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• How to re-add RAID-10 dropped drive?

  - by thiesdiggity

  I have a problem that I can't seem to solve. We have a Ubuntu server setup with RAID-10 and two of the drives dropped out of the array. When I try to re-add them using the following command: mdadm --manage --re-add /dev/md2 /dev/sdc1 I get the following error message: mdadm: Cannot open /dev/sdc1: Device or resource busy When I do a "cat /proc/mdstat" I get the following: Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [r$ md2 : active raid10 sdb1[0] sdd1[3] 1953519872 blocks 64K chunks 2 near-copies [4/2] [U__U] md1 : active raid1 sda2[0] sdc2[1] 468853696 blocks [2/2] [UU] md0 : active raid1 sda1[0] sdc1[1] 19530688 blocks [2/2] [UU] unused devices: <none> When I run "/sbin/mdadm --detail /dev/md2" I get the following: /dev/md2: Version : 00.90 Creation Time : Mon Sep 5 23:41:13 2011 Raid Level : raid10 Array Size : 1953519872 (1863.02 GiB 2000.40 GB) Used Dev Size : 976759936 (931.51 GiB 1000.20 GB) Raid Devices : 4 Total Devices : 2 Preferred Minor : 2 Persistence : Superblock is persistent Update Time : Thu Oct 25 09:25:08 2012 State : active, degraded Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Layout : near=2, far=1 Chunk Size : 64K UUID : c6d87d27:aeefcb2e:d4453e2e:0b7266cb Events : 0.6688691 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 0 0 1 removed 2 0 0 2 removed 3 8 49 3 active sync /dev/sdd1 Output of df -h is: Filesystem Size Used Avail Use% Mounted on /dev/md1 441G 2.0G 416G 1% / none 32G 236K 32G 1% /dev tmpfs 32G 0 32G 0% /dev/shm none 32G 112K 32G 1% /var/run none 32G 0 32G 0% /var/lock none 32G 0 32G 0% /lib/init/rw tmpfs 64G 215M 63G 1% /mnt/vmware none 441G 2.0G 416G 1% /var/lib/ureadahead/debugfs /dev/mapper/RAID10VG-RAID10LV 1.8T 139G 1.6T 8% /mnt/RAID10 When I do a "fdisk -l" I can see all the drives needed for the RAID-10. The RAID-10 is part of the /dev/mapper, could that be the reason why the device is coming back as busy? Anyone have any suggestions on what I can try to get the drives back into the array? Any help would be greatly appreciated. Thanks!

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• PostgreSQL RAID configuration

  - by Yoldar-Zi

  I'm stuck how best to configure disk array. We have Hp P2000 G3 disk array with 24 SAS physical disks 300Gb each. We need to configure this array got 2 copies of PostgreSQL 9.2 because two different system. As we know it's recommended to store database and transaction logs(pg_xlog) files on separate disks. So we must setup 4 logical disk: 2 for transaction logs with RAID 1 2 for database with RAID 10 Is this right scheme of distribution? Or may be it is best to just make one big RAID 10 with 4 logical disks?

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• Knowing state of game in real time

  - by evthim

  I'm trying to code a tic tac toe game in java and I need help figuring out how to efficiently and without freezing the program check if someone won the game. I'm only in the design stages now, I haven't started programming anything but I'm wondering how would I know at all times the state of the game and exactly when someone wins? Response to MarkR: (note: had to place comment here, it was too long for comment section) It's not a homework problem, I'm trying to get more practice programming GUI's which I've only done once as a freshman in my second introductory programming course. I understand I'll have a 2D array. I plan to have a 2D integer array where x would equal 1 and o would equal 0. However, won't it take too much time if I check after every move if someone won the game? Is there a way or a data structure or algorithm I can use so that the program will know the state (when I say state I mean not just knowing every position on the board, the int array will take care of that, I mean knowing that user 1 will win if he places x on this block) of the game at all times and thus can know automatically when someone won?

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• Cube chunk via list ToArray()

  - by Christian Frantz

  I've created a list of vertices that I call for each cube made in my array "cubes". When each cube is create, SetUpVertices is called which is a method that stores the 8 vertices of my cube. At the end of my list creation, I create a vertex buffer, and set the data of the list that contains vertices of all 25 cubes to that vertex buffer, effectively creating a "chunk" of cubes. The problem is that Invalid Operation Exception "The array is not the correct size for the amount of data requested." at the line vertices.ToArray(). I don't have an array for this, as the amount of cubes will be changing and arrays aren't dynamic. What could be the cause of this? for (int x = 0; x < 5; x++) { for (int z = 0; z < 5; z++) { SetUpVertices(); cubes.Add(new Cube(device, new Vector3(x, map[x, z], z), color)); } } vertexBuffer = new VertexBuffer(device, typeof(VertexPositionColor), 8, BufferUsage.WriteOnly); vertexBuffer.SetData<VertexPositionColor>(vertices.ToArray());

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• Unnamed Refactoring

  - by Liam McLennan

  This post is a message in a bottle. It cast it into the sea in the hope that it will one day return to me, stuffed to the cork with enlightenment. Yesterday I  tweeted, what is the name of the pattern where you replace a multi-way conditional with an associative array? I said ‘pattern’ but I meant ‘refactoring’. Anyway, no one replied so I will describe the refactoring here. Programmers tend to think imperatively, which leads to code such as: public int GetPopulation(string country) { if (country == "Australia") { return 22360793; } else if (country == "China") { return 1324655000; } else if (country == "Switzerland") { return 7782900; } else { throw new Exception("What ain't no country I ever heard of. They speak English in what?"); } } which is horrid. We can write a cleaner version, replacing the multi-way conditional with an associative array, treating the conditional as data: public int GetPopulation(string country) { if (!Populations.ContainsKey(country)) throw new Exception("The population of " + country + " could not be found."); return Populations[country]; } private Dictionary<string, int> Populations { get { return new Dictionary<string, int> { {"Australia", 22360793}, {"China", 1324655000}, {"Switzerland", 7782900} }; } } Does this refactoring already have a name? Otherwise, I propose Replace multi-way conditional with associative array

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• misaligned raid partition in Ubuntu 10.04

  - by Linux Jedi

  I attached two identical hard drives to my linux machine. Then using gparted I formated the first 1024 mb at the beginning of each drive as linux swap space. Then I went into system-administration-disk utility. In there I went to file-create-RAID array. I selected the remaining space in each of the two identical hard drives and created a striped raid array. After the array was created, a warning message appeared. It said "The partition is misaligned by 522240 bytes. This may result in very poor performance. Repartitioning is suggested." What do I do now? As far as I can tell, the partitions are identical.

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• Expanding RAID-5

  - by Garry

  I'm new to RAID and trying to get my head around things. I have owned a Drobo in the past (which I liked) but it failed. Here's a hypothetical scenario: Assume I set up a RAID-5 array consisting of four 1TB hot-swappable 2.5" SATA drives. I name this volume 'My Data'. By my calculations, that would give me 2.7TB of usable space and the ability to recover if a single drive fails. I have a few questions: What happens if I pull out a single 1TB drive and replace it with a 2TB drive? Would the array automatically rebuild itself with no issues? Would the maximum capacity remain 2.7TB? If number (1) above is true and the array rebuilds itself with three 1TB drives one 2TB drive what would happen if I then pulled another 1TB drive out and stuck in a 2TB drive (you can see where I'm going here can't you). Would I eventually be able to gain more storage by gradually adding bigger drives? From a practical point of view, how much input is required from me as the end user whilst these drives are being pulled out and put in? On the Drobo, the storage space just automagically handles itself. Would I have to be actively involved in telling Ubuntu what was going on or would any of it be automated? Thanks in advance,

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• OpenGL Application displays only 1 frame

  - by Avi

  EDIT: I have verified that the problem is not the VBO class or the vertex array class, but rather something else. I have a problem where my vertex buffer class works the first time its called, but displays nothing any other time its called. I don't know why this is, and it's also the same in my vertex array class. I'm calling the functions in this order to set up the buffers: enable client states bind buffers set buffer / array data unbind buffers disable client states Then in the draw function, that's called every frame: enable client states bind buffers set pointers unbind buffers bind index buffer draw elements unbind index buffer disable client states Is there something wrong with the order in which I'm calling the functions, or is it a more specific code error? EDIT: here's some of the code Code for setting pointers: //element is the vertex attribute being drawn (e.g. normals, colors, etc.) static void makeElementPointer(VertexBufferElements::VBOElement element, Shader *shade, void *elementLocation) { //elementLocation is BUFFER_OFFSET(n) if a buffer is bound switch (element) { .... glVertexPointer(3, GL_FLOAT, 0, elementLocation); //changes based on element .... //but I'm only dealing with } //vertices for now } And that's basically all the code that isn't just a straight OpenGL function call.

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• How can I design my classes to include calendar events stored in a database?

  - by Gianluca78

  I'm developing a web calendar in php (using Symfony2) inspired by iCal for a project of mine. At this moment, I have two classes: a class "Calendar" and a class "CalendarCell". Here you are the two classes properties and method declarations. class Calendar { private $month; private $monthName; private $year; private $calendarCellList = array(); private $translator; public function __construct($month, $year, $translator) {} public function getCalendarCellList() {} public function getMonth() {} public function getMonthName() {} public function getNextMonth() {} public function getNextYear() {} public function getPreviousMonth() {} public function getPreviousYear() {} public function getYear() {} private function calculateDaysPreviousMonth() {} private function calculateNumericDayOfTheFirstDayOfTheWeek() {} private function isCurrentDay(\DateTime $dateTime) {} private function isDifferentMonth(\DateTime $dateTime) {} } class CalendarCell { private $day; private $month; private $dayNameAbbreviation; private $numericDayOfTheWeek; private $isCurrentDay; private $isDifferentMonth; private $translator; public function __construct(array $parameters) {} public function getDay() {} public function getMonth() {} public function getDayNameAbbreviation() {} public function isCurrentDay() {} public function isDifferentMonth() {} } Each calendar day can includes many calendar events (such as appointments or schedules) stored in a database. My question is: which is the best way to manage these calendar events in my classes? I think to add a eventList property in CalendarCell and populate it with an array of CalendarEvent objects fetched by the database. This kind of solution doesn't allow other coders to reuse the classes without db (because I should inject at least a repository services also) just to create and visualize a calendar... so maybe it could be better to extend CalendarCell (for instance in CalendarCellEvent) and add the database features? I feel like I'm missing some crucial design pattern! Any suggestion will be very appreciated!

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• Retrieving database column using JSON [migrated]

  - by arokia

  I have a database consist of 4 columns (id-symbol-name-contractnumber). All 4 columns with their data are being displayed on the user interface using JSON. There is a function which is responisble to add new column to the database e.g (countrycode). The coulmn is added successfully to the database BUT not able to show the new added coulmn in the user interface. Below is my code that is displaying the columns. Can you help me? table.php $(document).ready(function () { // prepare the data var theme = getDemoTheme(); var source = { datatype: "json", datafields: [ { name: 'id' }, { name: 'symbol' }, { name: 'name' }, { name: 'contractnumber' } ], url: 'data.php', filter: function() { // update the grid and send a request to the server. $("#jqxgrid").jqxGrid('updatebounddata', 'filter'); }, cache: false }; var dataAdapter = new $.jqx.dataAdapter(source); // initialize jqxGrid $("#jqxgrid").jqxGrid( { source: dataAdapter, width: 670, theme: theme, showfilterrow: true, filterable: true, columns: [ { text: 'id', datafield: 'id', width: 200 }, { text: 'symbol', datafield: 'symbol', width: 200 }, { text: 'name', datafield: 'name', width: 100 }, { text: 'contractnumber', filtertype: 'list', datafield: 'contractnumber' } ] }); }); data.php <?php #Include the db.php file include('db.php'); $query = "SELECT * FROM pricelist"; $result = mysql_query($query) or die("SQL Error 1: " . mysql_error()); $orders = array(); // get data and store in a json array while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) { $pricelist[] = array( 'id' => $row['id'], 'symbol' => $row['symbol'], 'name' => $row['name'], 'contractnumber' => $row['contractnumber'] ); } echo json_encode($pricelist); ?>

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• How can I design my classes for a calendar based on database events?

  - by Gianluca78

  I'm developing a web calendar in php (using Symfony2) inspired by iCal for a project of mine. At this moment, I have two classes: a class "Calendar" and a class "CalendarCell". Here you are the two classes properties and method declarations. class Calendar { private $month; private $monthName; private $year; private $calendarCellList = array(); private $translator; public function __construct($month, $year, $translator) {} public function getCalendarCells() {} public function getMonth() {} public function getMonthName() {} public function getNextMonth() {} public function getNextYear() {} public function getPreviousMonth() {} public function getPreviousYear() {} public function getYear() {} private function calculateDaysPreviousMonth() {} private function calculateNumericDayOfTheFirstDayOfTheWeek() {} private function isCurrentDay(\DateTime $dateTime) {} private function isDifferentMonth(\DateTime $dateTime) {} } class CalendarCell { private $day; private $month; private $dayNameAbbreviation; private $numericDayOfTheWeek; private $isCurrentDay; private $isDifferentMonth; private $translator; public function __construct(array $parameters) {} public function getDay() {} public function getMonth() {} public function getDayNameAbbreviation() {} public function isCurrentDay() {} public function isDifferentMonth() {} } Each calendar day can includes many events stored in a database. My question is: which is the best way to manage these events in my classes? I think to add a eventList property in CalendarCell and populate it with an array of CalendarEvent objects fetched by the database. This kind of solution doesn't allow other coders to reuse the classes without db (because I should inject at least a repository services also) just to create and visualize a calendar... so maybe it could be better to extend CalendarCell (for instance in CalendarCellEvent) and add the database features? I feel like I'm missing some crucial design pattern! Any suggestion will be very appreciated!

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• Removing ocurrances of characters in a string

  - by DmainEvent

  I am reading this book, programming Interviews exposed by John Wiley and sons and in chapter 6 they are discussing removing all instances of characters in a src string using a removal string... so removeChars(string str, string remove) In there writeup they sey the steps to accomplish this are to have a boolean lookup array with all values initially set to false, then loop through each character in remove setting the corresponding value in the lookup array to true (note: this could also be a hash if the possible character set where huge like Unicode-16 or something like that or if str and remove are both relatively small... < 100 characters I suppose). You then iterate through the str with a source and destination index, copying each character only if its corresponding value in the lookup array is false... Which makes sense... I don't understand the code that they use however... They have for(src = 0; src < len; ++src){ flags[r[src]] == true; } which is turning the flag value at the remove string indexed at src to true... so if you start out with PLEASE HELP as your str and LEA as your remove you will be setting in your flag table at 0,1,2... t|t|t but after that you will get an out of bounds exception because r doesn't have have anything greater than 2 in it... even using there example you get an out of bounds exception... Am is there code example unworkable?

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• Windows XP 32-bit + RocketRaid 622 + 4 x 3TB = not quite a RAID setup

  - by gmoney

  I'm looking to make a 6TB RAID 10 array from my new pile of drives under Windows XP 32-bit, however they are only for auxiliary storage. After adding all the drives to an array, and initializing them XP sees only a fraction of the storage, 2TB. I'm assuming this has to do with MBR vs GPT. Is making a series of 2TB volumes and then spanning my only solution? Most questions online have to do with booting from this setup, but I'm just using them as extra storage. Hardware: 4 x 3TB Hitachi Deskstars + RocketRaid 622 + Sans Digital TR8M TowerRAID. The array is connected via eSATA.

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• RAID 10, how layout works ?

  - by Bastien974

  I'm trying to figure out how exactly works the RAID 10 in linux with mdadm. I want to create a RAID 10 out of 4 partitions, let's say a, b, c and d. a and b are on the array 1, c and d array 2. So what I want is to have the couple a and b, c and d in RAID 0. Then on top of that, a RAID 1. The option in the mdadm command to configure the layout is -p, --layout with option : near, far, offset see here I want to keep my data safe if the array 1 fails for example, that would mean that every chunk of data are always copied on both arrays. How do I have to set my RAID 10, near or far ?

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• LINQ – Skip() and Take() methods

  - by nmarun

  I had this issue recently where I have an array of integers and I’m doing some Skip(n) and then a Take(m) on the collection. Here’s an abstraction of the code: 1: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; 2: var taken = numbers.Skip(3).Take(3); 3: foreach (var i in taken) 4: { 5: Console.WriteLine(i); 6: } The output is as expected: 3, 9, 8 – skip the first three and then take the next three items. But, what happens if I do something like: 1: var taken = numbers.Skip(7).Take(5); In English – skip the first seven and the take the next 5 items from an array that contains only 10 elements. Think it’ll throw the IndexOutOfRangeException exception? Nope. These extension methods are a little smarter than that. Even though the user has requested more elements than what exists in the collection, the Take method only returns the first three thereby making the output of the program as: 7, 2, 0. The scenario is handled similarly when you do: 1: var taken = numbers.Take(5).Skip(7); This one takes the first 5 elements from the numbers array and then skips 7 of them. This is what is looks like in the debug mode: Just wanted to share this behavior.

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• Storing revisions of a document

  - by dev.e.loper

  This is a follow up question to my original question. I'm thinking of going with generating diffs and storing those diffs in the database 'History' table. I'm using diff-match-patch library to generate what is called a 'patch'. On every save, I compare previous and new version and generate this patch. The patch could be used to generate a document at specific point in time. My dilemma is how to store this data. Should I: a Insert a new database record for every patch? b. Store these patches in javascript array and store that array in history table. So there is only one db History record for document with an array of all the patches. Concerns with: a. Too many db records generated. Will be slow and CPU intensive to query. b. Only one record. If record is somehow corrupted/deleted. Entire revision history is gone. I'm looking for suggestions, concerns with either approach.

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• Should I always encapsulate an internal data structure entirely?

  - by Prog

  Please consider this class: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThings(){ return things; } } This class exposes the array it uses to store data, to any client code interested. I did this in an app I'm working on. I had a ChordProgression class that stores a sequence of Chords (and does some other things). It had a Chord[] getChords() method that returned the array of chords. When the data structure had to change (from an array to an ArrayList), all client code broke. This made me think - maybe the following approach is better: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThing(int index){ return things[index]; } public int getDataSize(){ return things.length; } public void setThing(int index, Thing thing){ things[index] = thing; } } Instead of exposing the data structure itself, all of the operations offered by the data structure are now offered directly by the class enclosing it, using public methods that delegate to the data structure. When the data structure changes, only these methods have to change - but after they do, all client code still works. Note that collections more complex than arrays might require the enclosing class to implement even more than three methods just to access the internal data structure. Is this approach common? What do you think of this? What downsides does it have other? Is it reasonable to have the enclosing class implement at least three public methods just to delegate to the inner data structure?

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• Enemy collision detection with movie clips

  - by user18080

  I have created multiple movieclips with animations within them. It is an obstacle avoidance game and I cannot seem to be able to get my enemies to contact my playableCharacter. The enemies I have created are each embedded on certain levels of my game. I have created an array, enemiesArray to have each of my enemies placed within it. Here is the code for that: //step 1: make sure array exists if(enemiesArray!=null && enemiesArray.length!=0) { //step 2: check all enemies against villain for(var i:int = 0;i < enemiesArray.length; i++) { //step 3: check for collision if(villain.hitTestObject(enemiesArray[i])) { //step 4: do stuff trace("HIT!"); removeChild(enemiesArray[i]); enemiesArray.splice(i,1); removeChild(villain); villain = null; } } } What I am unsure of is whether or not my enemiesArray is actually holding the movieclips I have suggested. If it was, this code would be tracing back a "HIT" for every time I ran into an enemy and would kill my character. It is not doing that however. I am thinking I have to push my movieclips into my array but I don't know how to do that or where for that matter. Any and all help would be much appreciated.

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• DB Object passing between classes singleton, static or other?

  - by Stephen

  So I'm designing a reporting system at work it's my first project written OOP and I'm stuck on the design choice for the DB class. Obviously I only want to create one instance of the DB class per-session/user and then pass it to each of the classes that need it. What I don't know it what's best practice for implementing this. Currently I have code like the following:- class db { private $user = 'USER'; private $pass = 'PASS'; private $tables = array( 'user','report', 'etc...'); function __construct(){ //SET UP CONNECTION AND TABLES } }; class report{ function __construct ($params = array(), $db, $user) { //Error checking/handling trimed //$db is the database object we created $this->db = $db; //$this->user is the user object for the logged in user $this->user = $user; $this->reportCreate(); } public function setPermission($permissionId = 1) { //Note the $this->db is this the best practise solution? $this->db->permission->find($permissionId) //Note the $this->user is this the best practise solution? $this->user->checkPermission(1) $data=array(); $this->db->reportpermission->insert($data) } };//end report I've been reading about using static classes and have just come across Singletons (though these appear to be passé already?) so what's current best practice for doing this?

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• Best way to generate pieces in match-3 games, and then tracking them?

  - by JonLim

  I've been working on a match-3 style game in Actionscript using Flixel, and so far, I've been able to build the core mechanics of the game, including board generation, piece generation, piece swapping and movement, and checking algorithms. However, I am now running into issues with clearing out pieces and letting the above pieces fall down and generating new pieces. The reason I'm running into these issues is that when all of the pieces are generated, the pertinent values (position, sprite ID, and sprite object) are pushed into an array that helps me track everything, all the time. When pieces are moved, I swap the values of the corresponding arrays and life goes on. And that array is the core of my problem: if a row in the middle of the board clears out, ideally, all of the pieces above the cleared pieces should fall down to take their place and new pieces are generated at the top and also fall into place. Except if I try to do that now, all the pieces can fall down, but then I'd have to bump all of their values into the right arrays (oh god my head) and then generate new pieces and fit THOSE into the correct place in the array. Am I overthinking this? Or is there a far better way to track these pieces? Thanks guys!

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• Create a Texture2D from larger image

  - by Dialock

  I am having trouble with the basic logic of this solution: Xna: Splitting one large texture into an array of smaller textures in respect to my specific problem (specifically, I'm looking at the second answer.) How can I use my source rectangle that I already use for drawing to create a new Texture2D? spriteBatch.Draw(CurrentMap.CollisionSet, currentMap.CellScreenRectangle(x, y), CurrentMap.TileSourceRectangle(currentMap.MapCells[x, y].TileDepths[4]), Color.FromNonPremultiplied(0,0,0, 45), 0.0f, Vector2.Zero, SpriteEffects.None, 0.91f); I know I want a method that I started so: //In Update Method of say the player's character. Texture2D CollisionTexture = ExtractTexture(MapManager.CurrentMap.CollisionSet, MapManager.TileWidth, MapManager.TileHeight); // In MapManager Class who knows everything about tiles that make up a level. public Texture2D ExtractTexture(Texture2D original, int partWidth, int partheight, MapTile mapCell) { var dataPerPart = partWidth * partheight; Color[] originalPixelData = new Color[original.Width * original.Height]; original.GetData<Color>(originalPixelData); Color[] newTextureData = new Color[dataPerPart]; original.GetData<Color>(0, CurrentMap.TileSourceRectangle(mapCell.TileDepths[4]), originalPixelData, 0, originalPixelData.Count()); Texture2D outTexture = new Texture2D(original.GraphicsDevice, partWidth, partheight); } I think the problem is I'm just not understanding the overload of Texture2D.GetData< Part of my concern is creating an array of the whole texture in the first place. Can I target the original texture and create an array of colors for copying based on what I already get from the method TileSourceRecatangle(int)?

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• Representing a world in memory

  - by user9993

  I'm attempting to write a chunk based map system for a game, where as the player moves around chunks are loaded/unloaded, so that the program doesn't run out of memory by having the whole map in memory. I have this part mostly working, however I've hit a wall regarding how to represent the contents of each chunk in memory because of my so far limited understanding of OOP languages. The design I have currently has a ChunkManager class that uses a .NET List type to store instances of Chunk classes. The "chunks" consist of "blocks". It's similar to a Minecraft style game. Inside the Chunk classes, I have some information such as the chunk's X/Y coordinate etc, and I also have a three dimensional array of Block objects. (Three dimensional because I need XYZ values) Here's the problem: The Block class has some basic properties, and I had planned on making different types of blocks inherit from this "base" class. So for example, I would have "StoneBlock", "WaterBlock" etc. So because I have blocks of many different types, I don't know how I would create an array with different object types in each cell. This is how I currently have the three dimensional array declared in my Chunk class: private Block[][][] ArrayOfBlocks; But obviously this will only accept Block objects, not any of the other classes that inherit from Block. How would I go about creating this? Or am I doing it completely wrong and there's a better way?

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• Can different drive speeds and sizes be used in a hardware RAID configuration w/o affecting performance?

  - by R. Dill

  Specifically, I have a RAID 1 array configuration with two 500gb 7200rpm SATA drives mirrored as logical drive 1 (a) and two of the same mirrored as logical drive 2 (b). I'd like to add two 1tb 5400rpm drives in the same mirrored fashion as logical drive 3 (c). These drives will only serve as file storage with occasional but necessary access, and therefore, space is more important than speed. In researching whether this configuration is doable, I've been told and have read that the array will only see the smallest drive size and slowest speed. However, my understanding is that as long as the pairs themselves aren't mixed (and in this case, they aren't) that the array should view and use all drives at their actual speed and size. I'd like to be sure before purchasing the additional drives. Insight anyone?

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• codility challenge, test case OK , Evaluation report Wrong Answer

  - by Hussein Fawzy

  the aluminium 2014 gives me wrong answer [3 , 9 , -6 , 7 ,-3 , 9 , -6 , -10] got 25 expected 28 but when i repeated the challenge with the same code and make case test it gives me the correct answer Your test case [3, 9, -6, 7, -3, 9, -6, -10] : NO RUNTIME ERRORS (returned value: 28) what is the wrong with it ??? the challenge :- A non-empty zero-indexed array A consisting of N integers is given. A pair of integers (P, Q), such that 0 = P = Q < N, is called a slice of array A. The sum of a slice (P, Q) is the total of A[P] + A[P+1] + ... + A[Q]. The maximum sum is the maximum sum of any slice of A. For example, consider array A such that: A[0] = 3 A[1] = 2 A[2] = -6 A[3] = 3 A[4] = 1 For example (0, 1) is a slice of A that has sum A[0] + A[1] = 5. This is the maximum sum of A. You can perform a single swap operation in array A. This operation takes two indices I and J, such that 0 = I = J < N, and exchanges the values of A[I] and A[J]. To goal is to find the maximum sum you can achieve after performing a single swap. For example, after swapping elements 2 and 4, you will get the following array A: A[0] = 3 A[1] = 2 A[2] = 1 A[3] = 3 A[4] = -6 After that, (0, 3) is a slice of A that has the sum A[0] + A[1] + A[2] + A[3] = 9. This is the maximum sum of A after a single swap. Write a function: class Solution { public int solution(int[] A); } that, given a non-empty zero-indexed array A of N integers, returns the maximum sum of any slice of A after a single swap operation. For example, given: A[0] = 3 A[1] = 2 A[2] = -6 A[3] = 3 A[4] = 1 the function should return 9, as explained above. and my code is :- import java.math.*; class Solution { public int solution(int[] A) { if(A.length == 1) return A[0]; else if (A.length==2) return A[0]+A[1]; else{ int finalMaxSum = A[0]; for (int l=0 ; l<A.length ; l++){ for (int k = l+1 ; k<A.length ; k++ ){ int [] newA = A; int temp = newA[l]; newA [l] = newA[k]; newA[k]=temp; int maxSum = newA[0]; int current_max = newA[0]; for(int i = 1; i < newA.length; i++) { current_max = Math.max(A[i], current_max + newA[i]); maxSum = Math.max(maxSum, current_max); } finalMaxSum = Math.max(finalMaxSum , maxSum); } } return finalMaxSum; } } } i don't know what's the wrong with it ??

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• Why does async BeginReceiveFrom never time out on a raw socket?

  - by James Hugard

  Writing an asynchronous Ping using Raw Sockets in F#, to enable parallel requests using as few threads as possible. Not using "System.Net.NetworkInformation.Ping", because it appears to allocate one thread per request. Am also interested in using F# async workflows. The synchronous version below correctly times out when the target host does not exist/respond, but the asynchronous version hangs. Both work when the host does respond. Not sure if this is a .NET issue, or an F# one... Any ideas? (note: the process must run as Admin to allow Raw Socket access) This throws a timeout: let result = Ping.Ping ( IPAddress.Parse( "192.168.33.22" ), 1000 ) However, this hangs: let result = Ping.AsyncPing ( IPAddress.Parse( "192.168.33.22" ), 1000 ) |> Async.RunSynchronously Here's the code... module Ping open System open System.Net open System.Net.Sockets open System.Threading //---- ICMP Packet Classes type IcmpMessage (t : byte) = let mutable m_type = t let mutable m_code = 0uy let mutable m_checksum = 0us member this.Type with get() = m_type member this.Code with get() = m_code member this.Checksum = m_checksum abstract Bytes : byte array default this.Bytes with get() = [| m_type m_code byte(m_checksum) byte(m_checksum >>> 8) |] member this.GetChecksum() = let mutable sum = 0ul let bytes = this.Bytes let mutable i = 0 // Sum up uint16s while i < bytes.Length - 1 do sum <- sum + uint32(BitConverter.ToUInt16( bytes, i )) i <- i + 2 // Add in last byte, if an odd size buffer if i <> bytes.Length then sum <- sum + uint32(bytes.[i]) // Shuffle the bits sum <- (sum >>> 16) + (sum &&& 0xFFFFul) sum <- sum + (sum >>> 16) sum <- ~~~sum uint16(sum) member this.UpdateChecksum() = m_checksum <- this.GetChecksum() type InformationMessage (t : byte) = inherit IcmpMessage(t) let mutable m_identifier = 0us let mutable m_sequenceNumber = 0us member this.Identifier = m_identifier member this.SequenceNumber = m_sequenceNumber override this.Bytes with get() = Array.append (base.Bytes) [| byte(m_identifier) byte(m_identifier >>> 8) byte(m_sequenceNumber) byte(m_sequenceNumber >>> 8) |] type EchoMessage() = inherit InformationMessage( 8uy ) let mutable m_data = Array.create 32 32uy do base.UpdateChecksum() member this.Data with get() = m_data and set(d) = m_data <- d this.UpdateChecksum() override this.Bytes with get() = Array.append (base.Bytes) (this.Data) //---- Synchronous Ping let Ping (host : IPAddress, timeout : int ) = let mutable ep = new IPEndPoint( host, 0 ) let socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout ) let packet = EchoMessage() let mutable buffer = packet.Bytes try if socket.SendTo( buffer, ep ) <= 0 then raise (SocketException()) buffer <- Array.create (buffer.Length + 20) 0uy let mutable epr = ep :> EndPoint if socket.ReceiveFrom( buffer, &epr ) <= 0 then raise (SocketException()) finally socket.Close() buffer //---- Entensions to the F# Async class to allow up to 5 paramters (not just 3) type Async with static member FromBeginEnd(arg1,arg2,arg3,arg4,beginAction,endAction,?cancelAction): Async<'T> = Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,iar,state)), endAction, ?cancelAction=cancelAction) static member FromBeginEnd(arg1,arg2,arg3,arg4,arg5,beginAction,endAction,?cancelAction): Async<'T> = Async.FromBeginEnd((fun (iar,state) -> beginAction(arg1,arg2,arg3,arg4,arg5,iar,state)), endAction, ?cancelAction=cancelAction) //---- Extensions to the Socket class to provide async SendTo and ReceiveFrom type System.Net.Sockets.Socket with member this.AsyncSendTo( buffer, offset, size, socketFlags, remoteEP ) = Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP, this.BeginSendTo, this.EndSendTo ) member this.AsyncReceiveFrom( buffer, offset, size, socketFlags, remoteEP ) = Async.FromBeginEnd( buffer, offset, size, socketFlags, remoteEP, this.BeginReceiveFrom, (fun asyncResult -> this.EndReceiveFrom(asyncResult, remoteEP) ) ) //---- Asynchronous Ping let AsyncPing (host : IPAddress, timeout : int ) = async { let ep = IPEndPoint( host, 0 ) use socket = new Socket( AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.Icmp ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.SendTimeout, timeout ) socket.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, timeout ) let packet = EchoMessage() let outbuffer = packet.Bytes try let! result = socket.AsyncSendTo( outbuffer, 0, outbuffer.Length, SocketFlags.None, ep ) if result <= 0 then raise (SocketException()) let epr = ref (ep :> EndPoint) let inbuffer = Array.create (outbuffer.Length + 256) 0uy let! result = socket.AsyncReceiveFrom( inbuffer, 0, inbuffer.Length, SocketFlags.None, epr ) if result <= 0 then raise (SocketException()) return inbuffer finally socket.Close() }

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