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• What's the best way to do base36 arithmetic in perl?

  - by DVK

  What's the best way to do base36 arithmetic in Perl? To be more specific, I need to be able to do the following: Operate on positive N-digit numbers in base 36 (e.g. digits are 0-9 A-Z) N is finite, say 9 Provide basic arithmetic, at the very least the following 3: Addition (A+B) Subtraction (A-B) Whole division, e.g. floor(A/B). Strictly speaking, I don't really need a base10 conversion ability - the numbers will 100% of time be in base36. So I'm quite OK if the solution does NOT implement conversion from base36 back to base10 and vice versa. I don't much care whether the solution is brute-force "convert to base 10 and back" or converting to binary, or some more elegant approach "natively" performing baseN operations (as stated above, to/from base10 conversion is not a requirement). My only 3 considerations are: It fits the minimum specifications above It's "standard". Currently we're using and old homegrown module based on base10 conversion done by hand that is buggy and sucks. I'd much rather replace that with some commonly used CPAN solution instead of re-writing my own bicycle from scratch, but I'm perfectly capable of building it if no better standard possibility exists. It must be fast-ish (though not lightning fast). Something that takes 1 second to sum up 2 9-digit base36 numbers is worse than anything I can roll on my own :) P.S. Just to provide some context in case people decide to solve my XY problem for me in addition to answering the technical question above :) We have a fairly large tree (stored in DB as a bunch of edges), and we need to superimpose order on a subset of that tree. The tree dimentions are big both depth- and breadth- wise. The tree is VERY actively updated (inserts and deletes and branch moves). This is currently done by having a second table with 3 columns: parent_vertex, child_vertex, local_order, where local_order is an 9-character string built of A-Z0-9 (e.g. base 36 number). Additional considerations: It is required that the local order is unique per child (and obviously unique per parent), Any complete re-ordering of a parent is somewhat expensive, and thus the implementation is to try and assign - for a parent with X children - the orders which are somewhat evenly distributed between 0 and 36**10-1, so that almost no tree inserts result in a full re-ordering.

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• Structuring Win32 GUI code

  - by kraf

  I wish to improve my code and file structure in larger Win32 projects with plenty of windows and controls. Currently, I tend to have one header and one source file for the entire implementation of a window or dialog. This works fine for small projects, but now it has come to the point where these implementations are starting to reach 1000-2000 lines, which is tedious to browse. A typical source file of mine looks like this: static LRESULT CALLBACK on_create(const HWND hwnd, WPARAM wp, LPARAM lp) { setup_menu(hwnd); setup_list(hwnd); setup_context_menu(hwnd); /* clip */ return 0; } static LRESULT CALLBACK on_notify(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) { const NMHDR* header = (const NMHDR*)lp; /* At this point I feel that the control's event handlers doesn't * necessarily belong in the same source file. Perhaps I could move * each control's creation code and event handlers into a separate * source file? Good practice or cause of confusion? */ switch (header->idFrom) { case IDC_WINDOW_LIST: switch (header->code) { case NM_RCLICK: return on_window_list_right_click(hwnd, wp, lp); /* clip */ } } } static LRESULT CALLBACK wndmain_proc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) { switch (msg) { case WM_CREATE: return on_create(hwnd, wp, lp); case WM_CLOSE: return on_close(hwnd, wp, lp); case WM_NOTIFY: return on_notify(hwnd, wp, lp); /* It doesn't matter much how the window proc looks as it just forwards * events to the appropriate handler. */ /* clip */ default: return DefWindowProc(hwnd, msg, wp, lp); } } But now as the window has a lot more controls, and these controls in turn have their own message handlers, and then there's the menu click handlers, and so on... I'm getting lost, and I really need advice on how to structure this mess up in a good and sensible way. I have tried to find good open source examples of structuring Win32 code, but I just get more confused since there are hundreds of files, and within each of these files that seem GUI related, the Win32 GUI code seems so far encapsulated away. And when I finally find a CreateWindowEx statement, the window proc is nowhere to be found. Any advice on how to structure all the code while remaining sane would be greatly appreciated. Thanks! I don't wish to use any libraries or frameworks as I find the Win32 API interesting and valuable for learning. Any insight into how you structure your own GUI code could perhaps serve as inspiration.

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• Unit finalization order for application, compiled with run-time packages?

  - by Alexander

  I need to execute my code after finalization of SysUtils unit. I've placed my code in separate unit and included it first in uses clause of dpr-file, like this: project Project1; uses MyUnit, // <- my separate unit SysUtils, Classes, SomeOtherUnits; procedure Test; begin // end; begin SetProc(Test); end. MyUnit looks like this: unit MyUnit; interface procedure SetProc(AProc: TProcedure); implementation var Test: TProcedure; procedure SetProc(AProc: TProcedure); begin Test := AProc; end; initialization finalization Test; end. Note that MyUnit doesn't have any uses. This is usual Windows exe, no console, without forms and compiled with default run-time packages. MyUnit is not part of any package (but I've tried to use it from package too). I expect that finalization section of MyUnit will be executed after finalization section of SysUtils. This is what Delphi's help tells me. However, this is not always the case. I have 2 test apps, which differs a bit by code in Test routine/dpr-file and units, listed in uses. MyUnit, however, is listed first in all cases. One application is run as expected: Halt0 - FinalizeUnits - ...other units... - SysUtils's finalization - MyUnit's finalization - ...other units... But the second is not. MyUnit's finalization is invoked before SysUtils's finalization. The actual call chain looks like this: Halt0 - FinalizeUnits - ...other units... - SysUtils's finalization (skipped) - MyUnit's finalization - ...other units... - SysUtils's finalization (executed) Both projects have very similar settings. I tried a lot to remove/minimize their differences, but I still do not see a reason for this behaviour. I've tried to debug this and found out that: it seems that every unit have some kind of reference counting. And it seems that InitTable contains multiply references to the same unit. When SysUtils's finalization section is called first time - it change reference counter and do nothing. Then MyUnit's finalization is executed. And then SysUtils is called again, but this time ref-count reaches zero and finalization section is executed: Finalization: // SysUtils' finalization 5003B3F0 55 push ebp // here and below is some form of stub 5003B3F1 8BEC mov ebp,esp 5003B3F3 33C0 xor eax,eax 5003B3F5 55 push ebp 5003B3F6 688EB50350 push $5003b58e 5003B3FB 64FF30 push dword ptr fs:[eax] 5003B3FE 648920 mov fs:[eax],esp 5003B401 FF05DCAD1150 inc dword ptr [$5011addc] // here: some sort of reference counter 5003B407 0F8573010000 jnz $5003b580 // <- this jump skips execution of finalization for first call 5003B40D B8CC4D0350 mov eax,$50034dcc // here and below is actual SysUtils' finalization section ... Can anyone can shred light on this issue? Am I missing something?

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• JPA One To Many Relationship Persistence Bug

  - by Brian

  Hey folks, I've got a really weird problem with a bi-directional relationship in jpa (hibernate implementation). A User is based in one Region, and a Region can contain many Users. So...relationship is as follows: Region object: @OneToMany(mappedBy = "region", fetch = FetchType.LAZY, cascade = CascadeType.ALL) public Set<User> getUsers() { return users; } public void setUsers(Set<User> users) { this.users = users; } User object: @ManyToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.EAGER) @JoinColumn(name = "region_fk") public Region getRegion() { return region; } public void setRegion(Region region) { this.region = region; } So, the relationship as you can see above is Lazy on the region side, ie, I don't want the region to eager load all the users. Therefore, I have the following code within my DAO layer to add a user to an existing user to an existing region object... public User setRegionForUser(String username, Long regionId){ Region r = (Region) this.get(Region.class, regionId); User u = (User) this.get(User.class, username); u.setRegion(r); Set<User> users = r.getUsers(); users.add(u); System.out.println("The number of users in the set is: "+users.size()); r.setUsers(users); this.update(r); return (User)this.update(u); } The problem is, when I run a little unit test to add 5 users to my region object, I see that the region.getUsers() set always stays stuck at 1 object...somehow the set isn't getting added to. My unit test code is as follows: public void setUp(){ System.out.println("calling setup method"); Region r = (Region)ManagerFactory.getCountryAndRegionManager().get(Region.class, Long.valueOf("2")); for(int i = 0; i<loop; i++){ User u = new User(); u.setUsername("username_"+i); ManagerFactory.getUserManager().update(u); ManagerFactory.getUserManager().setRegionForUser("username_"+i, Long.valueOf("2")); } } public void tearDown(){ System.out.println("calling teardown method"); for(int i = 0; i<loop; i++){ ManagerFactory.getUserManager().deleteUser("username_"+i); } } public void testGetUsersForRegion(){ Set<User> totalUsers = ManagerFactory.getCountryAndRegionManager().getUsersInRegion(Long.valueOf("2")); System.out.println("Expecting 5, got: "+totalUsers.size()); this.assertEquals(5, totalUsers.size()); } So the test keeps failing saying there is only 1 user instead of the expected 5. Any ideas what I'm doing wrong? thanks very much, Brian

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• Can't make my WCF extension work

  - by Sergio Romero

  I have a WCF solution that consists of the following class libraries: Exercise.Services: Contains the implementation classes for the services. Exercise.ServiceProxy: Contains the classes that are instantiated in the client. Exercise.HttpHost: Contains the services (*.svc files). I'm calling the service from a console application and the "first version" works really well so I took the next step which is to create a custom ServiceHostFactory, ServiceHost, and InstanceProvider so I can use constructor injection in my services as it is explained in this article. These classes are implemented in yet another class library: 4. Exercise.StructureMapWcfExtension Now even though I've modified my service this: <%@ ServiceHost Language="C#" Debug="true" Factory="Exercise.StructureMapWcfExtension.StructureMapServiceHostFactory" Service="Exercise.Services.PurchaseOrderService" %> I always get the following exception: System.ServiceModel.CommunicationException Security negotiation failed because the remote party did not send back a reply in a timely manner. This may be because the underlying transport connection was aborted. It fails in this line of code: public class PurchaseOrderProxy : ClientBase<IPurchaseOrderService>, IPurchaseOrderService { public PurchaseOrderResponse CreatePurchaseOrder(PurchaseOrderRequest purchaseOrderRequest) { return base.Channel.CreatePurchaseOrder(purchaseOrderRequest); //Fails here } } But that is not all, I added a trace to the web.config file and this is the error that appears in the log file: System.InvalidOperationException The service type provided could not be loaded as a service because it does not have a default (parameter-less) constructor. To fix the problem, add a default constructor to the type, or pass an instance of the type to the host. So this means that my ServiceHostFactory is never being hit, I even set a breakpoint in both its constructor and its method and they never get hit. I've added a reference of the StructureMapWcfExtension library to all the other ones (even the console client), one by one to no avail. I also tried to use the option in the host's web.config file to configure the factory like so: <serviceHostingEnvironment> <serviceActivations> <add service="Exercise.Services.PurchaseOrderService" relativeAddress="PurchaseOrderService.svc" factory="Exercise.StructureMapWcfExtension.StructureMapServiceHostFactory"/> </serviceActivations> </serviceHostingEnvironment> That didn't work either. Please I need help in getting this to work so I can incorporate it to our project. Thank you. UPDATE: Here's the service host factory's code: namespace Exercise.StructureMapWcfExtension { public class StructureMapServiceHostFactory : ServiceHostFactory { private readonly Container Container; public StructureMapServiceHostFactory() { Container = new Container(); new ContainerConfigurer().Configure(Container); } protected override ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses) { return new StructureMapServiceHost(Container, serviceType, baseAddresses); } } public class ContainerConfigurer { public void Configure(Container container) { container.Configure(r => r.For<IPurchaseOrderFacade>().Use<PurchaseOrderFacade>()); } } }

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• Help with iphone dev - beyond bounds error

  - by dusk

  I'm just learning iphone development, so please forgive me for what is probably a beginner error. I've searched around and haven't found anything specific to my problem, so hopefully it is an easy fix. The book has examples of building a table from data hard coded via an array. Unfortunately it never really tells you how to get data from a URL, so I've had to look that up and that is where my problems show up. When I debug in xcode, it seems like the count is correct, so I don't understand why it is going out of bounds? This is the error message: 2010-05-03 12:50:42.705 Simple Table[3310:20b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (0)' My URL returns the following string: first,second,third,fourth And here is the iphone code with the book's working example commented out #import "Simple_TableViewController.h" @implementation Simple_TableViewController @synthesize listData; - (void)viewDidLoad { /* //working code from book NSArray *array = [[NSArray alloc] initWithObjects:@"Sleepy", @"Sneezy", @"Bashful", @"Bashful", @"Happy", @"Doc", @"Grumpy", @"Thorin", @"Dorin", @"Norin", @"Ori", @"Balin", @"Dwalin", @"Fili", @"Kili", @"Oin", @"Gloin", @"Bifur", @"Bofur", @"Bombur", nil]; self.listData = array; [array release]; */ //code from interwebz that crashes NSString *urlstr = [[NSString alloc] initWithFormat:@"http://www.mysite.com/folder/iphone-test.php"]; NSURL *url = [[NSURL alloc] initWithString:urlstr]; NSString *ans = [NSString stringWithContentsOfURL:url]; NSArray *listItems = [ans componentsSeparatedByString:@","]; self.listData = listItems; [urlstr release]; [url release]; [ans release]; [listItems release]; [super viewDidLoad]; } - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; self.listData = nil; [super viewDidUnload]; } - (void)dealloc { [listData release]; [super dealloc]; } #pragma mark - #pragma mark Table View Data Source Methods - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [self.listData count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *SimpleTableIdentifier = @"SimpleTableIdentifier"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:SimpleTableIdentifier] autorelease]; } NSUInteger row = [indexPath row]; cell.textLabel.text = [listData objectAtIndex:row]; return cell; } @end

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• Help choosing authentication method

  - by Dima

  I need to choose an authentication method for an application installed and integrated in customers environment. There are two types of environments - windows and linux/unix. Application is user based, no web stuff, pure Java. The requirement is to authenticate users which will use my application against customer provided user base. Meaning, customer installs my app, but uses his own users to grant or deny access to my app. Typical, right? I have three options to consider and I need to pick up the one which would be a) the most flexible to cover most common modern environments and b) would take least effort while stay robust and standard. Option (1) - Authenticate locally managing user credentials in some local storage, e.g. file. Customer would then add his users to my application and it will then check the passwords. Simple, clumsy but would work. Customers would have to punch every user they want to grant access to my app using some UI we will have to provide. Lots of work for me, headache to the customer. Option (2) - Use LDAP authentication. Customers would tell my app where to look for users and I will walk their directory resolving names into user names and trying to bind with found password. This is better approach IMO, but more fragile because I will have to walk an unknown directory structure and who knows if this will be permitted everywhere. Would be harder to test since there are many LDAP implementation out there, last thing I want is drowning in this voodoo. Option(3) - Use plain Kerberos authentication. Customers would tell my app what realm (domain) and which KDC (key distribution center) to use. In ideal world these two parameters would be all I need to set while customers could use their own administration tools to configure domain and kdc. My application would simply delegate user credentials to this third party (using JAAS or Spring security) and consider success when third party is happy with them. I personally prefer #3, but not sure what surprises I might face. Would this cover windows and *nix systems entirely? Is there another option to consider?

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• Turn class "Interfaceable"

  - by scooterman

  Hi folks, On my company system, we use a class to represent beans. It is just a holder of information using boost::variant and some serialization/deserialization stuff. It works well, but we have a problem: it is not over an interface, and since we use modularization through dlls, building an interface for it is getting very complicated, since it is used in almost every part of our app, and sadly interfaces (abstract classes ) on c++ have to be accessed through pointers, witch makes almost impossible to refactor the entire system. Our structure is: dll A: interface definition through abstract class dll B: interface implementation there is a painless way to achieve that (maybe using templates, I don't know) or I should forget about making this work and simply link everything with dll B? thanks Edit: Here is my example. this is on dll A BeanProtocol is a holder of N dataprotocol itens, wich are acessed by a index. class DataProtocol; class UTILS_EXPORT BeanProtocol { public: virtual DataProtocol& get(const unsigned int ) const { throw std::runtime_error("Not implemented"); } virtual void getFields(std::list<unsigned int>&) const { throw std::runtime_error("Not implemented"); } virtual DataProtocol& operator[](const unsigned int ) { throw std::runtime_error("Not implemented"); } virtual DataProtocol& operator[](const unsigned int ) const { throw std::runtime_error("Not implemented"); } virtual void fromString(const std::string&) { throw std::runtime_error("Not implemented"); } virtual std::string toString() const { throw std::runtime_error("Not implemented"); } virtual void fromBinary(const std::string&) { throw std::runtime_error("Not implemented"); } virtual std::string toBinary() const { throw std::runtime_error("Not implemented"); } virtual BeanProtocol& operator=(const BeanProtocol&) { throw std::runtime_error("Not implemented"); } virtual bool operator==(const BeanProtocol&) const { throw std::runtime_error("Not implemented"); } virtual bool operator!=(const BeanProtocol&) const { throw std::runtime_error("Not implemented"); } virtual bool operator==(const char*) const { throw std::runtime_error("Not implemented"); } virtual bool hasKey(unsigned int field) const { throw std::runtime_error("Not implemented"); } }; the other class (named GenericBean) implements it. This is the only way I've found to make this work, but now I want to turn it in a truly interface and remove the UTILS_EXPORT (which is an _declspec macro), and finally remove the forced linkage of B with A.

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• ELMAH - Using custom error pages to collecting user feedback

  - by vdh_ant

  Hey guys I'm looking at using ELMAH for the first time but have a requirement that needs to be met that I'm not sure how to go about achieving... Basically, I am going to configure ELMAH to work under asp.net MVC and get it to log errors to the database when they occur. On top of this I be using customErrors to direct the user to a friendly message page when an error occurs. Fairly standard stuff... The requirement is that on this custom error page I have a form which enables to user to provide extra information if they wish. Now the problem arises due to the fact that at this point the error is already logged and I need to associate the loged error with the users feedback. Normally, if I was using my own custom implementation, after I log the error I would pass through the ID of the error to the custom error page so that an association can be made. But because of the way that ELMAH works, I don't think the same is quite possible. Hence I was wondering how people thought that one might go about doing this.... Cheers UPDATE: My solution to the problem is as follows: public class UserCurrentConextUsingWebContext : IUserCurrentConext { private const string _StoredExceptionName = "System.StoredException."; private const string _StoredExceptionIdName = "System.StoredExceptionId."; public virtual string UniqueAddress { get { return HttpContext.Current.Request.UserHostAddress; } } public Exception StoredException { get { return HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] as Exception; } set { HttpContext.Current.Application[_StoredExceptionName + this.UniqueAddress] = value; } } public string StoredExceptionId { get { return HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] as string; } set { HttpContext.Current.Application[_StoredExceptionIdName + this.UniqueAddress] = value; } } } Then when the error occurs, I have something like this in my Global.asax: public void ErrorLog_Logged(object sender, ErrorLoggedEventArgs args) { var item = new UserCurrentConextUsingWebContext(); item.StoredException = args.Entry.Error.Exception; item.StoredExceptionId = args.Entry.Id; } Then where ever you are later you can pull out the details by var item = new UserCurrentConextUsingWebContext(); var error = item.StoredException; var errorId = item.StoredExceptionId; item.StoredException = null; item.StoredExceptionId = null; Note this isn't 100% perfect as its possible for the same IP to have multiple requests to have errors at the same time. But the likely hood of that happening is remote. And this solution is independent of the session, which in our case is important, also some errors can cause sessions to be terminated, etc. Hence why this approach has worked nicely for us.

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• Function-Local Static Const variable Initialization semantics.

  - by Hassan Syed

  The questions are in bold, for those that cannot be bothered reading a question in depth. This is a followup to this question. It is to do with the initialization semantics of static variables in functions. Static variables should be initialized once, and their internal state might be altered later - as I (currently) do in the linked question. However, the code in question does not require the feature to change the state of the variable later. Let me clarrify my position, since I don't require the string object's internal state to change. The code is for a trait class for meta programming, and as such would would benifit from a const char * const ptr -- thus Ideally a local cost static const variable is needed. My educated guess is that in this case the string in question will be optimally placed in memory by the link-loader, and that the code is more secure and maps to the intended semantics. This leads to the semantics of such a variable "The C++ Programming language Third Edition -- Stroustrup" does not have anything (that I could find) to say about this matter. All that is said is that the variable is initialized once when the flow of control of the thread first reaches the code. This leads me to ponder if the following code would be sensible, and if not what are the intended semantics ?. #include <iostream> const char * const GetString(const char * x_in) { static const char * const x = x_in; return x; } int main() { const char * const temp = GetString("yahoo"); std::cout << temp << std::endl; const char * const temp2 = GetString("yahoo2"); std::cout << temp2 << std::endl; } The following compiles on GCC and prints "yahoo" twice. Which is what I want -- However it might not be standards compliant (which is why I post this question). It might be more elegant to have two functions, "SetString" and "String" where the latter forwards to the first. If it is standards compliant does someone know of a templates implementation in boost (or elsewhere) ?

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• Written a resharper plugin that modifies the TextControl?

  - by Ajaxx

  Resharper claims to eat it's own dogfood, specifically, they claim that many of the features of Resharper are written ontop of R# (OpenAPI). I'm writing a simple plugin to fix up comments of the current document of a selection. When this plugin is run, it throws an exception as follows: Document can be modified inside a command scope only I've researched the error and can't find anything to help with this, so I'm hoping that possibly, you've written a plugin to accomplish this. If not, I hope the snippet is enough to help others get their own plugins underway. using System; using System.IO; using System.Windows.Forms; using JetBrains.ActionManagement; using JetBrains.DocumentModel; using JetBrains.IDE; using JetBrains.TextControl; using JetBrains.Util; namespace TinkerToys.Actions { [ActionHandler("TinkerToys.RewriteComment")] public class RewriteCommentAction : IActionHandler { #region Implementation of IActionHandler /// <summary> /// Updates action visual presentation. If presentation.Enabled is set to false, Execute /// will not be called. /// </summary> /// <param name="context">DataContext</param> /// <param name="presentation">presentation to update</param> /// <param name="nextUpdate">delegate to call</param> public bool Update(IDataContext context, ActionPresentation presentation, DelegateUpdate nextUpdate) { ITextControl textControl = context.GetData(DataConstants.TEXT_CONTROL); return textControl != null; } /// <summary> /// Executes action. Called after Update, that set ActionPresentation.Enabled to true. /// </summary> /// <param name="context">DataContext</param> /// <param name="nextExecute">delegate to call</param> public void Execute(IDataContext context, DelegateExecute nextExecute) { ITextControl textControl = context.GetData(DataConstants.TEXT_CONTROL); if (textControl != null) { TextRange textSelectRange; ISelectionModel textSelectionModel = textControl.SelectionModel; if ((textSelectionModel != null) && textSelectionModel.HasSelection()) { textSelectRange = textSelectionModel.Range; } else { textSelectRange = new TextRange(0, textControl.Document.GetTextLength()); } IDocument textDocument = textControl.Document; String textSelection = textDocument.GetText(textSelectRange); if (textSelection != null) { StringReader sReader = new StringReader(textSelection); StringWriter sWriter = new StringWriter(); Converter.Convert(sReader, sWriter); textSelection = sWriter.ToString(); textDocument.ReplaceText(textSelectRange, textSelection); } } } #endregion } } So what is this command scope it wants so badly? I had some additional logging in this prior to posting it so I'm absolutely certain that both the range and text are valid. In addition, the error seems to indicate that I'm missing some scope that I've been, as yet, unable to find.

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• Advantage of creating a generic repository vs. specific repository for each object?

  - by LuckyLindy

  We are developing an ASP.NET MVC application, and are now building the repository/service classes. I'm wondering if there are any major advantages to creating a generic IRepository interface that all repositories implement, vs. each Repository having its own unique interface and set of methods. For example: a generic IRepository interface might look like (taken from this answer): public interface IRepository : IDisposable { T[] GetAll<T>(); T[] GetAll<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter, List<Expression<Func<T, object>>> subSelectors); void Delete<T>(T entity); void Add<T>(T entity); int SaveChanges(); DbTransaction BeginTransaction(); } Each Repository would implement this interface (e.g. CustomerRepository:IRepository, ProductRepository:IRepository, etc). The alternate that we've followed in prior projects would be: public interface IInvoiceRepository : IDisposable { EntityCollection<InvoiceEntity> GetAllInvoices(int accountId); EntityCollection<InvoiceEntity> GetAllInvoices(DateTime theDate); InvoiceEntity GetSingleInvoice(int id, bool doFetchRelated); InvoiceEntity GetSingleInvoice(DateTime invoiceDate, int accountId); //unique InvoiceEntity CreateInvoice(); InvoiceLineEntity CreateInvoiceLine(); void SaveChanges(InvoiceEntity); //handles inserts or updates void DeleteInvoice(InvoiceEntity); void DeleteInvoiceLine(InvoiceLineEntity); } In the second case, the expressions (LINQ or otherwise) would be entirely contained in the Repository implementation, whoever is implementing the service just needs to know which repository function to call. I guess I don't see the advantage of writing all the expression syntax in the service class and passing to the repository. Wouldn't this mean easy-to-messup LINQ code is being duplicated in many cases? For example, in our old invoicing system, we call InvoiceRepository.GetSingleInvoice(DateTime invoiceDate, int accountId) from a few different services (Customer, Invoice, Account, etc). That seems much cleaner than writing the following in multiple places: rep.GetSingle(x => x.AccountId = someId && x.InvoiceDate = someDate.Date); The only disadvantage I see to using the specific approach is that we could end up with many permutations of Get* functions, but this still seems preferable to pushing the expression logic up into the Service classes. What am I missing?

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• how to use a tree data structure in C#

  - by matti

  I found an implementation for a tree at this SO question. Unfortunately I don't know how to use it. Also I made a change to it since LinkedList does not have Add method: delegate void TreeVisitor<T>(T nodeData); class NTree<T> { T data; List<NTree<T>> children; public NTree(T data) { this.data = data; children = new List<NTree<T>>(); } public void AddChild(T data) { children.Add(new NTree<T>(data)); } public NTree<T> GetChild(int i) { return children[i]; } public void Traverse(NTree<T> node, TreeVisitor<T> visitor) { visitor(node.data); foreach (NTree<T> kid in node.children) Traverse(kid, visitor); } } I have class named tTable and I want to store it's children and their grandchildren (...) in this tree. My need is to find immediate children and not traverse entire tree. I also might need to find children with some criteria. Let's say tTable has only name and I want to find children with names matching some criteria. tTables constructor gives name a value according to int-value (somehow). How do I use Traverse (write delegate) if I have code like this; int i = 0; Dictionary<string, NTree<tTable>> tableTreeByRootTableName = new Dictionary<string, NTree<tTable>>(); tTable aTable = new tTable(i++); tableTreeByRootTableName[aTable.Name] = new NTree(aTable); tableTreeByRootTableName[aTable.Name].AddChild(new tTable(i++)); tableTreeByRootTableName[aTable.Name].AddChild(new tTable(i++)); tableTreeByRootTableName[aTable.Name].GetChild(1).AddChild(new tTable(i++));

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• Adding objects to an NSMutableArray, order seems odd when parsing from an XML file

  - by diatrevolo

  Hello: I am parsing an XML file for two elements: "title" and "noType". Once these are parsed, I am adding them to an object called aMaster, an instance of my own Master class that contains NSString variables. I am then adding these instances to an NSMutableArray on a singleton, in order to call them elsewhere in the program. The problem is that when I call them, they don't seem to be on the same NSMutableArray index... each index contains either the title OR the noType element, when it should be both... can anyone see what I may be doing wrong? Below is the code for the parser. Thanks so much!! #import "XMLParser.h" #import "Values.h" #import "Listing.h" #import "Master.h" @implementation XMLParser @synthesize sharedSingleton, aMaster; - (XMLParser *) initXMLParser { [super init]; sharedSingleton = [Values sharedValues]; aMaster = [[Master init] alloc]; return self; } - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict { aMaster = [[Master alloc] init]; //Extract the attribute here. if ([elementName isEqualToString:@"intro"]) { aMaster.intro = [attributeDict objectForKey:@"enabled"]; } else if ([elementName isEqualToString:@"item"]) { aMaster.item_type = [attributeDict objectForKey:@"type"]; //NSLog(@"Did find item with type %@", [attributeDict objectForKey:@"type"]); //NSLog(@"Reading id value :%@", aMaster.item_type); } else { //NSLog(@"No known elements"); } //NSLog(@"Processing Element: %@", elementName); //HERE } - (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string { if(!currentElementValue) currentElementValue = [[NSMutableString alloc] initWithString:string]; else { [currentElementValue appendString:string];//[tempString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]]; CFStringTrimWhitespace((CFMutableStringRef)currentElementValue); } } - (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName { if ([elementName isEqualToString:@"item"]) { [sharedSingleton.master addObject:aMaster]; NSLog(@"Added %@ and %@ to the shared singleton", aMaster.title, aMaster.noType); //Only having one at a time added... don't know why [aMaster release]; aMaster = nil; } else if ([elementName isEqualToString:@"title"]) { [aMaster setValue:currentElementValue forKey:@"title"]; } else if ([elementName isEqualToString:@"noType"]) { [aMaster setValue:currentElementValue forKey:@"noType"]; //NSLog(@"%@ should load into the singleton", aMaster.noType); } NSLog(@"delimiter"); NSLog(@"%@ should load into the singleton", aMaster.title); NSLog(@"%@ should load into the singleton", aMaster.noType); [currentElementValue release]; currentElementValue = nil; } - (void) dealloc { [aMaster release]; [currentElementValue release]; [super dealloc]; } @end

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• Lua and Objective C not running script.

  - by beta

  I am trying to create an objective c interface that encapsulates the functionality of storing and running a lua script (compiled or not.) My code for the script interface is as follows: #import <Cocoa/Cocoa.h> #import "Types.h" #import "lua.h" #include "lualib.h" #include "lauxlib.h" @interface Script : NSObject<NSCoding> { @public s32 size; s8* data; BOOL done; } @property s32 size; @property s8* data; @property BOOL done; - (id) initWithScript: (u8*)data andSize:(s32)size; - (id) initFromFile: (const char*)file; - (void) runWithState: (lua_State*)state; - (void) encodeWithCoder: (NSCoder*)coder; - (id) initWithCoder: (NSCoder*)coder; @end #import "Script.h" @implementation Script @synthesize size; @synthesize data; @synthesize done; - (id) initWithScript: (s8*)d andSize:(s32)s { self = [super init]; self->size = s; self->data = d; return self; } - (id) initFromFile:(const char *)file { FILE* p; p = fopen(file, "rb"); if(p == NULL) return [super init]; fseek(p, 0, SEEK_END); s32 fs = ftell(p); rewind(p); u8* buffer = (u8*)malloc(fs); fread(buffer, 1, fs, p); fclose(p); return [self initWithScript:buffer andSize:size]; } - (void) runWithState: (lua_State*)state { if(luaL_loadbuffer(state, [self data], [self size], "Script") != 0) { NSLog(@"Error loading lua chunk."); return; } lua_pcall(state, 0, LUA_MULTRET, 0); } - (void) encodeWithCoder: (NSCoder*)coder { [coder encodeInt: size forKey: @"Script.size"]; [coder encodeBytes:data length:size forKey:@"Script.data"]; } - (id) initWithCoder: (NSCoder*)coder { self = [super init]; NSUInteger actualSize; size = [coder decodeIntForKey: @"Script.size"]; data = [[coder decodeBytesForKey:@"Script.data" returnedLength:&actualSize] retain]; return self; } @end Here is the main method: #import "Script.h" int main(int argc, char* argv[]) { Script* script = [[Script alloc] initFromFile:"./test.lua"]; lua_State* state = luaL_newstate(); luaL_openlibs(state); luaL_dostring(state, "print(_VERSION)"); [script runWithState:state]; luaL_dostring(state, "print(_VERSION)"); lua_close(state); } And the lua script is just: print("O Hai World!") Loading the file is correct, but I think it messes up at pcall. Any Help is greatly appreciated. Heading

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• HttpClient response handler always returns closed stream

  - by Alex Ciminian

  I'm new to Java development so please bear with me. Also, I hope I'm not the champion of tl;dr :). I'm using HttpClient to make requests over Http (duh!) and I'd gotten it to work for a simple servlet that receives an URL as a query string parameter. I realized that my code could use some refactoring, so I decided to make my own HttpResponseHandler, to clean up the code, make it reusable and improve exception handling. I currently have something like this: public class HttpResponseHandler implements ResponseHandler<InputStream>{ public InputStream handleResponse(HttpResponse response) throws ClientProtocolException, IOException { int statusCode = response.getStatusLine().getStatusCode(); InputStream in = null; if (statusCode != HttpStatus.SC_OK) { throw new HttpResponseException(statusCode, null); } else { HttpEntity entity = response.getEntity(); if (entity != null) { in = entity.getContent(); // This works // for (int i;(i = in.read()) >= 0;) System.out.print((char)i); } } return in; } } And in the method where I make the actual request: HttpClient httpclient = new DefaultHttpClient(); HttpGet httpget = new HttpGet(target); ResponseHandler<InputStream> httpResponseHandler = new HttpResponseHandler(); try { InputStream in = httpclient.execute(httpget, httpResponseHandler); // This doesn't work // for (int i;(i = in.read()) >= 0;) System.out.print((char)i); return in; } catch (HttpResponseException e) { throw new HttpResponseException(e.getStatusCode(), null); } The problem is that the input stream returned from the handler is closed. I don't have any idea why, but I've checked it with the prints in my code (and no, I haven't used them both at the same time :). While the first print works, the other one gives a closed stream error. I need InputStreams, because all my other methods expect an InputStream and not a String. Also, I want to be able to retrieve images (or maybe other types of files), not just text files. I can work around this pretty easily by giving up on the response handler (I have a working implementation that doesn't use it), but I'm pretty curious about the following: Why does it do what it does? How do I open the stream, if something closes it? What's the right way to do this, anyway :)? I've checked the docs and I couldn't find anything useful regarding this issue. To save you a bit of Googling, here's the Javadoc and here's the HttpClient tutorial (Section 1.1.8 - Response handlers). Thanks, Alex

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• SBT run differences between scala and java?

  - by Eric Cartner

  I'm trying to follow the log4j2 configuration tutorials in a SBT 0.12.1 project. Here is my build.sbt: name := "Logging Test" version := "0.0" scalaVersion := "2.9.2" libraryDependencies ++= Seq( "org.apache.logging.log4j" % "log4j-api" % "2.0-beta3", "org.apache.logging.log4j" % "log4j-core" % "2.0-beta3" ) When I run the main() defined in src/main/scala/logtest/Foo.scala: package logtest import org.apache.logging.log4j.{Logger, LogManager} object Foo { private val logger = LogManager.getLogger(getClass()) def main(args: Array[String]) { logger.trace("Entering application.") val bar = new Bar() if (!bar.doIt()) logger.error("Didn't do it.") logger.trace("Exiting application.") } } I get the output I was expecting given that src/main/resources/log4j2.xml sets the root logging level to trace: [info] Running logtest.Foo 08:39:55.627 [run-main] TRACE logtest.Foo$ - Entering application. 08:39:55.630 [run-main] TRACE logtest.Bar - entry 08:39:55.630 [run-main] ERROR logtest.Bar - Did it again! 08:39:55.630 [run-main] TRACE logtest.Bar - exit with (false) 08:39:55.630 [run-main] ERROR logtest.Foo$ - Didn't do it. 08:39:55.630 [run-main] TRACE logtest.Foo$ - Exiting application. However, when I run the main() defined in src/main/java/logtest/LoggerTest.java: package logtest; import org.apache.logging.log4j.Logger; import org.apache.logging.log4j.LogManager; public class LoggerTest { private static Logger logger = LogManager.getLogger(LoggerTest.class.getName()); public static void main(String[] args) { logger.trace("Entering application."); Bar bar = new Bar(); if (!bar.doIt()) logger.error("Didn't do it."); logger.trace("Exiting application."); } } I get the output: [info] Running logtest.LoggerTest ERROR StatusLogger Unable to locate a logging implementation, using SimpleLogger ERROR Bar Did it again! ERROR LoggerTest Didn't do it. From what I can tell, ERROR StatusLogger Unable to ... is usually a sign that log4j-core is not on my classpath. The lack of TRACE messages seems to indicate that my log4j2.xml settings aren't on the classpath either. Why should there be any difference in classpath if I'm running Foo.main versus LoggerTest.main? Or is there something else causing this behavior? Update I used SBT Assembly to build a fat jar of this project and specified logtest.LoggerTest to be the main class. Running it from the command line produced correct results: Eric-Cartners-iMac:target ecartner$ java -jar "Logging Test-assembly-0.0.jar" 10:52:23.220 [main] TRACE logtest.LoggerTest - Entering application. 10:52:23.221 [main] TRACE logtest.Bar - entry 10:52:23.221 [main] ERROR logtest.Bar - Did it again! 10:52:23.221 [main] TRACE logtest.Bar - exit with (false) 10:52:23.221 [main] ERROR logtest.LoggerTest - Didn't do it. 10:52:23.221 [main] TRACE logtest.LoggerTest - Exiting application.

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• Is Java assert broken?

  - by BlairHippo

  While poking around the questions, I recently discovered the assert keyword in Java. At first, I was excited. Something useful I didn't already know! A more efficient way for me to check the validity of input parameters! Yay learning! But then I took a closer look, and my enthusiasm was not so much "tempered" as "snuffed-out completely" by one simple fact: you can turn assertions off.* This sounds like a nightmare. If I'm asserting that I don't want the code to keep going if the input listOfStuff is null, why on earth would I want that assertion ignored? It sounds like if I'm debugging a piece of production code and suspect that listOfStuff may have been erroneously passed a null but don't see any logfile evidence of that assertion being triggered, I can't trust that listOfStuff actually got sent a valid value; I also have to account for the possibility that assertions may have been turned off entirely. And this assumes that I'm the one debugging the code. Somebody unfamiliar with assertions might see that and assume (quite reasonably) that if the assertion message doesn't appear in the log, listOfStuff couldn't be the problem. If your first encounter with assert was in the wild, would it even occur to you that it could be turned-off entirely? It's not like there's a command-line option that lets you disable try/catch blocks, after all. All of which brings me to my question (and this is a question, not an excuse for a rant! I promise!): What am I missing? Is there some nuance that renders Java's implementation of assert far more useful than I'm giving it credit for? Is the ability to enable/disable it from the command line actually incredibly valuable in some contexts? Am I misconceptualizing it somehow when I envision using it in production code in lieu of statements like if (listOfStuff == null) barf();? I just feel like there's something important here that I'm not getting. *Okay, technically speaking, they're actually off by default; you have to go out of your way to turn them on. But still, you can knock them out entirely.

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• Observer pattern used with decorator pattern

  - by icelated

  I want to make a program that does an order entry system for beverages. ( i will probably do description, cost) I want to use the Decorator pattern and the observer pattern. I made a UML drawing and saved it as a pic for easy viewing. This site wont let me upload as a word doc so i have to upload a pic - i hope its easily viewable.... I need to know if i am doing the UML / design patterns correctly before moving on to the coding part. Beverage is my abstract component class. Espresso, houseblend, darkroast are my concrete subject classes.. I also have a condiment decorator class milk,mocha,soy,whip. would be my observer? because they would be interested in data changes to cost? Now, would the espresso,houseblend etc, be my SUBJECT and the condiments be my observer? My theory is that Cost is a changes and that the condiments need to know the changes? So, subject = esspresso,houseblend,darkroast,etc.. // they hold cost() Observer = milk,mocha,soy,whip? // they hold cost() would be the concrete components and the milk,mocha,soy,whip? would be the decorator! So, following good software engineering practices "design to an interface and not implementation" or "identify things that change from those that dont" would i need a costbehavior interface? If you look at the UML you will see where i am going with this and see if i am implementing observer + Decorator pattern correctly? I think the decorator is correct. since, the pic is not very viewable i will detail the classes here: Beverage class(register observer, remove observer, notify observer, description) these classes are the concrete beverage classes espresso, houseblend,darkroast, decaf(cost,getdescription,setcost,costchanged) interface observer class(update) // cost? interface costbehavior class(cost) // since this changes? condiment decorator class( getdescription) concrete classes that are linked to the 2 interface s and decorator are: milk,mocha,soy,whip(cost,getdescription,update) these are my decorator/ wrapper classes. Thank you.. Is there a way to make this picture bigger?

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• Performance Optimization for Matrix Rotation

  - by Summer_More_More_Tea

  Hello everyone: I'm now trapped by a performance optimization lab in the book "Computer System from a Programmer's Perspective" described as following: In a N*N matrix M, where N is multiple of 32, the rotate operation can be represented as: Transpose: interchange elements M(i,j) and M(j,i) Exchange rows: Row i is exchanged with row N-1-i A example for matrix rotation(N is 3 instead of 32 for simplicity): ------- ------- |1|2|3| |3|6|9| ------- ------- |4|5|6| after rotate is |2|5|8| ------- ------- |7|8|9| |1|4|7| ------- ------- A naive implementation is: #define RIDX(i,j,n) ((i)*(n)+(j)) void naive_rotate(int dim, pixel *src, pixel *dst) { int i, j; for (i = 0; i < dim; i++) for (j = 0; j < dim; j++) dst[RIDX(dim-1-j, i, dim)] = src[RIDX(i, j, dim)]; } I come up with an idea by inner-loop-unroll. The result is: Code Version Speed Up original 1x unrolled by 2 1.33x unrolled by 4 1.33x unrolled by 8 1.55x unrolled by 16 1.67x unrolled by 32 1.61x I also get a code snippet from pastebin.com that seems can solve this problem: void rotate(int dim, pixel *src, pixel *dst) { int stride = 32; int count = dim >> 5; src += dim - 1; int a1 = count; do { int a2 = dim; do { int a3 = stride; do { *dst++ = *src; src += dim; } while(--a3); src -= dim * stride + 1; dst += dim - stride; } while(--a2); src += dim * (stride + 1); dst -= dim * dim - stride; } while(--a1); } After carefully read the code, I think main idea of this solution is treat 32 rows as a data zone, and perform the rotating operation respectively. Speed up of this version is 1.85x, overwhelming all the loop-unroll version. Here are the questions: In the inner-loop-unroll version, why does increment slow down if the unrolling factor increase, especially change the unrolling factor from 8 to 16, which does not effect the same when switch from 4 to 8? Does the result have some relationship with depth of the CPU pipeline? If the answer is yes, could the degrade of increment reflect pipeline length? What is the probable reason for the optimization of data-zone version? It seems that there is no too much essential difference from the original naive version. EDIT: My test environment is Intel Centrino Duo processor and the verion of gcc is 4.4 Any advice will be highly appreciated! Kind regards!

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• Understanding CLR 2.0 Memory Model

  - by Eloff

  Joe Duffy, gives 6 rules that describe the CLR 2.0+ memory model (it's actual implementation, not any ECMA standard) I'm writing down my attempt at figuring this out, mostly as a way of rubber ducking, but if I make a mistake in my logic, at least someone here will be able to catch it before it causes me grief. Rule 1: Data dependence among loads and stores is never violated. Rule 2: All stores have release semantics, i.e. no load or store may move after one. Rule 3: All volatile loads are acquire, i.e. no load or store may move before one. Rule 4: No loads and stores may ever cross a full-barrier (e.g. Thread.MemoryBarrier, lock acquire, Interlocked.Exchange, Interlocked.CompareExchange, etc.). Rule 5: Loads and stores to the heap may never be introduced. Rule 6: Loads and stores may only be deleted when coalescing adjacent loads and stores from/to the same location. I'm attempting to understand these rules. x = y y = 0 // Cannot move before the previous line according to Rule 1. x = y z = 0 // equates to this sequence of loads and stores before possible re-ordering load y store x load 0 store z Looking at this, it appears that the load 0 can be moved up to before load y, but the stores may not be re-ordered at all. Therefore, if a thread sees z == 0, then it also will see x == y. If y was volatile, then load 0 could not move before load y, otherwise it may. Volatile stores don't seem to have any special properties, no stores can be re-ordered with respect to each other (which is a very strong guarantee!) Full barriers are like a line in the sand which loads and stores can not be moved over. No idea what rule 5 means. I guess rule 6 means if you do: x = y x = z Then it is possible for the CLR to delete both the load to y and the first store to x. x = y z = y // equates to this sequence of loads and stores before possible re-ordering load y store x load y store z // could be re-ordered like this load y load y store x store z // rule 6 applied means this is possible? load y store x // but don't pop y from stack (or first duplicate item on top of stack) store z What if y was volatile? I don't see anything in the rules that prohibits the above optimization from being carried out. This does not violate double-checked locking, because the lock() between the two identical conditions prevents the loads from being moved into adjacent positions, and according to rule 6, that's the only time they can be eliminated. So I think I understand all but rule 5, here. Anyone want to enlighten me (or correct me or add something to any of the above?)

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• How to have member variables and public methods in a jQuery plugin?

  - by user169867

  I'm trying to create a jQuery plugin that will create something like an autoCompleteBox but with custom features. How do I store member variables for each matching jQuery element? For example I'll need to store a timerID for each. I'd also like to store references to some of the DOM elements that make up the control. I'd like to be able to make a public method that works something like: $("#myCtrl").autoCompleteEx.addItem("1"); But in the implementation of addItem() how can I access the member variables for that particular object like its timerID or whatever? Below is what I have so far... Thanks for any help or suggestions! (function($) { //Attach this new method to jQuery $.fn.autoCompleteEx = function(options) { //Merge Given Options W/ Defaults, But Don't Alter Either var opts = $.extend({}, $.fn.autoCompleteEx.defaults, options); //Iterate over the current set of matched elements return this.each(function() { var acx = $(this); //Get JQuery Version Of Element (Should Be Div) //Give Div Correct Class & Add <ul> w/ input item to it acx.addClass("autoCompleteEx"); acx.html("<ul><li class=\"input\"><input type=\"text\"/></li></ul>"); //Grab Input As JQ Object var input = $("input", acx); //Wireup Div acx.click(function() { input.focus().val( input.val() ); }); //Wireup Input input.keydown(function(e) { var kc = e.keyCode; if(kc == 13) //Enter { } else if(kc == 27) //Esc { } else { //Resize TextArea To Input var width = 50 + (_txtArea.val().length*10); _txtArea.css("width", width+"px"); } }); }); //End Each JQ Element }; //End autoCompleteEx() //Private Functions function junk() { }; //Public Functions $.fn.autoCompleteEx.addItem = function(id,txt) { var x = this; var y = 0; }; //Default Settings $.fn.autoCompleteEx.defaults = { minChars: 2, delay: 300, maxItems: 1 }; //End Of Closure })(jQuery);

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• Java map / nio / NFS issue causing a VM fault: "a fault occurred in a recent unsafe memory access op

  - by Matthew Bloch

  I have written a parser class for a particular binary format (nfdump if anyone is interested) which uses java.nio's MappedByteBuffer to read through files of a few GB each. The binary format is just a series of headers and mostly fixed-size binary records, which are fed out to the called by calling nextRecord(), which pushes on the state machine, returning null when it's done. It performs well. It works on a development machine. On my production host, it can run for a few minutes or hours, but always seems to throw "java.lang.InternalError: a fault occurred in a recent unsafe memory access operation in compiled Java code", fingering one of the Map.getInt, getShort methods, i.e. a read operation in the map. The uncontroversial (?) code that sets up the map is this: /** Set up the map from the given filename and position */ protected void open() throws IOException { // Set up buffer, is this all the flexibility we'll need? channel = new FileInputStream(file).getChannel(); MappedByteBuffer map1 = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size()); map1.load(); // we want the whole thing, plus seems to reduce frequency of crashes? map = map1; // assumes the host writing the files is little-endian (x86), ought to be configurable map.order(java.nio.ByteOrder.LITTLE_ENDIAN); map.position(position); } and then I use the various map.get* methods to read shorts, ints, longs and other sequences of bytes, before hitting the end of the file and closing the map. I've never seen the exception thrown on my development host. But the significant point of difference between my production host and development is that on the former, I am reading sequences of these files over NFS (probably 6-8TB eventually, still growing). On my dev machine, I have a smaller selection of these files locally (60GB), but when it blows up on the production host it's usually well before it gets to 60GB of data. Both machines are running java 1.6.0_20-b02, though the production host is running Debian/lenny, the dev host is Ubuntu/karmic. I'm not convinced that will make any difference. Both machines have 16GB RAM, and are running with the same java heap settings. I take the view that if there is a bug in my code, there is enough of a bug in the JVM not to throw me a proper exception! But I think it is just a particular JVM implementation bug due to interactions between NFS and mmap, possibly a recurrence of 6244515 which is officially fixed. I already tried adding in a "load" call to force the MappedByteBuffer to load its contents into RAM - this seemed to delay the error in the one test run I've done, but not prevent it. Or it could be coincidence that was the longest it had gone before crashing! If you've read this far and have done this kind of thing with java.nio before, what would your instinct be? Right now mine is to rewrite it without nio :)

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• Double Buffering for Game objects, what's a nice clean generic C++ way?

  - by Gary

  This is in C++. So, I'm starting from scratch writing a game engine for fun and learning from the ground up. One of the ideas I want to implement is to have game object state (a struct) be double-buffered. For instance, I can have subsystems updating the new game object data while a render thread is rendering from the old data by guaranteeing there is a consistent state stored within the game object (the data from last time). After rendering of old and updating of new is finished, I can swap buffers and do it again. Question is, what's a good forward-looking and generic OOP way to expose this to my classes while trying to hide implementation details as much as possible? Would like to know your thoughts and considerations. I was thinking operator overloading could be used, but how do I overload assign for a templated class's member within my buffer class? for instance, I think this is an example of what I want: doublebuffer<Vector3> data; data.x=5; //would write to the member x within the new buffer int a=data.x; //would read from the old buffer's x member data.x+=1; //I guess this shouldn't be allowed If this is possible, I could choose to enable or disable double-buffering structs without changing much code. This is what I was considering: template <class T> class doublebuffer{ T T1; T T2; T * current=T1; T * old=T2; public: doublebuffer(); ~doublebuffer(); void swap(); operator=()?... }; and a game object would be like this: struct MyObjectData{ int x; float afloat; } class MyObject: public Node { doublebuffer<MyObjectData> data; functions... } What I have right now is functions that return pointers to the old and new buffer, and I guess any classes that use them have to be aware of this. Is there a better way?

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• C++ vs. C++/CLI: Const qualification of virtual function parameters

  - by James McNellis

  [All of the following was tested using Visual Studio 2008 SP1] In C++, const qualification of parameter types does not affect the type of a function (8.3.5/3: "Any cv-qualifier modifying a parameter type is deleted") So, for example, in the following class hierarchy, Derived::Foo overrides Base::Foo: struct Base { virtual void Foo(const int i) { } }; struct Derived : Base { virtual void Foo(int i) { } }; Consider a similar hierarchy in C++/CLI: ref class Base abstract { public: virtual void Foo(const int) = 0; }; ref class Derived : public Base { public: virtual void Foo(int i) override { } }; If I then create an instance of Derived: int main(array<System::String ^> ^args) { Derived^ d = gcnew Derived; } it compiles without errors or warnings. When I run it, it throws the following exception and then terminates: An unhandled exception of type 'System.TypeLoadException' occurred in ClrVirtualTest.exe Additional information: Method 'Foo' in type 'Derived'...does not have an implementation. That exception seems to indicate that the const qualification of the parameter does affect the type of the function in C++/CLI (or, at least it affects overriding in some way). However, if I comment out the line containing the definition of Derived::Foo, the compiler reports the following error (on the line in main where the instance of Derived is instantiated): error C2259: 'Derived': cannot instantiate abstract class If I add the const qualifier to the parameter of Derived::Foo or remove the const qualifier from the parameter of Base::Foo, it compiles and runs with no errors. I would think that if the const qualification of the parameter affects the type of the function, I should get this error if the const qualification of the parameter in the derived class virtual function does not match the const qualification of the parameter in the base class virtual function. If I change the type of Derived::Foo's parameter from an int to a double, I get the following warning (in addition to the aforementioned error, C2259): warning C4490: 'override': incorrect use of override specifier; 'Derived::Foo' does not match a base ref class method So, my question is, effectively, does the const qualification of function parameters affect the type of the function in C++/CLI? If so, why does this compile and why are there no errors or warnings? If not, why is an exception thrown?

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