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  • Implementing synchronous MediaTypeFormatters in ASP.NET Web API

    - by cibrax
    One of main characteristics of MediaTypeFormatter’s in ASP.NET Web API is that they leverage the Task Parallel Library (TPL) for reading or writing an model into an stream. When you derive your class from the base class MediaTypeFormatter, you have to either implement the WriteToStreamAsync or ReadFromStreamAsync methods for writing or reading a model from a stream respectively. These two methods return a Task, which internally does all the serialization work, as it is illustrated bellow. public abstract class MediaTypeFormatter { public virtual Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext); public virtual Task<object> ReadFromStreamAsync(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger); }   .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } However, most of the times, serialization is a safe operation that can be done synchronously. In fact, many of the serializer classes you will find in the .NET framework only provide sync methods. So the question is, how you can transform that synchronous work into a Task ?. Creating a new task using the method Task.Factory.StartNew for doing all the serialization work would be probably the typical answer. That would work, as a new task is going to be scheduled. However, that might involve some unnecessary context switches, which are out of our control and might be affect performance on server code specially.   If you take a look at the source code of the MediaTypeFormatters shipped as part of the framework, you will notice that they actually using another pattern, which uses a TaskCompletionSource class. public Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext) {   var tsc = new TaskCompletionSource<AsyncVoid>(); tsc.SetResult(default(AsyncVoid));   //Do all the serialization work here synchronously   return tsc.Task; }   /// <summary> /// Used as the T in a "conversion" of a Task into a Task{T} /// </summary> private struct AsyncVoid { } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } They are basically doing all the serialization work synchronously and using a TaskCompletionSource for returning a task already done. To conclude this post, this is another approach you might want to consider when using serializers that are not compatible with an async model. Update: Henrik Nielsen from the ASP.NET team pointed out the existence of a built-in media type formatter for writing sync formatters. BufferedMediaTypeFormatter http://t.co/FxOfeI5x

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  • Specs, Form and Function – What am I Missing?

    - by Barry Shulam
    0 0 1 628 3586 08041 29 8 4206 14.0 Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;} Friday October 26th the Microsoft Surface RT arrived at the office.  I was summoned to my boss’s office for the grand unpacking.  If I had planned ahead I could have used my iPhone 4 to film the event and post it on YouTube however the desire to hold the device and turn it ON was more inviting than becoming a proxy reviewer for Engadget’s website.  1980 was the first time we had a personal computer in our house.  It was a  Kaypro computer. It weighed 29 pounds more than any persons lap could hold.  Then the term “portable computer” meant you could remove it from the building and take it else where.  Today I am typing on this entry on a Macbook Air which weighs 2.38 pounds. This morning Amazons front page main title is: “Much More for Much Less” I was born at the right time to start with the CPM operating system on the Kaypro thru the DOS, Windows, Linux, Mac OSX and mobile phone operating systems and languages.  If you are not aware Technology is moving at a rapid pace.  The New iPad (those who are keeping score – iPad4) is replacing a 7 month old machine the New iPad (iPad 3) I have used and owned many technology devices in my life.  The main point that most of the reader who are in the USA overlook is the fact that we are in the USA.  The devices we purchase have a great digital garden to support them.  The Kaypro computer had a 7-inch screen.  It was a TV tube with two colors – Black and Green.  You could see the 80-column screen flicker with characters – have you every played Pac-Man emulated on the screen with the ABC characters. Traveling across the world you will find that not all apps on your device will function as they did back home because they are not offered outside of your country of origin. I think the main question a buyer of technology should be asking is Function.  The greatest Specs with out function limit you.  The most beautiful form with out function is the same as a crystal vase on your shelf – not a good cereal bowl in the morning. Microsoft Surface RT, Amazon Kindle Fire and Apple iPad all great devices in their respective customers hands. My advice for those looking to purchase on this year:  If the device is your only technology device you buy what you WANT and LIKE. Consider this parallel universe if its not your only device?  Ever go shopping for clothing, shoes, and accessories with your wife, girlfriend, sister or mother?  If you listen carefully you will hear the little voices coming out of there heads saying:  “This goes well with that and I can use it also with that outfit” ”Do you think this clashes with that?”  “Ohh I love how that combination looks on you”.  Portable devices such as tablets and computers can offer a whole lot more when they are combined with the digital echo system you have at home and the manufacturer offers online. Pros of each Device: Microsoft Surface RT: There is a new functionality named SmartGlass which will let you share the content off your tablet to your XBOX 360.  Microsoft office is loaded on the tablet.  You can have more than one user profile on the tablet if you share it with others.   Amazon Kindle or Kindle HD: If you are an Amazon consumer with an annual Amazon Prime service you can consume videos and read books off the Amazon site.  Its the cheapest device.  Its a step up from the kindle reader in many ways.   Apple Ipad or Ipad mini: Over 270 Thousand applications.  Airplay permits you the ability to share to your TV screen. If you are a cord cutter (a person who gets their entertainment content over the web or air vs Cable Providers) the Airplay or Smart glass are a huge bonus.  iPad mini or not: The mini will fit in a purse where the larger one will not.  Its lighter which makes it nice to hold for prolonged periods.  It has an option for LTE wireless which non of the other sub 9 inch tables offer.  The screen is non retina which means the applications are smaller.  Speaking with individuals who are above 50 in age that wear glasses they retina does not make a difference for them however they prefer the larger iPad over the new mini.   Happy Shopping this Channuka Season.   The Kosher Coder.   Follow me on twitter @KosherCoder

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  • Data management in unexpected places

    - by Ashok_Ora
    Normal 0 false false false EN-US X-NONE X-NONE Data management in unexpected places When you think of network switches, routers, firewall appliances, etc., it may not be obvious that at the heart of these kinds of solutions is an engine that can manage huge amounts of data at very high throughput with low latencies and high availability. Consider a network router that is processing tens (or hundreds) of thousands of network packets per second. So what really happens inside a router? Packets are streaming in at the rate of tens of thousands per second. Each packet has multiple attributes, for example, a destination, associated SLAs etc. For each packet, the router has to determine the address of the next “hop” to the destination; it has to determine how to prioritize this packet. If it’s a high priority packet, then it has to be sent on its way before lower priority packets. As a consequence of prioritizing high priority packets, lower priority data packets may need to be temporarily stored (held back), but addressed fairly. If there are security or privacy requirements associated with the data packet, those have to be enforced. You probably need to keep track of statistics related to the packets processed (someone’s sure to ask). You have to do all this (and more) while preserving high availability i.e. if one of the processors in the router goes down, you have to have a way to continue processing without interruption (the customer won’t be happy with a “choppy” VoIP conversation, right?). And all this has to be achieved without ANY intervention from a human operator – the router is most likely to be in a remote location – it must JUST CONTINUE TO WORK CORRECTLY, even when bad things happen. How is this implemented? As soon as a packet arrives, it is interpreted by the receiving software. The software decodes the packet headers in order to determine the destination, kind of packet (e.g. voice vs. data), SLAs associated with the “owner” of the packet etc. It looks up the internal database of “rules” of how to process this packet and handles the packet accordingly. The software might choose to hold on to the packet safely for some period of time, if it’s a low priority packet. Ah – this sounds very much like a database problem. For each packet, you have to minimally · Look up the most efficient next “hop” towards the destination. The “most efficient” next hop can change, depending on latency, availability etc. · Look up the SLA and determine the priority of this packet (e.g. voice calls get priority over data ftp) · Look up security information associated with this data packet. It may be necessary to retrieve the context for this network packet since a network packet is a small “slice” of a session. The context for the “header” packet needs to be stored in the router, in order to make this work. · If the priority of the packet is low, then “store” the packet temporarily in the router until it is time to forward the packet to the next hop. · Update various statistics about the packet. In most cases, you have to do all this in the context of a single transaction. For example, you want to look up the forwarding address and perform the “send” in a single transaction so that the forwarding address doesn’t change while you’re sending the packet. So, how do you do all this? Berkeley DB is a proven, reliable, high performance, highly available embeddable database, designed for exactly these kinds of usage scenarios. Berkeley DB is a robust, reliable, proven solution that is currently being used in these scenarios. First and foremost, Berkeley DB (or BDB for short) is very very fast. It can process tens or hundreds of thousands of transactions per second. It can be used as a pure in-memory database, or as a disk-persistent database. BDB provides high availability – if one board in the router fails, the system can automatically failover to another board – no manual intervention required. BDB is self-administering – there’s no need for manual intervention in order to maintain a BDB application. No need to send a technician to a remote site in the middle of nowhere on a freezing winter day to perform maintenance operations. BDB is used in over 200 million deployments worldwide for the past two decades for mission-critical applications such as the one described here. You have a choice of spending valuable resources to implement similar functionality, or, you could simply embed BDB in your application and off you go! I know what I’d do – choose BDB, so I can focus on my business problem. What will you do? /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}

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  • 7 Steps To Cut Recruiting Costs & Drive Exceptional Business Results

    - by Oracle Accelerate for Midsize Companies
    By Steve Viarengo, Vice President Product Management, Oracle Taleo Cloud Services  Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 In good times, trimming operational costs is an ongoing goal. In tough times, it’s a necessity. In both good times and bad, however, recruiting occurs. Growth increases headcount in good times, and opportunistic or replacement hiring occurs in slow business cycles. By employing creative recruiting strategies in tandem with the latest technology developments, you can reduce recruiting costs while driving exceptional business results. Here are some critical areas to focus on. 1.  Target Direct Cost Savings Total recruiting process expenses are the sum of external costs plus internal labor costs. Most organizations can reduce recruiting expenses with direct cost savings. While additional savings on indirect costs can be realized from process improvement and efficiency gains, there are direct cost savings and benefits readily available in three broad areas: sourcing, assessments, and green recruiting. 2. Sourcing: Reduce Agency Costs Agency search firm fees can amount to 35 percent of a new employee’s annual base salary. Typically taken from the hiring department budget, these fees may not be visible to HR. By relying on internal mobility programs, referrals, candidate pipelines, and corporate career Websites, organizations can reduce or eliminate this agency spend. And when you do have to pay third-party agency fees, you can optimize the value you receive by collaborating with agencies to identify referred candidates, ensure access to candidate data and history, and receive automatic notifications and correspondence. 3. Sourcing: Reduce Advertising Costs You can realize significant cost reductions by placing all job positions on your corporate career Website. This will allow you to reap a substantial number of candidates at minimal cost compared to job boards and other sourcing options. 4.  Sourcing: Internal Talent Pool Internal talent pools provide a way to reduce sourcing and advertising costs while delivering improved productivity and retention. Internal redeployment reduces costs and ramp-up time while increasing retention and employee satisfaction. 5.  Sourcing: External Talent Pool Strategic recruiting requires identifying and matching people with a given set of skills to a particular job while efficiently allocating sourcing expenditures. By using an e-recruiting system (which drives external talent pool management) with a candidate relationship database, you can automate prescreening and candidate matching while communicating with targeted candidates. Candidate relationship management can lower sourcing costs by marketing new job opportunities to candidates sourced in the past. By mining the talent pool in this fashion, you eliminate the need to source a new pool of candidates for each new requisition. Managing and mining the corporate candidate database can reduce the sourcing cost per candidate by as much as 50 percent. 6.  Assessments: Reduce Turnover Costs By taking advantage of assessments during the recruitment process, you can achieve a range of benefits, including better productivity, superior candidate performance, and lower turnover (providing considerable savings). Assessments also save recruiter and hiring manager time by focusing on a short list of qualified candidates. Hired for fit, such candidates tend to stay with the organization and produce quality work—ultimately driving revenue.  7. Green Recruiting: Reduce Paper and Processing Costs You can reduce recruiting costs by automating the process—and making it green. A paperless process informs candidates that you’re dedicated to green recruiting. It also leads to direct cost savings. E-recruiting reduces energy use and pollution associated with manufacturing, transporting, and recycling paper products. And process automation saves energy in mailing, storage, handling, filing, and reporting tasks. Direct cost savings come from reduced paperwork related to résumés, advertising, and onboarding. Improving the recruiting process through sourcing, assessments, and green recruiting not only saves costs. It also positions the company to improve the talent base during the recession while retaining the ability to grow appropriately in recovery. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";}

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  • How to Inspect Javascript Object

    - by Madhan ayyasamy
    You can inspect any JavaScript objects and list them as indented, ordered by levels.It shows you type and property name. If an object property can't be accessed, an error message will be shown.Here the snippets for inspect javascript object.function inspect(obj, maxLevels, level){  var str = '', type, msg;    // Start Input Validations    // Don't touch, we start iterating at level zero    if(level == null)  level = 0;    // At least you want to show the first level    if(maxLevels == null) maxLevels = 1;    if(maxLevels < 1)             return '<font color="red">Error: Levels number must be > 0</font>';    // We start with a non null object    if(obj == null)    return '<font color="red">Error: Object <b>NULL</b></font>';    // End Input Validations    // Each Iteration must be indented    str += '<ul>';    // Start iterations for all objects in obj    for(property in obj)    {      try      {          // Show "property" and "type property"          type =  typeof(obj[property]);          str += '<li>(' + type + ') ' + property +                  ( (obj[property]==null)?(': <b>null</b>'):('')) + '</li>';          // We keep iterating if this property is an Object, non null          // and we are inside the required number of levels          if((type == 'object') && (obj[property] != null) && (level+1 < maxLevels))          str += inspect(obj[property], maxLevels, level+1);      }      catch(err)      {        // Is there some properties in obj we can't access? Print it red.        if(typeof(err) == 'string') msg = err;        else if(err.message)        msg = err.message;        else if(err.description)    msg = err.description;        else                        msg = 'Unknown';        str += '<li><font color="red">(Error) ' + property + ': ' + msg +'</font></li>';      }    }      // Close indent      str += '</ul>';    return str;}Method Call:function inspect(obj [, maxLevels [, level]]) Input Vars * obj: Object to inspect * maxLevels: Optional. Number of levels you will inspect inside the object. Default MaxLevels=1 * level: RESERVED for internal use of the functionReturn ValueHTML formatted string containing all values of inspected object obj.

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  • Fonts in menu are larger than they should be under Awesome WM

    - by janjust
    I upgraded to oneiric ocelot, running awesome wm. Everything works, more or less, fine but one thing I've noticed is that now my menu fonts and my menu symbols are larger than I'd like them to be. I used to set them in font settings, but now (for one I don't even know where font settings are anymore, I tried gnome-tweak-tool) the font-settings are gone? Surely I'm missing something. My prime example is the program evince whose symbols are ginormous. Any hints how to tweak it?

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  • How to find and change the screen DPI

    - by Luis Alvarado
    I am trying to find and then change the screen DPI in 12.04 and 12.10 but I can't seem to find any app or config file that can do this. Is there any app or conf file that I can use to change my screen dpi? Note that this is for 12.04+ so the following will not work: How do I change the font DPI settings? How to change the screen DPI in 11.10? Is it possible to change font DPI in 11.04? They are basically changing the font size, not the actual screen DPI

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  • Configuring MySQL Cluster Data Nodes

    - by Mat Keep
    0 0 1 692 3948 Homework 32 9 4631 14.0 Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-ansi-language:EN-US;} In my previous blog post, I discussed the enhanced performance and scalability delivered by extensions to the multi-threaded data nodes in MySQL Cluster 7.2. In this post, I’ll share best practices on the configuration of data nodes to achieve optimum performance on the latest generations of multi-core, multi-thread CPU designs. Configuring the Data Nodes The configuration of data node threads can be managed in two ways via the config.ini file: - Simply set MaxNoOfExecutionThreads to the appropriate number of threads to be run in the data node, based on the number of threads presented by the processors used in the host or VM. - Use the new ThreadConfig variable that enables users to configure both the number of each thread type to use and also which CPUs to bind them too. The flexible configuration afforded by the multi-threaded data node enhancements means that it is possible to optimise data nodes to use anything from a single CPU/thread up to a 48 CPU/thread server. Co-locating the MySQL Server with a single data node can fully utilize servers with 64 – 80 CPU/threads. It is also possible to co-locate multiple data nodes per server, but this is now only required for very large servers with 4+ CPU sockets dense multi-core processors. 24 Threads and Beyond! An example of how to make best use of a 24 CPU/thread server box is to configure the following: - 8 ldm threads - 4 tc threads - 3 recv threads - 3 send threads - 1 rep thread for asynchronous replication. Each of those threads should be bound to a CPU. It is possible to bind the main thread (schema management domain) and the IO threads to the same CPU in most installations. In the configuration above, we have bound threads to 20 different CPUs. We should also protect these 20 CPUs from interrupts by using the IRQBALANCE_BANNED_CPUS configuration variable in /etc/sysconfig/irqbalance and setting it to 0x0FFFFF. The reason for doing this is that MySQL Cluster generates a lot of interrupt and OS kernel processing, and so it is recommended to separate activity across CPUs to ensure conflicts with the MySQL Cluster threads are eliminated. When booting a Linux kernel it is also possible to provide an option isolcpus=0-19 in grub.conf. The result is that the Linux scheduler won't use these CPUs for any task. Only by using CPU affinity syscalls can a process be made to run on those CPUs. By using this approach, together with binding MySQL Cluster threads to specific CPUs and banning CPUs IRQ processing on these tasks, a very stable performance environment is created for a MySQL Cluster data node. On a 32 CPU/Thread server: - Increase the number of ldm threads to 12 - Increase tc threads to 6 - Provide 2 more CPUs for the OS and interrupts. - The number of send and receive threads should, in most cases, still be sufficient. On a 40 CPU/Thread server, increase ldm threads to 16, tc threads to 8 and increment send and receive threads to 4. On a 48 CPU/Thread server it is possible to optimize further by using: - 12 tc threads - 2 more CPUs for the OS and interrupts - Avoid using IO threads and main thread on same CPU - Add 1 more receive thread. Summary As both this and the previous post seek to demonstrate, the multi-threaded data node extensions not only serve to increase performance of MySQL Cluster, they also enable users to achieve significantly improved levels of utilization from current and future generations of massively multi-core, multi-thread processor designs. A big thanks to Mikael Ronstrom, Senior MySQL Architect at Oracle, for his work in developing these enhancements and best practices. You can download MySQL Cluster 7.2 today and try out all of these enhancements. The Getting Started guides are an invaluable aid to quickly building a Proof of Concept Don’t forget to check out the MySQL Cluster 7.2 New Features whitepaper to discover everything that is new in the latest GA release

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  • css - use universal '*' selector vs. html or body selector?

    - by Michael Durrant
    Applying styles to the body tag will be applied to the whole page, so body { font-family: Verdana } will be applied to the whole page. This could also be done with * {font-family: Verdana} which would apply to all elements and so would seem to have the same effect. I understand the principle that in the first instance the style is being applied to one tag, body for the whole page whereas in the second example the font is being applied against each individual html elements. What I am asking is what is the practical difference in doing that, what are the implications and what is a reason, situation or best practice that leads to using one over another. One side-effect is certainly speed (+1 Rob). I am most interested in the actual reason to choose one over the other in terms of functionality.

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  • How to properly position 3rd level menu [migrated]

    - by drewrowalnd
    If you look here: http://snippetmagazine.com/ under about isl-board of trustees you can se I have created a third level dropdown, but how can I properly align that drop down? Below you will see my css. #menudiv { width: 999px; float: left; clear: left; height: 250px; background: url(images/top_bg.png) no-repeat; margin-top: 10px; } mainmenu { width: 948px; height: 63px; float: left; margin-left: 16px; margin-top:5px; border: 1px solid #D5D5D5; -moz-border-radius: 3px; -webkit-border-radius: 3px; -webkit-box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.1); -moz-box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.1); background:url(images/nav_bg.gif) repeat; } .mainnav { margin: 0; padding: 0; list-style: none; } .mainnav * { margin: 0; padding: 0; list-style: none; } .mainnav ul { position: absolute; top: -999em; display: none; } .mainnav li { float: left; position: relative; z-index: 999; height: 63px; line-height: 55px; margin-right: 0px; border-right: 1px solid #D5D5D5; } .mainnav li.last { border-right: none; } .mainnav a { display: block; font-size: 19px; margin: 0; color: #cc9900; font-family: Copperplate, Arial, Helvetica, Sans serif; font-weight:600; text-decoration: none; padding: 3px 13px 3px 12px; color: #555; text-shadow: 0 1px 1px white; } .mainnav li:hover { text-decoration: none; border-bottom: solid 0px #ccc; background: white; } .mainnav ul li{ width: 132px; } .mainnav li:hover ul, ul.mainnav li.sfHover ul { left: 0px; top: 50px; padding-top: 0px; width: 132px; border-bottom: solid 0px #eaeaea; background: url(images/nav_dropdown_shadow.gif) repeat-x top; padding: 6px 0 0px 0px; margin: 13px 0 0 -1px; border: 1px solid #D5D5D5; -moz-border-radius-bottomleft: 3px; -webkit-border-bottom-left-radius: 3px; -moz-border-radius-bottomright: 3px; -webkit-border-bottom-right-radius: 3px; -webkit-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.1); -moz-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.1); width: 175px; border-bottom-left-radius: 3px 3px; border-bottom-right-radius: 3px 3px; } .mainnav li:hover li ul, .mainnav li.sfHover li ul { top: -999em; } .mainnav li li:hover ul, ul.mainnav li li.sfHover ul { left: 132px; top: -8px; } .mainnav li:hover ul, .mainnav li li:hover ul { top: -999em; } .mainnav li li { color: #555; display: block; padding: 0px; height: auto !important; border: none; width:175px; background: url(images/nav_dropdown_bg.gif) repeat; margin: 0; } .mainnav li li a:link, .mainnav li li a:visited { display: block; height: auto !important; line-height: 30px; color: #333; font-weight: normal; font-family: arial, helvetica, sans-serif; font-size: 12px; border: none; margin: 0; padding-left: 10px; overflow:hidden; border-bottom: 1px solid #E3E3E3; } .mainnav li li :hover{ } .mainnav li li a:hover { background: none; color:#555 ; border-bottom: 1px solid #E3E3E3; }

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  • Engineered Systems Announcements at OOW

    - by Cinzia Mascanzoni
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} See below the  announcements of new Exa systems at OOW Oracle Exadata X3 Database In-Memory Machine and  Oracle Exalogic Elastic Cloud X3-2 announcements.

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  • Who could ask for more with LESS CSS? (Part 1 of 3&ndash;Features)

    - by ToStringTheory
    It wasn’t very long ago that I first began to get into CSS precompilers such as SASS (Syntactically Awesome Stylesheets) and LESS (The Dynamic Stylesheet Language) and I had been hooked on the idea since.  When I finally had a new project come up, I leapt at the opportunity to try out one of these languages. Introduction To be honest, I was hesitant at first to add either framework as I didn’t really know much more than what I had read on their homepages, and I didn’t like the idea of adding too much complexity to a project - I couldn’t guarantee I would be the only person to support it in the future. Thankfully, both of these languages just add things into CSS.  You don’t HAVE to know LESS or SASS to do anything, you can still do your old school CSS, and your output will be the same.  However, when you want to start doing more advanced things such as variables, mixins, and color functions, the functionality is all there for you to utilize. From what I had read, SASS has a few more features than LESS, which is why I initially tried to figure out how to incorporate it into a MVC 4 project. However, through my research, I couldn’t find a way to accomplish this without including some bit of the Ruby on Rails framework on the computer running it, and I hated the fact that I had to do that.  Besides SASS, there is little chance of me getting into the RoR framework, at least in the next couple years.  So in the end, I settled with using LESS. Features So, what can LESS (or SASS) do for you?  There are several reasons I have come to love it in the past few weeks. 1 – Constants Using LESS, you can finally declare a constant and use its value across an entire CSS file. The case that most people would be familiar with is colors.  Wanting to declare one or two color variables that comprise the theme of the site, and not have to retype out their specific hex code each time, but rather a variable name.  What’s great about this is that if you end up having to change it, you only have to change it in one place.  An important thing to note is that you aren’t limited to creating constants just for colors, but for strings and measurements as well. 2 – Inheritance This is a cool feature in my mind for simplicity and organization.  Both LESS and SASS allow you to place selectors within other selectors, and when it is compiled, the languages will break the rules out as necessary and keep the inheritance chain you created in the selectors. Example LESS Code: #header {   h1 {     font-size: 26px;     font-weight: bold;   }   p {     font-size: 12px;     a     {       text-decoration: none;       &:hover {         border-width: 1px       }     }   } } Example Compiled CSS: #header h1 {   font-size: 26px;   font-weight: bold; } #header p {   font-size: 12px; } #header p a {   text-decoration: none; } #header p a:hover {   border-width: 1px; } 3 - Mixins Mixins are where languages like this really shine.  The ability to mixin other definitions setup a parametric mixin.  There is really a lot of content in this area, so I would suggest looking at http://lesscss.org for more information.  One of the things I would suggest if you do begin to use LESS is to also grab the mixins.less file from the Twitter Bootstrap project.  This file already has a bunch of predefined mixins for things like border-radius with all of the browser specific prefixes.  This alone is of great use! 4 – Color Functions This is the last thing I wanted to point out as my final post in this series will be utilizing these functions in a more drawn out manner.  Both LESS and SASS provide functions for getting information from a color (R,G,B,H,S,L).  Using these, it is easy to define a primary color, and then darken or lighten it a little for your needs.  Example: Example LESS Code: @base-color: #111; @red:        #842210; #footer {   color: (@base-color + #003300);   border-left:  2px;   border-right: 2px;   border-color: desaturate(@red, 10%); } Example Compiled CSS: #footer {    color: #114411;    border-left:  2px;    border-right: 2px;    border-color: #7d2717; } I have found that these can be very useful and powerful when constructing a site theme. Conclusion I came across LESS and SASS when looking for the best way to implement some type of CSS variables for colors, because I hated having to do a Find and Replace in all of the files using the colors, and in some instances, you couldn’t just find/replace because of the color choices interfering with other colors (color to replace of #000, yet come colors existed like #0002bc).  So in many cases I would end up having to do a Find and manually check each one. In my next post, I am going to cover how I’ve come to set up these items and the structure for the items in the project, as well as the conventions that I have come to start using.  In the final post in the series, I will cover a neat little side project I built in LESS dealing with colors!

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  • CSS being Displayed by Google spiders

    - by vipul_vj
    I have written an article HTML Image Tag for the site and it has been indexed by Google. But when I search it, google displays HTML Image Tag - ProgrammingBulls http://programmingbulls.com/html-image-tag-1: content { font-family:verdana; font-size:14px; font-weight:normal } We often use images in a webpage. To insert images in our webpage < img tag is used in. Why is CSS displayed in the google search? I know that CSS and HTML is ignored by Google but due to some reason HTML is being displayed.

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  • Retrieving recent tweets using LINQ

    - by brian_ritchie
    There are a few different APIs for accessing Twitter from .NET.  In this example, I'll use linq2twitter.  Other APIs can be found on Twitter's development site. First off, we'll use the LINQ provider to pull in the recent tweets. .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: Consolas, "Courier New", Courier, Monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } 1: public static Status[] GetLatestTweets(string screenName, int numTweets) 2: { 3: try 4: { 5: var twitterCtx = new LinqToTwitter.TwitterContext(); 6: var list = from tweet in twitterCtx.Status 7: where tweet.Type == StatusType.User && 8: tweet.ScreenName == screenName 9: orderby tweet.CreatedAt descending 10: select tweet; 11: // using Take() on array because it was failing against the provider 12: var recentTweets = list.ToArray().Take(numTweets).ToArray(); 13: return recentTweets; 14: } 15: catch 16: { 17: return new Status[0]; 18: } 19: } Once they have been retrieved, they would be placed inside an MVC model. Next, the tweets need to be formatted for display. I've defined an extension method to aid with date formatting: .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: Consolas, "Courier New", Courier, Monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } 1: public static class DateTimeExtension 2: { 3: public static string ToAgo(this DateTime date2) 4: { 5: DateTime date1 = DateTime.Now; 6: if (DateTime.Compare(date1, date2) >= 0) 7: { 8: TimeSpan ts = date1.Subtract(date2); 9: if (ts.TotalDays >= 1) 10: return string.Format("{0} days", (int)ts.TotalDays); 11: else if (ts.Hours > 2) 12: return string.Format("{0} hours", ts.Hours); 13: else if (ts.Hours > 0) 14: return string.Format("{0} hours, {1} minutes", 15: ts.Hours, ts.Minutes); 16: else if (ts.Minutes > 5) 17: return string.Format("{0} minutes", ts.Minutes); 18: else if (ts.Minutes > 0) 19: return string.Format("{0} mintutes, {1} seconds", 20: ts.Minutes, ts.Seconds); 21: else 22: return string.Format("{0} seconds", ts.Seconds); 23: } 24: else 25: return "Not valid"; 26: } 27: } Finally, here is the piece of the view used to render the tweets. .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: Consolas, "Courier New", Courier, Monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } 1: <ul class="tweets"> 2: <% 3: foreach (var tweet in Model.Tweets) 4: { 5: %> 6: <li class="tweets"> 7: <span class="tweetTime"><%=tweet.CreatedAt.ToAgo() %> ago</span>: 8: <%=tweet.Text%> 9: </li> 10: <%} %> 11: </ul>  

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  • ?My Oracle Support???????????????

    - by user763198
    Normal 0 7.8 ? 0 2 false false false EN-US ZH-CN X-NONE Normal 0 7.8 ? 0 2 false false false EN-US ZH-CN X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:????; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:105%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Cambria","serif"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:major-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:major-latin; mso-fareast-language:EN-US; mso-bidi-language:EN-US;} l ????????? ??????Help ??????? Table of Contents? ????Certification? ??,????????: My Oracle Support Help - Certifications (Doc ID 870956.5) l ????????? ?????????????????????????,???My Oracle Support Help - Certifications (Doc ID 870956.5)????????????????????,??? Global Customer Support ????? l ??????????? ????????????: http://www.oracle.com/support/contact.html l ???????????? ????????????: https://shop.oracle.com/pls/ostore/f?p=dstore:home:0:::::&tz=8:00 ????????????????,???? “Contact Us” ??? l ???????,??? Export ??? ???????:    1. ???????,????,????Copy Selected Row,??Actions?????Copy Selected Rows? 2. ??????spreadsheet,??????? email ???? ?????????????table ??,????table ??,????Printable View????????????????,?????????????? ????tables????Export??, ??????export???????CSV???? ??:???Printable View ?Export?????????,??????????????? l ?????????? ?Oracle Education ??????????: http://education.oracle.com ????????????? ???????????,???Oracle Education ??(????????????)? l ????? License codes/Keys? http://www.oracle.com/us/support/licensecodes/index.html ?????????License Codes ?????????????(?????),????????????????????Oracle license code ?????????,????Customer Support Identifier (CSI)? l ???Software Delivery Cloud ????????? ???Software Delivery Cloud ???????? (Doc ID 1070969.1) ??? http://edelivery.oracle.com/ ,Oracle Software Delivery Cloud. ??“Sign In/Register” button. ??Terms & Restrictions ????Continue ????????,????Go ????????Continue ????????? l ??????Oracle.com ???? 1, ? www.oracle.com 2, ???????“Help” 3, ?????,???“Oracle.com login FAQ” 4, ???????????? 5, Oracle.com ???????????? l ????CRM Ondemand ????? ?CRMOD ??,????????: (i) CRMOD ??????: http://www.oracle.com/us/products/applications/crmondemand/support/customer-care-support-337680.html (ii) CRMOD ?????????,?????????????????: https://ebusiness.siebel.com/odcustomercare/contact/contact_cc.asp l ???? Oracle Software Delivery Cloud ??? ????Oracle Software Delivery Cloud – ??Oracle ??????,???/????????email ???????? ???????: 1. ? www.oracle.com ?????Single Sign-On (SSO) ?? 2. ?????"Account" 3. ????,?? "Please verify account(?????)" ,????????????email ID 4. ????????,???????? l ???My Oracle Support??????Oracle Database Patchset ? 1. ?????? 2. ??Product ?Product Family: Oracle database. 3. ????:? Oracle 10.2.0.4. 4. ????:?Microsoft x64 (64-bit). 5. ??????: Patchset/Minipack. 6. ?? Go. l ?????????????FTP ??? ???? CD/DVD ? FTP ??: ???My Oracle Support ( https://support.oracle.com ) ???????Contact Us?? ???????????? CD/DVD ? FTP ???????????? ????????,????????,?????????????,????????????

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  • Change DPI setting in Windows 8.1 for the Logon Screen

    - by jmc302005
    How can the DPI setting be changed for the Logon Screen in Windows 8.1? Microsoft has added per-user DPI settings. But this means that there is no adjustable DPI setting for the Lock/Logon screen. You can change the DPI setting to be the same across all displays and this does affect the icons and font on the lock/logon screen. However, it does not affect any app/program that can run on the lock/logon screen. Ex. I use a 44" flat screen TV for my monitor on my desktop. Big enough for me to sit in my recliner and use my computer. I use the on-screen keyboard most of the time. (I don't want to keep a keyboard next to me.) The problem is that with the new DPI setup the on-screen keyboard takes up nearly half the screen, which is too big. I tried looking through the registry to see if I could find a setting for it. In the key HKEY_USERS\.DEFAULT\Control Panel\Desktop there is a string value named LogicalDPIOverride with a value of -1. I have a feeling this is where I can fix the issue. I tried changing the value to 0 and to 1 with no change in the result. Instead I noticed that after logging out and back in the -1 value was back in the registry. How can I change this default DPI? Can I use the LogPixels string that worked for DPI in Windows 7? Here are two Screen shots, one of the Lock Screen and one of the Logon Screen:

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  • Problem IIS 7.0 Locking files durring upload

    - by viscious
    I am running a server 2008 with iis7 and the ftp addon on to iis 7.0 I have the ftp site configured and mostly working Except that about 70% of the time when transferring a file the upload will hang forever. If I disconnect the ftp client and reconnect and try to upload the same file I will get an error on the client saying the file is locked. I have to restart the ftp service to clear the lock. I fired up process explorer and did a search on the file in question and sure enough the ftp service has a lock on the file and it takes around 20 minutes to release the lock on its own (and sometimes longer). This lock stays around even after I disconnect the client. Like I said this only happens about 70% of the time, the other 30% of the time it goes through just fine. Things i have verified. -Not a firewall issue. Server is using passive port range 8000-9000 which is allowed on the firewall. -Not a nat issue, server has a globally rout-able ip address -all recommended/required updates installed I have 5 other servers in a very similar configuration and this is the only one i have problems with.

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  • Error when starting qpidd as a service

    - by Sparks
    I have recently swapped from CENTOS 5 to FEDORA 17. Previously I have created my own init.d scripts successfully (albeit not for qpidd) however, in FEDORA I cannot get it to work. I have created the following script (called qpidd) in the init.d directory: #!/bin/bash # # /etc/rc.d/init.d/qpidd # # QPID/AMQP Broker scripts # # # chkconfig: 2345 20 80 # description: QPID/AMQP Broker service # processname: qpidd # pidfile: /var/lock/subsys/qpidd # Source function library. . /etc/init.d/functions SERVICENAME=qpidd start() { echo -n "Starting $SERVICENAME: " daemon qpidd -d & retval=$? touch /var/lock/subsys/$SERVICENAME return $retval } stop() { echo -n "Shutting down $SERVICENAME: " qpidd -q & retval=$? rm -f /var/lock/subsys/$SERVICENAME return $retval } case "$1" in start) start ;; stop) stop ;; status) status qpidd ;; restart) stop start ;; condrestart) [ -f /var/lock/subsys/<service> ] && restart || : ;; *) echo "Usage: $SERVICENAME {start|stop|status|restart" exit 1 ;; esac exit $? After this, I ran chkconfig --add qpidd, however, now when I run sudo service qpidd start I get the following message: Starting qpidd (via systemctl): Job failed. See system journal and 'systemctl status' for details. If I then run systemctl status qpidd I get the following message: Failed to issue method call: Unit name qpidd is not valid. I am now lost, I have search the web and Stack Overflow but cannot find anybody with similar problem, any help or direction to a website that can help would be much appreciated Sparks :)

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  • Implications of disabling the AMD Phenom's TLB patch?

    - by DMA57361
    I'm currently running a AMD Phenom X4 9600 processor (yeah, it's aging a bit, but other recent problems mean it's not getting upgraded in the immediate future), which happens to be one of the chips that suffer from the TLB errata. I recall that the first time I played with disabling the TLB patch (probably over a year ago, while playing a game that had a severe performance problem such that it was almost unplayable unless the patch was disabled) I had at least one BSOD, but I can't remeber them being particularly frequent. However, because it decreased instability, I stopped disabling the patch once I was done with the game. Now, after some recent hardware changes I was experiancing much worse performance than expected from the new hardware under some circumstances, and the TLB jumped to mind - after testing I found that disabling the patch would improve the performance to expected levels. I'm now wondering if it's worthwhile always having the patch disabled to avoid any potential slowdowns cropping up in the future, or if it is too dangerous. Everything I read states that the bug, when not patched, can causes a system lock-up in "rare circumstances". So, with the TLB patch disabled: How frequently should system lock-ups be expected? Do we know what the circumstances that trigger the lock-ups are? (Don't worry too much about being highly technical, but essentially I wonder if the chip more vunerable under heavy load, or heavy memory usage, etc?) Are there any secondary problems I should be aware of? (Don't include things that are charateristic to all lock-ups, please)

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  • Why is XSP/mono giving me file/write errors with lucence?

    - by acidzombie24
    I am using mono 2.6.7, xsp 2.8.? and i am not sure what else. I'll try downgrading xsp and whatever else. Today i notice my server randomly gets Http Error 500, internal server error. I looked in my log files http://www.pastie.org/1426236 and it appears that the problem is locking lucence which it does by creating a file called write.lock. This use to work with no problem but now it gives me pain. It will fix itself if i refresh the page several times but it will break just as easily. My other site will not work everytime i restart apache and i need to by hand delete the file (at least it doesnt get random 500 errors). However now it just says Lock obtain timed out: NativeFSLock@/var/www/SITE_2/App_Data/LuceneIndex_a/write.lock no matter what. I even chmod -R 777 the directory and still no luck. write.lock doesnt even exist. I have no clue whats going on. Any ideas?

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  • Implementing Linked Lists in C#

    - by nijhawan.saurabh
    Why? The question is why you need Linked Lists and why it is the foundation of any Abstract Data Structure. Take any of the Data Structures - Stacks, Queues, Heaps, Trees; there are two ways to go about implementing them - Using Arrays Using Linked Lists Now you use Arrays when you know about the size of the Nodes in the list at Compile time and Linked Lists are helpful where you are free to add as many Nodes to the List as required at Runtime.   How? Now, let's see how we go about implementing a Simple Linked List in C#. Note: We'd be dealing with singly linked list for time being, there's also another version of linked lists - the Doubly Linked List which maintains two pointers (NEXT and BEFORE).   Class Diagram Let's see the Class Diagram first:     Code     1 // -----------------------------------------------------------------------     2 // <copyright file="Node.cs" company="">     3 // TODO: Update copyright text.     4 // </copyright>     5 // -----------------------------------------------------------------------     6      7 namespace CSharpAlgorithmsAndDS     8 {     9     using System;    10     using System.Collections.Generic;    11     using System.Linq;    12     using System.Text;    13     14     /// <summary>    15     /// TODO: Update summary.    16     /// </summary>    17     public class Node    18     {    19         public Object data { get; set; }    20     21         public Node Next { get; set; }    22     }    23 }    24         1 // -----------------------------------------------------------------------     2 // <copyright file="LinkedList.cs" company="">     3 // TODO: Update copyright text.     4 // </copyright>     5 // -----------------------------------------------------------------------     6      7 namespace CSharpAlgorithmsAndDS     8 {     9     using System;    10     using System.Collections.Generic;    11     using System.Linq;    12     using System.Text;    13     14     /// <summary>    15     /// TODO: Update summary.    16     /// </summary>    17     public class LinkedList    18     {    19         private Node Head;    20     21         public void AddNode(Node n)    22         {    23             n.Next = this.Head;    24             this.Head = n;    25     26         }    27     28         public void printNodes()    29         {    30     31             while (Head!=null)    32             {    33                 Console.WriteLine(Head.data);    34                 Head = Head.Next;    35     36             }    37     38         }    39     }    40 }    41          1 using System;     2 using System.Collections.Generic;     3 using System.Linq;     4 using System.Text;     5      6 namespace CSharpAlgorithmsAndDS     7 {     8     class Program     9     {    10         static void Main(string[] args)    11         {    12             LinkedList ll = new LinkedList();    13             Node A = new Node();    14             A.data = "A";    15     16             Node B = new Node();    17             B.data = "B";    18     19             Node C = new Node();    20             C.data = "C";    21             ll.AddNode(A);    22             ll.AddNode(B);    23             ll.AddNode(C);    24     25             ll.printNodes();    26         }    27     }    28 }    29        Final Words This is just a start, I will add more posts on Linked List covering more operations like Delete etc. and will also explore Doubly Linked List / Implementing Stacks/ Heaps/ Trees / Queues and what not using Linked Lists.   Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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  • Difference between Factory Method and Abstract Factory design patterns using C#.Net

    - by nijhawan.saurabh
    First of all I'll just put both these patterns in context and describe their intent as in the GOF book: Factory Method: Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.   Abstract Factory: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.   Points to note:   Abstract factory pattern adds a layer of abstraction to the factory method pattern. The type of factory is not known to the client at compile time, this information is passed to the client at runtime (How it is passed is again dependent on the system, you may store this information in configuration files and the client can read it on execution). While implementing Abstract factory pattern, the factory classes can have multiple factory methods. In Abstract factory, a factory is capable of creating more than one type of product (Simpilar products are grouped together in a factory)   Sample implementation of factory method pattern   Let's see the class diagram first:                   ProductFactory.cs // ----------------------------------------------------------------------- // <copyright file="ProductFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public abstract class ProductFactory     {         /// <summary>         /// </summary>         /// <returns>         /// </returns>         public abstract Product CreateProductInstance();     } }     ProductAFactory.cs // ----------------------------------------------------------------------- // <copyright file="ProductAFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductAFactory:ProductFactory     {         public override Product CreateProductInstance()         {             return new ProductA();         }     } }         // ----------------------------------------------------------------------- // <copyright file="ProductBFactory.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductBFactory:ProductFactory     {         public override Product CreateProductInstance()         {             return new ProductB();           }     } }     // ----------------------------------------------------------------------- // <copyright file="Product.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public abstract class Product     {         public abstract string Name { get; set; }     } }     // ----------------------------------------------------------------------- // <copyright file="ProductA.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductA:Product     {         public ProductA()         {               Name = "ProductA";         }           public override string Name { get; set; }     } }       // ----------------------------------------------------------------------- // <copyright file="ProductB.cs" company=""> // TODO: Update copyright text. // </copyright> // -----------------------------------------------------------------------   namespace FactoryMethod {     using System;     using System.Collections.Generic;     using System.Linq;     using System.Text;       /// <summary>     /// TODO: Update summary.     /// </summary>     public class ProductB:Product     {          public ProductB()         {               Name = "ProductA";         }         public override string Name { get; set; }     } }     Program.cs using System; using System.Collections.Generic; using System.Linq; using System.Text;   namespace FactoryMethod {     class Program     {         static void Main(string[] args)         {             ProductFactory pf = new ProductAFactory();               Product product = pf.CreateProductInstance();             Console.WriteLine(product.Name);         }     } }       Normal 0 false false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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  • How to Load Oracle Tables From Hadoop Tutorial (Part 5 - Leveraging Parallelism in OSCH)

    - by Bob Hanckel
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Using OSCH: Beyond Hello World In the previous post we discussed a “Hello World” example for OSCH focusing on the mechanics of getting a toy end-to-end example working. In this post we are going to talk about how to make it work for big data loads. We will explain how to optimize an OSCH external table for load, paying particular attention to Oracle’s DOP (degree of parallelism), the number of external table location files we use, and the number of HDFS files that make up the payload. We will provide some rules that serve as best practices when using OSCH. The assumption is that you have read the previous post and have some end to end OSCH external tables working and now you want to ramp up the size of the loads. Using OSCH External Tables for Access and Loading OSCH external tables are no different from any other Oracle external tables.  They can be used to access HDFS content using Oracle SQL: SELECT * FROM my_hdfs_external_table; or use the same SQL access to load a table in Oracle. INSERT INTO my_oracle_table SELECT * FROM my_hdfs_external_table; To speed up the load time, you will want to control the degree of parallelism (i.e. DOP) and add two SQL hints. ALTER SESSION FORCE PARALLEL DML PARALLEL  8; ALTER SESSION FORCE PARALLEL QUERY PARALLEL 8; INSERT /*+ append pq_distribute(my_oracle_table, none) */ INTO my_oracle_table SELECT * FROM my_hdfs_external_table; There are various ways of either hinting at what level of DOP you want to use.  The ALTER SESSION statements above force the issue assuming you (the user of the session) are allowed to assert the DOP (more on that in the next section).  Alternatively you could embed additional parallel hints directly into the INSERT and SELECT clause respectively. /*+ parallel(my_oracle_table,8) *//*+ parallel(my_hdfs_external_table,8) */ Note that the "append" hint lets you load a target table by reserving space above a given "high watermark" in storage and uses Direct Path load.  In other doesn't try to fill blocks that are already allocated and partially filled. It uses unallocated blocks.  It is an optimized way of loading a table without incurring the typical resource overhead associated with run-of-the-mill inserts.  The "pq_distribute" hint in this context unifies the INSERT and SELECT operators to make data flow during a load more efficient. Finally your target Oracle table should be defined with "NOLOGGING" and "PARALLEL" attributes.   The combination of the "NOLOGGING" and use of the "append" hint disables REDO logging, and its overhead.  The "PARALLEL" clause tells Oracle to try to use parallel execution when operating on the target table. Determine Your DOP It might feel natural to build your datasets in Hadoop, then afterwards figure out how to tune the OSCH external table definition, but you should start backwards. You should focus on Oracle database, specifically the DOP you want to use when loading (or accessing) HDFS content using external tables. The DOP in Oracle controls how many PQ slaves are launched in parallel when executing an external table. Typically the DOP is something you want to Oracle to control transparently, but for loading content from Hadoop with OSCH, it's something that you will want to control. Oracle computes the maximum DOP that can be used by an Oracle user. The maximum value that can be assigned is an integer value typically equal to the number of CPUs on your Oracle instances, times the number of cores per CPU, times the number of Oracle instances. For example, suppose you have a RAC environment with 2 Oracle instances. And suppose that each system has 2 CPUs with 32 cores. The maximum DOP would be 128 (i.e. 2*2*32). In point of fact if you are running on a production system, the maximum DOP you are allowed to use will be restricted by the Oracle DBA. This is because using a system maximum DOP can subsume all system resources on Oracle and starve anything else that is executing. Obviously on a production system where resources need to be shared 24x7, this can’t be allowed to happen. The use cases for being able to run OSCH with a maximum DOP are when you have exclusive access to all the resources on an Oracle system. This can be in situations when your are first seeding tables in a new Oracle database, or there is a time where normal activity in the production database can be safely taken off-line for a few hours to free up resources for a big incremental load. Using OSCH on high end machines (specifically Oracle Exadata and Oracle BDA cabled with Infiniband), this mode of operation can load up to 15TB per hour. The bottom line is that you should first figure out what DOP you will be allowed to run with by talking to the DBAs who manage the production system. You then use that number to derive the number of location files, and (optionally) the number of HDFS data files that you want to generate, assuming that is flexible. Rule 1: Find out the maximum DOP you will be allowed to use with OSCH on the target Oracle system Determining the Number of Location Files Let’s assume that the DBA told you that your maximum DOP was 8. You want the number of location files in your external table to be big enough to utilize all 8 PQ slaves, and you want them to represent equally balanced workloads. Remember location files in OSCH are metadata lists of HDFS files and are created using OSCH’s External Table tool. They also represent the workload size given to an individual Oracle PQ slave (i.e. a PQ slave is given one location file to process at a time, and only it will process the contents of the location file.) Rule 2: The size of the workload of a single location file (and the PQ slave that processes it) is the sum of the content size of the HDFS files it lists For example, if a location file lists 5 HDFS files which are each 100GB in size, the workload size for that location file is 500GB. The number of location files that you generate is something you control by providing a number as input to OSCH’s External Table tool. Rule 3: The number of location files chosen should be a small multiple of the DOP Each location file represents one workload for one PQ slave. So the goal is to keep all slaves busy and try to give them equivalent workloads. Obviously if you run with a DOP of 8 but have 5 location files, only five PQ slaves will have something to do and the other three will have nothing to do and will quietly exit. If you run with 9 location files, then the PQ slaves will pick up the first 8 location files, and assuming they have equal work loads, will finish up about the same time. But the first PQ slave to finish its job will then be rescheduled to process the ninth location file, potentially doubling the end to end processing time. So for this DOP using 8, 16, or 32 location files would be a good idea. Determining the Number of HDFS Files Let’s start with the next rule and then explain it: Rule 4: The number of HDFS files should try to be a multiple of the number of location files and try to be relatively the same size In our running example, the DOP is 8. This means that the number of location files should be a small multiple of 8. Remember that each location file represents a list of unique HDFS files to load, and that the sum of the files listed in each location file is a workload for one Oracle PQ slave. The OSCH External Table tool will look in an HDFS directory for a set of HDFS files to load.  It will generate N number of location files (where N is the value you gave to the tool). It will then try to divvy up the HDFS files and do its best to make sure the workload across location files is as balanced as possible. (The tool uses a greedy algorithm that grabs the biggest HDFS file and delegates it to a particular location file. It then looks for the next biggest file and puts in some other location file, and so on). The tools ability to balance is reduced if HDFS file sizes are grossly out of balance or are too few. For example suppose my DOP is 8 and the number of location files is 8. Suppose I have only 8 HDFS files, where one file is 900GB and the others are 100GB. When the tool tries to balance the load it will be forced to put the singleton 900GB into one location file, and put each of the 100GB files in the 7 remaining location files. The load balance skew is 9 to 1. One PQ slave will be working overtime, while the slacker PQ slaves are off enjoying happy hour. If however the total payload (1600 GB) were broken up into smaller HDFS files, the OSCH External Table tool would have an easier time generating a list where each workload for each location file is relatively the same.  Applying Rule 4 above to our DOP of 8, we could divide the workload into160 files that were approximately 10 GB in size.  For this scenario the OSCH External Table tool would populate each location file with 20 HDFS file references, and all location files would have similar workloads (approximately 200GB per location file.) As a rule, when the OSCH External Table tool has to deal with more and smaller files it will be able to create more balanced loads. How small should HDFS files get? Not so small that the HDFS open and close file overhead starts having a substantial impact. For our performance test system (Exadata/BDA with Infiniband), I compared three OSCH loads of 1 TiB. One load had 128 HDFS files living in 64 location files where each HDFS file was about 8GB. I then did the same load with 12800 files where each HDFS file was about 80MB size. The end to end load time was virtually the same. However when I got ridiculously small (i.e. 128000 files at about 8MB per file), it started to make an impact and slow down the load time. What happens if you break rules 3 or 4 above? Nothing draconian, everything will still function. You just won’t be taking full advantage of the generous DOP that was allocated to you by your friendly DBA. The key point of the rules articulated above is this: if you know that HDFS content is ultimately going to be loaded into Oracle using OSCH, it makes sense to chop them up into the right number of files roughly the same size, derived from the DOP that you expect to use for loading. Next Steps So far we have talked about OLH and OSCH as alternative models for loading. That’s not quite the whole story. They can be used together in a way that provides for more efficient OSCH loads and allows one to be more flexible about scheduling on a Hadoop cluster and an Oracle Database to perform load operations. The next lesson will talk about Oracle Data Pump files generated by OLH, and loaded using OSCH. It will also outline the pros and cons of using various load methods.  This will be followed up with a final tutorial lesson focusing on how to optimize OLH and OSCH for use on Oracle's engineered systems: specifically Exadata and the BDA. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}

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  • XNA Xbox 360 Content Manager Thread freezing Draw Thread

    - by Alikar
    I currently have a game that takes in large images, easily bigger than 1MB, to serve as backgrounds. I know exactly when this transition is supposed to take place, so I made a loader class to handle loading these large images in the background, but when I load the images it still freezes the main thread where the drawing takes place. Since this code runs on the 360 I move the thread to the 4th hardware thread, but that doesn't seem to help. Below is the class I am using. Any thoughts as to why my new content manager which should be in its own thread is interrupting the draw in my main thread would be appreciated. namespace FileSystem { /// <summary> /// This is used to reference how many objects reference this texture. /// Everytime someone references a texture we increase the iNumberOfReferences. /// When a class calls remove on a specific texture we check to see if anything /// else is referencing the class, if it is we don't remove it. If there isn't /// anything referencing the texture its safe to dispose of. /// </summary> class TextureContainer { public uint uiNumberOfReferences = 0; public Texture2D texture; } /// <summary> /// This class loads all the files from the Content. /// </summary> static class FileManager { static Microsoft.Xna.Framework.Content.ContentManager Content; static EventWaitHandle wh = new AutoResetEvent(false); static Dictionary<string, TextureContainer> Texture2DResourceDictionary; static List<Texture2D> TexturesToDispose; static List<String> TexturesToLoad; static int iProcessor = 4; private static object threadMutex = new object(); private static object Texture2DMutex = new object(); private static object loadingMutex = new object(); private static bool bLoadingTextures = false; /// <summary> /// Returns if we are loading textures or not. /// </summary> public static bool LoadingTexture { get { lock (loadingMutex) { return bLoadingTextures; } } } /// <summary> /// Since this is an static class. This is the constructor for the file loadeder. This is the version /// for the Xbox 360. /// </summary> /// <param name="_Content"></param> public static void Initalize(IServiceProvider serviceProvider, string rootDirectory, int _iProcessor ) { Content = new Microsoft.Xna.Framework.Content.ContentManager(serviceProvider, rootDirectory); Texture2DResourceDictionary = new Dictionary<string, TextureContainer>(); TexturesToDispose = new List<Texture2D>(); iProcessor = _iProcessor; CreateThread(); } /// <summary> /// Since this is an static class. This is the constructor for the file loadeder. /// </summary> /// <param name="_Content"></param> public static void Initalize(IServiceProvider serviceProvider, string rootDirectory) { Content = new Microsoft.Xna.Framework.Content.ContentManager(serviceProvider, rootDirectory); Texture2DResourceDictionary = new Dictionary<string, TextureContainer>(); TexturesToDispose = new List<Texture2D>(); CreateThread(); } /// <summary> /// Creates the thread incase we wanted to set up some parameters /// Outside of the constructor. /// </summary> static public void CreateThread() { Thread t = new Thread(new ThreadStart(StartThread)); t.Start(); } // This is the function that we thread. static public void StartThread() { //BBSThreadClass BBSTC = (BBSThreadClass)_oData; FileManager.Execute(); } /// <summary> /// This thread shouldn't be called by the outside world. /// It allows the File Manager to loop. /// </summary> static private void Execute() { // Make sure our thread is on the correct processor on the XBox 360. #if WINDOWS #else Thread.CurrentThread.SetProcessorAffinity(new int[] { iProcessor }); Thread.CurrentThread.IsBackground = true; #endif // This loop will load textures into ram for us away from the main thread. while (true) { wh.WaitOne(); // Locking down our data while we process it. lock (threadMutex) { lock (loadingMutex) { bLoadingTextures = true; } bool bContainsKey = false; for (int con = 0; con < TexturesToLoad.Count; con++) { // If we have already loaded the texture into memory reference // the one in the dictionary. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(TexturesToLoad[con]); } if (bContainsKey) { // Do nothing } // Otherwise load it into the dictionary and then reference the // copy in the dictionary else { TextureContainer TC = new TextureContainer(); TC.uiNumberOfReferences = 1; // We start out with 1 referece. // Loading the texture into memory. try { TC.texture = Content.Load<Texture2D>(TexturesToLoad[con]); // This is passed into the dictionary, thus there is only one copy of // the texture in memory. // There is an issue with Sprite Batch and disposing textures. // This will have to wait until its figured out. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(TexturesToLoad[con]); Texture2DResourceDictionary.Add(TexturesToLoad[con], TC); } // We don't have the find the reference to the container since we // already have it. } // Occasionally our texture will already by loaded by another thread while // this thread is operating. This mainly happens on the first level. catch (Exception e) { // If this happens we don't worry about it since this thread only loads // texture data and if its already there we don't need to load it. } } Thread.Sleep(100); } } lock (loadingMutex) { bLoadingTextures = false; } } } static public void LoadTextureList(List<string> _textureList) { // Ensuring that we can't creating threading problems. lock (threadMutex) { TexturesToLoad = _textureList; } wh.Set(); } /// <summary> /// This loads a 2D texture which represents a 2D grid of Texels. /// </summary> /// <param name="_textureName">The name of the picture you wish to load.</param> /// <returns>Holds the image data.</returns> public static Texture2D LoadTexture2D( string _textureName ) { TextureContainer temp; lock (Texture2DMutex) { bool bContainsKey = false; // If we have already loaded the texture into memory reference // the one in the dictionary. lock (Texture2DMutex) { bContainsKey = Texture2DResourceDictionary.ContainsKey(_textureName); if (bContainsKey) { temp = Texture2DResourceDictionary[_textureName]; temp.uiNumberOfReferences++; // Incrementing the number of references } // Otherwise load it into the dictionary and then reference the // copy in the dictionary else { TextureContainer TC = new TextureContainer(); TC.uiNumberOfReferences = 1; // We start out with 1 referece. // Loading the texture into memory. try { TC.texture = Content.Load<Texture2D>(_textureName); // This is passed into the dictionary, thus there is only one copy of // the texture in memory. } // Occasionally our texture will already by loaded by another thread while // this thread is operating. This mainly happens on the first level. catch(Exception e) { temp = Texture2DResourceDictionary[_textureName]; temp.uiNumberOfReferences++; // Incrementing the number of references } // There is an issue with Sprite Batch and disposing textures. // This will have to wait until its figured out. Texture2DResourceDictionary.Add(_textureName, TC); // We don't have the find the reference to the container since we // already have it. temp = TC; } } } // Return a reference to the texture return temp.texture; } /// <summary> /// Go through our dictionary and remove any references to the /// texture passed in. /// </summary> /// <param name="texture">Texture to remove from texture dictionary.</param> public static void RemoveTexture2D(Texture2D texture) { foreach (KeyValuePair<string, TextureContainer> pair in Texture2DResourceDictionary) { // Do our references match? if (pair.Value.texture == texture) { // Only one object or less holds a reference to the // texture. Logically it should be safe to remove. if (pair.Value.uiNumberOfReferences <= 1) { // Grabing referenc to texture TexturesToDispose.Add(pair.Value.texture); // We are about to release the memory of the texture, // thus we make sure no one else can call this member // in the dictionary. Texture2DResourceDictionary.Remove(pair.Key); // Once we have removed the texture we don't want to create an exception. // So we will stop looking in the list since it has changed. break; } // More than one Object has a reference to this texture. // So we will not be removing it from memory and instead // simply marking down the number of references by 1. else { pair.Value.uiNumberOfReferences--; } } } } /*public static void DisposeTextures() { int Count = TexturesToDispose.Count; // If there are any textures to dispose of. if (Count > 0) { for (int con = 0; con < TexturesToDispose.Count; con++) { // =!THIS REMOVES THE TEXTURE FROM MEMORY!= // This is not like a normal dispose. This will actually // remove the object from memory. Texture2D is inherited // from GraphicsResource which removes it self from // memory on dispose. Very nice for game efficency, // but "dangerous" in managed land. Texture2D Temp = TexturesToDispose[con]; Temp.Dispose(); } // Remove textures we've already disposed of. TexturesToDispose.Clear(); } }*/ /// <summary> /// This loads a 2D texture which represnets a font. /// </summary> /// <param name="_textureName">The name of the font you wish to load.</param> /// <returns>Holds the font data.</returns> public static SpriteFont LoadFont( string _fontName ) { SpriteFont temp = Content.Load<SpriteFont>( _fontName ); return temp; } /// <summary> /// This loads an XML document. /// </summary> /// <param name="_textureName">The name of the XML document you wish to load.</param> /// <returns>Holds the XML data.</returns> public static XmlDocument LoadXML( string _fileName ) { XmlDocument temp = Content.Load<XmlDocument>( _fileName ); return temp; } /// <summary> /// This loads a sound file. /// </summary> /// <param name="_fileName"></param> /// <returns></returns> public static SoundEffect LoadSound( string _fileName ) { SoundEffect temp = Content.Load<SoundEffect>(_fileName); return temp; } } }

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  • C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

    - by James Michael Hare
    So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton, the basic Design Pattern is that a Singleton class is one where there is only ever one instance of the class created.  This means that constructors must be private to avoid users creating their own instances, and a static property (or method in languages without properties) is defined that returns a single static instance. 1: public class Singleton 2: { 3: // the single instance is defined in a static field 4: private static readonly Singleton _instance = new Singleton(); 5:  6: // constructor private so users can't instantiate on their own 7: private Singleton() 8: { 9: } 10:  11: // read-only property that returns the static field 12: public static Singleton Instance 13: { 14: get 15: { 16: return _instance; 17: } 18: } 19: } This is the most basic singleton, notice the key features: Static readonly field that contains the one and only instance. Constructor is private so it can only be called by the class itself. Static property that returns the single instance. Looks like it satisfies, right?  There's just one (potential) problem.  C# gives you no guarantee of when the static field _instance will be created.  This is because the C# standard simply states that classes (which are marked in the IL as BeforeFieldInit) can have their static fields initialized any time before the field is accessed.  This means that they may be initialized on first use, they may be initialized at some other time before, you can't be sure when. So what if you want to guarantee your instance is truly lazy.  That is, that it is only created on first call to Instance?  Well, there's a few ways to do this.  First we'll show the old ways, and then talk about how .Net 4.0's new System.Lazy<T> type can help make the lazy-Singleton cleaner. Obviously, we could take on the lazy construction ourselves, but being that our Singleton may be accessed by many different threads, we'd need to lock it down. 1: public class LazySingleton1 2: { 3: // lock for thread-safety laziness 4: private static readonly object _mutex = new object(); 5:  6: // static field to hold single instance 7: private static LazySingleton1 _instance = null; 8:  9: // property that does some locking and then creates on first call 10: public static LazySingleton1 Instance 11: { 12: get 13: { 14: if (_instance == null) 15: { 16: lock (_mutex) 17: { 18: if (_instance == null) 19: { 20: _instance = new LazySingleton1(); 21: } 22: } 23: } 24:  25: return _instance; 26: } 27: } 28:  29: private LazySingleton1() 30: { 31: } 32: } This is a standard double-check algorithm so that you don't lock if the instance has already been created.  However, because it's possible two threads can go through the first if at the same time the first time back in, you need to check again after the lock is acquired to avoid creating two instances. Pretty straightforward, but ugly as all heck.  Well, you could also take advantage of the C# standard's BeforeFieldInit and define your class with a static constructor.  It need not have a body, just the presence of the static constructor will remove the BeforeFieldInit attribute on the class and guarantee that no fields are initialized until the first static field, property, or method is called.   1: public class LazySingleton2 2: { 3: // because of the static constructor, this won't get created until first use 4: private static readonly LazySingleton2 _instance = new LazySingleton2(); 5:  6: // Returns the singleton instance using lazy-instantiation 7: public static LazySingleton2 Instance 8: { 9: get { return _instance; } 10: } 11:  12: // private to prevent direct instantiation 13: private LazySingleton2() 14: { 15: } 16:  17: // removes BeforeFieldInit on class so static fields not 18: // initialized before they are used 19: static LazySingleton2() 20: { 21: } 22: } Now, while this works perfectly, I hate it.  Why?  Because it's relying on a non-obvious trick of the IL to guarantee laziness.  Just looking at this code, you'd have no idea that it's doing what it's doing.  Worse yet, you may decide that the empty static constructor serves no purpose and delete it (which removes your lazy guarantee).  Worse-worse yet, they may alter the rules around BeforeFieldInit in the future which could change this. So, what do I propose instead?  .Net 4.0 adds the System.Lazy type which guarantees thread-safe lazy-construction.  Using System.Lazy<T>, we get: 1: public class LazySingleton3 2: { 3: // static holder for instance, need to use lambda to construct since constructor private 4: private static readonly Lazy<LazySingleton3> _instance 5: = new Lazy<LazySingleton3>(() => new LazySingleton3()); 6:  7: // private to prevent direct instantiation. 8: private LazySingleton3() 9: { 10: } 11:  12: // accessor for instance 13: public static LazySingleton3 Instance 14: { 15: get 16: { 17: return _instance.Value; 18: } 19: } 20: } Note, you need your lambda to call the private constructor as Lazy's default constructor can only call public constructors of the type passed in (which we can't have by definition of a Singleton).  But, because the lambda is defined inside our type, it has access to the private members so it's perfect. Note how the Lazy<T> makes it obvious what you're doing (lazy construction), instead of relying on an IL generation side-effect.  This way, it's more maintainable.  Lazy<T> has many other uses as well, obviously, but I really love how elegant and readable it makes the lazy Singleton.

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