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  • What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

    - by fabrizioM
    I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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  • mysql circular dependency in foreign key constraints

    - by Flavius
    Given the schema: What I need is having every user_identities.belongs_to reference an users.id. At the same time, every users has a primary_identity as shown in the picture. However when I try to add this reference with ON DELETE NO ACTION ON UPDATE NO ACTION, MySQL says #1452 - Cannot add or update a child row: a foreign key constraint fails (yap.#sql-a3b_1bf, CONSTRAINT #sql-a3b_1bf_ibfk_1 FOREIGN KEY (belongs_to) REFERENCES users (id) ON DELETE NO ACTION ON UPDATE NO ACTION) I suspect this is due to the circular dependency, but how could I solve it (and maintain referential integrity)?

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  • Would this constructor be acceptable practice?

    - by Robb
    Let's assume I have a c++ class that have properly implemented a copy constructor and an overloaded = operator. By properly implemented I mean they are working and perform a deep copy: Class1::Class1(const Class1 &class1) { // Perform copy } Class1& Class1::operator=(const Class1 *class1) { // perform copy return *this; } Now lets say I have this constructor as well: Class1::Class1(Class1 *class1) { *this = *class1; } My question is would the above constructor be acceptable practice? This is code that i've inherited and maintaining.

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  • Projections.count() and Projections.countDistinct() both result in the same query

    - by Kim L
    EDIT: I've edited this post completely, so that the new description of my problem includes all the details and not only what I previously considered relevant. Maybe this new description will help to solve the problem I'm facing. I have two entity classes, Customer and CustomerGroup. The relation between customer and customer groups is ManyToMany. The customer groups are annotated in the following way in the Customer class. @Entity public class Customer { ... @ManyToMany(mappedBy = "customers", fetch = FetchType.LAZY) public Set<CustomerGroup> getCustomerGroups() { ... } ... public String getUuid() { return uuid; } ... } The customer reference in the customer groups class is annotated in the following way @Entity public class CustomerGroup { ... @ManyToMany public Set<Customer> getCustomers() { ... } ... public String getUuid() { return uuid; } ... } Note that both the CustomerGroup and Customer classes also have an UUID field. The UUID is a unique string (uniqueness is not forced in the datamodel, as you can see, it is handled as any other normal string). What I'm trying to do, is to fetch all customers which do not belong to any customer group OR the customer group is a "valid group". The validity of a customer group is defined with a list of valid UUIDs. I've created the following criteria query Criteria criteria = getSession().createCriteria(Customer.class); criteria.setProjection(Projections.countDistinct("uuid")); criteria = criteria.createCriteria("customerGroups", "groups", Criteria.LEFT_JOIN); List<String> uuids = getValidUUIDs(); Criterion criterion = Restrictions.isNull("groups.uuid"); if (uuids != null && uuids.size() > 0) { criterion = Restrictions.or(criterion, Restrictions.in( "groups.uuid", uuids)); } criteria.add(criterion); When executing the query, it will result in the following SQL query select count(*) as y0_ from Customer this_ left outer join CustomerGroup_Customer customergr3_ on this_.id=customergr3_.customers_id left outer join CustomerGroup groups1_ on customergr3_.customerGroups_id=groups1_.id where groups1_.uuid is null or groups1_.uuid in ( ?, ? ) The query is exactly what I wanted, but with one exception. Since a Customer can belong to multiple CustomerGroups, left joining the CustomerGroup will result in duplicated Customer objects. Hence the count(*) will give a false value, as it only counts how many results there are. I need to get the amount of unique customers and this I expected to achieve by using the Projections.countDistinct("uuid"); -projection. For some reason, as you can see, the projection will still result in a count(*) query instead of the expected count(distinct uuid). Replacing the projection countDistinct with just count("uuid") will result in the exactly same query. Am I doing something wrong or is this a bug? === "Problem" solved. Reason: PEBKAC (Problem Exists Between Keyboard And Chair). I had a branch in my code and didn't realize that the branch was executed. That branch used rowCount() instead of countDistinct().

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  • Should I be using the command pattern? Seems like a lot of work...

    - by Fedor
    My Room class has a lot of methods I used before I decided to use the command pattern. Previously, I was invoking a lot of commands and now it seems I have to make a method in my roomParser class for every method. If I wanted to invoke say, setHotelCode I would have to create a method in roomParser that iterates through and invokes the method. Is this the way I should be using the command pattern? <?php interface Parseable { public function parse( $arr, $dept ); } class Room implements Parseable { protected $_adults; protected $_kids; protected $_startDate; protected $_endDate; protected $_hotelCode; protected $_sessionNs; protected $_minRate; protected $_maxRate; protected $_groupCode; protected $_rateCode; protected $_promoCode; protected $_confCode; protected $_currency = 'USD'; protected $_soapAction; protected $_soapHeaders; protected $_soapServer; protected $_responseXml; protected $_requestXml; public function __construct( $startdate,$enddate,$rooms=1,$adults=2,$kids=0 ) { $this->setNamespace(SESSION_NAME); $this->verifyDates( $startdate, $enddate ); $this->_rooms= $rooms; $this->_adults= $adults; $this->_kids= $kids; $this->setSoapAction(); $this->setRates(); } public function parse( $arr, $dept ) { $this->_price = $arr * $dept * rand(); return $this; } public function setNamespace( $namespace ) { $this->_sessionNs = $namespace; } private function verifyDates( $startdate, $enddate ) {} public function setSoapAction( $str= 'CheckAvailability' ) { $this->_soapAction = $str; } public function setRates( $rates='' ) { } public function setHotelCode($code ) { $this->_hotelCode = $code; } private function getSoapHeader() { return '<?xml version="1.0" encoding="utf-8"?> <soap:Header> </soap:Header>'; } private function getSoapFooter() { return '</soap:Envelope>'; } private function getSource() { return '<POS> <Source><RequestorId ID="" ID_Context="" /></Source> </POS>'; } function requestXml() { $this->_requestXml = $this->getSoapHeader(); $this->_requestXml .='<soap:Body></soap:Body>'; return $this->_requestXml; } private function setSoapHeaders ($contentLength) { $this->_soapHeaders = array('POST /url HTTP/1.1', 'Host: '.SOAP_HOST, 'Content-Type: text/xml; charset=utf-8', 'Content-Length: '.$contentLength); } } class RoomParser extends SplObjectStorage { public function attach( Parseable $obj ) { parent::attach( $obj ); } public function parseRooms( $arr, $dept ) { for ( $this->rewind(); $this->valid(); $this->next() ) { $ret = $this->current()->parse( $arr, $dept ); echo $ret->getPrice(), PHP_EOL; } } } $arrive = '12/28/2010'; $depart = '01/02/2011'; $rooms = new RoomParser( $arrive, $depart); $rooms->attach( new Room( '12/28/2010', '01/02/2011') ); $rooms->attach( new Room( '12/29/2010', '01/04/2011') ); echo $rooms->count(), ' Rooms', PHP_EOL; Edit: I'm thinking it may be easier if I made the RoomParser less generic by storing properties that all the objects will share. Though I'll probably have to make methods if I want to override for a certain object.

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  • What is MVC and what are the advantages of it?

    - by Teifion
    I found What are mvp and mvc and what is the difference but it didn't really answer this question. I've recently started using MVC because it's part of the framework that myself and my work-partner are going to use. We chose it because it looked easy and separated process from display, are there advantages besides this that we don't know about and could be missing out on? Pros Display and Processing are seperated Cons None so far

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  • Magento - How can I move the Navigation Block to be in the right column?

    - by Hank
    I've been editing Magento's default CSS to change the look and have come to a point where I want to move around some content blocks. I've killed off the left column through CSS .col-left { display: none; } And then increased the width of the main content part to create a 'two column layout'. What I want to do now is move the navigation for the categories into the right column. I just have no idea how... How do I move content blocks around in Magento? :/

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  • Why does std::map operator[] create an object if the key doesn't exist?

    - by n1ck
    Hi, I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there either) but a quick search here doesn't seem to find it so here it is: Why does the std::map operator[] create an object if the key doesn't exist? I don't know but for me this seems counter-intuitive if you compare to most other operator[] (like std::vector) where if you use it you must be sure that the index exists. I'm wondering what's the rationale for implementing this behavior in std::map. Like I said wouldn't it be more intuitive to act more like an index in a vector and crash (well undefined behavior I guess) when accessed with an invalid key? Refining my question after seeing the answers: Ok so far I got a lot of answers saying basically it's cheap so why not or things similar. I totally agree with that but why not use a dedicated function for that (I think one of the comment said that in java there is no operator[] and the function is called put)? My point is why doesn't map operator[] work like a vector? If I use operator[] on an out of range index on a vector I wouldn't like it to insert an element even if it was cheap because that probably mean an error in my code. My point is why isn't it the same thing with map. I mean, for me, using operator[] on a map would mean: i know this key already exist (for whatever reason, i just inserted it, I have redundancy somewhere, whatever). I think it would be more intuitive that way. That said what are the advantage of doing the current behavior with operator[] (and only for that, I agree that a function with the current behavior should be there, just not operator[])? Maybe it give clearer code that way? I don't know. Another answer was that it already existed that way so why not keep it but then, probably when they (the ones before stl) choose to implement it that way they found it provided an advantage or something? So my question is basically: why choose to implement it that way, meaning a somewhat lack of consistency with other operator[]. What benefit do it give? Thanks

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  • How would I implement separate databases for reading and writing operations?

    - by Matt
    I am interested in implementing an architecture that has two databases one for read operations and the other for writes. I have never implemented something like this and have always built single database, highly normalised systems so I am not quite sure where to begin. I have a few parts to this question. 1. What would be a good resource to find out more about this achitecture? 2. Is it just a question of replicating between two identical schemas, or would your schemas differ depending on the operations, would normalisation vary too? 3. How do you insure that data written to one database is immediately available for reading from the second? Any further help, tips, resources would be appreciated. Thanks.

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  • New or not so well-known paradigms, syntax features and behaviours of programming languages?

    - by George B
    I've designed some educational programming languages and interpreters for them, but my problem always was that they ended up "normal" and "boring", mostly similar to some kind of existing language (ASM and BASIC). I find it really hard to come up with new ideas for syntax features, "neat things" and new or very modified programming paradigms for it. I always thought that it was hard to come up with good new things not fun/useless new things for this case. I wondered if you could help me out with your creativity: What features in terms of language syntax and built-in functions as well as maybe even new paradigms can I work into my language to keep it useless but more fun, enjoyable, interesting and/or different to program in?

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  • Why doesn't Java Map extends Collection?

    - by polygenelubricants
    I was surprised by the fact that Map<?,?> is not a Collection<?>. I thought it'd make a LOT of sense if it was declared as such: public interface Map<K,V> extends Collection<Map.Entry<K,V>> After all, a Map<K,V> is a collection of Map.Entry<K,V>, isn't it? So is there a good reason why it's not implemented as such?

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  • Building a service for a Drupal site to duplicate a node to another Drupal site in a multi-site setu

    - by EricP
    I'm trying to set up one of my Drupal sites to push a node to another Drupal site in a multi-site configuration. It looks like I need to do this with services somehow, but I can't find any tutorials out there and I need at least to be pointed in the right direction. What I believe I need is set up Services on the receiving site to accept a call from the sending site which will be sending the node object via Json or serialized PHP using a Key that was set up on the receiving site. Can anyone show me an example of this working or give me some insight? thanks

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  • How to force my method to accept objects from external software?

    - by Roman
    I have a method which needs to take a callback object as an argument and then (at the moment when it's needed) my method will call a specific method of the callback object. I wrote a class called Manager which has a method called addListener. As the argument for this method I need to use a callback object which is defined by the external software. So, I define the addListener in the following way: public void addListener(Listener listener). Of course Eclipse complains because it does not know what Listener is (because the Listener is defined by the external software). The only think that I know (should know) about the Listener is that it has a method called doSomething. So, to pleasure Eclipse I add an interface before my Manager class: interface Listener { void doSomething(); } public class CTManager { ... The problem seems to be solved but then I try to test my software. So, I create a class called test. In this class I create an instance of the Manager class and try to use addListener method of this instance. I also create a class Listener, instantiate it and give the instance to the addListener. And it's the place where the problem appears. Eclipse writes that addListener is not applicable to the given argument. I think it's because it expect something from my Listenr interface but gets something from the Listener class. How can I solve this problem?

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  • Voting Script, Possibility of Simplifying Database Queries

    - by Sev
    I have a voting script which stores the post_id and the user_id in a table, to determine whether a particular user has already voted on a post and disallow them in the future. To do that, I am doing the following 3 queries. SELECT user_id, post_id from votes_table where postid=? AND user_id=? If that returns no rows, then: UPDATE post_table set votecount = votecount-1 where post_id = ? Then SELECT votecount from post where post_id=? To display the new votecount on the web page Any better way to do this? 3 queries are seriously slowing down the user's voting experience Edit In the votes table, vote_id is a primary key In the post table, post_id is a primary key. Any other suggestions to speed things up?

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  • Unexpected space between DIV elements

    - by jon
    my code for the php page displaying the divs <?php session_start(); require_once("classlib/mainspace.php"); if (isset($_SESSION['username'])==FALSE) { header("location:login.php"); } $user = new User($_SESSION['username']); ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="style/style.css" /> <title>SimpleTask - Home</title> </head> <body> <div id="main"> <div id="menu"> <div id="items"> <ul> <li><a href="home.php">home</a></li> <li>&bull;</li> <li><a href="projects.php">my projects</a></li> <li>&bull;</li> <li><a href="comments.php">my comments</a></li> </ul> </div> <div id="user"> <p>Welcome, <?php echo $user->GetRealName(); ?><br/><a href="editprofile.php">edit profile</a> &bull; <a href="logout.php">logout</a></p> </div> </div> <div id="content"> <h1>HOME</h1> </div> <div id="footer"> <p>footer text goes here here here here</p> </div> </div> </body> </html> and you can find my CSS here http://tasker.efficaxdevelopment.com/style/style.css and to view the live page go here http://tasker.efficaxdevelopment.com/login.php username:admin password:password

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  • How to create a better tables Structure.

    - by user160820
    For my website i have tables Category :: id | name Product :: id | name | categoryid Now each category may have different sizes, for that I have also created a table Size :: id | name | categoryid | price Now the problem is that each category has also different ingredients that customer can choose to add to his purchased product. And these ingredients have different prices for different sizes. For that I also have a table like Ingredient :: id | name | sizeid | categoryid | price I am not sure if this Structure really normalized is. Can someone please help me to optimize this structure and which indexed do i need for this Structure?

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  • Filter Facebook Stream by Post privacy?

    - by fabian
    Hi there, i query some wall data within my facebook tab. I was wondering how to filter the data (query) to show only post which are visible to a certain country. $query = " SELECT post_id, created_time, attachment,action_links, privacy FROM stream WHERE source_id = ".$page_id." AND viewer_id = ".$user_id." AND actor_id = ".$actor_id." LIMIT 50"; The Output already show Australia: But how to filter for Australia-Only. Array ( [posts] => Array ( [0] => Array ( [post_id] => 123 [viewer_id] => 123 [source_id] => 123 [type] => 46 [app_id] => [attribution] => [actor_id] => 123 [target_id] => [message] => Only for Austria [attachment] => Array ( [description] => ) [app_data] => [action_links] => [comments] => Array ( [can_remove] => 1 [can_post] => 1 [count] => 0 [comment_list] => ) [likes] => Array ( [href] => http://www.facebook.com/social_graph.php?node_id=118229678189906&class=LikeManager [count] => 0 [sample] => [friends] => [user_likes] => 0 [can_like] => 1 ) [privacy] => Array ( [description] => Austria [value] => CUSTOM [friends] => [networks] => [allow] => [deny] => ) [updated_time] => 1271520716 [created_time] => 1271520716 [tagged_ids] => [is_hidden] => 0 [filter_key] => [permalink] => http://www.facebook.com/pages/ )

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  • Building a structure/object in a place other than the constructor

    - by Vishal Naidu
    I have different types of objects representing the same business entity. UIObject, PowershellObject, DevCodeModelObject, WMIObject all are different representation to the same entity. So say if the entity is Animal then I have AnimalUIObject, AnimalPSObject, AnimalModelObject, AnimalWMIObject, etc. Now the implementations of AnimalUIObject, AnimalPSObject, AnimalModelObject are all in separate assemblies. Now my scenario is I want to verify the contents of business entity Animal irrespective of the assembly it came from. So I created a GenericAnimal class to represent the Animal entity. Now in GenericAnimal I added the following constructors: GenericAnimal(AnimalUIObject) GenericAnimal(AnimalPSObject) GenericAnimal(AnimalModelObject) Basically I made GenericAnimal depend on all the underlying assemblies so that while verifying I deal with this abstraction. Now the other approach to do this is have GenericAnimal with an empty constructor an allow these underlying assemblies to have a Transform() method which would build the GenericAnimal. Both approaches have some pros and cons: The 1st approach: Pros: All construction logic is in one place in one class GenericAnimal Cons: GenericAnimal class must be touched every-time there is a new representation form. The 2nd approach: Pros: construction responsibility is delegated to the underlying assembly. Cons: As construction logic is spread accross assemblies, tomorrow if I need to add a property X in GenericAnimal then I have to touch all the assemblies to change the Transform method. Which approach looks better ? or Which would you consider a lesser evil ? Is there any alternative way better than the above two ?

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  • Command Query Separation validating for retries

    - by Neil Barnwell
    So I'm comfortable with the basic concept of CQS, where you might have a command that writes to one database, and that updates the query database that you read from. However, consider the scenario where you are entering data, and want to prevent duplicates. Using new employee data entry an employee register as an example, working through a pile of application forms to key in the new employees' details: Take top sheet. Key in employee name and unique payroll number to UI. Submit. Put paper in "completed pile". Repeat. How would you now prevent the user from keying in the same payroll number again, say for instance if they get distracted and can't remember whether they've keyed one in already and the "message" hasn't got all the way back to the query db for the user to search?

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  • Buffering db inserts in multithreaded program

    - by Winter
    I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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