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• How to mark empty in a single element in a float array

  - by Vineeth Mohan

  I have a large float (primitive) array and not every element in the array is filled. How can i mark a particular element as EMPTY. I understand this can be achieved by some special symbols but still i would like to know the standard way. Even if i am using some special symbol , how will i handle a situation where the actual data item is the value of special symbol. In short my question is how to implement the NULL feature in a primitive type array in java. PS - The reason why i am not using Float object is to achieve a high memory and speed performance. Thanks Vineeth

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• Linux Kernel - Slab Allocator Question

  - by Drex

  I am playing around with the kernel and am looking at the kmem_cache files_cachep belonging to fork.c. It detects the sizeof(files_struct). My question is this: I have altered files_struct and added a rb_root (red/black tree root) using the built-in functionality in linux/rbtree.h. I can properly insert values into this tree. However, at some point, a segfault occurs and GDB backtraces the following information: (gdb) backtrace 0 0x08066ad7 in page_ok (page=) at arch/um/os-Linux/sys-i386/task_size.c:31 1 0x08066bdf in os_get_top_address () at arch/um/os-Linux/sys-i386/task_size.c:100 2 0x0804a216 in linux_main (argc=1, argv=0xbfb05f14) at arch/um/kernel/um_arch.c:277 3 0x0804acdc in main (argc=1, argv=0xbfb05f14, envp=0xbfb05f1c) at arch/um/os-Linux/main.c:150 I have spent many hours trying to figure out why there is a segfault given that the red/black tree inserts properly. I'm thinking it's a memory allocation issue with new processes made by fork() of a parent process. Could this be the case and could it have something to do with kmem_cache files_cachep?

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• Fatal error with php code

  - by basma

  hello i have a problem in my php code that use recursion: <?php solveTowers(5, "A", "B", "C"); function solveTowers($count, $src, $dest, $spare) { if (count == 1) { echo "Move a disk from ".$src." to ".$dest ; } else { solveTowers($count - 1, $src, $spare, $dest); solveTowers(1, $src, $dest, $spare); solveTowers($count - 1, $spare, $dest, $src); } } ?> but it doesnt run !! this error accures : Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 261904 bytes) in C:\xampp\htdocs\cap492\towers.php on line 13 line 13 is the first call to the function in the else statment can you please help me with that ?!

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• Accessing ArrayBuffer from PHP $_POST after xmlHTTPrequest send()

  - by Dan

  I'm following the tuitions on XMLHttpRequest 2 from : https://developer.mozilla.org/en/DOM/XMLHttpRequest/Sending_and_Receiving_Binary_Data and http://www.html5rocks.com/en/tutorials/file/xhr2/#toc-send-arraybuffer They're great tutorials for the client side, and here is a working extract from my script: var imagebuffer = new ArrayBuffer(size); // create the readonly memory buffer var imagedata= new Uint8Array(imagebuffer); // create a view to manipulate data // do some cool stuff with imagedata var exchange=new XMLHttpRequest(); exchange.open("POST",url,true); exchange.send(arraybuffer); So far so good, and I can see from the both client and server control panels that plenty of data is being transferred. Here's my problem: how do I access the ArrayBuffer with PHP at the server? I'm used to the $_POST superglobal wanting parameters passing from a HTML form so it can be accessed as an array but I can't find any reference for how to access this binary array and stick it in my MySQL database.

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• How can you tell the source of the data when using the Stream.BeginRead Method?

  - by xarzu

  When using the Stream.BeginRead Method, and you are reading from a stream into a memory, how is it determined where you are reading the data from? See: http://msdn.microsoft.com/en-us/library/system.io.stream.beginread.aspx In the list of parameters, I do not see one that tells where the data is being read from: Parameters buffer Type: System.Byte[] The buffer to read the data into. offset Type: System.Int32 The byte offset in buffer at which to begin writing data read from the stream. count Type: System.Int32 The maximum number of bytes to read. callback Type: System.AsyncCallback An optional asynchronous callback, to be called when the read is complete. state Type: System.Object A user-provided object that distinguishes this particular asynchronous read request from other requests.

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• [C++]Advantage of using a static member function instead of an equivalent non-static member function

  - by jonathanasdf

  I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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• How to store images without taking up huge amounts of RAM

  - by Sheeo

  I'm working on a silverlight project where users get to create their own Collages. The problem When loading a bunch of images by using the BitmapImage class, Silverlight hogs up huge unreasonable amounts of RAM. 150 pictures where single ones fill up at most 4,5mb takes up about 1,6GB of RAM--thus ending up throwing memory exceptions. I'm loading them through streams, since the user selects their own photos. What I'm looking for A class, method or some process to eliminate the huge amount of RAM being sucked up. I've tried using a WriteableBitmap to render the images into, but I find this method forces me to reinvent the wheel when it comes to drag/drop and other things I want users to be able to do with the images.

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• Socket ping-pong performance

  - by Kamil_H

  I have written two simple programs (tried it in C++ and C#). This is pseudo code: -------- Client --------------- for(int i = 0; i < 200.000; i++) { socket_send("ping") socket_receive(buff) } --------- Server ------------- while(1) { socket_receive(buff) socket_send("pong") } I tried it on Windows. Execution time of client is about 45 seconds. Can somebody explain me why this takes so long? I understand that if there were real network connection between client and server the time of one 'ping-pong' would be: generate_ping + send_via_network + generate_pong + send_via_network but here everything is done in 'local' mode. Is there any way to make this inter process ping-pong faster using network sockets (I'm not asking about shared memory for example :) )

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• Is eclipse's Garbage Collector different than the default?

  - by Savvas Dalkitsis

  From questions posted here and an old one of mine I have created the impression that you cannot explicitly run the Java Garbage Collector whenever you please. If you call it, you simply instruct the system to call it whenever it can or thinks is appropriate. But in eclipse, if you press the "Run Garbage Collector" button you see an immediate reduction in memory usage. How is that possible? Is eclipse using a different Garbage Collector, does it have access to some secret API that we don't or is my conception of how the GC works wrong?

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• How is a new programming language actually formed/created ?

  - by hory.incpp

  Fortran-Algol-Cpl-Bcpl-C-C++-Java ..... Seems like every language is built upon an ancestor language. My question : New languages extend parent ones or there is some kind of a trick? e.g. System.out.print() in Java ; is it actually printf() in C, and so on (printf is actually .. in Cpl)? If so, doesn't this make every further language be slower and need more memory? What separates a new language from a framework?

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• Find the closest vector

  - by Alexey Lebedev

  Hello! Recently I wrote the algorithm to quantize an RGB image. Every pixel is represented by an (R,G,B) vector, and quantization codebook is a couple of 3-dimensional vectors. Every pixel of the image needs to be mapped to (say, "replaced by") the codebook pixel closest in terms of euclidean distance (more exactly, squared euclidean). I did it as follows: class EuclideanMetric(DistanceMetric): def __call__(self, x, y): d = x - y return sqrt(sum(d * d, -1)) class Quantizer(object): def __init__(self, codebook, distanceMetric = EuclideanMetric()): self._codebook = codebook self._distMetric = distanceMetric def quantize(self, imageArray): quantizedRaster = zeros(imageArray.shape) X = quantizedRaster.shape[0] Y = quantizedRaster.shape[1] for i in xrange(0, X): print i for j in xrange(0, Y): dist = self._distMetric(imageArray[i,j], self._codebook) code = argmin(dist) quantizedRaster[i,j] = self._codebook[code] return quantizedRaster ...and it works awfully, almost 800 seconds on my Pentium Core Duo 2.2 GHz, 4 Gigs of memory and an image of 2600*2700 pixels:( Is there a way to somewhat optimize this? Maybe the other algorithm or some Python-specific optimizations.

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• STL Vectors, pointers and classes

  - by anubis9

  Hey! Let's say i have 2 classes: class Class1 { public: std::vector<CustomClass3*> mVec; public: Class1(); ~Class1() { //iterate over all the members of the vector and delete the objects } }; class InitializerClass2 { private: Class1 * mPtrToClass1; public: InitializerClass2(); void Initialize() { mPtrToClass1->mVec.push_back(new CustomClass3(bla bla parameters)); } }; Will this work? Or the memory allocated in the InitializerClass2::Initialize() method might get corrupted after the method terminates? Thanks!

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• What is the best possible technology for pulling huge data from 4 remote servers

  - by Habib Ullah Bahar

  Hello, For one of our project, we need to pull huge real time stock data from 4 remote servers across two countries. The trivial process here, check the sources for a regular interval and save the update to database. But as these are real time stock data of more than 1000 companies, I have to pull every second, which isn't good in case of memory, bandwidth I think. Please give me suggestion on which technology/platform [We are flexible here. PHP, Python, Java, PERL - anyone of them will be OK for us] we should choose, it can be achieved easily and with better performance.

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• Are there Python ORMs out there that support multiple independent databases concurrently in use?

  - by sdt

  I'm writing an application in Python where I wish to use sqlite as the backing store for documents edited by the app, with documents generally living in memory, but being saved to disk-based databases when the application saves. Ideally I'd like to use something like an ORM to make access to the data from my Python application code simple. Unfortunately it seems like the majority of Python ORMs, including SQLAlchemy, SQLObject, Django, and Storm, associate the database connection (or engine or whatever) with the classes representing table data, rather than instances of those classes. This restricts these ORMs to working with a single database connection across all instances. Since I'd like to support having multiple documents open simultaneously, this isn't going to work for me. Are there any ORMs out there that support this usage model in Python? Bazaar seems to support this, but it's quite out of date, and at first glance appears to have some other shortcomings. Thanks for any suggestions!

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• Forbid GridView to load all views at once

  - by efpies

  I have about 700 items to display in the grid view. On a Samsung Galaxy Tab 10.1 this is not a problem: it has enough memory. On a HTC Explorer the heap is overflown. So I want to load data dynamically regarding current scroll position (N rows for screen + 5 rows as a tail). And I want to show a scrollbar which represents the position in total rows. But I don't want to draw items that I don't see. In other words, I want to create something similar to UITableView in iOS. How can I do this?

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• Slowness of Netbeans Platform Apps - how to mitigate?

  - by user559298

  Hi, We are developing a commerical application (pretty complex) in java using Netbeans IDE. We have 2 options in netbeans to create it- 1. Develop Java desktop app 2. Netbeans Platform app We have requirement that application startup and response times should be very very fast, should be modular etc. We did Proof of Technology by creating apps using both approaches mentioned above. We found Netbeans platform apps are very slow during startup and during screen navigation compared to pure Swing based desktop apps. We tried to implement suggestions provided at http://wiki.netbeans.org/Category:Performance:FAQ and in other blogs and forums to improve on speed of the app but were not successful. We feel for creating a complex desktop app Netbeans platform app would be better suited, but its not meeting our performance requirements (startup and response times, memory footprints, CPU usage guidelines etc). Can any one guide us on how to mitigate our problem of improving performance of Netbeans Platforms apps? Thanks in advance for your help. -bhan

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• How to scroll and zoom in/out large images on iPhone?

  - by Horace Ho

  I have a large image, size around 30000 (w) x 6000 (h) pixels. You may consider it's like a big map. I assume I need to crop it up into smaller tiles. Questions: what are the right ViewControllers to use? (link) what is the tile strategy? (I put this in another question, as it's not iPhone specific) Requirements: whole image (though cropped) can be scrolled up/down/left/right by swipes zoom in (up to pixel-to-pixel) out (down to screen-fit-by-height) by the 2-finger operation memory efficiency by lazy loading tiles Bonus requirements: automatic scroll, say from left to right slowly and smoothly Thanks!

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• Create Out-Of-Process COM in C#/.Net ?

  - by Huck

  Hi, I need to create an out-of-process COM server (.exe) in C# that will be accessed by multiple other processes on the same box. The component has to be a single process because it will cache the information it provides to its consumers in memory. Note: the processes that will access my COM Server are mostly Matlab processes, thus the necessity for a COM interface. I have seen threads regarding creating in-process COM components in .Net on stack overflow (Create COM ...) and on the web, but am having a hard time to find a way to create out-of-process components with .Net. How is this achievable? Any suggested references? Thanks.

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• How to reduce java concurrent mode failure and excessive gc

  - by jimx

  In Java, the concurrent mode failure means that the concurrent collector failed to free up enough memory space form tenured and permanent gen and has to give up and let the full stop-the-world gc kicks in. The end result could be very expensive. I understand this concept but never had a good comprehensive understanding of A) what could cause a concurrent mode failure and B) what's the solution?. This sort of unclearness leads me to write/debug code without much of hints in mind and often has to shop around those performance flags from Foo to Bar without particular reasons, just have to try. I'd like to learn from developers here how your experience is. If you had previous encountered such performance issue, what was the cause and how you addressed it? If you have coding recommendations, please don't be too general. Thanks!

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• Display Computer Info on C# Web Application

  - by Gene

  I want to build a page for end users to visit (in our MPLS Network) and it show the following information in regards to them: Computer Name OS Disk Space Memory IP Address Active Directory User Name Password Expiration Time (As defined by Global Policy) Maybe a few other things such as Trend Micro Office current version vs. their version, # of MS Updates needed (we utilize WSUS), and a few other things in the future. My question is how would I pull this information from the user when they visit the page? What is the proper function for this? Anyone have examples they wish to share for me to learn by if possible? Thanks so much in advance, Gene

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• How to read a file with variable multi-row data in Python

  - by dr.bunsen

  I have a file that is about 100Mb that looks like this: #meta data 1 skadjflaskdjfasljdfalskdjfl sdkfjhasdlkgjhsdlkjghlaskdj asdhfk #meta data 2 jflaksdjflaksjdflkjasdlfjas ldaksjflkdsajlkdfj #meta data 3 alsdkjflasdjkfglalaskdjf This file contains one row of meta data that corresponds to several, variable length data containing only alpha-numeric characters. What is the best way to read this data into a simple list like this: data = [[#meta data 1, skadjflaskdjfasljdfalskdjflsdkfjhasdlkgjhsdlkjghlaskdjasdhfk], [#meta data 2, jflaksdjflaksjdflkjasdlfjasldaksjflkdsajlkdfj], [#meta data 3, alsdkjflasdjkfglalaskdjf]] My initial idea was to use the read() method to read the whole file into memory and then use regular expressions to parse the data into the desired format. Is there a better more pythonic way? All metadata lines start with an octothorpe and all data lines are all alpha-numeric. Thanks!

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• Large ResultSet on postgresql query

  - by tuler

  I'm running a query against a table in a postgresql database. The database is on a remote machine. The table has around 30 sub-tables using postgresql partitioning capability. The query will return a large result set, something around 1.8 million rows. In my code I use spring jdbc support, method JdbcTemplate.query, but my RowCallbackHandler is not being called. My best guess is that the postgresql jdbc driver (I use version 8.3-603.jdbc4) is accumulating the result in memory before calling my code. I thought the fetchSize configuration could control this, but I tried it and nothing changes. I did this as postgresql manual recomended. This query worked fine when I used Oracle XE. But I'm trying to migrate to postgresql because of the partitioning feature, which is not available in Oracle XE. My environment: Postgresql 8.3 Windows Server 2008 Enterprise 64-bit JRE 1.6 64-bit Spring 2.5.6 Postgresql JDBC Driver 8.3-603

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• Puzzled with nib files...

  - by Michael

  I know nib files are serialized objects and they have owner, outlets to make connections. Using XCode Navigation window template I created application, which in its order created 2 nib files - MainWindow and SecondView. I can't understand how MainWindow is referring to SecondView, there is no connection between those two as far as I can see. SecondView's owner is UIViewController and in MainWindow there is a navigation tab which is also UIViewController. But how they are connected in IB I can't understand... Also I don't understand who is instanciating MainWindow's owner object and where that object is being kept, where is the variable which is UIApplication myApp = [[UIApplication alloc] init]. If I create 10 nib files with UIViewController owner, who will trigger their deserialization? If some class is nib file's owner, what is the essential responsibilities of that class? Is it deserializing nib file into memory? Sorry for unorganized questions, I've been reading numerous articles and docs about nib files, but it is still confusing.

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• VS2010's "Public Property <PropertyName> As <DataType> vs. Public var

  - by Velika2

  In VS2008, I used to type Public Property <PropName> As <dataType> and hit the Enter key and the IDE editor would automatically expand it out to a full blown property block. Now, from what I understand, a new feature of 2010 is that the compiler automatically "expands" the short syntax above into the same IL code that you would get with the full property GET AND SET sub methods that were are accustomed to seeing before in the editor. But functionality, how the heck is this any different than just having a Public class level variable? If the only diff is what it compiles to and if otehrwise there is no functional difference, isn't the new way less efficient than the old since it involves more code than just having a class level memory variable? Public as I thought that if you weren't going to have code behind your properties that they were essentially the same. I guess the diffrenece is that they just added the keyword "Property" but functionality, their is no diff, eh?

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• Exception on malloc for a structure in C

  - by Derek

  Hi all, I have a structure defined like so: typedef struct { int n; int *n_p; void **list_pp; size_t rec_size; int n_buffs; size_t buff_size } fl_hdr_type; and in my code I Have a function for initlialization that has the following fl_hdr_type *fl_hdr; fl_hdr = malloc(sizeof(fl_hdr_type) + (buff_size_n * rec_size_n)); where those buffer size are passed in to the function to allow space for the buffers as well. The size is pretty small typically..100*50 or something like that..plenty of memory on this system to allocate it. Any ideas why this fails?

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