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• What are the pros and cons of using an in memeory DB rather than a ThreadLocal

  - by Pangea

  we have been using ThreadLocal so far to carry some data so as to not clutter the API. However below are some of issues of using thread local that which I dont like 1) over the years the data items being carried in thread local has increased 2) Since we started using threads (for some light weight processing), we have also migrating these data to the threads in the pool and copying them back again I am thinking of using an in memory DB for these (we doesnt want to add this to the API). I wondering if this approach is good. What r the pros and cons. thx in advance.

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• How does a virtual machine work?

  - by Martin

  I've been looking into how programming languages work, and some of them have a so-called virtual machines. I understand that this is some form of emulation of the programming language within another programming language, and that it works like how a compiled language would be executed, with a stack. Did I get that right? With the proviso that I did, what bamboozles me is that many non-compiled languages allow variables with "liberal" type systems. In Python for example, I can write this: x = "Hello world!" x = 2**1000 Strings and big integers are completely unrelated and occupy different amounts of space in memory, so how can this code even be represented in a stack-based environment? What exactly happens here? Is x pointed to a new place on the stack and the old string data left unreferenced? Do these languages not use a stack? If not, how do they represent variables internally?

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• removing duplicate strings from a massive array in java efficiently?

  - by Preator Darmatheon

  I'm considering the best possible way to remove duplicates from an (Unsorted) array of strings - the array contains millions or tens of millions of stringz..The array is already prepopulated so the optimization goal is only on removing dups and not preventing dups from initially populating!! I was thinking along the lines of doing a sort and then binary search to get a log(n) search instead of n (linear) search. This would give me nlogn + n searches which althout is better than an unsorted (n^2) search = but this still seems slow. (Was also considering along the lines of hashing but not sure about the throughput) Please help! Looking for an efficient solution that addresses both speed and memory since there are millions of strings involved without using Collections API!

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• Why can final object be modified?

  - by Matt McCormick

  I came across the following code in a code base I am working on: public final class ConfigurationService { private static final ConfigurationService INSTANCE = new ConfigurationService(); private List providers; private ConfigurationService() { providers = new ArrayList(); } public static void addProvider(ConfigurationProvider provider) { INSTANCE.providers.add(provider); } ... INSTANCE is declared as final. Why can objects be added to INSTANCE? Shouldn't that invalidate the use of final. (It doesn't). I'm assuming the answer has to do something with pointers and memory but would like to know for sure.

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• How to serialize a collection of base type and see the concrete types in easy to read XML

  - by Jason Coyne

  I have a List which is populated with objects of various concrete types which subclass BaseType I am using the WCF DataContractSerializer <Children> <BaseType xmlns:d3p1="http://schemas.datacontract.org/2004/07/Tasks" i:type="d3p1:ConcreteTypeA"></BaseType> <BaseType xmlns:d3p1="http://schemas.datacontract.org/2004/07/Tasks" i:type="d3p1:ConcreteTypeB"></BaseType> </Children> Is there any way to get this to generate <Children> <ConcreteTypeA/> <ConcreteTypeB/> </Children> ? The real goal is to let users generate some XML to load into memory, and the users are of a skill level that asking them for the original XML is not going to be successful.

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• Optimizing a large iteration of PHP objects (EAV-based)

  - by Aron Rotteveel

  I am currently working on a project that utilizes the EAV model. This turns out to work quite well, but like many others I am now stumbling upon some performance issues. The data set in this particular case consists of aproximately 2500 entities, each with aprox. 150 attributes. Each entity and each attribute is represented by a PHP-object. Since most parts of the application only iterate through a filtered set of entities, we have not had very large issues yet. Now, however, I am working on an algorithm that requires iteration over the entire dataset, which causes a major impact on performance. This information is perhaps not very much to work with, but since this is an architectural problem, I am hoping for a architectural pattern to help me on the way as well. Each entity, including it's attributes takes up aprox. 500KB of memory.

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• BigDecimal precision not persisted with javax.persistence annotations

  - by dkaczynski

  I am using the javax.persistence API and Hibernate to create annotations and persist entities and their attributes in an Oracle 11g Express database. I have the following attribute in an entity: @Column(precision = 12, scale = 9) private BigDecimal weightedScore; The goal is to persist a decimal value with a maximum of 12 digits and a maximum of 9 of those digits to the right of the decimal place. After calculating the weightedScore, the result is 0.1234, but once I commit the entity with the Oracle database, the value displays as 0.12. I can see this by either by using an EntityManager object to query the entry or by viewing it directly in the Oracle Application Express (Apex) interface in a web browser. How should I annotate my BigDecimal attribute so that the precision is persisted correctly? Note: We use an in-memory HSQL database to run our unit tests, and it does not experience the issue with the lack of precision, with or without the @Column annotation.

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• Make compiler copy characters using movsd

  - by Suma

  I would like to copy a relatively short sequence of memory (less than 1 KB, typically 2-200 bytes) in a time critical function. The best code for this on CPU side seems to be rep movsd. However I somehow cannot make my compiler to generate this code. I hoped (and I vaguely remember seeing so) using memcpy would do this using compiler built-in instrinsic, but based on disassembly and debugging it seems compiler is using call to memcpy/memmove library implementation instead. I also hoped the compiler might be smart enough to recognize following loop and use rep movsd on its own, but it seems it does not. char *dst; const char *src; // ... for (int r=size; --r>=0; ) *dst++ = *src++; Is there some way to make the Visual Studio compiler to generate rep movsd sequence other than using inline assembly?

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• OSX: Why is GetProcessInformation() causing a segfault?

  - by anthony

  Here's my C method to get the pid of the Finder process. GetProcessInformation() is causing a segfault. Why? Here's the function: static OSStatus GetFinderPID(pid_t *pid) { ProcessSerialNumber psn = {kNoProcess, kNoProcess}; ProcessInfoRec info; OSStatus status = noErr; info.processInfoLength = sizeof(ProcessInfoRec); info.processName = nil; while (!status) { status = GetNextProcess(&psn); if (!status) { status = GetProcessInformation(&psn, &info); } if (!status && info.processType == 'FNDR' && info.processSignature == 'MACS') { return GetProcessPID(&psn, pid); } } return status; } Here's the backtrace: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_INVALID_ADDRESS at address: 0x0000000032aaaba7 0x00007fffffe00623 in __bzero () (gdb) bt #0 0x00007fffffe00623 in __bzero () #1 0x00007fff833adaed in CreateFSRef () #2 0x00007fff833ab53b in FSPathMakeRefInternal () #3 0x00007fff852fc32d in _CFGetFSRefFromURL () #4 0x00007fff852fbfe0 in CFURLGetFSRef () #5 0x00007fff85dd273f in GetProcessInformation () #6 0x0000000100000bef in GetFinderPID [inlined] () at /path/to/main.c:21

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• Caching generated QR Code

  - by Michal K

  I use zxing to encode a qr code and store it as a bitmap and then show it in ImageView. Since the image generation time is significant I'm planning to move it to a separate thread (AsyncTaskLoader will be fine I think). The problem is - it's an image and I know that to avoid memory leaks one should never store a strong reference to it in an Activity. So how would you do it? How to cache an image to survive config changes (phone rotation) and generally avoid generating it onCreate()? Just point me in the right direction, please.

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• Compiling my own PHP extension on Windows with Visual Studio 2008

  - by Mickey Shine

  I wrote a PHP extension and it could be compiled and run under linux successfully. But on windows, I met some problems. I did the compiling on windows according to http://blog.slickedit.com/?p=128 with PHP source version 5.2.10, and after the compiling it generated the dll file. But when I tried to use the dll file, it reported me the memory problems when starting Apache(Wamp server). And then I started the debugging process, it seemed that REGISTER_INI_ENTRIES() had problems. Here is the PHP extension source code, http://www.bluefly.cn/xsplit.tar.gz , and it works fine on Linux. But I also want to make it work on Windows. Sorry I am not a pro so that I hope someone can help me. Any help is appreciated and thanks in advance~

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• SQL CE not loading from network share

  - by David Veeneman

  I installed VS 2010 RC yesterday, and suddenly, SQL Server CE isn't loading files from a network share. In projects compiled with VS 2008, if I try to open a SQL CE file located on a network share, I get an error that reads like this: Internal error: Cannot open the shared memory region. If I try to create a data connection in VS 2010 to a SQL CE file on a network share, I get this error: SQL Server Compact does not support opening database files on a network share. Can anyone shed any light on what's going on? Thanks.

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• The speed of .NET in numerical computing

  - by Yin Zhu

  In my experience, .net is 2 to 3 times slower than native code. (I implemented L-BFGS for multivariate optimization). I have traced the ads on stackoverflow to http://www.centerspace.net/products/ the speed is really amazing, the speed is close to native code. How can they do that? They said that: Q. Is NMath "pure" .NET? A. The answer depends somewhat on your definition of "pure .NET". NMath is written in C#, plus a small Managed C++ layer. For better performance of basic linear algebra operations, however, NMath does rely on the native Intel Math Kernel Library (included with NMath). But there are no COM components, no DLLs--just .NET assemblies. Also, all memory allocated in the Managed C++ layer and used by native code is allocated from the managed heap. Can someone explain more to me? Thanks!

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• Is there a faster alternative to using textures in XNA?

  - by Matthew Bowen

  I am writing a map editing program for a 2D game using XNA. To create a Texture2D for all of the tiles that a map requires takes too long. Are there any alternatives to using textures for drawing with XNA? I attempted to create just one texture per tile set instead of a texture for every tile in a tile set, but there is a limit to the size of textures and I could not fit all the tiles of a tile set into one texture. Currently the program contains all the would-be textures in memory as Bitmap objects. Is there a way to simply draw a Bitmap object to the screen in XNA? I have searched but I cannot find any information on this. This approach would avoid having to create textures altogether, however any tinting or effects I would have to do to the bitmap directly. Any help would be very much appreciated. Thanks

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• Infix to Postfix and unary/binary operators

  - by Jaapjan

  I have a piece of code that converts an infix expression to an expression tree in memory. This works just fine. There's just one small trouble. I just connect work out how to involve the unary operators correctly (the right associative ones). With the following infix expression : +1 + +2 - -3 - -4 I would expect an RPN of: 1+2++3-4-- Yet, none of the online infix-post converters I can find handle this example in the way I would expect. Does anyone have a clear explanation of handling right associative operators, specifically the binary ones that can be mistaken for the unary ones?

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• Advantage of using a static member function instead of an equivalent non-static member function?

  - by jonathanasdf

  I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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• C++ Static array vs. Dynamic array?

  - by user69514

  What is the difference between a static array and a dynamic array in C++? I have to do an assignment for my class and it says not to use static arrays, only dynamic arrays. I've looked in the book and online, but I don't seem to understand. I thought static was created at compile time and dynamic at runtime, but I might be mistaken this with memory allocation. Can you explain to me the difference between static array and dynamic array in C++? Thnaks.

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• VC7.1 C1204 internal compiler error

  - by Nathan Ernst

  I'm working on modifying Firaxis' Civilization 4 core game DLL. The host application is built using VC7, hence the constraint (source not provided for the host EXE). I've been working on rewriting a large chunk of the code (focusing on low-hanging performance issues & memory leaks). I recently ran into an internal compiler error when trying to mod the code to use an array class instead of dynamically allocated 2-d arrays, I was going to use matrices from the boost lib (Civ4 is already using boost, so why not?). Basically, the issue comes down to: if I include "boost/numeric/ublas/matrix.hpp", I run into an internal compiler error C1204. MSDN has this to say: MSDN C1204 KB has this to say: KB 883655 So, I'm curious, is it possible to solve this error without a KB/SP being applied and dramatically reducing the complexity of the code? Additionally, as VC7 is no longer "supported", does anyone have a valid (supported) link for a VC7 service pack?

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• Disabling Xdebug's dumping of caught exceptions

  - by nuqqsa

  By default Xdebug will dump any exception regardless of whether it is caught or not: try { throw new Exception(); } catch (Exception $e) { } echo 'life goes on'; With XDebug enabled and the default settings this piece of code will actually output something like the following (nicely formatted): ( ! ) Exception: in /test.php on line 3 Call Stack # Time Memory Function Location 1 0.0003 52596 {main}( ) ../test.php:0 life goes on Is it possible to disable this behaviour and have it dumping only the uncaught exceptions? Thanks in advance. UPDATE: I'm about to conclude that this is a bug, since xdebug.show_exception_trace is disabled by default yet it doesn't behave as expected (using Xdebug v2.0.5 with PHP 5.2.10 on Ubuntu 9.10).

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• how to match a regulas expresion like (%i1) in python pexpect

  - by mike

  I want to use maxima from python using pexpect, whenever maxima starts it will print a bunch of stuff of this form: $ maxima Maxima 5.27.0 http://maxima.sourceforge.net using Lisp SBCL 1.0.57-1.fc17 Distributed under the GNU Public License. See the file COPYING. Dedicated to the memory of William Schelter. The function bug_report() provides bug reporting information. (%i1) i would like to start up pexpect like so: import pexpect cmd = 'maxima' child = pexpect.spawn(cmd) child.expect (' match all that stuff up to and including (%i1)') child.sendline ('integrate(sin(x),x)') chil.expect( match (%o1 ) ) print child.before how do i match the starting banner up to the prompt (%i1)? and so on, also maxima increments the (%i1)'s by one as the session goes along, so the next expect would be: child.expect ('match (%i2)') child.sendline ('integrate(sin(x),x)') chil.expect( match (%o2 ) ) print child.before how do i match the (incrementing) integers?

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• How do laziness and I/O work together in Haskell?

  - by Bill

  I'm trying to get a deeper understanding of laziness in Haskell. I was imagining the following snippet today: data Image = Image { name :: String, pixels :: String } image :: String -> IO Image image path = Image path <$> readFile path The appeal here is that I could simply create an Image instance and pass it around; if I need the image data it would be read lazily - if not, the time and memory cost of reading the file would be avoided: main = do image <- image "file" putStrLn $ length $ pixels image But is that how it actually works? How is laziness compatible with IO? Will readFile be called regardless of whether I access pixels image or will the runtime leave that thunk unevaluated if I never refer to it? If the image is indeed read lazily, then isn't it possible I/O actions could occur out of order? For example, what if immediately after calling image I delete the file? Now the putStrLn call will find nothing when it tries to read.

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• Processing potentially large STDIN data, more than once

  - by d11wtq

  I'd like to provide an accessor on a class that provides an NSInputStream for STDIN, which may be several hundred megabytes (or gigabytes, though unlikely, perhaps) of data. When I caller gets this NSInputStream it should be able to read from it without worrying about exhausting the data it contains. In other words, another block of code may request the NSInputStream and will expect to be able to read from it. Without first copying all of the data into an NSData object which (I assume) would cause memory exhaustion, what are my options for handling this? The returned NSInputStream does not have to be the same instance, it simply needs to provide the same data. The best I can come up with right now is to copy STDIN to a temporary file and then return NSInputStream instances using that file. Is this pretty much the only way to handle it? Is there anything I should be cautious of if I go the temporary file route?

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• What is the best way to manage one's session variables?

  - by donde

  In my .NET web app, I keep basic user info in a user session object. I also usually keep a director class in the session; which is basically just has info about whatever thing it being worked on on that screen (like a customer id). I am trying to keep from adding a ton of sessions. I also want to make sure at any given time ONLY the sessions that are necessary are in memory. This means I need an effective way of managing my session variables. Any suggestions?

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• Are these tables too big for SQL Server or Oracle

  - by Jeffrey Cameron

  Hey all, I'm not much of a database guru so I would like some advice. Background We have 4 tables that are currently stored in Sybase IQ. We don't currently have any choice over this, we're basically stuck with what someone else decided for us. Sybase IQ is a column-oriented database that is perfect for a data warehouse. Unfortunately, my project needs to do a lot of transactional updating (we're more of an operational database) so I'm looking for more mainstream alternatives. Question Given these tables' dimensions, would anyone consider SQL Server or Oracle to be a viable alternative? Table 1 : 172 columns * 32 million rows Table 2 : 453 columns * 7 million rows Table 3 : 112 columns * 13 million rows Table 4 : 147 columns * 2.5 million rows Given the size of data what are the things I should be concerned about in terms of database choice, server configuration, memory, platform, etc.?

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• Asp.net TreeView control - maximum number of nodes

  - by mas_oz2k1

  I have a treeView control in ASP.NET page that will be loaded with up to 12,000 nodes in different levels. For example: Node 1 Node 1.1 … Node 1.400 Node 1.400.1 … Node 1.400.6400 Node 2 Node 3 Node 4 According to this link: http://msdn.microsoft.com/en-us/library/ms529261.aspx the node limit is 1000. Is this correct or is it dependent on available memory(please specify value)? Assuming it is correct. is there any way to split the 4600 child nodes in say in chunks of 300 hundred? I am thinking that if dummy nodes are used (previous /next navigation) to navigate the chunks will easy the load of the html page. Sample code in C# will be greatly appreciated. (Or VB.NET if you can not translate it to C#)

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