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  • Which design pattern is most appropriate?

    - by Anon
    Hello, I want to create a class that can use one of four algorithms (and the algorithm to use is only known at run-time). I was thinking that the Strategy design pattern sounds appropriate, but my problem is that each algorithm requires slightly different parameters. Would it be a bad design to use strategy, but pass in the relevant parameters into the constructor?. Here is an example (for simplicity, let's say there are only two possible algorithms) ... class Foo { private: // At run-time the correct algorithm is used, e.g. a = new Algorithm1(1); AlgorithmInterface* a; }; class AlgorithmInterface { public: virtual void DoSomething = 0; }; class Algorithm1 : public AlgorithmInterface { public: Algorithm1( int i ) : value(i) {} virtual void DoSomething(){ // Does something with int value }; int value; }; class Algorithm2 : public AlgorithmInterface { public: Algorithm2( bool b ) : value(b) {} virtual void DoSomething(){ // Do something with bool value }; bool value; };

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  • Domain model for an optional many-many relationship

    - by Greg
    Let's say I'm modeling phone numbers. I have one entity for PhoneNumber, and one for Person. There's a link table that expresses the link (if any) between the PhoneNumber and Person. The link table also has a field for DisplayOrder. When accessing my domain model, I have several Use Cases for viewing a Person. I can look at them without any PhoneNumber information. I can look at them for a specific PhoneNumber. I can look at them and all of their current (or past) PhoneNumbers. I'm trying to model Person, not only for the standard CRUD operations, but for the (un)assignment of PhoneNumbers to a Person. I'm having trouble expressing the relationship between the two, especially with respects to the DisplayOrder property. I can think of several solutions but I'm not sure of which (if any) would be best. A PhoneNumberPerson class that has a Person and PhoneNumber property (most closely resembles database design) A PhoneCarryingPerson class that inherits from Person and has a PhoneNumber property. A PhoneNumber and/or PhoneNumbers property on Person (and vis-a-versa, a Person property on PhoneNumber) What would be a good way to model this that makes sense from a domain model perspective? How do I avoid misplaced properties (DisplayOrder on Person) or conditionally populated properties?

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  • PHP check http referer for form submitted by AJAX, secure?

    - by Michael Mao
    Hi all: This is the first time I am working for a front-end project that requires server-side authentication for AJAX requests. I've encountered problems like I cannot make a call of session_start as the beginning line of the "destination page", cuz that would get me a PHP Warning : Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\comic\app\ajaxInsert Book.php:1) in C:\xampp\htdocs\comic\app\common.php on line 10 I reckon this means I have to figure out a way other than checking PHP session variables to authenticate the "caller" of this PHP script, and this is my approach : I have a "protected" PHP page, which must be used as the "container" of my javascript that posts the form through jQuery $.ajax(); method In my "receiver" PHP script, what I've got is: <?php define(BOOKS_TABLE, "books"); define(APPROOT, "/comic/"); define(CORRECT_REFERER, "/protected/staff/addBook.php"); function isRefererCorrect() { // the following line evaluates the relative path for the referer uri, // Say, $_SERVER['HTTP_REFERER'] returns "http://localhost/comic/protected/staff/addBook.php" // Then the part we concern is just this "/protected/staff/addBook.php" $referer = substr($_SERVER['HTTP_REFERER'], 6 + strrpos($_SERVER['HTTP_REFERER'], APPROOT)); return (strnatcmp(CORRECT_REFERER, $referer) == 0) ? true : false; } //http://stackoverflow.com/questions/267546/correct-http-header-for-json-file header('Content-type: application/json charset=UTF-8'); header('Cache-Control: no-cache, must-revalidate'); echo json_encode(array ( "feedback"=>"ok", "info"=>isRefererCorrect() )); ?> My code works, but I wonder is there any security risks in this approach? Can someone manipulate the post request so that he can pretend that the caller javascript is from the "protected" page? Many thanks to any hints or suggestions.

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  • Replacing a word in a text file with a value using python

    - by Jamde Jam
    I have been trying to replace a word in a text file with a value (say 1), but my outfile is blank.I am new to python (its only been a month since I have been learning it). My file is relatively large, but I just want to replace a word with the value 1 for now. Here is a segment of what the file looks like: NAME SECOND_1 ATOM 1 6 0 0 0 # ORB 1 ATOM 2 2 0 12/24 0 # ORB 2 ATOM 3 2 12/24 0 0 # ORB 2 ATOM 4 2 0 0 4/24 # ORB 3 ATOM 5 2 0 0 20/24 # ORB 3 ATOM 6 2 0 0 8/24 # ORB 3 ATOM 7 2 0 0 16/24 # ORB 3 ATOM 8 6 0 0 12/24 # ORB 1 ATOM 9 2 12/24 0 12/24 # ORB 2 ATOM 10 2 0 12/24 12/24 # ORB 2 #1 #2 #3 I want to first replace the word ATOM with the value 1. Next I want to replace #ORB with a space. Here is what I am trying thus far. input = open('SECOND_orbitsJ22.txt','r') output=open('SECOND_orbitsJ22_out.txt','w') for line in input: word=line.split(',') if(word[0]=='ATOM'): word[0]='1' output.write(','.join(word)) Can anyone offer any suggestions or help? Thanks so much.

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  • Shared Memory and Process Sempahores (IPC)

    - by fsdfa
    This is an extract from Advanced Liniux Programming: Semaphores continue to exist even after all processes using them have terminated. The last process to use a semaphore set must explicitly remove it to ensure that the operating system does not run out of semaphores.To do so, invoke semctl with the semaphore identifier, the number of semaphores in the set, IPC_RMID as the third argument, and any union semun value as the fourth argument (which is ignored).The effective user ID of the calling process must match that of the semaphore’s allocator (or the caller must be root). Unlike shared memory segments, removing a semaphore set causes Linux to deallocate immediately. If a process allocate a shared memory, and many process use it and never set to delete it (with shmctl), if all them terminate, then the shared page continues being available. (We can see this with ipcs). If some process did the shmctl, then when the last process deattached, then the system will deallocate the shared memory. So far so good (I guess, if not, correct me). What I dont understand from that quote I did, is that first it say: "Semaphores continue to exist even after all processes using them have terminated." and then: "Unlike shared memory segments, removing a semaphore set causes Linux to deallocate immediately."

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  • Multiple Inheritence with same Base Classes in Python

    - by Jordan Reiter
    I'm trying to wrap my head around multiple inheritance in python. Suppose I have the following base class: class Structure(object): def build(self, *args): print "I am building a structure!" self.components = args And let's say I have two classes that inherit from it: class House(Structure): def build(self, *args): print "I am building a house!" super(House, self).build(*args) class School(Structure): def build(self, type="Elementary", *args): print "I am building a school!" super(School, self).build(*args) Finally, a create a class that uses multiple inheritance: class SchoolHouse(School, House): def build(self, *args): print "I am building a schoolhouse!" super(School, self).build(*args) Then, I create a SchoolHouse object and run build on it: >>> sh = SchoolHouse() >>> sh.build("roof", "walls") I am building a schoolhouse! I am building a house! I am building a structure! So I'm wondering -- what happened to the School class? Is there any way to get Python to run both somehow? I'm wondering specifically because there are a fair number of Django packages out there that provide custom Managers for models. But there doesn't appear to be a way to combine them without writing one or the other of the Managers as inheriting from the other one. It'd be nice to just import both and use both somehow, but looks like it can't be done? Also I guess it'd just help to be pointed to a good primer on multiple inheritance in Python. I have done some work with Mixins before and really enjoy using them. I guess I just wonder if there is any elegant way to combine functionality from two different classes when they inherit from the same base class.

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  • Typical Hadoop setup for remote job submission

    - by Artii
    So I am still a bit new to hadoop and am currently in the process of setting up a small test cluster on Amazonaws. So my question relates to some tips on the structuring of the cluster so it is possible to work submit jobs from remote machines. Currently I have 5 machines. 4 are basically the Hadoop cluster with the NameNodes, Yarn etc. One machine is used as a manager machine( Cloudera Manager). I am gonna describe my thinking process on the setup and if anyone can chime in the points I am not clear with, that would be great. I was thinking what was the best setup for a small cluster. So I decided to expose only one manager machine and probably use that to submit all the jobs through it. The other machines will see each other etc, but not be accessible from the outside world. I am have conceptual idea on how to do this,but I am not sure how to properly go about doing this though, if anyone could point me in the right direction that would great. Also another big point is, I want to be able to submit jobs to the cluster through exposed machine from a client machine (might be Windows). I am not so clear on this setup as well. Do I need to have Hadoop installed on the machine in order to use the normal hadoop commands, and to write/submit jobs say from Eclipse or something similar. So to sum it up my questions are, Is this an ok setup for a small test cluster How can I go about using one exposed machine to submit/route jobs to the cluster, without having any of the Hadoop nodes on it. How do I setup a client machine to submit jobs to a remote cluster, and an example on how to do it on Windows. Also if there are any reason not to use Windows as a client machine in this setup. Thanks I would greatly appreciate any advice or help on this.

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  • CSS overflow detection in JavaScript

    - by ring0
    In order to display a line of text (like in a forum), and end that line with "..." if the text would overflow the line (not truncating using the CSS overflow property), there are a number of ways. I'm still seeking the best solution. For instance, Adding in CSS a "..." as a background-image is a possibility, but it would appear all the time, and this is not a good solution. Some sites just count the characters and if over - say - 100, truncates the string to keep only 100 (or 97) chars and add a "..." at the end. But fonts are usually not proportional, so the result is not pretty. For instance the space - in pixels - taken by "AAA" and "iii" is clearly different "AAA" and "iii" via a proportional font have the same width There is another idea to get the exact size in pixels of the string: create in Javascript a DIV insert the text in it (via innerHTML for instance) measure the width (via .offsetWidth) which is not implemented yet. However, I wonder if there could be any browser compatibility problem? Did any one tried this solution? Other recommendations would be welcome.

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  • Linq merging results

    - by glenneroo
    I'm working with a list within a list. This is how I'm currently searching: var tags = from fd in BigList from tag in fd.Tags where tag.Id == selectedTag.Id || tag.Id == ID.TIMESTAMP select new { fd.Name, tag.Id, tag.Value }; I then iterate over the result-set and remembering when Timestamp pops up for the next entry, needless to say this is sloppy and I'm positive there's a better way using Linq, I just can't seem to find the syntax. Here's some sample output (Id indicates what type of data is stored inside e.g. a timestamp): Name | Id | Value -----|----|---------- 0000 | 1 | <timestamp> 0000 | 2 | 1.2 ... 9999 | 1 | <timestamp> 9999 | 2 | 6.3 I need all instances where Id = selectedTag.Id. I just want 1 list with Name, Id, Value and Timestamp, but the problem is my above attempt returns 2 entries for every item (1 for timestamp and 1 for the value). Is there a way to do this using Linq? Preferably using query syntax! :)

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  • pdf external streams in Max OS X Preview

    - by olpa
    According to the specification, a part of a PDF document can reside in an external file. An example for an image: 2 0 obj << /Type /XObject /Subtype /Image /Width 117 /Height 117 /BitsPerComponent 8 /Length 0 /ColorSpace /DeviceRGB /FFilter /DCTDecode /F (pinguine.jpg) >> stream endstream endobj I found that this functionality does work in Adobe Acrobat 5.0 for Windows (sample PDF with the image), also I managed to view this file in Adobe Acrobat Reader 8.1.3 for Mac OS X after I found the setting "Allow external content". Unfortunately, it seems that non-Adobe tools ignore the external stream feature. I hope I'm wrong, therefore ask the question: How to enable external streams in Mac OS X? (I think that all the system Mac OS X tools use the same library, therefore say "Mac OS X" instead of "Preview".) Or maybe there could be a programming hook to emulate external streams? My task is: store a big set of images (total ˜300Mb) outside of a small PDF (˜1Mb). At some moment, I want to filter PDF through a quartz filter and get a PDF with the images embedded. Any suggestions are welcome.

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  • No "redefinition of default parameter error" for class template member function?

    - by STingRaySC
    Why does the following give no compilation error?: // T.h template<class T> class X { public: void foo(int a = 42); }; // Main.cpp #include "T.h" #include <iostream> template<class T> void X<T>::foo(int a = 13) { std::cout << a << std::endl; } int main() { X<int> x; x.foo(); // prints 42 } It seems as though the 13 is just silently ignored by the compiler. Why is this? The cooky thing is that if the template declaration is in Main.cpp instead of a header file, I do indeed get the default parameter redefinition error. Now I know the compiler will complain about this if it were just an ordinary (non-template) function. What does the standard have to say about default parameters in class template member functions or function templates?

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  • jQuery and jQuery UI (Dual Licensing)

    - by John Hartsock
    OK I have read many posts regarding Dual Licensing using MIT and GPL licenses. But Im curious still, as the wording seems to be inclusive. Many of the Dual Licenses state that the software is licensed using "MIT AND GPL". The "AND" is what confuses me. It seems to me that the word "AND" in the terms, means you will be licensing the product using both licenses. Most of the posts, here on stackoverflow, say you can license the software using one "OR" the other. JQuery specifically states "OR", whereas JQuery UI specifically States "AND". Another Instance of the "AND" would be JQGrid. Im not a lawyer but, it seems to me that a legal interpretation of this would state that use of the software would mean that your using the software under both licenses. Has anyone who has contacted a lawyer gotten clarification or a definitive answer as to what is true? Can you use Dual licensed software products that state "AND" in the terms of agreement under either license?

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  • Determining polygon intersection and containment

    - by Victor Liu
    I have a set of simple (no holes, no self-intersections) polygons, and I need to check that they don't intersect each other (one can be entirely contained in another; that is okay). I can check this by simply checking the per-vertex inside-ness of one polygon versus other polygons. I also need to determine the containment tree, which is the set of relationships that say which polygon contains any given polygon. Since no polygon can intersect any other, then any contained polygon has a unique container; the "next-bigger" one. In other words, if A contains B contains C, then A is the parent of B, and B is the parent of C, and we don't consider A the parent of C. The question: How do I efficiently determine the containment relationships and check the non-intersection criterion? I ask this as one question because maybe a combined algorithm is more efficient than solving each problem separately. The algorithm should take as input a list of polygons, given by a list of their vertices. It should produce a boolean B indicating if none of the polygons intersect any other polygon, and also if B = true, a list of pairs (P, C) where polygon P is the parent of child C. This is not homework. This is for a hobby project I am working on.

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  • Query next/previous record

    - by Rob
    I'm trying to find a better way to get the next or previous record from a table. Let's say I have a blog or news table: CREATE TABLE news ( news_id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT, news_datestamp DATETIME NOT NULL, news_author VARCHAR(100) NOT NULL, news_title VARCHAR(100) NOT NULL, news_text MEDIUMTEXT NOT NULL ); Now on the frontend I want navigation buttons for the next or previous records, if i'm sorting by news_id, I can do something rather simple like: SELECT MIN(news_id) AS next_news_id FROM news WHERE news_id > '$old_news_id' LIMIT 1 SELECT MAX(news_id) AS prev_news_id FROM news WHERE news_id < '$old_news_id' LIMIT 1 But the news can be sorted by any field, and I don't necessarily know which field is sorted on, so this won't work if the user sorts on news_author for example. I've resorted to the rather ugly and inefficient method of sorting the entire table and looping through all records until I find the record I need. $res = mysql_query("SELECT news_id FROM news ORDER BY `$sort_column` $sort_way"); $found = $prev = $next = 0; while(list($id) = mysql_fetch_row($res)) { if($found) { $next = $id; break; } if($id == $old_news_id) { $found = true; continue; } $prev = $id; } There's got to be a better way.

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  • Apply PHP regex replace on a multi-line repeated pattern

    - by Hussain
    Let's say I have this input: I can haz a listz0rs! # 42 # 126 I can haz another list plox? # Hello, world! # Welcome! I want to split it so that each set of hash-started lines becomes a list: I can haz a listz0rs! <ul> <li>42</li> <li>126</li> </ul> I can haz another list plox? <ul> <li>Hello, world!</li> <li>Welcome!</li> </ul> If I run the input against the regex "/(?:(?:(?<=^# )(.*)$)+)/m", I get the following result: Array ( [0] => Array ( [0] => 42 ) [1] => Array ( [0] => 126 ) [2] => Array ( [0] => Hello, world! ) [3] => Array ( [0] => Welcome! ) ) This is fine and dandy, but it doesn't distinguish between the two different lists. I need a way to either make the quantifier return a concatenated string of all the occurrences, or, ideally, an array of all the occurrences. Ideally, this should be my output: Array ( [0] => Array ( [0] => 42 [1] => 126 ) [1] => Array ( [0] => Hello, world! [1] => Welcome! ) ) Is there any way of achieving this, and if not, is there a close alternative? Thanks in advance!

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  • Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

    - by SiegeX
    Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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  • Why is debugging better in an IDE?

    - by Bill Karwin
    I've been a software developer for over twenty years, programming in C, Perl, SQL, Java, PHP, JavaScript, and recently Python. I've never had a problem I could not debug using some careful thought, and well-placed debugging print statements. I respect that many people say that my techniques are primitive, and using a real debugger in an IDE is much better. Yet from my observation, IDE users don't appear to debug faster or more successfully than I can, using my stone knives and bear skins. I'm sincerely open to learning the right tools, I've just never been shown a compelling advantage to using visual debuggers. Moreover, I have never read a tutorial or book that showed how to debug effectively using an IDE, beyond the basics of how to set breakpoints and display the contents of variables. What am I missing? What makes IDE debugging tools so much more effective than thoughtful use of diagnostic print statements? Can you suggest resources (tutorials, books, screencasts) that show the finer techniques of IDE debugging? Sweet answers! Thanks much to everyone for taking the time. Very illuminating. I voted up many, and voted none down. Some notable points: Debuggers can help me do ad hoc inspection or alteration of variables, code, or any other aspect of the runtime environment, whereas manual debugging requires me to stop, edit, and re-execute the application (possibly requiring recompilation). Debuggers can attach to a running process or use a crash dump, whereas with manual debugging, "steps to reproduce" a defect are necessary. Debuggers can display complex data structures, multi-threaded environments, or full runtime stacks easily and in a more readable manner. Debuggers offer many ways to reduce the time and repetitive work to do almost any debugging tasks. Visual debuggers and console debuggers are both useful, and have many features in common. A visual debugger integrated into an IDE also gives you convenient access to smart editing and all the other features of the IDE, in a single integrated development environment (hence the name).

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  • Liskov Substition and Composition

    - by FlySwat
    Let say I have a class like this: public sealed class Foo { public void Bar { // Do Bar Stuff } } And I want to extend it to add something beyond what an extension method could do....My only option is composition: public class SuperFoo { private Foo _internalFoo; public SuperFoo() { _internalFoo = new Foo(); } public void Bar() { _internalFoo.Bar(); } public void Baz() { // Do Baz Stuff } } While this works, it is a lot of work...however I still run into a problem: public void AcceptsAFoo(Foo a) I can pass in a Foo here, but not a super Foo, because C# has no idea that SuperFoo truly does qualify in the Liskov Substitution sense...This means that my extended class via composition is of very limited use. So, the only way to fix it is to hope that the original API designers left an interface laying around: public interface IFoo { public Bar(); } public sealed class Foo : IFoo { // etc } Now, I can implement IFoo on SuperFoo (Which since SuperFoo already implements Foo, is just a matter of changing the signature). public class SuperFoo : IFoo And in the perfect world, the methods that consume Foo would consume IFoo's: public void AcceptsAFoo(IFoo a) Now, C# understands the relationship between SuperFoo and Foo due to the common interface and all is well. The big problem is that .NET seals lots of classes that would occasionally be nice to extend, and they don't usually implement a common interface, so API methods that take a Foo would not accept a SuperFoo and you can't add an overload. So, for all the composition fans out there....How do you get around this limitation? The only thing I can think of is to expose the internal Foo publicly, so that you can pass it on occasion, but that seems messy.

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  • Rename files and directories using substitution and variables

    - by rednectar
    I have found several similar questions that have solutions, except they don't involve variables. I have a particular pattern in a tree of files and directories - the pattern is the word TEMPLATE. I want a script file to rename all of the files and directories by replacing the word TEMPLATE with some other name that is contained in the variable ${newName} If I knew that the value of ${newName} was say "Fred lives here", then the command find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/Fred lives here}"' {} \; will do the job However, if my script is: newName="Fred lives here" find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/${newName}}"' {} \; then the word TEMPLATE is replaced by null rather than "Fred lives here" I need the "" around $0 because there are spaces in the path name, so I can't do something like: find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/"${newName}"}"' {} \; Can anyone help me get this script to work so that all files and directories that contain the word TEMPLATE have TEMPLATE replaced by whatever the value of ${newName} is eg, if newName="A different name" and a I had directory of /foo/bar/some TEMPLATE directory/with files then the directory would be renamed to /foo/bar/some A different name directory/with files and a file called some TEMPLATE file would be renamed to some A different name file

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  • how to model a follower stream in appengine?

    - by molicule
    I am trying to design tables to buildout a follower relationship. Say I have a stream of 140char records that have user, hashtag and other text. Users follow other users, and can also follow hashtags. I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal. The issues with this are The list of followers is copied in for each record If a new follower is added or one removed, 'all' the records have to be updated. The code class HashtagFollowers(db.Model): """ This table contains the followers for each hashtag """ hashtag = db.StringProperty() followers = db.StringListProperty() class UserFollowers(db.Model): """ This table contains the followers for each user """ username = db.StringProperty() followers = db.StringListProperty() class stream(db.Model): """ This table contains the data stream """ username = db.StringProperty() hashtag = db.StringProperty() text = db.TextProperty() def save(self): """ On each save all the followers for each hashtag and user are added into a another table with this record as the parent """ super(stream, self).save() hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10) for hf in hfs: sh = streamHashtags(parent=self, followers=hf.followers) sh.save() ufs = UserFollowers.all().filter("username =", self.username).fetch(10) for uf in ufs: uh = streamUsers(parent=self, followers=uf.followers) uh.save() class streamHashtags(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() class streamUsers(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() Now, to get the stream of followed hastags indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""") keys = [k,parent() for k in indexes[offset:numresults]] return db.get(keys) Is there a smarter way to do this?

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  • ObjectiveC - Releasing objects added as parameters

    - by NobleK
    Ok, here goes. Being a Java developer I'm still struggling with the memory management in ObjectiveC. I have all the basics covered, but once in a while I encounter a challenge. What I want to do is something which in Java would look like this: MyObject myObject = new MyObject(new MyParameterObject()); The constructor of MyObject class takes a parameter of type MyParameterObject which I initiate on-the-fly. In ObjectiveC I tried to do this using following code: MyObject *myObject = [[MyObject alloc] init:[[MyParameterObject alloc] init]]; However, running the Build and Analyze tool this gives me a "Potential leak of an object" warning for the MyParameter object which indeed occurs when I test it using Instruments. I do understand why this happens since I am taking ownership of the object with the alloc method and not relinquishing it, I just don't know the correct way of doing it. I tried using MyObject *myObject = [[MyObject alloc] init:[[[MyParameterObject alloc] init] autorelease]]; but then the Analyze tool told me that "Object sent -autorelease too many times". I could solve the issue by modifying the init method of MyParameterObject to say return [self autorelease]; in stead of just return self;. Analyze still warnes about a potential leak, but it doesn't actually occur. However I believe that this approach violates the convention for managing memory in ObjectiveC and I really want to do it the right way. Thanx in advance.

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  • Creating reusable chunks of Linq to SQL

    - by tia
    Hi, I am trying to break up horrible linq to sql queries to make them a bit more readable. Say I want to return all orders for product which in the previous year had more than 100 orders. So, original query is: from o in _context.Orders where (from o1 in _context.Orders where o1.Year == o.Year - 1 && o1.Product == o.Product select o1).Count() > 100 select o; Messy. What I'd like to be able to do is to be able to break it down, eg: private IEnumerable<Order> LastSeasonOrders(Order order) { return (from o in _context.Orders where o.Year == order.Year - 1 && o.Product == order.Product select o); } which then lets me change the original query to: from o in _context.Orders where LastSeasonOrders(o).Count() > 100 select o; This doesn't seem to work, as I get method Blah has no supported translation to SQL when the query is run. Any quick tips on the correct way to achieve this?

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  • Scheduling algorithm optimized to execute during low usage periods.

    - by The Rook
    Lets say there is a Web Application serving mostly one country. Because of normal sleep habits website traffic follows a Sine wave, where 1 period lasts 24 hours and the lowest part of the wave is at about midnight. Is there a scheduling algorithm optimized to execute during low usage periods? I am thinking of this as a liquid that is "pored into" this sine wave to flatten out resource usage. A ideal algorithm would take the integral of this empty space. If the same tasks need to be run daily the amount of resources consumed by previous executions could be used to predict future usage by looking at the rate in which resource usage is increasing. By knowing the amount of resources required this algorithm could fill in this empty space while leaving as much buffer as possible on either side such that its interference was reduced as much as possible. It would also be possible to detect if there isn't enough resources before execution begins, this opens the door for a cloud to help out. Does anything like this exist? Or should I build it into an existing scheduler like quartz and make it open source?

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  • Keeping sync in multiplayer RTS game that uses floating point arithmetic

    - by Calmarius
    I'm writing a 2D space RTS game in C#. Single player works. Now I want to add some multiplayer functionality. I googled for it and it seems there is only one way to have thousands of units continuously moving without a powerful net connection: send only the commands through the network while running the same simulation at every player. And now there is a problem the entire engine uses doubles everywhere. And floating point calculations are depends heavily on compiler optimalizations and cpu architecture so it is very hard to keep things syncronized. And it is not grid based at all, and have a simple phisics engine to move the space-ships (space ships have impulse and angular-momentum...). So recoding the entire stuff to use fixed point would be quite cumbersome (but probably the only solution). So I have 2 options so far: Say bye to the current code and restart from scratch using integers Make the game LAN only where there is enough bandwidth to have 8 players with thousands of units and sending the positions and orientation etc in (almost) every frame... So I looking for better opinions, (or even tips on migrating the code to fixed-point without messing everything up...)

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  • mmap only needed pages of kernel buffer to user space

    - by axeoth
    See also this answer: http://stackoverflow.com/a/10770582/1284631 I need something similar, but without having to allocate a buffer: the buffer is large, in theory, but the user space program only needs to access some parts of it (it mocks some registers of a hardware). As I cannot allocate with vmalloc_user() such a large buffer (kernel 32 bit, in embedded environment, no swap...), I followed the same approach as in the quoted answer, trying to allocate only those pages that are really requested by the user space. So: I use a my_mmap() function for the device file (actually, is the .mmap field of a struct uio_info) to set up the fields of the vma, then, in the vm_area_struct's .fault field (also named my_fault()), I should return a page. except that: In the my_fault() method of vm_area_struct, I cannot obtain a page through: vmf->page=vmalloc_to_page(my_buf + (vmf->pgoff << PAGE_SHIFT)); since there is no allocated buffer: my_buf = vmalloc_user(MY_BUF_SIZE); fails with "allocation failed: out of vmalloc space - use vmalloc= to increase size." (and there is no room or swap to increase that vmalloc= parameter). So, I would need to get a page from the kernel and fill the vmf->page field. How to allocate a page (I assume that the offset of the page is known, as it is vm->pgoff). What base memory should I use instead of my_buf? PS: I also did set up the vma->flags |= VM_NORESERVE; (in the my_mmap()), but not sure if it helps. Is there any vmalloc_user_unreserved()-like function? (let's say, lazy allocation) Also, writing 1 to /proc/sys/vm/overcommit_memory and large values (eg 500) to /proc/sys/vm/overcommit_ratio before trying to my_buf=vmalloc_user(<large_size>) didn't work.

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