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• Can getAttribute() method of Tomcat ServletContext implementation be called without synchronization?

  - by oo_olo_oo

  I would like to read some parameters during servlet initializtion (in init() method), and store them among servlet context attributes (using getServletContext().setAttribute()). I would like to read these parameters later - during some request processing (using getServletContext().getAttribute()). So, the multiple threads could do this simultaneously. My question is if such an attempt is safe? Could I be sure that multi threaded calls to the getAttribute() don't mess up any internal state of the servlet context? Please take into account that I'm not going to call the setAttribute() anywhere besides the initialization. So, only calls to the getAttribute() are going to be done from multiple threads. But depending on the internal implementation, this also could be dangerous. So, any information about Tomcat's implementation would be appreciated.

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• Strange findFn malfunction

  - by gd047

  I noticed a strange malfunction in using findFn function (library sos) and I can't find out the source. While it works fine on my Windows XP pc, it does not on my Vista one. library (sos) findFn("randomization test") # in both finds 72 results findFn("{randomization test}") # In XP finds 19 or about so, but in Vista whenever I use {} and more than one word inside, # I keep getting the following: found 0 matches x has zero rows; nothing to display. Warning message: In findFn("{randomization test}") : HIT not found in HTML; processing one page only. R ver = 2.10.1 and packages updated. Any ideas where the problem might be? Bonus: As it's obvious, I was looking for functions about tests for randomized experiments

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• A linq join combined with a regex

  - by Geert Beckx

  Is it possible to combine these 2 queries or would this make my code too complex? Also I think there should be a performance gain by combining these queries since I think in the near future my source table could be over 11000 records. This is what i came up with so far : Dim lit As LiteralControl ' check characters not in alphabet Dim r As New Regex("^[^a-zA-Z]+") Dim query = From o In source.ToTable _ Where r.IsMatch(o.Field(Of String)("nam")) lit = New LiteralControl(String.Format("letter: {0}, count: {1}<br />", "0-9", query.Count)) plhAlpabetLinks.Controls.Add(lit) Dim q = From l In "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToLower.ToCharArray _ Group Join o In source.ToTable _ On l Equals o.Field(Of String)("nam").ToLowerInvariant(0) Into g = Group _ Select l, g.Count ' iterate the alphabet to generate all the links. For Each letter In q.AsEnumerable lit = New LiteralControl(String.Format("letter: {0}, count: {1}<br />", letter.l, letter.Count)) plhAlpabetLinks.Controls.Add(lit) Next Kind regards, G.

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• What is the impact/limitation of oracle select with large number of bind variables?

  - by Igal Serban

  We had our oracle server chocking during processing a select statement with close to 3500(!!) bind variables. This select is, obviously, build dynamically by code that we can't change. During the execution of this select the db server went to 100% cpu usage and our system almost halted. We know how to reproduce this problem. So we can prevent this specific condition. But I am wondering if there is a way to protect the db ( by configuration) from this type of problems.

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• interfacing: simplified

  - by code wombat

  i've been doing some research on interfaces and a simple layman's explanation for what it truly is. For some reason people love using overly complex explanations and jargon to explain truly simple concepts (guess it makes them feel big) and i have a gut feeling it's the same in this case. so from what i could grasp, it seems like interfaces are nothing more than a way to reserve method names, their return type if any, and the type and amount of arguments they accept. so when a class implements an interface (or interfaces) it is forced to define the body of each method from the interface(s). Am i on the nose with this one or do i need to keep digging? p.s. i know javascript doesn't have support for interfaces, but i still need to understand the concept because there are quite a few places where it's shown how to emulate to an extent.

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• Using exponential smoothing with NaN values

  - by Eric

  I have a sample of some kind that can create somewhat noisy output. The sample is the result of some image processing from a camera, which indicates the heading of a blob of a certain color. It is an angle from around -45° to +45°, or a NaN, which means that the blob is not actually in view. In order to combat the noisy data, I felt that exponential smoothing would do the trick. However, I'm not sure how to handle the NaN values. On the one hand, involving them in the math would result in a NaN average, which would then prevent any meaningful results. On the other hand, ignoring NaN values completely would mean that a "no-detection" scenario would never be reported. And just to complicate things, the data is also noisy in that it can get false NaN value, which ideally would be smoothed somehow to prevent random noise. Any ideas about how I could implement such an exponential smoother?

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• how to write silverlight threading function in another file or project

  - by Piyush

  I am using three tier architecture.I have SilverlightUI and UIController two projects.SilverlightUI contains only UI pages and controls while UIController contains all proxies of WCF services. Now I have created threads to update my controls dynamically and to do processing parallel.AS the requirement I want to define all functionality of threads in UIController projects.What should I do? Currenty what I am doing - private void Button_Click(object sender, RoutedEventArgs e) { StartThreads(); } private void StartThreads() { private Thread _thread1; _thread1 = new Thread(DoThread1); _thread1.Start(); } public static void DoThread1() { _data1.Dispatcher.BeginInvoke(delegate() { _data1.Text = _count1.ToString(); }); System.Threading.Thread.Sleep(1000); } I Want to write DoThread1() method in UIController project and call that function from here button_click()

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• Return numerical array in python

  - by khan

  Okay..this is kind of an interesting question. I have a php form through which user enters values for x and y like this: X: [1,3,4] Y: [2,4,5] These values are stored into database as varchars. From there, these are called by a python program which is supposed to use them as numerical (numpy) arrays. However, these are called as plain strings, which means that calculation can not be performed over them. Is there a way to convert them into numerical arrays before processing or is there something else which is wrong? Helpp!!

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• Embedded C++, any tips to avoid a local thats only used to return a value on the stack?

  - by lisarc

  I have a local that's only used for the purposes of checking the result from another function and passing it on if it meets certain criteria. Most of the time, that criteria will never be met. Is there any way I can avoid this "extra" local? I only have about 1MB of storage for my binary, and I have several thousand function calls that follow this pattern. I know it's a minor thing, but if there's a better pattern I'd love to know! SomeDataType myclass::myFunction() { SomeDataType result; // do I really need this local??? // i need to check the result and pass it on if it meets a certain condition result = doSomething(); if ( ! result ) { return result; } // do other things here ... // normal result of processing return SomeDataType(whatever); }

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• Matlab: How to find the right-most point of a white line within the imrect?

  - by mchlfchr

  i've got a question regarding the imrect() function, which is part of the image processing toolbox in MatLab. I'd like to find a starting point within an image. I use the imrect function for setting a region to limit and specify the lookup area, but I can't get the point where the ROI mask is getting back mapped to the original size of the image. As you can see on the image there is a specified rectangle (cyan-colored), which I want to inspect for the white line, especially the nearest point to the right edge of the rectangle. I experimentated with only looking up on the last column of the rectangle, but as I mentioned before, the re-mapping onto the global image coordinates failed. So in this example, the white point I'd like to get would be around (98,302) The original (x,y) coordinates are relevant, so a cropping of the image to the rectangle is not acceptable. So, do you have any ideas? Thanks for any helping comments. Kind regards,

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• Recreating iPhone stock application with nested views

  - by john

  I am trying to create an app similar to the Yahoo Stocks app that comes on the iPhone, with the split-screen interface (table on the top, graph on the bottom). I'm struggling with the view hierarchy. What is the easiest way to implement a split-screen type of application. I basically want two views nested in a parent view. My problem is a little bit more complex because I want functionality like having a uipagecontrol (does this require another viewcontroller, or is simply implemented in the initial view controller)? To what degree do I need to use IB? I would prefer to do this all in Xcode. Thanks in advance!

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• HBase as a multimap

  - by Ibrahim

  Hi guys, I'm doing some large scale text processing work and I'm trying to get started with Hadoop and HBase. One of the things I need to do is build a multimap of some stuff, which I later use to look up things and get all items with a certain key (in a M/R job). Would it be OK to use HBase and insert many rows with the same key and rely on versions/timestamps to achieve a multimap-like setup or is this a bad idea? The multimap is built up in the reduce phase of a Mapreduce task by the way, or at least in the way I've formulated it on paper. Thanks! If more information is needed, I'd be happy to provide it. Not sure whether this question is clear.

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• ContextSwitchDeadlock Was Detected error in C#

  - by assassin

  Hi, I am running a C# application, and during run-time I get the following error: The CLR has been unable to transition from COM context 0x20e480 to COM context 0x20e5f0 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. Can anyone please help me out with the problem here? Thanks a lot.

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• C#: Why only integral enums?

  - by JamesBrownIsDead

  I've been writing C# for seven years now, and I keep wondering, why do enums have to be of an integral type? Wouldn't it be nice to do something like: enum ErrorMessage { NotFound: "Could not find", BadRequest: "Malformed request" } Is this a language design choice, or are there fundamental incompatibilities on a compiler, CLR, or IL level? Do other languages have enums with string or complex (i.e. object) types? What languages? (I'm aware of workarounds; my question is, why are they needed?) EDIT: "workarounds" = attributes or static classes with consts :)

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• Has anyone used an object database with a large amount of data?

  - by Jon Kruger

  Object databases like MongoDB and db4o are getting lots of pub lately. Everyone that plays with them seems to love it. I'm guessing that they are dealing with about 640K of data in their sample apps. Has anyone tried to use an object database with a large amount of data (say, 50GB or more)? Are you able to still execute complex queries against it (like from a search screen)? How does it compare to your usual relational database of choice? I'm just curious. I want to take the object database plunge, but I need to know if it'll work on something more than a sample app.

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• How does one SELECT block another?

  - by Krip

  I'm looking at output of SP_WhoIsActive on SQL Server 2005, and it's telling me one session is blocking another - fine. However they both are running a SELECT. How does one SELECT block another? Shouldn't they both be acquiring shared locks (which are compatible with one another)? Some more details: Neither session has an open transaction count - so they are stand-alone. The queries join a view with a table. They are complex queries which join lots of tables and results in 10,000 or so reads. Any insight much appreciated.

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• Learning to write organized and modular programs (C++)

  - by Peter

  Hi All, I'm a computer science student, and I'm just starting to write relatively larger programs for my coursework (between 750 - 1500 lines). Up until now, it's been possible to get by with any reasonable level of modularization and object oriented design. However, now that I'm writing more complex code for my assignments I'd like to learn to write better code. Can anyone point me in the direction of some resources for learning about what sort of things to look for when designing your program's architecture so that you can make it as modularized as possible? Thank you for any help. Best, Peter

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• What is the chance a CouchDB document update handler will get a revision conflict?

  - by jhs

  How likely is a revision conflict when using an update handler? Should I concern myself with conflict-handling code when writing a robust update function? As described in Document Update Handlers, CouchDB 0.10 and later allows on-demand server-side document modification. Update handlers can process non-JSON formats; but the other major features are these: An HTTP front-end to arbitrarily complex document modification code Similar code needn't be written for all possible clients—a DRY architecture Execution is faster and less likely to hit a revision conflict I am unclear about the third point. Executing locally, the update handler will run much faster and with lower latency. But in situations with high contention, that does not guarantee a successful update. Or does the update handler guarantee a successful update?

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• How do I control script execution time in PHP

  - by mathew

  for example I do have 5 PHP functions on a page which execute when loading. each functions has its own processing time and some of them take more time sometimes to complete the task. hence the total loading time of the said page is slow. my question is how do I control execution time for each script and set time limit for the same. I am aware that there is an in built function in PHP called set_time_limit(); but it gives fatal error if time is beyond the maximum limit...

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• VS2010 is removing code from designer without warning - causing issues

  - by schmoopy

  I have a WinForm with a pretty complex layout (has lots of controls, panels, etc.) Whenever i open the form the file is automatically checked out from source control and it removes anything in the designer file that refereces my menustrip or statusstrip ie: the following get removed (w/o warning) Me.MyMenuStip.SuspendLayout() Me.MyStatusStrip.SuspendLayout() Me.MyMenuStrip.ResumeLayout(False) Me.MyMenuStrip.PerformLayout() Me.MyStatusStrip.ResumeLayout(False) Me.MyStatusStrip.PerformLayout() The code still builds, but there are no Menu or Status items rendered. Any ideas on what i can do? I do not want to just remove/add the menustrip for instance cause i would loose all of my menu items (and there are a lot) Thanks in advance!

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• WCF: Callback is not asynchronous

  - by Aquarius

  Hi, I'm trying to program a client server based on the callback infrastructure provided by WCF but it isn't working asynchronously. My client connects to the server calling a login method, where I save the clients callback channel by doing MyCallback callback = OperationContext.Current.GetCallbackChannel() After that the server does some processing and uses the callback object to communicate with the client. All this works, the problem resides on the fact that even though I've set the method in the OperationContract as IsOneWay=true, the server still hangs when doing the call to the client. I've tested this by launching the server for debug in the visual studio, detaching it, launching the client, calling the above mentioned login method, putting a break point in the implemented callback method of the client, and making the server send a response to the client. The server stops doing what it's supposed to do, waiting for the response of the client. Any help is appreciated.

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• Legality Of Re-Implementing An Existing API (e.g. GNU implementing the UNIX APIs)

  - by splicer

  I've often wondered about this. I'm not looking for legal advice, just casual opinions ;) If some company publishes an API on the web for their closed-source library, would it be legal for another party to release an open-source implementation of that API? Are function declarations considered source code? Take GNU implementing the UNIX APIs, for example. The UNIX standard gives the following function declaration and defines its required behaviour in English: char * mktemp(char *template); Now, consider an API that lists and declares and describes several thousand (more much complex) functions, enums, etc.; an API which defines a solution to a non-trival set of problems. If an open-source project publishes C headers that copy (verbatim) the function definitions contained in the closed-source company's published API, doesn't that violate some sort copyright law?

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• Best practice to pass a value from pop up control on iPad.

  - by Tattat

  It is an iPad app based on SDK 3.2. I have a MainUIView, that is subclass from UIView, it have a UIButton and a UILabel. When user press the UIButton, the pop up control will be appeared with a table view. When the user select a cell from the table view, the UILabel changes content base on the user click, and the pop up table view will disappear. The question is, how can I pass the "selected cell" to the UILabel. I am thinking making a "middle man" object. When the user click the UIButton, and the "middle man" will pass to the table. When the cell is selected, the "middle man" will store the idx, and call the UILabel change content from the value of "middle man". But I think it is pretty complex to implement, is there any easier way to implement it? thz u.

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• Architecture of a single-page JavaScript web application?

  - by fig-gnuton

  How should a complex single-page JS web application be structured on the client-side? Specifically I'm curious about how to cleanly structure the application in terms of its model objects, UI components, any controllers, and objects handling server persistence. MVC seemed like a fit at first. But with UI components nested at various depths (each with their own way of acting on/reacting to model data, and each generating events which they themselves may or may not handle directly), it doesn't seem like MVC can be cleanly applied. (But please correct me if that's not the case.) -- (This question resulted in two suggestions of using ajax, which is obviously needed for anything other than the most trivial one-page app.)

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• MVVM and division of amongst multiple developers

  - by nlawalker

  Can anyone speak to the ease of dividing work amongst multiple developers when designing and building a medium- to large-complexity Silverlight or WPF application? My team is finding it difficult to cleanly split work when you've got, for example, a number of controls that provide different visualizations of a Model/ViewModel that's fairly complex and has a lot of properties and methods for interacting with data. It seems like a very big portion of the work ends up being the design and build of the Model/ViewModel, and much less inside each of the controls, which are naturally what are easy to ration out to multiple people.

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