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  • Mamimum page fetch with maximum bandwith

    - by Ehsan
    Hi I want to create an application like a spider I've implement fetching page as the following code in multi-thread application but there is two problem 1) I want to use my maximum bandwidth to send/receive request, how should I config my request to do so (Like Download Accelerator application and the like) cause I heard the normal application will use 66% of the available bandwidth. 2) I don't know what exactly HttpWebRequest.KeepAlive do, but as its name implies I think i can create a connection to a website and without closing the connection sending another request to that web site using existing connection. does it boost performance or Im wrong public PageFetchResult Fetch() { PageFetchResult fetchResult = new PageFetchResult(); try { HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URLAddress); HttpWebResponse resp = (HttpWebResponse)req.GetResponse(); Uri requestedURI = new Uri(URLAddress); Uri responseURI = resp.ResponseUri; if (Uri.Equals(requestedURI, responseURI)) { string resultHTML = ""; byte[] reqHTML = ResponseAsBytes(resp); if (!string.IsNullOrEmpty(FetchingEncoding)) resultHTML = Encoding.GetEncoding(FetchingEncoding).GetString(reqHTML); else if (!string.IsNullOrEmpty(resp.CharacterSet)) resultHTML = Encoding.GetEncoding(resp.CharacterSet).GetString(reqHTML); req.Abort(); resp.Close(); fetchResult.IsOK = true; fetchResult.ResultHTML = resultHTML; } else { URLAddress = responseURI.AbsoluteUri; relayPageCount++; if (relayPageCount > 5) { fetchResult.IsOK = false; fetchResult.ErrorMessage = "Maximum page redirection occured."; relayPageCount = 0; return fetchResult; } req.Abort(); resp.Close(); return Fetch(); } } catch (Exception ex) { fetchResult.IsOK = false; fetchResult.ErrorMessage = ex.Message; } return fetchResult; }

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  • Pros and Cons of using SqlCommand Prepare in C#?

    - by MadBoy
    When i was reading books to learn C# (might be some old Visual Studio 2005 books) I've encountered advice to always use SqlCommand.Prepare everytime I execute SQL call (whether its' a SELECT/UPDATE or INSERT on SQL SERVER 2005/2008) and I pass parameters to it. But is it really so? Should it be done every time? Or just sometimes? Does it matter whether it's one parameter being passed or five or twenty? What boost should it give if any? Would it be noticeable at all (I've been using SqlCommand.Prepare here and skipped it there and never had any problems or noticeable differences). For the sake of the question this is my usual code that I use, but this is more of a general question. public static decimal pobierzBenchmarkKolejny(string varPortfelID, DateTime data, decimal varBenchmarkPoprzedni, decimal varStopaOdniesienia) { const string preparedCommand = @"SELECT [dbo].[ufn_BenchmarkKolejny](@varPortfelID, @data, @varBenchmarkPoprzedni, @varStopaOdniesienia) AS 'Benchmark'"; using (var varConnection = Locale.sqlConnectOneTime(Locale.sqlDataConnectionDetailsDZP)) //if (varConnection != null) { using (var sqlQuery = new SqlCommand(preparedCommand, varConnection)) { sqlQuery.Prepare(); sqlQuery.Parameters.AddWithValue("@varPortfelID", varPortfelID); sqlQuery.Parameters.AddWithValue("@varStopaOdniesienia", varStopaOdniesienia); sqlQuery.Parameters.AddWithValue("@data", data); sqlQuery.Parameters.AddWithValue("@varBenchmarkPoprzedni", varBenchmarkPoprzedni); using (var sqlQueryResult = sqlQuery.ExecuteReader()) if (sqlQueryResult != null) { while (sqlQueryResult.Read()) { //sqlQueryResult["Benchmark"]; } } } }

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  • Remove then Query fails in JPA (deleted entity passed to persist)

    - by nag
    I have two entitys MobeeCustomer and CustomerRegion i want to remove the object from CustomerRegion first Im put join Coloumn in CustomerRegion is null then Remove the Object from the entityManager but Iam getting Exception MobeeCustomer: public class MobeeCustomer implements Serialization{ private Long id; private String custName; private String Address; private String phoneNo; private Set<CustomerRegion> customerRegion = new HashSet<CustomerRegion>(0); @OneToMany(cascade = { CascadeType.PERSIST, CascadeType.REMOVE }, fetch = FetchType.LAZY, mappedBy = "mobeeCustomer") public Set<CustomerRegion> getCustomerRegion() { return CustomerRegion; } public void setCustomerRegion(Set<CustomerRegion> customerRegion) { CustomerRegion = customerRegion; } } CustomerRegion public class CustomerRegion implements Serializable{ private Long id; private String custName; private String description; private String createdBy; private Date createdOn; private String updatedBy; private Date updatedOn; private MobeeCustomer mobeeCustomer; @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "MOBEE_CUSTOMER") public MobeeCustomer getMobeeCustomer() { return mobeeCustomer; } public void setMobeeCustomer(MobeeCustomer mobeeCustomer) { this.mobeeCustomer = mobeeCustomer; } } sample code: for (CustomerRegion region : deletedRegionList) { region.setMobeeCustomer(null); getEntityManager().remove(region); } StackTrace: please suggest me how to remove the CustomerRegion Object I am getting Exception javax.persistence.EntityNotFoundException: deleted entity passed to persist: [com.manam.mobee.persist.entity.CustomerRegion#<null>] 15:46:34,614 ERROR [STDERR] at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:613) 15:46:34,614 ERROR [STDERR] at org.hibernate.ejb.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:299) 15:46:34,614 ERROR [STDERR] at org.jboss.seam.persistence.EntityManagerProxy.flush(EntityManagerProxy.java:92) 15:46:34,614 ERROR [STDERR] at org.jboss.seam.framework.EntityHome.update(EntityHome.java:64)

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  • Parse string to create a list of element

    - by Nick
    I have a string like this: "\r color=\"red\" name=\"Jon\" \t\n depth=\"8.26\" " And I want to parse this string and create a std::list of this object: class data { std::string name; std::string value; }; Where for example: name = color value = red What is the fastest way? I can use boost. EDIT: This is what i've tried: vector<string> tokens; split(tokens, str, is_any_of(" \t\f\v\n\r")); if(tokens.size() > 1) { list<data> attr; for_each(tokens.begin(), tokens.end(), [&attr](const string& token) { if(token.empty() || !contains(token, "=")) return; vector<string> tokens; split(tokens, token, is_any_of("=")); erase_all(tokens[1], "\""); attr.push_back(data(tokens[0], tokens[1])); } ); } But it does not work if there are spaces inside " ": like color="red 1".

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  • Messages not forwarded to error queue when exception is thrown in handler (it works on my machine)

    - by darthjit
    e are using NServicebus 4.0.5 with sql server(sql server 2012) as transport. When the handler throws an exception, NSB does not retry or move the message to the error queue. Successful messages make it to the audit queue but the failed/errored ones don't! . Interestingly, all this works on our local machines(windows 7 ,sql server localdb) but not on windows server 2012 (sql server 2012). Here is the config info on the subscriber: <add name="NServiceBus/Transport" connectionString="Data Source=xxx;Initial Catalog=NServiceBus;Integrated Security=SSPI;Enlist=false;" /> <add name="NServiceBus/Persistence" connectionString="Data Source=xxx;Initial Catalog=NServiceBus;Integrated Security=SSPI;Enlist=false;" /> <MessageForwardingInCaseOfFaultConfig ErrorQueue="error" /> <UnicastBusConfig ForwardReceivedMessagesTo="audit"> <MessageEndpointMappings> <add Assembly="Services.Section.Messages" Endpoint= "Services.ACL.Worker" /> </MessageEndpointMappings> </UnicastBusConfig> And in code it is configured as follows: public class EndpointConfig : IConfigureThisEndpoint, AsA_Server, IWantCustomInitialization { public void Init() { IContainer container = ContainerInstanceProvider. GetContainerInstance(); Configure .Transactions.Enable(); Configure.With() .AutofacBuilder(container) .UseTransport<SqlServer>() .Log4Net() //.Serialization.Json() .UseNHibernateSubscriptionPersister() .UseNHibernateTimeoutPersister() .MessageForwardingInCaseOfFault() .RijndaelEncryptionService() .DefiningCommandsAs(type => type.Namespace != null &&type .Namespace.EndsWith("Commands")) .DefiningEventsAs(type => type.Namespace != null &&type .Namespace.EndsWith("Events")) .UnicastBus(); } } Any ideas on how to fix this? here is the log info (there is a lot there, search for error to see the relevant parts) https://gist.github.com/ranji/7378249

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  • template specialization of a auto_ptr<T>

    - by Chris Kaminski
    Maybe I'm overcomplicating things, but then again, I do sort of like clean interfaces. Let's say I want a specialization of auto_ptr for an fstream - I want a default fstream for the generic case, but allow a replacement pointer? tempate <> class auto_ptr<fstream> static fstream myfStream; fstream* ptr; public: auto_ptr() { // set ptr to &myfStream; } reset(fstream* newPtr) { // free old ptr if not the static one. ptr = newPtr }; } Would you consider something different or more elegant? And how would you keep something like the above from propagating outside this particular compilation unit? [The actual template is a boost::scoped_ptr.] EDIT: It's a contrived example. Ignore the fstream - it's about providing a default instance of object for an auto_ptr. I may not want to provide a specialized instance, but would like to keep the auto_ptr semantics for this static default object. class UserClass { public: auto_ptr<fstream> ptr; UserClass() { } } I may not provide an dynamic object at construction time - I still want it to have a meaningful default. Since I'm not looking at ownership-transfer semantics, it really shouldn't matter that my pointer class is pointing to a statically allocated object, no?

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  • Hashing the state of a complex object in .NET

    - by Jan
    Some background information: I am working on a C#/WPF application, which basically is about creating, editing, saving and loading some data model. The data model contains of a hierarchy of various objects. There is a "root" object of class A, which has a list of objects of class B, which each has a list of objects of class C, etc. Around 30 classes involved in total. Now my problem is that I want to prompt the user with the usual "you have unsaved changes, save?" dialog, if he tries to exit the program. But how do I know if the data in current loaded model is actually changed? There is of course ways to solve this, like e.g. reloading the model from file and compare against the one in memory value by value or make every UI control set a flag indicating the model has been changed. Now instead, I want to create a hash value based on the model state on load and generate a new value when the user tries to exit, and compare those two. Now the question: So inspired of that, I was wondering if there exist some way to generate a hash value from the (value)state of some arbitrary complex object? Preferably in a generic way, e.g. no need to apply attributes to each involved class/field. One idea could be to use some of .NET's serialization functionality (assuming it will work out-of-the-box in this case) and apply a hash function to the content of the resulting file. However, I guess there exist some more suitable approach. Thanks in advance.

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  • Design: How to declare a specialized memory handler class

    - by Michael Dorgan
    On an embedded type system, I have created a Small Object Allocator that piggy backs on top of a standard memory allocation system. This allocator is a Boost::simple_segregated_storage< class and it does exactly what I need - O(1) alloc/dealloc time on small objects at the cost of a touch of internal fragmentation. My question is how best to declare it. Right now, it's scope static declared in our mem code module, which is probably fine, but it feels a bit exposed there and is also now linked to that module forever. Normally, I declare it as a monostate or a singleton, but this uses the dynamic memory allocator (where this is located.) Furthermore, our dynamic memory allocator is being initialized and used before static object initialization occurs on our system (as again, the memory manager is pretty much the most fundamental component of an engine.) To get around this catch 22, I added an extra 'if the small memory allocator exists' to see if the small object allocator exists yet. That if that now must be run on every small object allocation. In the scheme of things, this is nearly negligable, but it still bothers me. So the question is, is there a better way to declare this portion of the memory manager that helps decouple it from the memory module and perhaps not costing that extra isinitialized() if statement? If this method uses dynamic memory, please explain how to get around lack of initialization of the small object portion of the manager.

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  • No Debug information of an iPhone app

    - by Markus Pilman
    Hi all, I wrote an iPhone app which uses a third party library. I crosscompiled this library successfully and everything works smoothly. But when I want to debug the application, it would make sense to also be able to debug the library. So I compiled also the external library with debuging information (usign the gcc option -ggdb). But when I want to debug it, I get the correct symbol names, but the positions are always wrong/extremly wierd (locale_facets.tcc:2505 or iostream:76). For example a stack trace could look like this: #0 0x000045e8 in zorba::serialization::SerializeBaseClass::SerializeBaseClass () at iostream:76 #1 0x0001d990 in zorba::RCObject::RCObject () at iostream:76 #2 0x00025187 in zorba::xqpStringStore::xqpStringStore () at iostream:76 #3 0x000719e4 in zorba::String::String () at locale_facets.tcc:2505 #4 0x00030513 in iphone::iLabelModule::getURI (this=0x533f710) at /Users/sausalito/eth/izorba/sandbox/ilabel.cpp:19 #5 0x00356766 in zorba::static_context::bind_external_module () at locale_facets.tcc:2505 #6 0x0006139d in zorba::StaticContextImpl::registerModule () at locale_facets.tcc:2505 #7 0x000333e5 in -[ZorbaCaller init] (self=0x53405c0, _cmd=0x95583398) at /Users/sausalito/eth/izorba/sandbox/ZorbaCaller.mm:61 #8 0x00033180 in +[ZorbaCaller instance] (self=0x11dc2bc, _cmd=0x93679591) at /Users/sausalito/eth/izorba/sandbox/ZorbaCaller.mm:37 #9 0x0003d998 in -[testOne execute:] (self=0x530d560, _cmd=0x9366b126, sender=0x5121da0) at /Users/sausalito/eth/izorba/sandbox/generator/testOne.mm:13 #10 0x01a21405 in -[UIApplication sendAction:to:from:forEvent:] () #11 0x01a84b4e in -[UIControl sendAction:to:forEvent:] () #12 0x01a86d6f in -[UIControl(Internal) _sendActionsForEvents:withEvent:] () #13 0x01a85abb in -[UIControl touchesEnded:withEvent:] () #14 0x01a3addf in -[UIWindow _sendTouchesForEvent:] () #15 0x01a247c8 in -[UIApplication sendEvent:] () #16 0x01a2b061 in _UIApplicationHandleEvent () #17 0x03b6fd59 in PurpleEventCallback () #18 0x034a8b80 in CFRunLoopRunSpecific () #19 0x034a7c48 in CFRunLoopRunInMode () #20 0x03b6e615 in GSEventRunModal () #21 0x03b6e6da in GSEventRun () #22 0x01a2bfaf in UIApplicationMain () #23 0x0002dd7e in main (argc=1, argv=0xbffff044) at /Users/sausalito/eth/izorba/sandbox/main.m:16 Does anybody have an idea, where these wrong locations come from?

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  • How to organize and manage multiple database credentials in application?

    - by Polaris878
    Okay, so I'm designing a stand-alone web service (using RestLET as my framework). My application is divided in to 3 layers: Data Layer (just above the database, provides APIs for connecting to/querying database, and a database object) Object layer (responsible for serialization from the data layer... provides objects which the client layer can use without worrying about database) Client layer (This layer is the RestLET web service... basically just creates objects from the object layer and fulfills webservice request) Now, for each object I create in the object layer, I want to use different credentials (so I can sandbox each object...). The object layer should not know the exact credentials (IE the login/pw/DB URL etc). What would be the best way to manage this? I'm thinking that I should have a super class Database object in my data layer... and each subclass will contain the required log-in information... this way my object layer can just go Database db = new SubDatabase(); and then continue using that database. On the client level, they would just be able to go ItemCollection items = new ItemCollection(); and have no idea/control over the database that gets connected. I'm asking this because I am trying to make my platform extensible, so that others can easily create services off of my platform. If anyone has any experience with these architectural problems or how to manage this sort of thing I'd appreciate any insight or advice... Feel free to ask questions if this is confusing. Thanks! My platform is Java, the REST framework I'm using is RestLET, my database is MySQL.

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  • How can I improve the performance of LinqToSql queries that use EntitySet properties?

    - by DanM
    I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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  • Is there any other way of using signed applets

    - by 640KB
    Hi There, If I want to deploy high privileged applets they need to be signed. For that a certificate is created and then a jar file is signed with a jarsigner. After that in the HTML code one has to specify code,codebase AND archive (jar) which we signed before. However I wrote a servlet which acts as two things: it sits at the URL pointed by the codebase and serves class bytecode to the applet. The same servlet also uses serialization to communicate with the applet whereby whenever the applet gets a class it does not know it goes to the codebase which ends up back at the servlet. Almost like a mini RMI setup but simpler. I hope you can see the power in this. Unfortunately for signed applets one needs the archive. Now the servlet is also able to load a Certificate object and can send it to the applet too. So here is the setup: At one point the applet receives class bytecode and it also has the Certificate. It would be nice if the applet could instantiate all received classes using that certificate (otherwise code from jar is signed and outside is not which prompts nasty messages to the user). So my question to you fine Java aficionados: Would there by any way for me to use the bytecode data and the Certificate to instantiate the class as a signed object so that the plugin pops the Security dialog, accepts teh certificate and elevates the object's privileges. What I could find is that the there is a class CodeSource that accepts codebase URL and certificate and is essential to the signing process. What I am not sure is how one could intercept the class loading inside applets to install additional certificates not obtained through a JAR file via archive. What do you say? Thanks a bunch.

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  • C++: Efficiently adding integers to strings

    - by Shinka
    I know how to add integers to strings, but I'm not sure I'm doing it in an efficient matters. I have a class where I often have to return a string plus an integer (a different integer each time), in Java I would do something like public class MyClass { final static String S = "MYSTRING"; private int id = 0; public String getString() { return S + (id++); } } But in C++ I have to do; class MyClass { private: std::string S; // For some reason I can't do const std::string S = "MYSTRING"; int id; public: MyClass() { S = "MYSTRING"; id = 0; } std::string getString() { std::ostringstream oss; oss << S << id++; return oss.str(); } } An additional constraint: I don't want (in fact, in can't) use Boost or any other librairies, I'll have to work with the standard library. So the thing is; the code works, but in C++ I have to create a bunch of ostringstream objects, so it seems inefficient. To be fair, perhaps Java do the same and I just don't notice it, I say it's inefficient mostly because I know very little about strings. Is there a more efficient way to do this ?

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  • Intel MKL memory management and exceptions

    - by Andrew
    Hello everyone, I am trying out Intel MKL and it appears that they have their own memory management (C-style). They suggest using their MKL_malloc/MKL_free pairs for vectors and matrices and I do not know what is a good way to handle it. One of the reasons for that is that memory-alignment is recommended to be at least 16-byte and with these routines it is specified explicitly. I used to rely on auto_ptr and boost::smart_ptr a lot to forget about memory clean-ups. How can I write an exception-safe program with MKL memory management or should I just use regular auto_ptr's and not bother? Thanks in advance. EDIT http://software.intel.com/sites/products/documentation/hpc/mkl/win/index.htm this link may explain why I brought up the question UPDATE I used an idea from the answer below for allocator. This is what I have now: template <typename T, size_t TALIGN=16, size_t TBLOCK=4> class aligned_allocator : public std::allocator<T> { public: pointer allocate(size_type n, const void *hint) { pointer p = NULL; size_t count = sizeof(T) * n; size_t count_left = count % TBLOCK; if( count_left != 0 ) count += TBLOCK - count_left; if ( !hint ) p = reinterpret_cast<pointer>(MKL_malloc (count,TALIGN)); else p = reinterpret_cast<pointer>(MKL_realloc((void*)hint,count,TALIGN)); return p; } void deallocate(pointer p, size_type n){ MKL_free(p); } }; If anybody has any suggestions, feel free to make it better.

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  • What -W values in gcc correspond to which actual warnings?

    - by SebastianK
    Preamble: I know, disabling warnings is not a good idea. Anyway, I have a technical question about this. Using GCC 3.3.6, I get the following warning: choosing ... over ... because conversion sequence for the argument is better. Now, I want to disable this warning as described in gcc warning options by providing an argument like -Wno-theNameOfTheWarning But I don't know the name of the warning. How can I find out the name of the option that disables this warning? I am not able to fix the warning, because it occurs in a header of an external library that can not be changed. It is in boost serialization (rx(s, count)): template<class Archive, class Container, class InputFunction, class R> inline void load_collection(Archive & ar, Container &s) { s.clear(); // retrieve number of elements collection_size_type count; unsigned int item_version; ar >> BOOST_SERIALIZATION_NVP(count); if(3 < ar.get_library_version()) ar >> BOOST_SERIALIZATION_NVP(item_version); else item_version = 0; R rx; rx(s, count); std::size_t c = count; InputFunction ifunc; while(c-- > 0){ ifunc(ar, s, item_version); } } I have already tried #pragma GCC system_header but this had no effect. Using -isystem instead of -I also does not work. The general question remains is: I know the text of the warning message. But I do not know the correlation to the gcc warning options.

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  • GNU C++ how to check when -std=c++0x is in effect?

    - by TerryP
    My system compiler (gcc42) works fine with the TR1 features that I want, but trying to support newer compiler versions other than the systems, trying to accessing TR1 headers an #error demanding the -std=c++0x option because of how it interfaces with library or some hub bub like that. /usr/local/lib/gcc45/include/c++/bits/c++0x_warning.h:31:2: error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options. Having to supply an extra switch is no problem, to support GCC 4.4 and 4.5 under this system (FreeBSD), but obviously it changes the picture! Using my system compiler (g++ 4.2 default dialect): #include <tr1/foo> using std::tr1::foo; Using newer (4.5) versions of the compiler with -std=c++0x: #include <foo> using std::foo; Is there anyway using the pre processor, that I can tell if g++ is running with C++0x features enabled? Something like this is what I'm looking for: #ifdef __CXX0X_MODE__ #endif but I have not found anything in the manual or off the web. At this rate, I'm starting to think that life would just be easier, to use Boost as a dependency, and not worry about a new language standard arriving before TR4... hehe.

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  • How to define a batching routing service in WCF

    - by mattx
    I have designed a custom silverlight wcf channel that I want to leverage to selectively batch calls from the client to the server and possibly to cache on the client and short circuit calls. So far I'm just using this channel as a transport and sending the generic WCF messages that result to the WCF router service example here http://msdn.microsoft.com/en-us/magazine/cc500646.aspx?pr=blog to prototype this on the server side. So my scenario looks like this: IFooClient-MyTransportChannel-IRouterService-IFooService-Return I now need to be able to send more than one message per call through the router and carve them up and service them on the server side. Since this is just an experiment and I'm taking baby steps I will dispatch and service all the messages right away on the server side and return the batch of results. Immediately I noticed that simply making the router interface take Message[] instead of Message doesn't work due to serialization problems. I guess this makes sense. I'm not sure soap envelopes can contain other soap envelopes etc. Is there a simple way to take a collection of WCF Message objects and send them to a single method on a service where they can be split up and forwarded as appropriate? If not I'd love suggestions on how I should approach this. I want to have minimal work to do on the router service side so the goal should be to get as close to being able to "slice and forward" as possible.

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  • Alternatives to static methods on interfaces for enforcing consistency

    - by jayshao
    In Java, I'd like to be able to define marker interfaces, that forced implementations to provide static methods. For example, for simple text-serialization/deserialization I'd like to be able to define an interface that looked something like this: public interface TextTransformable<T>{ public static T fromText(String text); public String toText(); Since interfaces in Java can't contain static methods though (as noted in a number of other posts/threads: here, here, and here this code doesn't work. What I'm looking for however is some reasonable paradigm to express the same intent, namely symmetric methods, one of which is static, and enforced by the compiler. Right now the best we can come up with is some kind of static factory object or generic factory, neither of which is really satisfactory. Note: in our case our primary use-case is we have many, many "value-object" types - enums, or other objects that have a limited number of values, typically carry no state beyond their value, and which we parse/de-parse thousands of time a second, so actually do care about reusing instances (like Float, Integer, etc.) and its impact on memory consumption/g.c. Any thoughts?

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  • A good data model for finding a user's favorite stories

    - by wings
    Original Design Here's how I originally had my Models set up: class UserData(db.Model): user = db.UserProperty() favorites = db.ListProperty(db.Key) # list of story keys # ... class Story(db.Model): title = db.StringProperty() # ... On every page that displayed a story I would query UserData for the current user: user_data = UserData.all().filter('user =' users.get_current_user()).get() story_is_favorited = (story in user_data.favorites) New Design After watching this talk: Google I/O 2009 - Scalable, Complex Apps on App Engine, I wondered if I could set things up more efficiently. class FavoriteIndex(db.Model): favorited_by = db.StringListProperty() The Story Model is the same, but I got rid of the UserData Model. Each instance of the new FavoriteIndex Model has a Story instance as a parent. And each FavoriteIndex stores a list of user id's in it's favorited_by property. If I want to find all of the stories that have been favorited by a certain user: index_keys = FavoriteIndex.all(keys_only=True).filter('favorited_by =', users.get_current_user().user_id()) story_keys = [k.parent() for k in index_keys] stories = db.get(story_keys) This approach avoids the serialization/deserialization that's otherwise associated with the ListProperty. Efficiency vs Simplicity I'm not sure how efficient the new design is, especially after a user decides to favorite 300 stories, but here's why I like it: A favorited story is associated with a user, not with her user data On a page where I display a story, it's pretty easy to ask the story if it's been favorited (without calling up a separate entity filled with user data). fav_index = FavoriteIndex.all().ancestor(story).get() fav_of_current_user = users.get_current_user().user_id() in fav_index.favorited_by It's also easy to get a list of all the users who have favorited a story (using the method in #2) Is there an easier way? Please help. How is this kind of thing normally done?

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  • SFINAE + sizeof = detect if expression compiles

    - by FredOverflow
    I just found out how to check if operator<< is provided for a type. template<class T> T& lvalue_of_type(); template<class T> T rvalue_of_type(); template<class T> struct is_printable { template<class U> static char test(char(*)[sizeof( lvalue_of_type<std::ostream>() << rvalue_of_type<U>() )]); template<class U> static long test(...); enum { value = 1 == sizeof test<T>(0) }; typedef boost::integral_constant<bool, value> type; }; Is this trick well-known, or have I just won the metaprogramming Nobel prize? ;) EDIT: I made the code simpler to understand and easier to adapt with two global function template declarations lvalue_of_type and rvalue_of_type.

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  • How to get rid of exceptions thrown by the .NET Framework

    - by Hans Løken
    In a recent project I'm using a lot of databinding and xml-serialization. I'm using C#/VS2008 and have downloaded symbol information for the .NET framework to help me when debugging. The app I'm working on has a global "catch all" exception handler to present a more presentable messages to users if there happens to be any uncaught exceptions being thrown. My problem is when I turn on Exceptions-Thrown to be able to debug exceptions before they are caught by the "catch all". It seems to me that the framework throws a lot of exceptions that are not immediately caught (for example in ReflectPropertyDescriptor) so that the exception I'm actually trying to debug gets lost in the noise. Is there any way to get rid of exceptions caused by the framework but keep the ones from my own code? Update: after more research and actually trying to get rid of the exceptions that get thrown by the framework (many which turn out to be known issues in the framework, example: http://stackoverflow.com/questions/1127431/xmlserializer-giving-filenotfoundexception-at-constructor) I finally found a solution that works for me, which is turning on "Just my code" in Tools Options Debugging General Enable Just My Code in VS2008.

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  • Putting all methods in class definition

    - by Amnon
    When I use the pimpl idiom, is it a good idea to put all the methods definitions inside the class definition? For example: // in A.h class A { class impl; boost::scoped_ptr<impl> pimpl; public: A(); int foo(); } // in A.cpp class A::impl { // method defined in class int foo() { return 42; } // as opposed to only declaring the method, and defining elsewhere: float bar(); }; A::A() : pimpl(new impl) { } int A::foo() { return pimpl->foo(); } As far as I know, the only problems with putting a method definition inside a class definition is that (1) the implementation is visible in files that include the class definition, and (2) the compiler may make the method inline. These are not problems in this case since the class is defined in a private file, and inlining has no effect since the methods are called in only one place. The advantage of putting the definition inside the class is that you don't have to repeat the method signature. So, is this OK? Are there any other issues to be aware of?

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  • How do you use stl's functions like for_each?

    - by thomas-gies
    I started using stl containers because they came in very handy when I needed functionality of a list, set and map and had nothing else available in my programming environment. I did not care much about the ideas behind it. STL documentations were only interesting up to the point where it came to functions, etc. Then I skipped reading and just used the containers. But yesterday, still being relaxed from my holidays, I just gave it a try and wanted to go a bit more the stl way. So I used the transform function (can I have a little bit of applause for me, thank you). From an academic point of view it really looked interesting and it worked. But the thing that boroughs me is that if you intensify the use of those functions, you need 10ks of helper classes for mostly everything you want to do in your code. The hole logic of the program is sliced in tiny pieces. This slicing is not the result of god coding habits. It's just a technical need. Something, that makes my life probably harder not easier. And I learned the hard way, that you should always choose the simplest approach that solves the problem at hand. And I can't see what, for example, the for_each function is doing for me that justifies the use of a helper class over several simple lines of code that sit inside a normal loop so that everybody can see what is going on. I would like to know, what you are thinking about my concerns? Did you see it like I do when you started working this way and have changed your mind when you got used to it? Are there benefits that I overlooked? Or do you just ignore this stuff as I did (and will go an doing it, probably). Thanks. PS: I know that there is a real for_each loop in boost. But I ignore it here since it is just a convenient way for my usual loops with iterators I guess.

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  • Rewriting jQuery to plain old javascript - are the performance gains worth it?

    - by Swader
    Since jQuery is an incredibly easy and banal library, I've developed a rather complex project fairly quickly with it. The entire interface is jQuery based, and memory is cleaned regularly to maintain optimum performance. Everything works very well in Firefox, and exceptionally so in Chrome (other browsers are of no concern for me as this is not a commercial or publicly available product). What I'm wondering now is - since pure plain old javascript is really not a complicated language to master, would it be performance enhancing to rewrite the whole thing in plain old JS, and if so, how much of a boost would you expect to get from it? If the answers prove positive enough, I'll go ahead and do it, run a benchmark and report back with the precise findings. Cheers Edit: Thanks guys, valuable insight. The purpose was not to "re-invent the wheel" - it was just for experience and personal improvement. Just because something exists, doesn't mean you shouldn't explore it into greater detail, know how it works or try to recreate it. This is the same reason I seldom use frameworks, I would much rather use my own code and iron it out and gain massive experience doing it, than start off by using someone else's code, regardless of how ironed out it is. Anyway, won't be doing it, thanks for saving me the effort :)

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  • Compiler turning a string& into a basic_string<>&

    - by Shtong
    Hello I'm coming back to C++ after long years spent on other technologies and i'm stuck on some weird behavior when calling some methods taking std::string as parameters : An example of call : LocalNodeConfiguration *LocalNodeConfiguration::ReadFromFile(std::string & path) { // ... throw configuration_file_error(string("Configuration file empty"), path); // ... } When I compile I get this (I cropped file names for readability) : /usr/bin/g++ -g -I/home/shtong/Dev/OmegaNoc/build -I/usr/share/include/boost-1.41.0 -o CMakeFiles/OmegaNocInternals.dir/configuration/localNodeConfiguration.cxx.o -c /home/shtong/Dev/OmegaNoc/source/configuration/localNodeConfiguration.cxx .../localNodeConfiguration.cxx: In static member function ‘static OmegaNoc::LocalNodeConfiguration* OmegaNoc::LocalNodeConfiguration::ReadFromFile(std::string&)’: .../localNodeConfiguration.cxx:72: error: no matching function for call to ‘OmegaNoc::configuration_file_error::configuration_file_error(std::string, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)’ .../configurationManager.hxx:25: note: candidates are: OmegaNoc::configuration_file_error::configuration_file_error(std::string&, std::string&) .../configurationManager.hxx:22: note: OmegaNoc::configuration_file_error::configuration_file_error(const OmegaNoc::configuration_file_error&) So as I understand it, the compiler is considering that my path parameter turned into a basic_string at some point, thus not finding the constructor overload I want to use. But I don't really get why this transformation happened. Some search on the net suggested me to use g++ but I was already using it. So any other advice would be appreciated :) Thanks

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