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• Interface for reading variable length files with header and footer.

  - by John S

  I could use some hints or tips for a decent interface for reading file of special characteristics. The files in question has a header (~120 bytes), a body (1 byte - 3gb) and a footer (4 bytes). The header contains information about the body and the footer is only a simple CRC32-value of the body. I use Java so my idea was to extend the "InputStream" class and add a constructor such as "public MyInStream( InputStream in)" where I immediately read the header and the direct the overridden read()'s the body. Problem is, I can't give the user of the class the CRC32-value until the whole body has been read. Because the file can be 3gb large, putting it all in memory is a be an idea. Reading it all in to a temporary file is going to be a performance hit if there are many small files. I don't know how large the file is because the InputStream doesn't have to be a file, it could be a socket. Looking at it again, maybe extending InputStream is a bad idea. Thank you for reading the confused thoughts of a tired programmer. :)

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• Calculate posterior distribution of unknown mis-classification with PRTools in MATLAB

  - by Samuel Lampa

  I'm using the PRTools MATLAB library to train some classifiers, generating test data and testing the classifiers. I have the following details: N: Total # of test examples k: # of mis-classification for each classifier and class I want to do: Calculate and plot Bayesian posterior distributions of the unknown probabilities of mis-classification (denoted q), that is, as probability density functions over q itself (so, P(q) will be plotted over q, from 0 to 1). I have that (math formulae, not matlab code!): P(q|k,N) = Posterior * Prior / Normalization constant = P(k|q,N) * P(q|N) / P(k|N) The prior is set to 1, so I only need to calculate the posterior and normalization constant. I know that the posterior can be expressed as (where B(N,k) is the binomial coefficient): P(k|q,N) = B(N,k) * q^k * (1-q)^(N-k) ... so the Normalization constant is simply an integral of the posterior above, from 0 to 1: P(k|N) = B(N,k) * integralFromZeroToOne( q^k * (1-q)^(N-k) ) (The Binomial coefficient ( B(N,k) ) can be omitted thoughappears in both the posterior and normalization constant, so it can be omitted.) Now, I've heard that the integral for the normalization constant should be able to be calculated as a series ... something like: k!(N-k)! / (N+1)! Is that correct? (I have some lecture notes from with this series, but can't figure out if it is for the normalization constant integral, or for the posterior distribution of mis-classification (q)) Also, hints are welcome as how to practically calculate this? (factorials are easily creating truncation errors right?) ... AND, how to practically calculate the final plot (the posterior distribution over q, from 0 to 1).

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• Are document-oriented databases any more suitable than relational ones for persisting objects?

  - by Owen Fraser-Green

  In terms of database usage, the last decade was the age of the ORM with hundreds competing to persist our object graphs in plain old-fashioned RMDBS. Now we seem to be witnessing the coming of age of document-oriented databases. These databases are highly optimized for schema-free documents but are also very attractive for their ability to scale out and query a cluster in parallel. Document-oriented databases also hold a couple of advantages over RDBMS's for persisting data models in object-oriented designs. As the tables are schema-free, one can store objects belonging to different classes in an inheritance hierarchy side-by-side. Also, as the domain model changes, so long as the code can cope with getting back objects from an old version of the domain classes, one can avoid having to migrate the whole database at every change. On the other hand, the performance benefits of document-oriented databases mainly appear to come about when storing deeper documents. In object-oriented terms, classes which are composed of other classes, for example, a blog post and its comments. In most of the examples of this I can come up with though, such as the blog one, the gain in read access would appear to be offset by the penalty in having to write the whole blog post "document" every time a new comment is added. It looks to me as though document-oriented databases can bring significant benefits to object-oriented systems if one takes extreme care to organize the objects in deep graphs optimized for the way the data will be read and written but this means knowing the use cases up front. In the real world, we often don't know until we actually have a live implementation we can profile. So is the case of relational vs. document-oriented databases one of swings and roundabouts? I'm interested in people's opinions and advice, in particular if anyone has built any significant applications on a document-oriented database.

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• Looking for combinations of server and embedded database engines

  - by codeelegance

  I'm redesigning an application that will be run as both a single user and multiuser application. It is a .NET 2.0 application. I'm looking for server and embedded databases that work well together. I want to deploy the embedded database in the single user setup and of course, the server in the multiuser setup. Past releases have been based on MSDE but in the past year we've been having a lot of install issues: new installs hanging and leaving the system in an unknown state, upgrades disconnecting the database, etc. I migrated the application to SQL Server 2005 and the install is more reliable (as long as a user doesn't try to install over a broken MSDE installation). Since next year's release will be a complete redesign I figured now's the best time to address the database issue as well. The database has been abstracted from the rest of the application so I just need to choose which database(s) to use and write an implementation for each one. So far I've considered: SQL Server/ SQL Server Compact Edition Firebird (same DB engine is available in two different server modes and an embedded dll) Each has its own merits but I'm also interested in any other suggestions. This is a fairly simple program and its data requirements are simple as well. I don't expect it to strain whatever database I eventually choose. So easy configuration and deployment hold more weight than performance.

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• PostgreSQL, Foreign Keys, Insert speed & Django

  - by Miles

  A few days ago, I ran into an unexpected performance problem with a pretty standard Django setup. For an upcoming feature, we have to regenerate a table hourly, containing about 100k rows of data, 9M on the disk, 10M indexes according to pgAdmin. The problem is that inserting them by whatever method literally takes ages, up to 3 minutes of 100% disk busy time. That's not something you want on a production site. It doesn't matter if the inserts were in a transaction, issued via plain insert, multi-row insert, COPY FROM or even INSERT INTO t1 SELECT * FROM t2. After noticing this isn't Django's fault, I followed a trial and error route, and hey, the problem disappeared after dropping all foreign keys! Instead of 3 minutes, the INSERT INTO SELECT FROM took less than a second to execute, which isn't too surprising for a table <= 20M on the disk. What is weird is that PostgreSQL manages to slow down inserts by 180x just by using 3 foreign keys. Oh, disk activity was pure writing, as everything is cached in RAM; only writes go to the disks. It looks like PostgreSQL is working very hard to touch every row in the referred tables, as 3MB/sec * 180s is way more data than the 20MB this new table takes on disk. No WAL for the 180s case, I was testing in psql directly, in Django, add ~50% overhead for WAL logging. Tried @commit_on_success, same slowness, I had even implemented multi row insert and COPY FROM with psycopg2. That's another weird thing, how can 10M worth of inserts generate 10x 16M log segments? Table layout: id serial primary, a bunch of int32, 3 foreign keys to small table, 198 rows, 16k on disk large table, 1.2M rows, 59 data + 89 index MB on disk large table, 2.2M rows, 198 + 210MB So, am I doomed to either drop the foreign keys manually or use the table in a very un-Django way by defining saving bla_id x3 and skip using models.ForeignKey? I'd love to hear about some magical antidote / pg setting to fix this.

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• POST xml to php with apache2

  - by Berry

  I'm working on an application that receives XML data via POST, processes it with a PHP script, and returns an XML response. I'm getting the XML with this PHP code: $requestStr = file_get_contents('php://input'); $requests = simplexml_load_string($requestStr); which works fine on the Linux-based product hardware using nginx as the server. However, for testing I'd like to be able to run it on my MacBook Pro, so I can avoid the "build image, install on product, reboot product, wait, test change" loop while I do targeted development on this XML processor. I enabled "web sharing" which starts up Apache, added a rewrite rule to point a convenient URI at my development source directory and used curl to send a request to my PHP script thus: curl -H "Content-Type:text/xml" -d @request.xml http://localhost/test/path/testscript "testscript" is handled by the PHP script fine, but when it goes to read "php:://input" I get nothing -- the empty string. Anyone have a clue why this would work under Linux with nginx and not under MacOS with Apache? I've googled and searched stackoverlow.com to no avail. Thanks for any answers. UPDATE: I've discovered that at least in this configuration, reading from php://stdin will work fine, while php://input will not. Who knew?

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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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• Have to login twice. PHP sessions and login troubles with Chrome and Opera.

  - by Robert

  The problem I am encountering is that for my login form I have to login twice for the session to register properly, but only in Chrome (my version is 4.0.249.89) and Opera (my version is 10.10). Here is the stripped down code that I am testing on: Login Page: session_start(); $_SESSION['user_id'] = 8; $_SESSION['user_name'] = 'Jim'; session_write_close(); header('Location: http://www.my-domain-name.com/'); exit(); Home Page: session_start(); if ( isset($_SESSION['user_id']) ) { echo "You are logged in!"; } else { echo "You are NOT logged in!"; } Logout Page: session_start(); session_unset(); session_destroy(); header('Location: http://www.my-domain-name.com/'); exit(); Currently, under a fresh load with no cookies, if I go to my-domain-name.com/login/ it will redirect to the home page and say "You are NOT logged in!" but if I go there again it will say "You are logged in!". Any ideas? Thanks for your help.

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• Can I get consistent CSS colors across browsers?

  - by Trevor Burnham

  I'm testing a new site, and I have a div with background-color: #bbf6bb; That seems innocuous enough to me. And yet, on my MacBook Pro, the color looks very different in Firefox 3.6 vs. Safari 4. In Safari, it's the color I'd expect from the hex value: a pale green. In Firefox, there's a definite bluish tint, making the color turquoise. I'm aware of color inconsistencies that result from different treatment of images across browsers, but in pure CSS? Really? I'm guessing that Firefox trying to correct for my display in hopes of delivering better consistency with print, but I'd much rather have my site look the same hue to my users regardless of their choice of browser. Any ideas? Can someone confirm that Firefox is the culprit here? [Update: This seems to have been a fluke. Specifically, it's a narrow issue with Firefox—see my answer below. I'm puzzled, but relieved.]

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• MySql too many connections

  - by MichaelMcCabe

  I hate to bring up a question which is widely asked on the web, but I cant seem to solve it. I started a project a while back and after a month of testing, I hit a "Too many connections" error. I looked into it, and "Solved" it by increasing the max_connections. This then worked. Since then more and more people started to use it, and it hit again. When I am the only user on the site, i type "show processlist" and it comes up with about 50 connections which are still open (saying "Sleep" in the command). Now, I dont know enough to speculate why these are open, but in my code I tripple checked and every connection I open, I close. ie. public int getSiteIdFromName(String name, String company)throws DataAccessException,java.sql.SQLException{ Connection conn = this.getSession().connection(); Statement smt = conn.createStatement(); ResultSet rs=null; String query="SELECT id FROM site WHERE name='"+name+"' and company_id='"+company+"'"; rs=smt.executeQuery(query); rs.next(); int id=rs.getInt("id"); rs.close(); smt.close(); conn.close(); return id; } Every time I do something else on the site, another load of connections are opened and not closed. Is there something wrong with my code? and if not, what could be the problem?

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• Is there a useDirtyFlag option for Tomcat 6 cluster configuration?

  - by kevinjansz

  In Tomcat 5.0.x you had the ability to set useDirtyFlag="false" to force replication of the session after every request rather than checking for set/removeAttribute calls. <Cluster className="org.apache.catalina.cluster.tcp.SimpleTcpCluster" managerClassName="org.apache.catalina.cluster.session.SimpleTcpReplicationManager" expireSessionsOnShutdown="false" **useDirtyFlag="false"** doClusterLog="true" clusterLogName="clusterLog"> ... The comments in the server.xml stated this may be used to make the following work: <% HashMap map = (HashMap)session.getAttribute("map"); map.put("key","value"); %> i.e. change the state of an object that has already been put in the session and you can be sure that this object still be replicated to the other nodes in the cluster. According to the Tomcat 6 documentation you only have two "Manager" options - DeltaManager & BackupManager ... neither of these seem to allow this option or anything like it. In my testing the default setup: <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/> where you get the DeltaManager by default, it's definitely behaving as useDirtyFlag="true" (as I'd expect). So my question is - is there an equivalent in Tomcat 6? Looking at the source I can see a manager implementation "org.apache.catalina.ha.session.SimpleTcpReplicationManager" which does have the useDirtyFlag but the javadoc comments in this state it's "Tomcat Session Replication for Tomcat 4.0" ... I don't know if this is ok to use - I'm guessing not as it's not mentioned in the main cluster configuration documentation.

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• Debugging a Google Web Toolkit application that has an error when deployed on Google App Engine

  - by gerdemb

  I have a Google Web Toolkit application that I am deploying to Google App Engine. In the deployed application, I am getting a JavaScript error Uncaught TypeError: Cannot read property 'f' of null. This sounds like the JavaScript equivalent of a Java NullPointerException. The problem is that the GWT JavaScript is obfuscated, so it's impossible to debug in the browser and I can't reproduce the same problem in hosted mode where I could use the Java debugger. I think the reason I'm only seeing the error on the deployed application is that the database I'm using on the GAE server is triggering something differently than the test database I'm using during testing and development. So, any ideas about the best way to proceed? I've thought of the following things: Deploy a non-obsfucated version of my application. Despite a lot of Googling, I can't figure out how to do this using the automatic deploy script provided with the Google Eclipse Plugin. Does anyone know? Download and copy my GAE data to the local server Somehow point my development code to use the GAE server for data instead of the local test database. This seems like the best idea... Can anyone suggest how to proceed here? Finally, is there a way to catch these JavaScript errors on the production server and log them somewhere? Without logging, I won't have anyway to know if my users are having errors that don't occur on the server. The GWT.log() function is automatically stripped out of the production code...

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• What is the base open source java package to filter/match URLs?

  - by Boaz

  Hi, I have an high performance application which deals with URLs. For every URL it needs to retrieve the appropriate settings from a predefined pool. Every settings object is associated with a URL pattern which indicates which URLs should use these settings. The matching rules are as follows: "google.com" match pattern should match all URLs pointing to the google domain (thus, maps.google.com and www.google.com/match are matched). "*.google.com" should match all URLs pointing to a subdomain of google.com (thus, maps.google.com matches, but google.com and www.google.com don't). "maps.google.com" should match all URLs pointing to this specific subdomain. Apart from the above rules, every match rule can contain a path, which means that the path part of the URL should start with the match rule path. So: "*.google.com/maps" matches "maps.google.com/maps" but not "maps.google.com/advanced". As you can see the rules above are overlapping. In the case two rules exist which match the same URL the most specific should apply. The list above is ranked from least specific to most specific. This seems to be such a standard problem that I was hoping to use a ready made library rather than program my self. Google reveals a couple of options but without a clear way to choose between them. What would you recommend as a good library for this task? Thanks, Boaz

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• How to choose light version of database system

  - by adopilot

  I am starting one POS (Point of sale) project. Targeting system is going to be written in C# .NET 2 WinForms and as main database server We are going to use MS-SQL Server. As we have a lot of POS devices in chain for one store I will love to have backend local data base system on each POS device. Scenario are following: When main server goes down!! POS application should continue working "off-line" with local database, until connection to main server come up again. Now I am in dilemma which local database is going to be most adoptable for me. Here is some notes for helping me point me in right direction: To be Light "My POS devices art usually old and suffering with performances" To be Free "I have a lot of devices and I do not wont additional cost beside main SQL serer" One day Ill love to try all that port on Mono and Linux OS. Here is what I've researched so far: Simple XML "Light but I am afraid of performance, My main table of items is average of 10K records" SQL-Express "I am afraid that my POS devices is poor with hardware for SQLExpress, and also hard to install on each device and configure" Less known Advantage Database Server have free distribution of offline ADT system. DBF with extended Library,"Respect for good old DBFs but that era is behind Me with clipper and DBFs" MS Access Sqlite "Mostly like for now, but I am afraid how it is going to pair with MS SQL do they have same Data types". I know that in this SO is a lot of subjective data, but at least can someone recommended some others lite database system, or things that I shod most take attention before I choice database.

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• Admob banner not getting remove from superview

  - by Gamer

  I am developing one 2d game using cocos2d framework, in this game i am using admob for advertising, in some classes not in all classes but admob banner is visible in every class and after some time game getting crash also. I am not getting how admob banner is comes in every class in fact i have not declare in Rootviewcontroller class. can any one suggest me how to integrate Admob in cocos2d game, i want Admob banner in particular classes not in every class, I am using latest google admob sdk, my code is below: Thanks in advance ` -(void)AdMob{ NSLog(@"ADMOB"); CGSize winSize = [[CCDirector sharedDirector]winSize]; // Create a view of the standard size at the bottom of the screen. if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad){ bannerView_ = [[GADBannerView alloc] initWithFrame:CGRectMake(size.width/2-364, size.height - GAD_SIZE_728x90.height, GAD_SIZE_728x90.width, GAD_SIZE_728x90.height)]; } else { // It's an iPhone bannerView_ = [[GADBannerView alloc] initWithFrame:CGRectMake(size.width/2-160, size.height - GAD_SIZE_320x50.height, GAD_SIZE_320x50.width, GAD_SIZE_320x50.height)]; } if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) { bannerView_.adUnitID =@"a15062384653c9e"; } else { bannerView_.adUnitID =@"a15062392a0aa0a"; } bannerView_.rootViewController = self; [[[CCDirector sharedDirector]openGLView]addSubview:bannerView_]; [bannerView_ loadRequest:[GADRequest request]]; GADRequest *request = [[GADRequest alloc] init]; request.testing = [NSArray arrayWithObjects: GAD_SIMULATOR_ID, nil]; // Simulator [bannerView_ loadRequest:request]; } //best practice for removing the barnnerView_ -(void)removeSubviews{ NSArray* subviews = [[CCDirector sharedDirector]openGLView].subviews; for (id SUB in subviews){ [(UIView*)SUB removeFromSuperview]; [SUB release]; } NSLog(@"remove from view"); } //this makes the refreshTimer count -(void)targetMethod:(NSTimer *)theTimer{ //INCREASE OF THE TIMER AND SECONDS elapsedTime++; seconds++; //INCREASE OF THE MINUTOS EACH 60 SECONDS if (seconds>=60) { seconds=0; minutes++; [self removeSubviews]; [self AdMob]; } NSLog(@"TIME: %02d:%02d", minutes, seconds); } `

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• SharpDevelop WIX project: MSBuild Configurations

  - by chezy525

  Using SharpDevelop, I wrote a windows service with a WIX setup project to install/auto-start it. For testing purposes, I've done a number of things I don't want to do in the release version (i.e. add an uninstall shortcut to the desktop). So, my question really boils down to this; how do you handle build configurations within a WiX project? I think I've solved most of my problems after I found this question Passing build parameters to .wxs file to dynamicaly build wix installers. And thus far I've done the following: Added a property that checks the Configuration variable <Product> ... <Property Id="DEBUG">$(var.Configuration) == 'Debug'</Property> ... Separated all of the debug files into unique components and setup as a separate feature with a condition checking the DEBUG property. <Product> ... <Feature> ... <Feature Id="DebugFiles" Level="1"> <ComponentRef Id="UninstallShortcutComponent" /> <Condition Level="0">DEBUG</Condition> </Feature> ... Then, finally, pointing to the correct file based on the configuration, using the Configuration variable <Directory> ... <Component> <File Source="..\mainProject\bin\$(var.Configuration)\main.exe" /> </Component> ... So, now my question is simplified to how to handle files that may not exist under certain build configurations (like .pdb files). Using all of the above (including pointing the file source to the ...\bin\Release\*.pdb, which I know isn't expected to exist) I get a LGHT0103 compiler error, it can't find the file.

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• Have I found a security problem in an API or do I just not understand SSL?

  - by jamieb

  I'm working on building a set of Python bindings around an XML-based API provided by a vendor. The vendor requires that all transactions be conducted over SSL. Using a Linux box, I created a key file and a CSR for my application. Using their self-service web portal, I then generate a certificate using that CSR. Both the key file and the certificate are used when making the SSL request to the API. I'm now working on designing exception classes to make error messages more verbose (and, hopefully, more useful to developers using my bindings). Part of my testing has included altering the key file: transpose a couple characters here, replace 4 or 5 with random characters there, etc. To my surprise, altering the key file had no effect! As long as I didn't change the total length of it, the API didn't complain about a bad key file. The only way I was able to throw an error was by swapping in a completely different key from another application. At that point, the API complained about the Common Name not matching. Is this normal behavior or has the vendor not properly implemented SSL?

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• When is a good time to start thinking about scaling?

  - by Slokun

  I've been designing a site over the past couple days, and been doing some research into different aspects of scaling a site horizontally. If things go as planned, in a few months (years?) I know I'd need to worry about scaling the site up and out, since the resources it would end up consuming would be huge. So, this got me to thinking, when is the best time to start thinking about, and designing for, scalability? If you start too early on, you could easily over complicate your design, and make it impossible to actually build. You could also get too caught up in the details, the architecture, whatever, and wind up getting nothing done. Also, if you do get it working, but the site never takes off, you may have wasted a good chunk of extra effort. On the other hand, you could be saving yourself a ton of effort down the road. Designing it from the ground up to be big would make it much easier later on to let it grow big, with very little rewriting going on. I know for what I'm working on, I've decided to make at least a few choices now on the side of scaling, but I'm not going to do a complete change of thinking to get it to scale completely. Notably, I've redesigned my database from a conventional relational design to one similar to what was suggested on the Reddit site linked below, and I'm going to give memcache a try. So, the basic question, when is a good time to start thinking or worrying about scaling, and what are some good designs, tips, etc. for when doing so? A couple of things I've been reading, for those who are interested: http://www.codinghorror.com/blog/2009/06/scaling-up-vs-scaling-out-hidden-costs.html http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html http://developer.yahoo.com/performance/rules.html

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• How do I protect the trunk from hapless newbies?

  - by Michael Haren

  A coworker relayed the following problem, let's say it's fictional to protect the guilty: A team of 5-10 works on a project which is issue-driven. That is, the typical flow goes like this: a chunk of work (bug, enhancement, etc.) is created as an issue in the issue tracker The issue is assigned to a developer The developer resolves the issue and commits their code changes to the trunk At release time, the frozen, and heavily tested trunk or release branch or whatever is built in release mode and released The problem he's having is that a couple newbies made several bad commits that weren't caught due to an unfortunate chain of events. This was followed by a bad release with a rollback or flurry of hot fixes. One idea we're toying with: Revoke commit access to the trunk for newbies and make them develop on a per-developer branch (we're using SVN): Good: newbies are isolated and can't hurt others Good: committers merge newbie branches with the trunk frequently Good: this enforces rigid code reviews Bad: this is burdensome on the committers (but there's probably no way around it since the code needs reviewed!) Bad: it might make traceability of trunk changes a little tougher since the reviewer would be doing the commit--not too sure on this. Update: Thank you, everyone, for your valuable input. I have concluded that this is far less a code/coder problem than I first presented. The root of the issue is that the release procedure failed to capture and test some poor quality changes to the trunk. Plugging that hole is most important. Relying on the false assumption that code in the trunk is "good" is not the solution. Once that hole--testing--is plugged, mistakes by everyone--newbie or senior--will be caught properly and dealt with accordingly. Next, a greater emphasis on code reviews and mentorship (probably driven by some systematic changes to encourage it) will go a long way toward improving code quality. With those two fixes in place, I don't think something as rigid or draconian as what I proposed above is necessary. Thanks!

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• Floating Point Arithmetic - Modulo Operator on Double Type

  - by CrimsonX

  So I'm trying to figure out why the modulo operator is returning such a large unusual value. If I have the code: double result = 1.0d % 0.1d; it will give a result of 0.09999999999999995. I would expect a value of 0 Note this problem doesn't exist using the dividing operator - double result = 1.0d / 0.1d; will give a result of 10.0, meaning that the remainder should be 0. Let me be clear: I'm not surprised that an error exists, I'm surprised that the error is so darn large compared to the numbers at play. 0.0999 ~= 0.1 and 0.1 is on the same order of magnitude as 0.1d and only one order of magnitude away from 1.0d. Its not like you can compare it to a double.epsilon, or say "its equal if its < 0.00001 difference". I've read up on this topic on StackOverflow, in the following posts one two three, amongst others. Can anyone suggest explain why this error is so large? Any any suggestions to avoid running into the problems in the future (I know I could use decimal instead but I'm concerned about the performance of that).

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• Bidirectional/Loopback UDP in .net

  - by Jason Williams

  I've got an app that needs to transmit and receive on the same port. This can happen in two cases: Where the PC is talking to a piece of remote hardware. It "replies to sender", so the datagrams come back in to my PC via the sending port. Where the PC is talking to itself (loopback mode) for testing and demoing (a test app feeds fake data into our main app via UDP). This only seems to fail when trying to achieve loopback. The only way I can get it working is to ensure that the receiver is set up first - something I cannot guarantee. Can anyone help narrow down my search by suggesting a "correct" way to implement the UdpClient(s) to handle the above situations reliably? (The only solution that I've found to work reliably with the remote hardware is to use a single UdpClient in a bidirectional manner, although I'm working with legacy code that may be influencing that finding. I've tried using two UdpClients, but they step on each others toes - In some cases, once one client is started up, the other client cannot connect. With ExclusiveAddressUse/ReuseAddress set up to allow port sharing, I can almost get it to work, apart from the receiver having to start first)

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• Is XMLReader a SAX parser, a DOM parser, or neither?

  - by Renesis

  I am testing various methods to read (possibly large, and very often) XML configuration files in PHP. No writing is ever needed. I have two successful implementations, one using SimpleXML (which I know is a DOM parser) and one using XMLReader. I know that a DOM reader must read the whole tree and therefore uses more memory. My tests reflect that. I also know that A SAX parser is an "event-based" parser that uses less memory because it reads each node from the stream without checking what is next. XMLReader also reads from a stream with the cursor providing data about the node it is currently at. So, it definitely sounds like XMLReader (http://us2.php.net/xmlreader) is not a DOM parser, but my question is, is it a SAX parser, or something else? It seems like XMLReader behaves the way a SAX parser does but does not throw the events themselves (in other words, can you construct a SAX parser with XMLReader?) If it is something else, does the classification it's in have a name?

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• jQuery modal dialog on ajaxStart event

  - by bdl

  I'm trying to use a jQuery UI modal dialog as a loading indicator via the ajaxStart, ajaxStop / ajaxComplete events. When the page fires, an Ajax handler loads some data, and the modal dialog shows just fine. However, it never hides or closes the dialog when the Ajax event is complete. It's a very small bit of code from the local server that is returned, so the actual Ajax event is very quick. Here's my actual code for the modal div: $("#modalwindow").dialog({ modal: true, height: 50, width: 200, zIndex: 999, resizable: false, title: "Please wait..." }) .bind("ajaxStart", function(){ $(this).show(); }) .bind("ajaxStop", function(){ $(this).hide(); }); The Ajax event is just a plain vanilla $.ajax({}) GET method call. Based on some searching here and Google, I've tried altering the ajaxStop handler to use $("#modalwindow").close(), $("#modalwindow").destroy(), etc. (#modalwindow referred to here as to give explicit context). I've also tried using the standard $("#modalwindow").dialog({}).ajaxStart(... as well. Should I be binding the events to a different object? Or calling them from within the $.ajax() complete event? I should mention, I'm testing on the latest IE8, FF 3.6 and Chrome. All have the same / effect.

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• ArrayAccess multidimensional (un)set?

  - by anomareh

  I have a class implementing ArrayAccess and I'm trying to get it to work with a multidimensional array. exists and get work. set and unset are giving me a problem though. class ArrayTest implements ArrayAccess { private $_arr = array( 'test' => array( 'bar' => 1, 'baz' => 2 ) ); public function offsetExists($name) { return isset($this->_arr[$name]); } public function offsetSet($name, $value) { $this->_arr[$name] = $value; } public function offsetGet($name) { return $this->_arr[$name]; } public function offsetUnset($name) { unset($this->_arr[$name]); } } $arrTest = new ArrayTest(); isset($arrTest['test']['bar']); // Returns TRUE echo $arrTest['test']['baz']; // Echo's 2 unset($arrTest['test']['bar']; // Error $arrTest['test']['bar'] = 5; // Error I know $_arr could just be made public so you could access it directly, but for my implementation it's not desired and is private. The last 2 lines throw an error: Notice: Indirect modification of overloaded element. I know ArrayAccess just generally doesn't work with multidimensional arrays, but is there anyway around this or any somewhat clean implementation that will allow the desired functionality? The best idea I could come up with is using a character as a separator and testing for it in set and unset and acting accordingly. Though this gets really ugly really fast if you're dealing with a variable depth. Does anyone know why exists and get work so as to maybe copy over the functionality? Thanks for any help anyone can offer.

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• Payment gateways and XSS

  - by Rowan Parker

  Hi all, I'm working on a website which takes payment from a customer. I'm using Kohana 2.3.4 and have created a library to handle the payment gateway I use (www.eway.com.au). Basically I'm just using their sample code, copied into it's own class. Anyway, the code works fine and I can make payments, etc. The issue I have is when the payment gateway is returning the user to my site. The payment gateway uses HTTPS so that is secure, and it is sending the user back to a HTTPS page on my site. However I have the NoScript plugin installed in Firefox, and when I get sent back to the page on my website (which also handles storing the transaction data) I get an error message saying that NoScript has blocked a potential XSS attack. Now I understand why it's unsecure (POST data being sent across two different domains) but what should I be doing instead? Obviously during my testing here I temporarily disable NoScript and it all works fine, but I can't rely on that for the end users. What's the best practice here?

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