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  • Can I remove items from a ConcurrentDictionary from within an enumeration loop of that dictionary?

    - by the-locster
    So for example: ConcurrentDictionary<string,Payload> itemCache = GetItems(); foreach(KeyValuePair<string,Payload> kvPair in itemCache) { if(TestItemExpiry(kvPair.Value)) { // Remove expired item. Payload removedItem; itemCache.TryRemove(kvPair.Key, out removedItem); } } Obviously with an ordinary Dictionary this will throw an exception because removing items changes the dictionary's internal state during the life of the enumeration. It's my understanding that this is not the case for a ConcurrentDictionary as the provided IEnumerable handles internal state changing. Am I understanding this right? Is there a better pattern to use?

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  • What is the difference between an Abstract Syntax Tree and a Concrete Syntax Tree?

    - by Jason Baker
    I've been reading a bit about how interpreters/compilers work, and one area where I'm getting confused is the difference between an AST and a CST. My understanding is that the parser makes a CST, hands it to the semantic analyzer which turns it into an AST. However, my understanding is that the semantic analyzer simply ensures that rules are followed. I don't really understand why it would actually make any changes to make it abstract rather than concrete. Is there something that I'm missing about the semantic analyzer, or is the difference between an AST and CST somewhat artificial?

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  • How does the linux kernel manage less than 1GB physical memory ?

    - by TheLoneJoker
    I'm learning the linux kernel internals and while reading "Understanding Linux Kernel", quite a few memory related questions struck me. One of them is, how the Linux kernel handles the memory mapping if the physical memory of say only 512 MB is installed on my system. As I read, kernel maps 0(or 16) MB-896MB physical RAM into 0xC0000000 linear address and can directly address it. So, in the above described case where I only have 512 MB: How can the kernel map 896 MB from only 512 MB ? What about user mode processes in this situation? Where are user mode processes in phys RAM? Every article explains only the situation, when you've installed 4 GB of memory and the kernel maps the 1 GB into kernel space and user processes uses the remaining amount of RAM. I would appreciate any help in improving my understanding. Thanks..!

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  • MySQL index cardinality - performance vs storage efficiency

    - by Sean
    Say you have a MySQL 5.0 MyISAM table with 100 million rows, with one index (other than primary key) on two integer columns. From my admittedly poor understanding of B-tree structure, I believe that a lower cardinality means the storage efficiency of the index is better, because there are less parent nodes. Whereas a higher cardinality means less efficient storage, but faster read performance, because it has to navigate through less branches to get to whatever data it is looking for to narrow down the rows for the query. (Note - by "low" vs "high", I don't mean e.g. 1 million vs 99 million for a 100 million row table. I mean more like 90 million vs 95 million) Is my understanding correct? Related question - How does cardinality affect write performance?

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  • Continuous builds and Agile vs commit often

    - by Mark Underwood
    Hi All, I'm just doing some formal training in Agile at the moment and one question I have is about the value of Continuous Builds vs value of committing to the version control system often. My understanding with version control is that its better to commit often, because then you have history and the ability to go back to previous changes in a fine grained way. My understanding with Agile and continuous build is that its there to put pressure on the developers to always have working code. That to break the source tree is a taboo thing to do. Now i agree with both of these sentiments, but it occurs to be that sometimes these might be working against each other. You maybe in the middle of a largish code change and want to commit code to make sure you have history, but this will break the source tree. Anybody got any thoughts on this? Cheers Mark.

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  • using array_sum() in a while loop

    - by m477
    Hi folks, I'm learning PHP. Having trouble understanding why this piece of code isn't working. In particular: why is the result of array_sum($x) (1596) greater than $cap? Perhaps I'm not understanding the nature of while loops, but it seems to me (looking at a print_r($x)), the loop should cut out a step before it actually does. <?php function fibonacci_sum($cap = 1000){ list( $cur, $nxt, $seq ) = array( 0, 1, array() ); while ( array_sum($seq) < $cap ) { $seq[] = $cur; $add = $cur + $nxt; $cur = $nxt; $nxt = $add; } return $seq; } $x = fibonacci_sum(); echo array_sum($x); ?> Any insight is appreciated. Best, matt

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  • X-Domain and P3P Headers

    - by Jackson
    Hi, I have a website A.com and a domain at B.com with a widget inside an iframe getting data from A.com. I want to allow x-domain cookies to be passed from a.com to inside the iframe using ASP.NET My understanding is that - I can do this in IE using P3P Headers - such that the A.com cookie is passed to the iframe and session | cookie data is preserved. The P3P headers have to be sent from the A.com and from the iframe. Is this correct ? In dev, my understanding is if I "accept all cookies" in IE - then P3P headers won't matter anyway and so this should all just work. If I put on Medium Security then P3P is required.

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  • Spring/Hibernate/Junit example of testing DAO against HSQLDB

    - by Ryan P.
    Hi guys, I'm working on trying to implement a JUnit test to check the functionality of a DAO. (The DAO will create/read a basic object/table relationship in HSQLDB). The trouble I'm having is the persistence of the DAO (for the non-test code) is being completed through an in-house solution using Spring/Hibernate, which eliminates the usual *.hbm.xml templates that most examples I have found contain. Beacuse of this, I'm having some trouble understanding how to setup a JUnit test to implement the DAO to create/read (just very basic funtionality) to an in-memory HSQLDB. I have found a few examples, but the usage of the in-house persistence means I can't extend some of the classes the examples show (I can't seem to get the application-context.xml setup properly). Can anyone suggest any projects/examples I could take a look at (or any documentation) to further my understanding of the best way to implement this test functionality? I feel like this should be really simple, but I keep running into problems implementing the examples I have found. Thanks in advance!

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  • Some basic COM question...

    - by smwikipedia
    I have just finished my first COM server DLL. And it runs smoothly. So I'd like to show my understanding for now and hear your critics. 1- How COM simply works? COM - "The Call Chain" COM Lib methods - Traditional DLL exports - Classes encapsulated in the COM DLL 2- With C++, the benefits like "interface" in OOP can only be taken advantage of at the source level. With COM, these benefits can be used at a binary level. 3- Some illustration about interface &pInterface ------- pInterface ---------- Interface----------------- methods Ixx ** Ixx * (method table) (void **) A Interface is a data structure in memory. It's nothing but a memory area containg a method table. Is my understanding alright? Thanks for your revision.

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  • Using Parallel Extensions In Web Applications

    - by Greg
    I'd like to hear some opinions as to what role, if any, parallel computing approaches, including the potential use of the parallel extensions (June CTP for example), have a in web applications. What scenarios does this approach fit and/or not fit for? My understanding of how exactly IIS and web browsers thread tasks is fairly limited. I would appreciate some insight on that if someone out there has a good understanding. I'm more curious to know if the way that IIS and web browsers work limits the ROI of creating threaded and/or asynchronous tasks in web applications in general. Thanks in advance.

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  • Cucumber vs. built-in testing? [Rails]

    - by yuval
    I asked a question about different testing frameworks yesterday. This question can be found here. Now that I have a better understanding of the different frameworks, I have a very simple question: With a basic understanding, but very limited experience with writing tests with rails' built in testing framework (basic assertions), would it be okay for me to jump directly to testing with RSpec, Webrat, and Cucumber? Thank you! As a side note: yes, this is an opinion based question, but I feel that the input received to this question is valuable enough to the community to keep this question open. Thanks.

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  • BufferedImage Help

    - by Eddy Freeman
    I posted a question in sun java forums sometime ago and i am finding it hard to understand the first response i received from the replier though it seems he gave me the correct approach to my problem. The link to the question is: http://forums.sun.com/thread.jspa?threadID=5436562&tstart=0 Someone replied that i should use BufferedImage and make tiles. I don't really understand what the tiles mean in connection with the BufferedImage. I would like someone to explain to me what the tiles are and how they are created in the BufferedImage. I have searched the web for a while but couldn't find any link that can help me understanding the basics of the tiles and creating the tiles. Any pointer to a site is also appreciated. I need help in understanding the tiles in connection with the BufferedImage and also how they are created.

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  • Should Marketing departments have basic HTML skills?

    - by Phil.Wheeler
    Working within an organisation as part of the in-house site development team, a lot of my team's throughput is driven by the colouring-in (marketing) department. It is their responsibility to provide approved content and imagery for the features or enhancements that we include on each iteration of the company site. One thing I've noticed in this job and several previous ones is that the Marketing department is extremely particular about wording and presentation, but has little to no understanding of the actual medium with which they're working - the web. I find that my team is constantly making best guesses for various HTML attributes like image alt text, titles, rel tags, blockquote cite attributes and the like. How reasonable is it to expect that marketing departments have a strong understanding of the purpose of HTML metadata? Should it be the developer's job to remind and inform each time or are marketing departments falling behind the technology they're working with? What could I reasonably expect our marketing department to understand and provide every time with each new work request?

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  • What knowledge/expertize is required to port android to custom arm device ?

    - by Sunny
    Hi Friends, I am working on a system on which currently linux kernel and microwindows windowing system is running. Code of current linux system drivers is available to me. I want to port android on it, just as a hobby project. can you please tell me what all understanding of linux-kernel is required to port it? Please give me references (Books, Tutorials) to build-up understandings. Thanks, Sunny. P.S. I have basic understanding of linux. Configuration of device is 450 Mhz ARM9, 64 MB RAM, 256 MB NAND 480x272 resolution.

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  • How Do I create a synchronous version of NSURLConnection

    - by quinn
    I am using NSURLConnection inside of an NSIncrementalStore to synchronize my NSManagedObject with rest based web service built in Rails. I am aware of +sendSynchronousRequest:returningResponse:error but my understanding is that will not allow me to access such things as the HTTP response status code which I will need to properly handle the response, my understanding is sendSynchronousRequest returns the data if it responds in the 200 range and fails if it doesn't and doesn't really give you much more than that. I'm assuming I will somehow have to block the current method call after the NSURLConnection is instantiated and unblock it after NSURLConnection's delegate sets some value that can be returned by the blocked method. I'm assuming this will involve some combination of NSLock and NSThread but I really don't know where to start with this, any help will be greatly appreciated, thank you.

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  • Security & Authentication: SSL vs SASL

    - by 4herpsand7derpsago
    My understanding is that SSL combines an encryption algorithm (like AES, DES, etc.) with akey exchange method (like Diffier-Hellman) to provide secure encryption and identification services between two endpoints on an un-secure network (like the Internet). My understanding is that SASL is an MD5/Kerberos protocol that pretty much does the same thing. So my question: what are the pros/cons to choosing both and what scenarios make both more preferable? Basically, I'm looking for a guidelines to follow when choosing SSL or to go with SASL instead. Thanks in advance!

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  • Must a Language that Implements Monads be Statically Typed?

    - by Morgan Cheng
    I am learning functional programming style. From this link http://channel9.msdn.com/shows/Going+Deep/Brian-Beckman-Dont-fear-the-Monads/, Brian Beckman gave a brilliant introduction about Monad. He mentioned that Monad is about composition of functions so as to address complexity. A Monad includes a unit function that transfers type T to an amplified type M(T); and a Bind function that, given function from T to M(U), transforms type M(T) to another type M(U). (U can be T, but is not necessarily). In my understanding, the language implementing monad should be type-checked statically. Otherwise, type errors cannot be found during compilation and "Complexity" is not controlled. Is my understanding correct?

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  • Using lock(obj) inside a recursive call

    - by Amby
    As per my understanding a lock is not released until the runtime completes the code block of the lock(obj) ( because when the block completes it calls Monitor.Exit(obj). With this understanding i am not able to understand the reason behind the behaviour of the following code. private static string obj = ""; private static void RecurseSome(int number) { Console.WriteLine(number); lock (obj) { RecurseSome(++number); } } //Call: RecurseSome(0) //Output: 0 1 2 3...... stack overflow exception There must be some concept that i am missing. Please help.

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  • Are returned locals automatically xvalues

    - by mark
    Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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  • How To? Use an Expression Tree to call a Generic Method when the Type is only known at runtime.

    - by David Williams
    Please bear with me; I am very new to expression trees and lambda expressions, but trying to learn. This is something that I solved using reflection, but would like to see how to do it using expression trees. I have a generic function: private void DoSomeThing<T>( param object[] args ) { // Some work is done here. } that I need to call from else where in my class. Now, normally, this would be be simple: DoSomeThing<int>( blah ); but only if I know, at design time that I am working with an int. When I do not know the type until runtime is where I need the help. Like I said, I know how to do it via reflection, but I would like to do it via expression trees, as my (very limited) understanding is that I can do so. Any suggestions or points to sites where I can get this understanding, preferably with sample code?

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  • ChoiceFormat.setChoices confusion about format parameter type and documentation

    - by polygenelubricants
    From the java.text.ChoiceFormat API: setChoices(double[] limits, String[] formats): Set the choices to be used in formatting. Parameters: limits - contains [...] formats - are the formats you want to use for each limit. They can be either Format objects or Strings. When formatting with object Y, if the object is a NumberFormat, then ((NumberFormat) Y).format(X) is called. Otherwise Y.toString() is called. I'm having difficulties understanding the documentation for the formats parameter: how can you possibly pass a Format/NumberFormat object to setChoices if it's declared String[] formats? Note that interestingly, the getters counterpart of setChoices are declared as follows: double[] getLimits() Object[] getFormats() -- not String[]!!! Is this a bug in the API? Should the setter have been declared setChoices(double[], Object[]) instead, or am I not understanding how to use setChoices correctly?

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