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• C++ smart pointer for a non-object type?

  - by Brian

  Hi, I'm trying to use smart pointers such as auto_ptr, shared_ptr. However, I don't know how to use it in this situation. CvMemStorage *storage = cvCreateMemStorage(); ... use the pointer ... cvReleaseMemStorage(&storage); I'm not sure, but I think that the storage variable is just a malloc'ed memory, not a C++ class object. Is there a way to use the smart pointers for the storage variable? Thank you.

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• How can I pass managed objects from one AppDomain to another?

  - by Dennis P

  I have two assemblies that I'm trying to link together. One is a sort of background process that's built with WinForms and will be designed to run as a Windows Service. I have a second project that will act as a UI for the background process whenever a user launches it. I've never tried attempting something like this with managed code before, so I've started trying to use windows messages to communicate between the two processes. I'm struggling when it comes to passing more than just IntPtrs back and forth, however. Here's the code from a control in my UI project that registers itself with the background process: public void Init() { IntPtr hwnd = IntPtr.Zero; Process[] ps = Process.GetProcessesByName("BGServiceApp"); Process mainProcess = null; if(ps == null || ps.GetLength(0) == 0) { mainProcess = LaunchApp(); } else { mainProcess = ps[0]; } SendMessage(mainProcess.MainWindowHandle, INIT_CONNECTION, this.Handle, IntPtr.Zero); } protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONFIRMED && InitComplete != null) { string message = Marshal.PtrToStringAuto(m.WParam); Marshal.FreeHGlobal(m.WParam); InitComplete(message, EventArgs.Empty); } base.WndProc(ref m); } This is the code from the background process that's supposed to receive a request from the UI process to register for status updates and send a confirmation message. protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONNECTION) { RegisterUIDispatcher(m.WParam); Respond(m.WParam); } if(m.Msg == UNINIT_CONNECTION) { UnregisterUIDispatcher(m.WParam); if(m_RegisteredDispatchers.Count == 0) { this.Close(); } } base.WndProc(ref m); } private void Respond(IntPtr caller) { string test = "Registration confirmed!"; IntPtr ptr = Marshal.StringToHGlobalAuto(test); SendMessage(caller, INIT_CONFIRMED, ptr, IntPtr.Zero); } } The UI process receives the INIT_CONFIRMED message from my background process, but when I try to marshal the IntPtr back into a string, I get an empty string. Is the area of heap I'm using out of scope to the other process or am I missing some security attribute maybe? Is there a better and cleaner way to go about something like this using an event driven model?

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• Why should i use EJB?

  - by Nitesh Panchal

  Hello, As we all know that EJB's in 3.1 or 3.0 are simple POJOs. You just need to give annotations here and there and it gets converted to EJB from simple class. So, now my question is why should i use EJBs at all? Can i not do without them? In .Net i created class library and got things done. I never felt the need for anything like EJB. Simple classes were enough. Then, why in Java people stress on EJB? What is difference between a simple POJO and EJB in terms of execution and memory? Further which function should i write in EJB and which should i write in simple class? Should i dump every function in EJB only? or there is some kind of strategy? Does EJB provide anything special?

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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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• So does Apple recommend to not use predicates and sort descriptors in an NSFetchRequest?

  - by dontWatchMyProfile

  From the docs: To summarize, though, if you execute a fetch directly, you should typically not add Objective-C-based predicates or sort descriptors to the fetch request. Instead you should apply these to the results of the fetch. If you use an array controller, you may need to subclass NSArrayController so you can have it not pass the sort descriptors to the persistent store and instead do the sorting after your data has been fetched. I don't get it. What's wrong with using them on fetch requests? Isn't it stupid to get back a whole big bunch of managed objects just to pick out a 1% of them in memory, leaving 99% garbage floating around? Isn't it much better to only fetch from the persistent store what you really need, in the order you need it? Probably I did get that wrong...

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• Passing arguments to java vm from NSIS script

  - by CodeBuddy

  I'm developing my first java application using Eclipse. I've recently needed to adjust the amount of memory allocated by passing -Xmx256M to the JVM. The application is currently package up as a runnable jar and installed using the NSIS. I'm having a problem passing arguments to the jar file once its installed. What is the common practice for doing this? Here is what I'm currently doing in my nsi file: CreateShortcut "$SMPROGRAMS\$StartMenuGroup\$(^Name).lnk" "$SYSDIR\javaw.exe" "-jar -Xmx256M $INSTDIR\Foo.jar" This results in the following being created as the shortcut Target on windows: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M C:\Program Files\Foo\Foo.jar Unfortunately this does not work due to the space in C:\Program Files, If I change the link created manually to include quotes all is well: C:\WINDOWS\system32\javaw.exe -jar -Xmx256M "C:\Program Files\Foo\Foo.jar"

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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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• Why do AlarmManager broadcasts get cancelled when app gets killed?

  - by skooter

  Ok so I have two BroadcastReceiver registered. When the app is closed they both fire at the appropriate times and do the appropriate things. If the app is closed then killed (say with an AppKiller), the receivers never receive their broadcasts, and nothing happens. Presumably the same thing happens if the parent app is killed due to low memory, so how do I ensure those broadcasts are fired/received. The API states that even if the app is killed it should fire, does anyone else have experience with this situation? If it helps my manifest is: <!-- receivers for AlarmManager --> <receiver android:exported="true" android:label="Shift roster updating calendar." android:name="com.skooter.shiftroster.backend.service.UpdateCalendar" > </receiver> <receiver android:exported="true" android:label="Shift roster checking alarm." android:name="com.skooter.shiftroster.backend.service.SetWakeup" > </receiver> and nothing esoteric is going on in the AlarmManager/BroadcastReceivers

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• Lamp with mod_fastcgi

  - by Jonathan

  Hi! I am building a cgi application, and now I would like it to be like an application that stands and parses each connection, with this, I can have all session variables saved in memory instead of saving them to file(or anyother place) and loading them again on a new connection I am using lamp within a linux vmware but I can't seem to find how to install the module for it to work and what to change in the httpd.conf. I tried to compile the module, but I couldn't because my apache isn't a regular instalation, its a lamp already built one, and it seems that the mod needs the apache directory to be compiled. I saw some coding examples out there, so I guess is not that hard once its runing ok with Apache Can you help me with this please? Thanks, Joe

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• C# "Could not find a part of the path" - Creating Local File

  - by Pyronaut

  I am trying to write to a folder that is located on my C:\ drive. I keep getting the error of : Could not find a part of the path .. etc My filepath looks basically like this : C:\WebRoot\ManagedFiles\folder\thumbs\5c27a312-343e-4bdf-b294-0d599330c42d\Image\lighthouse.jpg And I am writing to it like so : using (MemoryStream memoryStream = new MemoryStream()) { thumbImage.Save(memoryStream, ImageFormat.Jpeg); using (FileStream diskCacheStream = new FileStream(cachePath, FileMode.CreateNew)) { memoryStream.WriteTo(diskCacheStream); } memoryStream.WriteTo(context.Response.OutputStream); } Don't worry too much about the memory stream. It is just outputting it (After I save it). Since I am creating a file, I am a bit perplexed as to why it cannot find the file (Shouldn't it just write to where I tell it to, regardless?). The strange thing is, It has no issue when I'm testing it above using File.Exists. Obviously that is returning false, But it means that atleast my Filepath is semi legit. Any help is much appreciated.

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• Using C++, why can `throw` cause `terminate()`, and when are the stack variables to be freed?

  - by nbolton

  I'm pondering a question on Brainbench. I actually realised that I could answer my question easily by compiling the code, but it's an interesting question nonetheless, so I'll ask the question anyway and answer it myself shortly. Take a look at this snippet: The question considers what happens when we throw from a destructor (which causes terminate() to be called). It's become clear to me by asking the question that the memory is indeed freed and the destructor is called, but, is this before or after throw is called from foo? Perhaps the issue here is that throw is used while the stack is unwinding that is the problem... Actually this is slightly confusing.

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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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• 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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• 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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• 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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• 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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• [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 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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• 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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• Low cost way to host a large table yet keep the performance scalable?

  - by Leo Liang

  I have a growing table storing time series data, 500M entries now, and 200K new records every day. The total size is around 15GB for now. My clients are querying the table via a PHP script mostly, and the size of the result set is around 10K records (not very large). select * from T where timestamp > X and timestamp < Y and additionFilters And I want this operation cheap. Currently my table is hosting in Postgres 7, on a single 16G memory Box, and I would love to see some good suggestion for me to host this in low cost and also allow me to scale up for performance if needed. The table serves: 1. Query: 90% 2. Insert: 9.9% 2. Update: 0.1% <-- very rare.

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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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• How to optimize this SQL query for a rectangular region?

  - by Andrew B.

  I'm trying to optimize the following query, but it's not clear to me what index or indexes would be best. I'm storing tiles in a two-dimensional plane and querying for rectangular regions of that plane. The table has, for the purposes of this question, the following columns: id: a primary key integer world_id: an integer foreign key which acts as a namespace for a subset of tiles tileY: the Y-coordinate integer tileX: the X-coordinate integer value: the contents of this tile, a varchar if it matters. I have the following indexes: "ywot_tile_pkey" PRIMARY KEY, btree (id) "ywot_tile_world_id_key" UNIQUE, btree (world_id, "tileY", "tileX") "ywot_tile_world_id" btree (world_id) And this is the query I'm trying to optimize: ywot=> EXPLAIN ANALYZE SELECT * FROM "ywot_tile" WHERE ("world_id" = 27685 AND "tileY" <= 6 AND "tileX" <= 9 AND "tileX" >= -2 AND "tileY" >= -1 ); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on ywot_tile (cost=11384.13..149421.27 rows=65989 width=168) (actual time=79.646..80.075 rows=96 loops=1) Recheck Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) -> Bitmap Index Scan on ywot_tile_world_id_key (cost=0.00..11367.63 rows=65989 width=0) (actual time=79.615..79.615 rows=125 loops=1) Index Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) Total runtime: 80.194 ms So the world is fixed, and we are querying for a rectangular region of tiles. Some more information that might be relevant: All the tiles for a queried region may or may not be present The height and width of a queried rectangle are typically about 10x10-20x20 For any given (world, X) or (world, Y) pair, there may be an unbounded number of matching tiles, but the worst case is currently around 10,000, and typically there are far fewer. New tiles are created far less frequently than existing ones are updated (changing the 'value'), and that itself is far less frequent that just reading as in the query above. The only thing I can think of would be to index on (world, X) and (world, Y). My guess is that the database would be able to take those two sets and intersect them. The problem is that there is a potentially unbounded number of matches for either for either of those. Is there some other kind of index that would be more appropriate?

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• Arrays of different types

  - by Tyler

  Hi - Is it possible to have an array that contains two different types of data? I want to have an array that contains a double and also a string. I attempted: ArrayList<double><String> array; But that didn't work. Sorry for the silly question, but it has been a while since I have used something like this.. Can you refresh my memory on how would I declare and populate such an array? And then to take it a step further, I would like to sort the array by the double if possible? 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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