heap Space ) when the second image is read (using the same images as before). For bitmaps, if I try to read by passing the filename to ImageIcon, nothing is displayed, however by reading the image with ImageIO.read and then using this image in the ImageIcon constructor works fine. I understand from reading other forum posts that the reason that the two methods don't work the same for the different formats is down to java's compatability issues with bitmaps, however is there a way around my problem so that I can use the same method for both bitmaps and jpegs without an OutOfMemoryError? (I would like to avoid having to increase the heap size if possible!) The OutOfMemoryError is triggered by this line: img = getFileContentsAsImage(file); and the method definition is: public static BufferedImage getFileContentsAsImage(File file) throws FileNotFoundException { BufferedImage img = null; try { ImageIO.setUseCache(false); img = ImageIO.read(file); img.flush(); } catch (IOException ex) { //log error } return img; } The stack trace is: Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: Java heap space at java.awt.image.DataBufferByte.<init>(DataBufferByte.java:58) at java.awt.image.ComponentSampleModel.createDataBuffer(ComponentSampleModel.java:397) at java.awt.image.Raster.createWritableRaster(Raster.java:938) at javax.imageio.ImageTypeSpecifier.createBufferedImage(ImageTypeSpecifier.java:1056) at javax.imageio.ImageReader.getDestination(ImageReader.java:2879) at com.sun.imageio.plugins.jpeg.JPEGImageReader.readInternal(JPEGImageReader.java:925) at com.sun.imageio.plugins.jpeg.JPEGImageReader.read(JPEGImageReader.java:897) at javax.imageio.ImageIO.read(ImageIO.java:1422) at javax.imageio.ImageIO.read(ImageIO.java:1282) at framework.FileUtils.getFileContentsAsImage(FileUtils.java:33)

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  • Vim, LaTeX, and version controlI

    - by Bkkbrad
    I'm writing a LaTeX document in vim, and I have it hard wrapping at 80 characters to make reading easier. However, this causes problems with tracking changes with in version control. For example, inserting "Lorem ipsum" at the beginning of this text: 1 Dolor sit amet, consectetur adipiscing elit. Phasellus bibendum lobortis lectus 2 quis porta. Aenean vestibulum magna vel purus laoreet at molestie massa 3 suscipit. Vestibulum vestibulum, mauris nec convallis ultrices, tellus sapien 4 ullamcorper elit, dignissim consectetur justo tellus et nunc. results in: 1 Lorum ipsum dolor sit amet, consectetur adipiscing elit. Phasellus bibendum 2 lobortis lectus quis porta. Aenean vestibulum magna vel purus laoreet at 3 molestie massa suscipit. Vestibulum vestibulum, mauris nec convallis ultrices, 4 tellus sapien ullamcorper elit, dignissim consectetur justo tellus et nunc. When I review this change in git, it tells me that all the lines of the paragraph have changed because of the wrapping, even though only one semantic change has occurred. One way around this problem is to have every sentence on its own line. This looks the same in the rendered document, but the source now is harder to read, because each line has quite a different line length: 1 Lorum ipsum dolor sit amet, consectetur adipiscing elit. 2 Phasellus bibendum lobortis lectus quis porta. 3 Aenean vestibulum magna vel purus laoreet at molestie massa suscipit. 4 Vestibulum vestibulum, mauris nec convallis ultrices, tellus sapien ullamcorper elit, dignissim consectetur justo tellus et nunc. (If I soft wrap at 80, things still look bad, just in a different way.) Is it possible to have my text on disk with one newline per sentence, but display and edit it in vim as if the text of each paragraph was one long line, soft wrapped at 80 characters? I assume it requires some vim-foo rather than tweaking git or LaTeX.

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  • Java resource closing

    - by Bob
    Hi, I'm writing an app that connect to a website and read one line from it. I do it like this: try{ URLConnection connection = new URL("www.example.com").openConnection(); BufferedReader rd = new BufferedReader(new InputStreamReader(connection.getInputStream())); String response = rd.readLine(); rd.close(); }catch (Exception e) { //exception handling } Is it good? I mean, I close the BufferedReader in the last line, but I do not close the InputStreamReader. Should I create a standalone InputStreamReader from the connection.getInputStream, and a BufferedReader from the standalone InputStreamReader, than close all the two readers? I think it will be better to place the closing methods in the finally block like this: InputStreamReader isr = null; BufferedReader br = null; try{ URLConnection connection = new URL("www.example.com").openConnection(); isr = new InputStreamReader(connection.getInputStream()); br = new BufferedReader(isr); String response = br.readLine(); }catch (Exception e) { //exception handling }finally{ br.close(); isr.close(); } But it is ugly, because the closing methods can throw exception, so I have to handle or throw it. Which solution is better? Or what would be the best solution?

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  • How to configure database connection securely

    - by chiccodoro
    Similar but not the same: How to securely store database connection details Securely connecting to database within a application Hi all, I have a C# WinForms application connecting to a database server. The database connection string, including a generic user/pass, is placed in a NHibernate configuration file, which lies in the same directory as the exe file. Now I have this issue: The user that runs the application should not get to know the username/password of the general database user because I don't want him to rummage around in the database directly. Alternatively I could hardcode the connection string, which is bad because the administrator must be able to change it if the database is moved or if he wants to switch between dev/test/prod environments. So long I've found three possibilities: The first referenced question was generally answered by making the file only readable for the user that runs the application. But that's not not enough in my case (the user running the application is a person. The database user/pass are general and shouldn't even be accessible by the person.) The first answer additionally proposed to encrypt the connection data before writing it to the file. With this approach, the administrator is not able anymore to configure the connection string because he cannot encrypt it by hand. The second referenced question provides an approach for this very scenario but it seems very complicated. My questions to you: This is a very general issue, so isn't there any general "how-to-do-it" way, somehow a "design pattern"? Is there some support in .NET's config infrastructure? (optional, maybe out of scope) Can I combine that easily with the NHibernate configuration mechanism?

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  • Java Bucket Sort on Strings

    - by Michael
    I can't figure out what would be the best way to use Bucket Sort to sort a list of strings that will always be the same length. An algorithm would look like this: For the last character position down to the first: For each word in the list: Place the word into the appropriate bucket by current character For each of the 26 buckets(arraylists) Copy every word back to the list I'm writing in java and I'm using an arraylist for the main list that stores the unsorted strings. The strings will be five characters long each. This is what I started. It just abrubdly stops within the second for loop because I don't know what to do next or if I did the first part right. ArrayList<String> count = new ArrayList<String>(26); for (int i = wordlen; i > 0; i--) { for (int j = 0; i < myList.size(); i++) myList.get(j).charAt(i) } Thanks in advanced.

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  • How do I get the inserted id (or object) after an insert with the FormView/ObjectDataSource controls

    - by drs9222
    I have a series of classes that loosely fit the following pattern: public class CustomerInfo { public int Id {get; set;} public string Name {get; set;} } public class CustomerTable { public bool Insert(CustomerInfo info) { /*...*/ } public bool Update(CustomerInfo info) { /*...*/ } public CustomerInfo Get(int id) { /*...*/ } /*...*/ } After a successful insert the Insert method will set the Id property of the CustomerInfo object that was passed in. I've used these classes in several places and would prefer to altering them. Now I'm experimenting with writing an ASP.NET page for inserting and updating the records. I'm currently using the ObjectDataSource and FormView controls: <asp:ObjectDataSource TypeName="CustomerTable" DataObjectTypeName="CustomerInfo" InsertMethod="Insert" UpdateMethod="Update" SelectMethod="Get" /> I can successfully Insert and Update records. I would like to switch the FormView's mode from Insert to Edit after a successful insert. My first attempt was to switch the mode in the ItemInserted event. This of course did not work. I was using a QueryStringParameter for the id which of course wan't set when inserting. So, I switched to manually populating the InputParameters during the ObjectDataSource's Selecting event. The problem with this is I need to know the id of the newly inserted record which I can't find a good way to get. I understand that I can access the Insert method's return value, and out parameters in the ItemInserted event of course my method doesn't return the id using any of these methods. I can't find anyway to access the id or the CustomerInfo object that was inserted after the insert completes. The best I've been able to do is to save the CustomerInfo object in the ObjectDataSource's Inserting event. This feels like an odd way to do this. I figure that there must be a better way to do this and I'll kick myself when I see it. Any ideas?

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  • need primitive public key signature with out of band key distribution

    - by Mike D
    I pretty much a complete neophyte at this signature business so I don't know if what I'm asking is nonsense or not. Anyway, here goes... I want to send an out of band message (don't worry about how it gets there) to a program I've written on a distant machine. I want the program to have some confidence the message is legit by attaching a digital signature to the message. The message will be small less than 200 characters. It seems a public key based signature is what I want to use. I could embed the public key in the program. I understand that the program would be vulnerable to attack by anyone who modifies it BUT I'm not too worried about that. The consequences are not dire. I've looked through the MSDN and around the web but the prospect of diving in is daunting. I'm writing in straight c++, no NET framework or other fancy stuff. I've had no experience including NET framework stuff and little luck during previous attempts. Can anyone point me at some very basic resources to get me started? I need to know 1)how to generate the public and private keys 2)how to sign the message 3)how to verify the signature Any help much appreciated. TIA, Mike

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  • Outgoing UDP sniffer in python?

    - by twneale
    I want to figure out whether my computer is somehow causing a UDP flood that is originating from my network. So that's my underlying problem, and what follows is simply my non-network-person attempt to hypothesize a solution using python. I'm extrapolating from recipe 13.1 ("Passing Messages with Socket Datagrams") from the python cookbook (also here). Would it possible/sensible/not insane to try somehow writing an outgoing UDP proxy in python, so that outgoing packets could be logged before being sent on their merry way? If so, how would one go about it? Based on my quick research, perhaps I could start a server process listening on suspect UDP ports and log anything that gets sent, then forward it on, such as: import socket s =socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.bind(("", MYPORT)) while True: packet = dict(zip('data', 'addr'), s.recvfrom(1,024)) log.info("Recieved {data} from {addr}.".format(**packet)) But what about doing this for a large number of ports simultaneously? Impractical? Are there drawbacks or other reasons not to bother with this? Is there a better way to solve this problem (please be gentle).

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  • Basic syntax for an animation loop?

    - by Moshe
    I know that jQuery, for example, can do animation of sorts. I also know that at the very core of the animation, there must me some sort of loop doing the animation. What is an example of such a loop? A complete answer should ideally answer the following questions: What is a basic syntax for an effective animation recursion that can animate a single property of a particular object at a time? The function should be able to vary its target object and property of the object. What arguments/parameters should it take? What is a good range of reiterating the loop? In milliseconds? (Should this be a parameter/argument to the function?) REMEMBER: The answer is NOT necessarily language specific, but if you are writing in a specific language, please specify which one. Error handling is a plus. {Nothing is more irritating (for our purposes) than an animation that does something strange, like stopping halfway through.} Thanks!

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  • SSL certificate pre-fetch .NET

    - by Wil P
    I am writing a utility that would allow me to monitor the health of our websites. This consists of a series of validation tasks that I can run against a web application. One of the tests is to anticipate the expiration of a particular SSL certificate. I am looking for a way to pre-fetch the SSL certificate installed on a web site using .NET or a WINAPI so that I can validate the expiration date of the certificate associated with a particular website. One way I could do this is to cache the certificates when they are validated in the ServicePointManager.ServerCertificateValidationCallback handler and then match them up with configured web sites, but this seems a bit hackish. Another would be to configure the application with the certificate for the website, but I'd rather avoid this if I can in order to minimize configuration. What would be the easiest way for me to download an SSL certificate associated with a website using .NET so that I can inspect the information the certificate contains to validate it? EDIT: To extend on the answer below there is no need to manually create the ServicePoint prior to creating the request. It is generated on the request object as part of executing the request. private static string GetSSLExpiration(string url) { HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest; using (WebResponse response = request.GetResponse()) { } if (request.ServicePoint.Certificate != null) { return request.ServicePoint.Certificate.GetExpirationDateString(); } else { return string.Empty; } }

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  • Join + IEqualityComparer<T> and HashCode

    - by Jesus Rodriguez
    Im writing my own LINQ reference but Im getting troubles with some of the more complicated operators implementations. There is a Join implementation that takes a IEqualityComparer Im getting just crazy. Im trying to understand it first before I write (obviously) Image this two lists: List<string> initials = new List<string> {"A", "B", "C", "D", "E"}; List<string> words = new List<string> {"Ant", "Crawl", "Pig", "Boat", "Elephant", "Arc"}; Nothing weird here. I want to join both lists by the Initial, something like: Initial=A Word=Ant Initial=A Word=Arc Initial=B Word=Boat ... I need a comparator, I wrote this: public class InitialComparator : IEqualityComparer<string> { public bool Equals(string x, string y) { return x.StartsWith(y); } public int GetHashCode(string obj) { return obj[0].GetHashCode(); } } The Join itself: var blah = initials.Join(words, initial => initial, word => word, (initial, word) => new {Initial = initial, Word = word}, new InitialComparator()); It's the first time Im using HashCodes, after a good session of debugging I see that every word go to the comparator and look at its HashCode, if another word has the same HashCode it calls equals. Since I want to compare just the initial I though that I just need the first letter Hash (Am I wrong?) The thing is that this is not working correctly. Its says that "Ant" and "Arc" are equals, Ok, its comparing every word in the same list or not, But it adds only the last word it finds, in this case Arc, ignoring Ant and Ant is equals to "A" too... If I put "Ant" and "Ant" it add both. In short, What is the way of doing something like that? I know that Im doing something wrong. Thank you.

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  • Generating JavaScript in C# and subsequent testing

    - by Codebrain
    We are currently developing an ASP.NET MVC application which makes heavy use of attribute-based metadata to drive the generation of JavaScript. Below is a sample of the type of methods we are writing: function string GetJavascript<T>(string javascriptPresentationFunctionName, string inputId, T model) { return @"function updateFormInputs(value){ $('#" + inputId + @"_SelectedItemState').val(value); $('#" + inputId + @"_Presentation').val(value); } function clearInputs(){ " + helper.ClearHiddenInputs<T>(model) + @" updateFormInputs(''); } function handleJson(json){ clearInputs(); " + helper.UpdateHiddenInputsWithJson<T>("json", model) + @" updateFormInputs(" + javascriptPresentationFunctionName + @"()); " + model.GetCallBackFunctionForJavascript("json") + @" }"; } This method generates some boilerplace and hands off to various other methods which return strings. The whole lot is then returned as a string and written to the output. The question(s) I have are: 1) Is there a nicer way to do this other than using large string blocks? We've considered using a StringBuilder or the Response Stream but it seems quite 'noisy'. Using string.format starts to become difficult to comprehend. 2) How would you go about unit testing this code? It seems a little amateur just doing a string comparison looking for particular output in the string. 3) What about actually testing the eventual JavaScript output? Thanks for your input!

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  • Why is there unreachable code here?

    - by Richard
    I am writing a c# app and want to output error messages to either the console or a messagebox (Depending on the app type: enum AppTypeChoice { Console, Windows } ), and also control wether the app keeps running or not ( bool StopOnError ). I came up with this method that will check all the criteria, but I'm getting an "unreachable code detected" warning. I can't see why! Here is the whole method (Brace yourselves for some hobbyist code!) public void OutputError(string message) { string standardMessage = "Something went WRONG!. [ But I'm not telling you what! ]"; string defaultMsgBoxTitle = "Aaaaarrrggggggggggg!!!!!"; string dosBoxOutput = "\n\n*** " + defaultMsgBoxTitle + " *** \n\n Message was: '" + message + "'\n\n"; AppTypeChoice appType = DataDefs.AppType; DebugLevelChoice level = DataDefs.DebugLevel; // Decide how much info we should give out here... if (level != DebugLevelChoice.None) { // Give some info.... if (appType == AppTypeChoice.Windows) MessageBox.Show(message, defaultMsgBoxTitle, MessageBoxButtons.OK, MessageBoxIcon.Error); else Console.WriteLine(dosBoxOutput); } else { // Be very secretive... if (appType == AppTypeChoice.Windows) MessageBox.Show(standardMessage, defaultMsgBoxTitle, MessageBoxButtons.OK, MessageBoxIcon.Error); else Console.WriteLine(standardMessage); } // Decide if app falls over or not.. if (DataDefs.StopOnError == true) Environment.Exit(0); // UNREACHABLE CODE HERE } Also, while I have your attention, to get the app type, I'm just using a constant at the top of the file (ie. AppTypeChoice.Console in a Console app etc) - is there a better way of doing this (i mean finding out in code if it is a DOS or Windows app)? Also, I noticed that I can use a messagebox with a fully-qualified path in a Console app...How bad is is to do that ( I mean, will I get tarred and feathered when other developers see it?!) Thanks for your help

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  • Building a custom (dynamic) dataset and grid

    - by marko.ivanovski.nz
    Hi, I'm in the process of building a dynamic table in which you can add/remove rows & columns so it varies in size depending on what the user wants. Its purpose is to store properties for a product, but there can be from 1 to 10 different properties(columns) per product, and multiple instances(rows) of the product as well. Here's a screenshot of what I mean http://i40.tinypic.com/nbqkxc.jpg As you can see I need the structure to be completely up to the client which is where I'm getting stuck. I've started writing a custom DataSet that has "add column" & "add row" buttons, and have built a custom Table with Textboxes in each cell which builds from that dataset. I have no idea how to store the data on submit though, and to make it even more complex I need to store this in the database as a string which I think I can do by converting it to XML. Any help is appreciated, I think I just need a pointer in the right direction and am happy to do research from there. Thanks in advance. Marko

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  • notify listener inside or outside inner synchronization

    - by Jary Zeels
    Hello all, I am struggling with a decision. I am writing a thread-safe library/API. Listeners can be registered, so the client is notified when something interesting happens. Which of the two implementations is most common? class MyModule { protected Listener listener; protected void somethingHappens() { synchronized(this) { ... do useful stuff ... listener.notify(); } } } or class MyModule { protected Listener listener; protected void somethingHappens() { Listener l = null; synchronized(this) { ... do useful stuff ... l = listener; } l.notify(); } } In the first implementation, the listener is notified inside the synchronization. In the second implementation, this is done outside the synchronization. I feel that the second one is advised, as it makes less room for potential deadlocks. But I am having trouble to convince myself. A downside of the second imlementation is that the client might receive 'incorrect' notifications, which happens if it accessed the module prior to the l.notify() statement. thanks a lot

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  • Core principles, rules, and habits for CS students

    - by Asad Butt
    No doubt there is a lot to read on blogs, in books, and on Stack Overflow, but can we identify some guidelines for CS students to use while studying? For me these are: Finish your course books early and read 4-5 times more material relative to your course work. Programming is the one of the fastest evolving professions. Follow the blogs on a daily basis for the latest updates, news, and technologies. Instead of relying on assignments and exams, do at least one extra, non-graded, small to medium-sized project for every programming course. Fight hard for internships or work placements even if they are unpaid, since 3 months of work 1 year at college. Practice everything, every possible and impossible way. Try doing every bit of your assignments project yourself; i.e. fight for every inch. Rely on documentation as the first source for help and samples, Google, and online forums as the last source. Participate often in online communities and forums to learn the best possible approach for every solution to your problem. (After doing your bit.) Make testing one of your habits as it is getting more important everyday in programming. Make writing one of your habits. Write something productive once or twice a week and publish it.

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  • Why does setting this member in C fail?

    - by Lee Crabtree
    I'm writing a Python wrapper for a C++ library, and I'm getting a really weird when trying to set a struct's field in C. If I have a struct like this: struct Thing { PyOBJECT_HEAD unsigned int val; }; And have two functions like this: static PyObject* Thing_GetBit(Thing* self, PyObject* args) { unsigned int mask; if(!PyArg_ParseTuple(args, "I", &mask) Py_RETURN_FALSE; if((self->val & mask) != 0) Py_RETURN_TRUE; Py_RETURN_FALSE; } static PyObject* Thing_SetBit(Thing* self, PyObject* args) { unsigned int mask; bool on; if(!PyArg_ParseTuple(args, "Ii", &mask, &on)) Py_RETURN_FALSE; if(on) thing->val |= mask; else thing->val &= ~mask; Py_RETURN_TRUE; } Python code that calls the first method works just fine, giving back the value of the struct member. Calls to the SetBit method give an error about an object at address foo accessing memory at address bar, which couldn't be "written". I've poked around the code, and it's like I can look at the value all I want, both from C and Python, but the instant I try to set it, it blows up in my face. Am I missing something fundamental here?

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  • Putting a C++ Vector as a Member in a Class that Uses a Memory Pool

    - by Deep-B
    Hey, I've been writing a multi-threaded DLL for database access using ADO/ODBC for use with a legacy application. I need to keep multiple database connections for each thread, so I've put the ADO objects for each connection in an object and thinking of keeping an array of them inside a custom threadInfo object. Obviously a vector would serve better here - I need to delete/rearrange objects on the go and a vector would simplify that. Problem is, I'm allocating a heap for each thread to avoid heap contention and stuff and allocating all my memory from there. So my question is: how do I make the vector allocate from the thread-specific heap? (Or would it know internally to allocate memory from the same heap as its wrapper class - sounds unlikely, but I'm not a C++ guy) I've googled a bit and it looks like I might need to write an allocator or something - which looks like so much of work I don't want. Is there any other way? I've heard vector uses placement-new for all its stuff inside, so can overloading operator new be worked into it? My scant knowledge of the insides of C++ doesn't help, seeing as I'm mainly a C programmer (even that - relatively). It's very possible I'm missing something elementary somewhere. If nothing easier comes up - I might just go and do the array thing, but hopefully it won't come to that. I'm using MS-VC++ 6.0 (hey, it's rude to laugh! :-P ). Any/all help will be much appreciated.

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  • How to exit an if clause

    - by Roman Stolper
    What sorts of methods exist for prematurely exiting an if clause? There are times when I'm writing code and want to put a break statement inside of an if clause, only to remember that those can only be used for loops. Lets take the following code as an example: if some_condition: ... if condition_a: # do something # and then exit the outer if block ... if condition_b: # do something # and then exit the outer if block # more code here I can think of one way to do this: assuming the exit cases happen within nested if statements, wrap the remaining code in a big else block. Example: if some_condition: ... if condition_a: # do something # and then exit the outer if block else: ... if condition_b: # do something # and then exit the outer if block else: # more code here The problem with this is that more exit locations mean more nesting/indented code. Alternatively, I could write my code to have the if clauses be as small as possible and not require any exits. Does anyone know of a good/better way to exit an if clause? If there are any associated else-if and else clauses, I figure that exiting would skip over them.

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  • Compiled Haskell libraries with FFI imports are invalid when imported into GHCI

    - by John Millikin
    I am using GHC 6.12.1, in Ubuntu 10.04 When I try to use the FFI syntax for static storage, only modules running in interpreted mode (ie GHCI) work properly. Compiled modules have invalid pointers, and do not work. I'd like to know whether anybody can reproduce the problem, whether this an error in my code or GHC, and (if the latter) whether it's a known issue. I'm using sys_siglist because it's present in a standard library on my system, but I don't believe the actual storage used matters (I discovered this while writing a binding to libidn). If it helps, sys_siglist is defined in <signal.h> as: extern __const char *__const sys_siglist[_NSIG]; I thought this type might be the problem, so I also tried wrapping it in a plain C procedure: #include<stdio.h> const char **test_ffi_import() { printf("C think sys_siglist = %X\n", sys_siglist); return sys_siglist; } However, importing that doesn't change the result, and the printf() call prints the same pointer value as show siglist_a. My suspicion is that it's something to do with static and dynamic library loading. Update: somebody in #haskell suggested this might be 64-bit specific; if anybody tries to reproduce it, can you mention your architecture and whether it worked in a comment? Code as follows: -- A.hs {-# LANGUAGE ForeignFunctionInterface #-} module A where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_a :: Ptr CString -- -- B.hs {-# LANGUAGE ForeignFunctionInterface #-} module B where import Foreign import Foreign.C foreign import ccall "&sys_siglist" siglist_b :: Ptr CString -- -- Main.hs {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign import Foreign.C import A import B foreign import ccall "&sys_siglist" siglist_main :: Ptr CString main = do putStrLn $ "siglist_a = " ++ show siglist_a putStrLn $ "siglist_b = " ++ show siglist_b putStrLn $ "siglist_main = " ++ show siglist_main peekSiglist "a " siglist_a peekSiglist "b " siglist_b peekSiglist "main" siglist_main peekSiglist name siglist = do ptr <- peekElemOff siglist 2 str <- maybePeek peekCString ptr putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str I would expect something like this output, where all pointer values identical and valid: $ runhaskell Main.hs siglist_a = 0x00007f53a948fe00 siglist_b = 0x00007f53a948fe00 siglist_main = 0x00007f53a948fe00 siglist_a [2] = Just "Interrupt" siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt" However, if I compile A.hs (with ghc -c A.hs), then the output changes to: $ runhaskell Main.hs siglist_a = 0x0000000040378918 siglist_b = 0x00007fe7c029ce00 siglist_main = 0x00007fe7c029ce00 siglist_a [2] = Nothing siglist_b [2] = Just "Interrupt" siglist_main[2] = Just "Interrupt"

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  • documenting class attributes

    - by intuited
    I'm writing a lightweight class whose attributes are intended to be publicly accessible, and only sometimes overridden in specific instantiations. There's no provision in the Python language for creating docstrings for class attributes, or any sort of attributes, for that matter. What is the accepted way, should there be one, to document these attributes? Currently I'm doing this sort of thing: class Albatross(object): """A bird with a flight speed exceeding that of an unladen swallow. Attributes: """ flight_speed = 691 __doc__ += """ flight_speed (691) The maximum speed that such a bird can attain. """ nesting_grounds = "Raymond Luxury-Yacht" __doc__ += """ nesting_grounds ("Raymond Luxury-Yacht") The locale where these birds congregate to reproduce. """ def __init__(**keyargs): """Initialize the Albatross from the keyword arguments.""" self.__dict__.update(keyargs) Although this style doesn't seem to be expressly forbidden in the docstring style guidelines, it's also not mentioned as an option. The advantage here is that it provides a way to document attributes alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring. I'm still kind of annoyed that I have to actually write the attributes twice; I'm considering using the string representations of the values in the docstring to at least avoid duplication of the default values. Is this a heinous breach of the ad hoc community conventions? Is it okay? Is there a better way? For example, it's possible to create a dictionary containing values and docstrings for the attributes and then add the contents to the class __dict__ and docstring towards the end of the class declaration; this would alleviate the need to type the attribute names and values twice. edit: this last idea is, I think, not actually possible, at least not without dynamically building the class from data, which seems like a really bad idea unless there's some other reason to do that. I'm pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.

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