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• C++ Matrix class hierachy

  - by bpw1621

  Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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• Heroku: Postgres type operator error after migrating DB from MySQL

  - by sevennineteen

  This is a follow-up to a question I'd asked earlier which phrased this as more of a programming problem than a database problem. http://stackoverflow.com/questions/2935985/postgres-error-with-sinatra-haml-datamapper-on-heroku I believe the problem has been isolated to the storage of the ID column in Heroku's Postgres database after running db:push. In short, my app runs properly on my original MySQL database, but throws Postgres errors on Heroku when executing any query on the ID column, which seems to have been stored in Postgres as TEXT even though it is stored as INT in MySQL. My question is why the ID column is being created as INT in Postgres on the data transfer to Heroku, and whether there's any way for me to prevent this. Here's the output from a heroku console session which demonstrates the issue: Ruby console for myapp.heroku.com >> Post.first.title => "Welcome to First!" >> Post.first.title.class => String >> Post.first.id => 1 >> Post.first.id.class => Fixnum >> Post[1] PostgresError: ERROR: operator does not exist: text = integer LINE 1: ...", "title", "created_at" FROM "posts" WHERE ("id" = 1) ORDER... ^ HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts. Query: SELECT "id", "name", "email", "url", "title", "created_at" FROM "posts" WHERE ("id" = 1) ORDER BY "id" LIMIT 1 Thanks!

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• Mbean registered but not found in mbean Server

  - by Prisco

  I have a problem about the mbeans. I have created a simple mbean and I have registered it on the default mBeanServer that is run (Via eclipse or java -jar mbean.jar) and in the same process if I try to fouund the mbean registered with a simple query: for (ObjectInstance instance : mbs.queryMBeans(ObjectNameMbean, null)) { System.out.println(instance.toString()); } the query retuerns my mbean, but if I start another process and try to search this mbean registered the mbeas is not found! why? The approch is : (Process that is running) public static void main(String[] args) throws Exception { MBeanServer mbeanServer =ManagementFactory.getPlatformMBeanServer(); ObjectName objectName = new ObjectName(ObjectNameMbean); Simple simple = new Simple (1, 0); mbeanServer.registerMBean(simple, objectName); while (true) { wait (Is this necessary?) } } So this is the first process that is running (that has the only pourpose to registry the mbean, because there is another process that want to read these informations. So I start another process to search this mbean but nothing. I 'm not using jboss but the local Java virtual Machine but my scope is to deploy this simple application in one ejb (autostart) and another ejb will read all informations. All suggestions are really apprecciated. This example should be more useful : Object Hello: public class Hello implements HelloMBean { public void sayHello() { System.out.println("hello, world"); } public int add(int x, int y) { return x + y; } public String getName() { return this.name; } public int getCacheSize() { return this.cacheSize; } public synchronized void setCacheSize(int size) { this.cacheSize = size; System.out.println("Cache size now " + this.cacheSize); } private final String name = "Reginald"; private int cacheSize = DEFAULT_CACHE_SIZE; private static final int DEFAULT_CACHE_SIZE = 200; } Interface HelloBean (implemented by Hello) public interface HelloMBean { public void sayHello(); public int add(int x, int y); public String getName(); public int getCacheSize(); public void setCacheSize(int size); } Simple Main import java.lang.management.ManagementFactory; import java.util.logging.Logger; import javax.management.MBeanServer; import javax.management.ObjectName; public class Main { static Logger aLog = Logger.getLogger("MBeanTest"); public static void main(String[] args) { try{ MBeanServer mbs = ManagementFactory.getPlatformMBeanServer(); ObjectName name = new ObjectName("ApplicationDomain:type=Hello"); Hello mbean = new Hello(); mbs.registerMBean(mbean, name); // System.out.println(mbs.getAttribute(name, "Name")); aLog.info("Waiting forever..."); Thread.sleep(Long.MAX_VALUE); } catch(Exception x){ x.printStackTrace(); aLog.info("exception"); } } } So now I have exported this project as jar file and run it as "java -jar helloBean.jar" and by eclipse I have modified the main class to read informations of this read (Example "Name" attribute) by using the same objectname used to registry it . Main to read : public static void main(String[] args) { try{ MBeanServer mbs = ManagementFactory.getPlatformMBeanServer(); ObjectName name = new ObjectName("ApplicationDomain:type=Hello"); System.out.println(mbs.getAttribute(name, "Name")); } catch(Exception x){ x.printStackTrace(); aLog.info("exception"); } } But nothing, the bean is not found.

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• Design an Application That Stores and Processes Files

  - by phasetwenty

  I'm tasked with writing an application that acts as a central storage point for files (usually document formats) as provided by other applications. It also needs to take commands like "file 395 needs a copy in X format", at which point some work is offloaded to a 3rd party application. I'm having trouble coming up with a strategy for this. I'd like to keep the design as simple as possible, so I'd like to avoid big extra frameworks or techniques like threads for as long as it makes sense. The clients are expected to be web applications (for example, one is a django application that receives files from our customers; the others are not yet implemented). The platform it will be running on is likely going to be Python on Linux, unless I have a strong argument to use something else. In the beginning I thought I could fit the information I wanted to communicate in the filenames, and let my application parse the filename to figure out what it needed to do, but this is proving too inflexible with the amount of information I'm realizing I need to make available. Another idea is to pair FTP with a database used as a communication medium (client uploads a file and updates the database with a command as a row in a table) but I don't like this idea because adding commands (a known change) looks like it will require adding code as well as changing database schemas. It will also muddy up the interface my clients will have to use. I looked into Pyro to let applications communicate more directly but I don't like the idea of running an extra nameserver for this one purpose. I also don't see a good way to do file transfer within this framework. What I'm looking for is techniques and/or technologies applicable to my problem. At the simplest level, I need the ability to accept files and messages with them.

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• Including objects from external .js files

  - by Molle

  I have been searching for many hours over several days for this answer and though there are many topics on how to include files in a project (also here at Stack Overflow), I have not yet found THE solution to my problem. I'm working on a project where I want to include one single object at a time, from many different files (I do not want to include the files themselves, only their content). All the object in all the files have the same name, only the content is different. It is important that I do not get a SCRIPT tag in the head section of the page as all the content from the files will have the same names. None of the files will have functions anyways, only one single object, that will need to be loaded one at the time and then discarded when the next element is loaded. The objects will hold the data that will be shown on the page and they will be called from the menu by an 'onclick' event. function setMenu() // The menu is being build. { var html = ''; html += '<table border="0">'; for (var i = 0; i<menu.pages.length; i++) { html += '<tr class="menuPunkt"><td width="5"></td><td onclick="pageName(this)">'+ menu.pages[i] +'</td><td width="5"></td></tr>'; } // menu is a global object containing elements such as an array with // all the pages that needs to be shown and styling for the menu. html += '</table>'; document.getElementById("menu").innerHTML = html; style.setMenu(); // The menu is being positioned and styled. } Now, when I click on a menu item the pageName function is triggered and I'm sending the HTML element to the function as well, it is here that I want the content from my external file to be loaded into a local variable and used to display content on the page. ** The answer I want is "How to load the external obj into the function where I need it? (It may be an external file, but only in the term of not being included in the head section. I'm still loading the the file from my own local library.** function pageName(elm) // The element that I clicked is elm. { var page = info.innerHTML; // I need only the innerHTML from the element. var file = 'sites/' + page + '.js'; // The file to be loaded is created. var obj = ?? // Here I somehow want the object from the external file to be loaded. // Before doing stuff the the obj. style.content(); } The content from the external file could look like this: // The src for the external page: 'sites/page.js' var obj = new Object() { obj.innerHTML = 'Text to be shown'; obj.style = 'Not important for problem at hand'; obj.otherStuff = ' --||-- '; } Any help will be appreciated, Molle

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• java will this threading setup work or what can i be doing wrong

  - by Erik

  Im a bit unsure and have to get advice. I have the: public class MyApp extends JFrame{ And from there i do; MyServer = new MyServer (this); MyServer.execute(); MyServer is a: public class MyServer extends SwingWorker<String, Object> { MyServer is doing listen_socket.accept() in the doInBackground() and on connection it create a new class Connection implements Runnable { I have the belove DbHelper that are a singleton. It holds an Sqlite connected. Im initiating it in the above MyApp and passing references all the way in to my runnable: class Connection implements Runnable { My question is what will happen if there are two simultaneous read or `write? My thought here was the all methods in the singleton are synchronized and would put all calls in the queue waiting to get a lock on the synchronized method. Will this work or what can i change? public final class DbHelper { private boolean initalized = false; private String HomePath = ""; private File DBFile; private static final String SYSTEM_TABLE = "systemtable"; Connection con = null; private Statement stmt; private static final ContentProviderHelper instance = new ContentProviderHelper (); public static ContentProviderHelper getInstance() { return instance; } private DbHelper () { if (!initalized) { initDB(); initalized = true; } } private void initDB() { DBFile = locateDBFile(); try { Class.forName("org.sqlite.JDBC"); // create a database connection con = DriverManager.getConnection("jdbc:sqlite:J:/workspace/workComputer/user_ptpp"); } catch (SQLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } private File locateDBFile() { File f = null; try{ HomePath = System.getProperty("user.dir"); System.out.println("HomePath: " + HomePath); f = new File(HomePath + "/user_ptpp"); if (f.canRead()) return f; else { boolean success = f.createNewFile(); if (success) { System.out.println("File did not exist and was created " + HomePath); // File did not exist and was created } else { System.out.println("File already exists " + HomePath); // File already exists } } } catch (IOException e) { System.out.println("Maybe try a new directory. " + HomePath); //Maybe try a new directory. } return f; } public String getHomePath() { return HomePath; } private synchronized String getDate(){ SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date date = new Date(); return dateFormat.format(date); } public synchronized String getSelectedSystemTableColumn( String column) { String query = "select "+ column + " from " + SYSTEM_TABLE ; try { stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY); ResultSet rs = stmt.executeQuery(query); while (rs.next()) { String value = rs.getString(column); if(value == null || value == "") return ""; else return value; } } catch (SQLException e ) { e.printStackTrace(); return ""; } finally { } return ""; } }

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• Multithreaded linked list traversal

  - by Rob Bryce

  Given a (doubly) linked list of objects (C++), I have an operation that I would like multithread, to perform on each object. The cost of the operation is not uniform for each object. The linked list is the preferred storage for this set of objects for a variety of reasons. The 1st element in each object is the pointer to the next object; the 2nd element is the previous object in the list. I have solved the problem by building an array of nodes, and applying OpenMP. This gave decent performance. I then switched to my own threading routines (based off Windows primitives) and by using InterlockedIncrement() (acting on the index into the array), I can achieve higher overall CPU utilization and faster through-put. Essentially, the threads work by "leap-frog'ing" along the elements. My next approach to optimization is to try to eliminate creating/reusing the array of elements in my linked list. However, I'd like to continue with this "leap-frog" approach and somehow use some nonexistent routine that could be called "InterlockedCompareDereference" - to atomically compare against NULL (end of list) and conditionally dereference & store, returning the dereferenced value. I don't think InterlockedCompareExchangePointer() will work since I cannot atomically dereference the pointer and call this Interlocked() method. I've done some reading and others are suggesting critical sections or spin-locks. Critical sections seem heavy-weight here. I'm tempted to try spin-locks but I thought I'd first pose the question here and ask what other people are doing. I'm not convinced that the InterlockedCompareExchangePointer() method itself could be used like a spin-lock. Then one also has to consider acquire/release/fence semantics... Ideas? Thanks!

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• Making two Windows using CreateWindowsEx()

  - by Jamie Keeling

  Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a separate thread so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate thread 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I think that using CreateWindow will allow me to make another window but again i'm not sure how to access the message pump so I can respond to certain events like WM_CREATE on the second window. I hope it makes sense. Thanks! Edit: I've attempted to make a second window and although this does compile, no windows show atall on build. ////////////////////// // WINDOWS FUNCTION // ////////////////////// LRESULT CALLBACK WindowFunc(HWND hMainWindow, UINT message, WPARAM wParam, LPARAM lParam) { //Fields WCHAR buffer[256]; struct DiceData storage; HWND hwnd; // Act on current message switch(message) { case WM_CREATE: AddMenus(hMainWindow); hwnd = CreateWindowEx( 0, "ChildWClass", (LPCTSTR) NULL, WS_CHILD | WS_BORDER | WS_VISIBLE, 0, 0, 0, 0, hMainWindow, NULL, NULL, NULL); ShowWindow(hwnd, SW_SHOW); break; Any suggestions as to why this happens?

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• How to optimize a postgreSQL server for a "write once, read many"-type infrastructure ?

  - by mhu

  Greetings, I am working on a piece of software that logs entries (and related tagging) in a PostgreSQL database for storage and retrieval. We never update any data once it has been inserted; we might remove it when the entry gets too old, but this is done at most once a day. Stored entries can be retrieved by users. The insertion of new entries can happen rather fast and regularly, thus the database will commonly hold several millions elements. The tables used are pretty simple : one table for ids, raw content and insertion date; and one table storing tags and their values associated to an id. User search mostly concern tags values, so SELECTs usually consist of JOIN queries on ids on the two tables. To sum it up : 2 tables Lots of INSERT no UPDATE some DELETE, once a day at most some user-generated SELECT with JOIN huge data set What would an optimal server configuration (software and hardware, I assume for example that RAID10 could help) be for my PostgreSQL server, given these requirements ? By optimal, I mean one that allows SELECT queries taking a reasonably little amount of time. I can provide more information about the current setup (like tables, indexes ...) if needed.

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• Enforcing default time when only date in timestamptz provided

  - by Incognito

  Assume I have the table: postgres=# create table foo (datetimes timestamptz); CREATE TABLE postgres=# \d+ foo Table "public.foo" Column | Type | Modifiers | Storage | Description -----------+--------------------------+-----------+---------+------------- datetimes | timestamp with time zone | | plain | Has OIDs: no So lets insert some values into it... postgres=# insert into foo values ('2012-12-12'), --This is the value I want to catch for. (null), ('2012-12-12 12:12:12'), ('2012-12-12 12:12'); INSERT 0 4 And here's what we have: postgres=# select * from foo ; datetimes ------------------------ 2012-12-12 00:00:00+00 2012-12-12 12:12:12+00 2012-12-12 12:12:00+00 (4 rows) Ideally, I'd like to set up a default time-stamp value when a TIME is not provided with the input, rather than the de-facto time of 2012-12-12 being 00:00:00, I would like to set a default of 15:45:10. Meaning, my results should look like: postgres=# select * from foo ; datetimes ------------------------ 2012-12-12 15:45:10+00 --This one gets the default time. 2012-12-12 12:12:12+00 2012-12-12 12:12:00+00 (4 rows) I'm not really sure how to do this in postgres 8.4, I can't find anything in the datetime section of the manual or the sections regarding column default values.

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• XUL: Printing value from SQL query without using value attribute

  - by Grip

  I want to print the results of an SQL query in XUL with word-wrapping using the description tag. I have the following code: <grid> <columns> <column flex="2" /> <column flex="1" /> </columns> <rows datasources="chrome://glossary/content/db/development.sqlite3" ref="?" querytype="storage" > <template> <query>select distinct * from Terms</query> <action> <row uri="?"> <description value="?name" /> <description value="?desc" /> </row> </action> </template> </rows> This works for printing the data, but since I'm using the value attribute of description, there's no word-wrapping. I don't understand entirely what I'm doing with the value attribute, but I don't seem to be able to get the values of my SQL query in any other way. So, how could I get those values without the value tag? Thanks.

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• Fastest way to perform subset test operation on a large collection of sets with same domain

  - by niktech

  Assume we have trillions of sets stored somewhere. The domain for each of these sets is the same. It is also finite and discrete. So each set may be stored as a bit field (eg: 0000100111...) of a relatively short length (eg: 1024). That is, bit X in the bitfield indicates whether item X (of 1024 possible items) is included in the given set or not. Now, I want to devise a storage structure and an algorithm to efficiently answer the query: what sets in the data store have set Y as a subset. Set Y itself is not present in the data store and is specified at run time. Now the simplest way to solve this would be to AND the bitfield for set Y with bit fields of every set in the data store one by one, picking the ones whose AND result matches Y's bitfield. How can I speed this up? Is there a tree structure (index) or some smart algorithm that would allow me to perform this query without having to AND every stored set's bitfield? Are there databases that already support such operations on large collections of sets?

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• typedef a functions prototype

  - by bitmask

  I have a series of functions with the same prototype, say int func1(int a, int b) { // ... } int func2(int a, int b) { // ... } // ... Now, I want to simplify their definition and declaration. Of course I could use a macro like that: #define SP_FUNC(name) int name(int a, int b) But I'd like to keep it in C, so I tried to use the storage specifier typedef for this: typedef int SpFunc(int a, int b); This seems to work fine for the declaration: SpFunc func1; // compiles but not for the definition: SpFunc func1 { // ... } which gives me the following error: error: expected '=', ',', ';', 'asm' or '__attribute__' before '{' token Is there a way to do this correctly or is it impossible? To my understanding of C this should work, but it doesn't. Why? Note, gcc understands what I am trying to do, because, if I write SpFunc func1 = { /* ... */ } it tells me error: function 'func1' is initialized like a variable Which means that gcc understands that SpFunc is a function type.

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• How to create a new ID for the new added node?

  - by marknt15

  Hi, I can normally get the ID of the default tree nodes but my problem is onCreate then jsTree will add a new node but it doesn't have an ID. My question is how can I add an ID to the newly created tree node? What I'm thinking to do is adding the ID HTML attribute to the newly created tree node but how? I need to get the ID of all of the nodes because it will serve as a reference for the node's respective div storage. HTML code: <div class="demo" id="demo_1"> <ul> <li id="phtml_1" class="file"><a href="#"><ins>&nbsp;</ins>Root node 1</a></li> <li id="phtml_2" class="file"><a href="#"><ins>&nbsp;</ins>Root node 2</a></li> </ul> </div> JS code: $("#demo_1").tree({ ui : { theme_name : "apple" }, callback : { onrename : function (NODE, TREE_OBJ) { alert(TREE_OBJ.get_text(NODE)); alert($(NODE).attr('id')); } } }); Cheers, Mark

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• Catch a PHP Object Instantiation Error

  - by Rob Wilkerson

  It's really irking me that PHP considers the failure to instantiate an object a Fatal Error (which can't be caught) for the application as a whole. I have set of classes that aren't strictly necessary for my application to function--they're really a convenience. I have a factory object that attempts to instantiate the class variant that's indicated in a config file. This mechanism is being deployed for message storage and will support multiple store types: DatabaseMessageStore FileMessageStore MemcachedMessageStore etc. A MessageStoreFactory class will read the application's preference from a config file, instantiate and return an instance of the appropriate class. It might be easy enough to slap a conditional around the instantiation to ensure that class_exists(), but MemcachedMessageStore extends PHP's Memcached class. As a result, the class_exists() test will succeed--though instantiation will fail--if the memcached bindings for PHP aren't installed. Is there any other way to test whether a class can be instantiated properly? If it can't, all I need to do is tell the user which features won't be available to them, but let them continue one with the application. Thanks.

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• checking mongo database for data

  - by user1647484

  I'm playing around with this tutorial that uses Sinatra, backbone.js, and mongodb for the database. It's my first time using mongo. As far as I understand it the app uses both local storage and a database. it has these routes for the database. For example, it has these routes get '/api/:thing' do DB.collection(params[:thing]).find.to_a.map{|t| from_bson_id(t)}.to_json end get '/api/:thing/:id' do from_bson_id(DB.collection(params[:thing]).find_one(to_bson_id(params[:id]))).to_json end post '/api/:thing' do oid = DB.collection(params[:thing]).insert(JSON.parse(request.body.read.to_s)) "{\"_id\": \"#{oid.to_s}\"}" end After turning the server off and then on, I could see in the server getting data from the database routes 127.0.0.1 - - [17/Sep/2012 08:21:58] "GET /api/todos HTTP/1.1" 200 430 0.0033 My question is, how can I check from within the mongo shell whether the data's in the database? I started the mongo shell ./bin/mongo I selected the database 'use mydb' and then looking at the docs (http://www.mongodb.org/display/DOCS/Tutorial) I tried commands such as > var cursor = db.things.find(); > while (cursor.hasNext()) printjson(cursor.next()); but they didn't return anything.

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• hosting simple python scripts in a container to handle concurrency, configuration, caching, etc.

  - by Justin Grant

  My first real-world Python project is to write a simple framework (or re-use/adapt an existing one) which can wrap small python scripts (which are used to gather custom data for a monitoring tool) with a "container" to handle boilerplate tasks like: fetching a script's configuration from a file (and keeping that info up to date if the file changes and handle decryption of sensitive config data) running multiple instances of the same script in different threads instead of spinning up a new process for each one expose an API for caching expensive data and storing persistent state from one script invocation to the next Today, script authors must handle the issues above, which usually means that most script authors don't handle them correctly, causing bugs and performance problems. In addition to avoiding bugs, we want a solution which lowers the bar to create and maintain scripts, especially given that many script authors may not be trained programmers. Below are examples of the API I've been thinking of, and which I'm looking to get your feedback about. A scripter would need to build a single method which takes (as input) the configuration that the script needs to do its job, and either returns a python object or calls a method to stream back data in chunks. Optionally, a scripter could supply methods to handle startup and/or shutdown tasks. HTTP-fetching script example (in pseudocode, omitting the actual data-fetching details to focus on the container's API): def run (config, context, cache) : results = http_library_call (config.url, config.http_method, config.username, config.password, ...) return { html : results.html, status_code : results.status, headers : results.response_headers } def init(config, context, cache) : config.max_threads = 20 # up to 20 URLs at one time (per process) config.max_processes = 3 # launch up to 3 concurrent processes config.keepalive = 1200 # keep process alive for 10 mins without another call config.process_recycle.requests = 1000 # restart the process every 1000 requests (to avoid leaks) config.kill_timeout = 600 # kill the process if any call lasts longer than 10 minutes Database-data fetching script example might look like this (in pseudocode): def run (config, context, cache) : expensive = context.cache["something_expensive"] for record in db_library_call (expensive, context.checkpoint, config.connection_string) : context.log (record, "logDate") # log all properties, optionally specify name of timestamp property last_date = record["logDate"] context.checkpoint = last_date # persistent checkpoint, used next time through def init(config, context, cache) : cache["something_expensive"] = get_expensive_thing() def shutdown(config, context, cache) : expensive = cache["something_expensive"] expensive.release_me() Is this API appropriately "pythonic", or are there things I should do to make this more natural to the Python scripter? (I'm more familiar with building C++/C#/Java APIs so I suspect I'm missing useful Python idioms.) Specific questions: is it natural to pass a "config" object into a method and ask the callee to set various configuration options? Or is there another preferred way to do this? when a callee needs to stream data back to its caller, is a method like context.log() (see above) appropriate, or should I be using yield instead? (yeild seems natural, but I worry it'd be over the head of most scripters) My approach requires scripts to define functions with predefined names (e.g. "run", "init", "shutdown"). Is this a good way to do it? If not, what other mechanism would be more natural? I'm passing the same config, context, cache parameters into every method. Would it be better to use a single "context" parameter instead? Would it be better to use global variables instead? Finally, are there existing libraries you'd recommend to make this kind of simple "script-running container" easier to write?

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• Scalability 101: How can I design a scalable web application using PHP?

  - by Legend

  I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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• J2EE and alternatives

  - by Ilya K

  Hello, I am J2SE developer but I have rich web-background (php, perl/cgi and so on) and now I am starting new project. It will have web interface, spaghetti business logic, relational database as storage and connections to other services. I do it from the scratch. My colleagues told me to use spring, spring security and struts. I look briefly at J2EE spec and found that it covers almost all aspects of enterprise application. I asked my colleagues why do they need spring and struts, but looks like they use technologies simply because they are familiar with them and not familiar with classic J2EE stack. So, my question is: what is bad about J2EE? Why do I need spring if there are JNDI lookups? It will take a day or two to create fake InitialContext for unit-tests. And that is all: I stand with out of external tools like spring. Why do I need spring-security if there is a security built in Servlets spec? I can map any request to any servlet using web.xml, no struts.xml is needed. I can use servlet-filters instead of struts interceptors. There is RMI, so I do not need spring-remote. And so on.. Why should I bother my self with all that fancy stuff if there is J2EE? I really want to find situation when J2EE is not enough. Do you have any? Thanks!

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• WordPress issues with htaccess causing 500 server error

  - by Scott B

  I have a few customers of my custom wordpress theme that are reporting that their sites have went down over the past few weeks due to a 500 internal server error. In each case, it appears that the htaccess file has been to blame. In one case, the user's hosting company found a "_pvt/service.pwd" line in there that was apparently causing the problem. In another instance, the hosting company indicated that a chron job appeared to be causing the issue and sent the user the following as evidence... root@cherry [/home/login/public_html]# stat .htaccess File: `.htaccess.orig' Size: 587 Blocks: 8 IO Block: 4096 regular file Device: 811h/2065d Inode: 590021607 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 2234/login) Gid: ( 2231/login) Access: 2010-03-07 16:42:01.000000000 -0600 Modify: 2010-03-26 09:15:15.000000000 -0500 Change: 2010-03-26 09:45:05.000000000 -0500 In yet another instance, the user reported this as the cause... The permissions on my .index file somehow got changed to 777 instead of 644 I'm just seeking to help these users understand what's going on, the likely cause and how to prevent it. I also want to eliminate my theme as a potential contributing factor. I have two areas in which I want to submit here to make sure that they are not likely to cause such an issue. They are my permalink rewrite code as well as my upgrade script (which sets 755 on the destination folder (my theme folder). Here's the permalink rewrite code... if (file_exists(ABSPATH.'/wp-admin/includes/taxonomy.php')) { require_once(ABSPATH.'/wp-admin/includes/taxonomy.php'); if(get_option('permalink_structure') !== "/%postname%/" || get_option('mycustomtheme_permalinks') !=="/%postname%/") { $mycustomtheme_permalinks = get_option('mycustomtheme_permalinks'); require_once(ABSPATH . '/wp-admin/includes/misc.php'); require_once(ABSPATH . '/wp-admin/includes/file.php'); global $wp_rewrite; $wp_rewrite->set_permalink_structure($mycustomtheme_permalinks); $wp_rewrite->flush_rules(); } if(!get_cat_ID('topMenu')){wp_create_category('topMenu');} if(!get_cat_ID('hidden')){wp_create_category('hidden');} if(!get_cat_ID('noads')){wp_create_category('noads');} } if (!is_dir(ABSPATH.'wp-content/uploads')) { mkdir(ABSPATH.'wp-content/uploads'); } And here is the relevant lines from my uploader script... // permission settings for newly created folders $chmod = 0755; // Ensures that the correct file was chosen $accepted_types = array('application/zip', 'application/x-zip-compressed', 'multipart/x-zip', 'application/s-compressed'); foreach($accepted_types as $mime_type) { if($mime_type == $type) { $okay = true; break; } } //Safari and Chrome don't register zip mime types. Something better could be used here. $okay = strtolower($name[1]) == 'zip' ? true: false; if(!$okay) { die("This upgrader requires a zip file. Please make sure your file is a valid zip file with a .zip extension"); } //mkdir($target); $saved_file_location = $target . $filename; if(move_uploaded_file($source, $saved_file_location)) { openZip($saved_file_location); } else { die("There was a problem. Sorry!"); }

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• Drupal 6 Validation for Form Callback Function

  - by Wade

  I have a simple form with a select menu on the node display page. Is there an easy way to validate the form in my callback function? By validation I don't mean anything advanced, just to check that the values actually existed in the form array. For example, without ajax, if my select menu has 3 items and I add a 4th item and try to submit the form, drupal will give an error saying something similar to "an illegal choice was made, please contact the admin." With ajax this 4th item you created would get saved into the database. So do I have to write validation like if ($select_item > 0 && $select_item <= 3) { //insert into db } Or is there an easier way that will check that the item actually existed in the form array? I'm hoping there is since without ajax, drupal will not submit the form if it was manipulated. Thanks. EDIT: So I basically need this in my callback function? $form_state = array('storage' => NULL, 'submitted' => FALSE); $form_build_id = $_POST['form_build_id']; $form = form_get_cache($form_build_id, $form_state); $args = $form['#parameters']; $form_id = array_shift($args); $form_state['post'] = $form['#post'] = $_POST; $form['#programmed'] = $form['#redirect'] = FALSE; drupal_process_form($form_id, $form, $form_state); To get $_POST['form_build_id'], I sent it as a data param, is that right? Where I use form_get_cache, looks like there is no data. Kind of lost now.

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• L2S DataContext out of synch: row not found or changed

  - by awrigley

  The Problem I am getting a number of errors that imply that the DataContext, or rather, the way I am using the DataContext is getting out of synch. The error occurs on db.SubmitChanges() where db is my DataContext instance. The error is: Row not found or changed. The problem only occurs intermitently, for example, adding a row then deleting it. If I stop the dev server and restart, the added row is there and I can delete it no problem. Ie, it seems that the problem is related to the DataContext losing track of the rows that have been added. IMPORTANT: Before anyone votes to close this thread, on the basis of it being a duplicate, I have checked the sql server profiler and there is no "Where 0 = 1" in the SQL. I have also recreated the dbml file, so am satisfied that the database schema is in synch with the schema represented by the dbml file. Ie, no cases of mismatched nullable/not nullable columns, etc. My Diagnosis (for what it is worth): It seems to be a problem related to how I am using the DataContext. I am new to MVC, Repositories and Services patterns, so suspect that I have wired things up wrong. The Setup Simple eLearning app in its early stages. Pupils need to be able to add and delete courses (Courses table) to their UserCourses. To do this, I have a service that gets a specific DataContext instance Dependency Injected into its constructor. Service Class Constructor: public class SqlPupilBlockService : IPupilBlockService { DataContext db; public SqlPupilBlockService(DataContext db) { this.db = db; CoursesRepository = new SqlRepository<Course>(db); UserCoursesRepository = new SqlRepository<UserCourse>(db); } // Etc, etc } The CoursesRepository and UserCoursesRepository are both private properties of the service class that are of Type IRepository (just a simple generic repository interface). Sql Respoitory Code: public class SqlRepository<T> : IRepository<T> where T : class { DataContext db; public SqlRepository(DataContext db) { this.db = db; } #region IRepository<T> Members public IQueryable<T> Query { get { return db.GetTable<T>(); } } public List<T> FetchAll() { return Query.ToList(); } public void Add(T entity) { db.GetTable<T>().InsertOnSubmit(entity); } public void Delete(T entity) { db.GetTable<T>().DeleteOnSubmit(entity); } public void Save() { db.SubmitChanges(); } #endregion } The two methods for adding and deleting UserCourses are: Service Methods for Adding and Deleting UserCourses: public void AddUserCourse(int courseId) { UserCourse uc = new UserCourse(); uc.IdCourse = courseId; uc.IdUser = UserId; uc.DateCreated = DateTime.Now; uc.DateAmended = DateTime.Now; uc.Role = "Pupil"; uc.CourseNotes = string.Empty; uc.ActiveStepIndex = 0; UserCoursesRepository.Add(uc); UserCoursesRepository.Save(); } public void DeleteUserCourse(int courseId) { var uc = (UserCoursesRepository.Query.Where(x => x.IdUser == UserId && x.IdCourse == courseId)).Single(); UserCoursesRepository.Delete(uc); UserCoursesRepository.Save(); } Ajax I am using Ajax via Ajax.BeginForm I don't think that is relevant. ASP.NET MVC 3 I am using mvc3, but don't think that is relevant: the errors are related to model code.

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• Seeking C Union clarity

  - by mustISignUp

  typedef union { float flts[4]; struct { GLfloat r; GLfloat theta; GLfloat phi; GLfloat w; }; struct { GLfloat x; GLfloat y; GLfloat z; GLfloat w; }; } FltVector; Ok, so i think i get how to use this, (or, this is how i have seen it used) ie. FltVector fltVec1 = {{1.0f, 1.0f, 1.0f, 1.0f}}; float aaa = fltVec1.x; etc. But i'm not really groking how much storage has been declared by the union (4 floats? 8 floats? 12 floats?), how? and why? Also why two sets of curly braces when using FltVector {{}}? Any pointers much appreciated (sorry for the pun)

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• Use of extern in C++ dll

  - by dom_beau

  I declare then instantiate a static variable in a DLL. // DLL.h class A { //... }; static A* a; // DLL.cpp A* a = new A; So far, so good... I was suggested to use extern rather than static. extern A* a; // in DLL.h No problem with that but the extern variable must be declared somewhere. I got Invalid storage class member. In other words, what I was used to do is to declare a variable in a source file like this: // In src.cpp A a; then extern declare it in another source file in the same project: // In src2.cpp extern A a; so it is the same object a at link time. Maybe it is not the right thing to do? So, where to declare the variable that is now extern? Note that I used static declaration in order to see the variable instantiated as soon as the dll is loaded. Note that the current use of static works most of the time but I think I observe a delay or something like this in the variable instantiation while it should always be instantiated at load time. I'm investigating this problem for a week now and I can't find no solution.

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• Error monitoring/handling on webservers

  - by Industrial

  Hi everybody, We have a web server that we're about to launch a number of applications onto. They will all share database and memcached servers, but each application has it's own mySQL database and all memcached keys per application, is prefixed. Possible scenario: If a memcached server in our cluster goes boom, we want someone (operative system admin) to be automatically contacted by email/iphone push notification or in any other appropriate way. If we we're about to install 150 identical applications for our customers on our servers, and a memcached server dies - all 150 applications will individually find this out and contact our system admin, which most certainly is going to think about getting a new job where he or she isn't about to be woken up by getting 150 messages sent 4:15 in the morning. Possible solution: One idea is to set up an external server for error handling that gets a $_POST or cURL request sent, and handles storage of the error message depending on the seriousness of the actual error message. It would of course check upon receiving the error call, that if the same memcached server have already been reported as offline, there would be no need to spam the system admin with additional reminders... The questions: What's a good approach on how to handle errors? How does the big guys in the industry handle this? Thanks!

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