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• New computer hangs on shutdown/reboot, how to troubleshoot?

  - by Torben Gundtofte-Bruun

  My system is working perfectly but it freezes during shutdown/reboot/suspend/hibernate: All windows and the menu bar disappear but the desktop wallpaper remains. It doesn't even show the shutdown screen (the one with the animated dots) where I could hit ESC and watch the shutdown console text. The system is brand-new and fully updated using Update Manager. How can I determine what is causing the freeze? Is there a log I can investigate? How can I fix this? I see no obvious cause of the freeze. The only USB attachment is a mouse/keyboard; I don't have any external storage attached; and I don't have any programs running (the machine freezes even when doing shutdown right from the login screen). What I've tried so far: Based on other questions (this, this, and this) that suggest some ACPI settings, I've tried sudo shutdown -h now to see whether the shutdown console text display offers any hints, but the system doesn't even get that far - it still freezes while the screen shown the desktop background image, without any toolbars. Only sudo shutdown --force works, but that's not a solution. Editing the grub menu to add acpi=off to the kernel didn't help. I guess there's not much point in trying the other (lesser) ACPI suggestions? Adding noapic to the grub entry had no discernible effect. Adding nolapic instead did something (I had removed the quiet option) - the system managed to continue further with the shutdown, right until the line Checking for running unattended-upgrades: which were the last characters on the screen. I've also checked the system BIOS, especially regarding power options, but didn't see anything out of the ordinary. Switching the BIOS standby setting from S3 to S1 didn't help. The standby setting can't be disabled, and there are no other ACPI-related settings AFAIK. BIOS reset didn't help. Not surprised; hadn't changed anything. I tried going to a virtual console (CtrlAltF1) as suggested by djeikyb and from there did a shutdown -h now and it froze there too, after this console output. I didn't try killing processes one at a time because I'm still too newbie to figure out how to do that. Booting with kernel 2.6.35.22 rather than 2.6.35.25 didn't help. Disabling the Nvidia drivers didn't help. Booting from Live CD (USB stick in fact) didn't help; it freezes the same way. Booting from Live CD, with acpi=off noapic nolapic didn't help either. Neither did just nolapic. So evidently this is not some custom setting in my install, but some sort of basic issue. MemTest competed in 1 hour without errors.

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• Is there a usage count for packages or programs?

  - by math

  Motivation: I want to remove applications I do not use to speed up my package processing tasks like dist upgrades, regular updates, but also for saving disk space and other reasons. I know this is a complex topic so first I will ask my question and second I will give some answers I already found out. Question: How do I find out which package I did not used at all? For example I always use the VLC so I could remove totem package. (Which I could have been used some day, yes.) Of course package dependencies could force me to have programs installed which I will never use. Notes: Find the packages which consume much space via synaptic: Select "Status" in lower left, select "Installed" in upper left, sort column on "size" in upper right. Then you can decide which big packages you really need. Use aptitude autoremove Use ubuntu-tweak's Janitor for removing old kernel packages, old configs, apt-cache entries, etc. Manually search for applications for a given task that you usually solve with your standard app. E.g. Movie player, Music player, Office program, Browser etc. (BTW: this is what I want to be helped with my question) When removing packages I always favour "apt-get purge" over "aptitude remove --purge" as aptitude often will also remove essential packages due to package dependencies. E.g. when removing "evolution" (as I use thunderbird) aptitude wants to remove also "ubuntu-desktop" and 756 other packages as well, while apt-get just removes evolution and its helping pacakges like evolution-common. Ubuntu lense gives me most recent used applications which are candidates for keeping :) Employ deborphan as I read in this related answer: How do I clean up my harddrive? I should certainly keep essential packages: Keep only essential packages This question is pretty much a duplicate of How to see what installed packages I have never used for cleaning purposes but covering only few aspects. However one answer suggests to use a program called unusedpkg but the link seems down. There is also a program called Kleen http://code.google.com/p/kleen/ but it won't compile in 11.10. However I hacked it to compile but the results are unusable, as for example the g++ package was marked as not used for 203, but actually I used it seconds ago for compiling Kleen itself ;) So don't use this tool. On http://wiki.debian.org/DebianPackageInformation I read the the package popularity-contest will produce log files with usage statistics. Unfortunately I didn't enabled the popularity contest so I can't find this log file.

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• Running a program on boot without login, using the screen

  - by configurator

  Preface: I have a server running on an old laptop. The screen is always on with a login prompt, but because its keyboard is in pretty bad shape, I use it exclusively via ssh. The screen is in a good position, though; I want to use it to display a clock and some stats about what my server is doing. I have scripts to display all those things, but I want to always show them on the monitor screen. My question is, how do I get my script (called HUD) to run on /dev/tty1, instead of the login prompt. Hopefully, it should be possible to accept keyboard input as well as display its output, so that it can use the keyboard to show more info where needed in a future version. I'd also like tty2 etc. to remain active as login screens, in face I actually do need to login locally. For a start, I tried creating a script that I can run from ssh to start the HUD. It goes something like this: ( flock -n 9 watch --interval 0.2 --precise --color --notitle --exec /path/to/script & disown ) 9> /var/lock/hud > /dev/tty1 2> /dev/tty1 < /dev/tty1 (I had to use & disown instead of nohup because nohup recognized the tty and redirects output to nohup.out instead.) This sort-of works. However, it has a few issues: It doesn't steal the terminal's keyboard input, so you can't ctrl+c to get out of it (nor change the script to actually use the keyboard input), and if you press enter it show it and scrolls the display, never refreshing it correctly afterwards. Oddly, if I disconnect the ssh session which created it, it stops working and shows a message: exec: No such file or directory. If I reconnect to ssh, it resumes functioning properly. It feels hackish. Is there a better way to do this? How?

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• Homepage issue on Google [closed]

  - by nico

  We have recently updated our website www.blinds4uk.co.uk with a new homepage containing additional features and more on page content but since then we have lost primary keyword positions and the home page has disappeared completely. The only time it appears is for an exact search ‘blinds4uk’. Today I took snippets of 'unique content' from the homepage and put this into the 'google search' but our homepage was nowhere to be found. When I did the same in ‘Yahoo’ the homepage came up. Are we missing something? We ranked in the top 4 for primary kw terms 'blinds uk' & 'uk blinds' but now we don’t show anywhere for these terms. Our homepage has never ranked well for the primary kw 'blinds' yet our internal pages rank very well with many pages on page 1 of google uk. We employed an SEO firm for 9 months to help us establish issues with the homepage but they never could, so we got rid. We have been trying to get to the root cause of why the homepage ranks so poorly for a number of years and only yesterday we established that we had the meta tag directly below the tag and our title & meta description were further down the page; we have today corrected. Not sure what effect this would have on the way Google reads the homepage but we are trying everything to try and get the homepage ranking fro those primary kw's. Our current developers & ex SEO guys are all part of the same company and cannot pin-point anything other than saying carryon with their SEO team because it will take time but just comes across as a milking exercise. Another thing which I have found very strange is the data from our 'traffic audience'. We are a UK based website yet our traffic stats were showing as;- UK 36.6%, Denmark 35.8% and India 27.6%. – don’t make sense to me! Is there anybody out there that could simply point us in the right direction to the problem(s), so we can fix once and for all? Could there be anything within the code that is causing the home page not to display within google for our primary kw's terms such as blinds, window blinds etc. I would appreciate any advice at all that may help us in our quest to sort this homepage issue once and for all

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• Inherit one instance variable from the global scope

  - by Julian

  I'm using Curses to create a command line GUI with Ruby. Everything's going well, but I have hit a slight snag. I don't think Curses knowledge (esoteric to be fair) is required to answer this question, just Ruby concepts such as objects and inheritance. I'm going to explain my problem now, but if I'm banging on, just look at the example below. Basically, every Window instance needs to have .close called on it in order to close it. Some Window instances have other Windows associated with it. When closing a Window instance, I want to be able to close all of the other Window instances associated with it at the same time. Because associated Windows are generated in a logical fashion, (I append the name with a number: instance_variable_set(self + integer, Window.new(10,10,10,10)) ), it's easy to target generated windows, because methods can anticipate what assosiated windows will be called, (I can recreate the instance variable name from scratch, and almost query it: instance_variable_get(self + integer). I have a delete method that handles this. If the delete method is just a normal, global method (called like this: delete_window(@win543) then everything works perfectly. However, if the delete method is an instance method, which it needs to be in-order to use the self keyword, it doesn't work for a very clear reason; it can 'query' the correct instance variable perfectly well (instance_variable_get(self + integer)), however, because it's an instance method, the global instances aren't scoped to it! Now, one way around this would obviously be to simply make a global method like this: delete_window(@win543). But I have attributes associated with my window instances, and it all works very elegantly. This is very simplified, but it literally translates the problem exactly: class Dog def speak woof end end def woof if @dog_generic == nil puts "@dog_generic isn't scoped when .woof is called from a class method!\n" else puts "@dog_generic is scoped when .woof is called from the global scope. See:\n" + @dog_generic end end @dog_generic = "Woof!" lassie = Dog.new lassie.speak #=> @dog_generic isn't scoped when .woof is called from an instance method!\n woof #=> @dog_generic is scoped when .woof is called from the global scope. See:\nWoof! TL/DR: I need lassie.speak to return this string: "@dog_generic is scoped when .woof is called from the global scope. See:\nWoof!" @dog_generic must remain as an insance variable. The use of Globals or Constants is not acceptable. Could woof inherit from the Global scope? Maybe some sort of keyword: def woof < global # This 'code' is just to conceptualise what I want to do, don't take offence! end Is there some way the .woof method could 'pull in' @dog_generic from the global scope? Will @dog_generic have to be passed in as a parameter?

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• More elegant way to avoid hard coding the format of a a CSV file?

  - by dsollen

  I know this is trivial issue, but I just feel this can be more elegant. So I need to write/read data files for my program, lets say they are CSV for now. I can implement the format as I see fit, but I may have need to change that format later. The simply thing to do is something like out.write(For.getValue()+","+bar.getMinValue()+","+fi.toString()); This is easy to write, but obviously is guilty of hard coding and the general 'magic number' issue. The format is hard-coded, requires parsing of the code to figure out the file format, and changing the format requires changing multiple methods. I could instead have my constants specifying the location that I want each variable to be saved in the CSV file to remove some of the 'magic numbers'; then save/load into the an array at the location specified by the constants: int FOO_LOCATION=0; int BAR_MIN_VAL_LOCATION=1; int FI_LOCATION=2 int NUM_ARGUMENTS=3; String[] outputArguments=new String[NUM_ARGUMENTS]; outputArguments[FOO_LOCATION] = foo.getValue(); outputArgumetns[BAR_MIN_VAL_LOCATION] = bar.getMinValue(); outptArguments[FI_LOCATOIN==fi.toString(); writeAsCSV(outputArguments); But this is...extremely verbose and still a bit ugly. It makes it easy to see the format of existing CSV and to swap the location of variables within the file easily. However, if I decide to add an extra value to the csv I need to not only add a new constant, but also modify the read and write methods to add the logic that actually saves/reads the argument from the array; I still have to hunt down every method using these variables and change them by hand! If I use Java enums I can clean this up slightly, but the real issue is still present. Short of some sort of functional programming (and java's inner classes are too ugly to be considered functional) I still have no obvious way of clearly expressing what variable is associated with each constant short of writing (and maintaining) it in the read/write methods. For instance I still need to write somewhere that the FOO_LOCATION specifies the location of foo.getValue(). It seems as if there should be a prettier, easier to maintain, manner for approaching this? Incidentally, I'm working in java at the moment, however, I am interested conceptually about the design approach regardless of language. Some library in java that does all the work for me is definitely welcome (though it may prove more hassle to get permission to add it to the codebase then to just write something by hand quickly), but what I'm really asking is more about how to write elegant code if you had to do this by hand.

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• How do I randomly generate a top-down 2D level with separate sections and is infinite?

  - by Bagofsheep

  I've read many other questions/answers about random level generation but most of them deal with either randomly/proceduraly generating 2D levels viewed from the side or 3D levels. What I'm trying to achieve is sort of like you were looking straight down on a Minecraft map. There is no height, but the borders of each "biome" or "section" of the map are random and varied. I already have basic code that can generate a perfectly square level with the same tileset (randomly picking segments from the tileset image), but I've encountered a major issue for wanting the level to be infinite: Beyond a certain point, the tiles' positions become negative on one or both of the axis. The code I use to only draw tiles the player can see relies on taking the tiles position and converting it to the index number that represents it in the array. As you well know, arrays cannot have a negative index. Here is some of my code: This generates the square (or rectangle) of tiles: //Scale is in tiles public void Generate(int sX, int sY) { scaleX = sX; scaleY = sY; for (int y = 0; y <= scaleY; y++) { tiles.Add(new List<Tile>()); for (int x = 0; x <= scaleX; x++) { tiles[tiles.Count - 1].Add(tileset.randomTile(x * tileset.TileSize, y * tileset.TileSize)); } } } Before I changed the code after realizing an array index couldn't be negative my for loops looked something like this to center the map around (0, 0): for (int y = -scaleY / 2; y <= scaleY / 2; y++) for (int x = -scaleX / 2; x <= scaleX / 2; x++) Here is the code that draws the tiles: int startX = (int)Math.Floor((player.Position.X - (graphics.Viewport.Width) - tileset.TileSize) / tileset.TileSize); int endX = (int)Math.Ceiling((player.Position.X + (graphics.Viewport.Width) + tileset.TileSize) / tileset.TileSize); int startY = (int)Math.Floor((player.Position.Y - (graphics.Viewport.Height) - tileset.TileSize) / tileset.TileSize); int endY = (int)Math.Ceiling((player.Position.Y + (graphics.Viewport.Height) + tileset.TileSize) / tileset.TileSize); for (int y = startY; y < endY; y++) { for (int x = startX; x < endX; x++) { if (x >= 0 && y >= 0 && x <= scaleX && y <= scaleY) tiles[y][x].Draw(spriteBatch); } } So to summarize what I'm asking: First, how do I randomly generate a top-down 2D map with different sections (not chunks per se, but areas with different tile sets) and second, how do I get past this negative array index issue?

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• Can't change color of sprites in unity

  - by Aceleeon

  I would like to create a script that targets a 2d sprite "enemy" and changes their color to red (slightly opaque red if possible) when you hit tab. I have this code from a 3d tutorial hoping the transition would work. But it does not. I only get the script to cycle the enemy tags but never changes the color of the sprite. I have the code below I'm very new to coding, and any help would be FANTASTIC! HELP! hahah. TL;DR Cant get 3d color targeting to work for 2D. Check out the c#code below using UnityEngine; using System.Collections; using System.Collections.Generic; public class Targetting : MonoBehaviour { public List targets; public Transform selectedTarget; private Transform myTransform; // Use this for initialization void Start () { targets = new List(); selectedTarget = null; myTransform = transform; AddAllEnemies(); } public void AddAllEnemies() { GameObject[] go = GameObject.FindGameObjectsWithTag("Enemy"); foreach(GameObject enemy in go) AddTarget(enemy.transform); } public void AddTarget(Transform enemy) { targets.Add(enemy); } private void SortTargetsByDistance() { targets.Sort(delegate(Transform t1,Transform t2) { return Vector3.Distance(t1.position, myTransform.position).CompareTo(Vector3.Distance(t2.position, myTransform.position)); }); } private void TargetEnemy() { if(selectedTarget == null) { SortTargetsByDistance(); selectedTarget = targets[0]; } else { int index = targets.IndexOf(selectedTarget); if(index < targets.Count -1) { index++; } else { index = 0; } selectedTarget = targets[index]; } } private void SelectTarget() { selectedTarget.GetComponent().color = Color.red; } private void DeselectTarget() { selectedTarget.GetComponent().color = Color.blue; selectedTarget = null; } // Update is called once per frame void Update() { if(Input.GetKeyDown(KeyCode.Tab)) { TargetEnemy(); } } }

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• Java @Contented annotation to help reduce false sharing

  - by Dave

  See this posting by Aleksey Shipilev for details -- @Contended is something we've wanted for a long time. The JVM provides automatic layout and placement of fields. Usually it'll (a) sort fields by descending size to improve footprint, and (b) pack reference fields so the garbage collector can process a contiguous run of reference fields when tracing. @Contended gives the program a way to provide more explicit guidance with respect to concurrency and false sharing. Using this facility we can sequester hot frequently written shared fields away from other mostly read-only or cold fields. The simple rule is that read-sharing is cheap, and write-sharing is very expensive. We can also pack fields together that tend to be written together by the same thread at about the same time. More generally, we're trying to influence relative field placement to minimize coherency misses. Fields that are accessed closely together in time should be placed proximally in space to promote cache locality. That is, temporal locality should condition spatial locality. Fields accessed together in time should be nearby in space. That having been said, we have to be careful to avoid false sharing and excessive invalidation from coherence traffic. As such, we try to cluster or otherwise sequester fields that tend to written at approximately the same time by the same thread onto the same cache line. Note that there's a tension at play: if we try too hard to minimize single-threaded capacity misses then we can end up with excessive coherency misses running in a parallel environment. Theres no single optimal layout for both single-thread and multithreaded environments. And the ideal layout problem itself is NP-hard. Ideally, a JVM would employ hardware monitoring facilities to detect sharing behavior and change the layout on the fly. That's a bit difficult as we don't yet have the right plumbing to provide efficient and expedient information to the JVM. Hint: we need to disintermediate the OS and hypervisor. Another challenge is that raw field offsets are used in the unsafe facility, so we'd need to address that issue, possibly with an extra level of indirection. Finally, I'd like to be able to pack final fields together as well, as those are known to be read-only.

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• A solution for a PHP website without a framework

  - by lortabac

  One of our customers asked us to add some dynamic functionality to an existent website, made of several static HTML pages. We normally work with an MVC framework (mostly CodeIgniter), but in this case moving everything to a framework would require too much time. Since it is not a big project, not having the full functionality of a framework is not a problem. But the question is how to keep code clean. The solution I came up with is to divide code in libraries (the application's API) and models. So inside HTML there will only be API calls, and readability will not be sacrificed. I implemented this with a sort of static Registry (sorry if I'm wrong, I am not a design pattern expert): <?php class Custom_framework { //Global database instance private static $db; //Registered models private static $models = array(); //Registered libraries private static $libraries = array(); //Returns a database class instance static public function get_db(){ if(isset(self::$db)){ //If instance exists, returns it return self::$db; } else { //If instance doesn't exists, creates it self::$db = new DB; return self::$db; } } //Returns a model instance static public function get_model($model_name){ if(isset(self::$models[$model_name])){ //If instance exists, returns it return self::$models[$model_name]; } else { //If instance doesn't exists, creates it if(is_file(ROOT_DIR . 'application/models/' . $model_name . '.php')){ include_once ROOT_DIR . 'application/models/' . $model_name . '.php'; self::$models[$model_name] = new $model_name; return self::$models[$model_name]; } else { return FALSE; } } } //Returns a library instance static public function get_library($library_name){ if(isset(self::$libraries[$library_name])){ //If instance exists, returns it return self::$libraries[$library_name]; } else { //If instance doesn't exists, creates it if(is_file(ROOT_DIR . 'application/libraries/' . $library_name . '.php')){ include_once ROOT_DIR . 'application/libraries/' . $library_name . '.php'; self::$libraries[$library_name] = new $library_name; return self::$libraries[$library_name]; } else { return FALSE; } } } } Inside HTML, API methods are accessed like this: <?php echo Custom_framework::get_library('My_library')->my_method(); ?> It looks to me as a practical solution. But I wonder what its drawbacks are, and what the possible alternatives.

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• Understanding exceptional cases

  - by Justin

  I've been studying the use of exceptions in various php projects (such as Doctrine and Zend Framework). Exceptions seem to be thrown when unordinary input/state occurs. A perfect example is Doctrine throwing an exception when you try to use a invalid query string. I think the creators of the doctrine api understood that first, you can't query data by using an invalid DQL statement, and a developer should immediately be warned that an error has occurred, rather then letting execution continue with the possibility of an error code going un-checked. I also bet that this simplifies reading the code. I can't think of a situation where you would want to use an invalid DQL statement, except unit testing. Since this is true, it's better to avoid plaguing a bunch of code with null/error checks and use exceptions. I've read in books that exceptions shouldn't be thrown when validating dating user input. I've seen examples where of where the guideline is broken. One example is the Zend framework. If supplying an invalid controller or action name, an exception is thrown. Unlike doctrine, the user has more direct control over this sort of input. I know you can configure an error controller and set up a 404 message or what have you, but I'm curious why they have used an exception in this scenario? I guess you can argue the Zend Framework does not know how to continue processing the quest. One last example Is I wrote a function to return some html based on a given resource type. This resource type is hard-coded and sent when a user interacts with a web site (such as clicking a button to display the form to input data). I don't expect users to be mucking around with the request type. Under normal operating conditions, the resource type should be valid. To clean up some logic, I was going to throw an exception if a particular form wasn't found. This is mainly to find the correct form associated with a resource type so proper validation can occur. Does this sound like a valid use case for an exception? Right now it's pretty trivial, but I do plan to implement a restful consumer and re-using a function to map resources to their validation services would be very useful. I can then catch the exception and based on the consumer, return an error message suitable for the request type...

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• E-Business Suite 11.5.10 Fenntartó Támogatással és 12.1 Meghosszabbított Támogatással kapcsolatos külön bejelentés

  - by user552636

  Igaz, az idei Oracle Open World (OOW) már régen volt, de akkor ez a blog még nem létezett. Ugyanakkor azóta többektol kaptam kérdést az OOW-n tett E-Business Suite támogatással kapcsolatos bejelentés értelmezésére vonatkozóan. Ezért gondoltam, hasznos lehet a magyar felhasználók számára, ha írok pár sort a bejelentésrol. Az E-Business Suite (EBS) 11.5.10 verzióhoz kapcsolódó bejelentés: Az Oracle Élettartam Támogatási modellje szerint ez a verzió általánosan 2004. novembertol volt elérheto, melyre az Oracle 2010. november 30-ig biztosított Premier Támogatást, 2010. December 1-tol 2013. november végéig pedig Meghosszabbított Támogatást nyújt. Jövo év december 1-tol az EBS 11.5.10 verzió Fenntartó Támogatás szakaszba kerül. Fenntartó Támogatás szakaszban az újonnan felfedezett bug-okat már nem javítja a Fejlesztés. A bejelentés szerint Oracle a 11.5.10 esetében kivételt tesz és a 2013. december 1-tol 2014. november 30-ig terjedo idoszakban az éles üzemet érinto 1-es súlyossági szintu problémák esetében biztosítani fogja új hibák javítását is. Amire ügyelni érdemes, a rendszer a  Doc ID 883202.1 My Oracle Support dokumentumban részletezett minimum patch szinten kell legyen.   Ez a plusz szolgáltatás nem befolyásolja a támogatási díjat. Az E-Business Suite (EBS) 12.1 verzióhoz kapcsolódó bejelentés   Az EBS 12.1 verzió Meghosszabbított támogatásának eredetileg mehírdetett idoszaka 2014. május 1. – 2017. április 30. volt. Oracle ezt az idoszakot 19 hónappal megtoldotta, így ennek a verziónak a Meghosszabbított Támogatása 2018. december 31-ig tart majd. További jó hír e verziót használó Ügyfeleink számára, hogy a Meghosszabbított Támogatás emelt díjától az Oracle eltekint. Standard Oracle árazás szerint a Meghosszabbított Támogatás elso évében a szolgáltatási díj a Premier Támogatás díjának 110%-a, a második, ill. harmadik években a Premier Támogatás díjának 120%-a. Oracle jelen esetben a plusz 10%-tól, ill. a plusz 20 %-tól eltekint. Íly módon a Meghosszabbított Támogatást Oracle a Premier Támogatás díjért biztosítja majd. Amire ügyelni érdemes, a rendszer a  Doc ID 1195034.1 My Oracle Support dokumentumban részletezett minimum patch szinten kell legyen.   Az idoszakok egyszerubb megértése érdekében az alábbi grafikonon ábrázoltam a szóban forgó verziók támogatásának egyes szakaszait.  

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• Understanding the levels of computing

  - by RParadox

  Sorry, for my confused question. I'm looking for some pointers. Up to now I have been working mostly with Java and Python on the application layer and I have only a vague understanding of operating systems and hardware. I want to understand much more about the lower levels of computing, but it gets really overwhelming somehow. At university I took a class about microprogramming, i.e. how processors get hard-wired to implement the ASM codes. Up to now I always thought I wouldn't get more done if learned more about the "low level". One question I have is: how is it even possible that hardware gets hidden almost completely from the developer? Is it accurate to say that the operating system is a software layer for the hardware? One small example: in programming I have never come across the need to understand what L2 or L3 Cache is. For the typical business application environment one almost never needs to understand assembler and the lower levels of computing, because nowadays there is a technology stack for almost anything. I guess the whole point of these lower levels is to provide an interface to higher levels. On the other hand I wonder how much influence the lower levels can have, for example this whole graphics computing thing. So, on the other hand, there is this theoretical computer science branch, which works on abstract computing models. However, I also rarely encountered situations, where I found it helpful thinking in the categories of complexity models, proof verification, etc. I sort of know, that there is a complexity class called NP, and that they are kind of impossible to solve for a big number of N. What I'm missing is a reference for a framework to think about these things. It seems to me, that there all kinds of different camps, who rarely interact. The last few weeks I have been reading about security issues. Here somehow, much of the different layers come together. Attacks and exploits almost always occur on the lower level, so in this case it is necessary to learn about the details of the OSI layers, the inner workings of an OS, etc.

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• Accounting for waves when doing planar reflections

  - by CloseReflector

  I've been studying Nvidia's examples from the SDK, in particular the Island11 project and I've found something curious about a piece of HLSL code which corrects the reflections up and down depending on the state of the wave's height. Naturally, after examining the brief paragraph of code: // calculating correction that shifts reflection up/down according to water wave Y position float4 projected_waveheight = mul(float4(input.positionWS.x,input.positionWS.y,input.positionWS.z,1),g_ModelViewProjectionMatrix); float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; projected_waveheight = mul(float4(input.positionWS.x,-0.8,input.positionWS.z,1),g_ModelViewProjectionMatrix); waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; reflection_disturbance.y=max(-0.15,waveheight_correction+reflection_disturbance.y); My first guess was that it compensates for the planar reflection when it is subjected to vertical perturbation (the waves), shifting the reflected geometry to a point where is nothing and the water is just rendered as if there is nothing there or just the sky: Now, that's the sky reflecting where we should see the terrain's green/grey/yellowish reflection lerped with the water's baseline. My problem is now that I cannot really pinpoint what is the logic behind it. Projecting the actual world space position of a point of the wave/water geometry and then multiplying by -.5f, only to take another projection of the same point, this time with its y coordinate changed to -0.8 (why -0.8?). Clues in the code seem to indicate it was derived with trial and error because there is redundancy. For example, the author takes the negative half of the projected y coordinate (after the w divide): float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; And then does the same for the second point (only positive, to get a difference of some sort, I presume) and combines them: waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; By removing the divide by 2, I see no difference in quality improvement (if someone cares to correct me, please do). The crux of it seems to be the difference in the projected y, why is that? This redundancy and the seemingly arbitrary selection of -.8f and -0.15f lead me to conclude that this might be a combination of heuristics/guess work. Is there a logical underpinning to this or is it just a desperate hack? Here is an exaggeration of the initial problem which the code fragment fixes, observe on the lowest tessellation level. Hopefully, it might spark an idea I'm missing. The -.8f might be a reference height from which to deduce how much to disturb the texture coordinate sampling the planarly reflected geometry render and -.15f might be the lower bound, a security measure.

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• Strategy for avoiding duplicate object ids for data shared across devices using iCloud

  - by rmaddy

  I have a data intensive iOS app that is not using CoreData nor does it support iCloud synching (yet). All of my objects are created with unique keys. I use a simple long long initialized with the current time. Then as I need a new key I increment the value by 1. This has all worked well for a few years with the app running isolated on a single device. Now I want to add support for automatic data sync across devices using iCloud. As my app is written, there is the possibility that two objects created on two different devices could end up with the same key. I need to avoid this possibility. I'm looking for ideas for solving this issue. I have a few requirements that the solution must meet: 1) The key needs to remain a single integral data type. Converting all existing keys to a compound key or to a string or other type would affect the entire code base and likely result in more bugs than it's worth. 2) The solution can't depend on an Internet connection. A user must be able to run the app and add data even with no Internet connection. The data should still resolve properly later when the data syncs through iCloud once a connection is available. I'll accept one exception to this rule. If no other option is available, I may be open to requiring an Internet connection the first time the app's data is initialized. One idea I have been toying around with in my head is logically splitting the integer key into two parts. The high 4 or 5 bits could be used as some sort of device id while the rest represents the actual key. The fuzzy part is figuring out how to come up with non-conflicting device ids that fit in a few bits. This should be viable since I don't need to deal will millions of devices. I just need to deal with the few devices that would be shared by a given iCloud account. I'm open to suggestions. Thanks.

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• Tricky situation with EF and Include while projecting (Select / SelectMany)

  - by Vincent Grondin

  Originally posted on: http://geekswithblogs.net/vincentgrondin/archive/2014/06/07/tricky-situation-with-ef-and-include-while-projecting-select.aspxHello, the other day I stumbled on a problem I had a while back with EF and Include method calls and decided this was it and I was going to blog about it…  This would sort of to pin it inside my head and maybe help others too !  So I was using DBContext and wanted to query a DBSet and include some of it’s associations and in the end, do a projection to get a list of Ids…   At first it seems easy…  Query your DBSet, call Include right afterward, then code the rest of your statement with the appropriate where clause and then, do the projection…   Well it wasn’t that easy as my query required I code my where on some entities a few degree further in the association chain and most of these links where “Many”…  I had to do my projection right away with the SelectMany method.  So I did my stuff and tested the query….  no association where loaded…  My Include statement was simply ignored !  Then I remembered this behavior and how to get it to work…  You need to move the Include AFTER your first projection (Select or SelectMany).  So my sequence became:   Query the DBSet, do the projection with SelectMany, Include the associations, code the where clause and do the final projection…. but it wouldn’t compile…   It kept saying that it could not find an “Include” method on an IQueryable… which is perfectly true!  I knew this should work so I went to the definition of the DBset and saw it inherited DBQuery and sure enough the include method was there…  So I had to cast my statement from start until the end of the first projection in a DBQuery then do the Includes and then the rest of my query….   Bottom line is, whenever your Include statement seem to be ignored, then maybe you will need to move them further down in your query and cast your statement in whatever class gives you access to the Include…   Happy coding all !

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• Android Array Lag?

  - by Mike

  I am making a platform game for Android. It is sort of a tile based game. I added bullets and enemies with AI and a bunch of tile types. I created a simple map with no Enemies. Everything was running well and smooth until I shot a bunch of bullets randomly everywhere. A couple of hundreds of bullets later, the FPS lowered. I made a test to find out if the bullets were the problem so I made another simple map with just a tile to stand on and left it for a while. Minutes later, I played around with it a bit to check if the FPS changed and it didnt. I reloaded the same map and shot a lot of bullets. Minutes later, the FPS was visibly lower even after the number of bullets were zero. Points to note: Programmed FPS is 30 Tested on a Samsung Galaxy Y and Samsung Galaxy W Any tile, enemy, bullet that is off screen is not drawn to prevent lag Bullets collide with Tiles (if they dont collide with in 450 frames, they are removed from the array) I used List bullets = new ListArray(); I used bullets.add(new Bullet(x, y, params...)); I used for(...){ if(...){ bullets.remove(i); } } Code for bullet: private void drawBullets(Canvas canvas) { for (int i = 0; i < bullets.size(); i++) { Bullet b = bullets.get(i); b.update(canvas); //updates physics if (b.t > blm) { //if the bullet is past its expiry bullets.remove(i); i--; } else { if (svx((b.x)) > 0 && svx(b.x) < width && svy((b.y)) > 0 && svy(b.y) < height) { // if bullet is not off screen b.draw(canvas); // draw the bullet } } } } I tried searching for solutions and references but I have no luck. I'm guessing that the lag has something to do with the Array and the Bullets or Classes that I've loaded? I'm not sure! Someone please help! Thanks in advance! :)

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• Simulate 'Shock absorbtion' with tire rubber in PhysX (2.8.x)

  - by Mungoid

  This is a kinda tricky question and I fear there is no easy enough solution, but I figured I'd hit SE up before giving up on it and just doing what I can. A machine I am working on has no suspension or shocks or springs of any sort in the real machine, so you would think that when it drives over bumps, it would shake like crazy but because its tires (6 of them) are quite large they seem to absorb a lot of shock from the bumps. Part of this is because the machine is around 30k lbs and it just smashes/compresses any bumps in the ground down (This is another issue im still working on) and the other part is that the tires seem to have a lot of flex to them with a lot of air as well. So my current task is to simulate shock absorption in physx without visibly separating the tires from the spindle/axle.. I have been messing with all kinds of NxMaterial, NxSpring, Joints, etc. and have had no luck getting this to work. The main problem is that the spindle attached to the tire is directly in the center and the axle is basically solidly attached to the chassis, so if i give it any spring or suspension travel, that spindle on the tires will move upwards or downwards, looking very odd because now its not any longer in the center of the tire. I tried giving it a higher restitution but that just makes it bouncy without any shock absorption. Another avenue I am messing with is to actively smooth the terrain in front of the tires so that before it hits a bumpy patch, that patch is smoothed and it doesn't bounce. The only issue with this is that it is pretty expensive to do with 6 tires, high tesselation of the terrain and other complex things going on at the same time in this simulation. I am still working on this but I am hoping to mix and match a few different aspects to get the best possible outcome. This is a bit of a complex issue so I'm not expecting anyone to have a definitive answer, just hoping someone may think of something I haven't =-) -Side note: Yes i know PhysX 2.8.x is quite outdated but we have to stick with it for this implementation. We are in the process of going to another physics engine but it is out of scope to apply that engine to this project.

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• Forced to be trained [closed]

  - by steeb

  is it OK to force employees to take a training in order to make them sign a contract to stay in the job for X years? Here I'm the only developer in the company and before this job I've developed in VB6, VB.Net and others. There are others technicians here but they query the database server to make reports and make little programs but do not spend all day in programming. I was hired here to manage some legacy data to be migrated to a new system and I used my experience to accomplish the task. I also have made some utilities and other developments. Since we went live with the new system I've been developing a lot of side programs, add-ons and changed the source code of it and basically I've been learning from it since then and became some sort of jack of all trades when some feature needs to be changed or corrected. I have one and a half year in this company but during the last 8 months I've been entirely programming in the system. There have been times when even the implementers ask me how I accomplish certain things. The issue here is that the company has come and told me and other co-workers (which do not program in the system but know basic programming and databases) to have a basic training to program for the new system's platform and when we finish it we will sign a contract to stay in the company for an unspecified time. They have offered also an unspecified better salary. I'm feeling very suspicious cause I know the basics of system and I don't understand why I have to take it, being known by everybody all developments I've made. I gathered with my boss and told him that I should not take that course because I feel that I can learn more with all the daily requirements I've been asked and they should save that money. But he responded me that I have to take it and sign after that. I think they want me to be with them for a long time, and I'd like to, but my opinion is that I would like to stay in the company because I feel comfortable in all laboral aspects (including salary) but not because I signed a contract forced to do more tasks and forced to say no if I have others and better job offers. What advice can you give me in this kind of situation?

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• How is a switch statement better than a series of if statements? [closed]

  - by user1276078

  Possible Duplicate: Should I use switch statements or long if…else chains? I'm working on a small program that will conduct an Insertion Sort. A number will be inputted through the keyboard and stored in a variable I called "num." I've decided to use a switch statement in order to obtain the number inputted. switch( e.getKeyCode() ) { case KeyEvent.VK_0: num = 0; break; case KeyEvent.VK_1: num = 1; break; case KeyEvent.VK_2: num = 2; break; case KeyEvent.VK_3: num = 3; break; case KeyEvent.VK_4: num = 4; break; case KeyEvent.VK_5: num = 5; break; case KeyEvent.VK_6: num = 6; break; case KeyEvent.VK_7: num = 7; break; case KeyEvent.VK_8: num = 8; break; case KeyEvent.VK_9: num = 9; break; } I realized one other course of action could have been to use a set of if statements. if( e.getKeyCode() == KeyEvent.VK_0 ) num = 0; else if( e.getKeyCode() == KeyEvent.VK_1 ) num = 1; etc. for every number up until 9. I then wondered what the essential difference is between a switch statement and a series of if statements. I know it saves space and time to write, but it's not that much. So, my question is, aside from the space, does a switch statement differ from a series of if statments in any way? Is it faster, less error-prone, etc.? This question really doesn't affect my code that much. I was just wondering. Also, this question pertains to the JAVA language, not any other programming language.

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• 2D collision resolving

  - by Philippe Paré

  I've just worked out an AABB collision algorithm for my 2D game and I was very satisfied until I found out it only works properly with movements of 1 in X and 1 in Y... here it is: public bool Intersects(Rectanglef rectangle) { return this.Left < rectangle.Right && this.Right > rectangle.Left && this.Top < rectangle.Bottom && this.Bottom > rectangle.Top; } public bool IntersectsAny(params Rectanglef[] rectangles) { for (int i = 0; i < rectangles.Length; i++) { if (this.Left < rectangles[i].Right && this.Right > rectangles[i].Left && this.Top < rectangles[i].Bottom && this.Bottom > rectangles[i].Top) return true; } return false; } and here is how I use it in the update function of my player : public void Update(GameTime gameTime) { Rectanglef nextPosX = new Rectanglef(AABB.X, AABB.Y, AABB.Width, AABB.Height); Rectanglef nextPosY; if (Input.Key(Key.Left)) nextPosX.X--; if (Input.Key(Key.Right)) nextPosX.X++; bool xFree = !nextPosX.IntersectsAny(Boxes.ToArray()); if (xFree) nextPosY = new Rectanglef(nextPosX.X, nextPosX.Y, nextPosX.Width, nextPosX.Height); else nextPosY = new Rectanglef(AABB.X, AABB.Y, AABB.Width, AABB.Height); if (Input.Key(Key.Up)) nextPosY.Y--; if (Input.Key(Key.Down)) nextPosY.Y++; bool yFree = !nextPosY.IntersectsAny(Boxes.ToArray()); if (yFree) AABB = nextPosY; else if (xFree) AABB = nextPosX; } What I'm having trouble with, is a system where I can give float values to my movement and make it so there's a smooth acceleration. Do I have to retrieve the collision rectangle (the rectangle created by the other two colliding)? or should I do some sort of vector and go along this axis until I reach the collision? Thanks a lot!

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• Notes - Part I - Say Hello from Java

  - by Silviu Turuga

  Sometimes we need to take small notes to remember things, one way to do this is to use stick notes and have them all around our desktop. But what happening if you have a lot of notes and a small office? You'll need a piece of software that will sort things for you and also it will provide you a quick way to retrieve the notes when need. Did I mention that this will keep your desktop clean and also will reduce paper waste? During the next days we'll gonna create an application that will let you manage your notes, put them in different categories etc. I'll show you step by step what do you need to do and finally you'll have the application run on multiple systems, such as Mac, Windows, Linux, etc. The only pre-requisition for this lesson is to have JDK 7 with JavaFX installed and an IDE, preferably NetBeans. I'll call this application Notes…. Part I - Say Hello from Java  From NetBeans go to Files->New Project Chose JavaFX->JavaFX FXML Application Project Name: Notes FXML name: NotesUI Check Create Application Class and name it Main After this the project is created and you'll see the following structure As a best practice I advice you to have your code in your own package instead of the default one. right click on Source Packages and chose New->Java Package name it something like this: com.turuga.notes and click Next after the package is created, select all the 3 files from step #3 and drag them over the new package chose Refactor, as this will make sure all the references are correctly moved inside the new package now you should have the following structure if you'll try to run the project you'll get an error: Unable to find class: Main right click on project name Notes and click properties go to Run and you'll see Application Class set to Main, but because we have defined our own packages, this location has been change, so click on Browse and the correct one appear: com.turuga.notes.Main last modification before running the project is to right click on NotesUI.fxml and chose Edit (if you'll double click it will open in JavaFX Scene Builder) look around line 9 and change fx:controller="NotesUIController" to fx:controller="com.turuga.notes.NotesUIController" now you are ready to run it and you should see the following On the next lesson we'll continue to play with NetBeans and start working on the interface of our project

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• Developer career feeling like going back in time every new job [closed]

  - by komediant

  Is there a good category for this question? My background is bachelor in ICT and for a hobby I am programming already since I was around twelve I think. Started with QBasic, Pascal, C, Java et cetera. Currently I am working for about eight/nine years. Half academics/medical and half company world. A few years ago I started with frameworks and I began with Grails (underlying Spring/Hibernate), which was a heavenly job, very productive and no hassle. My previous job I developed in pure Spring/Hibernate Java, which was a bit more writing annotations and XML and no conventions like Grails. But still, I did like Spring/Hibernate a lot and the professional setup with a developmentstreet, versioning, Jenkins/Sonar, log4j and a good IDE like IntellIJ. It felt quite 'clear' and organised, although I knew Grails which felt a bit more productive. But...at my current job almost half the code is pure servlet, hard coded JDBC (connections handled by yourself), scriptlets in all JSP pages, no service layer, no versioning, no Maven, HTML in DAO-layer, JAR-hell, no hot swap deployment locally, every change you have to deploy and hope it works fine on the server. All local development needs ugly scriptlet tags to check which environment it is running. Et cetera. Now and then developers work over in the evening - I don't - and still lots of issues are not solved and new projects are waiting. I hear the developers complaining, but somehow they feel like what they have now is "advanced" or they are in a sort of comfore zone. The lead developer seems open for new things, but half of the times he says he can implement MVC-framework features himself instead of using what is already out there. So in short, I currently feel like I miss all the modern framework techniques and that the company is going so slow forward. I just work here for two months now. What I do now is also code some partially ugly stuff, but it goes in completely into my nature and I feel uncomfortable with it. Coding something takes long(er) than estimated and my manager complains about why it takes so long and I feel ashamed for myself needing so much time. Where I was used to just writing a query I now build up whole try catch methods. My manager knows my complaints and the developers do so too. There will come a meeting to line out plans for 2013 on technology and the issues I and the company are facing. I am not looking for another job yet, it's close to wehre I live and the economy is fragile. Does anyone else have had this kind of career, like feeling going backwards witch technology? And how did you cope with it?

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• reference list for non-IT driven algorithmic patterns

  - by Quicker

  I am looking for a reference list for non-IT driven algorithmic patterns (which still can be helped with IT implementations of IT). An Example List would be: name; short desc; reference Travelling Salesman; find the shortest possible route on a multiple target path; http://en.wikipedia.org/wiki/Travelling_salesman_problem Ressource Disposition (aka Regulation); Distribute a limited/exceeding input on a given number output receivers based on distribution rules; http://database-programmer.blogspot.de/2010/12/critical-analysis-of-algorithm-sproc.html If there is no such list, but you instantly think of something specific, please 'put it on the desk'. Maybe I can compile something out of the input I get here (actually I am very frustrated as I did not find any such list via research by myself). Details on Scoping: I found it very hard to formulate what I want in a way everything is out that I do not need (which may be the issue why I did not find anything at google). There is a database centric definition for what I am looking for in the section 'Processes' of the second example link. That somehow fits, but the database focus sort of drifts away from the pattern thinking, which I have in mind. So here are my own thoughts around what's in and what's out: I am NOT looking for a foundational algo ref list, which is implemented as basis for any programming language. Eg. the php reference describes substr and strlen. That implements algos, but is not what I am looking for. the problem the algo does address would even exist, if there were no computers (or other IT components) the main focus of the algo is NOT to help other algo's chances are high, that there are implementions of the solution or any workaround without any IT support out there in the world however the algo could be benefitialy implemented/fully supported by a software application = means: the problem of the algo has to be addressed anyway, but running an algo implementation with software automates the process (that is why I posted it on stackoverflow and not somewhere else) typically such algo implementations have more than one input field value and more than one output field value - which implies it could not be implemented as simple function (which is fixed to produce not more than one output value) in a normalized data model often times such algo implementation outputs span accross multiple rows (sometimes multiple tables), whereby the number of output rows depends on the input paraters and rows in the table(s) at start time - which implies that any algo implementation/procedure must interact with a database (read and/or write) I am mainly looking for patterns, not for specific implementations. Example: The Travelling Salesman assumes any coordinates, however it does not say: You need a table targets with fields x and y. - however sometimes descriptions are focussed on examples with specific implementations very much - no worries, as long as the pattern gets clear

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• Java Grade Calculator program for class kepp geting the error "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException." [migrated]

  - by user2880621

  this is my first question I've posted. I've used this site to look at other questions to help with similar problems I've had. After some cursory looking I couldn't find quite the answer I was looking for so I decided to finally succumb and create an account. I am fairly new to java, only a few weeks into my first class. Anyway, my project is to create a program which takes any amount of students and their grades, and then assign them a letter grade. The catch is, however, that it is on a sort of curve and the other grades' letter are dependent on the the highest. Anything equal to or 10 points below the best grade is an a, anything 11-20 points below is a b, and so on. I am to use an array, but I get this error when ran "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException." I will go ahead and post my code down below. Thanks for any advice you may be able to give. package grade.calculator; import java.util.Scanner; /** * * @author nichol57 */ public class GradeCalculator { /** * @param args the command line arguments */ public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println("Enter the number of students"); int number = input.nextInt(); double[]grades = new double [number]; for (int J = number; J >=0; J--) { System.out.println("Enter the students' grades"); grades[J] = input.nextDouble(); } double best = grades[0]; for (int J = 1; J < number; J++) { if (grades[J] >= best){ best = grades[J]; } } for (int J = 0;J < number; J++){ if (grades[J] >= best - 10){ System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "A"); } else if (grades[J] >= best - 20){ System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "B"); } else if (grades[J] >= best - 30) { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "C"); } else if (grades[J] >= best - 40) { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "D"); } else { System.out.println("Student " + J + " score is " + grades[J] + " and grade is " + "F"); } } // end for loop for output }// end main method }

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