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• Best cubicle toys for programming

  - by dlamblin

  I need some employee/co-worker Christmas gift ideas. Do you have any good cubicle toys that help you to do any of: think about programming problems solve programming problems by representing common abstractions can be directly programmed can interface with a PC based IDE to be programmed. it may present problems that can be solved, to kick start problem solving. Disallowed items are: reference material in book, pamphlet, poster or cheat-sheet form, even if it has kick ass pop-cultural references. edibles. [discuss separately] things that need their own lab-space and/or extensive tools to be worked with. So yes, Lego Mindstorms come to mind, but they aren't cubicle toys because they cost more than cubicle toys would, and they have too many losable parts. comments on the answers so far: The 20 Questions game sounds quite neat as it could get you thinking; The bean balls could be used as tokens in a problem, so I can see that working. The magnetic toys like ball of whacks or the ball-and-stick ones present hands on fun of a structural nature... now can there be a similar hands on fun toy that aids in representing a solution to a problem? The Gui Mags clearly could, but they're quite utility oriented. The AVR Butterfly is less of a toy but definitely priced attractively, cheaper and more responsive than a basic stamp. I'm not going to pick an answer; there's several great suggestions here. Thank you.

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• fast similarity detection

  - by reinierpost

  I have a large collection of objects and I need to figure out the similarities between them. To be exact: given two objects I can compute their dissimilarity as a number, a metric - higher values mean less similarity and 0 means the objects have identical contents. The cost of computing this number is proportional to the size of the smaller object (each object has a given size). I need the ability to quickly find, given an object, the set of objects similar to it. To be exact: I need to produce a data structure that maps any object o to the set of objects no more dissimilar to o than d, for some dissimilarity value d, such that listing the objects in the set takes no more time than if they were in an array or linked list (and perhaps they actually are). Typically, the set will be very much smaller than the total number of objects, so it is really worthwhile to perform this computation. It's good enough if the data structure assumes a fixed d, but if it works for an arbitrary d, even better. Have you seen this problem before, or something similar to it? What is a good solution? To be exact: a straightforward solution involves computing the dissimilarities between all pairs of objects, but this is slow - O(n2) where n is the number of objects. Is there a general solution with lower complexity?

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• Where can I find free and open data?

  - by kitsune

  Sooner or later, coders will feel the need to have access to "open data" in one of their projects, from knowing a city's zip to a more obscure information such as the axial tilt of Pluto. I know data.un.org which offers access to the UN's extensive array of databases that deal with human development and other socio-economic issues. The other usual suspects are NASA and the USGS for planetary data. There's an article at readwriteweb with more links. infochimps.org seems to stand out. Personally, I need to find historic commodity prices, stock values and other financial data. All these data sets seem to cost money however. Clarification To clarify, I'm interested in all kinds of open data, because sooner or later, I know I will be in a situation where I could need it. I will try to edit this answer and include the suggestions in a structured manners. A link for financial data was hidden in that readwriteweb article, doh! It's called opentick.com. Looks good so far! Update I stumbled over semantic data in another question of mine on here. There is opencyc ('the world's largest and most complete general knowledge base and commonsense reasoning engine'). A project called UMBEL provides a light-weight, distilled version of opencyc. Umbel has semantic data in rdf/owl/skos n3 syntax. The Worldbank also released a very nice API. It offers data from the last 50 years for about 200 countries

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• Remove In-App Purchase from free app and increase the price

  - by Arseniy Banayev

  The current version of an application in the App Store is free and has very limited functionality. An In-App Purchase unlocks everything else. I have decided to remove the In-App Purchase and just make the application cost the same price as the In-App Purchase did. But if I make the update now, then those users who have the free version but who have not yet paid for the In-App Purchase will get a free update into the full version. I have removed all traces of my singleton class, PurchaseManager, from the application, so that at this point, when I build/run it, all of the features are unlocked. At this point, how can I make sure that the free-version users don't just ride an update into the full version? Maybe there's a way to test whether the app is obtained through an update or through a purchase? That way, if it's through an update, I will see if it's the free version w/o the IAP and then force the user to purchase the IAP to continue playing. Any ideas?

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• Improve speed of own debug visualizer for Delphi 2010

  - by netcodecz

  I wrote Delphi debug visualizer for TDataSet to display values of current row, source + screenshot: http://delphi.netcode.cz/text/tdataset-debug-visualizer.aspx . Working good, but very slow. I did some optimalization (how to get fieldnames) but still for only 20 fields takes 10 seconds to show - very bad. Main problem seems to be slow IOTAThread90.Evaluate used by main code shown below, this procedure cost most of time, line with ** about 80% time. FExpression is name of TDataset in code. procedure TDataSetViewerFrame.mFillData; var iCount: Integer; I: Integer; // sw: TStopwatch; s: string; begin // sw := TStopwatch.StartNew; iCount := StrToIntDef(Evaluate(FExpression+'.Fields.Count'), 0); for I := 0 to iCount - 1 do begin s:= s + Format('%s.Fields[%d].FieldName+'',''+', [FExpression, I]); // FFields.Add(Evaluate(Format('%s.Fields[%d].FieldName', [FExpression, I]))); FValues.Add(Evaluate(Format('%s.Fields[%d].Value', [FExpression, I]))); //** end; if s<> '' then Delete(s, length(s)-4, 5); s := Evaluate(s); s:= Copy(s, 2, Length(s) -2); FFields.CommaText := s; { sw.Stop; s := sw.Elapsed; Application.MessageBox(Pchar(s), '');} end; Now I have no idea how to improve performance.

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• Upgrade to Delphi 2010, or stick with Delphi 7 "forever"?

  - by tim11g

  I am an individual user of Delphi, starting back in the early Turbo Pascal days. I have quite a bit of code developed over the years, but I have never sold software commercially or used it for business. Historically, Borland supported the non-professional users with lower cost versions, but Embarcadero does not. As I consider upgrading to Delphi 2010, I am put off by the high price. Embarcadero is also trying to "encourage" upgrading by threatening to charge "new user" prices for upgrades after Dec 31st. I have several questions for the community to help me decide whether to upgrade. 1) I have read about difficulties updating existing code to support the unicode string types. I have no need for unicode strings, and I am happy with the string support in D7. Will I have to modify existing code and components just to re-compile under D2010? Or are there compiler options to allow backward compatibility if new string types are not required? 2) The main reason I'm considering upgrading is for IDE improvements, and to get access to new APIs added to Windows since 2002. Are there any Windows 7 APIs or capabilities that would be impossible to support from my programs compiled using using Delphi 7 (assuming appropriate JEDI API libraries, for example)? 3) Is there anything else about Delphi 2010 that is really compelling for someone who is primarily interested in Win32 apps, and not working with databases? I have read that D2010 is slow to load, and other versions between D7 and D2010 have had stability issues, and the help system was "broken". What is the biggest benefit to D2010?

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• Crystal Reports .Net Guidance

  - by Ken Ray

  We have been using .Net and Visual Studio for the last six years, and early on developed a number of web based reporting applications using the .Net version of Crystal Reports that was bundled with Visual Studio. My overall opinion of that product has been, to say the least, rather unimpressed. It seemed to be incredibly difficult and convoluted to use, we had to make security changes, install various extra software, and so on. Now, we are moving to VS2008 and version 3.5 of the .Net framework, and the time has come to redevelop some of these old applications. The developers who used (and somehow mastered) Crystal .Net have long gone, and I am facing a decision - do we stick with Crystal Reports or move to something else. We also have the "full" version of Crystal Reports XI at our disposal. The way we use the product is to product pdf versions of data extracted from various databases. While some apps use the inbuilt Crystal Reports viewer as well, this seems to be redundant now with the flexibility of grid views - but there is still the need to produce a pdf version of the data in teh grid for printing, or in Excel format to download. What is the concensus? Is Crystal Reports .Net worth persisting with, or should we work out how to use version XI? Alternatively, is there a simple and low cost way to generate pdf reports without using Crystal? What good sources of "how to" information have others found and recommend? Are there suitable books, designed for VS2008 / .Net 3.5 development that you have used and found of benefit? Thanks in advance.

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• stock management of assemblys and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assembly) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• Developing a rich internet application

  - by Serge

  Hello, I have been a desktop developer for a few years mostly doing object oriented stuff. I am trying to branch out into web development, and as a hobby project trying to put a web application together. I have been reading quite alot of information, but I still can't seem to decide on the path to take and would really like some advice. Basically, I want to build something like this: http://mon.itor.us/ I have found this as well: http://www.trilancer.com/jpolite/#t1 But so far it is of little use as I am trying to grasp Javascript. I have been using visual studio for that, is that a good IDE for this tye of thing or should I try expression blend? Jpolite seems to do everything with javascript, which seems kind of cool, but I if I want to make a chart inside a widget that connects to a database, do I need something more? Is this where ASP.NET comes in? I am familiar with .NET, but if I use ASP.NET for my website, do I have to host it on IIS and windows server as opposed to Apache since mono is still being ironed out? Because that would cost more, so would PHP be a better choice? Also, for charting these guys as well as google seem to use flex: http://www.google.com/finance I have found this: http://www.reynoldsftw.com/2009/03/javascript-chart-alternatives/ Would that be sufficient to implement something like google fiance purely in javascript or is there a good reason they use flex? SOrry for the long post but I was trying to be as detailed as possible. Thanks.

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• Address Match Key Algorithm

  - by sestocker

  I have a list of addresses in two separate tables that are slightly off that I need to be able to match. For example, the same address can be entered in multiple ways: 110 Test St 110 Test St. 110 Test Street Although simple, you can imagine the situation in more complex scenerios. I am trying to develop a simple algorithm that will be able to match the above addresses as a key. For example. the key might be "11TEST" - first two of 110, first two of Test and first two of street variant. A full match key would also include first 5 of the zipcode as well so in the above example, the full key might look like "11TEST44680". I am looking for ideas for an effective algorithm or resources I can look at for considerations when developing this. Any ideas can be pseudo code or in your language of choice. We are only concerned with US addresses. In fact, we are only looking at addresses from 250 zip codes from Ohio and Michigan. We also do not have access to any postal software although would be open to ideas for cost effective solutions (it would essentially be a one time use). Please be mindful that this is an initial dump of data from a government source so suggestions of how users can clean it are helpful as I build out the application but I would love to have the best initial I possibly can by being able to match addresses as best as possible.

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• rails + sheevaplug = rails home development server and more

  - by microspino

  Hello I'd like to build a "Rails Brick" using a Sheevaplug from Marvell (O.S. is Ubuntu out of the box but You can install other distributions on It). It will be a home server and a silent, low cost (99$) low energy development machine. I'd like to add rails RVM, lot of gems, git-based heroku like deployment, passenger + nginx. This way I could have a portable server with a complete development environment and maybe I could find a hosting company where I can co-locate a grid of this devices or I can sell It as a simple little server for 10 or less users offices, with some centralized rails services (I think to a CMS, a BLOG, a WIKI, calendar or whatever this little jewel could afford). The usb port could make It a print server too or a UMTS link to the web via HUAWEI like usb UMTS keys. Can you give me some hint about: Is this project a crazy-close-to-failure idea? Why? which gem would You include? which rails open source app would you suggest? I have already an Excito Bubba Server at home, I saw the TonidoPlug so It came up in my mind to build something similiar but Rails based (Bubba is PHP based, TonidoPlug I don't know but It does not seems a Rails thing).

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• Optimal Serialization of Primitive Types

  - by Greg Dean

  We are beginning to roll out more and more WAN deployments of our product (.Net fat client w/ IIS hosted Remoting backend). Because of this we are trying to reduce the size of the data on the wire. We have overridden the default serialization by implementing ISerializable (similar to this), we are seeing anywhere from 12% to 50% gains. Most of our efforts focus on optimizing arrays of primitive types. I would like to know if anyone knows of any fancy way of serializing primitive types, beyond the obvious? For example today we serialize an array of ints as follows: [4-bytes (array length)][4-bytes][4-bytes] Can anyone do significantly better? The most obvious example of a significant improvement, for boolean arrays, is putting 8 bools in each byte, which we already do. Note: Saving 7 bits per bool may seem like a waste of time, but when you are dealing with large magnitudes of data (which we are), it adds up very fast. Note: We want to avoid general compression algorithms because of the latency associated with it. Remoting only supports buffered requests/responses(no chunked encoding). I realize there is a fine line between compression and optimal serialization, but our tests indicate we can afford very specific serialization optimizations at very little cost in latency. Whereas reprocessing the entire buffered response into new compressed buffer is too expensive.

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• Strange C++ performance difference?

  - by STingRaySC

  I just stumbled upon a change that seems to have counterintuitive performance ramifications. Can anyone provide a possible explanation for this behavior? Original code: for (int i = 0; i < ct; ++i) { // do some stuff... int iFreq = getFreq(i); double dFreq = iFreq; if (iFreq != 0) { // do some stuff with iFreq... // do some calculations with dFreq... } } While cleaning up this code during a "performance pass," I decided to move the definition of dFreq inside the if block, as it was only used inside the if. There are several calculations involving dFreq so I didn't eliminate it entirely as it does save the cost of multiple run-time conversions from int to double. I expected no performance difference, or if any at all, a negligible improvement. However, the perfomance decreased by nearly 10%. I have measured this many times, and this is indeed the only change I've made. The code snippet shown above executes inside a couple other loops. I get very consistent timings across runs and can definitely confirm that the change I'm describing decreases performance by ~10%. I would expect performance to increase because the int to double conversion would only occur when iFreq != 0. Chnaged code: for (int i = 0; i < ct; ++i) { // do some stuff... int iFreq = getFreq(i); if (iFreq != 0) { // do some stuff with iFreq... double dFreq = iFreq; // do some stuff with dFreq... } } Can anyone explain this? I am using VC++ 9.0 with /O2. I just want to understand what I'm not accounting for here.

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• TLS with SNI in Java clients

  - by ftrotter

  There is an ongoing discussion on the security and trust working group for NHIN Direct regarding the IP-to-domain mapping problem that is created with traditional SSL. If an HISP (as defined by NHIN Direct) wants to host thousands of NHIN Direct "Health Domains" for providers, then it will an "artificially inflated cost" to have to purchase an IP for each of those domains. Because Apache and OpenSSL have recently released TLS with support for the SNI extension, it is possible to use SNI as a solution to this problem on the server side. However, if we decide that we will allow server implementations of the NHINDirect transport layer to support TLS+SNI, then we must require that all clients support SNI too. OpenSSL based clients should do this by default and one could always us stunnel to implement an TLS+SNI aware client to proxy if your given programming language SSL implementation does not support SNI. It appears that native Java applications using OpenJDK do not yet support SNI, but I cannot get a straight answer out of that project. I know that there are OpenSSL Java libraries available but I have no idea if that would be considered viable. Can you give me a "state of the art" summary of where TLS+SNI support is for Java clients? I need a Java implementers perspective on this.

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• How can I write classes that don't rely on "global" variables?

  - by Joel

  When I took my first programming course in university, we were taught that global variables were evil & should be avoided at all cost (since you can quickly develop confusing and unmaintainable code). The following year, we were taught object oriented programming, and how to create modular code using classes. I find that whenever I work with OOP, I use my classes' private variables as global variables, i.e., they can be (and are) read and modified by any function within the class. This isn't really sitting right with me, as it seems to introduce the same problems global variables had in languages like C. So I guess my question is, how do I stop writing classes with "global" variables? Would it make more sense to pretend I'm writing in a functional language? By this I mean having all functions take parameters & return values instead of directly modifying class variables. If I need to set any fields, I can just take the output of the function and assign it instead of having the function do it directly. This seems like it might make more maintainable code, at least for larger classes. What's common practice? Thanks!

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• Perl XML SAX parser emulating XML::Simple record for record

  - by DVK

  Short Q summary: I am looking a fast XML parser (most likely a wrapper around some standard SAX parser) which will produce per-record data structure 100% identical to those produced by XML::Simple. Details: We have a large code infrastructure which depends on processing records one-by-one and expects the record to be a data structure in a format produced by XML::Simple since it always used XML::Simple since early Jurassic era. An example simple XML is: <root> <rec><f1>v1</f1><f2>v2</f2></rec> <rec><f1>v1b</f1><f2>v2b</f2></rec> <rec><f1>v1c</f1><f2>v2c</f2></rec> </root> And example rough code is: sub process_record { my ($obj, $record_hash) = @_; # do_stuff } my $records = XML::Simple->XMLin(@args)->{root}; foreach my $record (@$records) { $obj->process_record($record) }; As everyone knows XML::Simple is, well, simple. And more importantly, it is very slow and a memory hog - due to being a DOM parser and needing to build/store 100% of data in memory. So, it's not the best tool for parsing an XML file consisting of large amount of small records record-by-record. However, re-writing the entire code (which consist of large amount of "process_record"-like methods) to work with standard SAX parser seems like an big task not worth the resources, even at the cost of living with XML::Simple. What I'm looking for is an existing module which will probably be based on a SAX parser (or anything fast with small memory footprint) which can be used to produce $record hashrefs one by one based on the XML pictured above that can be passed to $obj->process_record($record) and be 100% identical to what XML::Simple's hashrefs would have been.

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• postgresql error - ERROR: input is out of range

  - by CaffeineIV

  The function below keeps returning this error message. I thought that maybe the double_precision field type was what was causing this, and I tried to use CAST, but either that's not it, or I didn't do it right... Help? Here's the error: ERROR: input is out of range CONTEXT: PL/pgSQL function "calculate_distance" line 7 at RETURN ********** Error ********** ERROR: input is out of range SQL state: 22003 Context: PL/pgSQL function "calculate_distance" line 7 at RETURN And here's the function: CREATE OR REPLACE FUNCTION calculate_distance(character varying, double precision, double precision, double precision, double precision) RETURNS double precision AS $BODY$ DECLARE earth_radius double precision; BEGIN earth_radius := 3959.0; RETURN earth_radius * acos(sin($2 / 57.2958) * sin($4 / 57.2958) + cos($2/ 57.2958) * cos($4 / 57.2958) * cos(($5 / 57.2958) - ($3 / 57.2958))); END; $BODY$ LANGUAGE 'plpgsql' VOLATILE COST 100; ALTER FUNCTION calculate_distance(character varying, double precision, double precision, double precision, double precision) OWNER TO postgres; //I tried changing (unsuccessfully) that RETURN line to: RETURN CAST( (earth_radius * acos(sin($2 / 57.2958) * sin($4 / 57.2958) + cos($2/ 57.2958) * cos($4 / 57.2958) * cos(($5 / 57.2958) - ($3 / 57.2958))) ) AS text);

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• RegularExpression Validator doesn't display error message.

  - by Rudi Ramey

  I have a regular expression validation control initialized to validate a textbox control. I want users to be able to enter U.S. Currency values ($12,115.85 or 1500.22 etc.). I found a regular expression off of regexlib website that does the trick. The validation control seems to be working except for one crucial thing. If invalid data is entered, the validation text dispalys (a red "*" next to the textbox), but the page will still submit and the error message won't pop up... I thought that the error message is supposed to display and the page won't submit if the validation control detects invalid data. Isn't this automatic with ASP .NET? I have searched extensively on how to create validation controls, but haven't found anything different than what I am already doing. Can anyone tell me what I am doing wrong here? <asp:TextBox ID="txtActualCost" runat="server" Width="120px" CausesValidation="true"></asp:TextBox> <asp:RegularExpressionValidator ID="regExValActualCost" ControlToValidate="txtActualCost" Text="*" ValidationExpression="^\$?(\d{1,3}(\,\d{3})*|(\d+))(\.\d{2})?$" ErrorMessage="Please enter a valid currency value for 'Actual Cost'" Display="Dynamic" EnableClientScript="true" runat="server" />

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• Stock management of assemblies and its sub parts

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• video streaming infrastructure

  - by alchemical

  We would like to set-up a live video-chat web site and are looking for basic architectural advice and/or a recomendation for a particular framework to use. Here are the basic features of the site: Most streams will be broadcast live from a single person with a web cam, etc., and viewed by typically 1-10 people, although there could be up to 100+ viewers on the high side. Audio and video do not have to be super-high quality, but do need to be "good enough". The main point is to convey the basic info in the video (and audio). If occasionally the frame-rate drops low and then goes back to normal fairly soon, we could live with that. Budget is an issue, so we are in general looking for a lower cost solution that will give us most of what we need in temers of performance and quality. We are looking at Peer1 for co-lo. The rest of our web site will be .Net / Windows platform. We are open to looking at any platform for the best streaming solution, although our technical expertise is currently more on the Windows side.

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• Cooperative/Non-preemptive threading avoiding threadlooks?

  - by Wayne

  Any creative ideas to avoid deadlocks on a yield or sleep with cooperative/non-preemptive multitasking without doing an O/S Thread.Sleep(10)? Typically the yield or sleep call will call back into the scheduler to run other tasks. But this can sometime produce deadlocks. Some background: This application has enormous need for speed and, so far, it's extremely fast as compared to other systems in the same industry. One of the speed techniques is cooperative/non-preemptive threading rather then the cost of a context switch from O/S threads. The high level design a priority manager which calls out to tasks depending on priority and processing time. Each task does one "iteration" of work and returns to wait its turn again in the priority queue. The tricky thing with non-preemptive threading is what to do when you want to a particular task to stop in the middle of work and wait for some other event from a different task before continuing. In this case, we have 3 tasks, A B and C where A is a controller that must synchronize the activity of B and C. First, A starts both B and C. Then B yields so C gets invoked. When C yields, A sees they are both inactive, decides it's time for B to run but not time for C yet. Well B is now stuck in a yield that has called C, so it can never run. Sincerely, Wayne

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• How do I find the most “Naturally" direct route using A-star (A*)

  - by Greg B

  I have implemented the A* algorithm in AS3 and it works great except for one thing. Often the resulting path does not take the most “natural” or smooth route to the target. In my environment the object can move diagonally as inexpensively as it can move horizontally or vertically. Here is a very simple example; the start point is marked by the S, and the end (or finish) point by the F. | | | | | | | | | | |S| | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | As you can see, during the 1st round of finding, nodes [0,2], [1,2], [2,2] will all be added to the list of possible node as they all have a score of N. The issue I’m having comes at the next point when I’m trying to decide which node to proceed with. In the example above I am using possibleNodes[0] to choose the next node. If I change this to possibleNodes[possibleNodes.length-1] I get the following path. | | | | | | | | | | |S| | | | | | | | | | |x| | | | | | | | | | |x| | | | | | | | | | |x| | | | | | | | |x| | | | | | | | |x| | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | And then with possibleNextNodes[Math.round(possibleNextNodes.length / 2)-1] | | | | | | | | | | |S| | | | | | | | | |x| | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | All these paths have the same cost as they all contain the same number of steps but, in this situation, the most sensible path would be as follows... | | | | | | | | | | |S| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Is there a formally accepted method of making the path appear more sensible rather than just mathematically correct?

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• Stock management of assemblies and its sub parts (relations)

  - by The Disintegrator

  I have to track the stock of individual parts and kits (assemblies) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. So, I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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• Can you force a crash if a write occurs to a given memory location with finer than page granularity?

  - by Joseph Garvin

  I'm writing a program that for performance reasons uses shared memory (alternatives have been evaluated, and they are not fast enough for my task, so suggestions to not use it will be downvoted). In the shared memory region I am writing many structs of a fixed size. There is one program responsible for writing the structs into shared memory, and many clients that read from it. However, there is one member of each struct that clients need to write to (a reference count, which they will update atomically). All of the other members should be read only to the clients. Because clients need to change that one member, they can't map the shared memory region as read only. But they shouldn't be tinkering with the other members either, and since these programs are written in C++, memory corruption is possible. Ideally, it should be as difficult as possible for one client to crash another. I'm only worried about buggy clients, not malicious ones, so imperfect solutions are allowed. I can try to stop clients from overwriting by declaring the members in the header they use as const, but that won't prevent memory corruption (buffer overflows, bad casts, etc.) from overwriting. I can insert canaries, but then I have to constantly pay the cost of checking them. Instead of storing the reference count member directly, I could store a pointer to the actual data in a separate mapped write only page, while keeping the structs in read only mapped pages. This will work, the OS will force my application to crash if I try to write to the pointed to data, but indirect storage can be undesirable when trying to write lock free algorithms, because needing to follow another level of indirection can change whether something can be done atomically. Is there any way to mark smaller areas of memory such that writing them will cause your app to blow up? Some platforms have hardware watchpoints, and maybe I could activate one of those with inline assembly, but I'd be limited to only 4 at a time on 32-bit x86 and each one could only cover part of the struct because they're limited to 4 bytes. It'd also make my program painful to debug ;)

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• Online voice chat: Why client-server model vs. peer-to-peer model?

  - by sstallings

  I am adding online voice chat to a Silverlight app. I've been reviewing current apps, services and SDKs found thru online searches and forums. I'm finding that the majority of these implement a client-server (C/S) model and I'm trying to understand why that model versus a peer-to-peer (PTP) model. To me PTP would be preferable because going direct between peers would be more efficient (fewer IP hops and no processing along the way by a server computer) and no need for a server and its costs and dependencies. I found some products offer the ability to switch from PTP to C/S if the PTP proves insufficient. As I thought more about it, I could see that C/S could be better if there are more than two peers involved in a conversation, then the server (supposedly with more bandwidth) could do a better job of relaying each peers outgoing traffic to the multiple other peers. In C/S many-to-many voice chatting, each peer's upstream broadband (which is where the bottleneck inherently is) would only have to carry each item of voice traffic once, then the server would use its superior bandwidth to relay the message to the multiple other peers. But, in a situation with one-on-one voice chatting it seems that PTP would be best. A server would not reduce each of the two peer's bandwidth requirements and would only add unnecessary overhead, dependency and cost. In one-on-one voice chatting: Am I mistaken on anything above? Would peer-to-peer be best? Would a server provide anything of value that could not be provided by a client-only program? Is there anything else that I should be taking into consideration? And lastly, can you recommend any Silverlight PTP or C/S voice chat products? Thanks in advance for any info.

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