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• Ubuntu 13.10 Unity doesn't load after upgrade

  - by William

  Just upgraded to Ubuntu 13.10 only to find that Unity won't load (login freezes, after doing ctrl+alt+F1, logging in and then doing startx, I get a blank desktop and the mouse pointer, and nothing else). I can right click, but the only operations that work are "create new file" and "create new folder". For example, "change desktop background" doesn't work. Also, after doing a few right clicks and choosing "change desktop background", I get a warning message box: "compiz closed unexpectedly." Guest login works fine. Tried creating a new user, but I experience the same thing with the new user. Tried removing all configuration files from my home directory... same thing. Doing dconf reset -f /org/compiz/ gives an error "error spawning command line..." Doing unity --reset also gives errors. Tried uninstalling unity (and compiz) and reinstalling, but that doesn't help. Tried reconfiguring lightdm, didn't help. I don't have any proprietary drivers installed. Once again, the funny thing is that the guest session works fine.

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• Are these advanced/unfair interview questions regarding Java concurrency?

  - by sparc_spread

  Here are some questions I've recently asked interviewees who say they know Java concurrency: Explain the hazard of "memory visibility" - the way the JVM can reorder certain operations on variables that are unprotected by a monitor and not declared volatile, such that one thread may not see the changes made by another thread. Usually I ask this one by showing code where this hazard is present (e.g. the NoVisibility example in Listing 3.1 from "Java Concurrency in Practice" by Goetz et al) and asking what is wrong. Explain how volatile affects not just the actual variable declared volatile, but also any changes to variables made by a thread before it changes the volatile variable. Why might you use volatile instead of synchronized? Implement a condition variable with wait() and notifyAll(). Explain why you should use notifyAll(). Explain why the condition variable should be tested with a while loop. My question is - are these appropriate or too advanced to ask someone who says they know Java concurrency? And while we're at it, do you think that someone working in Java concurrency should be expected to have an above-average knowledge of Java garbage collection?

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• How do I throttle a command in a terminal window?

  - by To Do

  I needed to run convert with a lot of images at the same time. The command took quite a while but this doesn't bother me. The issue is that this command rendered my computer unusable while the command was running (for about 15 minutes). So is it possible to throttle the command by limiting resources (processor and memory) to the command, directly from the command line? This can only work if I add something to the same line before pressing Enter because once I start the process the computer slows so much that it is impossible for example to switch to "System monitor" and reduce priority. Edit: top and iotop results I managed to run top and sudo iotop >iotop.txt while doing one of these convert operations. (The iotop.txt file produced is difficult to read) Results of top: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 14275 username 20 0 4043m 3.0g 1448 D 7.0 80.4 0:16.45 convert Results of iotop: [?1049h[1;24r(B[m[4l[?7h[?1h=[39;49m[?25l[39;49m(B[m[H[2JTotal DISK READ: 1269.04 K/s | Total DISK WRITE:[59G0.00 B/s (B[0;7m TID PRIO USER DISK READ DISK WRITE SWAPIN(B[0;1;7m IO(B[0;7m COMMAND [3;2H(B[m2516 be/4 username 350.08 K/s 0.00 B/s 0.00 % 0.00 % zeitgeist-datahub 7394 be/4 username 568.88 K/s 0.00 B/s 77.41 % 0.00 % --rendere~.530483991[5;1H14275 idle username 350.08 K/s 0.00 B/s 37.49 % 0.00 % convert S~f test.pdf[6;2H2048 be/4 root[6;24H0.00 B/s 0.00 B/s 0.00 % 0.00 % [kworker/3:2] [5G1 be/4 root[7;24H0.00 B/s 0.00 B/s 0.00 % 0.00 % init Furthermore, even after the process ends, the computer does not return to the previous performance. I found a way around this by running sudo swapoff -a followed by sudo swapon -a

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• TXPAUSE : polite waiting for hardware transactional memory

  - by Dave

  Classic locks are an appropriate tool to prevent potentially conflicting operations A and B, invoked by different threads, from running at the same time. In a sense the locks cause either A to run before B or vice-versa. Similarly, we can replace the locks with hardware transactional memory, or use transactional lock elision to leverage potential disjoint access parallelism between A and B. But often we want A to wait until B has run. In a Pthreads environment we'd usually use locks in conjunction with condition variables to implement our "wait until" constraint. MONITOR-MWAIT is another way to wait for a memory location to change, but it only allows us to track one cache line and it's only available on x86. There's no similar "wait until" construct for hardware transactions. At the instruction-set level a simple way to express "wait until" in transactions would be to add a new TXPAUSE instruction that could be used within an active hardware transaction. TXPAUSE would politely stall the invoking thread, possibly surrendering or yielding compute resources, while at the same time continuing to track the transaction's address-set. Once a transaction has executed TXPAUSE it can only abort. Ideally that'd happen when some other thread modifies a variable that's in the transaction's read-set or write-set. And since we're aborting all writes would be discarded. In a sense this gives us multi-location MWAIT but with much more flexibility. We could also augment the TXPAUSE with a cycle-count bound to cap the time spent stalled. I should note that we can already enter a tight spin loop in a transaction to wait for updates to address-set to cause an abort. Assuming that the implementation monitors the address-set via cache-coherence probes, by waiting in this fashion we actually communicate via the probes, and not via memory values. That is the updating thread signals the waiter via probes instead of by traditional memory values. But TXPAUSE gives us a polite way to spin.

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• Beginners guide to developing optimization software

  - by Florenc

  I am novice in "serious" programming i.e. applications that deal with real-life applications and software projects that go beyond school assignments. My interests include optimization, operations research, algorithms and lately i discovered how much I do like software design/development/engineering. I have already developed some simple desktop applications for some "famous" problems like TSP using heuristc approaches, a VRP solver (in progress) and so on. While developing this kind of software I actually used basic concepts taught at school such as object-orientation analysis and design. But, I found these courses rather elementary and quite boring (for my expectations). So I decided to go a little further and start developing "real" software (and this is where I realized how important and interesting software engineering/design is.) Now, here's my issue: I can not find a "study guide" for developing software of this kind. Currently, there are numerous resources out there (books, websites, tutorials) in designing and developing complex IS, web applications, smartphone apps but I can't find a book for example entitled "optimization software development". Definetly, someone could claim that "design patterns apply to software in general" but that's not my point. My point is that I could simply use my imagination for "simple" implementations, but what happens, when my imagination can not go further? In other words I'm looking for a guide/path to bridge the gap between: Mathematics-Algorithm Design-Software Engineering-Optimization-Software development

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• Why is apt-cache so slow?

  - by Damn Terminal

  After upgrade to Trusty (14.04) from Saucy (13.10), all apt operations are very slow. Even those that do not include downloading anything, or connecting to any servers. For example, displaying the apt policy # time apt-cache policy [...] real 0m8.951s user 0m5.069s sys 0m3.861s takes almost ten seconds! Mostly a weird lag right after issuing the command. And it's the same even if I issue the same command again. On another system it doesn't take a tenth of a second real 0m0.096s user 0m0.070s sys 0m0.023s The other system is a little beefier but there was no noticeable difference before the upgrade. It's the same with apt-get, anything apt-related. How do I find out the source of this lag and fix it? Additional info: # cat /etc/nsswitch.conf # /etc/nsswitch.conf # # Example configuration of GNU Name Service Switch functionality. # If you have the `glibc-doc-reference' and `info' packages installed, try: # `info libc "Name Service Switch"' for information about this file. passwd: compat group: compat shadow: compat hosts: files dns networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis BTW is my understanding of how apt-cache works correct? It doesn't make any network connections when I run apt-cache policy, right? In case I'm wrong and it matters, here are my sources https://gist.github.com/anonymous/02920270ff68e23fc3ec

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• Live Webcast: Discover Primavera Unifier - December 5th

  - by Melissa Centurio Lopes

  Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Join our live webcast to see what Primavera Unifier can do for you and your organization. We are very excited to introduce you to the newest addition to the Primavera product family, Primavera Unifier (formerly known as Skire Unifier). Attend this webcast and learn why this new cloud-based solution is the most comprehensive Enterprise Project Portfolio Management (EPPM) offering to manage the complete project lifecycle, from capital planning and construction to operations and maintenance. Save your seat: Register today for this online event and learn how the addition of Primavera Unifier can help your organization manage their projects and facilities with more predictability and financial control, improving profitability and operational efficiency

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• Name of the Countdown Numbers round problem - and algorithmic solutions?

  - by Dai

  For the non-Brits in the audience, there's a segment of a daytime game-show where contestants have a set of 6 numbers and a randomly generated target number. They have to reach the target number using any (but not necessarily all) of the 6 numbers using only arithmetic operators. All calculations must result in positive integers. An example: Youtube: Countdown - The Most Extraordinary Numbers Game Ever? A detailed description is given on Wikipedia: Countdown (Game Show) For example: The contentant selects 6 numbers - two large (possibilities include 25, 50, 75, 100) and four small (numbers 1 .. 10, each included twice in the pool). The numbers picked are 75, 50, 2, 3, 8, 7 are given with a target number of 812. One attempt is (75 + 50 - 8) * 7 - (3 * 2) = 813 (This scores 7 points for a solution within 5 of the target) An exact answer would be (50 + 8) * 7 * 2 = 812 (This would have scored 10 points exactly matching the target). Obviously this problem has existed before the advent of TV, but the Wikipedia article doesn't give it a name. I've also saw this game at a primary school I attended where the game was called "Crypto" as an inter-class competition - but searching for it now reveals nothing. I took part in it a few times and my dad wrote an Excel spreadsheet that attempted to brute-force the problem, I don't remember how it worked (only that it didn't work, what with Excel's 65535 row limit), but surely there must be an algorithmic solution for the problem. Maybe there's a solution that works the way human cognition does (e.g. in-parallel to find numbers 'close enough', then taking candidates and performing 'smaller' operations).

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• Anemic Domain Model, Business Logic and DataMapper (PHP)

  - by sunwukung

  I've implemented a rudimentary ORM layer based on DataMapper (I don't want to use a full blown ORM like Propel/Doctrine - for anything beyond simple fetch/save ops I prefer to access the data directly layer using a SQL abstraction layer). Following the DataMapper pattern, I've endeavoured to keep all persistence operations in the Mapper - including the location of related entities. My Entities have access to their Mapper, although I try not to call Mapper logic from the Entity interface (although this would be simple enough). The result is: // get a mapper and produce an entity $ProductMapper = $di->get('product_mapper'); $Product = $ProductMapper->find('[email protected]','email'); //.. mutaute some values.. save $ProductMapper->save($Product) // uses __get to trigger relation acquisition $Manufacturer = $Product->manufacturer; I've read some articles regarding the concept of an Anemic Domain model, i.e. a Model that does not contain any "business logic". When demonstrating the sort of business logic ideally suited to a Domain Model, however, acquiring related data items is a common example. Therefore I wanted to ask this question: Is persistence logic appropriate in Domain Model objects?

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• Using visitor pattern with large object hierarchy

  - by T. Fabre

  Context I've been using with a hierarchy of objects (an expression tree) a "pseudo" visitor pattern (pseudo, as in it does not use double dispatch) : public interface MyInterface { void Accept(SomeClass operationClass); } public class MyImpl : MyInterface { public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } } This design was, however questionnable, pretty comfortable since the number of implementations of MyInterface is significant (~50 or more) and I didn't need to add extra operations. Each implementation is unique (it's a different expression or operator), and some are composites (ie, operator nodes that will contain other operator/leaf nodes). Traversal is currently performed by calling the Accept operation on the root node of the tree, which in turns calls Accept on each of its child nodes, which in turn... and so on... But the time has come where I need to add a new operation, such as pretty printing : public class MyImpl : MyInterface { // Property does not come from MyInterface public string SomeProperty { get; set; } public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } public void Accept(SomePrettyPrinter printer) { printer.PrettyPrint(this.SomeProperty); } } I basically see two options : Keep the same design, adding a new method for my operation to each derived class, at the expense of maintainibility (not an option, IMHO) Use the "true" Visitor pattern, at the expense of extensibility (not an option, as I expect to have more implementations coming along the way...), with about 50+ overloads of the Visit method, each one matching a specific implementation ? Question Would you recommand using the Visitor pattern ? Is there any other pattern that could help solve this issue ?

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• String manipulation functions in SQL Server 2000 / 2005

  - by Vipin

  SQL Server provides a range of string manipulation functions. I was aware of most of those in back of the mind, but when I needed to use one, I had to dig it out either from SQL server help file or from google. So, I thought I will list some of the functions which performs some common operations in SQL server. Hope it will be helpful to you all. Len (' String_Expression' ) - returns the length of input String_Expression. Example - Select Len('Vipin') Output - 5 Left ( 'String_Expression', int_characters ) - returns int_characters characters from the left of the String_Expression.     Example - Select Left('Vipin',3), Right('Vipin',3) Output -  Vip,  Pin  LTrim ( 'String_Expression' ) - removes spaces from left of the input 'String_Expression'  RTrim ( 'String_Expression' ) - removes spaces from right of the input 'String_Expression' Note - To removes spaces from both ends of the string_expression use Ltrim and RTrim in conjunction Example - Select LTrim(' Vipin '), RTrim(' Vipin ') , LTrim ( RTrim(' Vipin ')) Output - 'Vipin ' , ' Vipin' , 'Vipin' (Single quote marks ' ' are not part of the SQL output, it's just been included to demonstrate the presence of space at the end of string.) Substring ( 'String_Expression' , int_start , int_length ) - this function returns the part of string_expression. Right ( 'String_Expression', int_characters ) - returns int_characters characters from the right of the String_Expression.

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• Is ZeroMQ a good choice to make a Python app and a C# managed assembly work together?

  - by Alex Bausk

  I have a task that involves talking to a .NET-based API (namely AutoCAD) to retrieve data, send commands, and react to events. I want to separate the API operations and the proper program logic (largely already implemented in Python) by using natural tools for both: a C# DLL for the former and a Python app for the latter. To connect these two pieces, I began exchanging JSON in ZeroMQ messages. I'm at early development stages but having recently discovered that ZeroMQ does not guarantee message delivery/order, I have reservations about whether this is a feasible way to go. Right now my app is a very basic REQ/REP pair and I plan to handle reacting to events and executing different commands by adding some sort of 'recipient-function' field to my message format. The reason that I want to use ZMQ is that I might be able to scale the software into a larger, multi-user, distributed solution sometime. I am a lay programmer so I would ask for your advice about this architecture. Should I just go ahead with it and plan to deal with message reliability/ordering when problems appear? Should I consider developing some kind of a REST wrapper around ZMQ?

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• Generic rule parser for RPG board game rules - how to do it?

  - by burzum

  I want to build a generic rule parser for pen and paper style RPG systems. A rule can involve usually 1 to N entities 1 to N roles of a dice and calculating values based on multiple attributes of an entity. For example: Player has STR 18, his currently equipped weapon gives him a bonus of +1 STR but a malus of DEX -1. He attacks a monster entity and the game logic now is required to run a set of rules or actions: Player rolls the dice, if he gets for example 8 or more (base attack value he needs to pass is one of his base attributes!) his attack is successfully. The monster then rolls the dice to calculate if the attack goes through it's armor. If yes the damage is taken if not the attack was blocked. Besides simple math rules can also have constraints like applying only to a certain class of user (warrior vs wizzard for example) or any other attribute. So this is not just limited to mathematical operations. If you're familiar with RPG systems like Dungeon and Dragons you'll know what I'm up to. My issue is now that I have no clue how to exactly build this the best possible way. I want people to be able to set up any kind of rule and later simply do an action like selecting a player and a monster and run an action (set of rules like an attack). I'm asking less for help with the database side of things but more about how to come up with a structure and a parser for it to keep my rules flexible. The language of choice for this is php by the way.

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• Debugger for file I/O development?

  - by datenwolf

  Okay, the question title may be a bit cryptic. But it aptly describes what I'm looking for: I think every experienced coder went through this numerous times: You get a binary file format specification, you implement the reader for it, and… nothing works like expected. So you run your code in the debugger, go execute through the code line by line, every header field is read in seemingly correct, but when it comes to the bulk data, offset and indices no longer match up. What would really help in this situation was a binary file viewer, that shows you the progress of your file pointer, as you step through the code, and ideally would also highlight all memory maps. Then you could see the context of the current I/O operations, most notably those darn "off-by-one" mistakes, which are even more annoying when reading a file. Implementing such a debugger should not be too hard. traces on the process' file descriptors/handles and triggers on the I/O functions, to update the display. Only: I don't know of such a kind of debugger to exist. Do I just lack knowledge about the existance of such a tool, or is there really no such thing?

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• How to handle monetary values in PHP and MySql?

  - by Songo

  I've inherited a huge pile of legacy code written in PHP on top of a MySQL database. The thing I noticed is that the application uses doubles for storage and manipulation of data. Now I came across of numerous posts mentioning how double are not suited for monetary operations because of the rounding errors. However, I have yet to come across a complete solution to how monetary values should be handled in PHP code and stored in a MySQL database. Is there a best practice when it comes to handling money specifically in PHP? Things I'm looking for are: How should the data be stored in the database? column type? size? How should the data be handling in normal addition, subtraction. multiplication or division? When should I round the values? How much rounding is acceptable if any? Is there a difference between handling large monetary values and low ones? Note: A VERY simplified sample code of how I might encounter money values in everyday life: $a= $_POST['price_in_dollars']; //-->(ex: 25.06) will be read as a string should it be cast to double? $b= $_POST['discount_rate'];//-->(ex: 0.35) value will always be less than 1 $valueToBeStored= $a * $b; //--> any hint here is welcomed $valueFromDatabase= $row['price']; //--> price column in database could be double, decimal,...etc. $priceToPrint=$valueFromDatabase * 0.25; //again cast needed or not? I hope you use this sample code as a means to bring out more use cases and not to take it literally of course. Bonus Question If I'm to use an ORM such as Doctrine or PROPEL, how different will it be to use money in my code.

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• How to represent a graph with multiple edges allowed between nodes and edges that can selectively disappear

  - by Pops

  I'm trying to figure out what sort of data structure to use for modeling some hypothetical, idealized network usage. In my scenario, a number of users who are hostile to each other are all trying to form networks of computers where all potential connections are known. The computers that one user needs to connect may not be the same as the ones another user needs to connect, though; user 1 might need to connect computers A, B and D while user 2 might need to connect computers B, C and E. Image generated with the help of NCTM Graph Creator I think the core of this is going to be an undirected cyclic graph, with nodes representing computers and edges representing Ethernet cables. However, due to the nature of the scenario, there are a few uncommon features that rule out adjacency lists and adjacency matrices (at least, without non-trivial modifications): edges can become restricted-use; that is, if one user acquires a given network connection, no other user may use that connection in the example, the green user cannot possibly connect to computer A, but the red user has connected B to E despite not having a direct link between them in some cases, a given pair of nodes will be connected by more than one edge in the example, there are two independent cables running from D to E, so the green and blue users were both able to connect those machines directly; however, red can no longer make such a connection if two computers are connected by more than one cable, each user may own no more than one of those cables I'll need to do several operations on this graph, such as: determining whether any particular pair of computers is connected for a given user identifying the optimal path for a given user to connect target computers identifying the highest-latency computer connection for a given user (i.e. longest path without branching) My first thought was to simply create a collection of all of the edges, but that's terrible for searching. The best thing I can think to do now is to modify an adjacency list so that each item in the list contains not only the edge length but also its cost and current owner. Is this a sensible approach? Assuming space is not a concern, would it be reasonable to create multiple copies of the graph (one for each user) rather than a single graph?

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• Data Synchronization in mobile apps - multiple devices, multiple users

  - by ProgrammerNewbie

  I'm looking into building my first mobile app. One of the core features of the application is that multiple devices/users will have access to the same data -- and all of them will have CRUD rights. I believe the architecture should involve a central server where all the data is stored. The devices will use an API to interact with the server to perform its data operations (e.g. adding a record, editing a record, deleting a record). I imagine a scenario where synchronizing the data will become a problem. Assume the application should work when it is not connected to the Internet, and thus cannot communicate with this central server. So: User A is offline and edits record #100 User B is offline and edits record #100 User C is offline and deletes record #100 User C goes online (presumably, record #100 should get deleted on the server) User A and B goes online, but the records they edited no longer exist All sorts of scenarios similar to the above can come up. How is this generally handled? I plan to use MySQL, but am wondering if it's not appropriate for such a problem.

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• Oracle Solaris 11.1 available today

  - by user12611852

  Today Oracle is pleased to announce availability of Oracle Solaris 11.1. Download Solaris 11.1 Order Solaris 11.1 media kitExisting customers can quickly and simply update using the network based repository Highlights include: 8x faster database startup and shutdown and online resizing of the database SGA with a new optimized shared memory interface between the database and Oracle Solaris 11.1 Up to 20% throughput increases for Oracle Real Application Clusters by offloading lock management into the Oracle Solaris kernel Expanded support for Software Defined Networks (SDN) with Edge Virtual Bridging enhancements to maximize network resource utilization and manage bandwidth in cloud environments 4x faster Solaris Zone updates with parallel operations shorten maintenance windows New built-in memory predictor monitors application memory use and provides optimized memory page sizes and resource location to speed overall application performance. Learn more and share these valuable tools with your customers to enable them to move to Oracle Solaris 11.1 quickly. Many customers wait for the first update --now is the time to encourage them to install Oracle Solaris 11.1. Oracle Solaris 11.1 Data Sheet  What's New in Oracle Solaris 11.1 Oracle Solaris 11.1 FAQs Oracle Solaris 11 .1 Customer Presentation Oracle Solaris 11.1 is recommended for all SPARC T4 Systems and will soon be available preinstalled.

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• [EF + Oracle]Object Context

  - by JTorrecilla

  Prologue After EF episodes I and II, we are going to see the Object Context. What is Object Context? It is a class which manages the DB connection, and the different Entities of our model. When Visual Studio creates the EF model, like I explain previously, also generates a Class that extends ObjectContext. ObjectContext provides: - DB connection - Add, update and delete functions. - Object Sets of Entities. - State of Pending Changes. This class will give a function, for each Entity, like  Esta clase va a contar con una función, para cada entidad, del tipo “AddTo{ENTITY}({Entity_Type } value)”, which are going to add a Entity to the related ObjectSet. In addition, it has a property, for each Entity, like “ObjectSet<TEntity> Entity”, does will keep the related record set. It will be filled with the CreateObjectSet<TEntity> function of Base class (ObjectContext). What is an ObjectSet? It is a class that allows us to manage the Entity Set from a Type. It inherits from: · ObjectQuery<TEntity> · IObjectSet<TEntity> · IQueryAble<TEntity · IEnumerable<TEntity · IQueryAble · IEnumerable An ObjectSet is a class property that allows query, insert, delete and update records from a determinate Entity. In following chapters we will see how to query Entities. LazyLoadingEnabled A very important property of the Context is “LazyLoadingEnabled”. This Boolean property lets indicate if the data loading is lazy, in other words, the Object will not be created and query until not be needed. Finally In this post we have seen what the VS generated context is, some of the characteristics, and where to see Entity data. In next chapters we will see, CRUD operations, and how to query ObjectSets.

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• How much overhead is there in persistent connections?

  - by nynex

  Ok so I'm musing over a little side project I want to start. Essentially its a multi-session web based FTP client. Multi-session in that you can log into several FTP servers at the same time and perform operations like moving a file from one FTP server to another. I'm doing this mainly to brush up on the new webdev technologies, particularly websockets. I'm using node.js + socket.io to keep a persistent bi-directional connection between the web browser and the web server. The web server will also have persistent connections to each FTP server the user has logged into. So if there are 100 concurrent users each logged into 5 ftp accounts, the web server will have 100 websocket connections + 500 ftp connections. Is servicing 600 connections a lot? I know it depends on the hardware resources of the server but is something like this doable on a budget? Are there more efficient means of doing something like this? I know its unlikely that this project will really get popular but I want it to scale well regardless. Thanks for any help, I've still got a lot to learn.

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• Unit testing to prove balanced tree

  - by Darrel Hoffman

  I've just built a self-balancing tree (red-black) in Java (language should be irrelevant for this question though), and I'm trying to come up with a good means of testing that it's properly balanced. I've tested all the basic tree operations, but I can't think of a way to test that it is indeed well and truly balanced. I've tried inserting a large dictionary of words, both pre-sorted and un-sorted. With a balanced tree, those should take roughly the same amount of time, but an unbalanced tree would take significantly longer on the already-sorted list. But I don't know how to go about testing for that in any reasonable, reproducible way. (I've tried doing millisecond tests on these, but there's no noticeable difference - probably because my source data is too small.) Is there a better way to be sure that the tree is really balanced? Say, by looking at the tree after it's created and seeing how deep it goes? (That is, without modifying the tree itself by adding a depth field to each node, which is just wasteful if you don't need it for anything other than testing.)

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• FP for simulation and modelling

  - by heaptobesquare

  I'm about to start a simulation/modelling project. I already know that OOP is used for this kind of projects. However, studying Haskell made me consider using the FP paradigm for modelling a system of components. Let me elaborate: Let's say I have a component of type A, characterised by a set of data (a parameter like temperature or pressure,a PDE and some boundary conditions,etc.) and a component of type B, characterised by a different set of data(different or same parameter, different PDE and boundary conditions). Let's also assume that the functions/methods that are going to be applied on each component are the same (a Galerkin method for example). If I were to use an OOP approach, I would create two objects that would encapsulate each type's data, the methods for solving the PDE(inheritance would be used here for code reuse) and the solution to the PDE. On the other hand, if I were to use an FP approach, each component would be broken down to data parts and the functions that would act upon the data in order to get the solution for the PDE. This approach seems simpler to me assuming that linear operations on data would be trivial and that the parameters are constant. What if the parameters are not constant(for example, temperature increases suddenly and therefore cannot be immutable)? In OOP, the object's (mutable) state can be used. I know that Haskell has Monads for that. To conclude, would implementing the FP approach be actually simpler,less time consuming and easier to manage (add a different type of component or new method to solve the pde) compared to the OOP one? I come from a C++/Fortran background, plus I'm not a professional programmer, so correct me on anything that I've got wrong.

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• I'm a Subversion geek, why should I consider or not consider Mercurial or Git or any other DVCS?

  - by user2567

  I try to understand the benefits of distributed version control system (DVCS). I found Subversion Re-education and this article by Martin Fowler very useful. Mercurial and others DVCS promote a new way of working on code with changesets and local commits. It prevents from merging hell and other collaboration issues We are not affected by this as I practice continuous integration and working alone in a private branch is not an option, unless we are experimenting. We use a branch for every major version, in which we fix bugs merged from the trunk. Mercurial allows you to have lieutenants I understand this can be useful for very large projects like Linux, but I don't see the value in small and highly collaborative teams (5 to 7 people). Mercurial is faster, takes less disk space and full local copy allows faster logs & diffs operations. I'm not concerned by this either, as I didn't notice speed or space problems with SVN even with very large projects I'm working on. I'm seeking for your personal experiences and/or opinions from former SVN geeks. Especially regarding the changesets concept and overall performance boost you measured. UPDATE (12th Jan): I'm now convinced that it worth a try. UPDATE (12th Jun): I kissed Mercurial and I liked it. The taste of his cherry local commits. I kissed Mercurial just to try it. I hope my SVN Server don't mind it. It felt so wrong. It felt so right. Don't mean I'm in love tonight. FINAL UPDATE (29th Jul): I had the privilege to review Eric Sink's next book called Version Control by Example. He finished to convince me. I'll go for Mercurial.

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• Is there a simple, flat, XML-based query-able data storage solution? [closed]

  - by alex gray

  I have been in long pursuit of an XML-based query-able data store, and despite continued searches and evaluations, I have yet to find a solution that meets the my needs, which include: Data is wholly contained within XML nodes, in flat text files. There is a "native" - or at least unobtrusive - method with which to perform Create/Read/Update/Delete (CRUD) operations onto the "schema". I would consider access via http, XHR, javascript, PHP, BASH, or PERL to be unobtrusive, dependent on the complexity of the set of dependencies. Server-side file-system reads and writes. A client-side interface element, accessible in any browser without a plug-in. Some extra, preferred (but optional) requirements include: Respond to simple SQL, or similarly syntax queries. Serve the data on a bare bones https server, with no "extra stuff", either via XMLHTTPRequest, HTTP proper, or JSON. A few thoughts: What I'm looking for may be possible via some Java server implementations, but for the sake of this question, please do not suggest that - unless it meets ALL the requirements. Java, especially on the client-side is not really an option, nor is it appealing from a development viewpoint.* I know walking the filesystem is a stretch, and I've heard it's possible with XPATH or XSLT, but as far as I know, that's not ready for primetime, nor even yet a recommendation. However the ability to recursively traverse the filesystem is needed for such a system to be of useful facility. At this point, I have basically implemented what I described via, of all things, CGI and Bash, but there has to be an easier way. Thoughts?

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• 724% Return on an SFA project with Oracle Sales Cloud and Marketing Cloud combined!

  - by Richard Lefebvre

  Oracle Sales Cloud and Marketing Cloud customer Apex IT gained just that?a 724% return on investment (ROI) when it implemented these Oracle Cloud solutions in its fast-moving, rapidly-growing business. Apex IT was just announced as a winner of the Nucleus Research 11th annual Technology ROI Awards. The award, given by the analyst firm, highlights organizations that have successfully leveraged IT deployments to maximize value per dollar spent. Fast Facts: Return on Investment – 724% Payback – 2 months Average annual benefit – $91,534 Cost : Benefit Ratio – 1:48 Business Benefits In addition to the ROI and cost metrics the award calls out improvements in Apex IT’s business operations—across both Sales and Marketing teams: Improved ability to identify new opportunities and focus sales resources on higher-probability deals Reduced administration and manual lead tracking—resulting in more time selling and a net new client increase of 46% Increased campaign productivity for both Marketing and Sales, including Oracle Marketing Cloud’s automation of campaign tracking and nurture programs Improved margins with more structured and disciplined sales processes—resulting in more effective deal negotiations Read the full Apex IT ROI Case Study. You also can learn more about Apex IT’s business, including the company’s work with Oracle Sales and Marketing Cloud on behalf of its clients. You can point your prospects and customers to the CX blog for a similar recap of the Apex IT award and a link to the Case Study.

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