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• C# parameter count mismatch when trying to add AsyncCallback into BeginInvoke()

  - by PunX

  I have main form (PrenosForm) and I am trying to run Form2 asynchronously. It works without callback delegate: this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, null); //works 1. Doesn't work with callback delegate (parameter count mismatch): this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, new AsyncCallback(callBackDelegate), null); //doesn't work parameter count mismatch 2. Works with callback delegate if I do it like this: cp.BeginInvoke(datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt, new AsyncCallback(callBackDelegate), null); //works 3. My question is why does one way work and the other doesn't? I'm new at this. Would anyone be so kind as to answer my question and point out my mistakes? private delegate void copyDelegat(List<ListViewItem> datoteke, string path, PrenosForm forma, DragDropEffects efekt); private delegate void callBackDelegat(IAsyncResult a); public void doCopy(List<ListViewItem> datoteke, string path, PrenosForm forma, DragDropEffects efekt) { new Form2(datoteke, path, forma, efekt); } public void callBackFunc(IAsyncResult a) { AsyncResult res = a.AsyncState as AsyncResult; copyDelegat delegat = res.AsyncDelegate as copyDelegat; delegat.EndInvoke(a); } public void kopiraj(List<ListViewItem> datoteke, DragDropEffects efekt) { copyDelegat cp = new copyDelegat(doCopy); callBackDelegat callBackDelegate = new callBackDelegat(callBackFunc); this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, new AsyncCallback(callBackDelegate), null); //doesn't work parameter count missmatch 2. this.BeginInvoke(cp, new object[] { datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt }, null); //works 1. cp.BeginInvoke(datoteke, this.treeView1.SelectedNode.FullPath.ToString(), this, efekt, new AsyncCallback(callBackDelegate), null); //works 3. }

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• Is this a valid pattern for raising events in C#?

  - by Will Vousden

  Update: For the benefit of anyone reading this, since .NET 4, the lock is unnecessary due to changes in synchronization of auto-generated events, so I just use this now: public static void Raise<T>(this EventHandler<T> handler, object sender, T e) where T : EventArgs { if (handler != null) { handlerCopy(sender, e); } } And to raise it: SomeEvent.Raise(this, new FooEventArgs()); Having been reading one of Jon Skeet's articles on multithreading, I've tried to encapsulate the approach he advocates to raising an event in an extension method like so (with a similar generic version): public static void Raise(this EventHandler handler, object @lock, object sender, EventArgs e) { EventHandler handlerCopy; lock (@lock) { handlerCopy = handler; } if (handlerCopy != null) { handlerCopy(sender, e); } } This can then be called like so: protected virtual void OnSomeEvent(EventArgs e) { this.someEvent.Raise(this.eventLock, this, e); } Are there any problems with doing this? Also, I'm a little confused about the necessity of the lock in the first place. As I understand it, the delegate is copied in the example in the article to avoid the possibility of it changing (and becoming null) between the null check and the delegate call. However, I was under the impression that access/assignment of this kind is atomic, so why is the lock necessary? Update: With regards to Mark Simpson's comment below, I threw together a test: static class Program { private static Action foo; private static Action bar; private static Action test; static void Main(string[] args) { foo = () => Console.WriteLine("Foo"); bar = () => Console.WriteLine("Bar"); test += foo; test += bar; test.Test(); Console.ReadKey(true); } public static void Test(this Action action) { action(); test -= foo; Console.WriteLine(); action(); } } This outputs: Foo Bar Foo Bar This illustrates that the delegate parameter to the method (action) does not mirror the argument that was passed into it (test), which is kind of expected, I guess. My question is will this affect the validity of the lock in the context of my Raise extension method? Update: Here is the code I'm now using. It's not quite as elegant as I'd have liked, but it seems to work: public static void Raise<T>(this object sender, ref EventHandler<T> handler, object eventLock, T e) where T : EventArgs { EventHandler<T> copy; lock (eventLock) { copy = handler; } if (copy != null) { copy(sender, e); } }

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Assemblies mysteriously loaded into new AppDomains

  - by Eric

  I'm testing some code that does work whenever assemblies are loaded into an appdomain. For unit testing (in VS2k8's built-in test host) I spin up a new, uniquely-named appdomain prior to each test with the idea that it should be "clean": [TestInitialize()] public void CalledBeforeEachTestMethod() { AppDomainSetup appSetup = new AppDomainSetup(); appSetup.ApplicationBase = @"G:\<ProjectDir>\bin\Debug"; Evidence baseEvidence = AppDomain.CurrentDomain.Evidence; Evidence evidence = new Evidence( baseEvidence ); _testAppDomain = AppDomain.CreateDomain( "myAppDomain" + _appDomainCounter++, evidence, appSetup ); } [TestMethod] public void MissingFactoryCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadMissingRegistrationAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } [TestMethod] public void InvalidFactoryMethodCausesAppDomainUnload() { SupportingClass supportClassObj = (SupportingClass)_testAppDomain.CreateInstanceAndUnwrap( GetType().Assembly.GetName().Name, typeof( SupportingClass ).FullName ); try { supportClassObj.LoadInvalidFactoriesAssembly(); Assert.Fail( "Should have nuked the app domain" ); } catch( AppDomainUnloadedException ) { } } public class SupportingClass : MarshalByRefObject { public void LoadMissingRegistrationAssembly() { MissingRegistration.Main(); } public void LoadInvalidFactoriesAssembly() { InvalidFactories.Main(); } } If every test is run individually I find that it works correctly; the appdomain is created and has only the few intended assemblies loaded. However, if multiple tests are run in succession then each _testAppDomain already has assemblies loaded from all previous tests. Oddly enough, the two tests get appdomains with different names. The test assemblies that define MissingRegistration and InvalidFactories (two different assemblies) are never loaded into the unit test's default appdomain. Can anyone explain this behavior?

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• What would be a correct implemantation of JSF Converter if I need to get an Integer to run a query?

  - by Ignacio

  HI here's my code: List.xhmtl <h:selectOneMenu value="#{produtosController.items}"> <f:selectItems value="#{produtosController.itemsAvailableSelectOne}"/> </h:selectOneMenu> <h:commandButton action="#{produtosController.createByCodigos}" value="Buscar" /> My Controller Class with innner Converter implemantation @ManagedBean (name="produtosController") @SessionScoped public class ProdutosController { private Produtos current; private DataModel items = null; @EJB private controladores.ProdutosFacade ejbFacade; private PaginationHelper pagination; private int selectedItemIndex; public ProdutosController() { } public Produtos getSelected() { if (current == null) { current = new Produtos(); selectedItemIndex = -1; } return current; } private ProdutosFacade getFacade() { return ejbFacade; } public PaginationHelper getPagination() { if (pagination == null) { pagination = new PaginationHelper(10) { @Override public int getItemsCount() { return getFacade().count(); } @Override public DataModel createPageDataModel() { return new ListDataModel(getFacade().findRange(new int[]{getPageFirstItem(), getPageFirstItem()+getPageSize()})); } }; } return pagination; } public String prepareList() { recreateModel(); return "List"; } public String prepareView() { current = (Produtos)getItems().getRowData(); selectedItemIndex = pagination.getPageFirstItem() + getItems().getRowIndex(); return "View"; } public String prepareCreate() { current = new Produtos(); selectedItemIndex = -1; return "Create"; } public String create() { try { getFacade().create(current); JsfUtil.addSuccessMessage(ResourceBundle.getBundle("/Bundle").getString("ProdutosCreated")); return prepareCreate(); } catch (Exception e) { JsfUtil.addErrorMessage(e, ResourceBundle.getBundle("/Bundle").getString("PersistenceErrorOccured")); return null; } } public String createByMarcas() { items = new ListDataModel(ejbFacade.findByMarcas(current.getIdMarca())); updateCurrentItem(); return "List"; } public String createByModelos() { items = new ListDataModel(ejbFacade.findByModelos(current.getIdModelo())); updateCurrentItem(); return "List"; } public String createByCodigos(){ items = new ListDataModel(ejbFacade.findByCodigo(current.getCodigo())); updateCurrentItem(); return "List"; } public String prepareEdit() { current = (Produtos)getItems().getRowData(); selectedItemIndex = pagination.getPageFirstItem() + getItems().getRowIndex(); return "Edit"; } public String update() { try { getFacade().edit(current); JsfUtil.addSuccessMessage(ResourceBundle.getBundle("/Bundle").getString("ProdutosUpdated")); return "View"; } catch (Exception e) { JsfUtil.addErrorMessage(e, ResourceBundle.getBundle("/Bundle").getString("PersistenceErrorOccured")); return null; } } public String destroy() { current = (Produtos)getItems().getRowData(); selectedItemIndex = pagination.getPageFirstItem() + getItems().getRowIndex(); performDestroy(); recreateModel(); return "List"; } public String destroyAndView() { performDestroy(); recreateModel(); updateCurrentItem(); if (selectedItemIndex >= 0) { return "View"; } else { // all items were removed - go back to list recreateModel(); return "List"; } } private void performDestroy() { try { getFacade().remove(current); JsfUtil.addSuccessMessage(ResourceBundle.getBundle("/Bundle").getString("ProdutosDeleted")); } catch (Exception e) { JsfUtil.addErrorMessage(e, ResourceBundle.getBundle("/Bundle").getString("PersistenceErrorOccured")); } } private void updateCurrentItem() { int count = getFacade().count(); if (selectedItemIndex >= count) { // selected index cannot be bigger than number of items: selectedItemIndex = count-1; // go to previous page if last page disappeared: if (pagination.getPageFirstItem() >= count) { pagination.previousPage(); } } if (selectedItemIndex >= 0) { current = getFacade().findRange(new int[]{selectedItemIndex, selectedItemIndex+1}).get(0); } } public DataModel getItems() { if (items == null) { items = getPagination().createPageDataModel(); } return items; } private void recreateModel() { items = null; } public String next() { getPagination().nextPage(); recreateModel(); return "List"; } public String previous() { getPagination().previousPage(); recreateModel(); return "List"; } public SelectItem[] getItemsAvailableSelectMany() { return JsfUtil.getSelectItems(ejbFacade.findAll(), false); } public SelectItem[] getItemsAvailableSelectOne() { return JsfUtil.getSelectItems(ejbFacade.findAll(), true); } @FacesConverter(forClass=Produtos.class) public static class ProdutosControllerConverter implements Converter{ public Object getAsObject(FacesContext facesContext, UIComponent component, String value) { if (value == null || value.length() == 0) { return null; } ProdutosController controller = (ProdutosController)facesContext.getApplication().getELResolver(). getValue(facesContext.getELContext(), null, "produtosController"); return controller.ejbFacade.find(getKey(value)); } java.lang.Integer getKey(String value) { java.lang.Integer key; key = Integer.decode(value); return key; } String getStringKey(java.lang.Integer value) { StringBuffer sb = new StringBuffer(); sb.append(value); return sb.toString(); } public String getAsString(FacesContext facesContext, UIComponent component, Object object) { if (object == null) { return null; } if (object instanceof Produtos) { Produtos o = (Produtos) object; return getStringKey(o.getCodigo()); } else { throw new IllegalArgumentException("object " + object + " is of type " + object.getClass().getName() + "; expected type: "+ProdutosController.class.getName()); } } } } and my EJB @Entity @ViewScoped @Table(name = "produtos") @NamedQueries({ @NamedQuery(name = "Produtos.findAll", query = "SELECT p FROM Produtos p"), @NamedQuery(name = "Produtos.findById", query = "SELECT p FROM Produtos p WHERE p.id = :id"), @NamedQuery(name = "Produtos.findByCodigo", query = "SELECT p FROM Produtos p WHERE p.codigo = :codigo"), @NamedQuery(name = "Produtos.findByDescripcion", query = "SELECT p FROM Produtos p WHERE p.descripcion = :descripcion"), @NamedQuery(name = "Produtos.findByImagen", query = "SELECT p FROM Produtos p WHERE p.imagen = :imagen"), @NamedQuery(name = "Produtos.findByMarcas", query="SELECT m FROM Produtos m WHERE m.idMarca.id = :idMarca"), @NamedQuery(name = "Produtos.findByModelos", query="SELECT m FROM Produtos m WHERE m.idModelo.id = :idModelo")}) public class Produtos implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Basic(optional = false) @Column(name = "id") private Integer id; @Column(name = "codigo") private Integer codigo; @Column(name = "descripcion") private String descripcion; @Column(name = "imagen") private String imagen; @JoinColumn(name = "id_modelo", referencedColumnName = "id") @ManyToOne(optional = false) private Modelos idModelo; @JoinColumn(name = "id_marca", referencedColumnName = "id") @ManyToOne(optional = false) private Marcas idMarca; public Produtos() { } public Produtos(Integer id) { this.id = id; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public Integer getCodigo() { return codigo; } public void setCodigo(Integer codigo) { this.codigo = codigo; } public String getDescripcion() { return descripcion; } public void setDescripcion(String descripcion) { this.descripcion = descripcion; } public String getImagen() { return imagen; } public void setImagen(String imagen) { this.imagen = imagen; } public Modelos getIdModelo() { return idModelo; } public void setIdModelo(Modelos idModelo) { this.idModelo = idModelo; } public Marcas getIdMarca() { return idMarca; } public void setIdMarca(Marcas idMarca) { this.idMarca = idMarca; } @Override public int hashCode() { int hash = 0; hash += (id != null ? id.hashCode() : 0); return hash; } @Override public boolean equals(Object object) { // TODO: Warning - this method won't work in the case the id fields are not set if (!(object instanceof Produtos)) { return false; } Produtos other = (Produtos) object; if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) { return false; } return true; } @Override public String toString() { return "" + codigo + ""; } }

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• C++0x rvalue references - lvalues-rvalue binding

  - by Doug

  This is a follow-on question to http://stackoverflow.com/questions/2748866/c0x-rvalue-references-and-temporaries In the previous question, I asked how this code should work: void f(const std::string &); //less efficient void f(std::string &&); //more efficient void g(const char * arg) { f(arg); } It seems that the move overload should probably be called because of the implicit temporary, and this happens in GCC but not MSVC (or the EDG front-end used in MSVC's Intellisense). What about this code? void f(std::string &&); //NB: No const string & overload supplied void g1(const char * arg) { f(arg); } void g2(const std::string & arg) { f(arg); } It seems that, based on the answers to my previous question that function g1 is legal (and is accepted by GCC 4.3-4.5, but not by MSVC). However, GCC and MSVC both reject g2 because of clause 13.3.3.1.4/3, which prohibits lvalues from binding to rvalue ref arguments. I understand the rationale behind this - it is explained in N2831 "Fixing a safety problem with rvalue references". I also think that GCC is probably implementing this clause as intended by the authors of that paper, because the original patch to GCC was written by one of the authors (Doug Gregor). However, I don't this is quite intuitive. To me, (a) a const string & is conceptually closer to a string && than a const char *, and (b) the compiler could create a temporary string in g2, as if it were written like this: void g2(const std::string & arg) { f(std::string(arg)); } Indeed, sometimes the copy constructor is considered to be an implicit conversion operator. Syntactically, this is suggested by the form of a copy constructor, and the standard even mentions this specifically in clause 13.3.3.1.2/4, where the copy constructor for derived-base conversions is given a higher conversion rank than other implicit conversions: A conversion of an expression of class type to the same class type is given Exact Match rank, and a conversion of an expression of class type to a base class of that type is given Conversion rank, in spite of the fact that a copy/move constructor (i.e., a user-defined conversion function) is called for those cases. (I assume this is used when passing a derived class to a function like void h(Base), which takes a base class by value.) Motivation My motivation for asking this is something like the question asked in http://stackoverflow.com/questions/2696156/how-to-reduce-redundant-code-when-adding-new-c0x-rvalue-reference-operator-over ("How to reduce redundant code when adding new c++0x rvalue reference operator overloads"). If you have a function that accepts a number of potentially-moveable arguments, and would move them if it can (e.g. a factory function/constructor: Object create_object(string, vector<string>, string) or the like), and want to move or copy each argument as appropriate, you quickly start writing a lot of code. If the argument types are movable, then one could just write one version that accepts the arguments by value, as above. But if the arguments are (legacy) non-movable-but-swappable classes a la C++03, and you can't change them, then writing rvalue reference overloads is more efficient. So if lvalues did bind to rvalues via an implicit copy, then you could write just one overload like create_object(legacy_string &&, legacy_vector<legacy_string> &&, legacy_string &&) and it would more or less work like providing all the combinations of rvalue/lvalue reference overloads - actual arguments that were lvalues would get copied and then bound to the arguments, actual arguments that were rvalues would get directly bound. Questions My questions are then: Is this a valid interpretation of the standard? It seems that it's not the conventional or intended one, at any rate. Does it make intuitive sense? Is there a problem with this idea that I"m not seeing? It seems like you could get copies being quietly created when that's not exactly expected, but that's the status quo in places in C++03 anyway. Also, it would make some overloads viable when they're currently not, but I don't see it being a problem in practice. Is this a significant enough improvement that it would be worth making e.g. an experimental patch for GCC?

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• use callback function to report stack backtrace

  - by user353394

  Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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• Android Google Analytics

  - by ibenot

  I'm trying to use Google Analytics in my Android application with Google Configuration Add .jar in my project Insert this in AndroidManifest Add this in my java file public class MainActivity extends Activity { GoogleAnalyticsTracker tracker; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); tracker = GoogleAnalyticsTracker.getInstance(); tracker.startNewSession("My-UA–XXXXXXXX", this); setContentView(R.layout.main); Button createEventButton = (Button)findViewById(R.id.NewEventButton); createEventButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { tracker.trackEvent( "Clicks", // Category "Button", // Action "clicked", // Label 77); // Value } }); setContentView(R.layout.main); Button createPageButton = (Button)findViewById(R.id.NewPageButton); createPageButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Add a Custom Variable to this pageview, with name of "Medium" and value "MobileApp" and // scope of session-level. tracker.setCustomVar(1, "Navigation Type", "Button click", 2); // Track a page view. This is probably the best way to track which parts of your application // are being used. // E.g. // tracker.trackPageView("/help"); to track someone looking at the help screen. // tracker.trackPageView("/level2"); to track someone reaching level 2 in a game. // tracker.trackPageView("/uploadScreen"); to track someone using an upload screen. tracker.trackPageView("/testApplicationHomeScreen"); } }); Button quitButton = (Button)findViewById(R.id.QuitButton); quitButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { finish(); } }); Button dispatchButton = (Button)findViewById(R.id.DispatchButton); dispatchButton.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Manually start a dispatch, not needed if the tracker was started with a dispatch // interval. tracker.dispatch(); } }); } @Override protected void onDestroy() { super.onDestroy(); // Stop the tracker when it is no longer needed. tracker.stopSession(); } } == And it's ok, no error, compiling and executing but i have created my ua account yesterday (more 24h) and i have nothing in my google analytics panel. My Question : is there an error in my code or i want to wait again ? Live trafic works for Android application (like tradicional website) ??? I have no information about Live trafic (when i play my app, i would like to show the number of person using my application) and Saved trafic (with viewed pages, time) Thank you for your replies and excuse my poor english :) bye

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• Enums and Annotations

  - by PeterMmm

  I want to use an Annotation in compile-safe form. To pass the value() to the Annotation i want to use the String representation of an enum. Is there a way to use @A with a value from enum E ? public class T { public enum E { a,b; } // C1: i want this, but it won't compile @A(E.a) void bar() { // C2: no chance, it won't compile @A(E.a.toString()) void bar2() { } // C3: this is ok @A("a"+"b") void bar3() { } // C4: is constant like C3, is'nt it ? @A(""+E.a) void bar4() { } } @interface A { String value(); }

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• How to specialize template for type derived from particular type

  - by relaxxx

  I have class World which manages creation of object... After creation it calls afterCreation method and I the created object is user-defined type derived from Entity (eg. MyEntity), I want to call addEntity. I the object was something else, I want to do nothing. addEntity must be called with appropriate T, because it generates unique IDs for every derived class etc. Here is my solution: template <int v> struct ToType { enum { value = v }; }; template <typename T> void World::afterCreation(T * t) { afterCreation(t, ToType<std::is_base_of<Entity, T>::value>()); } template <typename T> void World::afterCreation(T * t, ToType<true>) { addEntity(t); //here I cant pass Entity *, I need the real type, eg. MyEntity } template <typename T> void World::afterCreation(T * t, ToType<false>) { } My question is - Can in be done better way? How can I simulate following code without ToType or similar? template <typename T> void afterCreation(){/*generic impl*/} template <typename T where T is derived from Entity> void afterCreation(){/*some specific stuff*/} "specialize" in the title is only to describe my intention, no need to solve problem with template specialization

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• Abstract base class puzzle

  - by 0x80

  In my class design I ran into the following problem: class MyData { int foo; }; class AbstraktA { public: virtual void A() = 0; }; class AbstraktB : public AbstraktA { public: virtual void B() = 0; }; template<class T> class ImplA : public AbstraktA { public: void A(){ cout << "ImplA A()"; } }; class ImplB : public ImplA<MyData>, public AbstraktB { public: void B(){ cout << "ImplB B()"; } }; void TestAbstrakt() { AbstraktB *b = (AbstraktB *) new ImplB; b->A(); b->B(); }; The problem with the code above is that the compiler will complain that AbstraktA::A() is not defined. Interface A is shared by multiple objects. But the implementation of A is dependent on the template argument. Interface B is the seen by the outside world, and needs to be abstrakt. The reason I would like this is that it would allow me to define object C like this: Define the interface C inheriting from abstrakt A. Define the implementation of C using a different datatype for template A. I hope I'm clear. Is there any way to do this, or do I need to rethink my design?

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• Reference Value Parameter VS Return value which one is good?

  - by CodeYun

  When we want to modify some value in one object we may use two different methods, just want to know which one is better or there is no big different between them. void SomeMethod() { UserInfo newUser = New UserInfo(); ModifyUserInfo(newUser); //Modify UserInfo after calling void method GetUserInfo } void ModifyUserInfo(UseerInfo userInfo) { userInfo.UserName = "User Name"; ..... } void SomeMethod() { UserInfo newUser = New UserInfo(); //Assign new userinfo explicitly newUser = GetUserInfo(newUser); } UserInfo ModifyUserInfo(UseerInfo userInfo) { userInfo.UserName = "User Name"; ..... return userInfo; }

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• How to prevent duplicates, macro or something?

  - by blez

  Well, the problem is that I've got a lot of code like this for each event passed to the GUI, how can I shortify this? Macros wont do the work I guess. Is there a more generic way to do something like a 'template' ? private delegate void DownloadProgressDelegate(object sender, DownloaderProgressArgs e); void DownloadProgress(object sender, DownloaderProgressArgs e) { if (this.InvokeRequired) { this.BeginInvoke(new DownloadProgressDelegate(DownloadProgress), new object[] { sender, e }); return; } label2.Text = d.speedOutput.ToString(); } private delegate void DownloadSpeedDelegate(object sender, DownloaderProgressArgs e); void DownloadSpeed(object sender, DownloaderProgressArgs e) { if (this.InvokeRequired) { this.BeginInvoke(new DownloadSpeedDelegate(DownloadSpeed), new object[] { sender, e }); return; } string speed = ""; speed = (e.DownloadSpeed / 1024).ToString() + "kb/s"; label3.Text = speed; }

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• Castle, sharing a transient component between a decorator and a decorated component

  - by Marius

  Consider the following example: public interface ITask { void Execute(); } public class LoggingTaskRunner : ITask { private readonly ITask _taskToDecorate; private readonly MessageBuffer _messageBuffer; public LoggingTaskRunner(ITask taskToDecorate, MessageBuffer messageBuffer) { _taskToDecorate = taskToDecorate; _messageBuffer = messageBuffer; } public void Execute() { _taskToDecorate.Execute(); Log(_messageBuffer); } private void Log(MessageBuffer messageBuffer) {} } public class TaskRunner : ITask { public TaskRunner(MessageBuffer messageBuffer) { } public void Execute() { } } public class MessageBuffer { } public class Configuration { public void Configure() { IWindsorContainer container = null; container.Register( Component.For<MessageBuffer>() .LifeStyle.Transient); container.Register( Component.For<ITask>() .ImplementedBy<LoggingTaskRunner>() .ServiceOverrides(ServiceOverride.ForKey("taskToDecorate").Eq("task.to.decorate"))); container.Register( Component.For<ITask>() .ImplementedBy<TaskRunner>() .Named("task.to.decorate")); } } How can I make Windsor instantiate the "shared" transient component so that both "Decorator" and "Decorated" gets the same instance? Edit: since the design is being critiqued I am posting something closer to what is being done in the app. Maybe someone can suggest a better solution (if sharing the transient resource between a logger and the true task is considered a bad design)

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• how to implement windows service loop that waits for a period in C# / .NET2.0

  - by matti

  My question is that is this the best practice to do this. Couldn't find any good examples. I have following code in file created by VS2005: public partial class ObjectFolder : ServiceBase { protected override void OnStart(string[] args) { ObjectFolderApp.Initialize(); ObjectFolderApp.StartMonitorAndWork(); } protected override void OnStop() { // TODO: Add code here to perform any tear-down necessary to stop yourservice. } } then: class ObjectFolderApp { public static bool Initialize() { //all init stuff return true; } public static void StartMonitorAndWork() { Thread worker = new Thread(MonitorAndWork); worker.Start(); } private static void MonitorAndWork() { int loopTime = 60000; if (int.TryParse(_cfgValues.GetConfigValue("OfWaitLoop"), out loopTime)) loopTime = 1000 * loopTime; while (true) { /* create+open connection and fill DataSet */ DataSet ofDataSet = new DataSet("ObjectFolderSet"); using (_cnctn = _dbFactory.CreateConnection()) { _cnctn.Open(); //do all kinds of database stuff } Thread.Sleep(loopTime); } } }

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• Method Overloading for NULL parameter

  - by Phani

  I have added three methods with parameters: public static void doSomething(Object obj) { System.out.println("Object called"); } public static void doSomething(char[] obj) { System.out.println("Array called"); } public static void doSomething(Integer obj) { System.out.println("Array called"); } When I am calling doSomething(null) , then compiler throws error as ambiguous methods. So Is the issue because Integer and char[] methods or Integer and Object methods?

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• Why is this simple Mobile Form not closed when using the player

  - by ajhvdb

  Hi, I created this simple sample Form with the close button. Everything is working as expected when NOT using the Interop.WMPLib.dll I've seen other applications using this without problems but why isn't the Form process closed when I just add the line: SoundPlayer myPlayer = new SoundPlayer(); and of course dispose it: if (myPlayer != null) { myPlayer.Dispose(); myPlayer = null; } The Form closes but the debugger VS2008 is still active. The Form project and the dll are still active. If you send me an email to [email protected], I can send you the zipped project. Below is the class for the dll: using System; using System.Collections.Generic; using System.Text; using System.Threading; using System.Runtime.InteropServices; using WMPLib; namespace WindowsMobile.Utilities { public delegate void SoundPlayerStateChanged(SoundPlayer sender, SoundPlayerState newState); public enum SoundPlayerState { Stopped, Playing, Paused, } public class SoundPlayer : IDisposable { [DllImport("coredll")] public extern static int waveOutSetVolume(int hwo, uint dwVolume); [DllImport("coredll")] public extern static int waveOutGetVolume(int hwo, out uint dwVolume); WindowsMediaPlayer myPlayer = new WindowsMediaPlayer(); public SoundPlayer() { myPlayer.uiMode = "invisible"; myPlayer.settings.volume = 100; } string mySoundLocation = string.Empty; public string SoundLocation { get { return mySoundLocation; } set { mySoundLocation = value; } } public void Pause() { myPlayer.controls.pause(); } public void PlayLooping() { Stop(); myPlayer.URL = mySoundLocation; myPlayer.settings.setMode("loop", true); } public int Volume { get { return myPlayer.settings.volume; } set { myPlayer.settings.volume = value; } } public void Play() { Stop(); myPlayer.URL = mySoundLocation; myPlayer.controls.play(); } public void Stop() { myPlayer.controls.stop(); myPlayer.close(); } #region IDisposable Members public void Dispose() { try { Stop(); } catch (Exception) { } // need this otherwise the process won't exit?! try { int ret = Marshal.FinalReleaseComObject(myPlayer); } catch (Exception) { } myPlayer = null; GC.Collect(); } #endregion } }

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• c# multi inheritance

  - by user326839

  So ive got a base class which requires a Socket: class Sock { public Socket s; public Sock(Socket s) { this.s = s; } public virtual void Process(byte[] data) { } ... } then ive got another class. if a new socket gets accepted a new instance of this class will be created: class Game : Sock { public Random Random = new Random(); public Timerr Timers; public Test Test; public Game(Socket s) : base(s) { } public static void ReceiveNewSocket(object s) { Game Client = new Game((Socket)s); Client.Start(); } public override void Process(byte[] buf) { Timers = new Timerr(s); Test = new Test(s); Test.T(); } } in the Sock class ive got a virtual function that gets overwritten by the Game class.(Process function) in this function im calling a function from the Test Class(Test+ Timerr Class: class Test : Game { public Test(Socket s) : base(s) { } public void T() { Console.WriteLine(Random.Next(0, 10)); Timers.Start(); } } class Timerr : Game { public Timerr(Socket s) : base(s) { } public void Start() { Console.WriteLine("test"); } } ) So in the Process function im calling a function in Test. And in this function(T) i need to call a function from the Timerr Class.But the problem is its always NULL , although the constructor is called in Process. And e.g. the Random Class can be called, i guess its because its defined with the constructor.: public Random Random = new Random(); and thats why the other classes(without a constructor): public Timerr Timers; public Test Test; are always null in the inherited class Test.But its essentiel that i call other Methods of other classes in this function.How could i solve that?

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• sorting, average and finding the lowest number from a static array Java

  - by user3701322

  i'm trying to input students and input their results for course work and exams and what i'm having trouble with is finding the average total score, the lowest total score and printing all students in order of total scores highest - lowest import java.util.*; import java.text.*; public class Results { static String[] name = new String[100]; static int[] coursework = new int[100]; static int[] exam = new int[100]; static int count = 0; public static void main(String[] args) { Scanner input = new Scanner(System.in); boolean flag = true; while(flag) { System.out.println( "1. Add Student\n" + "2. List All Students\n" + "3. List Student Grades\n" + "4. Total Score Average\n" + "5. Highest Total Score\n" + "6. Lowest Total Score\n" + "7. List all Students and Total Scores\n" + "8. Quit\n"); System.out.print("Enter choice (1 - 8): "); int choice = input.nextInt(); switch(choice) { case 1: add(); break; case 2: listAll(); break; case 3: listGrades(); break; case 4: average(); break; case 5: highestTotal(); break; case 6: lowestTotal(); break; case 7: order(); break; case 8: flag = false; break; default: System.out.println("\nNot an option\n"); } DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"); Date date = new Date(); System.out.println(dateFormat.format(date)); } System.out.println("\n\nHave a nice day"); }//end of main static void add() { Scanner input = new Scanner(System.in); System.out.println("Insert Name: "); String names = input.nextLine(); System.out.println("Insert Coursework: "); int courseworks = input.nextInt(); System.out.println("Insert Exam: "); int exams = input.nextInt(); name[count] = names; coursework[count] = courseworks; exam[count] = exams; count++; } static void listAll() { for(int i=0;i<count;i++) { System.out.printf("%s %d %d\n", name[i], coursework[i], exam[i]); } } static void listGrades() { for(int i=0;i<count;i++){ if(coursework[i] + exam[i] > 79) { System.out.println(name[i] + " HD"); } else if(coursework[i] + exam[i] > 69) { System.out.println(name[i] + " DI"); } else if(coursework[i] + exam[i] > 59) { System.out.println(name[i] + " CR"); } else if(coursework[i] + exam[i] > 49) { System.out.println(name[i] + " PA"); } else { System.out.println(name[i] + " NN"); } } } static void average() { } static void highestTotal() { int largest=exam[0]; String student=name[0]; for(int i=0; i<exam.length; i++){ if(exam[i]>largest){ largest = exam[i] + coursework[i]; student = name[i]; } } System.out.printf(student + ": "+ largest + "\n" ); } static void lowestTotal() { int min = 0; for(int i=0; i<=exam[i]; i++){ for(int j =0; j<=exam[i]; j++){ if(exam[i]<=exam[j] && j==exam[j]){ min = exam[i] + coursework[i]; } else{ continue; } } } System.out.printf(name + ": "+ min + "\n" ); } static void order() { } }

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• Java Compiler Creation Help..Please

  - by Brian

  I need some help with my code here...What we are trying to do is make a compiler that will read a file containing Machine Code and converting it to 100 lines of 4 bits example: this code is the machine code being converting to opcode and operands. I need some help please.. thanks 799 798 198 499 1008 1108 899 909 898 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Everything compiles but when I go and run my Test.java I get the following OutPut: Exception in thread "main" java.util.NoSuchElementException: No line found at java.util.Scanner.nextLine(Scanner.java:1516) at Compiler.FirstPass(Compiler.java:22) at Compiler.compile(Compiler.java:11) at Test.main(Test.java:5) Here is my class Compiler: import java.io.*; import java.io.DataOutputStream; import java.util.NoSuchElementException; import java.util.Scanner; class Compiler{ private int lc = 0; private int dc = 99; public void compile(String filename) { SymbolList symbolTable = FirstPass(filename); SecondPass(symbolTable, filename); } public SymbolList FirstPass(String filename) { File file = new File(filename); SymbolList temp = new SymbolList(); int dc = 99; int lc = 0; try{ Scanner scan = new Scanner(file); String line = scan.nextLine(); String[] linearray = line.split(" "); while(line!=null){ if(!linearray[0].equals("REM")){ if(!this.isInstruction(linearray[0])){ linearray[0]=removeColon(linearray[0]); if(this.isInstruction(linearray[1])){ temp.add(new Symbol(linearray[0], lc, null)); lc++; } else { temp.add(new Symbol(linearray[0], dc, Integer.valueOf((linearr\ ay[2])))); dc--; } } else { if(!linearray[0].equals("REM")) lc++; } } try{ line = scan.nextLine(); } catch(NoSuchElementException e){ line=null; break; } linearray = line.split(" "); } } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } return temp; } public String makeFilename(String filename) { return filename + ".ex"; } public String removeColon(String str) { if(str.charAt(str.length()-1) == ':'){ return str.substring(0, str.length()-1); } else { return str; } } public void SecondPass(SymbolList symbolTable, String filename){ try { int dc = 99; //Open file for reading File file = new File(filename); Scanner scan = new Scanner(file); //Make filename of new executable file String newfile = makeFilename(filename); //Open Output Stream for writing new file. FileOutputStream os = new FileOutputStream(filename); DataOutputStream dos = new DataOutputStream(os); //Read First line. Split line by Spaces into linearray. String line = scan.nextLine(); String[] linearray = line.split(" "); while(scan.hasNextLine()){ if(!linearray[0].equals("REM")){ int inst=0, opcode, loc; if(isInstruction(linearray[0])){ opcode = getOpcode(linearray[0]); loc = symbolTable.searchName(linearray[1]).getMemloc(); inst = (opcode*100)+loc; } else if(!isInstruction(linearray[0])){ if(isInstruction(linearray[1])){ opcode = getOpcode(linearray[1]); if(linearray[1].equals("STOP")) inst=0000; else { loc = symbolTable.searchName(linearray[2]).getMemloc(); inst = (opcode*100)+loc; } } if(linearray[1].equals("DC")) dc--; } System.out.println(inst); dos.writeInt(inst); linearray = line.split(" "); } if(scan.hasNextLine()) { line = scan.nextLine(); } } scan.close(); for(int i = lc; i <= dc; i++) { dos.writeInt(0); } for(int i = dc+1; i<100; i++){ dos.writeInt(symbolTable.searchLocation(i).getValue()); if(i!=99) dos.writeInt(0); } dos.close(); os.close(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } public int getOpcode(String inst){ int toreturn = -1; if(isInstruction(inst)){ if(inst.equals("STOP")) toreturn=0; if(inst.equals("LD")) toreturn=1; if(inst.equals("STO")) toreturn=2; if(inst.equals("ADD")) toreturn=3; if(inst.equals("SUB")) toreturn=4; if(inst.equals("MPY")) toreturn=5; if(inst.equals("DIV")) toreturn=6; if(inst.equals("IN")) toreturn=7; if(inst.equals("OUT")) toreturn=8; if(inst.equals("B")) toreturn=9; if(inst.equals("BGTR")) toreturn=10; if(inst.equals("BZ")) toreturn=11; return toreturn; } else { return -1; } } public boolean isInstruction(String totest){ boolean toreturn = false; String[] labels = {"IN", "LD", "SUB", "BGTR", "BZ", "OUT", "B", "STO", "STOP", "AD\ D", "MTY", "DIV"}; for(int i = 0; i < 12; i++){ if(totest.equals(labels[i])) toreturn = true; } return toreturn; } } And here is my class Computer: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Computer{ private Cpu cpu; private Input in; private OutPut out; private Memory mem; public Computer() throws IOException { Memory mem = new Memory(100); Input in = new Input(); OutPut out = new OutPut(); Cpu cpu = new Cpu(); System.out.println(in.getInt()); } public void run() throws IOException { cpu.reset(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); while (!cpu.stop()) { cpu.decode(); if (cpu.OutFlag()) OutPut.display(mem.read(cpu.getMAR())); if (cpu.InFlag()) mem.write(cpu.getMDR(),in.getInt()); if (cpu.StoreFlag()) { mem.write(cpu.getMAR(),in.getInt()); cpu.getMDR(); } else { cpu.setMDR(mem.read(cpu.getMAR())); cpu.execute(); cpu.fetch(); cpu.setMDR(mem.read(cpu.getMAR())); cpu.fetch2(); } } } public void load() { mem.loadMemory(); } } Here is my Memory class: import java.io.*; import java.util.NoSuchElementException; import java.util.Scanner; class Memory{ private MemEl[] memArray; private int size; private int[] mem; public Memory(int s) {size = s; memArray = new MemEl[s]; for(int i = 0; i < s; i++) memArray[i] = new MemEl(); } public void write (int loc,int val) {if (loc >=0 && loc < size) memArray[loc].write(val); else System.out.println("Index Not in Domain"); } public int read (int loc) {return memArray[loc].read(); } public void dump() { for(int i = 0; i < size; i++) if(i%1 == 0) System.out.println(memArray[i].read()); else System.out.print(memArray[i].read()); } public void writeTo(int location, int value) { mem[location] = value; } public int readFrom(int location) { return mem[location]; } public int size() { return mem.length; } public void loadMemory() { this.write(0, 799); this.write(1, 798); this.write(2, 198); this.write(3, 499); this.write(4, 1008); this.write(5, 1108); this.write(6, 899); this.write(7, 909); this.write(8, 898); this.write(9, 0000); } public void loadFromFile(String filename){ try { FileReader fr = new FileReader(filename); BufferedReader br = new BufferedReader(fr); String read=null; int towrite=0; int l=0; do{ try{ read=br.readLine(); towrite = Integer.parseInt(read); }catch(Exception e){ } this.write(l, towrite); l++; }while(l<100); }catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } } Here is my Test class: public class Test{ public static void main(String[] args) throws java.io.IOException { Compiler compiler = new Compiler(); compiler.compile("program.txt"); } }

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• RAII: Initializing data member in const method

  - by Thomas Matthews

  In RAII, resources are not initialized until they are accessed. However, many access methods are declared constant. I need to call a mutable (non-const) function to initialize a data member. Example: Loading from a data base struct MyClass { int get_value(void) const; private: void load_from_database(void); // Loads the data member from database. int m_value; }; int MyClass :: get_value(void) const { static bool value_initialized(false); if (!value_initialized) { // The compiler complains about this call because // the method is non-const and called from a const // method. load_from_database(); } return m_value; } My primitive solution is to declare the data member as mutable. I would rather not do this, because it suggests that other methods can change the member. How would I cast the load_from_database() statement to get rid of the compiler errors?

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• Strange compilation error - GAS3 generated class

  - by subh

  I am pretty new to GraniteDS..So far I have been able to successfully configure it to work with my remote java services as well as generate the equivalent AS3 files from my POJO's. But I am getting this strange error while building one of the classes using GAS3 [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[77,29] Syntax error: expecting identifier before use. public function set use(value:String):void { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[77,52] Syntax error: expecting leftparen before leftbrace. public function set use(value:String):void { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[77,52] Syntax error: expecting identifier before leftbrace. public function set use(value:String):void { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[77,52] Syntax error: expecting rightparen before leftbrace. public function set use(value:String):void { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[80,29] Syntax error: expecting identifier before use. public function get use():String { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[80,42] Syntax error: expecting leftparen before leftbrace. public function get use():String { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[80,42] Syntax error: expecting identifier before leftbrace. public function get use():String { [ERROR] C:\TestGDS_All\TestGDS-flex-remoteobjects\target\generated-sources\com\mycompany\TestGDS\masterdata\model\TankGradesMlBas e.as:[80,42] Syntax error: expecting rightparen before leftbrace. public function get use():String { The java class appears like this @Entity` @Table(name = "mmd_tank_grades_ml") @SuppressWarnings("serial") public class TankGradesMl implements Serializable { .... private String use; @Basic @Column(name = "USE", length = 45) public String getUse() { return use; } public void setUse(String use) { this.use = use; } What am I doing wrong? How to resolve this error? I tried by changing the java source variable like below private String usedFor; ---- @Basic @Column(name = "USE", length = 45) public String getUsedFor() { return usedFor; } /** * @param use * new value for use */ public void setUsedFor(String usedFor) { this.usedFor = usedFor; } and the error is gone...not sure why it was throwing exception for 'use'..too small for variable name :-)

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• java bubblesort with acm dialog

  - by qzar

  Hi, the program gives following exception: Exception in thread "main" java.lang.NullPointerException at myclasses.BubbleSort.run(BubbleSort.java:42) at acm.program.Program.runHook(Program.java:1519) at acm.program.Program.startRun(Program.java:1508) at acm.program.Program.start(Program.java:729) at myclasses.BubbleSort.main(BubbleSort.java:49) what is wrong? thank you very much! package myclasses; import acm.program.DialogProgram; public class BubbleSort extends DialogProgram { int[] array; public int[] getArray() { return array; } public void setArray(int[] array) { this.array = array; } void swap(int firstPos, int secondPos) { int temp = array[firstPos]; array[firstPos] = array[secondPos]; array[secondPos] = temp; } public void bubblesort() { int i, j, k; for (i = 1; i < array.length; i++) { j = i; k = array[i]; while (j > 0 && array[j - 1] > k) { array[j] = array[j - 1]; --j; } array[j] = k; } } public void run() { BubbleSort a = new BubbleSort(); a.setArray(new int[] {1, 3, 5, 7, 6, 2}); a.bubblesort(); StringBuffer sb = new StringBuffer(a.array.length * 2); for (int i = 0; i < getArray().length; i++) sb.append(getArray()[i]).append(" "); println(sb); } public static void main(String[] args) { new BubbleSort().start(args); } }

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• How does the event dispatch thread work?

  - by Roman

  With the help of people on stackoverflow I was able to get the following working code of the simples GUI countdown (it just displays a window counting down seconds). My main problem with this code is the invokeLater stuff. As far as I understand the invokeLater send a task to the event dispatching thread (EDT) and then the EDT execute this task whenever it "can" (whatever it means). Is it right? To my understanding the code works like that: In the main method we use invokeLater to show the window (showGUI method). In other words, the code displaying the window will be executed in the EDT. In the main method we also start the counter and the counter (by construction) is executed in another thread (so it is not in the event dispatching thread). Right? The counter is executed in a separate thread and periodically it calls updateGUI. The updateGUI is supposed to update GUI. And GUI is working in the EDT. So, updateGUI should also be executed in the EDT. It is why the code for the updateGUI is inclosed in the invokeLater. Is it right? What is not clear to me is why we call the counter from the EDT. Anyway it is not executed in the EDT. It starts immediately a new thread and the counter is executed there. So, why we cannot call the counter in the main method after the invokeLater block? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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• Qthread - trouble shutting down threads

  - by Bryan Greenway

  For the last few days, I've been trying out the new preferred approach for using QThreads without subclassing QThread. The trouble I'm having is when I try to shutdown a set of threads that I created. I regularly get a "Destroyed while thread is still running" message (if I'm running in Debug mode, I also get a Segmentation Fault dialog). My code is very simple, and I've tried to follow the examples that I've been able to find on the internet. My basic setup is as follows: I've a simple class that I want to run in a separate thread; in fact, I want to run 5 instances of this class, each in a separate thread. I have a simple dialog with a button to start each thread, and a button to stop each thread (10 buttons). When I click one of the "start" buttons, a new instance of the test class is created, a new QThread is created, a movetothread is called to get the test class object to the thread...also, since I have a couple of other members in the test class that need to move to the thread, I call movetothread a few additional times with these other items. Note that one of these items is a QUdpSocket, and although this may not make sense, I wanted to make sure that sockets could be moved to a separate thread in this fashion...I haven't tested the use of the socket in the thread at this point. Starting of the threads all seem to work fine. When I use the linux top command to see if the threads are created and running, they show up as expected. The problem occurs when I begin stopping the threads. I randomly (or it appears to be random) get the error described above. Class that is to run in separate thread: // Declaration class TestClass : public QObject { Q_OBJECT public: explicit TestClass(QObject *parent = 0); QTimer m_workTimer; QUdpSocket m_socket; Q_SIGNALS: void finished(); public Q_SLOTS: void start(); void stop(); void doWork(); }; // Implementation TestClass::TestClass(QObject *parent) : QObject(parent) { } void TestClass::start() { connect(&m_workTimer, SIGNAL(timeout()),this,SLOT(doWork())); m_workTimer.start(50); } void TestClass::stop() { m_workTimer.stop(); emit finished(); } void TestClass::doWork() { int j; for(int i = 0; i<10000; i++) { j = i; } } Inside my main app, code called to start the first thread (similar code exists for each of the other threads): mp_thread1 = new QThread(); mp_testClass1 = new TestClass(); mp_testClass1->moveToThread(mp_thread1); mp_testClass1->m_socket.moveToThread(mp_thread1); mp_testClass1->m_workTimer.moveToThread(mp_thread1); connect(mp_thread1, SIGNAL(started()), mp_testClass1, SLOT(start())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(quit())); connect(mp_testClass1, SIGNAL(finished()), mp_testClass1, SLOT(deleteLater())); connect(mp_testClass1, SIGNAL(finished()), mp_thread1, SLOT(deleteLater())); connect(this,SIGNAL(stop1()),mp_testClass1,SLOT(stop())); mp_thread1->start(); Also inside my main app, this code is called when a stop button is clicked for a specific thread (in this case thread 1): emit stop1(); Sometimes it appears that threads are stopped and destroyed without issue. Other times, I get the error described above. Any guidance would be greatly appreciated. Thanks, Bryan

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