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• Recursive N-way merge/diff algorithm for directory trees?

  - by BobMcGee

  What algorithms or Java libraries are available to do N-way, recursive diff/merge of directories? I need to be able to generate a list of folder trees that have many identical files, and have subdirectories with many similar files. I want to be able to use 2-way merge operations to quickly remove as much redundancy as possible. Goals: Find pairs of directories that have many similar files between them. Generate short list of directory pairs that can be synchronized with 2-way merge to eliminate duplicates Should operate recursively (there may be nested duplicates of higher-level directories) Run time and storage should be O(n log n) in numbers of directories and files Should be able to use an embedded DB or page to disk for processing more files than fit in memory (100,000+). Optional: generate an ancestry and change-set between folders Optional: sort the merge operations by how many duplicates they can elliminate I know how to use hashes to find duplicate files in roughly O(n) space, but I'm at a loss for how to go from this to finding partially overlapping sets between folders and their children. EDIT: some clarification The tricky part is the difference between "exact same" contents (otherwise hashing file hashes would work) and "similar" (which will not). Basically, I want to feed this algorithm at a set of directories and have it return a set of 2-way merge operations I can perform in order to reduce duplicates as much as possible with as few conflicts possible. It's effectively constructing an ancestry tree showing which folders are derived from each other. The end goal is to let me incorporate a bunch of different folders into one common tree. For example, I may have a folder holding programming projects, and then copy some of its contents to another computer to work on it. Then I might back up and intermediate version to flash drive. Except I may have 8 or 10 different versions, with slightly different organizational structures or folder names. I need to be able to merge them one step at a time, so I can chose how to incorporate changes at each step of the way. This is actually more or less what I intend to do with my utility (bring together a bunch of scattered backups from different points in time). I figure if I can do it right I may as well release it as a small open source util. I think the same tricks might be useful for comparing XML trees though.

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• Optimizing tasks to reduce CPU in a trading application

  - by Joel

  Hello, I have designed a trading application that handles customers stocks investment portfolio. I am using two datastore kinds: Stocks - Contains unique stock name and its daily percent change. UserTransactions - Contains information regarding a specific purchase of a stock made by a user : the value of the purchase along with a reference to Stock for the current purchase. db.Model python modules: class Stocks (db.Model): stockname = db.StringProperty(multiline=True) dailyPercentChange=db.FloatProperty(default=1.0) class UserTransactions (db.Model): buyer = db.UserProperty() value=db.FloatProperty() stockref = db.ReferenceProperty(Stocks) Once an hour I need to update the database: update the daily percent change in Stocks and then update the value of all entities in UserTransactions that refer to that stock. The following python module iterates over all the stocks, update the dailyPercentChange property, and invoke a task to go over all UserTransactions entities which refer to the stock and update their value: Stocks.py # Iterate over all stocks in datastore for stock in Stocks.all(): # update daily percent change in datastore db.run_in_transaction(updateStockTxn, stock.key()) # create a task to update all user transactions entities referring to this stock taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock') }) def updateStockTxn(stock_key): #fetch the stock again - necessary to avoid concurrency updates stock = db.get(stock_key) stock.dailyPercentChange= data.get('some_val_for_stock') # I get this value from outside ... some more calculations here ... stock.put() Task.py (/task) # Amount of transaction per task amountPerCall=10 stock=db.get(self.request.get("stock_key")) # Get all user transactions which point to current stock user_transaction_query=stock.usertransactions_set cursor=self.request.get("cursor") if cursor: user_transaction_query.with_cursor(cursor) # Spawn another task if more than 10 transactions are in datastore transactions = user_transaction_query.fetch(amountPerCall) if len(transactions)==amountPerCall: taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock'), 'cursor': user_transaction_query.cursor() }) # Iterate over all transaction pointing to stock and update their value for transaction in transactions: db.run_in_transaction(updateUserTransactionTxn, transaction.key()) def updateUserTransactionTxn(transaction_key): #fetch the transaction again - necessary to avoid concurrency updates transaction = db.get(transaction_key) transaction.value= transaction.value* self.request.get ('some_val_for_stock') db.put(transaction) The problem: Currently the system works great, but the problem is that it is not scaling well… I have around 100 Stocks with 300 User Transactions, and I run the update every hour. In the dashboard, I see that the task.py takes around 65% of the CPU (Stock.py takes around 20%-30%) and I am using almost all of the 6.5 free CPU hours given to me by app engine. I have no problem to enable billing and pay for additional CPU, but the problem is the scaling of the system… Using 6.5 CPU hours for 100 stocks is very poor. I was wondering, given the requirements of the system as mentioned above, if there is a better and more efficient implementation (or just a small change that can help with the current implemntation) than the one presented here. Thanks!! Joel

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• How can I load a file into a DataBag from within a Yahoo PigLatin UDF?

  - by Cervo

  I have a Pig program where I am trying to compute the minimum center between two bags. In order for it to work, I found I need to COGROUP the bags into a single dataset. The entire operation takes a long time. I want to either open one of the bags from disk within the UDF, or to be able to pass another relation into the UDF without needing to COGROUP...... Code: # **** Load files for iteration **** register myudfs.jar; wordcounts = LOAD 'input/wordcounts.txt' USING PigStorage('\t') AS (PatentNumber:chararray, word:chararray, frequency:double); centerassignments = load 'input/centerassignments/part-*' USING PigStorage('\t') AS (PatentNumber: chararray, oldCenter: chararray, newCenter: chararray); kcenters = LOAD 'input/kcenters/part-*' USING PigStorage('\t') AS (CenterID:chararray, word:chararray, frequency:double); kcentersa1 = CROSS centerassignments, kcenters; kcentersa = FOREACH kcentersa1 GENERATE centerassignments::PatentNumber as PatentNumber, kcenters::CenterID as CenterID, kcenters::word as word, kcenters::frequency as frequency; #***** Assign to nearest k-mean ******* assignpre1 = COGROUP wordcounts by PatentNumber, kcentersa by PatentNumber; assignwork2 = FOREACH assignpre1 GENERATE group as PatentNumber, myudfs.kmeans(wordcounts, kcentersa) as CenterID; basically my issue is that for each patent I need to pass the sub relations (wordcounts, kcenters). In order to do this, I do a cross and then a COGROUP by PatentNumber in order to get the set PatentNumber, {wordcounts}, {kcenters}. If I could figure a way to pass a relation or open up the centers from within the UDF, then I could just GROUP wordcounts by PatentNumber and run myudfs.kmeans(wordcount) which is hopefully much faster without the CROSS/COGROUP. This is an expensive operation. Currently this takes about 20 minutes and appears to tack the CPU/RAM. I was thinking it might be more efficient without the CROSS. I'm not sure it will be faster, so I'd like to experiment. Anyway it looks like calling the Loading functions from within Pig needs a PigContext object which I don't get from an evalfunc. And to use the hadoop file system, I need some initial objects as well, which I don't see how to get. So my question is how can I open a file from the hadoop file system from within a PIG UDF? I also run the UDF via main for debugging. So I need to load from the normal filesystem when in debug mode. Another better idea would be if there was a way to pass a relation into a UDF without needing to CROSS/COGROUP. This would be ideal, particularly if the relation resides in memory.. ie being able to do myudfs.kmeans(wordcounts, kcenters) without needing the CROSS/COGROUP with kcenters... But the basic idea is to trade IO for RAM/CPU cycles. Anyway any help will be much appreciated, the PIG UDFs aren't super well documented beyond the most simple ones, even in the UDF manual.

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• Strange behavior of move with strings

  - by Umair Ahmed

  I am testing some enhanced string related functions with which I am trying to use move as a way to copy strings around for faster, more efficient use without delving into pointers. While testing a function for making a delimited string from a TStringList, I encountered a strange issue. The compiler referenced the bytes contained through the index when it was empty and when a string was added to it through move, index referenced the characters contained. Here is a small downsized barebone code sample:- unit UI; interface uses System.SysUtils, System.Types, System.UITypes, System.Rtti, System.Classes, System.Variants, FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, FMX.Layouts, FMX.Memo; type TForm1 = class(TForm) Results: TMemo; procedure FormCreate(Sender: TObject); end; var Form1: TForm1; implementation {$R *.fmx} function StringListToDelimitedString ( const AStringList: TStringList; const ADelimiter: String ): String; var Str : String; Temp1 : NativeInt; Temp2 : NativeInt; DelimiterSize : Byte; begin Result := ' '; Temp1 := 0; DelimiterSize := Length ( ADelimiter ) * 2; for Str in AStringList do Temp1 := Temp1 + Length ( Str ); SetLength ( Result, Temp1 ); Temp1 := 1; for Str in AStringList do begin Temp2 := Length ( Str ) * 2; // Here Index references bytes in Result Move ( Str [1], Result [Temp1], Temp2 ); // From here the index seems to address characters instead of bytes in Result Temp1 := Temp1 + Temp2; Move ( ADelimiter [1], Result [Temp1], DelimiterSize ); Temp1 := Temp1 + DelimiterSize; end; end; procedure TForm1.FormCreate(Sender: TObject); var StrList : TStringList; Str : String; begin // Test 1 : StringListToDelimitedString StrList := TStringList.Create; Str := ''; StrList.Add ( 'Hello1' ); StrList.Add ( 'Hello2' ); StrList.Add ( 'Hello3' ); StrList.Add ( 'Hello4' ); Str := StringListToDelimitedString ( StrList, ';' ); Results.Lines.Add ( Str ); StrList.Free; end; end. Please devise a solution and if possible, some explanation. Alternatives are welcome too.

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• Combinations and Permutations in F#

  - by Noldorin

  I've recently written the following combinations and permutations functions for an F# project, but I'm quite aware they're far from optimised. /// Rotates a list by one place forward. let rotate lst = List.tail lst @ [List.head lst] /// Gets all rotations of a list. let getRotations lst = let rec getAll lst i = if i = 0 then [] else lst :: (getAll (rotate lst) (i - 1)) getAll lst (List.length lst) /// Gets all permutations (without repetition) of specified length from a list. let rec getPerms n lst = match n, lst with | 0, _ -> seq [[]] | _, [] -> seq [] | k, _ -> lst |> getRotations |> Seq.collect (fun r -> Seq.map ((@) [List.head r]) (getPerms (k - 1) (List.tail r))) /// Gets all permutations (with repetition) of specified length from a list. let rec getPermsWithRep n lst = match n, lst with | 0, _ -> seq [[]] | _, [] -> seq [] | k, _ -> lst |> Seq.collect (fun x -> Seq.map ((@) [x]) (getPermsWithRep (k - 1) lst)) // equivalent: | k, _ -> lst |> getRotations |> Seq.collect (fun r -> List.map ((@) [List.head r]) (getPermsWithRep (k - 1) r)) /// Gets all combinations (without repetition) of specified length from a list. let rec getCombs n lst = match n, lst with | 0, _ -> seq [[]] | _, [] -> seq [] | k, (x :: xs) -> Seq.append (Seq.map ((@) [x]) (getCombs (k - 1) xs)) (getCombs k xs) /// Gets all combinations (with repetition) of specified length from a list. let rec getCombsWithRep n lst = match n, lst with | 0, _ -> seq [[]] | _, [] -> seq [] | k, (x :: xs) -> Seq.append (Seq.map ((@) [x]) (getCombsWithRep (k - 1) lst)) (getCombsWithRep k xs) Does anyone have any suggestions for how these functions (algorithms) can be sped up? I'm particularly interested in how the permutation (with and without repetition) ones can be improved. The business involving rotations of lists doesn't look too efficient to me in retrospect. Update Here's my new implementation for the getPerms function, inspired by Tomas's answer. Unfortunately, it's not really any fast than the existing one. Suggestions? let getPerms n lst = let rec getPermsImpl acc n lst = seq { match n, lst with | k, x :: xs -> if k > 0 then for r in getRotations lst do yield! getPermsImpl (List.head r :: acc) (k - 1) (List.tail r) if k >= 0 then yield! getPermsImpl acc k [] | 0, [] -> yield acc | _, [] -> () } getPermsImpl List.empty n lst

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• Wondering about a way to conserve memory in C# using List<> with structs

  - by Michael Ryan

  I'm not even sure how I should phrase this question. I'm passing some CustomStruct objects as parameters to a class method, and storing them in a List. What I'm wondering is if it's possible and more efficient to add multiple references to a particular instance of a CustomStruct if a equivalent instance it found. This is a dummy/example struct: public struct CustomStruct { readonly int _x; readonly int _y; readonly int _w; readonly int _h; readonly Enum _e; } Using the below method, you can pass one, two, or three CustomStruct objects as parameters. In the final method (that takes three parameters), it may be the case that the 3rd and possibly the 2nd will have the same value as the first. List<CustomStruct> _list; public void AddBackground(CustomStruct normal) { AddBackground(normal, normal, normal); } public void AddBackground(CustomStruct normal, CustomStruct hover) { AddBackground(normal, hover, hover); } public void AddBackground(CustomStruct normal, CustomStruct hover, CustomStruct active) { _list = new List<CustomStruct>(3); _list.Add(normal); _list.Add(hover); _list.Add(active); } As the method stands now, I believe it will create new instances of CustomStruct objects, and then adds a reference of each to the List. It is my understanding that if I instead check for equality between normal and hover and (if equal) insert normal again in place of hover, when the method completes, hover will lose all references and eventually be garbage collected, whereas normal will have two references in the List. The same could be done for active. That would be better, right? The CustomStruct is a ValueType, and therefore one instance would remain on the Stack, and the three List references would just point to it. The overall List size is determined not by the object Type is contains, but by its Capacity. By eliminating the "duplicate" CustomStuct objects, you allow them to be cleaned up. When the CustomStruct objects are passed to these methods, new instances are created each time. When the structs are added to the List, is another copy made? For example, if i pass just one CustomStruct, AddBackground(normal) creates a copy of the original variable, and then passes it three times to Addbackground(normal, hover, active). In this method, three copies are made of the original copy. When the three local variables are added to the List using Add(), are additional copies created inside Add(), and does that defeat the purpose of any equality checks as previously mentioned? Am I missing anything here?

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• Using multiple aggregate functions in an algebraic expression in (ANSI) SQL statement

  - by morpheous

  I have the following aggregate functions (AGG FUNCs): foo(), foobar(), fredstats(), barneystats(). I want to know if I can use multiple AGG FUNCs in an algebraic expression. This may seem a strange/simplistic question for seasoned SQL developers - however, the but the reason I ask is that so far, all AGG FUNCs examples I have seen are of the simplistic variety e.g. max(salary) < 100, rather than using the AGG FUNCs in an expression which involves using multiple AGG FUNCs in an expression (like agg_func1() agg_func2()). The information below should help clarify further. Given tables with the following schemas: CREATE TABLE item (id int, length float, weight float); CREATE TABLE item_info (item_id, name varchar(32)); # Is it legal (ANSI) SQL to write queries of this format ? SELECT id, name, foo, foobar, fredstats FROM A, B (SELECT id, foo(123) as foo, foobar('red') as foobar, fredstats('weight') as fredstats FROM item GROUP BY id HAVING [ALGEBRAIC EXPRESSION] ORDER BY id AS A), item_info AS B WHERE item.id = B.id Where: ALGEBRAIC EXPRESSION is the type of expression that can be used in a WHERE clause - for example: ((foo(x) < foobar(y)) AND foobar(y) IN (1,2,3)) OR (fredstats(x) <> 0)) I am using PostgreSQL as the db, but I would prefer to use ANSI SQL wherever possible. Assuming it is legal to include AGG FUNCS in the way I have done above, I'd like to know: Is there a more efficient way to write the above query ? Is there any way I can speed up the query in terms of a judicious choice of indexes on the tables item and item_info ? Is there a performance hit of using AGG FUNCs in an algebraic expression like I am (i.e. an expression involving the output of aggregate functions rather than constants? Can the expression also include 'scaled' AGG FUNC? (for example: 2*foo(123) < -3*foobar(456) ) - will scaling (i.e. multiplying an AGG FUNC by a number have an effect on performance?) How can I write the query above using INNER JOINS instead?

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• Increase efficiency for an R simulator of the Monty Hall Puzzle

  - by jahan_m

  The Monty Hall Problem is a simple puzzle involving probability that even stumps professionals in careers dealing with some heavy-duty math. Here's the basic problem: Suppose you're on a game show, and you're given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what's behind the doors, opens another door, say No. 3, which has a goat. He then says to you, "Do you want to pick door No. 2?" Is it to your advantage to switch your choice? You can find numerous explanations of the solution here: http://en.wikipedia.org/wiki/Monty_Hall_problem Goal of my simulation: Prove that a switching strategy will win you the car 2/3 of the time. I got curious and wanted to write a little function that simulates the problem many times and returns the proportion of wins if you switched and the proportion of wins if you stayed with your first choice. The function then plots the cumulative wins. First and foremost, I'm interested in hearing if my simulation is indeed replicating the Monty Problem, or if some aspect of the code got it wrong. Secondly, this function takes a long time to run once I get to about 10,000 simulations. I know I don't need this many simulations to prove this but I'd love to hear some ideas on how to make it more efficient. Thanks for your feedback! Monty_Hall=function(repetitions){ doors=c('A','B','C') stay_wins=0 switch_wins=0 series=data.frame(sim_num=seq(repetitions),cum_sum_stay=replicate(repetitions,0),cum_sum_switch=replicate(repetitions,0)) for(i in seq(repetitions)){ winning_door=sample(doors,1) contestant_chooses=sample(doors,1) if(contestant_chooses==winning_door) stay_wins=stay_wins+1 else switch_wins=switch_wins+1 series[i,'cum_sum_stay']=stay_wins series[i,'cum_sum_switch']=switch_wins } plot(series$sim_num,series$cum_sum_switch,col=2,ylab='Cumulative # of wins', xlab='Simulation #',main=sprintf('%d Simulations of the Monty Hall Paradox',repetitions),type='l') lines(series$sim_num,series$cum_sum_stay,col=4) legend('topleft',legend=c('Cumulative wins from switching', 'Cumulative wins from staying'),col=c(2,4),lty=1) result=list(series=series,stay_wins=stay_wins,switch_wins=switch_wins, proportion_stay_wins=stay_wins/repetitions, proportion_switch_wins=switch_wins/repetitions) return(result) } #Theory predicts that it is to the contestant's advantage if he #switches his choice to the other door. This function simulates the game #many times, and shows you the proportion of games in which staying or #switching would win the car. It also plots the cumulative wins for each strategy. Monty_Hall(100)

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• Help with Arrays in Objective C.

  - by NJTechie

  Problem : Take an integer as input and print out number equivalents of each number from input. I hacked my thoughts to work in this case but I know it is not an efficient solution. For instance : 110 Should give the following o/p : one one zero Could someone throw light on effective usage of Arrays for this problem? #import <Foundation/Foundation.h> int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; int input, i=0, j,k, checkit; int temp[i]; NSLog(@"Enter an integer :"); scanf("%d", &input); checkit = input; while(input > 0) { temp[i] = input%10; input = input/10; i++; } if(checkit != 0) { for(j=i-1;j>=0;j--) { //NSLog(@" %d", temp[j]); k = temp[j]; //NSLog(@" %d", k); switch (k) { case 0: NSLog(@"zero"); break; case 1: NSLog(@"one"); break; case 2: NSLog(@"two"); break; case 3: NSLog(@"three"); break; case 4: NSLog(@"four"); break; case 5: NSLog(@"five"); break; case 6: NSLog(@"six"); break; case 7: NSLog(@"seven"); break; case 8: NSLog(@"eight"); break; case 9: NSLog(@"nine"); break; default: break; } } } else NSLog(@"zero"); [pool drain]; return 0; }

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• [NEWVERSION]algorithm || method to write prog[UNSOLVED] [closed]

  - by fatai

  I am one of the computer science student. Everyone solve problem with a different or same method, ( but actually I dont know whether they use method or I dont know whether there are such common method to approach problem.) if there are common method, What is it ? If there are different method, which method are you using ? All teacher give us problem which in simple form sometimes, but they donot introduce any approach or method(s) so that we cannot make a decision to choose the method then apply that one to problem , afterward find solution then write code.No help from teacher , push us to find method to solve homework. Ex: my friend is using no method , he says "I start to construct algorithm while I try to write prog." I have found one method when I failed the course, More accurately, my method: When I counter problem in language , I will get more paper and then ; first, input/ output step ; my prog will take this / these there argument(s) and return namely X , ex : in c, input length is not known and at same type , so I must use pointer desired output is in form of package , so use structure second, execution part ; in that step , I am writing all step which are goes to final output ex : in python ; 1.) [ + , [- , 4 , [ * , 1 , 2 ]], 5] 2.) [ + , [- , 4 , 2 ],5 ] 3.) [ + , 2 , 5] 4.) 7 ==> return 7 third, I will write test code ex : in c++ input : append 3 4 5 6 vector_x remove 0 1 desired output vector_x holds : 5 6 now, my other question is ; What is/are other method(s) which have/has been; used to construct class :::: for c++ , python, java used to communicate classes / computers used for solving embedded system problem ::::: for c by other user? Some programmer uses generalized method without considering prog-language(java , perl .. ), what is this method ? Why I wonder , because I learn if you dont costruct algorithm on paper, you may achieve your goal. Like no money no lunch , I can say no algorithm no prog therefore , feel free when you write your own method , a way which is introduced by someone else but you are using and you find it is so efficient

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• What facets have I missed for creating a 3 person guerilla dev team?

  - by Penguinix

  Sorry for the Windows developers out there, this solution is for Macs only. This set of applications accounts for: Usability Testing, Screen Capture (Video and Still), Version Control, Task Lists, Bug Tracking, a Developer IDE, a Web Server, A Blog, Shared Doc Editing on the Web, Team and individual Chat, Email, Databases and Continuous Integration. This does assume your team members provide their own machines, and one person has a spare old computer to be the Source Repository and Web Server. All for under $200 bucks. Usability Silverback Licenses = 3 x $49.95 "Spontaneous, unobtrusive usability testing software for designers and developers." Source Control Server and Clients (multiple options) Subversion = Free Subversion is an open source version control system. Versions (Currently in Beta) = Free Versions provides a pleasant work with Subversion on your Mac. Diffly = Free "Diffly is a tool for exploring Subversion working copies. It shows all files with changes and, clicking on a file, shows a highlighted view of the changes for that file. When you are ready to commit Diffly makes it easy to select the files you want to check-in and assemble a useful commit message." Bug/Feature/Defect Tracking (multiple options) Bugzilla = Free Bugzilla is a "Defect Tracking System" or "Bug-Tracking System". Defect Tracking Systems allow individual or groups of developers to keep track of outstanding bugs in their product effectively. Most commercial defect-tracking software vendors charge enormous licensing fees. Trac = Free Trac is an enhanced wiki and issue tracking system for software development projects. Database Server & Clients MySQL = Free CocoaMySQL = Free Web Server Apache = Free Development and Build Tools XCode = Free CruiseControl = Free CruiseControl is a framework for a continuous build process. It includes, but is not limited to, plugins for email notification, Ant, and various source control tools. A web interface is provided to view the details of the current and previous builds. Collaboration Tools Writeboard = Free Ta-da List = Free Campfire Chat for 4 users = Free WordPress = Free "WordPress is a state-of-the-art publishing platform with a focus on aesthetics, web standards, and usability. WordPress is both free and priceless at the same time." Gmail = Free "Gmail is a new kind of webmail, built on the idea that email can be more intuitive, efficient, and useful." Screen Capture (Video / Still) Jing = Free "The concept of Jing is the always-ready program that instantly captures and shares images and video…from your computer to anywhere." Lots of great responses: TeamCity [Yo|||] Skype [Eric DeLabar] FogBugz [chakrit] IChatAV and Screen Sharing (built-in to OS) [amrox] Google Docs [amrox]

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• Sanity check on this idea for an Image Viewer in a web app

  - by Charlie Flowers

  I have an approach in mind for an image viewer in a web app, and want to get a sanity check and any thoughts you stackoverflowers might have. Here's the whirlwind nutshell summary: I'm working on an ASP.NET MVC application that will run in my company's retail stores. Even though it is a web application, we own the store machines and have control over them. We have a "windows agent" running on the store machine which we can talk to via http post (it is a WCF service, and our web app has permission to talk to it from the browser). One of the web pages needs to be an "image viewer" page with some common things like Rotate & Zoom. Now, there are some WebForms controls that offer Rotate and Zoom. However, they take up server resources and generate a good bit of traffic between the server and the browser. For example, the Rotate function would cause an ajax call to the server, which would then generate a new image written to a .NET Canvas object, which would then be written to a file on the server, which would then be returned from the ajax call and refreshed inside the browser. Normally, that's a pretty good way of doing things. But in our case, we have code running on the store machine that we can communicate with. This leads me to consider the following approach: When the user asks to view an image, we tell our "windows agent" to download it from our image server to the store machine. We then redirect our browser to our image viewer page, which will pull the image from the local file we just wrote to the store machine. When the user clicks "Rotate", we cause JavaScript code in the browser to call our "windows agent" software, asking it to perform the "Rotate" function. The "windows agent" does the rotation using the same kind of imaging control that would formerly have been used on the server, but it does so now on the store machine. Javascript in the browser then refreshes the image on the page to show the newly rotated image. Zoom and similar features would be implemented the same way. This seems to be much more efficient, scalable, and responsive for the end-users. However, I've never heard of anything like it being done, mostly because it's rare to have this combination of a web app plus a "windows agent" on the client machine. What do you think? Feasible? Reasonable? Any pitfalls I overlooked or improvements / suggestions you can see? Has anyone done anything like this who would like to offer the wisdom of experience? Thanks!

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• Performance tuning of a Hibernate+Spring+MySQL project operation that stores images uploaded by user

  - by Umar

  Hi I am working on a web project that is Spring+Hibernate+MySQL based. I am stuck at a point where I have to store images uploaded by a user into the database. Although I have written some code that works well for now, but I believe that things will mess up when the project would go live. Here's my domain class that carries the image bytes: @Entity public class Picture implements java.io.Serializable{ long id; byte[] data; ... // getters and setters } And here's my controller that saves the file on submit: public class PictureUploadFormController extends AbstractBaseFormController{ ... protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws Exception{ MutlipartFile file; // getting MultipartFile from the command object ... // beginning hibernate transaction ... Picture p=new Picture(); p.setData(file.getBytes()); pictureDAO.makePersistent(p); // this method simply calls getSession().saveOrUpdate(p) // committing hiernate transaction ... } ... } Obviously a bad piece of code. Is there anyway I could use InputStream or Blob to save the data, instead of first loading all the bytes from the user into the memory and then pushing them into the database? I did some research on hibernate's support for Blob, and found this in Hibernate In Action book: java.sql.Blob and java.sql.Clob are the most efficient way to handle large objects in Java. Unfortunately, an instance of Blob or Clob is only useable until the JDBC transaction completes. So if your persistent class defines a property of java.sql.Clob or java.sql.Blob (not a good idea anyway), you’ll be restricted in how instances of the class may be used. In particular, you won’t be able to use instances of that class as detached objects. Furthermore, many JDBC drivers don’t feature working support for java.sql.Blob and java.sql.Clob. Therefore, it makes more sense to map large objects using the binary or text mapping type, assuming retrieval of the entire large object into memory isn’t a performance killer. Note you can find up-to-date design patterns and tips for large object usage on the Hibernate website, with tricks for particular platforms. Now apparently the Blob cannot be used, as it is not a good idea anyway, what else could be used to improve the performance? I couldn't find any up-to-date design pattern or any useful information on Hibernate website. So any help/recommendations from stackoverflowers will be much appreciated. Thanks

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• Function Point Analysis -- a seriously over-estimating technique?

  - by kizzx2

  I know questions about FPA has been asked numerous times before, but this time I'm taking a more analytical angle at it, backed up with data. 1. First, some data This question is based on a tutorial. He had a "Sample Count" section where he demonstrated it step by step. You can see some screenshots of his sample application here. In the end, he calculated the unadjusted FP to be 99. There is another article on InformIT with industry data on typical hour/FP. It ranges from 2 hours/FP to 27.4 hours/FP. Let's try to stick with 2 for the moment (since SO readers are probably the more efficient crowd :p). 2. Reality check!? Now just check out the screenshots again. Do a little math here 99 * 2 = 198 hours 198 hours / 40 hours per week = 5 weeks Seriously? That sample application is going to take 5 weeks to implement? Is it just my feeling that it wouldn't take any decent programmer longer than one week to have it completed? Now let's try estimating the cost of the project. We'll use New York's minimum wage at the moment (Wikipedia), which is $7.25 198 * 7.25 = $1435.5 From what I could see from the screenshots, this application is a small excel-improvement app. I could have bought MS Office Pro for 200 bucks which gives me greater interoperability (.xls files) and flexibility (spreadsheets). (For the record, that same Web site has another article discussing productivity. It seems like they typically use 4.2 hours/FP, which gives us even more shocking stats: 99 * 4.2 = 415 hours = 10 weeks = almost 3 whopping months! 415 hours * $7.25 = $3000 zomg (That's even assuming that all our poor coders get the minimum wage!) 3. Am I missing something here? Right now, I could come up with several possible explanation: FPA is really only suited for bigger projects (1000+ FPs) so it becomes extremely inaccurate at smaller scale. The hours/FP metric fluctuates abruptly from team to team, project to project. For a small project like this, we could have used something like 0.5 hour/FP or something. (Now this kind of makes the whole estimation thing pointless, unless my firm does the same type of projects for several years with the same team, not really common.) From my experience with several software metrics, Function Point is really not a lightweight metric. If the hour/FP thing fluctuates so much, then what's the point, maybe I could have gone with User Story Points which is a lot faster to get and arguably almost as uncertain. What would be the FP experts' answers to this?

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• Should we denormalize database to improve performance?

  - by Groo

  We have a requirement to store 500 measurements per second, coming from several devices. Each measurement consists of a timestamp, a quantity type, and several vector values. Right now there is 8 vector values per measurement, and we may consider this number to be constant for needs of our prototype project. We are using HNibernate. Tests are done in SQLite (disk file db, not in-memory), but production will probably be MsSQL. Our Measurement entity class is the one that holds a single measurement, and looks like this: public class Measurement { public virtual Guid Id { get; private set; } public virtual Device Device { get; private set; } public virtual Timestamp Timestamp { get; private set; } public virtual IList<VectorValue> Vectors { get; private set; } } Vector values are stored in a separate table, so that each of them references its parent measurement through a foreign key. We have done a couple of things to ensure that generated SQL is (reasonably) efficient: we are using Guid.Comb for generating IDs, we are flushing around 500 items in a single transaction, ADO.Net batch size is set to 100 (I think SQLIte does not support batch updates? But it might be useful later). The problem Right now we can insert 150-200 measurements per second (which is not fast enough, although this is SQLite we are talking about). Looking at the generated SQL, we can see that in a single transaction we insert (as expected): 1 timestamp 1 measurement 8 vector values which means that we are actually doing 10x more single table inserts: 1500-2000 per second. If we placed everything (all 8 vector values and the timestamp) into the measurement table (adding 9 dedicated columns), it seems that we could increase our insert speed up to 10 times. Switching to SQL server will improve performance, but we would like to know if there might be a way to avoid unnecessary performance costs related to the way database is organized right now. [Edit] With in-memory SQLite I get around 350 items/sec (3500 single table inserts), which I believe is about as good as it gets with NHibernate (taking this post for reference: http://ayende.com/Blog/archive/2009/08/22/nhibernate-perf-tricks.aspx). But I might as well switch to SQL server and stop assuming things, right? I will update my post as soon as I test it.

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• Given a trace of packets, how would you group them into flows?

  - by zxcvbnm

  I've tried it these ways so far: 1) Make a hash with the source IP/port and destination IP/port as keys. Each position in the hash is a list of packets. The hash is then saved in a file, with each flow separated by some special characters/line. Problem: Not enough memory for large traces. 2) Make a hash with the same key as above, but only keep in memory the file handles. Each packet is then put into the hash[key] that points to the right file. Problems: Too many flows/files (~200k) and it might run out of memory as well. 3) Hash the source IP/port and destination IP/port, then put the info inside a file. The difference between 2 and 3 is that here the files are opened and closed for each operation, so I don't have to worry about running out of memory because I opened too many at the same time. Problems: WAY too slow, same number of files as 2 so also impractical. 4) Make a hash of the source IP/port pairs and then iterate over the whole trace for each flow. Take the packets that are part of that flow and place them into the output file. Problem: Suppose I have a 60 MB trace that has 200k flows. This way, I would process, say, a 60 MB file 200k times. Maybe removing the packets as I iterate would make it not so painful, but so far I'm not sure this would be a good solution. 5) Split them by IP source/destination and then create a single file for each one, separating the flows by special characters. Still too many files (+50k). Right now I'm using Ruby to do it, which might've been a bad idea, I guess. Currently I've filtered the traces with tshark so that they only have relevant info, so I can't really make them any smaller. I thought about loading everything in memory as described in 1) using C#/Java/C++, but I was wondering if there wouldn't be a better approach here, especially since I might also run out of memory later on even with a more efficient language if I have to use larger traces. In summary, the problem I'm facing is that I either have too many files or that I run out of memory. I've also tried searching for some tool to filter the info, but I don't think there is one. The ones I've found only return some statistics and wouldn't scan for every flow as I need.

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• NSLinguisticTagger on the contents of an NSTextStorage- crashing bug

  - by Remy Porter

  I'm trying to use an NSLinguisticTagger to monitor the contents of an NSTextStorage and provide some contextual information based on what the user types. To that end, I have an OverlayManager object, which wires up this relationship: -(void) setView:(NSTextView*) view { _view = view; _layout = view.layoutManager; _storage = view.layoutManager.textStorage; //get the TextStorage from the view [_tagger setString:_storage.string]; //pull the string out, this grabs the mutable version [self registerForNotificationsOn:self->_storage]; //subscribe to the willProcessEditing notification } When an edit occurs, I make sure to trap it and notify the tagger (and yes, I know I'm being annoyingly inconsistent with member access, I'm rusty on Obj-C, I'll fix it later): - (void) textStorageWillProcessEditing:(NSNotification*) notification{ if ([self->_storage editedMask] & NSTextStorageEditedCharacters) { NSRange editedRange = [self->_storage editedRange]; NSUInteger delta = [self->_storage changeInLength]; [_tagger stringEditedInRange:editedRange changeInLength:delta]; //should notify the tagger of the changes [self highlightEdits:self]; } } The highlightEdits message delegates the job out to a pool of "Overlay" objects. Each contains a block of code similar to this: [tagger enumerateTagsInRange:range scheme:NSLinguisticTagSchemeLexicalClass options:0 usingBlock:^(NSString *tag, NSRange tokenRange, NSRange sentenceRange, BOOL *stop) { if (tag == PartOfSpeech) { [self applyHighlightToRange:tokenRange onStorage:storage]; } }]; And that's where the problem is- the enumerateTagsInRange method crashes out with a message: 2014-06-04 10:07:19.692 WritersEditor[40191:303] NSMutableRLEArray replaceObjectsInRange:withObject:length:: Out of bounds This problem doesn't occur if I don't link to the mutable copy of the underlying string and instead do a [[_storage string] copy], but obviously I don't want to copy the entire backing store every time I want to do tagging. This all should be happening in the main run loop, so I don't think this is a threading issue. The NSRange I'm enumerating tags on exists both in the NSTextStorage and in the NSLinguisticTagger's view of the string. It's not even the fact that the applyHighlightToRange call adds attributes to the string, because it crashes before even reaching that line. I attempted to build a test case around the problem, but can't replicate it in those situations: - (void) testEdit { NSAttributedString* str = [[NSMutableAttributedString alloc] initWithString:@"Quickly, this is a test."]; text = [[NSTextStorage alloc] initWithAttributedString:str]; NSArray* schemes = [NSLinguisticTagger availableTagSchemesForLanguage:@"en"]; tagger = [[NSLinguisticTagger alloc] initWithTagSchemes:schemes options:0]; [tagger setString:[text string]]; [text beginEditing]; [[text mutableString] appendString:@"T"]; NSRange edited = [text editedRange]; NSUInteger length = [text changeInLength]; [text endEditing]; [tagger stringEditedInRange:edited changeInLength:length]; [tagger enumerateTagsInRange:edited scheme:NSLinguisticTagSchemeLexicalClass options:0 usingBlock:^(NSString *tag, NSRange tokenRange, NSRange sentenceRange, BOOL *stop) { //doesn't matter, this should crash }]; } That code doesn't crash.

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• Performance of looping over an Unboxed array in Haskell

  - by Joey Adams

  First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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• The Math of a Jump in a 2D game.

  - by ONi

  I have been all around with this question and I can't find the correct answer! So, behold, the description of my question: I'm working in J2ME, I have my gameloop that do the following: public void run() { Graphics g = this.getGraphics(); while (running) { long diff = System.currentTimeMillis() - lastLoop; lastLoop = System.currentTimeMillis(); input(); this.level.doLogic(); render(g, diff); try { Thread.sleep(10); } catch (InterruptedException e) { stop(e); } } } so it's just a basic gameloop, the doLogic() function calls for all the logic functions of the characters in the scene and render(g, diff) calls the animateChar function of every character on scene, following this, the animChar function in the Character class sets up everything in the screen as this: protected void animChar(long diff) { this.checkGravity(); this.move((int) ((diff * this.dx) / 1000), (int) ((diff * this.dy) / 1000)); if (this.acumFrame > this.framerate) { this.nextFrame(); this.acumFrame = 0; } else { this.acumFrame += diff; } } This ensures me that everything must to move according to the time that the machine takes to go from cycle to cycle (remember it's a phone, not a gaming rig). I'm sure it's not the most efficient way to achieve this behavior so I'm totally open for criticism of my programming skills in the comments, but here my problem: When I make I character jump, what I do is that I put his dy to a negative value, say -200 and I set the boolean jumping to true, that makes the character go up, and then I have this function called checkGravity() that ensure that everything that goes up has to go down, checkGravity also checks for the character being over platforms so I will strip it down a little for the sake of your time: public void checkGravity() { if (this.jumping) { this.jumpSpeed += 10; if (this.jumpSpeed > 0) { this.jumping = false; this.falling = true; } this.dy = this.jumpSpeed; } if (this.falling) { this.jumpSpeed += 10; if (this.jumpSpeed > 200) this.jumpSpeed = 200; this.dy = this.jumpSpeed; if (this.collidesWithPlatform()) { this.falling = false; this.standing = true; this.jumping = false; this.jumpSpeed = 0; this.dy = this.jumpSpeed; } } } So, the problem is, that this function updates the dy regardless of the diff, making the characters fly like Superman in slow machines, and I have no idea how to implement the diff factor so that when a character is jumping, his speed decrement in a proportional way to the game speed. Can anyone help me fix this issue? or give me pointers on how to make a 2D Jump in J2ME the right way. Thank you very much for your time.

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• Good object/DB set-up for CMS-esque app for managing content and user permissions?

  - by sah302

  Hi all, so I am writing a big CMS-esque app to allow users to manage web content through web applications, I've got a pretty good db-driven user permission system going, but am having trouble coming up with a good way to handle content groups and pages, I've got a couple options and not sure which one to take. Furthermore, I am not sure how to handle static page updates that have no 'widgets' in them. My current set-up for permissions is this: Objects: User, UserGroup, UserUserGroup, UserGroupType Standard many to many relationship User -> UserUserGroup <- UserGroup each Usergroup has a UserGroupType, which could be anything from Title, Department, to PermissionGroup. PermissionGroup manages the permissions. Right now on a per page basis I check permissions based on their PermissionsGroups. So for a page which has CMS features for a news widget, I check for permission groups of "Site Admin" and "News Admin". Now the issue I am coming to is, the site has many different departments involved. No problem I think, I can just have a EntityContentGroup so any widget app can be used for any departments. So my HR department, each of their news items would be in the EntityContentGroup with the news item ID, and content group of "HR" or "HR News". But maybe this isn't the most efficient way to go about it? I don't want to put the content group simply as a NewsItemType because some news items could apply to multiple areas, so I want to be able to assign them to as many areas as I want. Likewise, all of my widget apps have this, so that's why I decided to choose EntityContentGroup and not just NewsItemContentGroup. I was also thinking well instead of doing a contentGroup do a Page object that says which page some entity should be on. It seems almost like the same thing, but would I want to use Page for something else? I was thinking Page would be used for static pages with no widgets, a simple Rich Text Editor can edit the content of that page and I save that item to a page?? And then instead of doing a page level check for UserGroup permissions, would it be better to associate a usergroup to a contentgroup, and then just depending on what contentGroup content on the page is displayed, determine the permissions through that relationship? Is that better? I am not sure at this point. I guess I am just getting a tad overwhelmed at this is the largest app in scope and size that I have ever written. What is the best approach for this based on my current user permission set-up?

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• Autocomplete server-side implementation

  - by toluju

  What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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• SQL efficiency argument, add a column or solvable by query?

  - by theTurk

  I am a recent college graduate and a new hire for software development. Things have been a little slow lately so I was given a db task. My db skills are limited to pet projects with Rails and Django. So, I was a little surprised with my latest task. I have been asked by my manager to subclass Person with a 'Parent' table and add a reference to their custodian in the Person table. This is to facilitate going from Parent to Form when the custodian, not the Parent, is the FormContact. Here is a simplified, mock structure of a sql-db I am working with. I would have drawn the relationship tables if I had access to Visio. We have a table 'Person' and we have a table 'Form'. There is a table, 'FormContact', that relates a Person to a Form, not all Persons are related to a Form. There is a relationship table for Person to Person relationships (Employer, Parent, etc.) I've asked, "Why this couldn't be handled by a query?" Response, Inefficient. (Really!?!) So, I ask, "Why not have a reference to the Form? That would be more efficient since you wouldn't be querying the FormContacts table with the reference from child/custodian." Response, this would essentially make the Parent is a FormContact. (Fair enough.) I went ahead an wrote a query to get from non-FormContact Parent to Form, and tested on the production server. The response time was instantaneous. *SOME_VALUE* is the Parent's fk ID. SELECT FormID FROM FormContact WHERE FormContact.ContactID IN (SELECT SourceContactID FROM ContactRelationship WHERE (ContactRelationship.RelatedContactID = *SOME_VALUE*) AND (ContactRelationship.Relationship = 'Parent')); If I am right, "This is an unnecessary change." What should I do, defend my position or should I concede to the managers request? If I am wrong. What is my error? Is there a better solution than the manager's?

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• Flatten date range memberships retaining only the highest priority membership (TRANSACT-SQL)

  - by shadowranger

  Problem statement: A table contains an item_id, a category_id and a date range (begin_date and end_date). No item may be in more than one category on any given date (in general; during daily rebuilding it can be in an invalid state temporarily). By default, all items are added (and re-added if removed) to a category (derived from outside data) automatically on a daily basis, and their membership in that category matches the lifespan of the item (items have their own begin and end date, and usually spend their entire lives in the same category, which is why this matches). For items in category X, it is occasionally desirable to override the default category by adding them to category Y. Membership in category Y could entirely replace membership in category X (that is, the begin and end dates for membership in category Y would match the begin and end dates of the item itself), or it could override it for an arbitrary period of time (at the beginning, middle or end the item's lifespan, possibly overriding for short periods at multiple times). Membership in category Y is not renewed automatically and additions to that category is done by manual data entry. Every day, when category X is rebuilt, we get an overlap, where any item in category Y will now be in category X as well (which is forbidden, as noted previously). Goal: After each repopulation of category X (which is done in a rather complicated and fragile manner, and ideally would be left alone), I'm trying to find an efficient means of writing a stored procedure that: Identifies the overlaps Changes existing entries, adds new ones where necessary (such as in the case where an item starts in category X, switches to category Y, then eventually switches back to category X before ending), or removes entries (when an item is in category Y for its entire life) such that every item remains in category Y (and only Y) where specified, while category X membership is maintained when not overridden by category Y. Does not affect memberships of categories A, B, C, Z, etc., which do not have override categories and are built separately, by completely different rules. Note: It can be assumed that X membership covers the entire lifespan of the item before this procedure is called, so it is unnecessary to query any data outside this table. Bonus credit: If for some reason there are two adjacent or overlapping memberships in for the same item in category Y, stitching them together into a single entry is appreciated, but not necessary. Example: item_id category_id begin_date end_date 1 X 20080101 20090628 1 Y 20090101 20090131 1 Y 20090601 20090628 2 X 20080201 20080731 2 Y 20080201 20080731 Should become: item_id category_id begin_date end_date 1 X 20080101 20081231 1 Y 20090101 20090131 1 X 20090201 20090531 1 Y 20090601 20090628 2 Y 20080201 20080731 If it matters, this needs to work on SQL Server 2005 and SQL Server 2008

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• ASP.NET MVC 4/Web API Single Page App for Mobile Devices ... Needs Authentication

  - by lmttag

  We have developed an ASP.NET MVC 4/Web API single page, mobile website (also using jQuery Mobile) that is intended to be accessed only from mobile devices (e.g., iPads, iPhones, Android tables and phones, etc.), not desktop browsers. This mobile website will be hosted internally, like an intranet site. However, since we’re accessing it from mobile devices, we can’t use Windows authentication. We still need to know which user (and their role) is logging in to the mobile website app. We tried simply using ASP.NET’s forms authentication and membership provider, but couldn’t get it working exactly the way we wanted. What we need is for the user to be prompted for a user name and password only on the first time they access the site on their mobile device. After they enter a correct user name and password and have been authenticated once, each subsequent time they access the site they should just go right in. They shouldn’t have to re-enter their credentials (i.e., something needs to be saved locally to each device to identify the user after the first time). This is where we had troubles. Everything worked as expected the first time. That is, the user was prompted to enter a user name and password, and, after doing that, was authenticated and allowed into the site. The problem is every time after the browser was closed on the mobile device, the device and user were not know and the user had to re-enter user name and password. We tried lots of things too. We tried setting persistent cookies in JavaScript. No good. The cookies weren’t there to be read the second time. We tried manually setting persistent cookies from ASP.NET. No good. We, of course, used FormsAuthentication.SetAuthCookie(model.UserName, true); as part of the form authentication framework. No good. We tried using HTML5 local storage. No good. No matter what we tried, if the user was on a mobile device, they would have to log in every single time. (Note: we’ve tried on an iPad and iPhone running both iOS 5.1 and 6.0, with Safari configure to allow cookies, and we’ve tried on Android 2.3.4.) Is there some trick to getting a scenario like this working? Or, do we have to write some sort of custom authentication mechanism? If so, how? And, what? Or, should we use something like claims-based authentication and WIF? Or??? Any help is appreciated. Thanks!

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• What is the most effective way to test for combined keyboard arrow direction in ActionScript 3.0?

  - by Relee

  I need to monitor the direction a user is indicating using the four directional arrow keys on a keyboard in ActionScript 3.0 and I want to know the most efficient and effective way to do this. I've got several ideas of how to do it, and I'm not sure which would be best. I've found that when tracking Keyboard.KEY_DOWN events, the event repeats as long as the key is down, so the event function is repeated as well. This broke the method I had originally chosen to use, and the methods I've been able to think of require a lot of comparison operators. The best way I've been able to think of would be to use bitwise operators on a uint variable. Here's what I'm thinking var _direction:uint = 0x0; // The Current Direction That's the current direction variable. In the Keyboard.KEY_DOWN event handler I'll have it check what key is down, and use a bitwise AND operation to see if it's already toggled on, and if it's not, I'll add it in using basic addition. So, up would be 0x1 and down would be 0x2 and both up and down would be 0x3, for example. It would look something like this: private function keyDownHandler(e:KeyboardEvent):void { switch(e.keyCode) { case Keyboard.UP: if(!(_direction & 0x1)) _direction += 0x1; break; case Keyboard.DOWN: if(!(_direction & 0x2)) _direction += 0x2; break; // And So On... } } The keyUpHandler wouldn't need the if operation since it only triggers once when the key goes up, instead of repeating. I'll be able to test the current direction by using a switch statement labeled with numbers from 0 to 15 for the sixteen possible combinations. That should work, but it doesn't seem terribly elegant to me, given all of the if statements in the repeating keyDown event handler, and the huge switch. private function checkDirection():void { switch(_direction) { case 0: // Center break; case 1: // Up break; case 2: // Down break; case 3: // Up and Down break; case 4: // Left break; // And So On... } } Is there a better way to do this?

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