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• Lookup table size reduction

  - by Ryan

  Hello: I have an application in which I have to store a couple of millions of integers, I have to store them in a Look up table, obviously I cannot store such amount of data in memory and in my requirements I am very limited I have to store the data in an embebedded system so I am very limited in the space, so I would like to ask you about recommended methods that I can use for the reduction of the look up table. I cannot use function approximation such as neural networks, the values needs to be in a table. The range of the integers is not known at the moment. When I say integers I mean a 32 bit value. Basically the idea is use some copmpression method to reduce the amount of memory but without losing many precision. This thing needs to run in hardware so the computation overhead cannot be very high. In my algorithm I have to access to one value of the table do some operations with it and after update the value. In the end what I should have is a function which I pass an index to it and then I get a value, and after I have to use another function to write a value in the table. I found one called tile coding http://www.cs.ualberta.ca/~sutton/book/8/node6.html, this one is based on several look up tables, does anyone know any other method?. Thanks.

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• How is a referencing environment generally implemented for closures?

  - by Alexandr Kurilin

  Let's say I have a statically/lexically scoped language with deep binding and I create a closure. The closure will consist of the statements I want executed plus the so called referencing environment, or, to quote this post, the collection of variables which can be used. What does this referencing environment actually look like implementation-wise? I was recently reading about ObjectiveC's implementation of blocks, and the author suggests that behind the scenes you get a copy of all of the variables on the stack and also of all the references to heap objects. The explanation claims that you get a "snapshot" of the referencing environment at the point in time of the closure's creation. Is that more or less what happens, or did I misread that? Is anything done to "freeze" a separate copy of the heap objects, or is it safe to assume that if they get modified between closure creation and the closure executing, the closure will no longer be operating on the original version of the object? If indeed there's copying being made, are there memory usage considerations in situations where one might want to create plenty of closures and store them somewhere? I think that misunderstanding of some of these concepts might lead to tricky issues like the ones Eric Lippert mentions in this blog post. It's interesting because you'd think that it wouldn't make sense to keep a reference to a value type that might be gone by the time the closure is called, but I'm guessing that in C# the compiler will figure out that the variable is needed later and put it into the heap instead. It seems that in most memory-managed languages everything is a reference and thus ObjectiveC is a somewhat unique situation with having to deal with copying what's on the stack.

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• Problem with writing mobilesubstrate plugins for iOS

  - by overboming

  I am trying to hooking message sending for iOS 3.2, I implement my own hook on a working ExampleHook program I find on the web. But my hook apparently caused segmentation fault everytime it hooks and I don't know why. I want to hook to [NSURL initWithString:(NSString *)URLString relativeToURL:(NSURL *)baseURL; and here is my related implementation static id __$GFWInterceptor_NSURL_initWithString2(NSURL<GFWInterceptor> *_NSURL, NSString *URLString, NSURL* baseURL){ NSLog(@"We have intercepted this url: %@",URLString); [_NSURL __HelloNSURL_initWithString:URLString relativeToURL:baseURL]; establish hook Class _$NSURL = objc_getClass("NSURL"); MSHookMessage(_$NSURL, @selector(initWithString:relativeToURL:), (IMP) &__$GFWInterceptor_NSURL_initWithString2, "__HelloNSURL_"); original method declaration - (void)__HelloNSURL_initWithString:(NSString *)URLString relativeToURL:(NSURL *)baseURL; and here is my gdb backtrace Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x74696e71 0x335625f8 in objc_msgSend () (gdb) bt 0 0x335625f8 in objc_msgSend () 1 0x32c05b1a in CFStringGetLength () 2 0x32c108a8 in _CFStringIsLegalURLString () 3 0x32b1c32a in -[NSURL initWithString:relativeToURL:] () 4 0x000877c0 in __$GFWInterceptor_NSURL_initWithString2 () 5 0x32b1c220 in +[NSURL URLWithString:relativeToURL:] () 6 0x32b1c1f4 in +[NSURL URLWithString:] () 7 0x3061c614 in createUniqueWebDataURL () 8 0x3061c212 in +[WebFrame(WebInternal) _createMainFrameWithSimpleHTMLDocumentWithPage:frameView:withStyle:editable:] () and apparently it hooks, but there is some memory issue there and I can't find anything to blame now

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• How to know why an animation stutters?

  - by Patrick Klug

  I have a few fairly simple animations (moving text around, moving ellipses etc.) and running in full screen (1920x1080 minus the task bar) the WPF Performance Suite reports a good framerate around 50 FPS throughout the animation. Dirty Rect Addition is somewhere around 300 rect/s, the SW frames are between 0 and 4 and the HW frames are between 3 and 5. Video memory usage is around 80 MB. Problem is that the animations stutters every other half second. My machine is a new Dell laptop XPS 15 with the GeForce GT 435 with 2GB memory. - The drivers are up to date. (The same behavior occurs on my netbook (in full screen) as well so I don't think it is hardware related.) If I make the window smaller the stutter goes away. The stutter occurs with the simplest of animations - even with just a couple of elements but adding more elements certainly makes it more noticeable. How can I find out what causes this stutter? When I think of it, I have not actually seen any WPF animations which run smoothly in full screen. Is this even possible?

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• Read whole ASCII file into C++ std::string

  - by Arrieta

  Hello, I need to read a whole file into memory and place it in a C++ std::string. If I were to read it into a char, the answer would be very simple: std::ifstream t; int lenght; t.open("file.txt", "r"); // open input file t.seekg(0, std::ios::end); // go to the end length = t.tellg(); // report location (this is the lenght) t.seekg(0, std::ios::beg); // go back to the beginning buffer = new char[length]; // allocate memory for a buffer of appropriate dimension t.read(buffer, length); // read the whole file into the buffer t.close(); // close file handle // ... do stuff with buffer here ... Now, I want to do the exact same thing, but using a std::string instead of a char. I want to avoid loops, i. e., I don't want to: std::ifstream t; t.open("file.txt", "r"); std::string buffer; std::string line; while(t){ std::getline(t, line); // ... append line to buffer and go on } t.close() any ideas?

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• pure/const functions in C++

  - by Albert

  Hi, I'm thinking of using pure/const functions more heavily in my C++ code. (pure/const attribute in GCC) However, I am curious how strict I should be about it and what could possibly break. The most obvious case are debug outputs (in whatever form, could be on cout, in some file or in some custom debug class). I probably will have a lot of functions, which don't have any side effects despite this sort of debug output. No matter if the debug output is made or not, this will absolutely have no effect on the rest of my application. Or another case I'm thinking of is the use of my own SmartPointer class. In debug mode, my SmartPointer class has some global register where it does some extra checks. If I use such an object in a pure/const function, it does have some slight side effects (in the sense that some memory probably will be different) which should not have any real side effects though (in the sense that the behaviour is in any way different). Similar also for mutexes and other stuff. I can think of many complex cases where it has some side effects (in the sense of that some memory will be different, maybe even some threads are created, some filesystem manipulation is made, etc) but has no computational difference (all those side effects could very well be left out and I would even prefer that). How does it work out in practice? If I mark such functions as pure/const, could it break anything (considering that the code is all correct)?

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• Spring Integration 1.0 RC2: Streaming file content?

  - by gdm

  I've been trying to find information on this, but due to the immaturity of the Spring Integration framework I haven't had much luck. Here is my desired work flow: New files are placed in an 'Incoming' directory Files are picked up using a file:inbound-channel-adapter The file content is streamed, N lines at a time, to a 'Stage 1' channel, which parses the line into an intermediary (shared) representation. This parsed line is routed to multiple 'Stage 2' channels. Each 'Stage 2' channel does its own processing on the N available lines to convert them to a final representation. This channel must have a queue which ensures no Stage 2 channel is overwhelmed in the event that one channel processes significantly slower than the others. The final representation of the N lines is written to a file. There will be as many output files as there were routing destinations in step 4. *'N' above stands for any reasonable number of lines to read at a time, from [1, whatever I can fit into memory reasonably], but is guaranteed to always be less than the number of lines in the full file. How can I accomplish streaming (steps 3, 4, 5) in Spring Integration? It's fairly easy to do without streaming the files, but my files are large enough that I cannot read the entire file into memory. As a side note, I have a working implementation of this work flow without Spring Integration, but since we're using Spring Integration in other places in our project, I'd like to try it here to see how it performs and how the resulting code compares for length and clarity.

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• Handling user interface in a multi-threaded application (or being forced to have a UI-only main thre

  - by Patrick

  In my application, I have a 'logging' window, which shows all the logging, warnings, errors of the application. Last year my application was still single-threaded so this worked [quite] good. Now I am introducing multithreading. I quickly noticed that it's not a good idea to update the logging window from different threads. Reading some articles on keeping the UI in the main thread, I made a communication buffer, in which the other threads are adding their logging messages, and from which the main thread takes the messages and shows them in the logging window (this is done in the message loop). Now, in a part of my application, the memory usage increases dramatically, because the separate threads are generating lots of logging messages, and the main thread cannot empty the communication buffer quickly enough. After the while the memory decreases again (if the other threads have finished their work and the main thread gradually empties the communication buffer). I solved this problem by having a maximum size on the communication buffer, but then I run into a problem in the following situation: the main thread has to perform a complex action the main thread takes some parts of the action and let's separate threads execute this while the seperate threads are executing their logic, the main thread processes the results from the other threads and continues with its work if the other threads are finished Problem is that in this situation, if the other threads perform logging, there is no UI-message loop, and so the communication buffer is filled, but not emptied. I see two solutions in solving this problem: require the main thread to do regular polling of the communication buffer only performing user interface logic in the main thread (no other logic) I think the second solution seems the best, but this may not that easy to introduce in a big application (in my case it performs mathematical simulations). Are there any other solutions or tips? Or is one of the two proposed the best, easiest, most-pragmatic solution? Thanks, Patrick

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• Efficient algorithm for Next button on a MySQL result set

  - by David Grayson

  I have a website that lets people view rows in a table (each row is a picture). There are more than 100,000 rows. You can view different subsets of the rows, and you can view them with different sort orders. While you are viewing one of the rows, you can click the "Next" or "Previous" buttons to go the next/previous row in the list. How would you implement the "Next" and "Previous" features of the website? More specifically, if you have an arbitrary query that returns a list of up to 100,000+ rows, and you know some information about the current row someone is viewing, how do you determine the NEXT row efficiently? Here is the pseudo-code of the solution I came up with when the website was young, and it worked well when there were only 1000 rows, but now that there are 100,000 rows I think it is eating up too much memory. int nextRowId(string query, int currentRowId) { array allRowIds = mysql_query(query); // Takes up a lot of memory! int currentIndex = (index of currentRowId in allRowIds); // Takes time! return allRowIds[currentIndex+1]; } While you are thinking about this problem, remember that the website can store more information about the current row than just its ID (for example, the position of the current row in the result set), and this information can be used as a hint to help determine the ID of the next row. Edit: Sorry for not mentioning this earlier, but this isn't just a static website: rows can often be added to the list, and rows can be re-ordered in the list. (Much rarer, rows can be removed from the list.) I think that I should worry about that kind of thing, but maybe you can convince me otherwise.

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• Using shared_ptr to implement RCU (read-copy-update)?

  - by yongsun

  I'm very interested in the user-space RCU (read-copy-update), and trying to simulate one via tr1::shared_ptr, here is the code, while I'm really a newbie in concurrent programming, would some experts help me to review? The basic idea is, reader calls get_reading_copy() to gain the pointer of current protected data (let's say it's generation one, or G1). writer calls get_updating_copy() to gain a copy of the G1 (let's say it's G2), and only one writer is allowed to enter the critical section. After the updating is done, writer calls update() to do a swap, and make the m_data_ptr pointing to data G2. The ongoing readers and the writer now hold the shared_ptr of G1, and either a reader or a writer will eventually deallocate the G1 data. Any new readers would get the pointer to G2, and a new writer would get the copy of G2 (let's say G3). It's possible the G1 is not released yet, so multiple generations of data my co-exists. template <typename T> class rcu_protected { public: typedef T type; typedef std::tr1::shared_ptr<type> rcu_pointer; rcu_protected() : m_data_ptr (new type()) {} rcu_pointer get_reading_copy () { spin_until_eq (m_is_swapping, 0); return m_data_ptr; } rcu_pointer get_updating_copy () { spin_until_eq (m_is_swapping, 0); while (!CAS (m_is_writing, 0, 1)) {/* do sleep for back-off when exceeding maximum retry times */} rcu_pointer new_data_ptr(new type(*m_data_ptr)); // as spin_until_eq does not have memory barrier protection, // we need to place a read barrier to protect the loading of // new_data_ptr not to be re-ordered before its construction _ReadBarrier(); return new_data_ptr; } void update (rcu_pointer new_data_ptr) { while (!CAS (m_is_swapping, 0, 1)) {} m_data_ptr.swap (new_data_ptr); // as spin_until_eq does not have memory barrier protection, // we need to place a write barrier to protect the assignments of // m_is_writing/m_is_swapping be re-ordered bofore the swapping _WriteBarrier(); m_is_writing = 0; m_is_swapping = 0; } private: volatile long m_is_writing; volatile long m_is_swapping; rcu_pointer m_data_ptr; };

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• handle large Parcelable ArrayList in Android

  - by Gal Ben-Haim

  I'm developing an Android app that is a client to a JSON webservice API. I have classes of resource objects (some are nested) and I pass results from an IntentService that access the webserive using the Parcelable interface for all the resource classes. the webservice returns arrays or results that can be potentially large (because of the nesting, for example, a post object also contains comments array, each comment also contains a user object). currently I'm either inserting the results into a SQlite database or displaying them in a ListView. (my relevant methods are accepting ArrayList<resourceClass> as arguments). (some data need to be persistent stored and some should not). since I don't know what size of lists I can handle this way without reaching the memory limits, is this a good practice ? is it a better idea to save the parsed JSON to a local file immediately and pass the file path to the ResultReceiver, then either insert to database from that file or display the data ? is there a better way to handle this ? btw - I'm parsing the JSON as a stream with Gson's Reader so there shouldn't be memory issues at that stage.

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• Visual Studio project remains "stuck" when stopped

  - by Traveling Tech Guy

  Hi, Currently developing a connector DLL to HP's Quality Center. I'm using their (insert expelative) COM API to connect to the server. An Interop wrapper gets created automatically by VStudio. My solution has 2 projects: the DLL and a tester application - essentially a form with buttons that call functions in the DLL. Everything works well - I can create defects, update them and delete them. When I close the main form, the application stops nicely. But when I call a function that returns a list of all available projects (to fill a combo box), if I close the main form, VStudio still shows the solution as running and I have to stop it. I've managed to pinpoint a single function in my code that when I call, the solution remains "hung" and if I don't, it closes well. It's a call to a property in the TDC object get_VisibleProjects that returns a List (not the .Net one, but a type in the COM library) - I just iterate over it and return a proper list (that I later use to fill the combo box): public List<string> GetAvailableProjects() { List<string> projects = new List<string>(); foreach (string project in this.tdc.get_VisibleProjects(qcDomain)) { projects.Add(project); } return projects; } My assumption is that something gets retained in memory. If I run the EXE outside of VStudio it closes - but who knows what gets left behind in memory? My question is - how do I get rid of whatever calling this property returns? Shouldn't the GC handle this? Do I need to delve into pointers? Things I've tried: getting the list into a variable and setting it to null at the end of the function Adding a destructor to the class and nulling the tdc object Stepping through the tester function application all the way out, whne the form closes and the Main function ends - it closes, but VStudio still shows I'm running. Thanks for your assistance!

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• Qt application crashing immediately without debugging info. How do I track down the problem?

  - by jjacksonRIAB

  I run an Qt app I've built: ./App Segmentation fault I run it with strace: strace ./App execve("./App", ["./App"], [/* 27 vars */]) = 0 --- SIGSEGV (Segmentation fault) @ 0 (0) --- +++ killed by SIGSEGV +++ Process 868 detached Again, no useful info. I run it with gdb: (gdb) run Starting program: /root/test/App Reading symbols from shared object read from target memory...(no debugging symbols found)...done. Loaded system supplied DSO at 0xffffe000 Program received signal SIGSEGV, Segmentation fault. 0x00000001 in ?? () Again, nothing. I run it with valgrind: ==948== Process terminating with default action of signal 11 (SIGSEGV) ==948== Bad permissions for mapped region at address 0x0 ==948== at 0x1: (within /root/test/App) Even if I put in debugging symbols, it doesn't give any more useful info. ldd shows all libraries being linked properly. Is there any other way I can find out what's wrong? I can't even do standard printf, cout, etc debugging. The executable doesn't even seem to start running at all. I rebuilt with symbols, and tried the suggestion below (gdb) break main Breakpoint 1 at 0x45470 (gdb) run Starting program: /root/test/App Breakpoint 1 at 0x80045470 Reading symbols from shared object read from target memory...done. Loaded system supplied DSO at 0xffffe000 Program received signal SIGSEGV, Segmentation fault. 0x00000001 in ?? () I checked for static initializers and I don't seem to have any. Yep, I tried printf, cout, etc. It doesn't even make it into the main routine, so I'm looking for problems with static initializers in link libraries, adding them in one-by-one. I'm not getting any stack traces either.

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• Auto increment with a Unit Of Work

  - by Derick

  Context I'm building a persistence layer to abstract different types of databases that I'll be needing. On the relational part I have mySQL, Oracle and PostgreSQL. Let's take the following simplified MySQL tables: CREATE TABLE Contact ( ID varchar(15), NAME varchar(30) ); CREATE TABLE Address ( ID varchar(15), CONTACT_ID varchar(15), NAME varchar(50) ); I use code to generate system specific alpha numeric unique ID's fitting 15 chars in this case. Thus, if I insert a Contact record with it's Addresses I have my generated Contact.ID and Address.CONTACT_IDs before committing. I've created a Unit of Work (amongst others) as per Martin Fowler's patterns to add transaction support. I'm using a key based Identity Map in the UoW to track the changed records in memory. It works like a charm for the scenario above, all pretty standard stuff so far. The question scenario comes in when I have a database that is not under my control and the ID fields are auto-increment (or in Oracle sequences). In this case I do not have the db generated Contact.ID beforehand, so when I create my Address I do not have a value for Address.CONTACT_ID. The transaction has not been started on the DB session since all is kept in the Identity Map in memory. Question: What is a good approach to address this? (Avoiding unnecessary db round trips) Some ideas: Retrieve the last ID: I can do a call to the database to retrieve the last Id like: SELECT Auto_increment FROM information_schema.tables WHERE table_name='Contact'; But this is MySQL specific and probably something similar can be done for the other databases. If do this then would need to do the 1st insert, get the ID and then update the children (Address.CONTACT_IDs) – all in the current transaction context.

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• iPhone: Calling dealloc on parentViewController causes an exception

  - by arielcamus

  Hi, I'm dealing with viewDidUnload and dealloc methods and I've founded a problem when calling [super dealloc]; in parent view controller. I have a lot of view controllers with custom code which I have putted outside on a parent view controller. So, when defining my view controllers I set a reference to the super class: @interface LoginViewController : AbstractViewController Then, at the dealloc method I call the AbstractViewController dealloc method: //(Login View Controller code) - (void)dealloc { [user release]; [passwd release]; [super dealloc]; } [super dealloc] execute the following code: //(Abstract View Controller code) - (void)dealloc { [dbUtils release]; [loadingView release]; [super dealloc]; } If I simulate a memory warning on iPhone Simulator, the following exception is thrown: 2010-03-03 11:27:45.805 MyApp[71563:40b] Received simulated memory warning. 2010-03-03 11:27:45.808 MyApp[71563:40b] *** -[LoginViewController isViewLoaded]: message sent to deallocated instance 0x13b51b0 kill quit However, if I comment the [super dealloc] line in AbstractViewController the exception is not thrown and my app still running. Thank you for your help once again!

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• What about race condition in multithreaded reading?

  - by themoob

  Hi, According to an article on IBM.com, "a race condition is a situation in which two or more threads or processes are reading or writing some shared data, and the final result depends on the timing of how the threads are scheduled. Race conditions can lead to unpredictable results and subtle program bugs." . Although the article concerns Java, I have in general been taught the same definition. As far as I know, simple operation of reading from RAM is composed of setting the states of specific input lines (address, read etc.) and reading the states of output lines. This is an operation that obviously cannot be executed simultaneously by two devices and has to be serialized. Now let's suppose we have a situation when a couple of threads access an object in memory. In theory, this access should be serialized in order to prevent race conditions. But e.g. the readers/writers algorithm assumes that an arbitrary number of readers can use the shared memory at the same time. So, the question is: does one have to implement an exclusive lock for read when using multithreading (in WinAPI e.g.)? If not, why? Where is this control implemented - OS, hardware? Best regards, Kuba

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• JAXB, how to marshal without a namespace

  - by Alvin

  I have a fairly large repetitive XML to create using JAXB. Storing the whole object in the memory then do the marshaling takes too much memory. Essentially, my XML looks like this: <Store> <item /> <item /> <item /> ..... </Store> Currently my solution to the problem is to "hard code" the root tag to an output stream, and marshal each of the repetitive element one by one: aOutputStream.write("<?xml version="1.0"?>") aOutputStream.write("<Store>") foreach items as item aMarshaller.marshall(item, aOutputStream) end aOutputStream.write("</Store>") aOutputStream.close() Somehow the JAXB generate the XML like this <Store xmlns="http://stackoverflow.com"> <item xmlns="http://stackoverflow.com"/> <item xmlns="http://stackoverflow.com"/> <item xmlns="http://stackoverflow.com"/> ..... </Store> Although this is a valid XML, but it just look ugly, so I'm wonder is there any way to tell the marshaller not to put namespace for the item elements? Or is there better way to use JAXB to serialize to XML chunk by chunk?

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• Field Members vs Method Variables?

  - by Braveyard

  Recently I've been thinking about performance difference between class field members and method variables. What exactly I mean is in the example below : Lets say we have a DataContext object for Linq2SQL class DataLayer { ProductDataContext context = new ProductDataContext(); public IQueryable<Product> GetData() { return context.Where(t=>t.ProductId == 2); } } In the example above, context will be stored in heap and the GetData method variables will be removed from Stack after Method is executed. So lets examine the following example to make a distinction : class DataLayer { public IQueryable<Product> GetData() { ProductDataContext context = new ProductDataContext(); return context.Where(t=>t.ProductId == 2); } } (*1) So okay first thing we know is if we define ProductDataContext instance as a field, we can reach it everywhere in the class which means we don't have to create same object instance all the time. But lets say we are talking about Asp.NET and once the users press submit button the post data is sent to the server and the events are executed and the posted data stored in a database via the method above so it is probable that the same user can send different data after one another.If I know correctly after the page is executed, the finalizers come into play and clear things from memory (from heap) and that means we lose our instance variables from memory as well and after another post, DataContext should be created once again for the new page cycle. So it seems the only benefit of declaring it publicly to the whole class is the just number one text above. Or is there something other? Thanks in advance... (If I told something incorrect please fix me.. )

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• Do ORMs normally allow circular relations? If so, how would they handle it?

  - by SeanJA

  I was hacking around trying to make a basic orm that has support for the one => one and one => many relationships. I think I succeeded somewhat, but I am curious about how to handle circular relationships. Say you had something like this: user::hasOne('car'); car::hasMany('wheels'); car::property('type'); wheel::hasOne('car'); You could then do this (theoretically): $u = new user(); echo $u->car->wheels[0]->car->wheels[1]->car->wheels[2]->car->wheels[3]->type; #=> "monster truck" Now, I am not sure why you would want to do this. It seems like it wastes a whole pile of memory and time just to get to something that could have been done in a much shorter way. In my small ORM, I now have 4 copies of the wheel class, and 4 copies of the car class in memory, which causes a problem if I update one of them and save it back to the database, the rest get out of date, and could overwrite the changes that were already made. How do other ORMs handle circular references? Do they even allow it? Do they go back up the tree and create a pointer to one of the parents? DO they let the coder shoot themselves in the foot if they are silly enough to go around in circles?

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• Delphi fast large bitmap creation (without clearing)

  - by Ritsaert Hornstra

  When using the TBitmap wrapper for a GDI bitmap from the unit Graphics I noticed it will always clear out the bitmap (using a PatBlt call) when setting up a bitmap with SetSize( w, h ). When I copy in the bits later on (see routine below) it seems ScanLine is the fastest possibility and not SetDIBits. function ToBitmap: TBitmap; var i, N, x: Integer; S, D: PAnsiChar; begin Result := TBitmap.Create(); Result.PixelFormat := pf32bit; Result.SetSize( width, height ); S := Src; D := Result.ScanLine[ 0 ]; x := Integer( Result.ScanLine[ 1 ] ) - Integer( D ); N := width * sizeof( longword ); for i := 0 to height - 1 do begin Move( S^, D^, N ); Inc( S, N ); Inc( D, x ); end; end; The bitmaps I need to work with are quite large (150MB of RGB memory). With these iomages it takes 150ms to simply create an empty bitmap and a further 140ms to overwrite it's contents. Is there a way of initializing a TBitmap with the correct size WITHOUT initializing the pixels itself and leaving the memory of the pixels uninitialized (eg dirty)? Or is there another way to do such a thing. I know we could work on the pixels in place but this still leaves the 150ms of unnessesary initializtion of the pixels.

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• Virtual destructor - How does it work?

  - by Prabhu

  Hello All, Few hours back I was fiddling with a Memory Leak issue and it turned out that I really got some basic stuff about virtual destructor wrong!! Let me put explain my class design. class Base { virtual push_elements()<br>{}<br> }; class Derived:public Base { vector<int> x; public: void push_elements(){ for(int i=0;i <5;i++) x.push_back(i); } }; void main() { Base* b = new Derived(); b->push_elements(); delete b; } The bounds checker tool reported a memory leak in the derived class vector. And I figured out that the destructor is not virtual and the derived class destructor is not called.And it surprisingly got fixed when I made the destructor virtual. But my question is "isn't the vector deallocated automatically even if the derived class destructor is not called"? Is that a quirk in BoundsChecker tool or is my understanding of virtual destructor is wrong:)

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• Loading/Displaying large amount of data on webpage.

  - by jb

  I have a webpage which contains a table for displaying a large amount of data (on average from 2,000 to 10,000 rows). This page takes a long time to load/render. Which is understandable. The problem is, while the page is loading the PCs memory usage skyrockets (500mb on my test system is in use by iexplorer) and the whole PC grinds to a halt until it has finished, which can take a minute or two. IE hangs until it is complete, switching to another running program is the same. I need to fix this - and ideally i want to accomplish 2 things: 1) Load individual parts of the page seperately. So the page can render initially without the large data table. A loading div will be placed there until it is ready. 2) Dont use up so much memory or local resources while rendering - so at least they can use a different tab/application at the same time. How would I go about doing both or either of these? I'm an applications programmer by trade so i am still a little fizzy on the things I can do in a web environment. Cheers all.

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• Progressively stream the output of an ASP.NET page - or render a page outside of an HTTP request

  - by Evgeny

  I have an ASP.NET 2.0 page with many repeating blocks, including a third-party server-side control (so it's not just plain HTML). Each is quite expensive to generate, in terms of both CPU and RAM. I'm currently using a standard Repeater control for this. There are two problems with this simple approach: The entire page must be rendered before any of it is returned to the client, so the user must wait a long time before they see any data. (I write progress messages using Response.Write, so there is feedback, but no actual results.) The ASP.NET worker process must hold everything in memory at the same time. There is no inherent needs for this: once one block is processed it won't be changed, so it could be returned to the client and the memory could be freed. I would like to somehow return these blocks to the client one at a time, as each is generated. I'm thinking of extracting the stuff inside the Repeater into a separate page and getting it repeatedly using AJAX, but there are some complications involved in that and I wonder if there is some simper approach. Ideally I'd like to keep it as one page (from the client's point of view), but return it incrementally. Another way would be to do something similar, but on the server: still create a separate page, but have the server access it and then Response.Write() the HTML it gets to the response stream for the real client request. Is there a way to avoid an HTTP request here, though? Is there some ASP.NET method that would render a UserControl or a Page outside of an HTTP request and simply return the HTML to me as a string? I'm open to other ideas on how to do this as well.

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• How do virtual destructors work?

  - by Prabhu

  Few hours back I was fiddling with a Memory Leak issue and it turned out that I really got some basic stuff about virtual destructors wrong! Let me put explain my class design. class Base { virtual push_elements() {} }; class Derived:public Base { vector<int> x; public: void push_elements(){ for(int i=0;i <5;i++) x.push_back(i); } }; void main() { Base* b = new Derived(); b->push_elements(); delete b; } The bounds checker tool reported a memory leak in the derived class vector. And I figured out that the destructor is not virtual and the derived class destructor is not called. And it surprisingly got fixed when I made the destructor virtual. Isn't the vector deallocated automatically even if the derived class destructor is not called? Is that a quirk in BoundsChecker tool or is my understanding of virtual destructor wrong?

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• Animation management in COCOS2D iphone.

  - by shreya

  Hi All, I have near about 255 image frames for background animation, 99 frames of enemy sprite and 125 frames of player sprite. All animations are running simultaneously on the screen. That is background animation is running and 4-5 enemies are on the screen are present at a time, also player is there at the same time. Take a look at the code below, CCAnimation *_enemyAnimation = [CCAnimation animationWithName:@"Enemy" delay:0.1f]; for (int i = 1; i<99; i++) { [_enemyAnimation addFrameWithFilename:[NSString stringWithFormat:@"enemy %02d.jpg",i]]; } id action1 = [CCAnimate actionWithAnimation: _enemyAnimation]; [_enemySprite runAction:[CCRepeatForever actionWithAction: action1]]; [self schedule:@selector(BackToGameLogic:) interval:5.0]; This makes my game too slower and consumes memory about 65MB in the allocations. How should I manage my animations so there will be improvement in speed and memory consumption will be reduced?. Please suggest me the way. Thanks.

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