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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• jquery attribute indexOf

  - by Victor

  When I am getting at an attribute onclick of custom(Reporting Services) checkbox it gives me correct result. However when I am trying to use indexOf on that result it says "Object doesn't support this property or method", i.e. this is fine, gives me a long string $('input[id*=CustomCheckBox]').click(function() { alert( $(this).attr("onclick") ); }); But this gives an error(object doesn't support this property or method): $('input[id*=CustomCheckBox]').click(function() { if ($(this).attr("onclick").indexOf("SomeString") > -1 ) { //do some processing here } } What would I need to modify so that indexOf is working properly?

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• What FIX implementation do you recommend for use with .NET

  - by Ajaxx

  I am reviewing implementation choices for FIX when using .NET. A few obvious choices come to mind, but I want to know if there are other options, better choices or if we've made the same decision as a lot of you. QuickFIX - Stable, C++ implementation - so you've got unmanaged code to interop with. FIX4NET - C# implementation - seems to have some gaps in its implementation. DIY - Chime in here if you've made your own FIX engine Let me throw in some caveats here. I'm not looking for sub 100 microsecond processing. Performance is a requirement, but not so much that it's driving my decisions. A solid product that is stable, performs well and is flexible enough to deal with vendor specific dialects is the sweet spot. The more we can do in .NET the better.

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• C# Express 2010 Multi-Threading

  - by Chris Evans

  Hi, I have a windows app that I have been running in c# Express 2008 for a year and have been trying to convert it over the last few days to 2010. The problem I am having is it is a multi-threaded application that has to run a series of code every second. What it does is have a main thread, that calls 3 worker threads, waits for them to finish then does some additional processing, sleeps till 1 second and runs again. The problem is part of the code can call a web service that takes 8 seconds to respond, so this bit of code gets called using ThreadPool.QueueUserWorkItem. The problem is when running in 2010 when this part of the code gets called the main thread continues to run but when it awakens the sub threads it hangs until the Threadpool method finishes running. This never happens in 2008. Any suggestions? So far I put that bit of code in it's own thread rather than using Threadpool but same issue.

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• How can I kill a Perl system call after a timeout?

  - by Fergal

  I've got a Perl script I'm using for running a file processing tool which is started using backticks. The problem is that occasionally the tool hangs and It needs to be killed in order for the rest of the files to be processed. Whats the best way best way to apply a timeout after which the parent script will kill the hung process? At the moment I'm using: foreach $file (@FILES) { $runResult = `mytool $file >> $file.log`; } But when mytool hangs after n seconds I'd like to be able to kill it and continue to the next file.

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• how to close a windows form in c# when that form transfer control to an other form?

  - by moon

  i have encountered a problem in my application i have two windows forms one that is loaded when my application is started and ask for a password and other is shown when click log in with correct password , problem is how can i close the first form that is log in form when user proceed to next from that is actual application, currently i hide the first form but the requirement is to close that form to prevent extra processing when i close that log in form my application is closed and when i close the actual application form that log in form remain open. my application is not fully closed, log in form is running in background how can in fix this....

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• How to tell a UITableView to preload all Rows?

  - by Infinite

  Is there a way to tell a UITableView to preload all rows? The tableView is supposed to show several comments (up to 80 comments). So my CommentCell uses a Setter to adapt the cell to a specific comment. -(void)setComment:(Comment *)newComment { if (newComment != comment) { [comment release]; comment = [newComment retain]; /* * set the cells view variables here */ } } This specific setter takes quite a bunch of processing resources and scrolling gets kinda laggy. I am using a comment-specific reuseIdentifier instead of a static cellIdentifier when calling dequeueReusableCellWithIdentifier: in order to assure, that "newComment" equals the old "comment". And in fact this does work great when scrolling over cells which have already been loaded. But when scrolling through the comments for the first time, it still lags like hell. Which leads me to my question: Is there a way to tell the tableview to preload all cells? (which I doubt) or Do I have to implement my own cache instead of relying on "dequeueReusableCellWithIdentifier:"?

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• Ideally How many connections I have to open ?

  - by ranjith-kumar-u

  Hi All, Recently I attended interview in java, the interviewer asked a question like below: I have a request which go throgh A,B,C modules and response go back throgh A , in module A I need to talk to database and again in module C I need to talk to database, so in this situation how many connections you will open and where do you close those connections? My Answer: I said that in module A I will open a connection and I will close it then and there, then control go to module B then module C, in module C again I will open one more connection and i will close it again. then he asked me again another question I want to open one connection per one request processing, how can i do this?

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• What are the general strategies for the server of an FPS multiplayer game to update its clients?

  - by Hooray Im Helping

  A friend and I were having a discussion about how a FPS server updates the clients connected to it. We watched a video of a guy cheating in Battlefield: Bad Company 2 and saw how it highlighted the position of enemies on the screen and it got us thinking. His contention was that the server only updates the client with information that is immediately relevant to the client. I.e. the server won't send information about enemy players if they are too far away from the client or out of the client's line of sight for reasons of efficiency. He was unsure though - he brought up the example of someone hiding behind a rock, not able to see anyone. If the player were suddenly to pop up where he had three players in his line of sight, there would be a 50ms delay before they were rendered on his screen while the server transmitted the necessary information. My contention was the opposite: that the server sends the client all the information about every player and lets the client sort out what is allowed and what isn't. I figured it would actually be less expensive computationally for the server to just send everything to the client and let the client do the heavy lifting, so to speak. I also figured this is how cheat programs work - they intercept the server packets, get the location of enemies, then show them on the client's view. So the question: What are some general policies or strategies a modern first person shooter server employs to keep its clients updated?

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• How to rename the original file before sending it to user

  - by Manish Jangir

  Actually I have some download link on my website something like "http://www.example.com/somesong.mp3". Now when user click on this link they get somesong.mp3 but I want to change it before they download. I found many scripts that made it possible but didn't get exact right script. Because I want that when the user clicks on download link the file downloading should be started just after the click with the new file name as I want to use. But in all the scripts which I downloaded, first the php processing starts for a few minute (I think it depends on the file size) and then rename it. Is there a way to direct force the file in header with new file name. Thanks.

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• Share Link - Perform action in background

  - by Justin

  I have an application that will accept URLs from the built in web browser via the "Share page" menu item. I'm using the send intent and it works just fine. However, I'd like to accept a URL and process it in the background without bringing my application to the front. I don't want the user to have to actually leave the web browser. It will notify the user it has finished processing the URL with a Toast message. I'm just not sure what type of activity should be used for this. A good example of this behavior is the "Read Later" instapaper application in the android market. Any help would be greatly appreciated.

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• Is select() Ok to implement single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• Would it be simply better to use the system's functions rather than use the language?

  - by Nullw0rm

  There are many scenarios where I've questioned PHP's performance with some of its functions, and whether I should build a complex class to handle specific things using its seemingly slow tools. For example, Complex regular expressions with sed and processing with awk would seemingly be exponential in performance rather than making PHP's regular expression and seemingly excessive functions parse and in time manage to finish it. If I were to do a lot of network tasks such as MX lookups/DIGging/retrieving simultaneously I would rather pass it via system() and let the OS handle it itself. There are simply too many functions in PHP, that are inefficient and result in slow pages or can be handled easier by the OS. What are your opinions? Do you think I should do the hard work with the OS in its own/custom functions?

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• Efficient Multiplication of Varying-Length #s [Conceptual]

  - by Milan Patel

  Write the pseudocode of an algorithm that takes in two arbitrary length numbers (provided as strings), and computes the product of these numbers. Use an efficient procedure for multiplication of large numbers of arbitrary length. Analyze the efficiency of your algorithm. I decided to take the (semi) easy way out and use the Russian Peasant Algorithm. It works like this: a * b = a/2 * 2b if a is even a * b = (a-1)/2 * 2b + a if a is odd My pseudocode is: rpa(x, y){ if x is 1 return y if x is even return rpa(x/2, 2y) if x is odd return rpa((x-1)/2, 2y) + y } I have 3 questions: Is this efficient for arbitrary length numbers? I implemented it in C and tried varying length numbers. The run-time in was near-instant in all cases so it's hard to tell empirically... Can I apply the Master's Theorem to understand the complexity...? a = # subproblems in recursion = 1 (max 1 recursive call across all states) n / b = size of each subproblem = n / 1 - b = 1 (problem doesn't change size...?) f(n^d) = work done outside recursive calls = 1 - d = 0 (the addition when a is odd) a = 1, b^d = 1, a = b^d - complexity is in n^d*log(n) = log(n) this makes sense logically since we are halving the problem at each step, right? What might my professor mean by providing arbitrary length numbers "as strings". Why do that? Many thanks in advance

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• How does the default Camera iPhone app manages to save a photo so fast?

  - by worriorbg

  Hello everyone. So far I've managed to create an app for iPhone that takes multiple images with about a 3 second interval between each. I`m processing each image in a separate thread asynchronously and everything is great till it gets to the moment for saving the image on the iPhone disk. Then it takes about 12 seconds to save the image to the disk using JPEG representation. How does Apple do it, how do they manage to save a single image so fast to the disk is there a trick they are using? I saw that the animations distract the user for a while, but still the time needed is below 12 seconds! Thanks in advance.

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• What is the most suitable for writing a high speed server C, C++ or C# ?

  - by wniroshan

  I'm goint to write a server which does lots of image processing. Server-end processsing is expected to be very tedious. Server will maily have mobile phones as its clients. I am really concerend about speed and effciency. Security is pretty important too. Server will be running on a windows platform. Can anyone tell me what should I use as the language C, C++ or C#? or at least what are the ares that I should be looking at when selecting one of them Thank you.

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• Return an object after parsing xml with SAX

  - by sentimental_turtle

  I have some large XML files to parse and have created an object class to contain my relevant data. Unfortunately, I am unsure how to return the object for later processing. Right now I pickle my data and moments later depickle the object for access. This seems wasteful, and there surely must be a way of grabbing my data without hitting the disk. def endElement(self, name): if name == "info": # done collecting this iteration self.data.setX(self.x) self.data.setY(self.y) elif name == "lastTagOfInterest": # done with file # want to return my object from here filehandler = open(self.outputname + ".pi", "w") pickle.dump(self.data, filehandler) filehandler.close() I have tried putting a return statement in my endElement tag, but that does not seem to get passed up the chain to where I call the SAX parser. Thanks for any tips.

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• SSIS - Connection Management Within a Loop

  - by Rob Bowman

  Hi I have the following SSIS package: The problem is that within the Foreach loop a connection is opened and closed for each iteration. On running SQL Profiler I see a series of: Audit Login RPC:Completed Audit Lout The duration for the login and the RPC that actually does the work is minimal. However, the duration for the logout is significant, running into several seconds each. This causes the JOB to run very slowly - taking many hours. I get the same problem when running either on a test server or stand-alone laptop. Could anyone please suggest how I may change the package to improve performance? Also, I have noticed that when running the package from Visual Studio, it looks as though it continues to run with the component blocks going amber then green but actually all the processing has been completed and SQL profiler has dropped silent? Thanks, Rob.

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• Triggering Quartz job from JSF (Any front end)- How to wait for the job execution to be over

  - by Maximus

  I am developing a front end to trigger a quartz job on the fly. I have a form in the JSF page whose click action will dynamically trigger a quartz job. The job is invoked by the following statement, the job is triggered and everything works fine. scheduler.triggerJob("Job1",Scheduler.DEFAULT_GROUP,jobDataMap); From what I understand the job seems to run in a separate thread and the execution of the calling function does not wait for the job to be over. Since I am invoking the job from front end, I would like to wait till the job is over before I navigate to a different JSF page. So I can display an error message if the job fails. I would also like to display a message to the user, "Processing job, please wait.." until the job is actually over. Any ideas on how to accomplish this will be appreciated. Thanks !

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• Where can I find a control similar to the Firefox Rich List Box for use in my application?

  - by bsruth

  I'm trying to implement a control similar to Firefox's Rich List Box: However, I can only find the XUL implementation of this control, and I don't want to have to include a XUL processing engine in my application just to get a cool looking listbox. I've been trying to implement one on my own by customizing MFC's CListBox control, but am starting to realize it may take more time than I had intended. Before continuing to implement this control from scratch, I was wondering if anyone knew of a similar control that already exists, either commercial or open source. The main functionality I would like to have is: Small display for non selected items that expands when selected. Ability to add arbitrary controls to the expanded view. Preferably native code, but can probably use managed controls via native/managed interop with out too much extra work. Any help would be appreciated, I don't want to have to reinvent the wheel if I don't have to.

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• catching the value of a time_select in rails.

  - by ZeroSoul13

  Hello, I have a form that has two field (time_selects), the idea is that the user can select the beginning of a call and end time of the call. I've setup a observe field and works fine: <%= observe_field "llamada_inicio_4i", :update => "total", :with => "llamada_inicio_4i", :url => { :controller => "llamadas", :action => "time_tracker"}%> Sends the value out: Processing LlamadasController#time_tracker (for 127.0.0.1 at 2010-04-22 17:48:41) [POST] Parameters:"llamada_inicio_4i"="23",authenticity_token"="+D+yPSVue6yQNfPMuVLkrJn7B9tP6z5S1icKpPFTiso="} Rendering template within layouts/llamadas Rendering llamadas/time_tracker Completed in 5ms (View: 3, DB: 0) | 200 OK [http://0.0.0.0/llamadas /time_tracker] How can i catch this value Parameters:"llamada_inicio_4i"="23"

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• Import data from an SSRS report via SSIS package

  - by Chris

  First, I ask that you not ask 'why.' In the famous words of Tennyson "Ours is not to reason why. Ours is but to do and die." It's one of those, "This is what you have, deal with it." situations. The source data comes from SSRS report. The goal is to load the data into a database via SSIS. The hopeful goal is to avoid human intervention in having to download the SSRS report into Excel or CSV. There will be complex SSIS processing from there on out. Any suggestions are humbly appreciated.

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• How to evade writing a lot of repetitive code when mapping?

  - by JPCF

  I have a data access layer (DAL) using Entity Framework, and I want to use Automapper to communicate with upper layers. I will have to map data transfer objects (DTOs) to entities as the first operation on every method, process my inputs, then proceed to map from entities to DTOs. What would you do to skip writing this code? As an example, see this: //This is a common method in my DAL public CarDTO getCarByOwnerAndCreditStatus(OwnerDTO ownerDto, CreditDto creditDto) { //I want to automatize this code on all methods similar to this Mapper.CreateMap<OwnerDTO,Owner>(); Mapper.CreateMap<CreditDTO,Credit>(); Owner owner = Mapper.map(ownerDto); Owner credit = Mapper.map(creditDto) //... Some code processing the mapped DTOs //I want to automatize this code on all methods similar to this Mapper.CreateMap<Car,CarDTO>(); Car car = Mapper.map(ownedCar); return car; }

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• Updatating DataGrid From a BackGroundWorker

  - by subbu

  I hava a Background Worker and a DataGrid in my c# Application. In do work of my Backgroundworker which will call an Api in my dlls which will enter some Data in a SQLite Database. After the Completion of my Api call I report a progress and In progress event of my Backgroundworker I get the contents from Db and assign it as a DataSource to my grid. I call same API in same backgroundworker. In the middle of processing my application crashes. But If I dont assign the dataSource in ProgressChanged my application doesnt crashes.

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• Stealing the contents of another application's tree view

  - by User1

  I have an application with a very large TreeView control in Java. I want to get the contents of the tree control in a list (just strings not a JList) of XPath-like elements of leaves only. Here's an example root |-Item1 |-Item1.1 |-Item1.1.1 (leaf) |-Item1.2 (leaf) |-Item2 |-Item2.1 (leaf) Would output: /Item1/Item1.1/Item1.1.1 /Item1/Item1.2 /Item2/Item2.1 I don't have any source code or anything handy like that. Is there I tool I can use to dig into the Window item itself and pull out this data? I don't mind if there are a few post-processing steps because typing it in by hand is my only other option.

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