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• Unable to make the session state request to the session state server

  - by Angry_IT_Guru

  For about 4-5 months now, I seem to be having this sporadic issue--mainly during our busiest time of the day between 10:30-11:45AM, where all my Windows 2003 web servers in a Microsoft NLB cluster start throwing session state server errors. A sample error is below. System.Web.HttpException: Unable to make the session state request to the session state server. Please ensure that the ASP.NET State service is started and that the client and server ports are the same. If the server is on a remote machine, please ensure that it accepts remote requests by checking the value of HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\aspnet_state\Parameters\AllowRemoteConnection. If the server is on the local machine, and if the before mentioned registry value does not exist or is set to 0, then the state server connection string must use either 'localhost' or '127.0.0.1' as the server name. at System.Web.SessionState.OutOfProcSessionStateStore.MakeRequest(StateProtocolVerb verb, String id, StateProtocolExclusive exclusiveAccess, Int32 extraFlags, Int32 timeout, Int32 lockCookie, Byte[] buf, Int32 cb, Int32 networkTimeout, SessionNDMakeRequestResults& results) at System.Web.SessionState.OutOfProcSessionStateStore.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) at System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) Now I'm using ASP.NET State service on a centralized back-end Windows 2003 server that all servers communicate to. I was originally using SQL Server state for a couple years as well prior to having this issue. The problem with SQL wqas that when the issue occurred, it created a blocking situation which essentially impacted all users across all servers. The product company recommended that I use the standard ASP.NET State service as that was what they technically supported. Why this would make a difference is beyond me -- but I had no choice but to try it! I have attempted to create multiple application pools, adding additional servers, chaning TCP/IP timeout from 20 to 30 seconds, and even calling Microsoft ASP.NET product support, with very little success. I even recommended that they review whether they are using read-only session state instead of read/write per page request -- as I understand that this basically causes every page to make round-trips to state server even if state isn't being used on the page. Unfortunately, the application is developed by our product company and they insist that it is something with my environment because other clients do not have these sort of issues. However, I've talked to other clients and they tell me when they've seen issues like they, they've basically had to create another web farm. This issue almost seems like I've simply reached some architectural limit within the application... Microsoft's position on the issue is that the session state needs to be reduced and the returncode being reported back from the state server indicates buffers are full. To better understand the scope of issues (rather than wait for customers to call and complain), I installed ELMAH and configured it to send me e-mails when unhandled exceptions occur. I basically get 500-1000 e-mails during the time period of high activity! If any one has any other ideas I could try or better ways to troubleshoot, I'd appreciate it.

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• Finite state machine in C++

  - by Electro

  So, I've read a lot about using FSMs to do game state management, things like what and FSM is, and using a stack or set of states for building one. I've gone through all that. But I'm stuck at writing an actual, well-designed implementation of an FSM for that purpose. Specifically, how does one cleanly resolve the problem of transitioning between states, (how) should a state be able to use data from other states, and so on. Does anyone have any tips on designing and writing a implementation in C++, or better yet, code examples?

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• Throwing exception from a property when my object state is invalid

  - by Rumi P.

  Microsoft guidelines say: "Avoid throwing exceptions from property getters", and I normally follow that. But my application uses Linq2SQL, and there is the case where my object can be in invalid state because somebody or something wrote nonsense into the database. Consider this toy example: [Table(Name="Rectangle")] public class Rectangle { [Column(Name="ID", IsPrimaryKey = true, IsDbGenerated = true)] public int ID {get; set;} [Column(Name="firstSide")] public double firstSide {get; set;} [Column(Name="secondSide")] public double secondSide {get; set;} public double sideRatio { get { return firstSide/secondSide; } } } Here, I could write code which ensures that my application never writes a Rectangle with a zero-length side into the database. But no matter how bulletproof I make my own code, somebody could open the database with a different application and create an invalid Rectangle, especially one with a 0 for secondSide. (For this example, please forget that it is possible to design the database in a way such that writing a side length of zero into the rectangle table is impossible; my domain model is very complex and there are constraints on model state which cannot be expressed in a relational database). So, the solution I am gravitating to is to change the getter to: get { if(firstSide > 0 && secondSide > 0) return firstSide/secondSide; else throw new System.InvalidOperationException("All rectangle sides should have a positive length"); } The reasoning behind not throwing exceptions from properties is that programmers should be able to use them without having to make precautions about catching and handling them them. But in this case, I think that it is OK to continue to use this property without such precautions: if the exception is thrown because my application wrote a non-zero rectangle side into the database, then this is a serious bug. It cannot and shouldn't be handled in the application, but there should be code which prevents it. It is good that the exception is visibly thrown, because that way the bug is caught. if the exception is thrown because a different application changed the data in the database, then handling it is outside of the scope of my application. So I can't do anything about it if I catch it. Is this a good enough reasoning to get over the "avoid" part of the guideline and throw the exception? Or should I turn it into a method after all? Note that in the real code, the properties which can have an invalid state feel less like the result of a calculation, so they are "natural" properties, not methods.

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• Modeling player mechanics with a finite state machine

  - by K..

  I have three states standing walking jumping When I press D standing transitions to walking. The velocity will be set to a defined value and the player moves. When I release D walking transitions back to standing, which sets the velocity back to 0. When I press W and the state is walking it transitions to jumping, but when the player hits the ground, it goes back to standing. jumping has a transition land that always leads to standing because a state doesn't know about its previous states. Since standing sets a velocity of 0 the player stops walking, when he hits the ground. How do I prevent this?

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• Implementing a State Machine in Angular.js to control routing

  - by ldn_tech_exec

  Can anyone help me with integrating a state machine to control routing? What's the best method to do this? Create a service? I need to basically intercept every $location request, run the state machine and let it figure out what the next $location.path should be. Think of the problem like a bank of questions that get added and removed over time. The user visits once in a while, passes in the user's answers object to the statemachine, and the statemachine figures out which question to load. This is my pseudocode, but i need to figure out where to put this or what event I can hook into to make sure all route requests are passed through the machine. Do I need a specific stateMachine controller? Do I create a service? Where do I use the service? Do I need to override $locationProvider? $scope.user.answers = [{ id: 32, answer: "whatever" }, { id:33, answer: "another answer" }] $scope.questions = [{ id:32, question:"what is your name?", path:"/question/1" },{ id:34, question:"how old are you?", path:"/question/2" }] var questions = $scope.questions; angular.forEach(questions, function(question) { if(question.id !exist in $scope.user.answers.id) { $location.path = question.path break; }); Thanks

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• Code Golf: Finite-state machine!

  - by Adam Matan

  Finite state machine A deterministic finite state machine is a simple computation model, widely used as an introduction to automata theory in basic CS courses. It is a simple model, equivalent to regular expression, which determines of a certain input string is Accepted or Rejected. Leaving some formalities aside, A run of a finite state machine is composed of: alphabet, a set of characters. states, usually visualized as circles. One of the states must be the start state. Some of the states might be accepting, usually visualized as double circles. transitions, usually visualized as directed arches between states, are directed links between states associated with an alphabet letter. input string, a list of alphabet characters. A run on the machine begins at the starting state. Each letter of the input string is read; If there is a transition between the current state and another state which corresponds to the letter, the current state is changed to the new state. After the last letter was read, if the current state is an accepting state, the input string is accepted. If the last state was not an accepting state, or a letter had no corresponding arch from a state during the run, the input string is rejected. Note: This short descruption is far from being a full, formal definition of a FSM; Wikipedia's fine article is a great introduction to the subject. Example For example, the following machine tells if a binary number, read from left to right, has an even number of 0s: The alphabet is the set {0,1}. The states are S1 and S2. The transitions are (S1, 0) -> S2, (S1, 1) -> S1, (S2, 0) -> S1 and (S2, 1) -> S2. The input string is any binary number, including an empty string. The rules: Implement a FSM in a language of your choice. Input The FSM should accept the following input: <States> List of state, separated by space mark. The first state in the list is the start state. Accepting states begin with a capital letter. <transitions> One or more lines. Each line is a three-tuple: origin state, letter, destination state) <input word> Zero or more characters, followed by a newline. For example, the aforementioned machine with 1001010 as an input string, would be written as: S1 s2 S1 0 s2 S1 1 S1 s2 0 S1 s2 1 s2 1001010 Output The FSM's run, written as <State> <letter> -> <state>, followed by the final state. The output for the example input would be: S1 1 -> S1 S1 0 -> s2 s2 0 -> S1 S1 1 -> S1 S1 0 -> s2 s2 1 -> s2 s2 0 -> S1 ACCEPT For the empty input '': S1 ACCEPT For 101: S1 1 -> S1 S1 0 -> s2 s2 1 -> s2 REJECT For '10X': S1 1 -> S1 S1 0 -> s2 s2 X REJECT Prize A nice bounty will be given to the most elegant and short solution. Reference implementation A reference Python implementation will be published soon.

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• What methods should save/load a game state

  - by vedi

  There are a lot of articles about how to save a state of a game and they are pretty good. But I have one conceptual misunderstanding where should I save the state? My game has number of screens and pair of them are MainMenuScreen and MainSceneScreen these are inherited from Screen class. MainMenuScreen is shown at start of the game the MainSceneScreen little later. What is the problem? I navigated to MainSceneScreen, forced Android to stop the application (I change a language settings on the device to achieve it, please let me know if I'm wrong). After that I select the application again and I can see MainMenuScreen is shown. But I want MainSceneScreen to be shown. I suppose I should override resume method. But what class I should override? I have class PsGame that extends Game class of libgdx. I put breakpoints to its resume method and it turned out that method was not called. I investigated the problem and I've found little strange code in onResume method of AndroidApplication class of libgdx: if (!firstResume) graphics.resume(); else firstResume = false; My debugger said firstResume was true and didn't go to *graphics.resume()*line. Sorry for a lot of words but could you answer following question: What did I do wrong? What methods should I override? Thank you in advance.

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• Sharing ASP.NET State databases between multiple apps

  - by MikeWyatt

  Is it better for a collection of ASP.NET web apps to share the same session database, or should each one have its own? If there is no significant difference, having a single database would be preferable due to easier maintenance. Background My team has an assortment of ASP.NET web apps, all written in either Monorail 1.1 or ASP.NET MVC 1.0. Each app currently uses a dedicated session state database. I'm working on adding a new site to that list, and am debating whether I should create another new session database, or just share an existing one with another app.

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• Java: How to manage UDP client-server state

  - by user92947

  I am trying to write a Java application that works similar to MapReduce. There is a server and several workers. Workers may come and go as they please and the membership to the group has a soft-state. To become a part of the group, the worker must send a UDP datagram to the server, but to continue to be part of the group, the worker must send the UDP datagram to the server every 5 minutes. In order to accommodate temporary errors, a worker is allowed to miss as many as two consecutive periodic UDP datagrams. So, the server must keep track of the current set of workers as well as the last time each worker had sent a UDP datagram. I've implemented a class called WorkerListener that implements Runnable and listens to UDP datagrams on a particular UDP port. Now, to keep track of active workers, this class may maintain a HashSet (or HashMap). When a datagram is received, the server may query the HashSet to check if it is a new member. If so, it can add the new worker to the group by adding an entry into the HashSet. If not, it must reset a "timer" for the worker, noting that it has just heard from the corresponding worker. I'm using the word timer in a generic sense. It doesn't have to be a clock of sorts. Perhaps this could also be implemented using int or long variables. Also, the server must run a thread that continuously monitors the timers for the workers to see that a client that times out on two consecutive datagram intervals, it is removed from the HashSet. I don't want to do this in the WorkerListener thread because it would be blocking on the UDP datagram receive() function. If I create a separate thread to monitor the worker HashSet, it would need to be a different class, perhaps WorkerRegistrar. I must share the HashSet with that thread. Mutual exclusion must also be implemented, then. My question is, what is the best way to do this? Pointers to some sample implementation would be great. I want to use the barebones JDK implementation, and not some fancy state maintenance API that takes care of everything, because I want this to be a useful demonstration for a class that I am teaching. Thanks

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• RK4 Bouncing a Ball

  - by Jonathan Dickinson

  I am trying to wrap my head around RK4. I decided to do the most basic 'ball with gravity that bounces' simulation. I have implemented the following integrator given Glenn Fiedler's tutorial: /// <summary> /// Represents physics state. /// </summary> public struct State { // Also used internally as derivative. // S: Position // D: Velocity. /// <summary> /// Gets or sets the Position. /// </summary> public Vector2 X; // S: Position // D: Acceleration. /// <summary> /// Gets or sets the Velocity. /// </summary> public Vector2 V; } /// <summary> /// Calculates the force given the specified state. /// </summary> /// <param name="state">The state.</param> /// <param name="t">The time.</param> /// <param name="acceleration">The value that should be updated with the acceleration.</param> public delegate void EulerIntegrator(ref State state, float t, ref Vector2 acceleration); /// <summary> /// Represents the RK4 Integrator. /// </summary> public static class RK4 { private const float OneSixth = 1.0f / 6.0f; private static void Evaluate(EulerIntegrator integrator, ref State initial, float t, float dt, ref State derivative, ref State output) { var state = new State(); // These are a premature optimization. I like premature optimization. // So let's not concentrate on that. state.X.X = initial.X.X + derivative.X.X * dt; state.X.Y = initial.X.Y + derivative.X.Y * dt; state.V.X = initial.V.X + derivative.V.X * dt; state.V.Y = initial.V.Y + derivative.V.Y * dt; output = new State(); output.X.X = state.V.X; output.X.Y = state.V.Y; integrator(ref state, t + dt, ref output.V); } /// <summary> /// Performs RK4 integration over the specified state. /// </summary> /// <param name="eulerIntegrator">The euler integrator.</param> /// <param name="state">The state.</param> /// <param name="t">The t.</param> /// <param name="dt">The dt.</param> public static void Integrate(EulerIntegrator eulerIntegrator, ref State state, float t, float dt) { var a = new State(); var b = new State(); var c = new State(); var d = new State(); Evaluate(eulerIntegrator, ref state, t, 0.0f, ref a, ref a); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref a, ref b); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref b, ref c); Evaluate(eulerIntegrator, ref state, t + dt, dt, ref c, ref d); a.X.X = OneSixth * (a.X.X + 2.0f * (b.X.X + c.X.X) + d.X.X); a.X.Y = OneSixth * (a.X.Y + 2.0f * (b.X.Y + c.X.Y) + d.X.Y); a.V.X = OneSixth * (a.V.X + 2.0f * (b.V.X + c.V.X) + d.V.X); a.V.Y = OneSixth * (a.V.Y + 2.0f * (b.V.Y + c.V.Y) + d.V.Y); state.X.X = state.X.X + a.X.X * dt; state.X.Y = state.X.Y + a.X.Y * dt; state.V.X = state.V.X + a.V.X * dt; state.V.Y = state.V.Y + a.V.Y * dt; } } After reading over the tutorial I noticed a few things that just seemed 'out' to me. Notably how the entire simulation revolves around t at 0 and state at 0 - considering that we are working out a curve over the duration it seems logical that RK4 wouldn't be able to handle this simple scenario. Never-the-less I forged on and wrote a very simple Euler integrator: static void Integrator(ref State state, float t, ref Vector2 acceleration) { if (state.X.Y > 100 && state.V.Y > 0) { // Bounce vertically. acceleration.Y = -state.V.Y * t; } else { acceleration.Y = 9.8f; } } I then ran the code against a simple fixed-time step loop and this is what I got: 0.05 0.20 0.44 0.78 1.23 1.76 ... 74.53 78.40 82.37 86.44 90.60 94.86 99.23 103.05 105.45 106.94 107.86 108.42 108.76 108.96 109.08 109.15 109.19 109.21 109.23 109.23 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 ... As I said, I was expecting it to break - however I am unsure of how to fix it. I am currently looking into keeping the previous state and time, and working from that - although at the same time I assume that will defeat the purpose of RK4. How would I get this simulation to print the expected results?

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• Change players state and controls in-game

  - by Samurai Fox

  I'm using Unity 3D Let's say the player is an ice cube. You control it like a normal player. On press of a button, ice transforms (with animation) into water. You control it completely different than the ice cube. Another great example would be: Player is human being and has normal FPS controls. On press of a button human transforms into birds and now has completely different controls. Now, my question is, what would be easier and better: make one object with animation transition and to stay in that state of anim. until button is pressed again make two object: ice and water. Ice has an animation of turning into water. So replace ice (with animation) with water object And if anyone knows this one too: how to switch between 2 different types of player controls.

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• Implementing a "state-machine" logic for methods required by an object in C++

  - by user827992

  What I have: 1 hypothetical object/class + other classes and related methods that gives me functionality. What I want: linking this object to 0 to N methods in realtime on request when an event is triggered Each event is related to a single method or a class, so a single event does not necessarily mean "connect this 1 method only" but can also mean "connect all the methods from that class or a group of methods" Avoiding linked lists because I have to browse the entire list to know what methods are linked, because this does not ensure me that the linked methods are kept in a particular order (let's say an alphabetic order by their names or classes), and also because this involve a massive amount of pointers usage. Example: I have an object Employee Jon, Jon acquires knowledge and forgets things pretty easily, so his skills may vary during a period of time, I'm responsible for what Jon can add or remove from his CV, how can I implement this logic?

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• Can an object oriented program be seen as a Finite State Machine?

  - by Peretz

  This might be a philosophical/fundamental question, but I just want to clarify it. In my understanding a Finite State Machine is a way of modeling a system in which the system's output will not only depend on the current inputs, but also the current state of the system. Additionally, as the name suggests it, a finite state machine can be segmented in a finite N number of states with its respective state and behavior. If this is correct, shouldn't every single object with data and function members be a state in our object oriented model, making any object oriented design a finite state machine? If that is not the interpretation of a FSM in object design, what exactly people mean when they implement a FSM in software? am I missing something? Thanks

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• Deferred contexts and inheriting state from the immediate context

  - by dreijer

  I took my first stab at using deferred contexts in DirectX 11 today. Basically, I created my deferred context using CreateDeferredContext() and then drew a simple triangle strip with it. Early on in my test application, I call OMSetRenderTargets() on the immediate context in order to render to the swap chain's back buffer. Now, after having read the documentation on MSDN about deferred contexts, I assumed that calling ExecuteCommandList() on the immediate context would execute all of the deferred commands as "an extension" to the commands that had already been executed on the immediate context, i.e. the triangle strip I rendered in the deferred context would be rendered to the swap chain's back buffer. That didn't seem to be the case, however. Instead, I had to manually pull out the immediate context's render target (using OMGetRenderTargets()) and then set it on the deferred context with OMSetRenderTargets(). Am I doing something wrong or is that the way deferred contexts work?

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• Resolving a Forward Declaration Issue Involving a State Machine in C++

  - by hypersonicninja

  I've recently returned to C++ development after a hiatus, and have a question regarding implementation of the State Design Pattern. I'm using the vanilla pattern, exactly as per the GoF book. My problem is that the state machine itself is based on some hardware used as part of an embedded system - so the design is fixed and can't be changed. This results in a circular dependency between two of the states (in particular), and I'm trying to resolve this. Here's the simplified code (note that I tried to resolve this by using headers as usual but still had problems - I've omitted them in this code snippet): #include <iostream> #include <memory> using namespace std; class Context { public: friend class State; Context() { } private: State* m_state; }; class State { public: State() { } virtual void Trigger1() = 0; virtual void Trigger2() = 0; }; class LLT : public State { public: LLT() { } void Trigger1() { new DH(); } void Trigger2() { new DL(); } }; class ALL : public State { public: ALL() { } void Trigger1() { new LLT(); } void Trigger2() { new DH(); } }; // DL needs to 'know' about DH. class DL : public State { public: DL() { } void Trigger1() { new ALL(); } void Trigger2() { new DH(); } }; class HLT : public State { public: HLT() { } void Trigger1() { new DH(); } void Trigger2() { new DL(); } }; class AHL : public State { public: AHL() { } void Trigger1() { new DH(); } void Trigger2() { new HLT(); } }; // DH needs to 'know' about DL. class DH : public State { public: DH () { } void Trigger1() { new AHL(); } void Trigger2() { new DL(); } }; int main() { auto_ptr<LLT> llt (new LLT); auto_ptr<ALL> all (new ALL); auto_ptr<DL> dl (new DL); auto_ptr<HLT> hlt (new HLT); auto_ptr<AHL> ahl (new AHL); auto_ptr<DH> dh (new DH); return 0; } The problem is basically that in the State Pattern, state transitions are made by invoking the the ChangeState method in the Context class, which invokes the constructor of the next state. Because of the circular dependency, I can't invoke the constructor because it's not possible to pre-define both of the constructors of the 'problem' states. I had a look at this article, and the template method which seemed to be the ideal solution - but it doesn't compile and my knowledge of templates is a rather limited... The other idea I had is to try and introduce a Helper class to the subclassed states, via multiple inheritance, to see if it's possible to specify the base class's constructor and have a reference to the state subclasse's constructor. But I think that was rather ambitious... Finally, would a direct implmentation of the Factory Method Design Pattern be the best way to resolve the entire problem?

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• State Changes in a Component Based Architecture [closed]

  - by Maxem

  I'm currently working on a game and using the naive component based architecture thingie (Entities are a bag of components, entity.Update() calls Update on each updateable component), while the addition of new features is really simple, it makes a few things really difficult: a) multithreading / currency b) networking c) unit testing. Multithreading / Concurrency is difficult because I basically have to do poor mans concurrency (running the entity updates in separate threads while locking only stuff that crashes (like lists) and ignoring the staleness of read state (some states are already updated, others aren't)) Networking: There are no explicit state changes that I could efficiently push over the net. Unit testing: All updates may or may not conflict, so automated testing is at least awkward. I was thinking about these issues a bit and would like your input on these changes / idea: Switch from the naive cba to a cba with sub systems that work on lists of components Make all state changes explicit Combine 1 and 2 :p Example world update: statePostProcessing.Wait() // ensure that post processing has finished Apply(postProcessedState) state = new StateBag() Concurrently( () => LifeCycleSubSystem.Update(state), // populates the state bag () => MovementSubSystem.Update(state), // populates the state bag .... }) statePostProcessing = Future(() => PostProcess(state)) statePostProcessing.Start() // Tick is finished, the post processing happens in the background So basically the changes are (consistently) based on the data for the last tick; the post processing can a) generate network packages and b) fix conflicts / remove useless changes (example: entity has been destroyed - ignore movement etc.). EDIT: To clarify the granularity of the state changes: If I save these post processed state bags and apply them to an empty world, I see exactly what has happened in the game these state bags originated from - "Free" replay capability. EDIT2: I guess I should have used the term Event instead of State Change and point out that I kind of want to use the Event Sourcing pattern

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• Is a finite state machine an appropriate solution for this situation?

  - by user1936

  I was writing some test code as an example where I had a washing machine class. It has a door state that should be open or closed, and also a running state, either on or off. I want to prevent the running state from changing from 'off' to 'on' when the door is 'open', and also prevent the door from being set to 'open' while the machine is 'on'. I have this functionality rigged up with a bunch of if statements. It feels inelegant and it could quickly turn into spaghetti code if I want to add another state that puts additional conditions on the changes of other states. I wonder, is a finite state machine a solution for this situation? Would it simplify adding states and defining valid transitions?

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• Validation with State Pattern for Multi-Page Forms in ASP.NET

  - by philrabin

  I'm trying to implement the state pattern for a multi-page registration form. The data on each page will be accumulated and stored in a session object. Should validation (including service layer calls to the DB) occur on the page level or inside each state class? In other words, should the concrete implementation of IState be concerned with the validation or should it be given a fully populated and valid object? See "EmptyFormState" class below: namespace Example { public class Registrar { private readonly IState formEmptyState; private readonly IState baseInformationComplete; public RegistrarSessionData RegistrarSessionData { get; set;} public Registrar() { RegistrarSessionData = new RegistrarSessionData(); formEmptyState = new EmptyFormState(this); baseInformationComplete = new BasicInfoCompleteState(this); State = formEmptyState; } public IState State { get; set; } public void SubmitData(RegistrarSessionData data) { State.SubmitData(data); } public void ProceedToNextStep() { State.ProceedToNextStep(); } } //actual data stored in the session //to be populated by page public class RegistrarSessionData { public string FirstName { get; set; } public string LastName { get; set; } //will include values of all 4 forms } //State Interface public interface IState { void SubmitData(RegistrarSessionData data); void ProceedToNextStep(); } //Concrete implementation of IState //Beginning state - no data public class EmptyFormState : IState { private readonly Registrar registrar; public EmptyFormState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //Should Validation occur here? //Should each state object contain a validation class? (IValidator ?) //Should this throw an exception? } public void ProceedToNextStep() { registrar.State = new BasicInfoCompleteState(registrar); } } //Next step, will have 4 in total public class BasicInfoCompleteState : IState { private readonly Registrar registrar; public BasicInfoCompleteState(Registrar registrar) { this.registrar = registrar; } public void SubmitData(RegistrarSessionData data) { //etc } public void ProceedToNextStep() { //etc } } }

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• Do Ruby/Rails state machines exist that execute event transitions when a state change occurs?

  - by Bryan

  Hello All, Hopefully this isn't a silly question and I'm just not overlooking something in Ruby/Rails state machines (AASM, Transitions, AlterEgo, etc). From what I can tell, these state machine implementations operate on the preface that an event will get fired and the appropriate transition for that event will be triggered based on the old and new state. However, they don't seem to work the other way; say a user wants to change state from 'created' to 'assigned' and have the correct transition occur (rather than firing the event that causes the current state to be transitioned to the new state). Essentially, I want the user to be able to select a new state from a select box of available states and have the appropriate transition, guards, success callbacks, etc executed. Does anyone know if the existing state machine implementations support this?

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• System State Backups using NTbackup fail with error 0x800423f4 (relating to volume shadow copy)

  - by Paul Zimmerman

  We have a Windows Server 2003 R2 running Service Pack 2. It is a domain controller (Global Catalog) and our main internal DNS server. We run a System State backup of the machine to back up Active Directory information and save the backup to a different server. This server has a single drive (C:), and we do have Shadow Copies enabled for the volume (which are completing successfully). The System State Backup is now failing with the following listed in the backup logs: Volume shadow copy creation: Attempt 1. "Event Log Writer" has reported an error 0x800423f4. This is part of System State. The backup cannot continue. Error returned while creating the volume shadow copy:800423f4 Aborting Backup. The operation did not successfully complete. When doing a vssadmin list writers, we sometimes get the following reported for the Event Log Writer (other times it says that it is in the state of "[1] Stable" with "No error"): Writer name: 'Event Log Writer' Writer Id: {eee8c692-67ed-4250-8d86-390603070d00} Writer Instance Id: {c7194e96-868a-49e5-ba99-89b61977753c} State: [8] Failed Last error: Retryable error We have tried disabling the event log service via the registry, rebooting, deleting the event log files from the drive, then re-enabling the service via the registry and rebooting, but this didn't seem to solve the issue. We also get an error message when in the event viewer when trying to open the log for the "File Replication Service" of "Unable to complete the operation on 'File Replication Service'. The security descriptor structure is invalid." I have searched the error via Google and tried a number of different things, but nothing has seemed to help. Any suggestions on what we might try to get the Event Log Writer to behave would be greatly appreciated!

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• Alternative to Game State System?

  - by Ricket

  As far as I can tell, most games have some sort of "game state system" which switches between the different game states; these might be things like "Intro", "MainMenu", "CharacterSelect", "Loading", and "Game". On the one hand, it totally makes sense to separate these into a state system. After all, they are disparate and would otherwise need to be in a large switch statement, which is obviously messy; and they certainly are well represented by a state system. But at the same time, I look at the "Game" state and wonder if there's something wrong about this state system approach. Because it's like the elephant in the room; it's HUGE and obvious but nobody questions the game state system approach. It seems silly to me that "Game" is put on the same level as "Main Menu". Yet there isn't a way to break up the "Game" state. Is a game state system the best way to go? Is there some different, better technique to managing, well, the "game state"? Is it okay to have an intro state which draws a movie and listens for enter, and then a loading state which loops on the resource manager, and then the game state which does practically everything? Doesn't this seem sort of unbalanced to you, too? Am I missing something?

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• C# - Coding a nested stateflow diagram

  - by weberc2

  I have the following state diagram. I know how to make a simple state machine that transitions between non-nested states; however, I don't know how to transition between nested states. Could someone explain how to do this at an appropriately high level (i.e., you don't need to write the code for me--unless you're feeling particularly generous :P). State Diagram [EDIT: The bottom "A", "C", and "E" should be "B", "D", and "F" respectively; sorry!] What I know how to do public class MyState : State // State enumeration { public static MyState A = new MyState("State A"); public static MyState B = new MyState("State B"); public static MyState C = new MyState("State C"); public static MyState D = new MyState("State D"); public static MyState E = new MyState("State E"); public static MyState F = new MyState("State F"); public static MyState NEUT = new MyState("Neutral"); public static MyState P = new MyState("P"); protected MyState(string name) : base(name) { } } public class MyEvent : Event // Event enumeration { public static MyEvent X_POS = new MyEvent("X+"); public static MyEvent X_NEG = new MyEvent("X-"); public static MyEvent Y_POS = new MyEvent("Y+"); public static MyEvent Y_NEG = new MyEvent("Y-"); protected MyEvent(string name) : base(name) { } } public class MyStateMachine : StateMachine<MyState, MyEvent> // State Machine implementation { public MyStateMachine() : base(MyState.P) // MyState.P = initial state { // Set up the transition table // P this.addTransition(MYState.P, MyState.NEUT, MyEvent.Y_NEG); // NEUTRAL this.addTransition(MyState.NEUT, MyState.P, MyEvent.Y_POS); this.addTransition(MyState.NEUT, MyState.A, MyEvent.Y_NEG); this.addTransition(MyState.NEUT, MyState.B, MyEvent.Y_POS); this.addTransition(MyState.NEUT, MyState.C, MyEvent.Y_NEG); this.addTransition(MyState.NEUT, MyState.D, MyEvent.Y_POS); this.addTransition(MyState.NEUT, MyState.E, MyEvent.Y_NEG); this.addTransition(MyState.NEUT, MyState.F, MyEvent.Y_POS); // A this.addTransition(MyState.A, MyState.NEUT, MyEvent.Y_POS); // B this.addTransition(MyState.B, MyState.NEUT, MyEvent.Y_NEG); // C this.addTransition(MyState.C, MyState.NEUT, MyEvent.Y_POS); // D this.addTransition(MyState.D, MyState.NEUT, MyEvent.Y_NEG); // E this.addTransition(MyState.E, MyState.NEUT, MyEvent.Y_POS); // F this.addTransition(MyState.F, MyState.NEUT, MyEvent.Y_NEG); } public void move(MyEvent eevent) { try { this.moveNext(eevent); } catch (Exception e) { } } }

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• Unable to change the value of the variable

  - by Legend

  I'm using a discrete event simulator called ns-2 that was built using Tcl and C++. I was trying to write some code in TCL: set ns [new Simulator] set state 0 $ns at 0.0 "puts \"At 0.0 value of state is: $state\"" $ns at 1.0 "changeVal" $ns at 2.0 "puts \"At 2.0 values of state is: $state\"" proc changeVal {} { global state global ns $ns at-now "set state [expr $state+1]" puts "Changed value of state to $state" } $ns run Here's the output: At 0.0 value of state is: 0 Changed value of state to 0 At 2.0 values of state is: 0 The value of state does not seem to change. I am not sure if I am doing something wrong in using TCL. Anyone has an idea as to what might be going wrong here? EDIT: Thanks for the help. Actually, ns-2 is something over which I do not have much control (unless I recompile the simulator itself). I tried out the suggestions and here's the output: for the code: set ns [new Simulator] set state 0 $ns at 0.0 "puts \"At 0.0 value of state is: $state\"" $ns at 1.0 "changeVal" $ns at 9.0 "puts \"At 2.0 values of state is: $state\"" proc changeVal {} { global ns set ::state [expr {$::state+1}] $ns at-now "puts \"At [$ns now] changed value of state to $::state\"" } $ns run the output is: At 0.0 value of state is: 0 At 1 changed value of state to 1 At 2.0 values of state is: 0 And for the code: set ns [new Simulator] set state 0 $ns at 0.0 "puts \"At 0.0 value of state is: $state\"" $ns at 1.0 "changeVal" $ns at 9.0 "puts \"At 2.0 values of state is: $state\"" proc changeVal {} { global ns set ::state [expr {$::state+1}] $ns at 1.0 {puts "At 1.0 values of state is: $::state"} } $ns run the output is: At 0.0 value of state is: 0 At 1.0 values of state is: 1 At 2.0 values of state is: 0 Doesn't seem to work... Not sure if its a problem with ns2 or my code...

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• Data-driven animation states

  - by user8363

  I'm trying to handle animations in a 2D game engine hobby project, without hard-coding them. Hard coding animation states seems like a common but very strange phenomenon, to me. A little background: I'm working with an entity system where components are bags of data and subsystems act upon them. I chose to use a polling system to update animation states. With animation states I mean: "walking_left", "running_left", "walking_right", "shooting", ... My idea to handle animations was to design it as a data driven model. Data could be stored in an xml file, a rdbms, ... And could be loaded at the start of a game / level/ ... This way you can easily edit animations and transitions without having to go change the code everywhere in your game. As an example I made an xml draft of the data definitions I had in mind. One very important piece of data would simply be the description of an animation. An animation would have a unique id (a descriptive name). It would hold a reference id to an image (the sprite sheet it uses, because different animations may use different sprite sheets). The frames per second to run the animation on. The "replay" here defines if an animation should be run once or infinitely. Then I defined a list of rectangles as frames. <animation id='WIZARD_WALK_LEFT'> <image id='WIZARD_WALKING' /> <fps>50</fps> <replay>true</replay> <frames> <rectangle> <x>0</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> <rectangle> <x>45</x> <y>0</y> <width>45</width> <height>45</height> </rectangle> </frames> </animation> Animation data would be loaded and held in an animation resource pool and referenced by game entities that are using it. It would be treated as a resource like an image, a sound, a texture, ... The second piece of data to define would be a state machine to handle animation states and transitions. This defines each state a game entity can be in, which states it can transition to and what triggers that state change. This state machine would differ from entity to entity. Because a bird might have states "walking" and "flying" while a human would only have the state "walking". However it could be shared by different entities because multiple humans will probably have the same states (especially when you define some common NPCs like monsters, etc). Additionally an orc might have the same states as a human. Just to demonstrate that this state definition might be shared but only by a select group of game entities. <state id='IDLE'> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_LEFT'> <event trigger='LEFT_UP' goto='IDLE' /> <event trigger='RIGHT_DOWN' goto='MOVING_RIGHT' /> </state> <state id='MOVING_RIGHT'> <event trigger='RIGHT_UP' goto='IDLE' /> <event trigger='LEFT_DOWN' goto='MOVING_LEFT' /> </state> These states can be handled by a polling system. Each game tick it grabs the current state of a game entity and checks all triggers. If a condition is met it changes the entity's state to the "goto" state. The last part I was struggling with was how to bind animation data and animation states to an entity. The most logical approach seemed to me to add a pointer to the state machine data an entity uses and to define for each state in that machine what animation it uses. Here is an xml example how I would define the animation behavior and graphical representation of some common entities in a game, by addressing animation state and animation data id. Note that both "wizard" and "orc" have the same animation states but a different animation. Also, a different animation could mean a different sprite sheet, or even a different sequence of animations (an animation could be longer or shorter). <entity name="wizard"> <state id="IDLE" animation="WIZARD_IDLE" /> <state id="MOVING_LEFT" animation="WIZARD_WALK_LEFT" /> </entity> <entity name="orc"> <state id="IDLE" animation="ORC_IDLE" /> <state id="MOVING_LEFT" animation="ORC_WALK_LEFT" /> </entity> When the entity is being created it would add a list of states with state machine data and an animation data reference. In the future I would use the entity system to build whole entities by defining components in a similar xml format. -- This is what I have come up with after some research. However I had some trouble getting my head around it, so I was hoping op some feedback. Is there something here what doesn't make sense, or is there a better way to handle these things? I grasped the idea of iterating through frames but I'm having trouble to take it a step further and this is my attempt to do that.

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• ASP.NET 2.0 in Virtual Trying to Use SQL State Server

  - by user251660

  We have IIS 6 running on a W2003 Server. The root web site is running a v1.1 site. Under this site we have a virtual running a v2.0 site (with a separate application pool). The web.config for the root site is using SQL as its state server and has a 1.1 SQL state server database installed. The 2.0 virtual web.config does not need state and its web.config has no reference to a state server. When we attempt to call the virtual we receive this error message. "Unable to use SQL Server because ASP.NET version 2.0 Session State is not installed on the SQL server. Please install ASP.NET Session State SQL Server version 2.0 or above. This issue is currently only occurring on one web server. The rest are able to run the 2.0 virtual application. I also notice that if we call the 2.0 virtual with the IP address it does not generate the error, however if we call it with the host header name it generates the error (this behavior is only on the 1 web server with the error, all the others can be called with either the ip or host header without error). As an additional note the root and virtual are running with SSL. My theory is that the virtual 2.0 application is inheriting the 1.1 web.config state server entry from the root and when it looks at the state server it sees it as a 1.1 version and reports the error that it needs a 2.0 state server. I however cannot understand why the other servers are not behaving in this matter. All of the servers are on the same OS service pack as well as the same version of .net framework. Any ideas? Thanks

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