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  • Instance caching in Objective C

    - by zoul
    Hello! I want to cache the instances of a certain class. The class keeps a dictionary of all its instances and when somebody requests a new instance, the class tries to satisfy the request from the cache first. There is a small problem with memory management though: The dictionary cache retains the inserted objects, so that they never get deallocated. I do want them to get deallocated, so that I had to overload the release method and when the retain count drops to one, I can remove the instance from cache and let it get deallocated. This works, but I am not comfortable mucking around the release method and find the solution overly complicated. I thought I could use some hashing class that does not retain the objects it stores. Is there such? The idea is that when the last user of a certain instance releases it, the instance would automatically disappear from the cache. NSHashTable seems to be what I am looking for, but the documentation talks about “supporting weak relationships in a garbage-collected environment.” Does it also work without garbage collection? Clarification: I cannot afford to keep the instances in memory unless somebody really needs them, that is why I want to purge the instance from the cache when the last “real” user releases it. Better solution: This was on the iPhone, I wanted to cache some textures and on the other hand I wanted to free them from memory as soon as the last real holder released them. The easier way to code this is through another class (let’s call it TextureManager). This class manages the texture instances and caches them, so that subsequent calls for texture with the same name are served from the cache. There is no need to purge the cache immediately as the last user releases the texture. We can simply keep the texture cached in memory and when the device gets short on memory, we receive the low memory warning and can purge the cache. This is a better solution, because the caching stuff does not pollute the Texture class, we do not have to mess with release and there is even a higher chance for cache hits. The TextureManager can be abstracted into a ResourceManager, so that it can cache other data, not only textures.

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  • What's faster to parse lots of data (5Mb): eval or json?

    - by AlfaTeK
    I want to get, via ajax, a collection of data objects and parse them into JS data. Currently I have 2 choices: - Server returns valid javascript code and then I eval it. - Server returns JSON object and then I eval the json object What is the fastest of these in Firefox? (I only care about the "parsing" performance, not server or data transfer)

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  • VBScript: Passing Object to Function?

    - by ioplex
    The below example generates an error: VBScript compilation error: Cannot use parentheses when calling a Sub This error does not occur if all parameters are not objects. Is there a special way to pass object parameters to VBScript functions? Option Explicit Dim obj Function TestFunc(obj) WScript.Echo "Why doesn't this work?" End Function Set obj = CreateObject("Scripting.Dictionary") obj.Add("key", "val") TestFunc(obj) ' Error here!

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  • Schema to support dynamic properties

    - by Johan Fredrik Varen
    Hi people. I'm working on an editor that enables its users to create "object" definitions in real-time. A definition can contain zero or more properties. A property has a name a type. Once a definition is created, a user can create an object of that definition and set the property values of that object. So by the click of a mouse-button, the user should ie. be able to create a new definition called "Bicycle", and add the property "Size" of type "Numeric". Then another property called "Name" of type "Text", and then another property called "Price" of type "Numeric". Once that is done, the user should be able to create a couple of "Bicycle" objects and fill in the "Name" and "Price" property values of each bike. Now, I've seen this feature in several software products, so it must be a well-known concept. My problem started when I sat down and tried to come up with a DB schema to support this data structure, because I want the property values to be stored using the appropriate column types. Ie. a numeric property value is stored as, say, an INT in the database, and a textual property value is stored as VARCHAR. First, I need a table that will hold all my object definitions: Table obj_defs id | name | ---------------- 1 | "Bicycle" | 2 | "Book" | Then I need a table for holding what sort of properties each object definition should have: Table prop_defs id | obj_def_id | name | type | ------------------------------------ 1 | 1 | "Size" | ? | 2 | 1 | "Name" | ? | 3 | 1 | "Price" | ? | 4 | 2 | "Title" | ? | 5 | 2 | "Author" | ? | 6 | 2 | "ISBN" | ? | I would also need a table that holds each object: Table objects id | created | updated | ------------------------------ 1 | 2011-05-14 | 2011-06-15 | 2 | 2011-05-14 | 2011-06-15 | 3 | 2011-05-14 | 2011-06-15 | Finally, I need a table that will hold the actual property values of each object, and one solution is for this table to have one column for each possible value type, such as this: Table prop_vals id | prop_def_id | object_id | numeric | textual | boolean | ------------------------------------------------------------ 1 | 1 | 1 | 27 | | | 2 | 2 | 1 | | "Trek" | | 3 | 3 | 1 | 1249 | | | 4 | 1 | 2 | 26 | | | 5 | 2 | 2 | | "GT" | | 6 | 3 | 2 | 159 | | | 7 | 4 | 3 | | "It" | | 8 | 5 | 3 | | "King" | | 9 | 6 | 4 | 9 | | | If I implemented this schema, what would the "type" column of the prop_defs table hold? Integers that each map to a column name, varchars that simply hold the column name? Any other possibilities? Would a stored procedure help me out here in some way? And what would the SQL for fetching the "name" property of object 2 look like?

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  • Multi-threaded Pooled Allocators

    - by Darren Engwirda
    I'm having some issues using pooled memory allocators for std::list objects in a multi-threaded application. The part of the code I'm concerned with runs each thread function in isolation (i.e. there is no communication or synchronization between threads) and therefore I'd like to setup separate memory pools for each thread, where each pool is not thread-safe (and hence fast). I've tried using a shared thread-safe singleton memory pool and found the performance to be poor, as expected. This is a heavily simplified version of the type of thing I'm trying to do. A lot has been included in a pseudo-code kind of way, sorry if it's confusing. /* The thread functor - one instance of MAKE_QUADTREE created for each thread */ class make_quadtree { private: /* A non-thread-safe memory pool for int linked list items, let's say that it's * something along the lines of BOOST::OBJECT_POOL */ pooled_allocator<int> item_pool; /* The problem! - a local class that would be constructed within each std::list as the * allocator but really just delegates to ITEM_POOL */ class local_alloc { public : //!! I understand that I can't access ITEM_POOL from within a nested class like //!! this, that's really my question - can I get something along these lines to //!! work?? pointer allocate (size_t n) { return ( item_pool.allocate(n) ); } }; public : make_quadtree (): item_pool() // only construct 1 instance of ITEM_POOL per // MAKE_QUADTREE object { /* The kind of data structures - vectors of linked lists * The idea is that all of the linked lists should share a local pooled allocator */ std::vector<std::list<int, local_alloc>> lists; /* The actual operations - too complicated to show, but in general: * * - The vector LISTS is grown as a quadtree is built, it's size is the number of * quadtree "boxes" * * - Each element of LISTS (each linked list) represents the ID's of items * contained within each quadtree box (say they're xy points), as the quadtree * is grown a lot of ID pop/push-ing between lists occurs, hence the memory pool * is important for performance */ } }; So really my problem is that I'd like to have one memory pool instance per thread functor instance, but within each thread functor share the pool between multiple std::list objects.

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  • ahow can I resolve Django Error: str' object has no attribute 'autoescape'?

    - by Angelbit
    Hi have tried to create a inclusion tag on Django but don't work and return str' object has no attribute 'autoescape' this is the code of custom tag: from django import template from quotes.models import Quotes register = template.Library() def show_quote(): quote = Quotes.objects.values('quote', 'author').get(id=0) return {'quote': quote['quote']} register.inclusion_tag('quotes.html')(show_quote) EDIT: Quote class from django.db import models class Quotes(models.Model): quote = models.CharField(max_length=255) author = models.CharField(max_length=100) class Meta: db_table = 'quotes' quotes.html <blockquote id="quotes">{{ quote }}</blockquote>

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  • Simplest way to print an array in Java

    - by Alex Spurling
    What's the simplest way of printing an array of primitives or of objects in Java? Here are some example inputs and outputs: int[] intArray = new int[] {1, 2, 3, 4, 5}; //output: [1, 2, 3, 4, 5] String[] strArray = new String[] {"John", "Mary", "Bob"}; //output: [John, Mary, Bob]

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  • Question about factory classes

    - by devoured elysium
    Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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  • Why do I not get low memory issues until images are draw on the screen?

    - by maxpower
    I am able to load over 200 UIImage objects into a NSMutableDictionary without any memorry warning issues. When I start displaying them on the screen (after about showing 10-20 images) I get low memory warnings and an eventual crash. Only about 8 images are displayed at anyone time. Does it take additional memory to actually draw a UIImage on the screen? No memory leaks are showing up and i've reviewed code for leaks many many times.

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  • Why might my Xcode be crashing (or at least displaying an error on launch)?

    - by dsobol
    I am getting an error thrown when I launch my Xcode 3.2 all of a sudden: Uncaught Exception: * -[NSCFArray initWithObjects:count:]: attempt to insert nil object at objects[0] I can click through the error and Xcode seems to launch properly. I removed and reinstalled Xcode to no avail, and yet cannot find a config or perference that might be the culprit. I am running on 10.6.3 fwiw.... Has anyone else run into this problkem? TIA! Regards, Steve O'Sullivan

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  • Is there a way to create a python object that will be not sortable?

    - by Graf
    Is there a possibility to create any python object that will be not sortable? So that will be an exception when trying to sort a list of that objects? I created a very simple class, didn't define any comparison methods, but still instances of this class are comparable and thus sortable. Maybe, my class inherits comparison methods from somewhere. But I don't want this behaviour.

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  • should_receive in RSpec

    - by gmile
    As far as I know, should_receive is applied only to mock objects. What I want is to check, if a certain Class (not object) received a certain message, like: User.should_receive(:all).once How do I do that?

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  • Dynamic casting using a generic interface

    - by Phil Whittaker
    Hi Is there any way to cast to a dynamic generic interface.. Site s = new Site(); IRepository<Site> obj = (IRepository<s.GetType()>)ServiceLocator.Current.GetInstance(t) obviously the above won't compile with this cast. Is there anyway to do a dynamic cast of a generic interface. I have tried adding a non generic interface but the system is looses objects in the Loc container. Thanks Phil

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  • postgresql drop table

    - by Russell
    I have two tables (tbl and tbl_new) that both use the same sequence (tbl_id_seq). I'd like to drop one of those tables. On tbl, I've removed the modifier "not null default nextval('tbl_id_seq'::regclass)" but that modifier remains on tbl_new. I'm getting the following error: ERROR: cannot drop table tbl because other objects depend on it DETAIL: default for table tbl_new column id depends on sequence tbl_id_seq After reviewing http://www.postgresql.org/docs/9.1/static/sql-droptable.html It looks like there is only CASCADE and RESTRICT as options.

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  • Avoiding 'Buffer Overrun' C6386 warning

    - by bdhar
    In my code, I am using an array xyz of 10 objects. When I am trying to access an element of the array using an unsigned int index like this: xyz[level], I get 'Buffer overrun' warning. Logically, I am pretty sure that level won't exceed 10. How to avoid this warning?

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  • C# SQL: What is the best way to implement a dynamic table?

    - by SirMoreno
    I want to allow the user to add columns to a table in the UI. The UI: Columns Name:__ Columns Type: Number/String/Date My Question is how to build the SQL tables and C# objects so the implementation will be efficient and scalable. My thought is to build two SQL tables: TBL 1 - ColumnsDefinition: ColId, ColName, ColType[Text] TBL 2 - ColumnsValues: RowId, ColId, Value [Text] I want the solution to be efficient in DB space, and I want to allow the user to sort the dynamic columns. I work on .NET 3.5 MSSQL 2008. Thanks.

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  • stop thread that does not get interrupted

    - by prmatta
    I have a thread that sits and reads objects off of an ObjectInputStream: public void run() { try { ois = new ObjectInputStream(clientSocket.getInputStream()); Object o; while ((o = ois.readObject()) != null) { //do something with object } } catch (Exception ex) { //Log exception } } readObject does not throw InterruptedException and as far as I can tell, no exception is thrown when this thread is interrupted. How do I stop this thread?

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  • Size of abstract class

    - by webgenius
    How can I find the size of an abstract class? class A { virtual void PureVirtualFunction() = 0; }; Since this is an abstract class, I can't create objects of this class. How will I be able to find the size of the abstract class A using the 'sizeof' operator?

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