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• Using transactions with ADO.NET Data Adapters.

  - by Ergwun

  Scenario: I want to let multiple (2 to 20, probably) server applications use a single database using ADO.NET. I want individual applications to be able to take ownership of sets of records in the database, hold them in memory (for speed) in DataSets, respond to client requests on the data, perform updates, and prevent other applications from updating those records until ownership has been relinquished. I'm new to ADO.NET, but it seems like this should be possible using transactions with Data Adapters (ADO.NET disconnected layer). Question part 1: Is that the right way to try and do this? Question part 2: If that is the right way, can anyone point me at any tutorials or examples of this kind of approach (in C#)? Question part 3: If I want to be able to take ownership of individual records and release them independently, am I going to need a separate transaction for each record, and by extension a separate DataAdapter and DataSet to hold each record, or is there a better way to do that? Each application will likely hold ownership of thousands of records simultaneously.

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• Shared Source CLI 4.0?

  - by Paul Alexander

  Microsoft released the Shared Source Common Language Infrastructure (the code previously known as ROTOR) code some years ago basically as a reference implementation of the .NET runtime. While the actual .NET runtime (mscorlib, mscoree, mscorjit, etc.) aren't compiled from the code, debugging them shows that they are remarkably similar and at a minimum share much of the same memory structures. This has been an invaluable resource when debugging tricky system behavior with .NET 2.0 compiled assemblies. Now that 4.0 has been released with major changes to the runtime I'd love to find the reference source for that as well. Microsoft has changed names for the source in the past so I'm either searching for the wrong thing, or it hasn't been released. Is there reference source for a .NET 4.0 compatible runtime?

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• How to handle a C# console application terminating?

  - by Nick R

  If I have a console application, is there any way I can handle the following: Ctrl-C (I know the answer to this. Using Console.TreatControlCAsInput and Console.CancelKeyPress) Session termination, such as when someone logs off Process exit, such as when someone uses the task manager to close the application. I know that if I was writing a unix application, I would handle various signals to catch the request to close (SIGTERM from memory), but I also know I need to handle these messages pretty quickly and exit before the system does a kill -9 (SIGKILL). But for a C# console application, I'm not sure how to do this.

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• UIImages on UITableView?

  - by babu Kong

  what is the best method to display about 300 png images into a UITableView.. i dont wanna display them at the same time... i have 3 tableViewControllers that will each display about 100 imgaes.. (its for a catalog so the images are important to display) i used [uiimage imageNamed:] but that method caches the images and they dont get released so the memory usage is big.... is there any way to release the cache when the nav controller pushes a different view controller? i also tried [uiimage alloc] initWithContentsOfFile] but the images wont display.... any help?

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• Someone is using the struct name as a variable name too. What does the code really say? (c++)

  - by EvilTeach

  This morning we found an old chunk of code that was causing a library call to crash. struct fred { int a; int b; int c; }; fred fred[MAX_SIZE+1]; memset( fred, 0, sizeof(fred) * MAX_SIZE+1 ); It appears that the sizeof(fred) may have been the full array size, rather than the structure size, as it was overwriting a great deal of memory. The fact that it compiled without warning on several different systems seemed odd. Is there a correct semantic for this case where the type and variable name are colliding? or is this some sort of undefined behavior? or just a defect? I haven't been been clever enough to find anything on Google or our language help. Thanks Evil

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• HTTP status code for "success with errors"?

  - by Richard Levasseur

  I've poked around a bit, but I don't see an HTTP status code for when a request's succeeds, but there is an error after the "point of no return". e.g., Say you process a request, its committed to the database, but while returning the result you run of memory, or encounter a NPE, or what have you. It would have been a 200 response, but now, internally, you aren't able to return the proper, well-formed response. 202 Accepted doesn't seem to fit since we've already processed the request. What status code means "Success, but errors"? Does one even exist?

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• Dereferencing pointers without pointing them at a variable

  - by Miguel

  I'm having trouble understanding how some pointers work. I always thought that when you created a pointer variable (p), you couldn't deference and assign (*p = value) unless you either malloc'd space for it (p = malloc(x)), or set it to the address of another variable (p = &a) However in this code, the first assignment works consistently, while the last one causes a segfault: typedef struct { int value; } test_struct; int main(void) { //This works int* colin; *colin = 5; //This never works test_struct* carter; carter->value = 5; } Why does the first one work when colin isn't pointing at any spare memory? And why does the 2nd never work? I'm writing this in C, but people with C++ knowledge should be able to answer this as well.

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• How to prevent a globally overridden "new" operator from being linked in from external library

  - by mprudhom

  In our iPhone XCode 3.2.1 project, we're linking in 2 external static C++ libraries, libBlue.a and libGreen.a. libBlue.a globally overrides the "new" operator for it's own memory management. However, when we build our project, libGreen.a winds up using libBlue's new operator, which results in a crash (presumably because libBlue.a is making assumptions about the kinds of structures being allocated). Both libBlue.a and libGreen.a are provided by 3rd parties, so we can't change any of their source code or build options. When we remove libBlue.a from the project, libGreen.a doesn't have any issues. However, no amount of shuffling the linking order of the libraries seems to fix the problem, nor does any experimentation with the various linking flags. Is there some way to tell XCode to tell the linker to "have libGreen's use of the new operator use the standard C++ new operator rather than the one redefined by libBlue"?

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• fastest (low latency) method for Inter Process Communication between Java and C/C++

  - by Bastien

  Hello, I have a Java app, connecting through TCP socket to a "server" developed in C/C++. both app & server are running on the same machine, a Solaris box (but we're considering migrating to Linux eventually). type of data exchanged is simple messages (login, login ACK, then client asks for something, server replies). each message is around 300 bytes long. Currently we're using Sockets, and all is OK, however I'm looking for a faster way to exchange data (lower latency), using IPC methods. I've been researching the net and came up with references to the following technologies: - shared memory - pipes - queues but I couldn't find proper analysis of their respective performances, neither how to implement them in both JAVA and C/C++ (so that they can talk to each other), except maybe pipes that I could imagine how to do. can anyone comment about performances & feasibility of each method in this context ? any pointer / link to useful implementation information ? thanks for your help

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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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• Application crash when using an NSTimer and pushViewController

  - by Cesar

  I'm using an NSTimer to implement a 3 seconds splash screen. If a don't use a timer the view it's correctly pushed but if I use the timer for adding a little delay the application crash with a EXC_BAD_ACCESS. I'm pretty sure the answer contains "memory management" but I can't get the point... @interface RootViewController : UIViewController { NSTimer *timer; } -(void)changeView:(NSTimer*)theTimer; @property(nonatomic,retain) NSTimer *timer; ... @implementation RootViewController @synthesize timer; - (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; [[self navigationController] setNavigationBarHidden:YES]; timer = [NSTimer scheduledTimerWithTimeInterval:3.0 target:self selector:@selector(changeView:) userInfo:nil repeats:NO]; } -(void)changeView:(NSTimer*)theTimer { NSLog(@"timer fired"); //Crash here, but only if called using a timer [[self navigationController] pushViewController:list animated:YES]; }

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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