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• How to optimize paging for large in memory database

  - by snakefoot

  I have an application where the entire database is implemented in memory using a stl-map for each table in the database. Each item in the stl-map is a complex object with references to other items in the other stl-maps. The application works with a large amount of data, so it uses more than 500 MByte RAM. Clients are able to contact the application and get a filtered version of the entire database. This is done by running through the entire database, and finding items relevant for the client. When the application have been running for an hour or so, then Windows 2003 SP2 starts to page out parts of the RAM for the application (Eventhough there is 16 GByte RAM on the machine). After the application have been partly paged out then a client logon takes a long time (10 mins) because it now generates a page fault for each pointer lookup in the stl-map. I can see it is possible to tell Windows to lock memory in RAM, but this is generally only recommended for device drivers, and only for "small" amounts of memory. I guess a poor mans solution could be to loop through the entire memory database, and thus tell Windows we are still interested in keeping the datamodel in RAM. I guess another poor mans solution could be to disable the pagefile completely on Windows. I guess the expensive solution would be a SQL database, and then rewrite the entire application to use a database layer. Then hopefully the database system will have implemented means to for fast access. Are there other more elegant solutions ?

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• (Weak) ETags and Last-Modified

  - by Kai Moritz

  As far as I understand the specs, the ETag, which was introduced in RFC 2616 (HTTP/1.1) is a predecessor of the Last-Modified-Header, which is proposet to give the software-architect more controll over the cache-revalidating process. If both Cache-Validation-Headers (If-None-Match and If-Modified-Since) are present, according to RFC 2616, the client (i.e. the browser) should use the ETag when checking, if a resource has changed. According to section 14.26 of RFC 2616, the server MUST NOT respond with a 304 Not Modified, if the ETag presented in a If-None-Match-Header has changed, and the server has to ignore an additional If-Modified-Since-Header, if present. If the presented ETag matches, he MUST NOT perform the request, unless the Date in the Last-Modified-Header says so. (If the presented ETag matches, the server should respond with a 304 Not Modified in case of a GET- or HEAD-request...) This section leaves room for some speculations: A strong ETag is supposed to change ''everytime'', the resource changes. So, having to responde with something else as 304 Not Modified to a request with an unchanged ETag and an If-Modified-Since-Header, which dose not match is a bit of a contradiction, because the strong ETag says, that the resource was not modified. (Though, this is not that fatal, because the server can send the same unchanged resource again.) ... ... o.k. While I was writing this, the question was boiling down to this answer: The (small) contradiction stated above, was made because of Weak ETags. A resource marked with a Weak ETag may have changed, although the ETag has not. So, in case of a Weak ETag it would be wrong, to answer with 304 Not Modified, when the ETag has not changed, but the date presented in the If-Modified-Since does not match, right?

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• How to avoid resetting the java Scanner position

  - by Derek

  I have some code that looks more or less like this: while(scanner.hasNext()) { if(scanner.findInLine("Test") !=null) { //do some things }else{ scanner.nextLine(); } } I am using this to parse an ~10MB text file. The problem is, if I put a breakpoint on the while() and the scanner.nextLine(), I can see that sometimes the scanners position (in the debug window) goes back to zero. I think this is causing me some kind of loop blow up, because the regext in findInLine() starts at zero, looks through some amount of text, advancing the position, and then it randomly gets set back to zero, so it has to re-parse all that text again. Any ideas what can be causing that? Am I even doing this the right way? Thanks Some additional info: The Scanner is instantiated from an InputStream. After diubg sine debugging, it appears that there is a HearCharBuffer that Scanner uses and it only allows 1024 characters at a time, and then resets. Is there a way to avoid this, or do things differently? That seems like a small amount of characters to be able to scan. Derek

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• How to store and locate multiple interface types within a Delphi TInterfaceList

  - by Brian Frost

  Hi, I'm storing small interfaces from a range of objects into a single TInterfaceList 'store' with the intention of offering list of specific interface types to the end user, so each interface will expose a 'GetName' function but all other methods are unique to that interface type. For example here are two interfaces: IBase = interface //---------------------------------------- function GetName : string; //---------------------------------------- end; IMeasureTemperature = interface(IBase) //------------------------------------ function MeasureTemperature : double; //---------------------------------------- end; IMeasureHumidity = interface(IBase) //---------------------------------------- function MeasureHumidity: double; //---------------------------------------- end; I put several of these interfaces into a single TInterfaceList and then I'd like to scan the list for a specific interface type (e.g. 'IMeasureTemperature') building another list of pointers to the objects exporting those interfaces. I wish to make no assumptions about the locations of those objects, some may export more than one type of interface. I know I could do this with a class hierarchy using something like: If FList[I] is TMeasureTemperature then .. but I'd like to do something simliar with an interface type, Is this possible?

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• Jquery thumbnail popup on link Mouseover

  - by Charles Marsh

  Hello All, I have this peice of coding which simply swaps an image when a link is clicked, I also show some hidden html content which is positioned over the image. <script> if($.browser.msie && parseInt($.browser.version) <= 6){ $('#contentone, #contenttwo, #contentthree, #contentfour, .linksBackground').hide(); } $('#contentone, #contenttwo, #contentthree, #contentfour').hide(); $("#linkone").click(function() { $('#contenttwo, #contentthree, #contentfour').hide("1500"); $("#imageone").attr("src","Resources/Images/TEMP-homeOne.jpg"); $("#contentone").show("1500"); }); $("#linktwo").click(function() { $('#contentone, #contentthree, #contentfour').hide("1500"); $("#imageone").attr("src","Resources/Images/TEMP-homeTwo.jpg"); $("#contenttwo").show("1500"); }); $("#linkthree").click(function() { $('#contentone, #contenttwo, #contentfour').hide("1500"); $("#imageone").attr("src","Resources/Images/TEMP-homeThree.jpg"); $("#contentthree").show("1500"); }); $("#linkfour").click(function() { $('#contentone, #contenttwo, #contentthree').hide("1500"); $("#imageone").attr("src","Resources/Images/TEMP-homeFour.jpg"); $("#contentfour").show("1500"); }); </script> Does anyone know how I can further modify this to show a small thumbnail image when the user rolls over the link? I just need a hint because I'm not sure where to turn to... can I achieve it with mouseover?

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• SWIG: From Plain C++ to working Wrapper

  - by duckworthd

  Hi everyone. I've been trying to create a SWIG wrapper for this tiny little C++ class for the better part of 3 hours with no success, so I was hoping one of you out there could lend me a small hand. I have the following class: #include <stdio.h> class Example { public: Example(); ~Example(); int test(); }; #include "example.h" Along with the implementation: Example::Example() { printf("Example constructor called\n"); } Example::~Example() { printf("Example destructor called\n"); } int Example::test() { printf("Holy shit, I work!\n"); return 42; } I've read through the introduction page ( www.swig.org/Doc1.3/Java.html ) a few times without gaining a whole lot of insight into the situation. My steps were Create an example.i file Compile original alongside example_wrap.cxx (no linking) link resulting object files together Create a little java test file (see below) javac all .java files there and run Well steps 4 and 5 have created a host of problems for me, starting with the basic ( library 'example' not found due to not being in java's path ) to the weird ( library not found even unless LD_LIBRARY_PATH is set to something, even if it's nothing at all). I've included my little testing code below public class test2 { static { String libpath = System.getProperty("java.library.path"); String currentDir = System.getProperty("user.dir"); System.setProperty("java.library.path", currentDir + ":" + libpath); System.out.println(System.getProperty("java.library.path")); System.loadLibrary("example"); } public static void main(String[] args){ System.out.println("It loads!"); } } Well, if anyone has navigated these murky waters of wrapping, I could not be happier than if you could light the way, particularly if you could provide the example.i and bash commands to go along with it.

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• What is the simplest way to map a folder on the file system to a url in Tomcat?

  - by Simon

  Here's my problem... I have a small prototype app (happens to be in Grails hosted on AWS) and I want to add the ability of the user to upload a few (max 10) images. I want to persist these images on disk on the server machine, in a folder location which is outside my WAR. I realise that there is probably a super-scalable solution involving more web servers and optimised static asset serving, but for the approximately 100 users I am likely to get, it's really not worth the effort and cost. So, what is the simplest way I can have a virtual folder from my url map to a physical folder on disk? I sort of want... http://myapp.com/static to map to a folder which I can configure e.g. /var/www/static so I can then have in my code... <img src="/static/user1/picture.jpg"/> I don't particularly mind whether the resulting physical folders are directly browsable. Security will eventually be an issue, but it isn't at the start. So, what are my options? I have looked at virtual hosts on the apache site, but it feels more complicated than I need. I don't want to use the Grails static rendering plugins.

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• How much does an InnoDB table benefit from having fixed-length rows?

  - by Philip Eve

  I know that dependent on the database storage engine in use, a performance benefit can be found if all of the rows in the table can be guaranteed to be the same length (by avoiding nullable columns and not using any VARCHAR, TEXT or BLOB columns). I'm not clear on how far this applies to InnoDB, with its funny table arrangements. Let's give an example: I have the following table CREATE TABLE `PlayerGameRcd` ( `User` SMALLINT UNSIGNED NOT NULL, `Game` MEDIUMINT UNSIGNED NOT NULL, `GameResult` ENUM('Quit', 'Kicked by Vote', 'Kicked by Admin', 'Kicked by System', 'Finished 5th', 'Finished 4th', 'Finished 3rd', 'Finished 2nd', 'Finished 1st', 'Game Aborted', 'Playing', 'Hide' ) NOT NULL DEFAULT 'Playing', `Inherited` TINYINT NOT NULL, `GameCounts` TINYINT NOT NULL, `Colour` TINYINT UNSIGNED NOT NULL, `Score` SMALLINT UNSIGNED NOT NULL DEFAULT 0, `NumLongTurns` TINYINT UNSIGNED NOT NULL DEFAULT 0, `Notes` MEDIUMTEXT, `CurrentOccupant` TINYINT UNSIGNED NOT NULL DEFAULT 0, PRIMARY KEY (`Game`, `User`), UNIQUE KEY `PGR_multi_uk` (`Game`, `CurrentOccupant`, `Colour`), INDEX `Stats_ind_PGR` (`GameCounts`, `GameResult`, `Score`, `User`), INDEX `GameList_ind_PGR` (`User`, `CurrentOccupant`, `Game`, `Colour`), CONSTRAINT `Constr_PlayerGameRcd_User_fk` FOREIGN KEY `User_fk` (`User`) REFERENCES `User` (`UserID`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `Constr_PlayerGameRcd_Game_fk` FOREIGN KEY `Game_fk` (`Game`) REFERENCES `Game` (`GameID`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=INNODB CHARACTER SET utf8 COLLATE utf8_general_ci The only column that is nullable is Notes, which is MEDIUMTEXT. This table presently has 33097 rows (which I appreciate is small as yet). Of these rows, only 61 have values in Notes. How much of an improvement might I see from, say, adding a new table to store the Notes column in and performing LEFT JOINs when necessary?

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• Generic that takes only numeric types (int double etc)?

  - by brandon

  In a program I'm working on, I need to write a function to take any numeric type (int, short, long etc) and shove it in to a byte array at a specific offset. There exists a Bitconverter.GetBytes() method that takes the numeric type and returns it as a byte array, and this method only takes numeric types. So far I have: private void AddToByteArray<T>(byte[] destination, int offset, T toAdd) where T : struct { Buffer.BlockCopy(BitConverter.GetBytes(toAdd), 0, destination, offset, sizeof(toAdd)); } So basically my goal is that, for example, a call to AddToByteArray(array, 3, (short)10) would take 10 and store it in the 4th slot of array. The explicit cast exists because I know exactly how many bytes I want it to take up. There are cases where I would want a number that is small enough to be a short to really take up 4 bytes. On the flip side, there are times when I want an int to be crunched down to just a single byte. I'm doing this to create a custom network packet, if that makes any ideas pop in to your heads. If the where clause of a generic supported something like "where T : int || long || etc" I would be ok. (And no need to explain why they don't support that, the reason is fairly obvious) Any help would be greatly appreciated! Edit: I realize that I could just do a bunch of overloads, one for each type I want to support... but I'm asking this question because I want to avoid precisely that :)

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• Threads are blocked in malloc and free, virtual size

  - by Albert Wang

  Hi, I'm running a 64-bit multi-threaded program on the windows server 2003 server (X64), It run into a case that some of the threads seem to be blocked in the malloc or free function forever. The stack trace is like follows: ntdll.dll!NtWaitForSingleObject() + 0xa bytes ntdll.dll!RtlpWaitOnCriticalSection() - 0x1aa bytes ntdll.dll!RtlEnterCriticalSection() + 0xb040 bytes ntdll.dll!RtlpDebugPageHeapAllocate() + 0x2f6 bytes ntdll.dll!RtlDebugAllocateHeap() + 0x40 bytes ntdll.dll!RtlAllocateHeapSlowly() + 0x5e898 bytes ntdll.dll!RtlAllocateHeap() - 0x1711a bytes MyProg.exe!malloc(unsigned __int64 size=0) Line 168 C MyProg.exe!operator new(unsigned __int64 size=1) Line 59 + 0x5 bytes C++ ntdll.dll!NtWaitForSingleObject() ntdll.dll!RtlpWaitOnCriticalSection() ntdll.dll!RtlEnterCriticalSection() ntdll.dll!RtlpDebugPageHeapFree() ntdll.dll!RtlDebugFreeHeap() ntdll.dll!RtlFreeHeapSlowly() ntdll.dll!RtlFreeHeap() MyProg.exe!free(void * pBlock=0x000000007e8e4fe0) C BTW, the param values passed to the new operator is not correct here maybe due to optimization. Also, at the same time, I found in the process Explorer, the virtual size of this program is 10GB, but the private bytes and working set is very small (<2GB). We did have some threads using virtualalloc but in a way that commit the memory in the call, and these threads are not blocked. m_pBuf = VirtualAlloc(NULL, m_size, MEM_COMMIT, PAGE_READWRITE); ...... VirtualFree(m_pBuf, 0, MEM_RELEASE); This looks strange to me, seems a lot of virtual space is reserved but not committed, and malloc/free is blocked by lock. I'm guessing if there's any corruptions in the memory/object, so plan to turn on gflag with pageheap to troubleshoot this. Does anyone has similar experience on this before? Could you share with me so I may get more hints? Thanks a lot!

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• Using a variable in a mysql query, in a C++ MFC program.

  - by D.Gaughan

  Hi, after extensive trawling of the internet I still havent found any solution for this problem. I`m writing a small C++ app that connects to an online database and outputs the data in a listbox. I need to enable a search function using an edit box, but I cant get the query to work while using a variable. My code is: res = mysql_perform_query (conn, "select distinct artist from Artists"); //res = mysql_perform_query (conn, "select album from Artists where artist = ' ' "); while((row = mysql_fetch_row(res)) != NULL){ CString str; UpdateData(); str = ("%s\n", row[0]); UpdateData(FALSE); m_list_control.AddString(str); } the first "res = " line is working fine, but I need the second one to work. I have a member variable m_search_edit set up for the edit box, but any way I try to include it in the sql statement causes errors. eg. res = mysql_perform_query (conn, "select album from Artists where artist = '"+m_search_edit+" ' "); causes this error: error C2664: 'mysql_perform_query' : cannot convert parameter 2 from 'class CString' to 'char *' No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called" And when I convert m_search_edit to a char* it gives me a " Cannot add 2 pointers" error. Any way around this???

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• Understanding REST through an example

  - by grifaton

  My only real exposure to the ideas of REST has been through Ruby on Rails' RESTful routing. This has suited me well for the kind of CRUD-based applications I have built with Rails, but consequently my understanding of RESTfulness is somewhat limited. Let's say we have a finite collection of Items, each of which has a unique ID, and a number of properties, such as colour, shape, and size (which might be undefined for some Items). Items can be used by a client for a period of time, but each Item can only be used by one client at once. Access to Items is regulated by a server. Clients can request the temporary use of certain items from a server. Usually, clients will only be interested in getting access to a number of Items with particular properties, rather than getting access to specific Items. When a client requests use of a number of Items, the server responds with a list of IDs corresponding to the request, or with a response that says that the requested Items are not currently available or do not exist. A client can make the following kinds of request: Tell me how many green triangle Items there are (in total/available). Give me use of 200 large red Items. I have finished with Items 21, 23, 23. Add 100 new red square Items. Delete 50 small green Items. Modify all big yellow pentagon Items to be blue. The toy example above is like a resource allocation problem I have had to deal with recently. How should I go about thinking about it RESTfully?

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• Lite-Javascript Gallery - Can I position the img absolutely in relationship to the lis?

  - by blackessej

  I have a lite-javascript run image gallery. The javascript grabs each element in the list and places it as a background in the parent element. Then the CSS styles the thumbnails as small blocks with a defined height/width. A click-event for each object toggles it’s child’s element’s visibility and adds an “active” class name to the . Using CSS, I'm trying to place the absolutely to make it appear at the same position for each thumb, but it's moving in relation to the thumbs. Here's the CSS: #jgal li { background-position:50% 50%; background-repeat:no-repeat; border:solid #999 4px; cursor:pointer; display:block; float:left; height:60px; width:60px; margin-bottom:14px; margin-right:14px; opacity:0.5; } #jgal li img { position:absolute; top:0px; left:210px; display:none; } And the site: http://www.erisdesigns.net Thanks in advance for any help!

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• How do I see if an established socket is stuck on a server that's expecting input?

  - by Parker

  I have a script that scans ports for open proxy servers. Problem is if it encounters a login program (specifically telnet) then it hangs there forever since it doesn't know what to do and eventually the server closes the connection. The simple solution would be to create a bunch of cases. If telnet, do this. If SSH, do that. If something else, blah blah blah. I'd like an umbrella solution since the script is not a high priority for me. The script, as it is now, is available at http://parkrrr.net/socks/scan.phps On a small scale (the page maybe averages 15 hits/day) it's fine but on a larger scale I'd be worried about a lot of open zombie sockets. Swapping the !$strpos doesn't work since servers can return more information than what you requested (headers, ads, etc). Only accepting a fixed number of bytes (as opposed to appending until EOF, which it does now) from the $fgets also does not seem to work. I am sure this is where it gets stuck: while (!feof($fp)) { $data.=fgets($fp,512); } But what can I do? Any other suggestions/warnings would also be welcomed.

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• File IO with Streams - Best Memory Buffer Size

  - by AJ

  I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance).

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• Serving static media in django application

  - by Ed

  I notice that when I reference my java scripts and static image files from my templates, they show up in development, but not from the production server. From development, I access them as such: <img src="/my_proj/media/css/images/collapsed.png" /> but from production, I have to remove the project directory: <img src="/media/css/images/collapsed.png" /> I'm assuming I'm doing something wrong with regard to serving static media. I'm caught between a number of seemingly different options for serving static media in Django. On one hand, it's been recommended that I use django-staticfiles to serve media. On the other I see reference to STATIC_ROOT and STATIC_URL in the documentation (with caveats about use in production). I have small .png files of "plus" and "minus" symbols for use in some of my jQuery scripts. In addition, the scripts themselves need to be referenced. 1) Am I correctly categorizing scripts and site images as static media? 2) What is the best method to access this media (from production)?

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• Best way to sign data in web form with user certificate

  - by salgiza

  We have a C# web app where users will connect using a digital certificate stored in their browsers. From the examples that we have seen, verifying their identity will be easy once we enable SSL, as we can access the fields in the certificate, using Request.ClientCertificate, to check the user's name. We have also been requested, however, to sign the data sent by the user (a few simple fields and a binary file) so that we can prove, without doubt, which user entered each record in our database. Our first thought was creating a small text signature including the fields (and, if possible, the md5 of the file) and encrypt it with the private key of the certificate, but... As far as I know we can't access the private key of the certificate to sign the data, and I don't know if there is any way to sign the fields in the browser, or we have no other option than using a Java applet. And if it's the latter, how we would do it (Is there any open source applet we can use? Would it be better if we create one ourselves?) Of course, it would be better if there was any way to "sign" the fields received in the server, using the data that we can access from the user's certificate. But if not, any info on the best way to solve the problem would be appreciated.

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• Question on Split usage in Perl

  - by Nano HE

  Hello. I wrote an small script to use Split() as this, use strict; use warnings; use Data::Dumper; my $fh = \*DATA; while(my $line = <$fh>) { my @values = split(':', $line); foreach my $val (@values) { print "$val\n"; } } __DATA__ 1 : Hello World String10 : NO : A1B2,B3 11 : Hello World String11 : YES : A11B2,B3,B14,B25 A1B2,B3 and A11B2,B3 are characters form like Only One Letter A and One or Two Number 2, 3, 14,25 etc then concatenated with Only One Letter B and one or two Numbers like 2, 3, 14,25. etc Now out put as this 1 Hello World String10 NO A1B2,B3 11 Hello World String11 YES A11B2,B3,B14,B25 How can I hold the last array member from @values and made concatenation and out put as this. 1 Hello World String1 NO A1B2,A1B3 11 Hello World String11 YES A11B2,A11B3,A11B14,A11B25 Appreciated for your comments and replies. [update] My out put need the concatenation followed the rule. A and one or two numbers and joined by B and one or two numbers split by ,

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• PHP mail may be filtered out by spam?

  - by Derek

  I am creating a small company, and would like to send out emails to my clients once they have signed up for my service to activate their accounts. I am currently using PHP's mail() function, however I am worried that my emails are being filtered out by spam filters. Is there a better way to go about this? $email = 'XZY Client Email address @ somedomain.com'; $emailSubject = "Welcome to XYZ Service!"; $to = $email; $subject .= "".$emailSubject.""; $headers .= "From: [email protected]\r\n" . "X-Mailer: php"; $headers .= "MIME-Version: 1.0\r\n"; $headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n"; $message = "<html><body>"; $message .= "Welcome to XYZ Service! \n Activate your account by clicking the following link: link..."; mail($to, $subject, $message, $headers); Is there a way to authenticate these emails so that my clients know that they are from my actual service? Thank you in advance!

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• byte + byte = int... why?

  - by Robert C. Cartaino

  Looking at this C# code... byte x = 1; byte y = 2; byte z = x + y; // ERROR: Cannot implicitly convert type 'int' to 'byte' The result of any math performed on byte (or short) types is implicitly cast back to an integer. The solution is to explicitly cast the result back to a byte, so... byte z = (byte)(x + y); // works What I am wondering is why? Is it architectural? Philosophical? We have: int + int = int long + long = long float + float = float double + double = double So why not: byte + byte = byte short + short = short ? A bit of background: I am performing a long list of calculations on "small numbers" (i.e. < 8) and storing the intermediate results in a large array. Using a byte array (instead of an int array) is faster (because of cache hits). But the extensive byte-casts spread through the code make it that much more unreadable.

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• Concrete examples of state sharing between multiple viewmodels (WPF MVVM)

  - by JohnMetta

  I have a WPF/Entity Framework (4.0) project with many objects. I'd like to build the application so that that I can have object selection state shared across viewmodels. For Example: We have Cars, Drivers, Passengers, and Cargo classes. We also have UserControls for CarList, DriverList, etc. and editor windows for CarEditor, DriverEditor, etc. Furthermore, we have viewmodels for all of these (CarListViewModel, DriverListViewModel, CargoEditorViewModel, etc). This all composes a dockable interface where the user can have multiple object lists, editors, and viewers open. What I want is a concrete code example of how to wireup multiple viewmodels so that selecting a car in the CarList will cause that car to go live in the CarEditorView, but also be selected in any other view for which the context is valid (such as a DriverByCarView- or just DriverList if there is a filter predicate). There are a number of suggestions and discussions based on this question. The two methods that seem to dominate are: 3018307: Discusses state sharing by mentioning a messaging subsystem 1159035: Discusses state sharing by using an enclosing viewmodel Is one of these approaches better than the other? Does anyone have a concrete example of either/both of these methods in the form of a write-up or small code project? I'm still learning WPF, so pointers to entry points for reading API fundamentals are appreciated, but looking at code examples is where I usually go. Thanks In case anyone is interested, here are some other similar discussions: 3816961: Discusses returning multiple viewmodels depending on object type (i.e. a collection of arbitrary types adhering to a specific interface) 1928130: Discusses whether it is a good idea to aggregate viewmodels as properties of other viewmodels (e.g. a MainWindow viewmodel composed of panel viewmodels) 1120061: Essentially discusses whether to have use a viewmodel-per-model strategy or a viewmodel-per-view-element strategy. 4244222: Discusses whether or not to nest the viewmodels when using a nested object hierarchy. 4429708: Discusses sharing collections between viewmodels directly, but doesn't go into detail. List item: Discusses managing multiple selections within a single viewmodel.

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• gcc compilations (sometimes) result in cpu underload

  - by confusedCoder

  I have a larger C++ program which starts out by reading thousands of small text files into memory and storing data in stl containers. This takes about a minute. Periodically, a compilation will exhibit behavior where that initial part of the program will run at about 22-23% CPU load. Once that step is over, it goes back to ~100% CPU. It is more likely to happen with O2 flag turned on but not consistently. It happens even less often with the -p flag which makes it almost impossible to profile. I did capture it once but the gprof output wasn't helpful - everything runs with the same relative speed just at low cpu usage. I am quite certain that this has nothing to do with multiple cores. I do have a quad-core cpu, and most of the code is multi-threaded, but I tested this issue running a single thread. Also, when I run the problematic step in multiple threads, each thread only runs at ~20% CPU. I apologize ahead of time for the vagueness of the question but I have run out of ideas as to how to troubleshoot it further, so any hints might be helpful. UPDATE: Just to make sure it's clear, the problematic part of the code does sometimes (~30-40% of the compilations) run at 100% CPU, so it's hard to buy the (otherwise reasonable) argument that I/O is the bottleneck

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• GWT + JDO + ArrayList

  - by dvieira

  Hi, I'm getting a Null ArrayList in a program i'm developing. For testing purposes I created this really small example that still has the same problem. I already tried diferent Primary Keys, but the problem persists. Any ideas or suggestions? 1-Employee class @PersistenceCapable(identityType = IdentityType.APPLICATION) public class Employee { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; @Persistent private ArrayList<String> nicks; public Employee(ArrayList<String> nicks) { this.setNicks(nicks); } public String getKey() { return key; } public void setNicks(ArrayList<String> nicks) { this.nicks = nicks; } public ArrayList<String> getNicks() { return nicks; } } 2-EmployeeService public class BookServiceImpl extends RemoteServiceServlet implements EmployeeService { public void addEmployee(){ ArrayList<String> nicks = new ArrayList<String>(); nicks.add("name1"); nicks.add("name2"); Employee employee = new Employee(nicks); PersistenceManager pm = PMF.get().getPersistenceManager(); try { pm.makePersistent(employee); } finally { pm.close(); } } /** * @return * @throws NotLoggedInException * @gwt.typeArgs <Employee> */ public Collection<Employee> getEmployees() { PersistenceManager pm = getPersistenceManager(); try { Query q = pm.newQuery("SELECT FROM " + Employee.class.getName()); Collection<Employee> list = pm.detachCopyAll((Collection<Employee>)q.execute()); return list; } finally { pm.close(); } } }

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• "end()" iterator for back inserters?

  - by Thanatos

  For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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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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