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• Lambda Expressions and Memory Management

  - by Surya

  How do the Lambda Expressions / Closures in C++0x complicate the memory management in C++? Why do some people say that closures have no place in languages with manual memory management? Is there claim valid and if yes, what are the reasons behind it?

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• Memory efficient collection class

  - by Joe

  I'm building an array of dictionaries (called keys) in my iphone application to hold the section names and row counts for a tableview. the code looks like this: [self.results removeAllObjects]; [self.keys removeAllObjects]; NSUInteger i,j = 0; NSString *key = [NSString string]; NSString *prevKey = [NSString string]; if ([self.allResults count] > 0) { prevKey = [NSString stringWithString:[[[self.allResults objectAtIndex:0] valueForKey:@"name"] substringToIndex:1]]; for (NSDictionary *theDict in self.allResults) { key = [NSString stringWithString:[[theDict valueForKey:@"name"] substringToIndex:1]]; if (![key isEqualToString:prevKey]) { NSDictionary *newDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:i],@"count", prevKey,@"section", [NSNumber numberWithInt:j], @"total",nil]; [self.keys addObject:newDictionary]; prevKey = [NSString stringWithString:key]; i = 1; } else { i++; } j++; } NSDictionary *newDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:i],@"count", prevKey,@"section", [NSNumber numberWithInt:j], @"total",nil]; [self.keys addObject:newDictionary]; } [self.tableview reloadData]; The code works fine first time through but I sometimes have to rebuild the entire table so I redo this code which orks fine on the simulator, but on my device the program bombs when I execute the reloadData line : malloc: *** mmap(size=3772944384) failed (error code=12) *** error: can't allocate region *** set a breakpoint in malloc_error_break to debug malloc: *** mmap(size=3772944384) failed (error code=12) *** error: can't allocate region *** set a breakpoint in malloc_error_break to debug Program received signal: “EXC_BAD_ACCESS”. If I remove the reloadData line the code works on the device. I'm wondering if this is something to do with the way I've built the keys array (ie using autoreleased strings and dictionaries).

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• Equiv of glDrawpixels that operates on GPU memory?

  - by anon

  glDrawPixels(GLsizei width, GLsizei height, GLenum format, GLenum type, const ovid *pixels); Is there a function like this, except instead of accessing CPU memory, it accesses GPU memory? [Either a texture of a frame buffer object]

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• Writing shorter code/algorithms, is more efficient (performance)?

  - by Carlos

  After coming across the code golf trivia around the site it is obvious people try to find ways to write code and algorithms as short as the possibly can in terms of characters, lines and total size, even if that means writing something like: n=input() while n>1:n=(n/2,n*3+1)[n%2];print n So as a beginner I start to wonder whether size actually matters :D. It is obviously a very subjective question highly dependent on the actual code being used, but what is the rule of thumb in the real world. In the case that size wont matter, how come then we don't focus more on performance rather than size?

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• How to delete images from memory in a browser

  - by trefeater

  Hi all. Is it possible to delete some images from the browser (firefox2) memory using javascript? By doing this, I want to save some precious browser memory and let my web app to work better. I guess that if possible, it will be something like this: delete (document.images[7]); document.images[7].src = null; document.images[7] = null; Thanks guys!

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• vps running out of memory, 200MB free

  - by demon

  At the beginning of this year I took a VPS for my website because I was running against the resource limits from a shared hosting. Here are the things I know: 2GB memory, with 1GB swap Debian X64 server ED installed Software running on the webserver: mysql apache postfix pop3 imap amavisd clamd cron fail2ban munin-node pure-ftpd spamd nginx Now for the setup: Nginx listens on port 80 and handles the static files, the php side is done by apache2 running mod_php in combi with apc(no var caching!). Iam using a pretty 'busy' drupal and phpbb stack on the server, for drupal iam using boost and authcache to handle of the server load with a pressflow stack. phpbb is just phpbb3 with some mods installed, but has at max 30 users online at a time.. The problem is that its staring to use the swap after a few days after a reboot and thus the site becomes slower. I'v added pictures of monit and munin, so maybe somebody can help me out... Monit: Munin:

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• efficient android rendering

  - by llll

  I've read quite a few tutorials on game programming on android, and all of them provide basically the same solution as to drawing the game, that is having a dedicated thread spinning like this: public void run() { while(true) { if(!surfaceHolder.getSurface().isValid()) continue; Canvas canvas = surfaceHolder.lockCanvas(); drawGame(canvas); /* do actual drawing here */ surfaceHolder.unlockCanvasAndPost(canvas); } } now I'm wondering, isn't this wasteful? Suppose I've a game with very simple graphics, so that the actual time in drawGame is little; then I'm going to draw the same things on and on, stealing cpu from the other threads; a possibility could be skipping the drawing and sleeping a bit if the game state hasn't changed, which I could check by having the state update thread mantaining a suitable status flag. But maybe there are other options. For example, couldn'it be possible to synchronize with rendering, so that I don't post updates too often? Or am I missing something and that is precisely what lockCanvas does, that is it blocks and burns no cpu until proper time? Thanks in advance L.

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• Efficient persistent storage for simple id to table of values map for java

  - by wds

  I need to store some data that follows the simple pattern of mapping an "id" to a full table (with multiple rows) of several columns (i.e. some integer values [u, v, w]). The size of one of these tables would be a couple of KB. Basically what I need is to store a persistent cache of some intermediary results. This could quite easily be implemented as simple sql, but there's a couple of problems, namely I need to compress the size of this structure on disk as much as possible. (because of amount of values I'm storing) Also, it's not transactional, I just need to write once and simply read the contents of the entire table, so a relational DB isn't actually a very good fit. I was wondering if anyone had any good suggestions? For some reason I can't seem to come up with something decent atm. Especially something with an API in java would be nice.

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• Word 2007 "Out of Memory or Disk Space" Error on launch

  - by Adam

  Word 2007 is installed on a Vista Home Premium machine and whenever it starts up it opens what appears to be a dynamic installer to do something and then throws up the "Out of Memory or Disk Space" error. Word 2007 never completes starting up. Reinstalling Word hasn't helped and if I can avoid reinstalling Windows until Windows 7 is released and get Word working in the mean time, that would be ideal. I've been looking around for a solution, once of which seemed to point to a problem with the user account. I created a second user on the machine and Word still had the same problem. The other solution that seems possible is a corrupted normal.dot/normal.dotm file. However, even in the location it should be, I can't seem to find it. Am I going in the right direction with this? Is there another solution I haven't come across that will fix this? If it is possible that renaming normal.dot/normal.dotm how can I find it?

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• What is an efficient way to erase substrings?

  - by Legend

  I have a long string and a set of <end-index, string> list like the following: long_sentence = "This is a long long long long sentence" indices = [[6, "is"], [8, "is a"], [18, "long"], [23, "long"]] An element 6, "is" indicates that 6 is the end index of the word "is" in the string. I want to get the following string in the end: >> print long_sentence This .... long ......... long sentence" I tried an approach like this: temp = long_sentence for i in indices: temp = temp[:int(i[0]) - len(i[1])] + '.'*(len(i[1])+1) + temp[i[0]+1:] While this seems to be working, it is taking exceptionally long time (more than 6 hours on 5000 strings inside a 300 MB file). Is there a way to speed this up?

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• kvm process has too large a memory footprint on host

  - by gucki

  I'm using latest ubuntu quantal and start a kvm guest which should have 2048 MB of memory. Now after a few hours I can see that the kvm process of this guest is around 2700 MB, so 700 MB more than the guest should be able to consume. I mean a small overhead like 1% would be ok, but not 30%?! root 8631 74.0 22.2 4767484 2752336 ? Sl Nov07 512:58 kvm -cpu kvm64 -smp sockets=1,cores=2 -cpu kvm64 -m 2048 -device virtio-blk-pci,drive=drive-virtio0,id=virtio0,bus=pci.0,addr=0xa,bootindex=100 -drive file=rbd:data/vm-disk-1,if=none,id=drive-virtio0,cache=writeback,aio=native -device virtio-net-pci,netdev=net0,bus=pci.0,addr=0x12,id=net0,mac=02:7a:86:e6:1a:6c,bootindex=200 -netdev type=tap,id=net0,vhost=on -usbdevice tablet -nodefaults -enable-kvm -daemonize -boot menu=on -vga cirrus root 8694 0.0 0.0 0 0 ? S Nov07 0:00 [kvm-pit/8631] How is this possible and how to prevent it?

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• Most efficient way of checking for a return from a function call in Perl

  - by Gaurav Dadhania

  I want to add the return value from the function call to an array iff something is returned (not by default, i.e. if I have a return statement in the subroutine.) so I'm using unshift @{$errors}, "HashValidator::$vfunction($hashref)"; but this actually adds the string of the function call to the array. I also tried unshift @{$errors}, $temp if defined my $temp = "HashValidator::$vfunction($hashref)"; with the same result. What would a perl one-liner look like that does this efficiently (I know I can do the ugly, multi-line check but I want to learn). Thanks,

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• Most Efficient way to set Register to 1 or (-1)

  - by Bob

  I am taking an assembly course now, and the guy who checks our home assignments is a very pedantic old-school optimization freak. For example he deducts 10% if he sees: mov ax, 0 instead of: xor ax,ax even if it's only used once. I am not a complete beginner in assembly programing but I'm not an optimization expert, so I need your help in something (might be a very stupid question but I'll ask anyway): if I need to set a register value to 1 or (-1) is it better to use: mov ax, 1 or do something like: xor ax,ax inc ax I really need a good grade, so I'm trying to get it as optimized as possible. ( I need to optimize both time and code size)

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• Stack overflow - how to increase memory allocation to programme

  - by Vaibhav

  When i try to initialize a 3D array of size 300*300*4 in c programme , my programme stops runnig and reports stack overflow error. my pc has 3GB RAM and disk i am working on also has aboy 3GB free memory which should be sufficeint. Is there any way to increase memory allocated to a programme. I am using Dev c++ on windows vista

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• Have parameters in Dao methods to get entities the most efficient way for read-only access

  - by Blankman

  Allot of my use of hibernate, at least for that data that is presented on many parts of the web application, is for read-only purposes. I want to add some parameters to my Dao methods so I can modify the way hibernate pulls the data and how it handles transactions etc. Example usage: Data on the front page of my website is displayed to the users, it is read-only, so I want to avoid any session/entity tracking that hibernate usually does. This is data that is read-only, will not be changed in this transaction, etc. What would be the most performant way to pull the data? (the code below is c#/nhibernate, I'm implementing this in java as I learn it) public IList<Article> GetArticles() { return Session.CreateCriteria(typeof(Article)) // some where cluase }

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• What is an efficient way to find a non-colliding rectangle nearest to a location

  - by hyn

  For a 2D game I am working on, I am using y axis sorting in a simple rectangle-based collision detection. This is working fine, and now I want to find the nearest empty rectangle at a given location with a given size, efficiently. How can I do this? Is there an algorithm? I could think of a simple brute force grid test (with each grid the size of the empty space we're looking for) but obviously this is slow and not even a complete test.

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• How to keep program always in memory (no swapping)

  - by Yossarian

  I'm using KeePass (on Windows 7) for storing passwords. The application is running on my laptop almost 100% of the time, but I'm using it rarely. The problem is, that activating the window after long time takes huge amount of time, I'd say that OS realized the application is no longer used and swapped it. I don't want OS to swap my KeePass (because of the loading lag, and also because of security - I don't like the idea of password keeping program's memory to be stored anywhere on HDD). Is there any possibility how to tell OS not to swap some program? Or, is this achievable by some programming?

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• Simple and efficient distribution of C++/Boost source code (amalgamation)

  - by Arrieta

  Hello: My job mostly consists of engineering analysis, but I find myself distributing code more and more frequently among my colleagues. A big pain is that not every user is proficient in the intricacies of compiling source code, and I cannot distribute executables. I've been working with C++ using Boost, and the problem is that I cannot request every sysadmin of every network to install the libraries. Instead, I want to distribute a single source file (or as few as possible) so that the user can g++ source.c -o program. So, the question is: can you pack the Boost libraries with your code, and end up with a single file? I am talking about the Boost libraries which are "headers only" or "templates only". As an inspiration, please look at the distribution of SQlite or the Lemon Parser Generator; the author amalgamates the stuff into a single source file which is trivial to compile. Thank you.

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• more efficient way to pickle a string

  - by gatoatigrado

  The pickle module seems to use string escape characters when pickling; this becomes inefficient e.g. on numpy arrays. Consider the following z = numpy.zeros(1000, numpy.uint8) len(z.dumps()) len(cPickle.dumps(z.dumps())) The lengths are 1133 characters and 4249 characters respectively. z.dumps() reveals something like "\x00\x00" (actual zeros in string), but pickle seems to be using the string's repr() function, yielding "'\x00\x00'" (zeros being ascii zeros). i.e. ("0" in z.dumps() == False) and ("0" in cPickle.dumps(z.dumps()) == True)

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• More efficient R / Sweave / TeXShop work-flow?

  - by user594795

  I've now got everything to work properly on my Mac OS X 10.6 machine so that I can create decent looking LaTeX documents with Sweave that include snippets of R code, output, and LaTeX formatting together. Unfortunately, I feel like my work-flow is a bit clunky and inefficient: Using TextWrangler, I write LaTeX code and R code (surrounded by <<= above and @ below R code chunk) together in one .Rnw file. After saving changes, I call the .Rnw file from R using the Sweave command Sweave(file="/Users/mymachine/Documents/Assign4.Rnw", syntax="SweaveSyntaxNoweb") In response, R outputs the following message: You can now run LaTeX on 'Assign4.tex' So then I find the .tex file (Assign4.tex) in the R directory and copy it over to the folder in my documents ~/Documents/ where the .Rnw file is sitting (to keep everything in one place). Then I open the .tex file (e.g. Assign4.tex) in TeXShop and compile it there into pdf format. It is only at this point that I get to see any changes I have made to the document and see if it 'looks nice'. Is there a way that I can compile everything with one button click? Specifically it would be nice to either call Sweave / R directly from TextWrangler or TeXShop. I suspect it might be possible to code a script in Terminal to do it, but I have no experience with Terminal. Please let me know if there's any other things I can do to streamline or improve my work flow.

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• Setting the first two bytes of a block of memory

  - by idealistikz

  Suppose I have a block of memory as such: void *block = malloc(sizeof(void *) + size); How do I set the first two bytes of the block as NULL or have it point somewhere? I do not want to simply assign 'block' to NULL or to another pointer because I want to access the rest of the memory I malloc'ed.

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• Efficient copy of entire directory

  - by Hui Jin

  I want to copy one directory and the two files under it to another shared location of shared storage. Is it possible to combine the three(one directory and two files) as a continuous file writing and decompose it at another side to save the cost? I am limited to c language and Unix/Linux. I am considering to create a structure with the inode info and get the data at receiver. Thanks!

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• What is the most efficient way to delete all selected items in a ListViewItem collection

  - by Andrew

  My user is able to select multiple items in a ListView collection that is configured to show details (that is, a list of rows). What I want to do is add a Delete button that will delete all of the selected items from the ListViewItem collection associated with the ListView. The collection of selected items is available in ListView.SelectedItems, but ListView.Items doesn't appear to have a single method that lets me delete the entire range. I have to iterate through the range and delete them one by one, which will potentially modify a collection I'm iterating over. Any hints? Edit: What I'm basically after is the opposite of AddRange().

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• Slurm: How to find out how much memory is not allocated at a given Node

  - by PlagTag

  i am new to SLURM. I am searching for a comfortable way, to see how many memory at an node/nodelist is available for my srun allocation. I already played around with sinfo and scontrol and sstat but none of them gives me the information i need in one comfortable overview. I had the idea to write a shell script, in order to fetch all fields of all jobs from scontrol and sum them up. But there must be an easier way. Would be great if anyone has an hint or idea!

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• Passenger/Rails not releasing memory

  - by michaeldelorenzo

  I have an Ubuntu server running three separate Rails (2.3.8) applications with Passenger, REE and Apache. Recently we started experiencing problems with ruby processes eating up memory and consuming entire cores on our server. Here's what we're getting... %CPU PID USER COMMAND 99.9 1717 nobody Rails: /var/www/api 99.6 5542 nobody Rails: /var/www/api 97.3 1223 nobody Rails: /var/www/api 4.7 5537 nobody Passenger ApplicationSpawner: /var/www/api 10.5 1801 nobody Rails: /var/www/api We've also seen instances where there have been over 100 instances of Apache running. These applications have been running for a few months without an of these issues, but in the last day or so we've been noticing this. The site referenced here is a Rails application that is a RESTful API so it serves many requests every minute. Any guidance on what we should be checking or looking out for would be appreciated.

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