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  • MySQL slow query

    - by andrhamm
    SELECT items.item_id, items.category_id, items.title, items.description, items.quality, items.type, items.status, items.price, items.posted, items.modified, zip_code.state_prefix, zip_code.city, books.isbn13, books.isbn10, books.authors, books.publisher FROM ( ( items LEFT JOIN bookitems ON items.item_id = bookitems.item_id ) LEFT JOIN books ON books.isbn13 = bookitems.isbn13 ) LEFT JOIN zip_code ON zip_code.zip_code = items.item_zip WHERE items.rid = $rid` I am running this query to get the list of a user's items and their location. The zip_code table has over 40k records and this might be the issue. It currently takes up to 15 seconds to return a list of about 20 items! What can I do to make this query more efficient?

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  • Avoiding exceptions when uploading files in laravel

    - by occam98
    I've got a file upload field (attachment1) in a form that may or may not have a file uploaded in it when I process the form in laravel. When I'm trying to process the page, this line generates an exception: Input::upload('attachment1',path('storage').'attachments/'.$name); Here is the text of the exception: Message: Call to a member function move() on a non-object it seems that I need to check in advance to see if 'attachment1' has a file, and I found that the function Input::has_file('attachment1') is supposed to tell me whether or not 'attachment1' has a file, but even when I submit an empty form, it returns true. Also, from reading documentation, it seems that Input::upload is supposed to just return false when trying to upload a non-existant file, so why does it produce this exception instead, and how can I fix it?

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  • How to save big "database-like" class in python

    - by Rafal
    Hi there, I'm doing a project with reasonalby big DataBase. It's not a probper DB file, but a class with format as follows: DataBase.Nodes.Data=[[] for i in range(1,1000)] f.e. this DataBase is all together something like few thousands rows. Fisrt question - is the way I'm doing efficient, or is it better to use SQL, or any other "proper" DB, which I've never used actually. And the main question - I'd like to save my DataBase class with all record, and then re-open it with Python in another session. Is that possible, what tool should I use? cPickle - it seems to be only for strings, any other? In matlab there's very useful functionality named save workspace - it saves all Your variables to a file that You can open at another session - this would be vary useful in python!

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  • Silverlight 3-4 reference kind (e-)book.

    - by Bubba88
    Hello! I'm looking for a source of information about Microsoft Silverlight to begin practically efficient programming custom functionality applications. I want to pretend just for now that I don't need any ideologically correct refresher (SL tips, top patterns, VS tutorials :) and etc.). Basically, what I want is a reference kind e-book, where I could find any practically relevant info outlined in a minimalistic manner. If you do remember something fitting the above description, I ask you to give me a hint. Thank you very much!

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  • Position of least significant bit that is set

    - by peterchen
    I am looking for an efficient way to determine the position of the least significant bit that is set in an integer, e.g. for 0x0FF0 it would be 4. A trivial implementation is this: unsigned GetLowestBitPos(unsigned value) { assert(value != 0); // handled separately unsigned pos = 0; while (!(value & 1)) { value >>= 1; ++pos; } return pos; } Any ideas how to squeeze some cycles out of it? (Note: this question is for people that enjoy such things, not for people to tell me xyzoptimization is evil.) [edit] Thanks everyone for the ideas! I've learnt a few other things, too. Cool!

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  • Matrix Comparison algorithm

    - by SysAdmin
    If you have 2 Matrices of dimensions N*M. what is the best way to get the difference Rect? Example: 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 4 5 4 3 2 3 <---> 2 3 2 3 2 3 2 3 2 3 4 5 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 | | \ / Rect([2,2] , [3,4]) 4 5 4 4 5 2-> A (2 x 3 Matrix) The best I could think of is to scan from Top-Left hit the point where there is difference. Then scan from Bottom Right and hit the point where there is a difference. But In worst case, this is O(N*M). is there a better efficient algorithm?

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  • How to combine elements of a list

    - by Addie
    I'm working in c#. I have a sorted List of structures. The structure has a DateTime object which stores month and year and an integer which stores a value. The list is sorted by date. I need to traverse the list and combine it so that I only have one instance of the structure per date. For example: My initial list would look like this: { (Apr10, 3), (Apr10, 2), (Apr10, -3), (May10, 1), (May10, 1), (May10, -3), (Jun10, 3) } The resulting list should look like this: { (Apr10, 2), (May10, -1), (Jun10, 3) } I'm looking for a simple / efficient solution. The struct is: class CurrentTrade { public DateTime date; public int dwBuy; } The list is: private List<CurrentTrade> FillList

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  • Web Page Opinions and Suggestions

    - by MrEnder
    Been working my * off on this for a few days trying to keep updating it to make it most efficient with everything I learn... I'm quite proud of it so far considering I'm not actually the best coder lol most JS and PHP confuses the crap outa me unless I do it from scratch. So anyways here is the link. Tell me what you think. Suggestions would be amazing. I'd love to know what I screwed up as long as you explain in detail as to why and how to fix it. I really hate when people hand me a huge snippet and expect me to understand it -_- Thanks Shelby LINK http://opentech.durhamcollege.ca/~in...rittains/labs/

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  • Can UMDF drivers be packaged/shipped via WiX?

    - by Rafael Rivera
    Howdy Internets: I put together a WiX 3.0 package, utilizing the DIFx extensions, with the intentions to install a Windows 7 Sensor (UMDF driver). During installation, DIFXAPP logged "No matching devices found in INF" and simply threw the driver into storage. I read I'm to populate my INF with an appropriate DriverPackageType, but according to MSDN's enumerated list, nothing fits. Is UMDF driver installation a supported scenario? If not, what's the best practice for using WiX to install such drivers? Disassembling the DIfx extension shows intent to support Co-installer packages, I have yet to try 3.5 beta.

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  • Finding the heaviest length-constrained path in a weighted Binary Tree

    - by Hristo
    UPDATE I worked out an algorithm that I think runs in O(n*k) running time. Below is the pseudo-code: routine heaviestKPath( T, k ) // create 2D matrix with n rows and k columns with each element = -8 // we make it size k+1 because the 0th column must be all 0s for a later // function to work properly and simplicity in our algorithm matrix = new array[ T.getVertexCount() ][ k + 1 ] (-8); // set all elements in the first column of this matrix = 0 matrix[ n ][ 0 ] = 0; // fill our matrix by traversing the tree traverseToFillMatrix( T.root, k ); // consider a path that would arc over a node globalMaxWeight = -8; findArcs( T.root, k ); return globalMaxWeight end routine // node = the current node; k = the path length; node.lc = node’s left child; // node.rc = node’s right child; node.idx = node’s index (row) in the matrix; // node.lc.wt/node.rc.wt = weight of the edge to left/right child; routine traverseToFillMatrix( node, k ) if (node == null) return; traverseToFillMatrix(node.lc, k ); // recurse left traverseToFillMatrix(node.rc, k ); // recurse right // in the case that a left/right child doesn’t exist, or both, // let’s assume the code is smart enough to handle these cases matrix[ node.idx ][ 1 ] = max( node.lc.wt, node.rc.wt ); for i = 2 to k { // max returns the heavier of the 2 paths matrix[node.idx][i] = max( matrix[node.lc.idx][i-1] + node.lc.wt, matrix[node.rc.idx][i-1] + node.rc.wt); } end routine // node = the current node, k = the path length routine findArcs( node, k ) if (node == null) return; nodeMax = matrix[node.idx][k]; longPath = path[node.idx][k]; i = 1; j = k-1; while ( i+j == k AND i < k ) { left = node.lc.wt + matrix[node.lc.idx][i-1]; right = node.rc.wt + matrix[node.rc.idx][j-1]; if ( left + right > nodeMax ) { nodeMax = left + right; } i++; j--; } // if this node’s max weight is larger than the global max weight, update if ( globalMaxWeight < nodeMax ) { globalMaxWeight = nodeMax; } findArcs( node.lc, k ); // recurse left findArcs( node.rc, k ); // recurse right end routine Let me know what you think. Feedback is welcome. I think have come up with two naive algorithms that find the heaviest length-constrained path in a weighted Binary Tree. Firstly, the description of the algorithm is as follows: given an n-vertex Binary Tree with weighted edges and some value k, find the heaviest path of length k. For both algorithms, I'll need a reference to all vertices so I'll just do a simple traversal of the Tree to have a reference to all vertices, with each vertex having a reference to its left, right, and parent nodes in the tree. Algorithm 1 For this algorithm, I'm basically planning on running DFS from each node in the Tree, with consideration to the fixed path length. In addition, since the path I'm looking for has the potential of going from left subtree to root to right subtree, I will have to consider 3 choices at each node. But this will result in a O(n*3^k) algorithm and I don't like that. Algorithm 2 I'm essentially thinking about using a modified version of Dijkstra's Algorithm in order to consider a fixed path length. Since I'm looking for heaviest and Dijkstra's Algorithm finds the lightest, I'm planning on negating all edge weights before starting the traversal. Actually... this doesn't make sense since I'd have to run Dijkstra's on each node and that doesn't seem very efficient much better than the above algorithm. So I guess my main questions are several. Firstly, do the algorithms I've described above solve the problem at hand? I'm not totally certain the Dijkstra's version will work as Dijkstra's is meant for positive edge values. Now, I am sure there exist more clever/efficient algorithms for this... what is a better algorithm? I've read about "Using spine decompositions to efficiently solve the length-constrained heaviest path problem for trees" but that is really complicated and I don't understand it at all. Are there other algorithms that tackle this problem, maybe not as efficiently as spine decomposition but easier to understand? Thanks.

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  • [wxWidgets] How to store wxImage into database, using C++?

    - by Thomas Matthews
    I have some wxImages and I would like to store them into a BLOB (Binary Large OBject) field in a MySQL database. There are no methods in wxImage nor wxBitmap for obtaining the binary data as an array of unsigned char so I can load into the database. My current workaround is to write the image to a temporary file, then load the BLOB field directly from the file. Is there a more efficient method to load and store a wxImage object into a MySQL BLOB field? I am using MySql C++ connector 1.05, MS Visual Studio 2008, wxWidgets and C++.

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  • Logging from symfony's model layer

    - by naag
    I'm currently working on a project with symfony 1.4 and Doctrine 1.2. I'm looking for a proper way to do logging from the model layer. In some model classes I use the record hook postSave() to create a ZIP file using exec() (since PHP zip doesn't provide for storage method 'Stored'). To be sure that everythings works fine I check the return code and log an error if something goes wrong. My first naive approach was to do it like this: if ($returnCode != 0) { sfContext::getInstance()->getLogger()->debug(...); } As you know, this doesn't work so well because sfContext belongs to the controller layer and shouldn't be used from the model layer. My next try was to use the model's constructor to pass in an sfLogger instance, but this doesn't work due to Doctrine 1.2 reserving the constructor for internal use (Doctrine 1.2 Documentation). I'm looking forward for your suggestions!

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  • Are all languages used within .net Equally performant?

    - by WeNeedAnswers
    I know the "Sales pitch" answer is yes to this question, but is it technically true. The Common Language Runtime (CLR) is designed as an intermediate language based on Imperative Programming (IP), but this has obvious implications when dealing with Declarative Programming (DP). So how efficient is a language based on a different paradigm than the Imperative Style when implemented in the CLR? I also get the feeling that the step to DP would incur an extra level of abstraction that might not model at all performant, would this be a fair comment? I have done some simple tests using F# and it all looks great, but am I missing something if the programs get more complex?

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  • Initializing "new users" in Rails

    - by mathee
    I'm creating a Ruby on Rails application, and I'm trying to create/login/logout users. This is the schema for Users: create_table "users", :force => true do |t| t.string "first_name" t.string "last_name" t.text "reputation" t.integer "questions_asked" t.integer "answers_given" t.string "request" t.datetime "created_at" t.datetime "updated_at" t.string "email_hash" t.string "username" t.string "hashed_password" t.string "salt" end The user's personal information (username, first/last names, email) is populated through a POST. Other things such as questions_asked, reputation, etc. are set by the application, so should be initialized when we create new users. Right now, I'm just setting each of those manually in the create method for UsersController: def create @user = User.new(params[:user]) @user.reputation = 0 @user.questions_asked = 0 @user.answers_given = 0 @user.request = nil ... end Is there a more elegant/efficient way of doing this?

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  • Why would it be a bad idea to have database connection open between client requests?

    - by AspOnMyNet
    1) Book I’m reading argues that connections shouldn’t be opened between client requests, since they are a finite resource. I realize that max pool size can quickly be reached and thus any further attempts to open a connection will be queued until connection becomes available and for that reason it would be imperative that we release connection as soon as possible. But assuming all request will open connection to the same DB, then I’m not sure how having a connection open between two client requests would be any less efficient than having each request first acquiring a connection from connection pool and later returning that object to connection pool? 2) Book also recommends that when database code is encapsulated in a dedicated data access class, then method M opening a database connection should also close that connection. a) I assume one reason why M should also close it, is because if method M opening the connection doesn’t also close it, but instead this connection object is used inside several methods, then it’s more likely that a programmer will forget to close it. b) Are there any other reasons why a method opening the connection should also close it? thanx

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  • Drawing Rounded Rectangle in DirectX/3D for 2D

    - by Jengerer
    I'm using Direct3D to draw 2D elements in a C++ application of mine, and it'd be neat if I could create rounded-rectangle GUI elements that were varying in size, but I'm not sure how to do that in the most efficient manner possible. I thought of the "easy" way which would be to have images of the four corners and then just place them in the proper positions, and fill in the rest, but varying radii for the rectangle corners would be a definite plus, and this method doesn't accommodate that feature well. Through my searches I've come across the terms Pixel Shader, Stencil Buffering, and HLSL, but I'm not sure whether these terms are relevant and which one to jump into if so. Thanks in advance, Jengerer

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  • how to autocenter jquery ui dialog whenb resizing browser?

    - by Jorre
    When you use jquery UI dialog, all works well, except for one thing. When the browser is resized, the dialog just stays in it's initial position which can be really annoying. You can test it out on: http://jqueryui.com/demos/dialog/ Click on the "modal dialog" example and resize your browser. I'd love to be able to let dialogs autocenter when the browser resizes. Can this be done in an efficient way for all my dialogs in my app? Thanks a lot!

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  • Definitive best practice for injecting, manipulating AJAX data

    - by Nic
    Ever since my foray into AJAX, I've always used the "whatever works" method of manipulating AJAX data returns. I'd like to know what the definitive and modern best practice is for handling data. Is it best practice to generate the HTML via the server script and introduce the returned data on the onComplete function? Should XML/JSON be looked at first before anything? How about manipulating the returned data? Using .live() doesn't seem like it is the most efficient way. I've never seen a definitive answer to this question. Your expertise is much appreciated.

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  • Displaying Google Calendar event data on FullCalendar

    - by aurealus
    I am using Google Calendar as a storage engine for a calendar system I am building, however, I am using a single Google user account with multiple calendars, i.e. each user on my system has their own calendar within the one user account. I'm able to create a calendar per user just fine, but I would like to have FullCalendar retrieve the events for display purposes, without manually getting the magic cookie url from Google Calendar settings. I would like to be able to retrieve it programmatically or 'proxy' the feed via an authenticated call to get event data that I'm doing in Django. $('#calendar').fullCalendar({ events: $.fullCalendar.gcalFeed( "http://www.google.com/calendar_url/" <-- or /my/event/feed/url ) });

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  • Cascading S3 Sink Tap not being deleted with SinkMode.REPLACE

    - by Eric Charles
    We are running Cascading with a Sink Tap being configured to store in Amazon S3 and were facing some FileAlreadyExistsException (see [1]). This was only from time to time (1 time on around 100) and was not reproducable. Digging into the Cascading codem, we discovered the Hfs.deleteResource() is called (among others) by the BaseFlow.deleteSinksIfNotUpdate(). Btw, we were quite intrigued with the silent NPE (with comment "hack to get around npe thrown when fs reaches root directory"). From there, we extended the Hfs tap with our own Tap to add more action in the deleteResource() method (see [2]) with a retry mechanism calling directly the getFileSystem(conf).delete. The retry mechanism seemed to bring improvement, but we are still sometimes facing failures (see example in [3]): it sounds like HDFS returns isDeleted=true, but asking directly after if the folder exists, we receive exists=true, which should not happen. Logs also shows randomly isDeleted true or false when the flow succeeds, which sounds like the returned value is irrelevant or not to be trusted. Can anybody bring his own S3 experience with such a behavior: "folder should be deleted, but it is not"? We suspect a S3 issue, but could it also be in Cascading or HDFS? We run on Hadoop Cloudera-cdh3u5 and Cascading 2.0.1-wip-dev. [1] org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory s3n://... already exists at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:132) at com.twitter.elephantbird.mapred.output.DeprecatedOutputFormatWrapper.checkOutputSpecs(DeprecatedOutputFormatWrapper.java:75) at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:923) at org.apache.hadoop.mapred.JobClient$2.run(JobClient.java:882) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1278) at org.apache.hadoop.mapred.JobClient.submitJobInternal(JobClient.java:882) at org.apache.hadoop.mapred.JobClient.submitJob(JobClient.java:856) at cascading.flow.hadoop.planner.HadoopFlowStepJob.internalNonBlockingStart(HadoopFlowStepJob.java:104) at cascading.flow.planner.FlowStepJob.blockOnJob(FlowStepJob.java:174) at cascading.flow.planner.FlowStepJob.start(FlowStepJob.java:137) at cascading.flow.planner.FlowStepJob.call(FlowStepJob.java:122) at cascading.flow.planner.FlowStepJob.call(FlowStepJob.java:42) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.j [2] @Override public boolean deleteResource(JobConf conf) throws IOException { LOGGER.info("Deleting resource {}", getIdentifier()); boolean isDeleted = super.deleteResource(conf); LOGGER.info("Hfs Sink Tap isDeleted is {} for {}", isDeleted, getIdentifier()); Path path = new Path(getIdentifier()); int retryCount = 0; int cumulativeSleepTime = 0; int sleepTime = 1000; while (getFileSystem(conf).exists(path)) { LOGGER .info( "Resource {} still exists, it should not... - I will continue to wait patiently...", getIdentifier()); try { LOGGER.info("Now I will sleep " + sleepTime / 1000 + " seconds while trying to delete {} - attempt: {}", getIdentifier(), retryCount + 1); Thread.sleep(sleepTime); cumulativeSleepTime += sleepTime; sleepTime *= 2; } catch (InterruptedException e) { e.printStackTrace(); LOGGER .error( "Interrupted while sleeping trying to delete {} with message {}...", getIdentifier(), e.getMessage()); throw new RuntimeException(e); } if (retryCount == 0) { getFileSystem(conf).delete(getPath(), true); } retryCount++; if (cumulativeSleepTime > MAXIMUM_TIME_TO_WAIT_TO_DELETE_MS) { break; } } if (getFileSystem(conf).exists(path)) { LOGGER .error( "We didn't succeed to delete the resource {}. Throwing now a runtime exception.", getIdentifier()); throw new RuntimeException( "Although we waited to delete the resource for " + getIdentifier() + ' ' + retryCount + " iterations, it still exists - This must be an issue in the underlying storage system."); } return isDeleted; } [3] INFO [pool-2-thread-15] (BaseFlow.java:1287) - [...] at least one sink is marked for delete INFO [pool-2-thread-15] (BaseFlow.java:1287) - [...] sink oldest modified date: Wed Dec 31 23:59:59 UTC 1969 INFO [pool-2-thread-15] (HiveSinkTap.java:148) - Now I will sleep 1 seconds while trying to delete s3n://... - attempt: 1 INFO [pool-2-thread-15] (HiveSinkTap.java:130) - Deleting resource s3n://... INFO [pool-2-thread-15] (HiveSinkTap.java:133) - Hfs Sink Tap isDeleted is true for s3n://... ERROR [pool-2-thread-15] (HiveSinkTap.java:175) - We didn't succeed to delete the resource s3n://... Throwing now a runtime exception. WARN [pool-2-thread-15] (Cascade.java:706) - [...] flow failed: ... java.lang.RuntimeException: Although we waited to delete the resource for s3n://... 0 iterations, it still exists - This must be an issue in the underlying storage system. at com.qubit.hive.tap.HiveSinkTap.deleteResource(HiveSinkTap.java:179) at com.qubit.hive.tap.HiveSinkTap.deleteResource(HiveSinkTap.java:40) at cascading.flow.BaseFlow.deleteSinksIfNotUpdate(BaseFlow.java:971) at cascading.flow.BaseFlow.prepare(BaseFlow.java:733) at cascading.cascade.Cascade$CascadeJob.call(Cascade.java:761) at cascading.cascade.Cascade$CascadeJob.call(Cascade.java:710) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619)

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  • setting up/installing/configuring nginx LEMP stack on fresh VPS server

    - by grant tailor
    I need some help in settingup/installing and configuring nginx LEMP stack on a fresh new VPS i have. The specs of the CentOS 5.7 VPS are 2GB DDR3 ECC RAM(4GB burst), 1 core 1.5Ghz(3Ghz burst) and 100GB RAID 10 storage, unmetered bandwidth @ 100Mpbs all for a whopping $25/month(unbeatable, yeah i know :) Anyways i have followed this LEMP(will also need MySQL and PHP) stack guide on linode http://library.linode.com/lemp-guides/centos-5 but basically what i want is to be able to host multiple website on this webserver after everything is setup. I am used to using DirectAdmin control panel on other server and want to have things setup so i can host multiple websites...mostly wordpress and drupal themes. Lets say 10 websites on this nginx web server. So can someone please help me on what i need to do to take "full" advantage of nginx power and performance, while been able to easily manage these multiple websites (wordpress and drupal themes)? Thanks.

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  • jQuery - improve/reduce my ipod-style dropdown code! - challenge?

    - by aSeptik
    Hi all guys! by keeping inspiration from this http://www.filamentgroup.com/examples/menus/ipod.php i have maked my own from scratch cause i have needed this smarty dropdown solution for a client, but more lightweight & efficient! so with a good cup of coffe in my hand i have maked this DEMO: http://jsbin.com/ufuga SOURCE: http://jsbin.com/ufuga/edit since this is a proof o concept, whould be nice to know, before port this into a plugin, what you think about it! is good, bad or can be improved or reduced in size!? i'm glad to share this code with you and whould be nice if you want give me any feedback! ;-) PS: work perfectly in IE6+, Firefox, Chrome, Opera and of course support the jQuery Theme Roller and have zero configuration steps! thank you guys!

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  • Making swap faster, easier to use and exception-safe

    - by FredOverflow
    I could not sleep last night and started thinking about std::swap. Here is the familiar C++98 version: template <typename T> void swap(T& a, T& b) { T c(a); a = b; b = c; } If a user-defined class Foo uses external ressources, this is inefficient. The common idiom is to provide a method void Foo::swap(Foo& other) and a specialization of std::swap<Foo>. Note that this does not work with class templates since you cannot partially specialize a function template, and overloading names in the std namespace is illegal. The solution is to write a template function in one's own namespace and rely on argument dependent lookup to find it. This depends critically on the client to follow the "using std::swap idiom" instead of calling std::swap directly. Very brittle. In C++0x, if Foo has a user-defined move constructor and a move assignment operator, providing a custom swap method and a std::swap<Foo> specialization has little to no performance benefit, because the C++0x version of std::swap uses efficient moves instead of copies: #include <utility> template <typename T> void swap(T& a, T& b) { T c(std::move(a)); a = std::move(b); b = std::move(c); } Not having to fiddle with swap anymore already takes a lot of burden away from the programmer. Current compilers do not generate move constructors and move assignment operators automatically yet, but as far as I know, this will change. The only problem left then is exception-safety, because in general, move operations are allowed to throw, and this opens up a whole can of worms. The question "What exactly is the state of a moved-from object?" complicates things further. Then I was thinking, what exactly are the semantics of std::swap in C++0x if everything goes fine? What is the state of the objects before and after the swap? Typically, swapping via move operations does not touch external resources, only the "flat" object representations themselves. So why not simply write a swap template that does exactly that: swap the object representations? #include <cstring> template <typename T> void swap(T& a, T& b) { unsigned char c[sizeof(T)]; memcpy( c, &a, sizeof(T)); memcpy(&a, &b, sizeof(T)); memcpy(&b, c, sizeof(T)); } This is as efficient as it gets: it simply blasts through raw memory. It does not require any intervention from the user: no special swap methods or move operations have to be defined. This means that it even works in C++98 (which does not have rvalue references, mind you). But even more importantly, we can now forget about the exception-safety issues, because memcpy never throws. I can see two potential problems with this approach: First, not all objects are meant to be swapped. If a class designer hides the copy constructor or the copy assignment operator, trying to swap objects of the class should fail at compile-time. We can simply introduce some dead code that checks whether copying and assignment are legal on the type: template <typename T> void swap(T& a, T& b) { if (false) // dead code, never executed { T c(a); // copy-constructible? a = b; // assignable? } unsigned char c[sizeof(T)]; std::memcpy( c, &a, sizeof(T)); std::memcpy(&a, &b, sizeof(T)); std::memcpy(&b, c, sizeof(T)); } Any decent compiler can trivially get rid of the dead code. (There are probably better ways to check the "swap conformance", but that is not the point. What matters is that it's possible). Second, some types might perform "unusual" actions in the copy constructor and copy assignment operator. For example, they might notify observers of their change. I deem this a minor issue, because such kinds of objects probably should not have provided copy operations in the first place. Please let me know what you think of this approach to swapping. Would it work in practice? Would you use it? Can you identify library types where this would break? Do you see additional problems? Discuss!

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  • [PHP] Invalid argument supplied for foreach()

    - by Roberto Aloi
    It often happens to me to handle data that can be either an array or a null variable and to feed some foreach with these data. $values = get_values(); foreach ($values as $value){ ... } When you feed a foreach with data that are not an array, you get a warning: Warning: Invalid argument supplied for foreach() in [...] Assuming it's not possible to refactor the get_values() function to always return an array (backward compatibility, not available source code, whatever other reason), I'm wondering which is the cleanest and most efficient way to avoid these warnings: Casting $values to array Initializing $values to array Wrapping the foreach with an if Other (please suggest)

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  • Can I use array_push on a SESSION array in php?

    - by zeckdude
    I have an array that I want on multiple pages, so I made it a SESSION array. I want to add a series of names and then on another page, I want to be able to use a foreach loop to echo out all the names in that array. This is the session: $_SESSION['names'] I want to add a series of names to that array using array_push like this: array_push($_SESSION['names'],$name); I am getting this error: array_push() [function.array-push]: First argument should be an array Can I use array_push to put multiple values into that array? Or perhaps there is a better, more efficient way of doing what I am trying to achieve?

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