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  • How to Program AWS Spot Instances to Strategically Bid So the Auction is Never Lost Until a Competitor Beats the Maximum I'm Willing to Pay?

    - by Taal
    I believe I'm in the right section of stack exchange to ask this. If not, let me know. I only use Amazon Web Services for temporary type hosting services, so the spot instances are quite valuable to me. I would also just make an instance and start and stop it - but - that doesn't necessarily fit my bootstrapped budget sadly. Anyways, it really kills me when someone outbids me on a spot instance I have (I tend to go for the larger ones which there are fewer of available) and I get randomly kicked off. I know or at least I believe there is a way to program in something somehow to dynamically change your bidding price to beat a potential competitor's if their's is higher than yours. Now, I previously believed Amazon would just charge me for the highest price right above the next lowest competitor automatically (eliminating the need for this) - so if I bid too high, then I only pay what I would of needed to in order to win and keep the auction. Essentially, I thought my bid price was my max bid price. Apparently, according to my bills and several experiments I've done - this is not the case. They charge me for whatever I bid even when I know there is no one else around to counter bid me. I needed to clarify that, but let me get back to the main point: Let's say I'm bidding $0.50, competitor comes in and bids 0.55 cents. I get kicked off. I want to have it to where I'd set a maximum I'm willing to pay (let's say $1.00 here), and then when competitor comes in and tries to bid $.55, my bid is dynamically adjusted to beat his at $0.56 up until he breaks my $1.00 threshold. I've been reading the guides and although they are more or less straightforward, I feel like they leave a few holes in them that end up confusing me. Like, for instance, where do I input said command or when do I do it? Maybe I'm just tech illiterate and need help deciphering these guides. A good start for someone willing to answer/help me decipher this problem would be here: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-as-update-bid.html

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  • Does OO, TDD, and Refactoring to Smaller Functions affect Speed of Code?

    - by Dennis
    In Computer Science field, I have noticed a notable shift in thinking when it comes to programming. The advice as it stands now is write smaller, more testable code refactor existing code into smaller and smaller chunks of code until most of your methods/functions are just a few lines long write functions that only do one thing (which makes them smaller again) This is a change compared to the "old" or "bad" code practices where you have methods spanning 2500 lines, and big classes doing everything. My question is this: when it call comes down to machine code, to 1s and 0s, to assembly instructions, should I be at all concerned that my class-separated code with variety of small-to-tiny functions generates too much extra overhead? While I am not exactly familiar with how OO code and function calls are handled in ASM in the end, I do have some idea. I assume that each extra function call, object call, or include call (in some languages), generate an extra set of instructions, thereby increasing code's volume and adding various overhead, without adding actual "useful" code. I also imagine that good optimizations can be done to ASM before it is actually ran on the hardware, but that optimization can only do so much too. Hence, my question -- how much overhead (in space and speed) does well-separated code (split up across hundreds of files, classes, and methods) actually introduce compared to having "one big method that contains everything", due to this overhead? UPDATE for clarity: I am assuming that adding more and more functions and more and more objects and classes in a code will result in more and more parameter passing between smaller code pieces. It was said somewhere (quote TBD) that up to 70% of all code is made up of ASM's MOV instruction - loading CPU registers with proper variables, not the actual computation being done. In my case, you load up CPU's time with PUSH/POP instructions to provide linkage and parameter passing between various pieces of code. The smaller you make your pieces of code, the more overhead "linkage" is required. I am concerned that this linkage adds to software bloat and slow-down and I am wondering if I should be concerned about this, and how much, if any at all, because current and future generations of programmers who are building software for the next century, will have to live with and consume software built using these practices. UPDATE: Multiple files I am writing new code now that is slowly replacing old code. In particular I've noted that one of the old classes was a ~3000 line file (as mentioned earlier). Now it is becoming a set of 15-20 files located across various directories, including test files and not including PHP framework I am using to bind some things together. More files are coming as well. When it comes to disk I/O, loading multiple files is slower than loading one large file. Of course not all files are loaded, they are loaded as needed, and disk caching and memory caching options exist, and yet still I believe that loading multiple files takes more processing than loading a single file into memory. I am adding that to my concern.

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  • How is this "interface"-like structure/pattern called?

    - by Sebastian Negraszus
    Let's assume we have an XmlDoc class that contains basic functionality for dealing with an XML data structure and saving/loading data to/from a file. Now we have several subclasses, A, B and C. They all inherit from XmlDoc and add component-specific methods for setting and getting lots of data. They are like "interfaces" but also add an implementation for the signatures. Finally, we have an ABCDoc class that joins all the "interfaces" via virtual multiple inheritence and adds some ABCDoc-specific stuff, such as using XMLDoc-methods to set an appropriate doc type. We may also have an ADoc class for only saving A data. How is this pattern called? "Interface" is not really the right word since interfaces usually do not contain an implementation. Bonus points for C++ code conventions.

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  • Best Practice to return responses from service

    - by A9S6
    I am writing a SOAP based ASP.NET Web Service having a number of methods to deal with Client objects. e.g: int AddClient(Client c) = returns Client ID when successful List GetClients() Client GetClientInfo(int clientId) In the above methods, the return value/object for each method corresponds to the "all good" scenario i.e. A client Id will be returned if AddClient was successful or a List< of Client objects will be returned by GetClients. But what if an error occurs, how do I convey the error message to the caller? I was thinking of having a Response class: Response { StatusCode, StatusMessage, Details } where Details will hold the actual response but in that case the caller will have to cast the response every time. What are your views on the above? Is there a better solution? ---------- UPDATED ----------- Is there something new in WCF for the above? What difference will it make If I change the ASP.NET Web Service to a WCF Service?

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  • "more than 3 levels of indentation, you're screwed" How should I understand this quote ?

    - by jokoon
    The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program. What can I deduct from this quote ? On top of the fact that too long methods are hard to maintain, are they hard or impossible to optimize for the compiler ? I don't really understand if this quote encourages better coding practice or is really a mathematical/algorithmic sort of truth... I also read in some C++ optimizing guide that dividing up a program into more function improves its design is a common thing taught at school, but it should be not done too much, since it can turn into a lot of JMP calls (even if the compiler can inline some methods by itself).

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  • Guidelines for creating referentially transparent callables

    - by max
    In some cases, I want to use referentially transparent callables while coding in Python. My goals are to help with handling concurrency, memoization, unit testing, and verification of code correctness. I want to write down clear rules for myself and other developers to follow that would ensure referential transparency. I don't mind that Python won't enforce any rules - we trust ourselves to follow them. Note that we never modify functions or methods in place (i.e., by hacking into the bytecode). Would the following make sense? A callable object c of class C will be referentially transparent if: Whenever the returned value of c(...) depends on any instance attributes, global variables, or disk files, such attributes, variables, and files must not change for the duration of the program execution; the only exception is that instance attributes may be changed during instance initialization. When c(...) is executed, no modifications to the program state occur that may affect the behavior of any object accessed through its "public interface" (as defined by us). If we don't put any restrictions on what "public interface" includes, then rule #2 becomes: When c(...) is executed, no objects are modified that are visible outside the scope of c.__call__. Note: I unsuccessfully tried to ask this question on SO, but I'm hoping it's more appropriate to this site.

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  • Imperative vs. component based programming [closed]

    - by AlexW
    I've been thinking about how programming and more specifically the teaching of programming is advocated amongst the community (online). Often I've heard that Ruby and RoR is an ideal platform for learning to program. I completely disagree... RoR and Ruby are based on the application of the component based paradigm, which means they are ideal for rapid application development. This is much like the MVC model in PHP and ASP.NET But, learning a proper imperative language like Java or C/C++ (or even Perl and PHP) is the only way for a new programmer to explore logic itself, and not get too bogged down in architectural concerns like the need for separation of concerns, and the preference for components. Maybe it's a personal preference thing. I rather think that the most interesting aspects to programming are the procedural bits of code I write that actually do stuff rather than the project planning, and modelling that comes about from fully object oriented engineering or simply using the MVC model. I know this may sound confused to some of you. I feel strongly though that the best way for programming to be taught is through imperative and procedural methods. Architectural (component) methods come later, if at all. After all, none of the amazing algorithms that exist were based on OOP practice! It's all procedural code when it comes to the 'magic'. OOP is useful in creating products and utilities. Algorithms are what makes things happen, and move data around, and so imperative (and/or procedural) code are what matters most. When I see programmers recommending Ruby on Rails to newbie developers, I think it's just so wrong. Just because you write less code with Ruby does not make it easier to do! It's the opposite... you have to know loads more to appreciate its succinct nature. New coders who really want to understand the nuts and bolts of coding need to go away and figure out writing methods/functions (i.e. imperative programming) and working in procedural style, in order to grasp the fundamentals, first, before looking into architectural ways of working. So, my question is: should Ruby ever be recommended as a first language? I think no (obviously)... what arguments are there for it?

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  • Should I implement an interface directly or have the superclass do it?

    - by c_maker
    Is there a difference between public class A extends AbstractB implements C {...} versus... public class A extends AbstractB {...} AbstractB implements C {...} I understand that in both cases, class A will end up conforming to the interface. In the second case, AbstractB can provide implementation for interface methods in C. Is that the only difference? If I do NOT want to provide an implementation for any of the interface methods in AbstractB, which style should I be using? Does using one or the other have some hidden 'documentation' purpose?

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  • Amazon EC2 Sign In

    - by Barry
    When I change the home directory of my Amazon EC2 instance from /home/ubuntu to /home/ubuntu/folder in the /etc/passwd file, I am no longer able to access the instance using my existing keypair. Once I switch it back to the original directory I have no problems and can log into my instance as normal. I have checked the permissions on the new folder and they are drwxr-xr-x, which is the same the /home/ubuntu folder. I have a number of instances running at the minute and because of this change I have no way of logging back into them to rectify the situation. Does anyone have an idea what is going on? Thanks in advance

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  • Port forwarding using IP Tables

    - by Darider
    I have a server with a LAN facing address of 192.168.5.100 (eth0) and another LAN facing address of 192.168.6.6 (eth1). On this server I have a Virtualbox instance of fedora running an apache webserver (on port 8080) with a bridged interface to eth1 on the host server with address of 192.168.6.7 Users on the 192.168.6.x network can access the Webserver on the Vbox instance (192.168.6.7) with no problems. My question is what kind of iptables entries or commands should be made/executed so as to allow for users on the 192.168.5.x network to access the webserver on the vbox instance. (I'm hoping their url can be something like: http://192.168.5.100:8080)

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  • Need Information On Importing Data Into The Oracle Product Hub?

    - by LuciaC
    One of the key challenges of implementing a Master Data Management solution is importing data into the system. Oracle Product Hub offers numerous ways of importing the setup data and the actual product data.  Review all available methods to import data in the White Paper Doc ID 1504980.1 which provides details and examples of each method, discusses special cases, and provides some troubleshooting tips.The methods reviewed include:     FNDLOAD     iSetup     Interfaces and Public APIs     Import from Excel     Web Application Desktop Integrator     Webservices

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  • Cannot login SQL Server after changing machine name

    - by Ucodia
    After installing and setting up new machines in a domain, we decided to rename one of them which had a SQL Server instance installed. So I changed the hostname, everything went fine regarding the domain but now, the server is logging a approximatively 2 SQL Server errors every 5 minutes and I cannot connect to the instance localy or from anywhere within the domain. Here is the error from the event log: SSPI handshake failed with error code 0x8009030c, state 14 while establishing a connection with integrated security; the connection has been closed. Reason: AcceptSecurityContext failed. The Windows error code indicates the cause of failure. The logon attempt failed [CLIENT: x.x.x.x] Concerning the instance, everything is started and restarted without any extra error.

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  • "Collection Wrapper" pattern - is this common?

    - by Prog
    A different question of mine had to do with encapsulating member data structures inside classes. In order to understand this question better please read that question and look at the approach discussed. One of the guys who answered that question said that the approach is good, but if I understood him correctly - he said that there should be a class existing just for the purpose of wrapping the collection, instead of an ordinary class offering a number of public methods just to access the member collection. For example, instead of this: class SomeClass{ // downright exposing the concrete collection. Things[] someCollection; // other stuff omitted Thing[] getCollection(){return someCollection;} } Or this: class SomeClass{ // encapsulating the collection, but inflating the class' public interface. Thing[] someCollection; // class functionality omitted. public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } We'll have this: // encapsulating the collection - in a different class, dedicated to this. class SomeClass{ CollectionWrapper someCollection; CollectionWrapper getCollection(){return someCollection;} } class CollectionWrapper{ Thing[] someCollection; public Thing getThing(int index){ return someCollection[index]; } public int getSize(){ return someCollection.length; } public void setThing(int index, Thing thing){ someCollection[index] = thing; } public void removeThing(int index){ someCollection[index] = null; } } This way, the inner data structure in SomeClass can change without affecting client code, and without forcing SomeClass to offer a lot of public methods just to access the inner collection. CollectionWrapper does this instead. E.g. if the collection changes from an array to a List, the internal implementation of CollectionWrapper changes, but client code stays the same. Also, the CollectionWrapper can hide certain things from the client code - from example, it can disallow mutation to the collection by not having the methods setThing and removeThing. This approach to decoupling client code from the concrete data structure seems IMHO pretty good. Is this approach common? What are it's downfalls? Is this used in practice?

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  • Windows 7: How to stop/start service from commandline (like services.msc does it)?

    - by john
    I have developed a program in Java that uses on a local SQL Server instance to store its data. On some installations the SQL Server instance is not running sometimes. Users can fix this problem by manually starting the SQL Server instance (via services.msc). I am thinking about automating this task: the software would check if the database server is reachable, if not try to (re)start it. The problem is that on the same user account the Services can be stopped /started via services.msc (without any UAC prompt), but not via (non-elevated) command line. The operating system seems to treat services.msc differently: c:\>sc start mssql$db1 [SC] StartService: OpenService FEHLER 5: Zugriff verweigert (Access denied) c:\>net start mssql$db1 Systemfehler 5 aufgetreten. Zugriff verweigert (Access denied) So the question is: how can I stop/start the service from a java-program/command line without having my users to use services.msc (preferrably via on-board-tools)

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  • If you need more than 3 levels of indentation, you're screwed?

    - by jokoon
    Per the Linux kernel coding style document: The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program. What can I deduce from this quote? On top of the fact that too long methods are hard to maintain, are they hard or impossible to optimize for the compiler? I don't really understand if this quote encourages better coding practice or is really a mathematical / algorithmic sort of truth. I also read in some C++ optimizing guide that "dividing up a program into more functions improves its design" is frequently taught in CS courses, but it should be not done too much, since it can turn into a lot of JMP calls (even if the compiler can inline some methods by itself).

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  • What is the better design decision approach?

    - by palm snow
    I have two classes (MyFoo1 and MyFoo2) that share some common functionality. So far it does not seem like I need any polymorphic inheritence but at this point I am considering the following options: Have the common functionality in a utility class. Both of these classes call these methods from that utility class. Have an abstract class and implement common methods in that abstract class. Then derive MyFoo1 and MyFoo2 from that abstract class. Any suggestion on what would be a better design decision?

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  • OOP PHP make separate classes or one

    - by user2956219
    I'm studying OOP PHP and working on a small personal project but I have hard time grasping some concepts. Let's say I have a list of items, each item belongs to subcategory, and each subcategory belongs to category. So should I make separate classes for category (with methods to list all categories, add new category, delete category), class for subcategories and class for items? Or should I make creating, listing and deleting categories as methods for item class? Both category and subcategory are very simple and basically consist of ID, Name and parentID (for subcategory).

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  • System Virtualization

    Methods and applications of system virtualization using Intel virtualization technology Intel Corporation - Intel - Companies - Product Support - Hardware

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  • Contructor parameters for dependent classes with Unity Framework

    - by Onisemus
    I just started using the Unity Application Block to try to decouple my classes and make it easier for unit testing. I ran into a problem though that I'm not sure how to get around. Looked through the documentation and did some Googling but I'm coming up dry. Here's the situation: I have a facade-type class which is a chat bot. It is a singleton class which handles all sort of secondary classes and provides a central place to launch and configure the bot. I also have a class called AccessManager which, well, manages access to bot commands and resources. Boiled down to the essence, I have the classes set up like so. public class Bot { public string Owner { get; private set; } public string WorkingDirectory { get; private set; } private IAccessManager AccessManager; private Bot() { // do some setup // LoadConfig sets the Owner & WorkingDirectory variables LoadConfig(); // init the access mmanager AccessManager = new MyAccessManager(this); } public static Bot Instance() { // singleton code } ... } And the AccessManager class: public class MyAccessManager : IAccessManager { private Bot botReference; public MyAccesManager(Bot botReference) { this.botReference = botReference; SetOwnerAccess(botReference.Owner); } private void LoadConfig() { string configPath = Path.Combine( botReference.WorkingDirectory, "access.config"); // do stuff to read from config file } ... } I would like to change this design to use the Unity Application Block. I'd like to use Unity to generate the Bot singleton and to load the AccessManager interface in some sort of bootstrapping method that runs before anything else does. public static void BootStrapSystem() { IUnityContainer container = new UnityContainer(); // create new bot instance Bot newBot = Bot.Instance(); // register bot instance container.RegisterInstance<Bot>(newBot); // register access manager container.RegisterType<IAccessManager,MyAccessManager>(newBot); } And when I want to get a reference to the Access Manager inside the Bot constructor I can just do: IAcessManager accessManager = container.Resolve<IAccessManager>(); And elsewhere in the system to get a reference to the Bot singleton: // do this Bot botInstance = container.Resolve<Bot>(); // instead of this Bot botInstance = Bot.Instance(); The problem is the method BootStrapSystem() is going to blow up. When I create a bot instance it's going to try to resolve IAccessManager but won't be able to because I haven't registered the types yet (that's the next line). But I can't move the registration in front of the Bot creation because as part of the registration I need to pass the Bot as a parameter! Circular dependencies!! Gah!!! This indicates to me I have a flaw in the way I have this structured. But how do I fix it? Help!!

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  • Create Hello World with RESTful web service and Jersey

    - by Harry Pham
    I follow tutorial here on how to create web service using RESTful web service and Jersey and I get kind of stuck. The code is from HelloWorld3 in the tutorial I linked above. Here is the code. I use Netbean6.8 + glassfish v3 RESTGreeting.java create using JAXB. This class represents the HTML message in Java package com.sun.rest; import javax.xml.bind.annotation.XmlRootElement; import javax.xml.bind.annotation.XmlElement; @XmlRootElement(name = "restgreeting") public class RESTGreeting { private String message; private String name; /** * Creates new instance of Greeting */ public RESTGreeting() { } /* Create new instance of Greeting * with parameters message and name */ public RESTGreeting( String message, String name) { this.message = message; this.name = name; } /** Getter for message * return value for message * */ @XmlElement public String getMessage() { return message; } public void setMessage(String message) { this.message = message; } /* Getter for name * return name */ @XmlElement public String getName() { return name; } public void setName(String name) { this.name = name; } } HelloGreetingService.java creates a RESTful web service that returns an HTML message package com.sun.rest; import javax.ws.rs.core.Context; import javax.ws.rs.core.UriInfo; import javax.ws.rs.Consumes; import javax.ws.rs.PUT; import javax.ws.rs.Path; import javax.ws.rs.GET; import javax.ws.rs.Produces; import javax.ws.rs.QueryParam; @Path("helloGreeting") public class HelloGreetingService { @Context private UriInfo context; /** Creates a new instance of HelloGreetingService */ public HelloGreetingService() { } /** * Retrieves representation of an instance of com.sun.rest.HelloGreetingService * @return an instance of java.lang.String */ @GET @Produces("text/html") public RESTGreeting getHtml(@QueryParam("name") String name) { return new RESTGreeting( getGreeting(), name); } private String getGreeting() { return "Hello "; } /** * PUT method for updating or creating an instance of HelloGreetingService * @param content representation for the resource * @return an HTTP response with content of the updated or created resource. */ @PUT @Consumes("text/html") public void putHtml(String content) { } } However when i deploy it on Glassfish, and run it. It generate an exception. I try to debug using netbean 6.8, and figure out that this line return new RESTGreeting(getGreeting(), name); in HelloGreetingService.java cause the exception. But not sure why. Here is the stacktrace javax.ws.rs.WebApplicationException at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:268) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1029) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:941) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:932) at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:384) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:451) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:632) at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1523) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641) at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97) at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185) at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:332) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:233) at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165) at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791) at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693) at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954) at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170) at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88) at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76) at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53) at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57) at com.sun.grizzly.ContextTask.run(ContextTask.java:69) at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330) at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309) at java.lang.Thread.run(Thread.java:637)

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