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  • Bacula & Multiple Tape Devices, and so on

    - by Tom O'Connor
    Bacula won't make use of 2 tape devices simultaneously. (Search for #-#-# for the TL;DR) A little background, perhaps. In the process of trying to get a decent working backup solution (backing up 20TB ain't cheap, or easy) at $dayjob, we bought a bunch of things to make it work. Firstly, there's a Spectra Logic T50e autochanger, 40 slots of LTO5 goodness, and that robot's got a pair of IBM HH5 Ultrium LTO5 drives, connected via FibreChannel Arbitrated Loop to our backup server. There's the backup server.. A Dell R715 with 2x 16 core AMD 62xx CPUs, and 32GB of RAM. Yummy. That server's got 2 Emulex FCe-12000E cards, and an Intel X520-SR dual port 10GE NIC. We were also sold Commvault Backup (non-NDMP). Here's where it gets really complicated. Spectra Logic and Commvault both sent respective engineers, who set up the library and the software. Commvault was running fine, in so far as the controller was working fine. The Dell server has Ubuntu 12.04 server, and runs the MediaAgent for CommVault, and mounts our BlueArc NAS as NFS to a few mountpoints, like /home, and some stuff in /mnt. When backing up from the NFS mountpoints, we were seeing ~= 290GB/hr throughput. That's CRAP, considering we've got 20-odd TB to get through, in a <48 hour backup window. The rated maximum on the BlueArc is 700MB/s (2460GB/hr), the rated maximum write speed on the tape devices is 140MB/s, per drive, so that's 492GB/hr (or double it, for the total throughput). So, the next step was to benchmark NFS performance with IOzone, and it turns out that we get epic write performance (across 20 threads), and it's like 1.5-2.5TB/hr write, but read performance is fecking hopeless. I couldn't ever get higher than 343GB/hr maximum. So let's assume that the 343GB/hr is a theoretical maximum for read performance on the NAS, then we should in theory be able to get that performance out of a) CommVault, and b) any other backup agent. Not the case. Commvault seems to only ever give me 200-250GB/hr throughput, and out of experimentation, I installed Bacula to see what the state of play there is. If, for example, Bacula gave consistently better performance and speeds than Commvault, then we'd be able to say "**$.$ Refunds Plz $.$**" #-#-# Alas, I found a different problem with Bacula. Commvault seems pretty happy to read from one part of the mountpoint with one thread, and stream that to a Tape device, whilst reading from some other directory with the other thread, and writing to the 2nd drive in the autochanger. I can't for the life of me get Bacula to mount and write to two tape drives simultaneously. Things I've tried: Setting Maximum Concurrent Jobs = 20 in the Director, File and Storage Daemons Setting Prefer Mounted Volumes = no in the Job Definition Setting multiple devices in the Autochanger resource. Documentation seems to be very single-drive centric, and we feel a little like we've strapped a rocket to a hamster, with this one. The majority of example Bacula configurations are for DDS4 drives, manual tape swapping, and FreeBSD or IRIX systems. I should probably add that I'm not too bothered if this isn't possible, but I'd be surprised. I basically want to use Bacula as proof to stick it to the software vendors that they're overpriced ;) I read somewhere that @KyleBrandt has done something similar with a modern Tape solution.. Configuration Files: *bacula-dir.conf* # # Default Bacula Director Configuration file Director { # define myself Name = backuphost-1-dir DIRport = 9101 # where we listen for UA connections QueryFile = "/etc/bacula/scripts/query.sql" WorkingDirectory = "/var/lib/bacula" PidDirectory = "/var/run/bacula" Maximum Concurrent Jobs = 20 Password = "yourekiddingright" # Console password Messages = Daemon DirAddress = 0.0.0.0 #DirAddress = 127.0.0.1 } JobDefs { Name = "DefaultFileJob" Type = Backup Level = Incremental Client = backuphost-1-fd FileSet = "Full Set" Schedule = "WeeklyCycle" Storage = File Messages = Standard Pool = File Priority = 10 Write Bootstrap = "/var/lib/bacula/%c.bsr" } JobDefs { Name = "DefaultTapeJob" Type = Backup Level = Incremental Client = backuphost-1-fd FileSet = "Full Set" Schedule = "WeeklyCycle" Storage = "SpectraLogic" Messages = Standard Pool = AllTapes Priority = 10 Write Bootstrap = "/var/lib/bacula/%c.bsr" Prefer Mounted Volumes = no } # # Define the main nightly save backup job # By default, this job will back up to disk in /nonexistant/path/to/file/archive/dir Job { Name = "BackupClient1" JobDefs = "DefaultFileJob" } Job { Name = "BackupThisVolume" JobDefs = "DefaultTapeJob" FileSet = "SpecialVolume" } #Job { # Name = "BackupClient2" # Client = backuphost-12-fd # JobDefs = "DefaultJob" #} # Backup the catalog database (after the nightly save) Job { Name = "BackupCatalog" JobDefs = "DefaultFileJob" Level = Full FileSet="Catalog" Schedule = "WeeklyCycleAfterBackup" # This creates an ASCII copy of the catalog # Arguments to make_catalog_backup.pl are: # make_catalog_backup.pl <catalog-name> RunBeforeJob = "/etc/bacula/scripts/make_catalog_backup.pl MyCatalog" # This deletes the copy of the catalog RunAfterJob = "/etc/bacula/scripts/delete_catalog_backup" Write Bootstrap = "/var/lib/bacula/%n.bsr" Priority = 11 # run after main backup } # # Standard Restore template, to be changed by Console program # Only one such job is needed for all Jobs/Clients/Storage ... # Job { Name = "RestoreFiles" Type = Restore Client=backuphost-1-fd FileSet="Full Set" Storage = File Pool = Default Messages = Standard Where = /srv/bacula/restore } FileSet { Name = "SpecialVolume" Include { Options { signature = MD5 } File = /mnt/SpecialVolume } Exclude { File = /var/lib/bacula File = /nonexistant/path/to/file/archive/dir File = /proc File = /tmp File = /.journal File = /.fsck } } # List of files to be backed up FileSet { Name = "Full Set" Include { Options { signature = MD5 } File = /usr/sbin } Exclude { File = /var/lib/bacula File = /nonexistant/path/to/file/archive/dir File = /proc File = /tmp File = /.journal File = /.fsck } } Schedule { Name = "WeeklyCycle" Run = Full 1st sun at 23:05 Run = Differential 2nd-5th sun at 23:05 Run = Incremental mon-sat at 23:05 } # This schedule does the catalog. It starts after the WeeklyCycle Schedule { Name = "WeeklyCycleAfterBackup" Run = Full sun-sat at 23:10 } # This is the backup of the catalog FileSet { Name = "Catalog" Include { Options { signature = MD5 } File = "/var/lib/bacula/bacula.sql" } } # Client (File Services) to backup Client { Name = backuphost-1-fd Address = localhost FDPort = 9102 Catalog = MyCatalog Password = "surelyyourejoking" # password for FileDaemon File Retention = 30 days # 30 days Job Retention = 6 months # six months AutoPrune = yes # Prune expired Jobs/Files } # # Second Client (File Services) to backup # You should change Name, Address, and Password before using # #Client { # Name = backuphost-12-fd # Address = localhost2 # FDPort = 9102 # Catalog = MyCatalog # Password = "i'mnotjokinganddontcallmeshirley" # password for FileDaemon 2 # File Retention = 30 days # 30 days # Job Retention = 6 months # six months # AutoPrune = yes # Prune expired Jobs/Files #} # Definition of file storage device Storage { Name = File # Do not use "localhost" here Address = localhost # N.B. Use a fully qualified name here SDPort = 9103 Password = "lalalalala" Device = FileStorage Media Type = File } Storage { Name = "SpectraLogic" Address = localhost SDPort = 9103 Password = "linkedinmakethebestpasswords" Device = Drive-1 Device = Drive-2 Media Type = LTO5 Autochanger = yes } # Generic catalog service Catalog { Name = MyCatalog # Uncomment the following line if you want the dbi driver # dbdriver = "dbi:sqlite3"; dbaddress = 127.0.0.1; dbport = dbname = "bacula"; DB Address = ""; dbuser = "bacula"; dbpassword = "bbmaster63" } # Reasonable message delivery -- send most everything to email address # and to the console Messages { Name = Standard mailcommand = "/usr/lib/bacula/bsmtp -h localhost -f \"\(Bacula\) \<%r\>\" -s \"Bacula: %t %e of %c %l\" %r" operatorcommand = "/usr/lib/bacula/bsmtp -h localhost -f \"\(Bacula\) \<%r\>\" -s \"Bacula: Intervention needed for %j\" %r" mail = root@localhost = all, !skipped operator = root@localhost = mount console = all, !skipped, !saved # # WARNING! the following will create a file that you must cycle from # time to time as it will grow indefinitely. However, it will # also keep all your messages if they scroll off the console. # append = "/var/lib/bacula/log" = all, !skipped catalog = all } # # Message delivery for daemon messages (no job). Messages { Name = Daemon mailcommand = "/usr/lib/bacula/bsmtp -h localhost -f \"\(Bacula\) \<%r\>\" -s \"Bacula daemon message\" %r" mail = root@localhost = all, !skipped console = all, !skipped, !saved append = "/var/lib/bacula/log" = all, !skipped } # Default pool definition Pool { Name = Default Pool Type = Backup Recycle = yes # Bacula can automatically recycle Volumes AutoPrune = yes # Prune expired volumes Volume Retention = 365 days # one year } # File Pool definition Pool { Name = File Pool Type = Backup Recycle = yes # Bacula can automatically recycle Volumes AutoPrune = yes # Prune expired volumes Volume Retention = 365 days # one year Maximum Volume Bytes = 50G # Limit Volume size to something reasonable Maximum Volumes = 100 # Limit number of Volumes in Pool } Pool { Name = AllTapes Pool Type = Backup Recycle = yes AutoPrune = yes # Prune expired volumes Volume Retention = 31 days # one Moth } # Scratch pool definition Pool { Name = Scratch Pool Type = Backup } # # Restricted console used by tray-monitor to get the status of the director # Console { Name = backuphost-1-mon Password = "LastFMalsostorePasswordsLikeThis" CommandACL = status, .status } bacula-sd.conf # # Default Bacula Storage Daemon Configuration file # Storage { # definition of myself Name = backuphost-1-sd SDPort = 9103 # Director's port WorkingDirectory = "/var/lib/bacula" Pid Directory = "/var/run/bacula" Maximum Concurrent Jobs = 20 SDAddress = 0.0.0.0 # SDAddress = 127.0.0.1 } # # List Directors who are permitted to contact Storage daemon # Director { Name = backuphost-1-dir Password = "passwordslinplaintext" } # # Restricted Director, used by tray-monitor to get the # status of the storage daemon # Director { Name = backuphost-1-mon Password = "totalinsecurityabound" Monitor = yes } Device { Name = FileStorage Media Type = File Archive Device = /srv/bacula/archive LabelMedia = yes; # lets Bacula label unlabeled media Random Access = Yes; AutomaticMount = yes; # when device opened, read it RemovableMedia = no; AlwaysOpen = no; } Autochanger { Name = SpectraLogic Device = Drive-1 Device = Drive-2 Changer Command = "/etc/bacula/scripts/mtx-changer %c %o %S %a %d" Changer Device = /dev/sg4 } Device { Name = Drive-1 Drive Index = 0 Archive Device = /dev/nst0 Changer Device = /dev/sg4 Media Type = LTO5 AutoChanger = yes RemovableMedia = yes; AutomaticMount = yes; AlwaysOpen = yes; RandomAccess = no; LabelMedia = yes } Device { Name = Drive-2 Drive Index = 1 Archive Device = /dev/nst1 Changer Device = /dev/sg4 Media Type = LTO5 AutoChanger = yes RemovableMedia = yes; AutomaticMount = yes; AlwaysOpen = yes; RandomAccess = no; LabelMedia = yes } # # Send all messages to the Director, # mount messages also are sent to the email address # Messages { Name = Standard director = backuphost-1-dir = all } bacula-fd.conf # # Default Bacula File Daemon Configuration file # # # List Directors who are permitted to contact this File daemon # Director { Name = backuphost-1-dir Password = "hahahahahaha" } # # Restricted Director, used by tray-monitor to get the # status of the file daemon # Director { Name = backuphost-1-mon Password = "hohohohohho" Monitor = yes } # # "Global" File daemon configuration specifications # FileDaemon { # this is me Name = backuphost-1-fd FDport = 9102 # where we listen for the director WorkingDirectory = /var/lib/bacula Pid Directory = /var/run/bacula Maximum Concurrent Jobs = 20 #FDAddress = 127.0.0.1 FDAddress = 0.0.0.0 } # Send all messages except skipped files back to Director Messages { Name = Standard director = backuphost-1-dir = all, !skipped, !restored }

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  • Wikipedia API: list=alllinks confusion

    - by Chris Salij
    I'm doing a research project for the summer and I've got to use get some data from Wikipedia, store it and then do some analysis on it. I'm using the Wikipedia API to gather the data and I've got that down pretty well. What my questions is in regards to the links-alllinks option in the API doc here After reading the description, both there and in the API itself (it's down and bit and I can't link directly to the section), I think I understand what it's supposed to return. However when I ran a query it gave me back something I didn't expect. Here's the query I ran: http://en.wikipedia.org/w/api.php?action=query&prop=revisions&titles=google&rvprop=ids|timestamp|user|comment|content&rvlimit=1&list=alllinks&alunique&allimit=40&format=xml Which in essence says: Get the last revision of the Google page, include the id, timestamp, user, comment and content of each revision, and return it in XML format. The allinks (I thought) should give me back a list of wikipedia pages which point to the google page (In this case the first 40 unique ones). I'm not sure what the policy is on swears, but this is the result I got back exactly: <?xml version="1.0"?> <api> <query><normalized> <n from="google" to="Google" /> </normalized> <pages> <page pageid="1092923" ns="0" title="Google"> <revisions> <rev revid="366826294" parentid="366673948" user="Citation bot" timestamp="2010-06-08T17:18:31Z" comment="Citations: [161]Tweaked: url. [[User:Mono|Mono]]" xml:space="preserve"> <!-- The page content, I've replaced this cos its not of interest --> </rev> </revisions> </page> </pages> <alllinks> <l ns="0" title="!" /> <l ns="0" title="!!" /> <l ns="0" title="!!!" /> <l ns="0" title="!!!!" /> <l ns="0" title="!!!!!!!!!!!!!!!!!!!!!" /> <l ns="0" title="!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!" /> <l ns="0" title="!!!!!!!!!!!!!!!!!!!!*was up all u hater just stopingby to show u some love*!!!!!!!!!!!!!!!!!!!!!!!!!!!" /> <l ns="0" title="!!!!!!!!!!!!&amp;&amp;&amp;&amp;&amp;&amp;&amp;&amp;&amp;&amp;&amp;********(( )))))F/W///CHRYSLER/FUCKING/FUCKING/FUCKING/I HATE THE QUEEN!!!/I AM HORRID HENRY/Chrysler Cirrus/php" /> <l ns="0" title="!!!!!Hephaestos IS A FUCKING WHINY GUY!!!!!!" /> <l ns="0" title="!!!!Do you really want to see this article on your default search?" /> <l ns="0" title="!!!!Legal!!!!" /> <l ns="0" title="!!!!YOU ARE A COCKSUCKING WHINY GREASER!!!!" /> <l ns="0" title="!!!BESQUERKAN!!!" /> <l ns="0" title="!!!Fuck You!!!" /> <l ns="0" title="!!!Fuck You!!! And Then Some" /> <l ns="0" title="!!!Fuck You!!! And Then some" /> <l ns="0" title="!!!Fuck You!!! And then Some" /> <l ns="0" title="!!!Fuck You!!! and Then Some" /> <l ns="0" title="!!!Three !!! Amigos!!!" /> <l ns="0" title="!!! (album)" /> <l ns="0" title="!!! (band)" /> <l ns="0" title="!!1" /> <l ns="0" title="!!BOSS!!" /> <l ns="0" title="!!Destroy-Oh-Boy!!" /> <l ns="0" title="!!Fuck you!!" /> <l ns="0" title="!!M" /> <l ns="0" title="!!Que Corra La Voz!!" /> <l ns="0" title="!! (chess)" /> <l ns="0" title="!! (disambiguation)" /> <l ns="0" title="!! 6- -.4rtist.com" /> <l ns="0" title="!!m" /> <l ns="0" title="!!suck my balls!!" /> <l ns="0" title="!!~~YOU WIN~~!!" /> <l ns="0" title="!&#039;O-!khung language" /> <l ns="0" title="!(1)Full Name:(2)Age:(3)Sex:(4)Occupation:(5)Phone Number: (6)Delivery Address:(7)Country of Residence:. Dr.John Aboh" /> <l ns="0" title="!-" /> <l ns="0" title="!-My Degrassi Top 10 Episodes" /> <l ns="0" title="!10 Show" /> <l ns="0" title="!2005" /> <l ns="0" title="!2006" /> </alllinks> </query> <query-continue> <revisions rvstartid="366673948" /> <alllinks alfrom="!2009" /> </query-continue> </api> As you can see if you look at the <alllinks> part, its just a load of random gobbledy-gook. No nearly what I thought I'd get. I've done a fair bit of searching but I can't seem to find a direct answer to my question. What should the list=alllinks option return? Why am I getting this crap in there? Thanks for your help

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  • Using the West Wind Web Toolkit to set up AJAX and REST Services

    - by Rick Strahl
    I frequently get questions about which option to use for creating AJAX and REST backends for ASP.NET applications. There are many solutions out there to do this actually, but when I have a choice - not surprisingly - I fall back to my own tools in the West Wind West Wind Web Toolkit. I've talked a bunch about the 'in-the-box' solutions in the past so for a change in this post I'll talk about the tools that I use in my own and customer applications to handle AJAX and REST based access to service resources using the West Wind West Wind Web Toolkit. Let me preface this by saying that I like things to be easy. Yes flexible is very important as well but not at the expense of over-complexity. The goal I've had with my tools is make it drop dead easy, with good performance while providing the core features that I'm after, which are: Easy AJAX/JSON Callbacks Ability to return any kind of non JSON content (string, stream, byte[], images) Ability to work with both XML and JSON interchangeably for input/output Access endpoints via POST data, RPC JSON calls, GET QueryString values or Routing interface Easy to use generic JavaScript client to make RPC calls (same syntax, just what you need) Ability to create clean URLS with Routing Ability to use standard ASP.NET HTTP Stack for HTTP semantics It's all about options! In this post I'll demonstrate most of these features (except XML) in a few simple and short samples which you can download. So let's take a look and see how you can build an AJAX callback solution with the West Wind Web Toolkit. Installing the Toolkit Assemblies The easiest and leanest way of using the Toolkit in your Web project is to grab it via NuGet: West Wind Web and AJAX Utilities (Westwind.Web) and drop it into the project by right clicking in your Project and choosing Manage NuGet Packages from anywhere in the Project.   When done you end up with your project looking like this: What just happened? Nuget added two assemblies - Westwind.Web and Westwind.Utilities and the client ww.jquery.js library. It also added a couple of references into web.config: The default namespaces so they can be accessed in pages/views and a ScriptCompressionModule that the toolkit optionally uses to compress script resources served from within the assembly (namely ww.jquery.js and optionally jquery.js). Creating a new Service The West Wind Web Toolkit supports several ways of creating and accessing AJAX services, but for this post I'll stick to the lower level approach that works from any plain HTML page or of course MVC, WebForms, WebPages. There's also a WebForms specific control that makes this even easier but I'll leave that for another post. So, to create a new standalone AJAX/REST service we can create a new HttpHandler in the new project either as a pure class based handler or as a generic .ASHX handler. Both work equally well, but generic handlers don't require any web.config configuration so I'll use that here. In the root of the project add a Generic Handler. I'm going to call this one StockService.ashx. Once the handler has been created, edit the code and remove all of the handler body code. Then change the base class to CallbackHandler and add methods that have a [CallbackMethod] attribute. Here's the modified base handler implementation now looks like with an added HelloWorld method: using System; using Westwind.Web; namespace WestWindWebAjax { /// <summary> /// Handler implements CallbackHandler to provide REST/AJAX services /// </summary> public class SampleService : CallbackHandler { [CallbackMethod] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } } } Notice that the class inherits from CallbackHandler and that the HelloWorld service method is marked up with [CallbackMethod]. We're done here. Services Urlbased Syntax Once you compile, the 'service' is live can respond to requests. All CallbackHandlers support input in GET and POST formats, and can return results as JSON or XML. To check our fancy HelloWorld method we can now access the service like this: http://localhost/WestWindWebAjax/StockService.ashx?Method=HelloWorld&name=Rick which produces a default JSON response - in this case a string (wrapped in quotes as it's JSON): (note by default JSON will be downloaded by most browsers not displayed - various options are available to view JSON right in the browser) If I want to return the same data as XML I can tack on a &format=xml at the end of the querystring which produces: <string>Hello Rick. Time is: 11/1/2011 12:11:13 PM</string> Cleaner URLs with Routing Syntax If you want cleaner URLs for each operation you can also configure custom routes on a per URL basis similar to the way that WCF REST does. To do this you need to add a new RouteHandler to your application's startup code in global.asax.cs one for each CallbackHandler based service you create: protected void Application_Start(object sender, EventArgs e) { CallbackHandlerRouteHandler.RegisterRoutes<StockService>(RouteTable.Routes); } With this code in place you can now add RouteUrl properties to any of your service methods. For the HelloWorld method that doesn't make a ton of sense but here is what a routed clean URL might look like in definition: [CallbackMethod(RouteUrl="stocks/HelloWorld/{name}")] public string HelloWorld(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } The same URL I previously used now becomes a bit shorter and more readable with: http://localhost/WestWindWebAjax/HelloWorld/Rick It's an easy way to create cleaner URLs and still get the same functionality. Calling the Service with $.getJSON() Since the result produced is JSON you can now easily consume this data using jQuery's getJSON method. First we need a couple of scripts - jquery.js and ww.jquery.js in the page: <!DOCTYPE html> <html> <head> <link href="Css/Westwind.css" rel="stylesheet" type="text/css" /> <script src="scripts/jquery.min.js" type="text/javascript"></script> <script src="scripts/ww.jquery.min.js" type="text/javascript"></script> </head> <body> Next let's add a small HelloWorld example form (what else) that has a single textbox to type a name, a button and a div tag to receive the result: <fieldset> <legend>Hello World</legend> Please enter a name: <input type="text" name="txtHello" id="txtHello" value="" /> <input type="button" id="btnSayHello" value="Say Hello (POST)" /> <input type="button" id="btnSayHelloGet" value="Say Hello (GET)" /> <div id="divHelloMessage" class="errordisplay" style="display:none;width: 450px;" > </div> </fieldset> Then to call the HelloWorld method a little jQuery is used to hook the document startup and the button click followed by the $.getJSON call to retrieve the data from the server. <script type="text/javascript"> $(document).ready(function () { $("#btnSayHelloGet").click(function () { $.getJSON("SampleService.ashx", { Method: "HelloWorld", name: $("#txtHello").val() }, function (result) { $("#divHelloMessage") .text(result) .fadeIn(1000); }); });</script> .getJSON() expects a full URL to the endpoint of our service, which is the ASHX file. We can either provide a full URL (SampleService.ashx?Method=HelloWorld&name=Rick) or we can just provide the base URL and an object that encodes the query string parameters for us using an object map that has a property that matches each parameter for the server method. We can also use the clean URL routing syntax, but using the object parameter encoding actually is safer as the parameters will get properly encoded by jQuery. The result returned is whatever the result on the server method is - in this case a string. The string is applied to the divHelloMessage element and we're done. Obviously this is a trivial example, but it demonstrates the basics of getting a JSON response back to the browser. AJAX Post Syntax - using ajaxCallMethod() The previous example allows you basic control over the data that you send to the server via querystring parameters. This works OK for simple values like short strings, numbers and boolean values, but doesn't really work if you need to pass something more complex like an object or an array back up to the server. To handle traditional RPC type messaging where the idea is to map server side functions and results to a client side invokation, POST operations can be used. The easiest way to use this functionality is to use ww.jquery.js and the ajaxCallMethod() function. ww.jquery wraps jQuery's AJAX functions and knows implicitly how to call a CallbackServer method with parameters and parse the result. Let's look at another simple example that posts a simple value but returns something more interesting. Let's start with the service method: [CallbackMethod(RouteUrl="stocks/{symbol}")] public StockQuote GetStockQuote(string symbol) { Response.Cache.SetExpires(DateTime.UtcNow.Add(new TimeSpan(0, 2, 0))); StockServer server = new StockServer(); var quote = server.GetStockQuote(symbol); if (quote == null) throw new ApplicationException("Invalid Symbol passed."); return quote; } This sample utilizes a small StockServer helper class (included in the sample) that downloads a stock quote from Yahoo's financial site via plain HTTP GET requests and formats it into a StockQuote object. Lets create a small HTML block that lets us query for the quote and display it: <fieldset> <legend>Single Stock Quote</legend> Please enter a stock symbol: <input type="text" name="txtSymbol" id="txtSymbol" value="msft" /> <input type="button" id="btnStockQuote" value="Get Quote" /> <div id="divStockDisplay" class="errordisplay" style="display:none; width: 450px;"> <div class="label-left">Company:</div> <div id="stockCompany"></div> <div class="label-left">Last Price:</div> <div id="stockLastPrice"></div> <div class="label-left">Quote Time:</div> <div id="stockQuoteTime"></div> </div> </fieldset> The final result looks something like this:   Let's hook up the button handler to fire the request and fill in the data as shown: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").show().fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, HH:mm EST")); }, onPageError); }); So we point at SampleService.ashx and the GetStockQuote method, passing a single parameter of the input symbol value. Then there are two handlers for success and failure callbacks.  The success handler is the interesting part - it receives the stock quote as a result and assigns its values to various 'holes' in the stock display elements. The data that comes back over the wire is JSON and it looks like this: { "Symbol":"MSFT", "Company":"Microsoft Corpora", "OpenPrice":26.11, "LastPrice":26.01, "NetChange":0.02, "LastQuoteTime":"2011-11-03T02:00:00Z", "LastQuoteTimeString":"Nov. 11, 2011 4:20pm" } which is an object representation of the data. JavaScript can evaluate this JSON string back into an object easily and that's the reslut that gets passed to the success function. The quote data is then applied to existing page content by manually selecting items and applying them. There are other ways to do this more elegantly like using templates, but here we're only interested in seeing how the data is returned. The data in the object is typed - LastPrice is a number and QuoteTime is a date. Note about the date value: JavaScript doesn't have a date literal although the JSON embedded ISO string format used above  ("2011-11-03T02:00:00Z") is becoming fairly standard for JSON serializers. However, JSON parsers don't deserialize dates by default and return them by string. This is why the StockQuote actually returns a string value of LastQuoteTimeString for the same date. ajaxMethodCallback always converts dates properly into 'real' dates and the example above uses the real date value along with a .formatDate() data extension (also in ww.jquery.js) to display the raw date properly. Errors and Exceptions So what happens if your code fails? For example if I pass an invalid stock symbol to the GetStockQuote() method you notice that the code does this: if (quote == null) throw new ApplicationException("Invalid Symbol passed."); CallbackHandler automatically pushes the exception message back to the client so it's easy to pick up the error message. Regardless of what kind of error occurs: Server side, client side, protocol errors - any error will fire the failure handler with an error object parameter. The error is returned to the client via a JSON response in the error callback. In the previous examples I called onPageError which is a generic routine in ww.jquery that displays a status message on the bottom of the screen. But of course you can also take over the error handling yourself: $("#btnStockQuote").click(function () { ajaxCallMethod("SampleService.ashx", "GetStockQuote", [$("#txtSymbol").val()], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); }, function (error, xhr) { $("#divErrorDisplay").text(error.message).fadeIn(1000); }); }); The error object has a isCallbackError, message and  stackTrace properties, the latter of which is only populated when running in Debug mode, and this object is returned for all errors: Client side, transport and server side errors. Regardless of which type of error you get the same object passed (as well as the XHR instance optionally) which makes for a consistent error retrieval mechanism. Specifying HttpVerbs You can also specify HTTP Verbs that are allowed using the AllowedHttpVerbs option on the CallbackMethod attribute: [CallbackMethod(AllowedHttpVerbs=HttpVerbs.GET | HttpVerbs.POST)] public string HelloWorld(string name) { … } If you're building REST style API's this might be useful to force certain request semantics onto the client calling. For the above if call with a non-allowed HttpVerb the request returns a 405 error response along with a JSON (or XML) error object result. The default behavior is to allow all verbs access (HttpVerbs.All). Passing in object Parameters Up to now the parameters I passed were very simple. But what if you need to send something more complex like an object or an array? Let's look at another example now that passes an object from the client to the server. Keeping with the Stock theme here lets add a method called BuyOrder that lets us buy some shares for a stock. Consider the following service method that receives an StockBuyOrder object as a parameter: [CallbackMethod] public string BuyStock(StockBuyOrder buyOrder) { var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } public class StockBuyOrder { public string Symbol { get; set; } public int Quantity { get; set; } public DateTime BuyOn { get; set; } public StockBuyOrder() { BuyOn = DateTime.Now; } } This is a contrived do-nothing example that simply echoes back what was passed in, but it demonstrates how you can pass complex data to a callback method. On the client side we now have a very simple form that captures the three values on a form: <fieldset> <legend>Post a Stock Buy Order</legend> Enter a symbol: <input type="text" name="txtBuySymbol" id="txtBuySymbol" value="GLD" />&nbsp;&nbsp; Qty: <input type="text" name="txtBuyQty" id="txtBuyQty" value="10" style="width: 50px" />&nbsp;&nbsp; Buy on: <input type="text" name="txtBuyOn" id="txtBuyOn" value="<%= DateTime.Now.ToString("d") %>" style="width: 70px;" /> <input type="button" id="btnBuyStock" value="Buy Stock" /> <div id="divStockBuyMessage" class="errordisplay" style="display:none"></div> </fieldset> The completed form and demo then looks something like this:   The client side code that picks up the input values and assigns them to object properties and sends the AJAX request looks like this: $("#btnBuyStock").click(function () { // create an object map that matches StockBuyOrder signature var buyOrder = { Symbol: $("#txtBuySymbol").val(), Quantity: $("#txtBuyQty").val() * 1, // number Entered: new Date() } ajaxCallMethod("SampleService.ashx", "BuyStock", [buyOrder], function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError); }); The code creates an object and attaches the properties that match the server side object passed to the BuyStock method. Each property that you want to update needs to be included and the type must match (ie. string, number, date in this case). Any missing properties will not be set but also not cause any errors. Pass POST data instead of Objects In the last example I collected a bunch of values from form variables and stuffed them into object variables in JavaScript code. While that works, often times this isn't really helping - I end up converting my types on the client and then doing another conversion on the server. If lots of input controls are on a page and you just want to pick up the values on the server via plain POST variables - that can be done too - and it makes sense especially if you're creating and filling the client side object only to push data to the server. Let's add another method to the server that once again lets us buy a stock. But this time let's not accept a parameter but rather send POST data to the server. Here's the server method receiving POST data: [CallbackMethod] public string BuyStockPost() { StockBuyOrder buyOrder = new StockBuyOrder(); buyOrder.Symbol = Request.Form["txtBuySymbol"]; ; int qty; int.TryParse(Request.Form["txtBuyQuantity"], out qty); buyOrder.Quantity = qty; DateTime time; DateTime.TryParse(Request.Form["txtBuyBuyOn"], out time); buyOrder.BuyOn = time; // Or easier way yet //FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); var server = new StockServer(); var quote = server.GetStockQuote(buyOrder.Symbol); if (quote == null) throw new ApplicationException("Invalid or missing stock symbol."); return string.Format("You're buying {0} shares of {1} ({2}) stock at {3} for a total of {4} on {5}.", buyOrder.Quantity, quote.Company, quote.Symbol, quote.LastPrice.ToString("c"), (quote.LastPrice * buyOrder.Quantity).ToString("c"), buyOrder.BuyOn.ToString("MMM d")); } Clearly we've made this server method take more code than it did with the object parameter. We've basically moved the parameter assignment logic from the client to the server. As a result the client code to call this method is now a bit shorter since there's no client side shuffling of values from the controls to an object. $("#btnBuyStockPost").click(function () { ajaxCallMethod("SampleService.ashx", "BuyStockPost", [], // Note: No parameters - function (result) { $("#divStockBuyMessage").text(result).fadeIn(1000); }, onPageError, // Force all page Form Variables to be posted { postbackMode: "Post" }); }); The client simply calls the BuyStockQuote method and pushes all the form variables from the page up to the server which parses them instead. The feature that makes this work is one of the options you can pass to the ajaxCallMethod() function: { postbackMode: "Post" }); which directs the function to include form variable POST data when making the service call. Other options include PostNoViewState (for WebForms to strip out WebForms crap vars), PostParametersOnly (default), None. If you pass parameters those are always posted to the server except when None is set. The above code can be simplified a bit by using the FormVariableBinder helper, which can unbind form variables directly into an object: FormVariableBinder.Unbind(buyOrder,null,"txtBuy"); which replaces the manual Request.Form[] reading code. It receives the object to unbind into, a string of properties to skip, and an optional prefix which is stripped off form variables to match property names. The component is similar to the MVC model binder but it's independent of MVC. Returning non-JSON Data CallbackHandler also supports returning non-JSON/XML data via special return types. You can return raw non-JSON encoded strings like this: [CallbackMethod(ReturnAsRawString=true,ContentType="text/plain")] public string HelloWorldNoJSON(string name) { return "Hello " + name + ". Time is: " + DateTime.Now.ToString(); } Calling this method results in just a plain string - no JSON encoding with quotes around the result. This can be useful if your server handling code needs to return a string or HTML result that doesn't fit well for a page or other UI component. Any string output can be returned. You can also return binary data. Stream, byte[] and Bitmap/Image results are automatically streamed back to the client. Notice that you should set the ContentType of the request either on the CallbackMethod attribute or using Response.ContentType. This ensures the Web Server knows how to display your binary response. Using a stream response makes it possible to return any of data. Streamed data can be pretty handy to return bitmap data from a method. The following is a method that returns a stock history graph for a particular stock over a provided number of years: [CallbackMethod(ContentType="image/png",RouteUrl="stocks/history/graph/{symbol}/{years}")] public Stream GetStockHistoryGraph(string symbol, int years = 2,int width = 500, int height=350) { if (width == 0) width = 500; if (height == 0) height = 350; StockServer server = new StockServer(); return server.GetStockHistoryGraph(symbol,"Stock History for " + symbol,width,height,years); } I can now hook this up into the JavaScript code when I get a stock quote. At the end of the process I can assign the URL to the service that returns the image into the src property and so force the image to display. Here's the changed code: $("#btnStockQuote").click(function () { var symbol = $("#txtSymbol").val(); ajaxCallMethod("SampleService.ashx", "GetStockQuote", [symbol], function (quote) { $("#divStockDisplay").fadeIn(1000); $("#stockCompany").text(quote.Company + " (" + quote.Symbol + ")"); $("#stockLastPrice").text(quote.LastPrice); $("#stockQuoteTime").text(quote.LastQuoteTime.formatDate("MMM dd, hh:mmt")); // display a stock chart $("#imgStockHistory").attr("src", "stocks/history/graph/" + symbol + "/2"); },onPageError); }); The resulting output then looks like this: The charting code uses the new ASP.NET 4.0 Chart components via code to display a bar chart of the 2 year stock data as part of the StockServer class which you can find in the sample download. The ability to return arbitrary data from a service is useful as you can see - in this case the chart is clearly associated with the service and it's nice that the graph generation can happen off a handler rather than through a page. Images are common resources, but output can also be PDF reports, zip files for downloads etc. which is becoming increasingly more common to be returned from REST endpoints and other applications. Why reinvent? Obviously the examples I've shown here are pretty basic in terms of functionality. But I hope they demonstrate the core features of AJAX callbacks that you need to work through in most applications which is simple: return data, send back data and potentially retrieve data in various formats. While there are other solutions when it comes down to making AJAX callbacks and servicing REST like requests, I like the flexibility my home grown solution provides. Simply put it's still the easiest solution that I've found that addresses my common use cases: AJAX JSON RPC style callbacks Url based access XML and JSON Output from single method endpoint XML and JSON POST support, querystring input, routing parameter mapping UrlEncoded POST data support on callbacks Ability to return stream/raw string data Essentially ability to return ANYTHING from Service and pass anything All these features are available in various solutions but not together in one place. I've been using this code base for over 4 years now in a number of projects both for myself and commercial work and it's served me extremely well. Besides the AJAX functionality CallbackHandler provides, it's also an easy way to create any kind of output endpoint I need to create. Need to create a few simple routines that spit back some data, but don't want to create a Page or View or full blown handler for it? Create a CallbackHandler and add a method or multiple methods and you have your generic endpoints.  It's a quick and easy way to add small code pieces that are pretty efficient as they're running through a pretty small handler implementation. I can have this up and running in a couple of minutes literally without any setup and returning just about any kind of data. Resources Download the Sample NuGet: Westwind Web and AJAX Utilities (Westwind.Web) ajaxCallMethod() Documentation Using the AjaxMethodCallback WebForms Control West Wind Web Toolkit Home Page West Wind Web Toolkit Source Code © Rick Strahl, West Wind Technologies, 2005-2011Posted in ASP.NET  jQuery  AJAX   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Red Gate Coder interviews: Alex Davies

    - by Michael Williamson
    Alex Davies has been a software engineer at Red Gate since graduating from university, and is currently busy working on .NET Demon. We talked about tackling parallel programming with his actors framework, a scientific approach to debugging, and how JavaScript is going to affect the programming languages we use in years to come. So, if we start at the start, how did you get started in programming? When I was seven or eight, I was given a BBC Micro for Christmas. I had asked for a Game Boy, but my dad thought it would be better to give me a proper computer. For a year or so, I only played games on it, but then I found the user guide for writing programs in it. I gradually started doing more stuff on it and found it fun. I liked creating. As I went into senior school I continued to write stuff on there, trying to write games that weren’t very good. I got a real computer when I was fourteen and found ways to write BASIC on it. Visual Basic to start with, and then something more interesting than that. How did you learn to program? Was there someone helping you out? Absolutely not! I learnt out of a book, or by experimenting. I remember the first time I found a loop, I was like “Oh my God! I don’t have to write out the same line over and over and over again any more. It’s amazing!” When did you think this might be something that you actually wanted to do as a career? For a long time, I thought it wasn’t something that you would do as a career, because it was too much fun to be a career. I thought I’d do chemistry at university and some kind of career based on chemical engineering. And then I went to a careers fair at school when I was seventeen or eighteen, and it just didn’t interest me whatsoever. I thought “I could be a programmer, and there’s loads of money there, and I’m good at it, and it’s fun”, but also that I shouldn’t spoil my hobby. Now I don’t really program in my spare time any more, which is a bit of a shame, but I program all the rest of the time, so I can live with it. Do you think you learnt much about programming at university? Yes, definitely! I went into university knowing how to make computers do anything I wanted them to do. However, I didn’t have the language to talk about algorithms, so the algorithms course in my first year was massively important. Learning other language paradigms like functional programming was really good for breadth of understanding. Functional programming influences normal programming through design rather than actually using it all the time. I draw inspiration from it to write imperative programs which I think is actually becoming really fashionable now, but I’ve been doing it for ages. I did it first! There were also some courses on really odd programming languages, a bit of Prolog, a little bit of C. Having a little bit of each of those is something that I would have never done on my own, so it was important. And then there are knowledge-based courses which are about not programming itself but things that have been programmed like TCP. Those are really important for examples for how to approach things. Did you do any internships while you were at university? Yeah, I spent both of my summers at the same company. I thought I could code well before I went there. Looking back at the crap that I produced, it was only surpassed in its crappiness by all of the other code already in that company. I’m so much better at writing nice code now than I used to be back then. Was there just not a culture of looking after your code? There was, they just didn’t hire people for their abilities in that area. They hired people for raw IQ. The first indicator of it going wrong was that they didn’t have any computer scientists, which is a bit odd in a programming company. But even beyond that they didn’t have people who learnt architecture from anyone else. Most of them had started straight out of university, so never really had experience or mentors to learn from. There wasn’t the experience to draw from to teach each other. In the second half of my second internship, I was being given tasks like looking at new technologies and teaching people stuff. Interns shouldn’t be teaching people how to do their jobs! All interns are going to have little nuggets of things that you don’t know about, but they shouldn’t consistently be the ones who know the most. It’s not a good environment to learn. I was going to ask how you found working with people who were more experienced than you… When I reached Red Gate, I found some people who were more experienced programmers than me, and that was difficult. I’ve been coding since I was tiny. At university there were people who were cleverer than me, but there weren’t very many who were more experienced programmers than me. During my internship, I didn’t find anyone who I classed as being a noticeably more experienced programmer than me. So, it was a shock to the system to have valid criticisms rather than just formatting criticisms. However, Red Gate’s not so big on the actual code review, at least it wasn’t when I started. We did an entire product release and then somebody looked over all of the UI of that product which I’d written and say what they didn’t like. By that point, it was way too late and I’d disagree with them. Do you think the lack of code reviews was a bad thing? I think if there’s going to be any oversight of new people, then it should be continuous rather than chunky. For me I don’t mind too much, I could go out and get oversight if I wanted it, and in those situations I felt comfortable without it. If I was managing the new person, then maybe I’d be keener on oversight and then the right way to do it is continuously and in very, very small chunks. Have you had any significant projects you’ve worked on outside of a job? When I was a teenager I wrote all sorts of stuff. I used to write games, I derived how to do isomorphic projections myself once. I didn’t know what the word was so I couldn’t Google for it, so I worked it out myself. It was horrifically complicated. But it sort of tailed off when I started at university, and is now basically zero. If I do side-projects now, they tend to be work-related side projects like my actors framework, NAct, which I started in a down tools week. Could you explain a little more about NAct? It is a little C# framework for writing parallel code more easily. Parallel programming is difficult when you need to write to shared data. Sometimes parallel programming is easy because you don’t need to write to shared data. When you do need to access shared data, you could just have your threads pile in and do their work, but then you would screw up the data because the threads would trample on each other’s toes. You could lock, but locks are really dangerous if you’re using more than one of them. You get interactions like deadlocks, and that’s just nasty. Actors instead allows you to say this piece of data belongs to this thread of execution, and nobody else can read it. If you want to read it, then ask that thread of execution for a piece of it by sending a message, and it will send the data back by a message. And that avoids deadlocks as long as you follow some obvious rules about not making your actors sit around waiting for other actors to do something. There are lots of ways to write actors, NAct allows you to do it as if it was method calls on other objects, which means you get all the strong type-safety that C# programmers like. Do you think that this is suitable for the majority of parallel programming, or do you think it’s only suitable for specific cases? It’s suitable for most difficult parallel programming. If you’ve just got a hundred web requests which are all independent of each other, then I wouldn’t bother because it’s easier to just spin them up in separate threads and they can proceed independently of each other. But where you’ve got difficult parallel programming, where you’ve got multiple threads accessing multiple bits of data in multiple ways at different times, then actors is at least as good as all other ways, and is, I reckon, easier to think about. When you’re using actors, you presumably still have to write your code in a different way from you would otherwise using single-threaded code. You can’t use actors with any methods that have return types, because you’re not allowed to call into another actor and wait for it. If you want to get a piece of data out of another actor, then you’ve got to use tasks so that you can use “async” and “await” to await asynchronously for it. But other than that, you can still stick things in classes so it’s not too different really. Rather than having thousands of objects with mutable state, you can use component-orientated design, where there are only a few mutable classes which each have a small number of instances. Then there can be thousands of immutable objects. If you tend to do that anyway, then actors isn’t much of a jump. If I’ve already built my system without any parallelism, how hard is it to add actors to exploit all eight cores on my desktop? Usually pretty easy. If you can identify even one boundary where things look like messages and you have components where some objects live on one side and these other objects live on the other side, then you can have a granddaddy object on one side be an actor and it will parallelise as it goes across that boundary. Not too difficult. If we do get 1000-core desktop PCs, do you think actors will scale up? It’s hard. There are always in the order of twenty to fifty actors in my whole program because I tend to write each component as actors, and I tend to have one instance of each component. So this won’t scale to a thousand cores. What you can do is write data structures out of actors. I use dictionaries all over the place, and if you need a dictionary that is going to be accessed concurrently, then you could build one of those out of actors in no time. You can use queuing to marshal requests between different slices of the dictionary which are living on different threads. So it’s like a distributed hash table but all of the chunks of it are on the same machine. That means that each of these thousand processors has cached one small piece of the dictionary. I reckon it wouldn’t be too big a leap to start doing proper parallelism. Do you think it helps if actors get baked into the language, similarly to Erlang? Erlang is excellent in that it has thread-local garbage collection. C# doesn’t, so there’s a limit to how well C# actors can possibly scale because there’s a single garbage collected heap shared between all of them. When you do a global garbage collection, you’ve got to stop all of the actors, which is seriously expensive, whereas in Erlang garbage collections happen per-actor, so they’re insanely cheap. However, Erlang deviated from all the sensible language design that people have used recently and has just come up with crazy stuff. You can definitely retrofit thread-local garbage collection to .NET, and then it’s quite well-suited to support actors, even if it’s not baked into the language. Speaking of language design, do you have a favourite programming language? I’ll choose a language which I’ve never written before. I like the idea of Scala. It sounds like C#, only with some of the niggles gone. I enjoy writing static types. It means you don’t have to writing tests so much. When you say it doesn’t have some of the niggles? C# doesn’t allow the use of a property as a method group. It doesn’t have Scala case classes, or sum types, where you can do a switch statement and the compiler checks that you’ve checked all the cases, which is really useful in functional-style programming. Pattern-matching, in other words. That’s actually the major niggle. C# is pretty good, and I’m quite happy with C#. And what about going even further with the type system to remove the need for tests to something like Haskell? Or is that a step too far? I’m quite a pragmatist, I don’t think I could deal with trying to write big systems in languages with too few other users, especially when learning how to structure things. I just don’t know anyone who can teach me, and the Internet won’t teach me. That’s the main reason I wouldn’t use it. If I turned up at a company that writes big systems in Haskell, I would have no objection to that, but I wouldn’t instigate it. What about things in C#? For instance, there’s contracts in C#, so you can try to statically verify a bit more about your code. Do you think that’s useful, or just not worthwhile? I’ve not really tried it. My hunch is that it needs to be built into the language and be quite mathematical for it to work in real life, and that doesn’t seem to have ended up true for C# contracts. I don’t think anyone who’s tried them thinks they’re any good. I might be wrong. On a slightly different note, how do you like to debug code? I think I’m quite an odd debugger. I use guesswork extremely rarely, especially if something seems quite difficult to debug. I’ve been bitten spending hours and hours on guesswork and not being scientific about debugging in the past, so now I’m scientific to a fault. What I want is to see the bug happening in the debugger, to step through the bug happening. To watch the program going from a valid state to an invalid state. When there’s a bug and I can’t work out why it’s happening, I try to find some piece of evidence which places the bug in one section of the code. From that experiment, I binary chop on the possible causes of the bug. I suppose that means binary chopping on places in the code, or binary chopping on a stage through a processing cycle. Basically, I’m very stupid about how I debug. I won’t make any guesses, I won’t use any intuition, I will only identify the experiment that’s going to binary chop most effectively and repeat rather than trying to guess anything. I suppose it’s quite top-down. Is most of the time then spent in the debugger? Absolutely, if at all possible I will never debug using print statements or logs. I don’t really hold much stock in outputting logs. If there’s any bug which can be reproduced locally, I’d rather do it in the debugger than outputting logs. And with SmartAssembly error reporting, there’s not a lot that can’t be either observed in an error report and just fixed, or reproduced locally. And in those other situations, maybe I’ll use logs. But I hate using logs. You stare at the log, trying to guess what’s going on, and that’s exactly what I don’t like doing. You have to just look at it and see does this look right or wrong. We’ve covered how you get to grip with bugs. How do you get to grips with an entire codebase? I watch it in the debugger. I find little bugs and then try to fix them, and mostly do it by watching them in the debugger and gradually getting an understanding of how the code works using my process of binary chopping. I have to do a lot of reading and watching code to choose where my slicing-in-half experiment is going to be. The last time I did it was SmartAssembly. The old code was a complete mess, but at least it did things top to bottom. There wasn’t too much of some of the big abstractions where flow of control goes all over the place, into a base class and back again. Code’s really hard to understand when that happens. So I like to choose a little bug and try to fix it, and choose a bigger bug and try to fix it. Definitely learn by doing. I want to always have an aim so that I get a little achievement after every few hours of debugging. Once I’ve learnt the codebase I might be able to fix all the bugs in an hour, but I’d rather be using them as an aim while I’m learning the codebase. If I was a maintainer of a codebase, what should I do to make it as easy as possible for you to understand? Keep distinct concepts in different places. And name your stuff so that it’s obvious which concepts live there. You shouldn’t have some variable that gets set miles up the top of somewhere, and then is read miles down to choose some later behaviour. I’m talking from a very much SmartAssembly point of view because the old SmartAssembly codebase had tons and tons of these things, where it would read some property of the code and then deal with it later. Just thousands of variables in scope. Loads of things to think about. If you can keep concepts separate, then it aids me in my process of fixing bugs one at a time, because each bug is going to more or less be understandable in the one place where it is. And what about tests? Do you think they help at all? I’ve never had the opportunity to learn a codebase which has had tests, I don’t know what it’s like! What about when you’re actually developing? How useful do you find tests in finding bugs or regressions? Finding regressions, absolutely. Running bits of code that would be quite hard to run otherwise, definitely. It doesn’t happen very often that a test finds a bug in the first place. I don’t really buy nebulous promises like tests being a good way to think about the spec of the code. My thinking goes something like “This code works at the moment, great, ship it! Ah, there’s a way that this code doesn’t work. Okay, write a test, demonstrate that it doesn’t work, fix it, use the test to demonstrate that it’s now fixed, and keep the test for future regressions.” The most valuable tests are for bugs that have actually happened at some point, because bugs that have actually happened at some point, despite the fact that you think you’ve fixed them, are way more likely to appear again than new bugs are. Does that mean that when you write your code the first time, there are no tests? Often. The chance of there being a bug in a new feature is relatively unaffected by whether I’ve written a test for that new feature because I’m not good enough at writing tests to think of bugs that I would have written into the code. So not writing regression tests for all of your code hasn’t affected you too badly? There are different kinds of features. Some of them just always work, and are just not flaky, they just continue working whatever you throw at them. Maybe because the type-checker is particularly effective around them. Writing tests for those features which just tend to always work is a waste of time. And because it’s a waste of time I’ll tend to wait until a feature has demonstrated its flakiness by having bugs in it before I start trying to test it. You can get a feel for whether it’s going to be flaky code as you’re writing it. I try to write it to make it not flaky, but there are some things that are just inherently flaky. And very occasionally, I’ll think “this is going to be flaky” as I’m writing, and then maybe do a test, but not most of the time. How do you think your programming style has changed over time? I’ve got clearer about what the right way of doing things is. I used to flip-flop a lot between different ideas. Five years ago I came up with some really good ideas and some really terrible ideas. All of them seemed great when I thought of them, but they were quite diverse ideas, whereas now I have a smaller set of reliable ideas that are actually good for structuring code. So my code is probably more similar to itself than it used to be back in the day, when I was trying stuff out. I’ve got more disciplined about encapsulation, I think. There are operational things like I use actors more now than I used to, and that forces me to use immutability more than I used to. The first code that I wrote in Red Gate was the memory profiler UI, and that was an actor, I just didn’t know the name of it at the time. I don’t really use object-orientation. By object-orientation, I mean having n objects of the same type which are mutable. I want a constant number of objects that are mutable, and they should be different types. I stick stuff in dictionaries and then have one thing that owns the dictionary and puts stuff in and out of it. That’s definitely a pattern that I’ve seen recently. I think maybe I’m doing functional programming. Possibly. It’s plausible. If you had to summarise the essence of programming in a pithy sentence, how would you do it? Programming is the form of art that, without losing any of the beauty of architecture or fine art, allows you to produce things that people love and you make money from. So you think it’s an art rather than a science? It’s a little bit of engineering, a smidgeon of maths, but it’s not science. Like architecture, programming is on that boundary between art and engineering. If you want to do it really nicely, it’s mostly art. You can get away with doing architecture and programming entirely by having a good engineering mind, but you’re not going to produce anything nice. You’re not going to have joy doing it if you’re an engineering mind. Architects who are just engineering minds are not going to enjoy their job. I suppose engineering is the foundation on which you build the art. Exactly. How do you think programming is going to change over the next ten years? There will be an unfortunate shift towards dynamically-typed languages, because of JavaScript. JavaScript has an unfair advantage. JavaScript’s unfair advantage will cause more people to be exposed to dynamically-typed languages, which means other dynamically-typed languages crop up and the best features go into dynamically-typed languages. Then people conflate the good features with the fact that it’s dynamically-typed, and more investment goes into dynamically-typed languages. They end up better, so people use them. What about the idea of compiling other languages, possibly statically-typed, to JavaScript? It’s a reasonable idea. I would like to do it, but I don’t think enough people in the world are going to do it to make it pick up. The hordes of beginners are the lifeblood of a language community. They are what makes there be good tools and what makes there be vibrant community websites. And any particular thing which is the same as JavaScript only with extra stuff added to it, although it might be technically great, is not going to have the hordes of beginners. JavaScript is always to be quickest and easiest way for a beginner to start programming in the browser. And dynamically-typed languages are great for beginners. Compilers are pretty scary and beginners don’t write big code. And having your errors come up in the same place, whether they’re statically checkable errors or not, is quite nice for a beginner. If someone asked me to teach them some programming, I’d teach them JavaScript. If dynamically-typed languages are great for beginners, when do you think the benefits of static typing start to kick in? The value of having a statically typed program is in the tools that rely on the static types to produce a smooth IDE experience rather than actually telling me my compile errors. And only once you’re experienced enough a programmer that having a really smooth IDE experience makes a blind bit of difference, does static typing make a blind bit of difference. So it’s not really about size of codebase. If I go and write up a tiny program, I’m still going to get value out of writing it in C# using ReSharper because I’m experienced with C# and ReSharper enough to be able to write code five times faster if I have that help. Any other visions of the future? Nobody’s going to use actors. Because everyone’s going to be running on single-core VMs connected over network-ready protocols like JSON over HTTP. So, parallelism within one operating system is going to die. But until then, you should use actors. More Red Gater Coder interviews

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  • Adding Custom Object to NSMutableArray

    - by Fozz
    Developing ios app. I have an object class Product.h and .m respectively along with my picker class which implements my vehicle selection to match products to vehicle. The files product.h #import <Foundation/Foundation.h> @interface Product : NSObject { } @property (nonatomic, retain) NSString *iProductID; @property (nonatomic, retain) NSString *vchProductCode; @property (nonatomic, retain) NSString *vchPriceCode; @property (nonatomic, retain) NSString *vchHitchUPC; @property (nonatomic, retain) NSString *mHitchList; @property (nonatomic, retain) NSString *mHitchMap; @property (nonatomic, retain) NSString *fShippingWeight; @property (nonatomic, retain) NSString *vchWC; @property (nonatomic, retain) NSString *vchCapacity; @property (nonatomic, retain) NSString *txtNote1; @property (nonatomic, retain) NSString *txtNote2; @property (nonatomic, retain) NSString *txtNote3; @property (nonatomic, retain) NSString *txtNote4; @property (nonatomic, retain) NSString *vchDrilling; @property (nonatomic, retain) NSString *vchUPCList; @property (nonatomic, retain) NSString *vchExposed; @property (nonatomic, retain) NSString *vchShortDesc; @property (nonatomic, retain) NSString *iVehicleID; @property (nonatomic, retain) NSString *iProductClassID; @property (nonatomic, retain) NSString *dtDateMod; @property (nonatomic, retain) NSString *txtBullet1; @property (nonatomic, retain) NSString *txtBullet2; @property (nonatomic, retain) NSString *txtBullet3; @property (nonatomic, retain) NSString *txtBullet4; @property (nonatomic, retain) NSString *txtBullet5; @property (nonatomic, retain) NSString *iUniqueIdentifier; @property (nonatomic, retain) NSString *dtDateLastTouched; @property (nonatomic, retain) NSString *txtNote6; @property (nonatomic, retain) NSString *InstallTime; @property (nonatomic, retain) NSString *SGID; @property (nonatomic, retain) NSString *CURTID; @property (nonatomic, retain) NSString *SGRetail; @property (nonatomic, retain) NSString *SGMemPrice; @property (nonatomic, retain) NSString *InstallSheet; @property (nonatomic, retain) NSString *mHitchJobber; @property (nonatomic, retain) NSString *CatID; @property (nonatomic, retain) NSString *ParentID; -(id) initWithDict:(NSDictionary *)dic; -(NSString *) description; @end Product implementation .m #import "Product.h" @implementation Product @synthesize iProductID; @synthesize vchProductCode; @synthesize vchPriceCode; @synthesize vchHitchUPC; @synthesize mHitchList; @synthesize mHitchMap; @synthesize fShippingWeight; @synthesize vchWC; @synthesize vchCapacity; @synthesize txtNote1; @synthesize txtNote2; @synthesize txtNote3; @synthesize txtNote4; @synthesize vchDrilling; @synthesize vchUPCList; @synthesize vchExposed; @synthesize vchShortDesc; @synthesize iVehicleID; @synthesize iProductClassID; @synthesize dtDateMod; @synthesize txtBullet1; @synthesize txtBullet2; @synthesize txtBullet3; @synthesize txtBullet4; @synthesize txtBullet5; @synthesize iUniqueIdentifier; @synthesize dtDateLastTouched; @synthesize txtNote6; @synthesize InstallTime; @synthesize SGID; @synthesize CURTID; @synthesize SGRetail; @synthesize SGMemPrice; @synthesize InstallSheet; @synthesize mHitchJobber; @synthesize CatID; @synthesize ParentID; -(id) initWithDict:(NSDictionary *)dic { [super init]; //Initialize all variables self.iProductID = [[NSString alloc] initWithString:[dic objectForKey:@"iProductID"]]; self.vchProductCode = [[NSString alloc] initWithString:[dic objectForKey:@"vchProductCode"]]; self.vchPriceCode = [[NSString alloc] initWithString:[dic objectForKey:@"vchPriceCode"]]; self.vchHitchUPC = [[NSString alloc] initWithString:[dic objectForKey:@"vchHitchUPC"]]; self.mHitchList = [[NSString alloc] initWithString:[dic objectForKey:@"mHitchList"]]; self.mHitchMap = [[NSString alloc] initWithString:[dic objectForKey:@"mHitchMap"]]; self.fShippingWeight = [[NSString alloc] initWithString:[dic objectForKey:@"fShippingWeight"]]; self.vchWC = [[NSString alloc] initWithString:[dic objectForKey:@"vchWC"]]; self.vchCapacity = [[NSString alloc] initWithString:[dic objectForKey:@"vchCapacity"]]; self.txtNote1 = [[NSString alloc] initWithString:[dic objectForKey:@"txtNote1"]]; self.txtNote2 = [[NSString alloc] initWithString:[dic objectForKey:@"txtNote2"]]; self.txtNote3 = [[NSString alloc] initWithString:[dic objectForKey:@"txtNote3"]]; self.txtNote4 = [[NSString alloc] initWithString:[dic objectForKey:@"txtNote4"]]; self.vchDrilling = [[NSString alloc] initWithString:[dic objectForKey:@"vchDrilling"]]; self.vchUPCList = [[NSString alloc] initWithString:[dic objectForKey:@"vchUPCList"]]; self.vchExposed = [[NSString alloc] initWithString:[dic objectForKey:@"vchExposed"]]; self.vchShortDesc = [[NSString alloc] initWithString:[dic objectForKey:@"vchShortDesc"]]; self.iVehicleID = [[NSString alloc] initWithString:[dic objectForKey:@"iVehicleID"]]; self.iProductClassID = [[NSString alloc] initWithString:[dic objectForKey:@"iProductClassID"]]; self.dtDateMod = [[NSString alloc] initWithString:[dic objectForKey:@"dtDateMod"]]; self.txtBullet1 = [[NSString alloc] initWithString:[dic objectForKey:@"txtBullet1"]]; self.txtBullet2 = [[NSString alloc] initWithString:[dic objectForKey:@"txtBullet2"]]; self.txtBullet3 = [[NSString alloc] initWithString:[dic objectForKey:@"txtBullet3"]]; self.txtBullet4 = [[NSString alloc] initWithString:[dic objectForKey:@"txtBullet4"]]; self.txtBullet5 = [[NSString alloc] initWithString:[dic objectForKey:@"txtBullet5"]]; self.iUniqueIdentifier = [[NSString alloc] initWithString:[dic objectForKey:@"iUniqueIdentifier"]]; self.dtDateLastTouched = [[NSString alloc] initWithString:[dic objectForKey:@"dtDateLastTouched"]]; self.txtNote6 = [[NSString alloc] initWithString:[dic objectForKey:@"txtNote6"]]; self.InstallTime = [[NSString alloc] initWithString:[dic objectForKey:@"InstallTime"]]; self.SGID = [[NSString alloc] initWithString:[dic objectForKey:@"SGID"]]; self.CURTID = [[NSString alloc] initWithString:[dic objectForKey:@"CURTID"]]; self.SGRetail = [[NSString alloc] initWithString:[dic objectForKey:@"SGRetail"]]; self.SGMemPrice = [[NSString alloc] initWithString:[dic objectForKey:@"SGMemPrice"]]; self.InstallSheet = [[NSString alloc] initWithString:[dic objectForKey:@"InstallSheet"]]; self.mHitchJobber = [[NSString alloc] initWithString:[dic objectForKey:@"mHitchJobber"]]; self.CatID = [[NSString alloc] initWithString:[dic objectForKey:@"CatID"]]; self.ParentID = [[NSString alloc] initWithString:[dic objectForKey:@"ParentID"]]; return self; } -(NSString *) description { return [NSString stringWithFormat:@"iProductID = %@\n vchProductCode = %@\n vchPriceCode = %@\n vchHitchUPC = %@\n mHitchList = %@\n mHitchMap = %@\n fShippingWeight = %@\n vchWC = %@\n vchCapacity = %@\n txtNote1 = %@\n txtNote2 = %@\n txtNote3 = %@\n txtNote4 = %@\n vchDrilling = %@\n vchUPCList = %@\n vchExposed = %@\n vchShortDesc = %@\n iVehicleID = %@\n iProductClassID = %@\n dtDateMod = %@\n txtBullet1 = %@\n txtBullet2 = %@\n txtBullet3 = %@\n txtBullet4 = %@\n txtBullet4 = %@\n txtBullet5 = %@\n iUniqueIdentifier = %@\n dtDateLastTouched = %@\n txtNote6 = %@\n InstallTime = %@\n SGID = %@\n CURTID = %@\n SGRetail = %@\n SGMemPrice = %@\n InstallSheet = %@\n mHitchJobber = %@\n CatID = %@\n ParentID = %@\n", iProductID, vchProductCode, vchPriceCode, vchHitchUPC, mHitchList, mHitchMap, fShippingWeight, vchWC, vchCapacity, txtNote1, txtNote2, txtNote3, txtNote4, vchDrilling, vchUPCList, vchExposed, vchShortDesc, iVehicleID, iProductClassID, dtDateMod, txtBullet1, txtBullet2, txtBullet3, txtBullet4,txtBullet5, iUniqueIdentifier, dtDateLastTouched,txtNote6,InstallTime,SGID,CURTID,SGRetail,SGMemPrice,InstallSheet,mHitchJobber,CatID, ParentID]; } @end Ignoring the fact that its really long I also tried to just set the property but then my product didnt have any values. So I alloc'd for all properties, not sure which is "correct" the use of product picker.h #import <UIKit/UIKit.h> @class Vehicle; @class Product; @interface Picker : UITableViewController <NSXMLParserDelegate> { NSString *currentRow; NSString *currentElement; Vehicle *vehicle; } @property (nonatomic, retain) NSMutableArray *dataArray; //@property (readwrite, copy) NSString *currentRow; //@property (readwrite, copy) NSString *currentElement; -(void) getYears:(NSString *)string; -(void) getMakes:(NSString *)year; -(void) getModels:(NSString *)year: (NSString *)make; -(void) getStyles:(NSString *)year: (NSString *)make: (NSString *)model; -(void) getHitch:(NSString *)year: (NSString *)make: (NSString *)model: (NSString *)style; -(void) parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName; -(void) parser:(NSXMLParser *)parser foundCharacters:(NSString *)string; -(void) parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict; @end The implementation .m #import "Product.h" #import "Picker.h" #import "KioskAppDelegate.h" #import "JSON.h" #import "Vehicle.h" @implementation Picker @synthesize dataArray; -(void) getHitch:(NSString *)year: (NSString *)make: (NSString *)model: (NSString *)style{ currentRow = [NSString stringWithString:@"z:row"]; currentElement = [NSString stringWithString:@"gethitch"]; //Reinitialize data array [self.dataArray removeAllObjects]; [self.dataArray release]; self.dataArray = [[NSArray alloc] initWithObjects:nil]; //Build url & string NSString *thisString = [[NSString alloc] initWithString:@""]; thisString = [NSString stringWithFormat:@"http://api.curthitch.biz/AJAX_CURT.aspx?action=GetHitch&dataType=json&year=%@&make=%@&model=%@&style=%@",year,make,model,style]; //Request NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:thisString]]; //Perform request and fill data with json NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil]; //Get string from data NSString *json_string = [[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding]; //set up parser SBJsonParser *parser = [[SBJsonParser alloc] init]; //parse json into object NSArray *tempArray = [parser objectWithString:json_string error:nil]; for (NSDictionary *dic in tempArray) { Product *tempProduct = [[Product alloc] initWithDict:dic]; NSLog(@"is tempProduct valid %@", (tempProduct) ? @"YES" : @"NO"); [self.dataArray addObject:tempProduct]; } } @end So I stripped out all the table methods and misc crap that doesnt matter. In the end my problem is adding the "tempProduct" object to the mutable array dataArray so that I can customize the table cells. Using the json framework im parsing out some json which returns an array of NSDictionary objects. Stepping through that my dictionary objects look good, I populate my custom object with properties for all my fields which goes through fine, and the values look right. However I cant add this to the array, I've tried several different implementations doesn't work. Not sure what I'm doing wrong. In some instances doing a po tempProduct prints the description and sometimes it does not. same with right clicking on the variable and choosing print description. Actual error message 2011-02-22 15:53:56.058 Kiosk[8547:207] -[__NSArrayI addObject:]: unrecognized selector sent to instance 0x4e1ba40 2011-02-22 15:53:56.060 Kiosk[8547:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayI addObject:]: unrecognized selector sent to instance 0x4e1ba40' *** Call stack at first throw: ( 0 CoreFoundation 0x00dbabe9 __exceptionPreprocess + 185 1 libobjc.A.dylib 0x00f0f5c2 objc_exception_throw + 47 2 CoreFoundation 0x00dbc6fb -[NSObject(NSObject) doesNotRecognizeSelector:] + 187 3 CoreFoundation 0x00d2c366 ___forwarding___ + 966 4 CoreFoundation 0x00d2bf22 _CF_forwarding_prep_0 + 50 5 Kiosk 0x00003ead -[Picker getHitch::::] + 1091 6 Kiosk 0x00003007 -[Picker tableView:didSelectRowAtIndexPath:] + 1407 7 UIKit 0x0009b794 -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 1140 8 UIKit 0x00091d50 -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 219 9 Foundation 0x007937f6 __NSFireDelayedPerform + 441 10 CoreFoundation 0x00d9bfe3 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 19 11 CoreFoundation 0x00d9d594 __CFRunLoopDoTimer + 1220 12 CoreFoundation 0x00cf9cc9 __CFRunLoopRun + 1817 13 CoreFoundation 0x00cf9240 CFRunLoopRunSpecific + 208 14 CoreFoundation 0x00cf9161 CFRunLoopRunInMode + 97 15 GraphicsServices 0x0102e268 GSEventRunModal + 217 16 GraphicsServices 0x0102e32d GSEventRun + 115 17 UIKit 0x0003442e UIApplicationMain + 1160 18 Kiosk 0x0000239a main + 104 19 Kiosk 0x00002329 start + 53 ) terminate called after throwing an instance of 'NSException'

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