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• EC2 persistence of machine

  - by Seagull

  I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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• how would you like computer science classes to be taught?

  - by aaa

  hello I am a graduate student now, and hopefully someday I will teach. my interests are C++, Python, embedded languages, and scientific computing. Meanwhile I daydream about how I would teach. I was not quite happy with my undergraduate university as I found many computer science classes lacking. so I would like to ask you, if you were a student, how would you like your computer science classes to be taught? I understand it is a very subjective question, but nevertheless I think it's important to know what people want. Some specific points I am interested in: should computer languages be taught explicitly, or should students be required to pick up language on their own? what is better for learning, tests, projects, some sort of take-home exam? how do you think classtime should be used? theory, introduction, explanations, etc.? do you think the group projects are important? how much about computer architecture do you want to learn in computer science class, not necessarily assembler class. should particular operating system/editor be mandated or encouraged? Thanks thank you for your comments. Question has been closed because it is a discussion question rather than Q&A. If you know appropriate website for discussions of such sort with low noise ratio, please let me know.

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• Acceessing some aggregate functions in a linq datasource in a GridView

  - by Stephen Pellicer

  I am working on a traditional WebForms project. In the project I am trying out some Linq datasources with plans to eventually migrate to an MVC architecture. I am still very new to Linq. I have a GridView using a Linq datasource. The entities I am showing has a to many relationship and I would like to get the maximum value of a column in the many side of the relationship. I can show properties of the base entity in the gridview: <asp:TemplateField HeaderText="Number" SortExpression="tJobBase.tJob.JobNumber"> <ItemTemplate> <asp:Label ID="Label1" runat="server" Text='<%# Bind("tJobBase.tJob.JobNumber") %>'> </asp:Label> </ItemTemplate> </asp:TemplateField> I can also show the count of the many related property: <asp:TemplateField HeaderText="Number" SortExpression="tJobBase.tJob.tHourlies.Count"> <ItemTemplate> <asp:Label ID="Label1" runat="server" Text='<%# Bind("tJobBase.tJob.tHourlies.Count") %>'> </asp:Label> </ItemTemplate> </asp:TemplateField> Is there a way to get the max value of a column called WeekEnding in the tHourlies collection to show in the GridView?

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• JAVASCRIPT ENABLED [closed]

  - by kirchoffs415

  HI, I hope somebody can help, i keep getting the following message when i log on-- Your Javascript is disabled. Limited functionality is available. it will stay for maybe a day sometimes two.I have uninstalled javascript and reinstalled but still the same. Iam using chrome. any help would be gratefull many thanks Dominic p.s. my system spec is as follows System InformationOS Name Microsoft® Windows Vista™ Home Premium Version 6.0.6002 Service Pack 2 Build 6002 Other OS Description Not Available OS Manufacturer Microsoft Corporation System Name DOM-PC System Manufacturer Dell Inc. System Model Inspiron 1545 System Type X86-based PC Processor Pentium(R) Dual-Core CPU T4200 @ 2.00GHz, 2000 Mhz, 2 Core(s), 2 Logical Processor(s) BIOS Version/Date Dell Inc. A05, 25/02/2009 SMBIOS Version 2.4 Windows Directory C:\Windows System Directory C:\Windows\system32 Boot Device \Device\HarddiskVolume3 Locale United Kingdom Hardware Abstraction Layer Version = "6.0.6002.18005" User Name DOM-PC\DOM Time Zone GMT Standard Time Installed Physical Memory (RAM) 3.00 GB Total Physical Memory 2.96 GB Available Physical Memory 1.38 GB Total Virtual Memory 5.89 GB Available Virtual Memory 4.25 GB Page File Space 3.00 GB Page File C:\pagefile.sys My System Specs

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• need to add secure ftp file upload area to a client's website

  - by user346602

  This is a variation on a previous question as I am having tons of trouble finding answers in all my relentless online searches. Am designing a website for an architecture firm. They want their clients to be able to upload files to them, through a link on their site, via ftp. They also want to have a sign in for their clients, and ensure the uploads are secure. I can figure out how to make a form that has a file upload area - but just don't understand the ftp and the secure part... I understand html, css and a bit of JQuery; the rest is still very challenging to me. Have found something called net2ftp that claims to do what I'm looking for - but the even the installation instructions (for administrators, here: http://www.net2ftp.com/help.html) confuse me. Do I need a MySQL database? Where do I put in Admin password they refer to? It goes on... Is there anything "easier" out there that anyone knows of? I have read that I should be Googling "file managers" - but don't know if these can be embedded in a client's website. I even need to understand of what happens to said file, and where it ends up, when client clicks the upload link. Oh - I am so in over head on this one.

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• .NET multithreading, volatile and memory model

  - by fedor-serdukov

  Assume that we have the following code: class Program { static volatile bool flag1; static volatile bool flag2; static volatile int val; static void Main(string[] args) { for (int i = 0; i < 10000 * 10000; i++) { if (i % 500000 == 0) { Console.WriteLine("{0:#,0}",i); } flag1 = false; flag2 = false; val = 0; Parallel.Invoke(A1, A2); if (val == 0) throw new Exception(string.Format("{0:#,0}: {1}, {2}", i, flag1, flag2)); } } static void A1() { flag2 = true; if (flag1) val = 1; } static void A2() { flag1 = true; if (flag2) val = 2; } } } It's fault! The main quastion is Why... I suppose that CPU reorder operations with flag1 = true; and if(flag2) statement, but variables flag1 and flag2 marked as volatile fields...

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• Linux time sample based profiler.

  - by Caspin

  short version: Is there a good time based sampling profiler for Linux? long version: I generally use OProfile to optimize my applications. I recently found a shortcoming that has me wondering. The problem was a tight loop spawning c++filt to demangle a c++ name. I only stumbled upon the code by accident while chasing down another bottleneck. The OProfile didn't show anything unusual about the code so I almost ignored it but my code sense told me to optimize the call and see what happened. I changed the popen of c++filt to abi::__cxa_demangle. The runtime went from more than a minute to a little over a second. About a x60 speed up. Is there a way I could have configured OProfile to flag the popen call? As the profile data sits now OProfile thinks the bottle neck was the heap and std::string calls (which BTW once optimized dropped the runtime to less than a second, more than x2 speed up). Here is my OProfile configuration: $ sudo opcontrol --status Daemon not running Event 0: CPU_CLK_UNHALTED:90000:0:1:1 Separate options: library vmlinux file: none Image filter: /path/to/excutable Call-graph depth: 7 Buffer size: 65536 Is there another profiler for Linux that could have found the bottleneck? I suspect the issue is that OProfile only logs its samples to the currently running process. I'd like it to always log its samples to the process I'm profiling. So if the process is currently switched out (blocking on IO or a popen call) OProfile would just place its sample at the blocked call. If I can't fix this, OProfile will only be useful when the executable is pushing near 100% CPU. It can't help with executables that that have inefficient blocking calls.

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• erlang design of a card game [closed]

  - by user601836

  I would like to discuss with you a possible implementation for a card game in erlang. The only full example I found online is OpenPoker. I would like to create one myself, so here is the implementation I have in mind: A gen_server to represent a deck: when started creates a deck of cards (shuffled). And stores it in its state. provides an handle_call (draw_card) A gen_server to represent the chat room. Stores in its state the registered name of a player process (e.g. player1, player2, luke etc etc). Exports handle_cast to join the chat (executed by default when somebody joins successfully the game) and one to broadcast a chat message to all users by calling an handle_cast on the gen_server representing a player. a gen_fsm to represent a game instance. Has two states (wait_join, and turn). Exports join/1 to join the game, play_card/2 and send_msg/2. One parameter is the pid of the player process. a gen_server to represent the player. Exports only start_link/1 where the parameter is the name to use to register the process (inside the init I call join method of gen_fsm). Has different handle_calls (e.g. get_hand, draw_card) and handle_casts (e.g. play_card, deliver_msg, and send_msg) A gen_server to represent the main process. Exports (join_game/1 which calls player:start_link/1, send_msg/2 to call player's send_msg, play_card/3 to call player's play_card). What do you think of this architecture? Thanks in advance

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• Call method immediately after object construction in LINQ query

  - by Steffen

  I've got some objects which implement this interface: public interface IRow { void Fill(DataRow dr); } Usually when I select something out of db, I go: public IEnumerable<IRow> SelectSomeRows { DataTable table = GetTableFromDatabase(); foreach (DataRow dr in table.Rows) { IRow row = new MySQLRow(); // Disregard the MySQLRow type, it's not important row.Fill(dr); yield return row; } } Now with .Net 4, I'd like to use AsParallel, and thus LINQ. I've done some testing on it, and it speeds up things alot (IRow.Fill uses Reflection, so it's hard on the CPU) Anyway my problem is, how do I go about creating a LINQ query, which calls Fills as part of the query, so it's properly parallelized? For testing performance I created a constructor which took the DataRow as argument, however I'd really love to avoid this if somehow possible. With the constructor in place, it's obviously simple enough: public IEnumerable<IRow> SelectSomeRowsParallel { DataTable table = GetTableFromDatabase(); return from DataRow dr in table.Rows.AsParallel() select new MySQLRow(dr); } However like I said, I'd really love to be able to just stuff my Fill method into the LINQ query, and thus not need the constructor overload.

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• Trying to find a PHP5 API-based embeddable CMS

  - by StrangeElement

  I've been making the rounds for a CMS that I can use as an API, in a sort of "embedded" mode. I mean by this that I don't want the CMS to do any logic or presentation. I want it to be used as an API, which I can then use within an existing site. I don't want to be tied to the architecture of the CMS. A good example of this is NC-CMS (http://www.nconsulting.ca/nc-cms/). All it needs is an include at the top, then wherever editable content is desired it's only a function call with a unique label. It's also perfect in the sense that it allows to differentiate between small strings (like titles, labels) and texts (which require a rich-text editor). It's the only CMS I found that fits this description, but it is a little too light as it does not handle site structure. I need to be able to allow my client to add pages, choosing an existing template for the layout. A minimal back-end is required. Wordpress also fits some requirements in that it handles only content editing and allows freedom for the themes by letting them call the content where and how they want it. But it is article-based and backwards, in that it embeds sites (as themes) within its structure, rather than being embeddable in sites like NC. It's funny how checking out all the CMS out there, almost all of them claim that most CMS are not self-sufficient, that they do not handle application logic, while (almost) every single on I found with only one exception do so. Many are mostly article-based blog engines, which does not fit my need. I would appreciate any CMS that fits the general description.

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• querying huge database table takes too much of time in mysql

  - by Vijay

  Hi all, I am running sql queries on a mysql db table that has 110Mn+ unique records for whole day. Problem: Whenever I run any query with "where" clause it takes at least 30-40 mins. Since I want to generate most of data on the next day, I need access to whole db table. Could you please guide me to optimize / restructure the deployment model? Site description: mysql Ver 14.12 Distrib 5.0.24, for pc-linux-gnu (i686) using readline 5.0 4 GB RAM, Dual Core dual CPU 3GHz RHEL 3 my.cnf contents : [root@reports root]# cat /etc/my.cnf [mysqld] datadir=/data/mysql/data/ socket=/tmp/mysql.sock sort_buffer_size = 2000000 table_cache = 1024 key_buffer = 128M myisam_sort_buffer_size = 64M # Default to using old password format for compatibility with mysql 3.x # clients (those using the mysqlclient10 compatibility package). old_passwords=1 [mysql.server] user=mysql basedir=/data/mysql/data/ [mysqld_safe] err-log=/data/mysql/data/mysqld.log pid-file=/data/mysql/data/mysqld.pid [root@reports root]# DB table details: CREATE TABLE `RAW_LOG_20100504` ( `DT` date default NULL, `GATEWAY` varchar(15) default NULL, `USER` bigint(12) default NULL, `CACHE` varchar(12) default NULL, `TIMESTAMP` varchar(30) default NULL, `URL` varchar(60) default NULL, `VERSION` varchar(6) default NULL, `PROTOCOL` varchar(6) default NULL, `WEB_STATUS` int(5) default NULL, `BYTES_RETURNED` int(10) default NULL, `RTT` int(5) default NULL, `UA` varchar(100) default NULL, `REQ_SIZE` int(6) default NULL, `CONTENT_TYPE` varchar(50) default NULL, `CUST_TYPE` int(1) default NULL, `DEL_STATUS_DEVICE` int(1) default NULL, `IP` varchar(16) default NULL, `CP_FLAG` int(1) default NULL, `USER_LOCATE` bigint(15) default NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=200000000; Thanks in advance! Regards,

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• MSSQL in ASP.NET application getting unstable after a certain period

  - by Barslett

  Hello, I have an ASP.NET 2.0 application that I made to keep track of disruption reports about our public transport system. The architecture is pretty straight-forward; an MSSQL Express 2008 database, ADO.NET and a DataSet/DAL with a few methods to access the database. There is a set of .aspx pages for the UI in use by our dispatchers and on our public website, as well as a set of SOAP and REST webservices and an RSS feed. Everything worked just fine for more than a year, until two weeks ago. Now and then, it seems as the database enters an unstable mode, and the application starts responding something right, something wrong. The typical error is that apparently, an empty DataTable is returned to the public disruption overview or to the RSS generator. Thus, the user gets e.g. an empty GridView, but no exception is thrown AFAIK, and nothing is written to the Windows Application log. After a restart of the MSSQL Express service, the situation is back to normal. It has to be said that the situation first time appeared a few days after I made a new minor upgrade of the application. The RSS generator was slightly rewritten, and I added a WCF REST service. But the DAL and the database schema were untouched... Any hints of how we could keep the database stable? It is a bit annoying not to have a clue ;-)

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• Is there a way to implement Caliburn-like co-routines in VB.NET since there's no yield keyword

  - by Miroslav Popovic

  Note that I'm aware of other yield in vb.net questions here on SO. I'm playing around with Caliburn lately. Bunch of great stuff there, including co-routines implementation. Most of the work I'm doing is C# based, but now I'm also creating an architecture guideline for a VB.NET only shop, based on Rob's small MVVM framework. Everything looks very well except using co-routines from VB. Since VB 10 is used, we can try something like Bill McCarthy's suggestion: Public Function Lines(ByVal rdr as TextReader) As IEnumerable(Of String) Return New GenericIterator(Of String) (Function(ByRef nextItem As String) As Boolean nextItem = rdr.ReadLine Return nextItem IsNot Nothing End Function) End Function I'm just failing to comprehend how a little more complex co-routine method like the one below (taken from Rob's GameLibrary) could be written in VB: public IEnumerable<IResult> ExecuteSearch() { var search = new SearchGames { SearchText = SearchText }.AsResult(); yield return Show.Busy(); yield return search; var resultCount = search.Response.Count(); if (resultCount == 0) SearchResults = _noResults.WithTitle(SearchText); else if (resultCount == 1 && search.Response.First().Title == SearchText) { var getGame = new GetGame { Id = search.Response.First().Id }.AsResult(); yield return getGame; yield return Show.Screen<ExploreGameViewModel>() .Configured(x => x.WithGame(getGame.Response)); } else SearchResults = _results.With(search.Response); yield return Show.NotBusy(); } Any idea how to achieve that, or any thoughts on using Caliburn co-routines in VB?

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• How can I use JSONP to download client-side javascript objects?

  - by Alex Mcp

  I'm trying to get client-side javascript objects saved as a file locally. I'm not sure if this is possible. The basic architecture is this: Ping an external API to get back a JSON object Work client-side with that object, and eventually have a "download me" link This link sends the data to my server, which processes it and sends it back with a mime type application/json, which (should) prompt the user to download the file locally. Right now here are my pieces: Server Side Code <?php $data = array('zero', 'one', 'two', 'testing the encoding'); $json = json_encode($data); //$json = json_encode($_GET['']); //eventually I'll encode their data, but I'm testing header("Content-type: application/json"); header('Content-Disposition: attachment; filename="backup.json"'); echo $_GET['callback'] . ' (' . $json . ');'; ?> Relevant Client Side Code $("#download").click(function(){ var json = JSON.stringify(collection); //serializes their object $.ajax({ type: "GET", url: "http://www.myURL.com/api.php?callback=?", //this is the above script dataType: "jsonp", contentType: 'jsonp', data: json, success: function(data){ console.log( "Data Received: " + data[3] ); } }); return false; }); Right now when I visit the api.php site with Firefox, it prompts a download of download.json and that results in this text file, as expected: (["zero","one","two","testing the encoding"]); And when I click #download to run the AJAX call, it logs in Firebug Data Received: testing the encoding which is almost what I'd expect. I'm receiving the JSON string and serializing it, which is great. I'm missing two things: The Actual Questions What do I need to do to get the same prompt-to-download behavior that I get when I visit the page in a browser (much simpler) How do I access, server-side, the json object being sent to the server to serialize it? I don't know what index it is in the GET array (silly, I know, but I've tried almost everything)

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• Calling delegate methods and calling selectors

  - by Crystal

  I'm new to the concept of delegates and selectors when used with notifications. So my first question is, 1) Let's say you have a button that has a delegate that implements some doWork method. If you want the same functionality that's in the method, is it 'ok' to just call that method? I didn't know if that was considered good coding practices and/or if you should do that, or do something different in getting that type of functionality. Like if that is ok architecture? 2) Similarly, with NSNotificationCenter, I see some code that posts a notification. Then there's a HandleSegmentedControl:(NSNotification *)notification method. If I want to manually have that functionality, but without pressing the segment control, is it 'ok' to just take that functionality out of that method and put it in a new method so it would look like this: Original: - (void)HandleSegmentedControl:(NSNotification *)notification { NSDictionary *dict = [userInfo notification]; // do stuff with the dictionary } New: - (void)HandleSegmentedControl:(NSNotification *)notification { NSDictionary *dict = [userInfo notification]; [self newMethod:dict]; } - (void)newMethod:(NSDictionary *)dict { // do stuff with the dictionary } - (void)myOtherMethodThatNeedsTheSameFunctionality { NSDictionary *dict = // create some dictionary [self newMethod:dict]; } Sorry if these are basic questions. I'm not sure what the best practices are for things like this and wanted to start the right way. Thanks.

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• What's a way for a client to automatically resolve the ip address of a server?

  - by zooropa

  The project I am working on is a client/server architecture. In a LAN environment, I want the client's to be able to automatically determine the server's address. I want to avoid having to manually configure each client with the ip address of the server. What is the best way to do this? Some alternatives I have thought about doing are: The server could listen for broadcast packets from the clients. The message from the client would be a request for the IP address of the server. The server would respond with its address. The machine running my project's server could also have a bind server running. The LAN's router could be configured to use it as one of its DNS servers. I think I saw that there is a bind library. Does that mean I can build the bind service into my server so that bind doesn't have to be installed on the server? Any other ideas? What have you done in the past? What are the pros/cons of these approaches and others that might be suggested? Thanks for your help!

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• Dynamic stack allocation in C++

  - by Poni

  I want to allocate memory on the stack. Heard of _alloca / alloca and I understand that these are compiler-specific stuff, which I don't like. So, I came-up with my own solution (which might have it's own flaws) and I want you to review/improve it so for once and for all we'll have this code working: /*#define allocate_on_stack(pointer, size) \ __asm \ { \ mov [pointer], esp; \ sub esp, [size]; \ }*/ /*#define deallocate_from_stack(size) \ __asm \ { \ add esp, [size]; \ }*/ void test() { int buff_size = 4 * 2; char *buff = 0; __asm { // allocate mov [buff], esp; sub esp, [buff_size]; } // playing with the stack-allocated memory for(int i = 0; i < buff_size; i++) buff[i] = 0x11; __asm { // deallocate add esp, [buff_size]; } } void main() { __asm int 3h; test(); } Compiled with VC9. What flaws do you see in it? Me for example, not sure that subtracting from ESP is the solution for "any kind of CPU". Also, I'd like to make the commented-out macros work but for some reason I can't.

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• how could application installations/configurations be easier in linux? [closed]

  - by ajsie

  although you can do anything in linux it tends to require a lot of tweaking in config files and reading a lot of manuals/tutorials before you can have it running in your way. i know that it gets a lot easier by time, and the apt-get installations with ubuntu/debian is heading the right way. but how can linux be more userfriendly for us in the future? i thought that if more is automated like an IDE environment, eg. typing svn will give us all the commands and description about each command when you move between commands with your keyboard. that would be great. but that's just one example. another is the navigation in the terminal between folders. now you have to type a lot just to jump from/to different folders. would be great with some more automatization here too. i know that these extra features will slow down the server, but its 2010 now, and these features are not that heavy for the cpu, but makes it more userfriendly and encourage maintainance of a server, not frighten u off. what do you think about this? should/could we have more user friendly linux environment in servers, something that has annoyed you a lot? a lot of things are done in the unix way, but maybe we should reinvent the wheel in some areas, cause apparently, its so...repeatingly today and difficult to do easy tasks. it should be easier i think..

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• 32/64 bit problems with Eclipse CDT on Ubuntu

  - by waffleShirt

  I have just recently started running Linux on my PC and I am trying to start learning OpenGL. I am using the latest version of Eclipse CDT as my IDE, and my system is Ubuntu 10.10, 64 bit version. The problem I am having is that whenever I try to run a build from within the IDE I get the error message "Launch Failed. Binary Not Found." Ive done a lot of looking around on the internet but I still cant solve the problem. I know for a fact that the binary is built, it can be run from a terminal window. According to posts I have seen the problem is that Eclipse tries to run a 32 bit binary, but GCC 4.4.5 defaults to 64 bit binaries on a 64 bit system. Ive seen a lot of information about using the -m32 flag in makefiles, but then I still get the following output in Eclipse: make all g++ -o HelloWorld2 main.o /usr/bin/ld: i386 architecture of input file `main.o' is incompatible with i386:x86-64 output /usr/bin/ld: final link failed: Invalid operation collect2: ld returned 1 exit status make: *** [HelloWorld2] Error 1 What I would like to know is how to either get Eclipse to launch the 64 bit binaries, or have Eclipse correctly compile 32 bit binaries.

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• Excel 2010 64 bit can't create .net object

  - by aboes81

  I have a simple class library that I use in Excel. Here is a simplification of my class... using System; using System.Runtime.InteropServices; namespace SimpleLibrary { [ComVisible(true)] public interface ISixGenerator { int Six(); } public class SixGenerator : ISixGenerator { public int Six() { return 6; } } } In Excel 2007 I would create a macro enabled workbook and add a module with the following code: Public Function GetSix() Dim lib As SimpleLibrary.SixGenerator lib = New SimpleLibrary.SixGenerator Six = lib.Six End Function Then in Excel I could call the function GetSix() and it would return six. This no longer works in Excel 2010 64bit. I get a Run-time error '429': ActiveX component can't create object. I tried changing the platform target to x64 instead of Any CPU but then my code wouldn't compile unless I unchecked the Register for COM interop option, doing so makes it so my macro enable workbook cannot see SimpleLibrary.dll as it is no longer regsitered. Any ideas how I can use my library with Excel 2010 64 bit?

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• Events and references pattern

  - by serhio

  In a project I have the following relation between BO and GUI By e.g. G could represent a graphic with time lines, C a TimeLine curve, P - points of that curve and T the time that represents each point. Each GUI object is associated with the BO corresponding object. When T changes GUI P captures the Changed event and changes its location. So, when G should be modified, it modifies internally its objects and as result T changes, P moves and the GuiG visually changes, everything is OK. But there is an inconvenient of this architecture... BO should not be recreated, because this will breack the link between BO and GUIO. In particular, GUI P should always have the same reference of T. If in a business logic I do by e.g. P1.T = new T(this.T + 10) GUI_P1 will not move anymore, because it wait an event from the reference of former P1.T object, that does not belongs to P1 anymore. So the solution was to always modify the existing objects, not to recreate it. But here is an other inconvenient: performance. Say I have a ready newC object that should replace the older one. Instead of doing G1.C = newC I should do foreach T in foreach P in C replace with T from P from newC. Is there an other more optimal way to do it?

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• Swing GUI using JNI crashes

  - by Div

  Hi, A java swing application(GUI) using JNI code to communicate with native C code. The Swing application launches properly and works fine. The GUI is used to start some customized system level tests(io,memory,cpu) and show their progress. The tests have to be left running at-least overnight to get the results. But, the next morning, GUI crashes and throws following message. Any pointers on source of the issue will be greatly appreciated. Java version: java 1.5 / java 1.6 OS: Solaris 10. Thanks, Div =============MESSAGES================== # uname -a SunOS Generic_127127-11 sun4v sparc SUNW, # # # # An unexpected error has been detected by HotSpot Virtual Machine: # # SIGSEGV (0xb) at pc=0xff268924, pid=9473, tid=272 # # Java VM: Java HotSpot(TM) Server VM (1.5.0_14-b03 mixed mode) # Problematic frame: # C [libc.so.1+0x68924] strstr+0x20 # # An error report file with more information is saved as hs_err_pid9473.log # # If you would like to submit a bug report, please visit: # HotSpot Virtual Machine Error Reporting Page # ============================= Another machine: # A fatal error has been detected by the Java Runtime Environment: # # SIGSEGV (0xb) at pc=0xff231fd0, pid=1406, tid=180 # # JRE version: 6.0_18-b07 # Java VM: Java HotSpot(TM) Server VM (16.0-b13 mixed mode solaris-sparc ) # Problematic frame: # C [libc.so.1+0x31fd0] strcpy+0x70 # # An error report file with more information is saved as: # /usr/sunvts/bin/hs_err_pid1406.log #

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• Correct Delphi compiler switches to stop in the user's code, not my component's

  - by Jeremy Mullin

  I'm modifying our VCL components so the end user's application links to our dcu files, instead of building our source code each time. We have everything working, but I want the debugger to stop on the user's code when an exception is raised. At first it would stop in our dcu and open the CPU window. I was able to prevent that by removing debug info from the dcu files. But now it still doesn't stop in the users code (like DevExpress libraries and others do). The following screencast is a short example. The first time I cause an exception in the DevExpress code, and the debugger correctly stops in my button event. The second time I cause an exception in my components, but the debugger doesn't have my button event on the call stack, and doesn't show me where the problem was. Any ideas why? http://screencast.com/t/NjhlOTRk Currently building the DCU's with these options: -$W+ -$D- -h -w -q Update: The TDataSet methods in between my component and the button event seem to cause this behavior. If I instead call a direct method of my table, I get the expected behavior. I'm guessing there isn't anything I can do about this, but I'm still curious why it happens.

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• floating point equality in Python and in general

  - by eric.frederich

  I have a piece of code that behaves differently depending on whether I go through a dictionary to get conversion factors or whether I use them directly. The following piece of code will print 1.0 == 1.0 -> False But if you replace factors[units_from] with 10.0 and factors[units_to ] with 1.0 / 2.54 it will print 1.0 == 1.0 -> True #!/usr/bin/env python base = 'cm' factors = { 'cm' : 1.0, 'mm' : 10.0, 'm' : 0.01, 'km' : 1.0e-5, 'in' : 1.0 / 2.54, 'ft' : 1.0 / 2.54 / 12.0, 'yd' : 1.0 / 2.54 / 12.0 / 3.0, 'mile' : 1.0 / 2.54 / 12.0 / 5280, 'lightyear' : 1.0 / 2.54 / 12.0 / 5280 / 5.87849981e12, } # convert 25.4 mm to inches val = 25.4 units_from = 'mm' units_to = 'in' base_value = val / factors[units_from] ret = base_value * factors[units_to ] print ret, '==', 1.0, '->', ret == 1.0 Let me first say that I am pretty sure what is going on here. I have seen it before in C, just never in Python but since Python in implemented in C we're seeing it. I know that floating point numbers will change values going from a CPU register to cache and back. I know that comparing what should be two equal variables will return false if one of them was paged out while the other stayed resident in a register. Questions What is the best way to avoid problems like this?... In Python or in general. Am I doing something completely wrong? Side Note This is obviously part of a stripped down example but what I'm trying to do is come with with classes of length, volume, etc that can compare against other objects of the same class but with different units. Rhetorical Questions If this is a potentially dangerous problem since it makes programs behave in an undetermanistic matter, should compilers warn or error when they detect that you're checking equality of floats Should compilers support an option to replace all float equality checks with a 'close enough' function? Do compilers already do this and I just can't find the information.

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• Any merit to a lazy-ish juxt function?

  - by NielsK

  In answering a question about a function that maps over multiple functions with the same arguments (A: juxt), I came up with a function that basically took the same form as juxt, but used map: (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply %1 %2) funs (repeat args)))) => ((juxt inc dec str) 1) [2 0 "1"] => ((could-be-lazy-juxt inc dec str) 1) (2 0 "1") => ((juxt * / -) 6 2) [12 3 4] => ((could-be-lazy-juxt * / -) 6 2) (12 3 4) As posted in the original question, I have little clue about the laziness or performance of it, but timing in the REPL does suggest something lazy-ish is going on. => (time (apply (juxt + -) (range 1 100))) "Elapsed time: 0.097198 msecs" [4950 -4948] => (time (apply (could-be-lazy-juxt + -) (range 1 100))) "Elapsed time: 0.074558 msecs" (4950 -4948) => (time (apply (juxt + -) (range 10000000))) "Elapsed time: 1019.317913 msecs" [49999995000000 -49999995000000] => (time (apply (could-be-lazy-juxt + -) (range 10000000))) "Elapsed time: 0.070332 msecs" (49999995000000 -49999995000000) I'm sure this function is not really that quick (the print of the outcome 'feels' about as long in both). Doing a 'take x' on the function only limits the amount of functions evaluated, which probably is limited in it's applicability, and limiting the other parameters by 'take' should be just as lazy in normal juxt. Is this juxt really lazy ? Would a lazy juxt bring anything useful to the table, for instance as a compositing step between other lazy functions ? What are the performance (mem / cpu / object count / compilation) implications ? Is that why the Clojure juxt implementation is done with a reduce and returns a vector ? Edit: Somehow things can always be done simpler in Clojure. (defn could-be-lazy-juxt [& funs] (fn [& args] (map #(apply % args) funs)))

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