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• Repeated host lookups failing in urllib2

  - by reve_etrange

  I have code which issues many HTTP GET requests using Python's urllib2, in several threads, writing the responses into files (one per thread). During execution, it looks like many of the host lookups fail (causing a name or service unknown error, see appended error log for an example). Is this due to a flaky DNS service? Is it bad practice to rely on DNS caching, if the host name isn't changing? I.e. should a single lookup's result be passed into the urlopen? Exception in thread Thread-16: Traceback (most recent call last): File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner self.run() File "/home/da/local/bin/ThreadedDownloader.py", line 61, in run page = urllib2.urlopen(url) # get the page File "/usr/lib/python2.6/urllib2.py", line 126, in urlopen return _opener.open(url, data, timeout) File "/usr/lib/python2.6/urllib2.py", line 391, in open response = self._open(req, data) File "/usr/lib/python2.6/urllib2.py", line 409, in _open '_open', req) File "/usr/lib/python2.6/urllib2.py", line 369, in _call_chain result = func(*args) File "/usr/lib/python2.6/urllib2.py", line 1170, in http_open return self.do_open(httplib.HTTPConnection, req) File "/usr/lib/python2.6/urllib2.py", line 1145, in do_open raise URLError(err) URLError: <urlopen error [Errno -2] Name or service not known>

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• Freeing ImageData when deleting a Canvas

  - by user578770

  I'm writing a XUL application using HTML Canvas to display Bitmap images. I'm generating ImageDatas and imporingt them in a canvas using the putImageData function : for(var pageIndex=0;pageIndex<100;pageIndex++){ this.img = imageDatas[pageIndex]; /* Create the Canvas element */ var imgCanvasTmp = document.createElementNS("http://www.w3.org/1999/xhtml",'html:canvas'); imgCanvasTmp.setAttribute('width', this.img.width); imgCanvasTmp.setAttribute('height', this.img.height); /* Import the image into the Canvas */ imgCanvasTmp.getContext('2d').putImageData(this.img, 0, 0); /* Use the Canvas into another part of the program (Commented out for testing) */ // this.displayCanvas(imgCanvasTmp,pageIndex); } The images are well imported but there seems to be a memory leak due to the putImageData function. When exiting the "for" loop, I would expect the memory allocated for the Canvas to be freed but, by executing the code without executing putImageData, I noticed that my program at the end use 100Mb less (my images are quite big). I came to the conclusion that the putImageData function prevent the garbage collector to free the allocated memory. Do you have any idea how I could force the garbage collector to free the memory? Is there any way to empty the Canvas? I already tried to delete the canvas using the delete operator or to use the clearRect function but it did nothing. I also tried to reuse the same canvas to display the image at each iteration but the amount of memory used did not changed, as if the image where imported without deleting the existing ones...

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• Perl TCP Server handling multiple Client connections

  - by Matt

  I'll preface this by saying I have minimal experience with both Perl and Socket programming, so I appreciate any help I can get. I have a TCP Server which needs to handle multiple Client connections simultaneously and be able to receive data from any one of the Clients at any time and also be able to send data back to the Clients based on information it's received. For example, Client1 and Client2 connect to my Server. Client2 sends "Ready", the server interprets that and sends "Go" to Client1. The following is what I have written so far: my $sock = new IO::Socket::INET { LocalHost => $host, // defined earlier in code LocalPort => $port, // defined earlier in code Proto => 'tcp', Listen => SOMAXCONN, Reuse => 1, }; die "Could not create socket $!\n" unless $sock; while ( my ($new_sock,$c_addr) = $sock->accept() ) { my ($client_port, $c_ip) = sockaddr_in($c_addr); my $client_ipnum = inet_ntoa($c_ip); my $client_host = ""; my @threads; print "got a connection from $client_host", "[$client_ipnum]\n"; my $command; my $data; while ($data = <$new_sock>) { push @threads, async \&Execute, $data; } } sub Execute { my ($command) = @_; // if($command) = "test" { // send "go" to socket1 print "Executing command: $command\n"; system($command); } I know both of my while loops will be blocking and I need a way to implement my accept command as a thread, but I'm not sure the proper way of writing it.

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• How to detect the root recursive call?

  - by ahmadabdolkader

  Say we're writing a simple recursive function fib(n) that calculates the nth Fibonacci number. Now, we want the function to print that nth number. As the same function is being called repeatedly, there has to be a condition that allows only the root call to print. The question is: how to write this condition without passing any additional arguments, or using global/static variables. So, we're dealing with something like this: int fib(int n) { if(n <= 0) return 0; int fn = 1; if(n > 2) fn = fib(n-2) + fib(n-1); if(???) cout << fn << endl; return fn; } int main() { fib(5); return 0; } I thought that the root call differs from all children by returning to a different caller, namely the main method in this example. I wanted to know whether it is possible to use this property to write the condition and how. Update: please note that this is a contrived example that only serves to present the idea. This should be clear from the tags. I'm not looking for standard solutions. Thanks.

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• When destroying one record, another one gets destroyed

  - by normalocity

  Products (like an iPod Classic) :has_many = :listings, :dependent = :destroy Listings (like "My name is Joe, and I have an iPod for sale) :belongs_to = :product So, if I delete a given Product, all the listings that point to it get deleted. That makes sense, and is by design. However, I am writing a "merge" function, where you merge two Products into one, and combine their Listings. So, let's say my two products are "iPod Color" and "iPod Classic", and I want to merge the two. What I want to do is say, "iPod Color, merge into iPod Classic", and result should be that: All the iPod Color Listings are re-pointed to the iPod Classic product After the product_id change, the Listing(s) are saved I then delete the "iPod Color" product Well, that should all work fine, without deleting any Listings. However, I've got this controller, and for whatever reason when I destroy the "iPod Color" Product, even after confirming that the Listings have been moved to "iPod Classic" and saved to the database, the Listings that were previously pointed to "iPod Color" get destroyed as well, and I can't figure out why. It's as if they are retaining some kind of link to the destroyed product, and therefore begin destroyed themselves. What painfully obvious thing am I missing? def merge merging_from = Product.find(params[:id]) merging_to = Product.find_by_model(params[:merging_to]) unless merging_to.nil? unless merging_from.nil? unless merging_from == merging_to # you don't want to merge something with itself merging_from.listings.each do |l| l.product = merging_to l.save end # through some debugging, I've confirmed that my missing Listings are disappearing as a result of the following destroy call merging_from.destroy end end end

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• c++ overloading delete, retrieve size

  - by user300713

  Hi, I am currently writing a small custom memory Allocator in c++, and want to use it together with operator overloading of new/delete. Anyways, my memory Allocator basicall checks if the requested memory is over a certain threshold, and if so uses malloc to allocate the requested memory chunk. Otherwise the memory will be provided by some fixedPool allocators. that generally works, but for my deallocation function looks like this: void MemoryManager::deallocate(void * _ptr, size_t _size){ if(_size heapThreshold) deallocHeap(_ptr); else deallocFixedPool(_ptr, _size); } so I need to provide the size of the chunk pointed to, to deallocate from the right place. No the problem is that the delete keyword does not provide any hint on the size of the deleted chunk, so I would need something like this: void operator delete(void * _ptr, size_t _size){ MemoryManager::deallocate(_ptr, _size); } But as far as I can see, there is no way to determine the size inside the delete operator.- If I want to keep things the way it is right now, would I have to save the size of the memory chunks myself? Any ideas on how to solve this are welcome! Thanks!

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• JSP includes and MVC pattern

  - by xingyu

  I am new to JSP/Servlets/MVC and am writing a JSP page (using Servlets and MVC pattern) that displays information about recipies, and want the ability for users to "comment" on it too. So for the Servlet, on doGet(), it grabs all the required info into a Model POJO and forwards the request on to a JSP View for rendering. That is working just fine. I'd like the "comment" part to be a separate JSP, so on the RecipeView.jsp I can use to separate these views out. So I've made that, but am now a little stuck. The form in the CommentOnRecipe.jsp posts to a CommentAction servlet that handles the recording of the comment just fine. So when I reload the Recipe page, I can see the comment I just made. I'd like to: Reload the page automatically after commenting (no AJAX for now) Block the user from making more than one comment on each Recipe over a 1 day timeframe (via a Cookie). So I store a cookie indicating the product ID whenever the user makes a comment, so we can check this later? How would it work in a MVC context? Show a message to the user that they have already commented on the Recipe when they visit one which they have commented on I'm confused about using beans/including JSPs etc on how to achieve this. I know in ASP.NET land, it would be a UseControl that I would place on a page, or in ASP.NET MVC, it would be a PartialView of some sort. I'm just confused with the way this works in a JSP/Servlets/MVC context.

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• Write to the second line of a PHP file

  - by Woz

  I have a php file that I want to add an include path to on the second line. I need to open the file and inset a line of code on line 2. I have tried a few techniques none of which are working but I think it has something to do with the text I am trying to write and possibly not escaping character correctly as I am not too familiar with file writing. So here is the file I want to write to: $file = $_SERVER['DOCUMENT_ROOT'].'/'.$domaindir.'/test.php'; Here is the piece of text I want to insert into the file: $dbfile = "include('".$_SERVER['DOCUMENT_ROOT']."/".$domaindir."/web_".$dbname.".inc.php');"; Then what I was doing was a string replace but all it did was bump the "session_start();" bit to a newline! Can anyone point me in the direction of a tutorial that might tell me how to insert this into the second line of my php file or indeed if anyone has any ideas? I can say for sure that the path to the PHP file is fully tested so i know its not that the file is not being open or written to. Any ideas would be much appreciated. Thanks in advance.

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• C#/.NET: FInd out whether a server exists, Query DNS for SVC records.

  - by TomTom

  Writing a cleint/Server tool I am tasked trying to find a server to connect to. I would love to make things as easy as possible for the user. As such, my idea is to: CHeck whether specific servers (coded by name) exist (like "mail.xxx" for a mail server, for example - my exampüle is not a mail server;) Query otherwise for DNS SVC records, allowing the admin to configure a server location for a specific serivce (that the client connects to). The result is that the user may have to enter only a domain name, possibly even not even that (using the registered standard domain of the computer in a LAN environment). Anyone ideas how: To find out whether a server exists and answers (i.e. is online) in the fastest way? TCP can take a long time if the server is not there. A UDP style ping sounds like a good idea to me. PING itself may be unavailable. Anyonw knows how to ask from withint .NET best for a SVC record in a specific (the default) domain?

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• SQL developer here -- Nesting with select * finicky in Oracle 10g?

  - by John Sullivan

  I am writing a simple diagnostic query I will execute in my Oracle 10g scratchpad. I am trying to do this as part of a step to build the query. In the SQL Scratchpad for Oracle 10g Enterprise Manager Console, this statement runs fine. SELECT * FROM v$session sess, v$sql sql WHERE sql.sql_id(+) = sess.sql_id and sql.sql_text <> ' ' If I try to wrap that up in Select * from () tb2 I get an error, "ORA-00918: Column Ambiguously Defined". I didn't think that could ever happen with this kind of statement so I am a bit confused. select * from (SELECT * FROM v$session sess, v$sql sql WHERE sql.sql_id(+) = sess.sql_id and sql.sql_text <> ' ') tb2 You should always be able to select * from the result set of another select * statement using this structure as far as I'm aware... right? Is Oracle/10g/the scratchpad trying to force me to accept a certain syntactic structure to prevent excessive nesting? Is this a bug in scratchpad or something about how oracle works?

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• Freetype2 (error-)return value documentation

  - by Awaki

  In short, I'm looking for documentation that would limit the error situations to check for after a Freetype library function failed, much like the OpenGL and Win32 APIs document the error codes generated by their respective functions. I can't seem to find such documentation though, so I was wondering how to best handle translation of Freetype errors to typed exceptions. Background: I am currently in the process of implementing font-rendering capability (using Freetype) for my GUI framework, which makes strong use of typed exceptions to indicate error situations. However, the Freetype docs seem to completely omit what errors can be expected from what functions. That, if such documentation does indeed not exist, would basically leave me with two options: either guessing which errors make sense for a certain Freetype function (obviously prone to mistakes on my part), or considering every error code for translation into appropriate exceptions (less verbose since I would have to write the translation only once). Performance isn't really critical in the code that calls the Freetype library, so even the latter option would probably be acceptable, but surely there must be some kind of documentation on which library calls may return what Freetype error? Is there any such documentation which I just somehow managed to not find? Should I go the route of generically expecting every error code for translation? Or are there other ways to approach this problem? By the way, I wanted to avoid introducing some kind of generic FreetypeException (containing a description of the Freetype error) since I intended to completely hide what libraries I'm using (not from a legal point-of-view, mind you), but I guess I can be convinced to do this anyway if the consensus is that it would be the best option. I don't think it matters for this question, but I'm writing in C++.

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• What's the "correct way" to organize this project?

  - by user571747

  I'm working on a project that allows multiple users to submit large data files and perform operations on them. The "backend" which performs these operations is written in Perl while the "frontend" uses PHP to load HTML template files and determines which content to deliver. Data is stored in a database (MySQL, SQLite, Oracle) and while there is data which has not yet been acted upon, Perl adds it to a running queue which delivers data to other threads based on system load. In addition, there may be pre- and post-processing of the data before and after the main Perl script operates (the specifications are unclear) so I may want to allow these processors to be user-selectable plugins. I had been writing this project in a more procedural fashion but I am quickly realizing the benefit of separating concerns as to limit the scope one change has on the rest of the project. I'm quite unexperienced with design patterns and am curious what the best way to proceed is. I've heard MVC thrown around quite a bit but I am unsure of how to apply it. Specifically, what are some good options to structure this code (in terms of design patterns and folder hierarchy)? How can I achieve this with both PHP and Perl while minimizing duplicated code between languages? Should I keep my PHP files in the top level so I don't have ugly paths in the URL? Also, if I want to provide interchangeable databases, does each table need its own DAO implementation?

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• Deterministic floating point and .NET

  - by code2code

  How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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• Cannot connect to MySQL server using JSP

  - by Dibya

  I just set foot on JSP. I started writing simple programs to display dates, system info. Then I tried to connect a MySQL database I have a free hosting account, but I am not able to connect to MySQL database. Here is my code: <%@ page import="java.sql.*" %> <%@ page import="java.io.*" %>  <html> <head> <title>Connection with mysql database</title> </head> <body> <h1>Connection status</h1> <% try { String connectionURL = "jdbc:mysql://mysql2.000webhost.com/a3932573_product"; Connection connection = null; Class.forName("com.mysql.jdbc.Driver").newInstance(); connection = DriverManager.getConnection(connectionURL, "a3932573_dibya", "******"); if(!connection.isClosed()) out.println("Successfully connected to " + "MySQL server using TCP/IP..."); connection.close(); }catch(Exception ex){ out.println("Unable to connect to database."); } %> </font> </body> </html> I am getting Message as Connection Status unable to connect to database. I have tested this connection using PHP using the same username, password and database name. Where am I making mistake?

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• How do I vertcally align thumbnails of unknown height using jQuery?

  - by playahabana

  Ok, I am a complete beginner to this, in fact I am still building my first website. I am attempting to do this all by hand-coding without a CMS in order to try and learn as much possible as quickly as possible. If this post is in the wrong place I apologise, and a pointer to right place would be appreciated. Here goes, I am trying to peice together a bit of jQuery that will automatically vertically align my thumbnails in my image gallery (they are all different sizes). They are within fixed size div's and the function I am attempting looks something like this: <script type="text/javascript"> $('#ul.photo).bind(function() { var smartVert=$(this); var phty=ob.("ul.photo img").height(); //get height of photos var phtdif=Math.floor(208 - phty); //subtract height of photo from div height var phttop=Math.floor(phtdif / 2); //gets padding reqd. $ob.("ul.photo").css({'padding-top' : phttop}) //sets padding to center thumbnail }); smartVert(); unsurprisingly this doesn't work, if some kindly soul could take pity on a total noob, and point out where I am going wrong (probably in writing complete gibberish would be my first guess) it would be greatly appreciated- even if you could just point me in the direcion of a tutorial regarding these things, I have looked and found one reference that said such a function was easy to create, but it did not elaborate. thankyou in advance

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• Could this be considered a well-written PHP5 class?

  - by Ben Dauphinee

  I have been learning OOP principals on my own for a while, and taken a few cracks at writing classes. What I really need to know now is if I am actually using what I have learned correctly, or if I could improve as far as OOP is concerned. I have chopped a massive portion of code out of a class that I have been working on for a while now, and pasted it here. To all you skilled and knowledgeable programmers here I ask: Am I doing it wrong? class acl extends genericAPI{ // -- Copied from genericAPI class protected final function sanityCheck($what, $check, $vars){ switch($check){ case 'set': if(isset($vars[$what])){return(1);}else{return(0);} break; } } // --------------------------------- protected $db = null; protected $dataQuery = null; public function __construct(Zend_Db_Adapter_Abstract $db, $config = array()){ $this->db = $db; if(!empty($config)){$this->config = $config;} } protected function _buildQuery($selectType = null, $vars = array()){ // Removed switches for simplicity sake $this->dataQuery = $this->db->select( )->from( $this->config['table_users'], array('tf' => '(CASE WHEN count(*) > 0 THEN 1 ELSE 0 END)') )->where( $this->config['uidcol'] . ' = ?', $vars['uid'] ); } protected function _sanityRun_acl($sanitycheck, &$vars){ switch($sanitycheck){ case 'uid_set': if(!$this->sanityCheck('uid', 'set', $vars)){ throw new Exception(ERR_ACL_NOUID); } $vars['uid'] = settype($vars['uid'], 'integer'); break; } } private function user($action = null, $vars = array()){ switch($action){ case 'exists': $this->_sanityRun_acl('uid_set', $vars); $this->_buildQuery('user_exists_idcheck', $vars); return($this->db->fetchOne($this->dataQuery->__toString())); break; } } public function user_exists($uid){ return($this->user('exists', array('uid' => $uid))); } } $return = $acl_test->user_exists(1);

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• Cost of logic in a query

  - by FrustratedWithFormsDesigner

  I have a query that looks something like this: select xmlelement("rootNode", (case when XH.ID is not null then xmlelement("xhID", XH.ID) else xmlelement("xhID", xmlattributes('true' AS "xsi:nil"), XH.ID) end), (case when XH.SER_NUM is not null then xmlelement("serialNumber", XH.SER_NUM) else xmlelement("serialNumber", xmlattributes('true' AS "xsi:nil"), XH.SER_NUM) end), /*repeat this pattern for many more columns from the same table...*/ FROM XH WHERE XH.ID = 'SOMETHINGOROTHER' It's ugly and I don't like it, and it is also the slowest executing query (there are others of similar form, but much smaller and they aren't causing any major problems - yet). Maintenance is relatively easy as this is mostly a generated query, but my concern now is for performance. I am wondering how much of an overhead there is for all of these case expressions. To see if there was any difference, I wrote another version of this query as: select xmlelement("rootNode", xmlforest(XH.ID, XH.SER_NUM,... (I know that this query does not produce exactly the same, thing, my plan was to move the logic to PL/SQL or XSL) I tried to get execution plans for both versions, but they are the same. I'm guessing that the logic does not get factored into the execution plan. My gut tells me the second version should execute faster, but I'd like some way to prove that (other than writing a PL/SQL test function with timing statements before and after the query and running that code over and over again to get a test sample). Is it possible to get a good idea of how much the case-when will cost? Also, I could write the case-when using the decode function instead. Would that perform better (than case-statements)?

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• AttributeError in my Python program regarding classes

  - by Axel Finkel

  I'm doing an exercise out of the Python book that involves creating a class and a subclass. I am getting the following error when I try to run the program: AttributeError: 'Customer' object has no attribute 'name', when it tries to go through this bit of code: self.name.append(name) As this is my first time dealing with classes and objects in Python, I'm sure I am making some overt mistake somewhere, but I can't seem to figure it out. I've looked over the documentation for creating classes and writing member functions, and it looks correct, but it is obviously not. I want the Customer subclass to inherit the name, address, and telephone attributes from the Person superclass, but it doesn't seem to be doing so? Here is my code: class Person: def __init__(self): self.name = None self.address = None self.telephone = None def changeName(self, name): self.name.append(name) def changeAddress(self, address): self.address.append(address) def changeTelephone(self, telephone): self.telephone.append(telephone) class Customer(Person): def __init__(self): self.customerNumber = None self.onMailingList = False def changeCustomerNumber(self, customerNumber): self.customerNumber.append(customerNumber) def changeOnMailingList(): if onMailingList == False: onMailingList == True else: onMailingList == False def main(): customer1 = Customer() name = 'Bob Smith' address = '123 Somewhere Road' telephone = '111 222 3333' customerNumber = '12345' customer1.changeName(name) customer1.changeAddress(address) customer1.changeTelephone(telephone) customer1.changeCustomerNumber(customerNumber) print("Customer name: " + customer1.name) print("Customer address: " + customer1.address) print("Customer telephone number: " + customer1.telephone) print("Customer number: " + customer1.customerNumber) print("On mailing list: " + customer1.OnMailingList) customer1.changeOnMailingList() print("On mailing list: " + customer1.OnMailingList) main()

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• Emulating a computer running MS-DOS

  - by Richard

  Writing emulators has always fascinated me. Now I want to write an emulator for an IBM PC and run MS-DOS on it (I've got the floppy image files). I have good experience in C++ and C and basic knowledge of assembler and the architecture of a CPU. I also know that there are thousands of emulators out there doing exactly what I want to do, but I'd be doing this for pure joy only. How much work do I have to expect? (If my goal is to boot DOS and create a text file with it, all emulated) What CPU should I emulate ? Where can I find documentation on how the machine code is organized and which opcodes mean what, so I can unpack and execute them correctly with my emulator? Does MS-DOS still run on the newest generations of processors? Would it theoretically be able to natively run on a 64-bit AMD Phenom 2 processor w/ a modern mainboard, HDD, RAM, etc.? What else, besides emulating the CPU, could be an important factor (in terms of difficulty)? I would only aim for outputting / inputting text to the system via the host system's console, no sound or other more advanced IO etc. Have you written an emulator yet? What was your first one for? How hard was it? Do you have any special tips for me? Thanks in advance

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• how to make a CUDA Histogram kernel?

  - by kitw

  Hi all, I am writing a CUDA kernel for Histogram on a picture, but I had no idea how to return a array from the kernel, and the array will change when other thread read it. Any possible solution for it? __global__ void Hist( TColor *dst, //input image int imageW, int imageH, int*data ){ const int ix = blockDim.x * blockIdx.x + threadIdx.x; const int iy = blockDim.y * blockIdx.y + threadIdx.y; if(ix < imageW && iy < imageH) { int pixel = get_red(dst[imageW * (iy) + (ix)]); //this assign specific RED value of image to pixel data[pixel] ++; // ?? problem statement ... } } @para d_dst: input image TColor is equals to float4. @para data: the array for histogram size [255] extern "C" void cuda_Hist(TColor *d_dst, int imageW, int imageH,int* data) { dim3 threads(BLOCKDIM_X, BLOCKDIM_Y); dim3 grid(iDivUp(imageW, BLOCKDIM_X), iDivUp(imageH, BLOCKDIM_Y)); Hist<<<grid, threads>>>(d_dst, imageW, imageH, data); }

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• Image creation performance / image caching

  - by Kilnr

  Hello, I'm writing an application that has a scrollable image (used to display a map). The map background consists of several tiles (premade from a big JPG file), that I draw on a Graphics object. I also use a cache (Hashtable), to prevent from having to create every image when I need it. I don't keep everything in memory, because that would be too much. The problem is that when I'm scrolling through the map, and I need an image that wasn't cached, it takes about 60-80 ms to create it. Depending on screen resolution, tile size and scroll direction, this can occur multiple times in one scroll operation (for different tiles). In my case, it often happens that this needs to be done 4 times, which introduces a delay of more than 300 ms, which is extremely noticeable. The easiest thing for me would be that there's some way to speed up the creation of Images, but I guess that's just wishful thinking... Besides that, I suppose the most obvious thing to do is to load the tiles predictively (e.g. when scrolling to the right, precache the tiles to the right), but then I'm faced with the rather difficult task of thinking up a halfway decent algorithm for this. My actual question then is: how can I best do this predictive loading? Maybe I could offload the creation of images to a separate thread? Other things to consider? Thanks in advance.

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• Audio Streaming Latency

  - by killianmcc

  I'm writing a UDP local area network video chat system and have got the video and audio streams working. However I'm experiencing a little latency (about half a second) in the audio and was wondering what codecs would provide the least latency. I'm using NAudio (http://naudio.codeplex.com/) which provides me access to the following codecs for streaming; Speex Narrow Band (VBR) Speex Wide Band (16kHz)(VBR) Speex Ultra Wide Band (32kHz)(VBR) DSP Group TrueSpeech (8.5kbps) GSM 6.10 (13kbps) Microsoft ADPCM (32.8kbps) G.711 a-law (64kbps) G.722 16kHz (64kbps) G.711 mu-law (64kbps) PCM 8kHz 16 bit uncompressed (128kbps) I've tried them out and I'm not noticing much difference. Is there any others that I should download and try to reduce latency? I'm only going to be sending voice over the connection but I'm not really worried about quality or background noises too much. UPDATE I'm sending the audio in blocks like so; waveIn = new WaveIn(); waveIn.BufferMilliseconds = 50; waveIn.DeviceNumber = inputDeviceNumber; waveIn.WaveFormat = codec.RecordFormat; waveIn.DataAvailable += waveIn_DataAvailable; void waveIn_DataAvailable(object sender, WaveInEventArgs e) { if (connected) { byte[] encoded = codec.Encode(e.Buffer, 0, e.BytesRecorded); udpSender.Send(encoded, encoded.Length); } }

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• Add Source file link to the default ASP.NET Server Error page?

  - by Max Schilling

  Has anyone ever thought to attempt to modify the default ASP.NET Server error page to provide a link BACK to the error source in Visual Studio? Consider the following standard error page in ASP.NET: Server Error in '/myproject' Application. Invalid object name 'usp_DoSomething'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.SqlClient.SqlException: Invalid object name 'usp_DoSomething'. Source Error: Line 4323: cmd.CommandText = "usp_DoSomething"; Line 4324: Line 4325: using (var dr = cmd.ExecuteReader()) Line 4326: { Line 4327: if (dr != null) Source File: c:\development\myproject\myproject.components\providers\sql\sqldataprovider.cs Line: 4325 When an error like this is generated, the HTML has the source back to the file the error occurs in and the line number. Has anyone ever written or thought of writing some mechanism to turn the text into a link back to the error in Visual Studio? I've never seen anything that does it, but it just seems like it would be a helluva nice feature and I think about it in the back of my mind every time an error occurs when I have to manually go find it in the source. It would just be nice to be able to click a link to take me straight there. Anyone written any, or know of any solutions for this. I use Chrome or Firefox as my browsers of choice, but I'd even consider using IE again if someone found a plugin that did this. Thanks, Max

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• What would happen if a same file being read and appended at the same time(python programming)?

  - by Shane

  I'm writing a script using two separate thread one doing file reading operation and the other doing appending, both threads run fairly frequently. My question is, if one thread happens to read the file while the other is just in the middle of appending strings such as "This is a test" into this file, what would happen? I know if you are appending a smaller-than-buffer string, no matter how frequently you read the file in other threads, there would never be incomplete line such as "This i" appearing in your read file, I mean the os would either do: append "This is a test" - read info from the file; or: read info from the file - append "This is a test" to the file; and such would never happen: append "This i" - read info from the file - append "s a test". But if "This is a test" is big enough(assuming it's a bigger-than-buffer string), the os can't do appending job in one operation, so the appending job would be divided into two: first append "This i" to the file, then append "s a test", so in this kind of situation if I happen to read the file in the middle of the whole appending operation, would I get such result: append "This i" - read info from the file - append "s a test", which means I might read a file that includes an incomplete string?

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• insert multiple rows into database from arrays

  - by Mark

  Hi, i need some help with inserting multiple rows from different arrays into my database. I am making the database for a seating plan, for each seating block there is 5 rows (A-E) with each row having 15 seats. my DB rows are seat_id, seat_block, seat_row, seat_number, therefore i need to add 15 seat_numbers for each seat_row and 5 seat_rows for each seat_block. I mocked it up with some foreach loops but need some help turning it into an (hopefully single) SQL statement. $blocks = array("A","B","C","D"); $seat_rows = array("A","B","C","D","E"); $seat_nums = array("1","2","3","4","5","6","7","8","9","10","11","12","13","14","15"); foreach($blocks as $block){ echo "<br><br>"; echo "Block: " . $block . " - "; foreach($seat_rows as $rows){ echo "Row: " . $rows . ", "; foreach($seat_nums as $seats){ echo "seat:" . $seats . " "; } } } Maybe there's a better way of doing it instead of using arrays? i just want to avoid writing an SQL statement that is over 100 lines long ;) (im using codeigniter too if anyone knows of a CI specific way of doing it but im not too bothered about that)

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