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• error detection/correction/recovery in serial protocols

  - by Jason S

  I have some designing to do for a serial protocol and am running into some questions that I figure must have been considered elsewhere. So I'm wondering if there are some recommendations for best practices in designing serial protocols. (Please either state a fact that is easily verifiable, or cite a reputable source if you make a claim.) General recommendations for websites/books are also welcome. In particular I have to deal with issues like parsing a stream of bytes into packets verifying a packet is correct (easy with a CRC, for instance) identifying reasonable types of errors that can occur (e.g. in a point-to-point serial stream, sporadic single bit errors, and dropped series of bytes, are both likely, but extra phantom bytes are unlikely; whereas with a record stored in flash memory or on a disk drive the types of errors that predominate are different) error correction or recovery (if I detect an error in a packet, can I correct it? If not, can I resync to the boundary of the next packet?) how to make variable-length packets robust to error correction / recovery. Any suggestions?

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• Automatic .NET code, nhibernate session, and LINQ datacontext clean-up?

  - by AverageJoe719

  Hi all, in my goal to adopt better coding practices I have a few questions in general about automatic handling of code. I have heard different answers both from online and talking with other developers/programmers at my work. I am not sure if I should have split them into 3 questions, but they all seem sort of related: 1) How does .NET handle instances of classes and other code things that take up memory? I recently found out about using the factory pattern for certain things like service classes so that they are only instantiated once in the entire application, but then I was told that '.NET handles a lot of that stuff automatically when mentioning it.' 2) How does Nhibernate's session handle automatic clean-up of un-used things? I've seen some say that it is great at handling things automatically and you should just use a session factory and that's it, no need to close it. But I have also read and seem many examples where people close the hibernate session. 3) How does LINQ's datacontext handle this? Most of the time I never .disposed my datacontext's and the app didn't see to take a performance hit (though I am not running anything super intensively), but it seems like most people recommend disposing of your datacontext after you are done with it. However, I have seen many many code examples where the dispose method is never called. Also in general I found it kind of annoying that you couldn't access even one-deep child related objects after disposing of the datacontext unless you explicity also grabbed them in the query. Thanks all. I am loving this site so far, I kind of get lost and spend hours just reading things on here. =)

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• Runtime Exception when using Custom Healthmonitoring event in medium trust

  - by Elementenfresser

  Hi, I'm using custom healthmonitoring events in ASP.NET We recently moved to a new server with default High Trust Permissions. Literature says that healthmonitoring and custom events should work under Medium or higher trust (http://msdn.microsoft.com/en-us/library/bb398933.aspx). Problem is it doesn't. In less than high trust I get a SecurityException saying The application attempted to perform an operation not allowed by the security policy It works in Full trust or when I remove the inheritance of System.Web.Management.WebErrorEvent. Any suggestions anyone? Here is the super simple code behind with a custom event defined: public partial class Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { try { CallCustomEvent(); } catch (Exception ex) { Response.Write(ex.Message); throw ex; } } /// <summary> /// this metho is never called due to lacking permissions... /// </summary> private void CallCustomEvent() { try { //do something useful here } catch (Exception) { //code to instantiate the forbidden inheritance... WebBaseEvent.Raise(new CustomEvent()); } } } /// <summary> /// custom error inheriting WebErrorEvent which is not allowed in high trust? can't believe that... /// </summary> public class CustomEvent : WebErrorEvent { public CustomEvent() : base("test", HttpContext.Current.Request, 100001, new ApplicationException("dummy")) { } } and the Web Config excerpt for high trust: <system.web> <trust level="High" originUrl="" />

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• Need to call original function from detoured function

  - by peachykeen

  I'm using Detours to hook into an executable's message function, but I need to run my own code and then call the original code. From what I've seen in the Detours docs, it definitely sounds like that should happen automatically. The original function prints a message to the screen, but as soon as I attach a detour it starts running my code and stops printing. The original function code is roughly: void CGuiObject::AppendMsgToBuffer(classA, unsigned long, unsigned long, int, classB); My function is: void CGuiObject_AppendMsgToBuffer( [same params, with names] ); I know the memory position the original function resides in, so using: DWORD OrigPos = 0x0040592C; DetourAttach( (void*)OrigPos, CGuiObject_AppendMsgToBuffer); gets me into the function. This code works almost perfectly: my function is called with the proper parameters. However, execution leaves my function and the original code is not called. I've tried jmping back in, but that crashes the program (I'm assuming the code Detours moved to fit the hook is responsible for the crash). Edit: I've managed to fix the first issue, with no returning to program execution. By calling the OrigPos value as a function, I'm able to go to the "trampoline" function and from there on to the original code. However, somewhere along the lines the registers are changing and that is causing the program to crash with a segfault as soon as I get back into the original code.

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• What is the best database structure for this scenario?

  - by Ricketts

  I have a database that is holding real estate MLS (Multiple Listing Service) data. Currently, I have a single table that holds all the listing attributes (price, address, sqft, etc.). There are several different property types (residential, commercial, rental, income, land, etc.) and each property type share a majority of the attributes, but there are a few that are unique to that property type. My question is the shared attributes are in excess of 250 fields and this seems like too many fields to have in a single table. My thought is I could break them out into an EAV (Entity-Attribute-Value) format, but I've read many bad things about that and it would make running queries a real pain as any of the 250 fields could be searched on. If I were to go that route, I'd literally have to pull all the data out of the EAV table, grouped by listing id, merge it on the application side, then run my query against the in memory object collection. This also does not seem very efficient. I am looking for some ideas or recommendations on which way to proceed. Perhaps the 250+ field table is the only way to proceed. Just as a note, I'm using SQL Server 2012, .NET 4.5 w/ Entity Framework 5, C# and data is passed to asp.net web application via WCF service. Thanks in advance.

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• Optimizing MySQL for ALTER TABLE of InnoDB

  - by schuilr

  Sometime soon we will need to make schema changes to our production database. We need to minimize downtime for this effort, however, the ALTER TABLE statements are going to run for quite a while. Our largest tables have 150 million records, largest table file is 50G. All tables are InnoDB, and it was set up as one big data file (instead of a file-per-table). We're running MySQL 5.0.46 on an 8 core machine, 16G memory and a RAID10 config. I have some experience with MySQL tuning, but this usually focusses on reads or writes from multiple clients. There is lots of info to be found on the Internet on this subject, however, there seems to be very little information available on best practices for (temporarily) tuning your MySQL server to speed up ALTER TABLE on InnoDB tables, or for INSERT INTO .. SELECT FROM (we will probably use this instead of ALTER TABLE to have some more opportunities to speed things up a bit). The schema changes we are planning to do is adding a integer column to all tables and make it the primary key, instead of the current primary key. We need to keep the 'old' column as well so overwriting the existing values is not an option. What would be the ideal settings to get this task done as quick as possible?

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• Is there a fast alternative to creating a Texture2D from a Bitmap object in XNA?

  - by Matthew Bowen

  I've looked around a lot and the only methods I've found for creating a Texture2D from a Bitmap are: using (MemoryStream s = new MemoryStream()) { bmp.Save(s, System.Drawing.Imaging.ImageFormat.Png); s.Seek(0, SeekOrigin.Begin); Texture2D tx = Texture2D.FromFile(device, s); } and Texture2D tx = new Texture2D(device, bmp.Width, bmp.Height, 0, TextureUsage.None, SurfaceFormat.Color); tx.SetData<byte>(rgbValues, 0, rgbValues.Length, SetDataOptions.NoOverwrite); Where rgbValues is a byte array containing the bitmap's pixel data in 32-bit ARGB format. My question is, are there any faster approaches that I can try? I am writing a map editor which has to read in custom-format images (map tiles) and convert them into Texture2D textures to display. The previous version of the editor, which was a C++ implementation, converted the images first into bitmaps and then into textures to be drawn using DirectX. I have attempted the same approach here, however both of the above approaches are significantly too slow. To load into memory all of the textures required for a map takes for the first approach ~250 seconds and for the second approach ~110 seconds on a reasonable spec computer. If there is a method to edit the data of a texture directly (such as with the Bitmap class's LockBits method) then I would be able to convert the custom-format images straight into a Texture2D and hopefully save processing time. Any help would be very much appreciated. Thanks

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• how to implement a really efficient bitvector sorting in python

  - by xiao

  Hello guys! Actually this is an interesting topic from programming pearls, sorting 10 digits telephone numbers in a limited memory with an efficient algorithm. You can find the whole story here What I am interested in is just how fast the implementation could be in python. I have done a naive implementation with the module bitvector. The code is as following: from BitVector import BitVector import timeit import random import time import sys def sort(input_li): return sorted(input_li) def vec_sort(input_li): bv = BitVector( size = len(input_li) ) for i in input_li: bv[i] = 1 res_li = [] for i in range(len(bv)): if bv[i]: res_li.append(i) return res_li if __name__ == "__main__": test_data = range(int(sys.argv[1])) print 'test_data size is:', sys.argv[1] random.shuffle(test_data) start = time.time() sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "sort function takes " + str(elapsed) start = time.time() vec_sort(test_data) elapsed = (time.time() - start) print "vec_sort function takes " + str(elapsed) I have tested from array size 100 to 10,000,000 in my macbook(2GHz Intel Core 2 Duo 2GB SDRAM), the result is as following: test_data size is: 1000 sort function takes 0.000274896621704 vec_sort function takes 0.00383687019348 test_data size is: 10000 sort function takes 0.00380706787109 vec_sort function takes 0.0371489524841 test_data size is: 100000 sort function takes 0.0520560741425 vec_sort function takes 0.374383926392 test_data size is: 1000000 sort function takes 0.867373943329 vec_sort function takes 3.80475401878 test_data size is: 10000000 sort function takes 12.9204008579 vec_sort function takes 38.8053860664 What disappoints me is that even when the test_data size is 100,000,000, the sort function is still faster than vec_sort. Is there any way to accelerate the vec_sort function?

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• Segmentation fault on writing char to char* address

  - by Lukas Dojcak

  hi guys, i've got problem with my little C program. Maybe you could help me. char* shiftujVzorku(char* text, char* pattern, int offset){ char* pom = text; int size = 0; int index = 0; while(*(text + size) != '\0'){ size++; } while(*(pom + index) != '\0'){ if(overVzorku(pom + index, pattern)){ while(*pattern != '\0'){ //vyment *pom s *pom + offset if(pom + index + offset < text + size){ char x = *(pom + index + offset); char y = *(pom + index); int adresa = *(pom + index + offset); *(pom + index + offset) = y; <<<<<< SEGMENTATION FAULT *(pom + index) = x; //*pom = *pom - *(pom + offset); //*(pom + offset) = *(pom + offset) + *pom; //*pom = *(pom + offset) - *pom; } else{ *pom = *pom - *(pom + offset - size); *(pom + offset - size) = *(pom + offset - size) + *pom; *pom = *(pom + offset - size) - *pom; } pattern++; } break; } index++; } return text; } Isn't important what's the programm doing. Mayby there's lot of bugs. But, why do I get SEGMENTATION FAULT (for destination see code) at this line? I'm, trying to write some char value to memory space, with help of address "pom + offset + index". Thanks for everything helpful. :)

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• Fast Lightweight Image Comparisson Metric Algorithm

  - by gav

  Hi All, I am developing an application for the Android platform which contains 1000+ image filters that have been 'evolved'. When a user selects a photo I want to present the most relevant filters first. This 'relevance' should be dependent on previous use cases. I have already developed tools that register when a filtered image is saved; this combination of filter and image can be seen as the training data for my system. The issue is that the comparison must occur between selecting an image and the next screen coming up. From a UI point of view I need the whole process to take less that 4 seconds; select an image- obtain a metric to use for similarity - check against use cases - return 6 closest matches. I figure with 4 seconds I can use animations and progress dialogs to keep the user happy. Due to platform contraints I am fairly limited in the computational expense of the algorithm. I have implemented a technique adapted from various online tutorials for running C code on the G1 and hence this language is available Specific Constraints; Qualcomm® MSM7201A™, 528 MHz Processor 320 x 480 Pixel bitmap in 32 bit ARGB ~ 2 seconds computational time for the native method to get the metric ~ 2 seconds to compare the metric of the current image with training data This is an academic project so all ideas are welcome, anything you can think of or have heard about would be of interest to me. My ideas; I want to keep the complexity down (O(n*m)?) by using pixel data only rather than a neighbourhood function I was looking at using the Colour historgram/Greyscale histogram/Texture/Entropy of the image, combining them to make the measure. There will be an obvious loss of information but I need the resultant metric to be substantially smaller than the memory footprint of the image (~0.512 MB) As I said, any ideas to direct my research would be fantastic. Kind regards, Gavin

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• AS3 using PrintJob to print a MovieClip

  - by Chris Waugh

  Hello, I am currently trying to create a function which will allow me to pass in a movieclip and print it. Here is the simplified version of the function: function printMovieClip(clip:MovieClip) { var printJob:PrintJob = new PrintJob(); var numPages:int = 0; var printY:int = 0; var printHeight:Number; if ( printJob.start() ) { /* Resize movie clip to fit within page width */ if (clip.width > printJob.pageWidth) { clip.width = printJob.pageWidth; clip.scaleY = clip.scaleX; } numPages = Math.ceil(clip.height / printJob.pageHeight); /* Add pages to print job */ for (var i:int = 0; i < numPages; i++) { printJob.addPage(clip, new Rectangle(0, printY, printJob.pageWidth, printJob.pageHeight)); printY += printJob.pageHeight; } /* Send print job to printer */ printJob.send(); /* Delete job from memory */ printJob = null; } } printMovieClip( testMC ); Unfortunately this is not working as expected i.e. printing the full width of the Movieclip and doing page breaks on the length. Any help with this would be greatly appreciated. Many thanks, Chris

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• vector::erase with pointer member

  - by matt

  I am manipulating vectors of objects defined as follow: class Hyp{ public: int x; int y; double wFactor; double hFactor; char shapeNum; double* visibleShape; int xmin, xmax, ymin, ymax; Hyp(int xx, int yy, double ww, double hh, char s): x(xx), y(yy), wFactor(ww), hFactor(hh), shapeNum(s) {visibleShape=0;shapeNum=-1;}; //Copy constructor necessary for support of vector::push_back() with visibleShape Hyp(const Hyp &other) { x = other.x; y = other.y; wFactor = other.wFactor; hFactor = other.hFactor; shapeNum = other.shapeNum; xmin = other.xmin; xmax = other.xmax; ymin = other.ymin; ymax = other.ymax; int visShapeSize = (xmax-xmin+1)*(ymax-ymin+1); visibleShape = new double[visShapeSize]; for (int ind=0; ind<visShapeSize; ind++) { visibleShape[ind] = other.visibleShape[ind]; } }; ~Hyp(){delete[] visibleShape;}; }; When I create a Hyp object, allocate/write memory to visibleShape and add the object to a vector with vector::push_back, everything works as expected: the data pointed by visibleShape is copied using the copy-constructor. But when I use vector::erase to remove a Hyp from the vector, the other elements are moved correctly EXCEPT the pointer members visibleShape that are now pointing to wrong addresses! How to avoid this problem? Am I missing something?

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• "Downloading" a computed value form JavaScript

  - by Travis Jensen

  I'm hoping you can prove me wrong here (please, please, please! ;). I have a situation where I need to download encrypted data from a Server D (for "Data"). Server K (for "Key") has the encryption key. For security sake, I would really prefer that Server D never know the key that Server K knows. What I want is my client (e.g. your browser) to connect to Server D for the data and Server K for the key and doe the decryption locally so the unencrypted stuff never leaves your computer. I can do this fine for text areas in the dom by replacing the contents of the HTML. However, sometimes, I would like to do larger files that I stream to the file system. For instance, perhaps I want to encrypt a movie and decrypt it and stream the contents to the my video player. I am not a JavaScript guru by any stretch, especially when it comes to the edge cases of things like the security sandbox. For Small D, I can handle the decryption, but I don't know how to save the decrypted file. Large D seems problematic as memory runs out. Anybody have any ideas that don't involve native plugins? Thanks!

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• What is the best approach for creating a Common Information Model?

  - by Kaiser Advisor

  Hi, I would like to know the best approach to create a Common Information Model. Just to be clear, I've also heard it referred to as a canonical information model, semantic information model, and master data model - As far as I can tell, they are all referring to the same concept. I've heard in the past that a combined "top-down" and "bottom-up" approach is best. This has the advantage of incorporating "Ivory tower" architects and developers - The work will meet somewhere in the middle and usually be both logical and practical. However, this involves bringing in a lot of people with different skill sets. I've also seen a couple of references to the Distributed Management Task Force, but I can't glean much on best practices in terms of CIM development. This is something I'm quite interested in getting some feedback on since having a strong CIM is a prerequisite to SOA. Thanks for your help! KA Update I've heard another strategy goes along with overall SOA implementation: Get the business involved, and seek executive sponsorship. This would be part of the "Top-down" effort.

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• Fixing a multi-threaded pycurl crash.

  - by Rook

  If I run pycurl in a single thread everything works great. If I run pycurl in 2 threads python will access violate. The first thing I did was report the problem to pycurl, but the project died about 3 years ago so I'm not holding my breath. My (hackish) solution is to build a 2nd version of pycurl called "pycurl_thread" which will only be used by the 2nd thread. I downloaded the pycurl module from sourceforge and I made a total of 4 line changes. But python is still crashing. My guess is that even though this is a module with a different name (import pycurl_thread), its still sharing memory with the original module (import pycurl). How should I solve this problem? Changes in pycurl.c: initpycurl(void) to initpycurl_thread(void) and m = Py_InitModule3("pycurl", curl_methods, module_doc); to m = Py_InitModule3("pycurl_thread", curl_methods, module_doc); Changes in setup.py: PACKAGE = "pycurl" PY_PACKAGE = "curl" to PACKAGE = "pycurl_thread" PY_PACKAGE = "curl_thread" Here is the seg fault i'm getting. This is happening within the C function do_curl_perform(). *** longjmp causes uninitialized stack frame ***: python2.7 terminated ======= Backtrace: ========= /lib/libc.so.6(__fortify_fail+0x37)[0x7f209421b537] /lib/libc.so.6(+0xff4c9)[0x7f209421b4c9] /lib/libc.so.6(__longjmp_chk+0x33)[0x7f209421b433] /usr/lib/libcurl.so.4(+0xe3a5)[0x7f20931da3a5] /lib/libpthread.so.0(+0xfb40)[0x7f209532eb40] /lib/libc.so.6(__poll+0x53)[0x7f20941f6203] /usr/lib/libcurl.so.4(Curl_socket_ready+0x116)[0x7f2093208876] /usr/lib/libcurl.so.4(+0x2faec)[0x7f20931fbaec] /usr/local/lib/python2.7/dist-packages/pycurl.so(+0x892b)[0x7f209342c92b] python2.7(PyEval_EvalFrameEx+0x58a1)[0x4adf81] python2.7(PyEval_EvalCodeEx+0x891)[0x4af7c1] python2.7(PyEval_EvalFrameEx+0x538b)[0x4ada6b] python2.7(PyEval_EvalFrameEx+0x65f9)[0x4aecd9]

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• Database Functional Programming in Clojure

  - by Ralph

  "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail." - Abraham Maslow I need to write a tool to dump a large hierarchical (SQL) database to XML. The hierarchy consists of a Person table with subsidiary Address, Phone, etc. tables. I have to dump thousands of rows, so I would like to do so incrementally and not keep the whole XML file in memory. I would like to isolate non-pure function code to a small portion of the application. I am thinking that this might be a good opportunity to explore FP and concurrency in Clojure. I can also show the benefits of immutable data and multi-core utilization to my skeptical co-workers. I'm not sure how the overall architecture of the application should be. I am thinking that I can use an impure function to retrieve the database rows and return a lazy sequence that can then be processed by a pure function that returns an XML fragment. For each Person row, I can create a Future and have several processed in parallel (the output order does not matter). As each Person is processed, the task will retrieve the appropriate rows from the Address, Phone, etc. tables and generate the nested XML. I can use a a generic function to process most of the tables, relying on database meta-data to get the column information, with special functions for the few tables that need custom processing. These functions could be listed in a map(table name -> function). Am I going about this in the right way? I can easily fall back to doing it in OO using Java, but that would be no fun. BTW, are there any good books on FP patterns or architecture? I have several good books on Clojure, Scala, and F#, but although each covers the language well, none look at the "big picture" of function programming design.

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• Insert a datetime value with GetDate() function to a SQL server (2005) table?

  - by David.Chu.ca

  I am working (or fixing bugs) on an application which was developed in VS 2005 C#. The application saves data to a SQL server 2005. One of insert SQL statement tries to insert a time-stamp value to a field with GetDate() TSQL function as date time value. Insert into table1 (field1, ... fieldDt) values ('value1', ... GetDate()); The reason to use GetDate() function is that the SQL server may be at a remove site, and the date time may be in a difference time zone. Therefore, GetDate() will always get a date from the server. As the function can be verified in SQL Management Studio, this is what I get: SELECT GetDate(), LEN(GetDate()); -- 2010-06-10 14:04:48.293 19 One thing I realize is that the length is not up to the milliseconds, i.e., 19 is actually for '2010-06-10 14:04:48'. Anyway, the issue I have right now is that after the insert, the fieldDt actually has a date time value up to minutes, for example, '2010-06-10 14:04:00'. I am not sure why. I don't have permission to update or change the table with a trigger to update the field. My question is that how I can use a INSERT T-SQL to add a new row with a date time value ( SQL server's local date time) with a precision up to milliseconds?

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• Passing data between ViewControllers versus doing local Fetch in each VC

  - by Tofrizer

  Hi All, I'm developing an iPhone app using Core Data and I'm looking for some general advice and recommendations on whether its acceptable to pass data between ViewControllers versus doing a local fetch in each ViewController as you navigate to it. Ordinarily I would say it all depends on various factors (e.g. performance etc) but the passing data approach is so prevalent in my app and I'm spooked by all the stories about Apple rejecting apps because of not conforming to their standard guidelines. So let me put another way -- is it non-standard to pass data between VC's? The reason I pass data so much is because each ViewController is just another view on to data present in my object model / graph. Once I have a handle on my first object in the first view controller (which I of course do have to fetch), I can use the existing object composition / relationships to drill down into the next level of detail into data and so I just pass these objects to the next VC. Separately, one possible downside with this passing-data-to-each-VC approach is I don't benefit from (what I perceive to be) the optimisation/benefits that NSFetchedResultsController provides in terms of efficient memory usage and section handling. My app is read-only but I do have one table with 5000 rows and I'm curious if I am missing out on NSFetchedResultsController benefits. Any thoughts on this as well? Can I somehow still benefit from NSFetchedResultsController goodness without having to do a full fetch (as I would have already passed in the data from my previous VC)? Thanks a lot.

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• Reuse, Rewrite, or Refactor?

  - by Jon Purdy

  At work I inherited development of a PHP-based Web site after the consultant who originally produced it bailed out and left without a trace. Literally half of the code is ripped from online tutorials, and there are thousands of lines of cruft that, being incomplete, do precious little. Hardly any of it actually works. I've been trying to pull out the usable components, such as the layout (cleverly intermixed with code), session management (delicately seasoned with unescaped, unvalidated SQL queries), and a few other things, but it's very difficult to force all of this junk into place. Further, I don't speak idiomatic PHP, being more of a Perl user, and I'm supposed to be on this project principally for maintenance, so rewriting everything seems like it would take just as long as wrestling the existing monster back into place. As an aside, I have literally never seen anything as badly written as this. Welcome me to the world of working with other people's code, I guess, but I do hope it's not this common in the real world to have such gems as these: // WHY IS THIS NOT WORKING // I know this is bad but were going for working stuff right now... // This is a PHP code outputing Javascript code outputting HTML...do not go further // Not userful I'm looking for the best advice I can get here. What would you do if you were in my position?

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• Reversible pseudo-random sequence generator

  - by user350651

  I would like some sort of method to create a fairly long sequence of random numbers that I can flip through backwards and forwards. Like a machine with "next" and "previous" buttons, that will give you random numbers. Something like 10-bit resolution (i.e. positive integers in a range from 0 to 1023) is enough, and a sequence of 100k numbers. It's for a simple game-type app, I don't need encryption-strength randomness or anything, but I want it to feel fairly random. I have a limited amount of memory available though, so I can't just generate a chunk of random data and go through it. I need to get the numbers in "interactive time" - I can easily spend a few ms thinking about the next number, but not comfortably much more than that. Eventually it will run on some sort of microcontroller, probably just an Arduino. I could do it with a simple linear congruential generator (LCG). Going forwards is simple, to go backwards I'd have to cache the most recent numbers and store some points at intervals so I can recreate the sequence from there. But maybe there IS some pseudo-random generator that allows you to go both forwards and forwards? It should be possible to hook up two linear feedback shift registers (LFSRs) to roll in different directions, no? Or maybe I can just get by with garbling the index number using a hash function of some sort? I'm going to try that first. Any other ideas?

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• x86 .net application with system.OutOfMemoryException

  - by Allen

  Hi,Guys I got OutOfMemoryException after the app running for 1 day, the app totally use 1.5G memory , all consumed by managed heap, gen 2 used 200mb , and LOB used 1.3mb, however the weired thing is, 900mb of space are Free. from perf counter I saw there had number of gen 2 gc collection happened, why GC collector cannot collect those 900mb free space in gen2 and LOB? I'm really appreicate for your help. following info are from windbg: 0:000> !eeheap -gc Number of GC Heaps: 1 generation 0 starts at 0x183153f0 generation 1 starts at 0x182aa834 generation 2 starts at 0x02131000 ephemeral segment allocation context: none segment begin allocated size 02130000 02131000 0312f284 0xffe284(16769668) 07750000 07751000 0874fc5c 0xffec5c(16772188) 09e30000 09e31000 0ae2fc2c 0xffec2c(16772140) 0b230000 0b231000 0c22ffec 0xffefec(16773100) 0c230000 0c231000 0d22f6f0 0xffe6f0(16770800) 0d230000 0d231000 0e22ea10 0xffda10(16767504) 0e230000 0e231000 0f22c1c4 0xffb1c4(16757188) 10390000 10391000 1138ddf4 0xffcdf4(16764404) 154e0000 154e1000 164da90c 0xff990c(16750860) 34aa0000 34aa1000 35a9dbfc 0xffcbfc(16763900) 7aca0000 7aca1000 7bc9edfc 0xffddfc(16768508) 49760000 49761000 4a75ef64 0xffdf64(16768868) 7bca0000 7bca1000 7cc99bac 0xff8bac(16747436) 17a70000 17a71000 183313fc 0x8c03fc(9176060) Large object heap starts at 0x03131000 segment begin allocated size 03130000 03131000 041250c8 0xff40c8(16728264) 08920000 08921000 099102f8 0xfef2f8(16708344) .... .... 4c760000 4c761000 4d71d578 0xfbc578(16500088) 1bb10000 1bb11000 1ca110d0 0xf000d0(15728848) 57760000 57761000 5862d7f8 0xecc7f8(15517688) Total Size: Size: 0x5ab13450 (1521562704) bytes. ------------------------------ GC Heap Size: Size: 0x5ab13450 (1521562704) bytes. 0:000> !dumpheap -stat total 0 objects Statistics: MT Count TotalSize Class Name 73037c78 1 12 System.Configuration.GenericEnumConverter 73036da0 1 12 System.Configuration.InfiniteIntConverter .... .... 69161c3c 35025 6809420 System.Windows.EffectiveValueEntry[] 69164748 54 12471072 MS.Internal.WeakEventTable+EventKey[] 710e2228 9540 190389260 System.Byte[] 710dd2b8 1317031 339257932 System.String 0035a670 6427 902224056 Free Total 3615631 objects

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• Why doesn't gcc remove this check of a non-volatile variable?

  - by Thomas

  This question is mostly academic. I ask out of curiosity, not because this poses an actual problem for me. Consider the following incorrect C program. #include <signal.h> #include <stdio.h> static int running = 1; void handler(int u) { running = 0; } int main() { signal(SIGTERM, handler); while (running) ; printf("Bye!\n"); return 0; } This program is incorrect because the handler interrupts the program flow, so running can be modified at any time and should therefore be declared volatile. But let's say the programmer forgot that. gcc 4.3.3, with the -O3 flag, compiles the loop body (after one initial check of the running flag) down to the infinite loop .L7: jmp .L7 which was to be expected. Now we put something trivial inside the while loop, like: while (running) putchar('.'); And suddenly, gcc does not optimize the loop condition anymore! The loop body's assembly now looks like this (again at -O3): .L7: movq stdout(%rip), %rsi movl $46, %edi call _IO_putc movl running(%rip), %eax testl %eax, %eax jne .L7 We see that running is re-loaded from memory each time through the loop; it is not even cached in a register. Apparently gcc now thinks that the value of running could have changed. So why does gcc suddenly decide that it needs to re-check the value of running in this case?

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• Do fluent interfaces significantly impact runtime performance of a .NET application?

  - by stakx

  I'm currently occupying myself with implementing a fluent interface for an existing technology, which would allow code similar to the following snippet: using (var directory = Open.Directory(@"path\to\some\directory")) { using (var file = Open.File("foobar.html").In(directory)) { // ... } } In order to implement such constructs, classes are needed that accumulate arguments and pass them on to other objects. For example, to implement the Open.File(...).In(...) construct, you would need two classes: // handles 'Open.XXX': public static class OpenPhrase { // handles 'Open.File(XXX)': public static OpenFilePhrase File(string filename) { return new OpenFilePhrase(filename); } // handles 'Open.Directory(XXX)': public static DirectoryObject Directory(string path) { // ... } } // handles 'Open.File(XXX).XXX': public class OpenFilePhrase { internal OpenFilePhrase(string filename) { _filename = filename } // handles 'Open.File(XXX).In(XXX): public FileObject In(DirectoryObject directory) { // ... } private readonly string _filename; } That is, the more constituent parts statements such as the initial examples have, the more objects need to be created for passing on arguments to subsequent objects in the chain until the actual statement can finally execute. Question: I am interested in some opinions: Does a fluent interface which is implemented using the above technique significantly impact the runtime performance of an application that uses it? With runtime performance, I refer to both speed and memory usage aspects. Bear in mind that a potentially large number of temporary, argument-saving objects would have to be created for only very brief timespans, which I assume may put a certain pressure on the garbage collector. If you think there is significant performance impact, do you know of a better way to implement fluent interfaces?

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• Convert asp.net webforms logic to asp.net MVC

  - by gmcalab

  I had this code in an old asp.net webforms app to take a MemoryStream and pass it as the Response showing a PDF as the response. I am now working with an asp.net MVC application and looking to do this this same thing, but how should I go about showing the MemoryStream as PDF using MVC? Here's my asp.net webforms code: private void ShowPDF(MemoryStream ms) { try { //get byte array of pdf in memory byte[] fileArray = ms.ToArray(); //send file to the user Page.Response.Cache.SetCacheability(HttpCacheability.NoCache); Page.Response.Buffer = true; Response.Clear(); Response.ClearContent(); Response.ClearHeaders(); Response.Charset = string.Empty; Response.ContentType = "application/pdf"; Response.AddHeader("content-length", fileArray.Length.ToString()); Response.AddHeader("Content-Disposition", "attachment;filename=TID.pdf;"); Response.BinaryWrite(fileArray); Response.Flush(); Response.Close(); } catch { // and boom goes the dynamite... } }

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• bug in NHunspell spelling checker

  - by Nikhil K

  I am using NHunspell for checking spelling.I added NHunspell.dll as a reference to my asp.net page.I added the namespace System.NHunspell. The problem i am facing is related to IDisposible. I put the downloaded code of NHunspell inside the button event. protected void Button1_Click(object sender, EventArgs e) { using (Hunspell hunspell = new Hunspell("en_us.aff", "en_us.dic")) { bool correct = hunspell.Spell("Recommendation"); var suggestions = hunspell.Suggest("Recommendatio"); foreach (string suggestion in suggestions) { Console.WriteLine("Suggestion is: " + suggestion); } } // Hyphen using (Hyphen hyphen = new Hyphen("hyph_en_us.dic")) { var hyphenated = hyphen.Hyphenate("Recommendation"); } * using (MyThes thes = new MyThes("th_en_us_new.idx", "th_en_us_new.dat")) { using (Hunspell hunspell = new Hunspell("en_us.aff", "en_us.dic")) { ThesResult tr = thes.Lookup("cars", hunspell); foreach (ThesMeaning meaning in tr.Meanings) { Console.WriteLine(" Meaning: " + meaning.Description); foreach (string synonym in meaning.Synonyms) { Console.WriteLine(" Synonym: " + synonym); } } } } The * shown above is the line of error.The error is: " type used in a using statement must be implicitly convertible to 'System.IDisposable'". Also there is a warning on that line :"'NHunspell.MyThes.MyThes(string, string)' is obsolete: 'idx File is not longer needed, MyThes works completely in memory'"; Can any one help me to correct this???

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