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partial entity loading and management in silverlight / wcf ria

- by Dan Wray

I have a Silverlight 4 app which pulls entities down from a database using WCF RIA services. These data objects are fairly simple, just a few fields but one of those fields contains binary data of an arbitrarily size. The application needs access to this data basically asap after a user has logged in, to display in a list, enable selection etc. My problem is because of the size of this data, the load times are not acceptable and can approach the default timeout of the RIA service. I'd like to somehow partially load the objects into my local data context so that I have the IDs, names etc but not the binary data. I could then at a later point (ie when it's actually needed) populate the binary fields of those objects I need to display. Any suggestions on how to accomplish this would be welcome. Another approach which has occurred to me whilst writing this question (how often does that happen?!) is that I could move the binary data into a seperate database table joined to the original record 1:1 which would allow me to make use of RIA's lazy loading on that binary data. again.. comments welcome! Thanks.

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How to configure database connection securely

- by chiccodoro

Similar but not the same: How to securely store database connection details Securely connecting to database within a application Hi all, I have a C# WinForms application connecting to a database server. The database connection string, including a generic user/pass, is placed in a NHibernate configuration file, which lies in the same directory as the exe file. Now I have this issue: The user that runs the application should not get to know the username/password of the general database user because I don't want him to rummage around in the database directly. Alternatively I could hardcode the connection string, which is bad because the administrator must be able to change it if the database is moved or if he wants to switch between dev/test/prod environments. So long I've found three possibilities: The first referenced question was generally answered by making the file only readable for the user that runs the application. But that's not not enough in my case (the user running the application is a person. The database user/pass are general and shouldn't even be accessible by the person.) The first answer additionally proposed to encrypt the connection data before writing it to the file. With this approach, the administrator is not able anymore to configure the connection string because he cannot encrypt it by hand. The second referenced question provides an approach for this very scenario but it seems very complicated. My questions to you: This is a very general issue, so isn't there any general "how-to-do-it" way, somehow a "design pattern"? Is there some support in .NET's config infrastructure? (optional, maybe out of scope) Can I combine that easily with the NHibernate configuration mechanism?

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standard way to perform a clean shutdown with Boost.Asio

- by Timothy003

I'm writing a cross-platform server program in C++ using Boost.Asio. Following the HTTP Server example on this page, I'd like to handle a user termination request without using implementation-specific APIs. I've initially attempted to use the standard C signal library, but have been unable to find a design pattern suitable for Asio. The Windows example's design seems to resemble the signal library closest, but there's a race condition where the console ctrl handler could be called after the server object has been destroyed. I'm trying to avoid race conditions that cause undefined behavior as specified by the C++ standard. Is there a standard (correct) way to stop the server? So far: #include <csignal> #include <functional> #include <boost/asio.hpp> using std::signal; using boost::asio::io_service; extern "C" { static void handle_signal(int); } namespace { std::function<void ()> sighandler; } void handle_signal(int) { sighandler(); } int main() { io_service s; sighandler = std::bind(&io_service::stop, &s); auto res = signal(SIGINT, &handle_signal); // race condition? SIGINT raised before I could set ignore back if (res == SIG_IGN) signal(SIGINT, SIG_IGN); res = signal(SIGTERM, &handle_signal); // race condition? SIGTERM raised before I could set ignore back if (res == SIG_IGN) signal(SIGTERM, SIG_IGN); s.run(); // reset signals signal(SIGTERM, SIG_DFL); signal(SIGINT, SIG_DFL); // is it defined whether handle_signal can still be in execution at this // point? sighandler = nullptr; }

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Generating JavaScript in C# and subsequent testing

- by Codebrain

We are currently developing an ASP.NET MVC application which makes heavy use of attribute-based metadata to drive the generation of JavaScript. Below is a sample of the type of methods we are writing: function string GetJavascript<T>(string javascriptPresentationFunctionName, string inputId, T model) { return @"function updateFormInputs(value){ $('#" + inputId + @"_SelectedItemState').val(value); $('#" + inputId + @"_Presentation').val(value); } function clearInputs(){ " + helper.ClearHiddenInputs<T>(model) + @" updateFormInputs(''); } function handleJson(json){ clearInputs(); " + helper.UpdateHiddenInputsWithJson<T>("json", model) + @" updateFormInputs(" + javascriptPresentationFunctionName + @"()); " + model.GetCallBackFunctionForJavascript("json") + @" }"; } This method generates some boilerplace and hands off to various other methods which return strings. The whole lot is then returned as a string and written to the output. The question(s) I have are: 1) Is there a nicer way to do this other than using large string blocks? We've considered using a StringBuilder or the Response Stream but it seems quite 'noisy'. Using string.format starts to become difficult to comprehend. 2) How would you go about unit testing this code? It seems a little amateur just doing a string comparison looking for particular output in the string. 3) What about actually testing the eventual JavaScript output? Thanks for your input!

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Is using YIELD a read-only way to return a collection?

- by Eric

I'm writing an interface which has a collection property which I want to be read only. I don't want users of the interface to be able to modify the collection. The typical suggestion I've found for creating a read only collection property is to set the type of the property to IEnumerable like this: private List<string> _mylist; public IEnumerable<string> MyList { get { return this._mylist; } } Yet this does not prevent the user from casting the IEnumerable back to a List and modifying it. If I use a Yield keyword instead of returning _mylist directly would this prevent users of my interface from being able to modify the collection. I think so because then I'm only returning the objects one by one, and not the actual collection. private List<string> _mylist; public IEnumerable<string> MyList { get { foreach(string str in this._mylist) { yield return str; } } }

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Margin on the top in LaTex

- by Tim

I am now writing a thesis which is required to have 1 and half inches on the left or binding side, and 1 inch on the other three sides. I just have my print-out checked in the binding office and I was told the margins are not okay, especially the one on the top is not enough, a little less than 1 inch. See the figure below: I wonder which commands are responsible for the margins on the four sides, especially for the one on the top? I provide links to two files I believe that control the layout and format of the thesis:jhu12.clo and thesis.cls. Or instead of modifying the LaTex files, is thre some setting when printing the pdf file to control these margins on the print-out? Thanks and regards! EDIT: This is the print-out of command \layout It shows "one inch + \voffset" for the top (the NO. 2 item). But the staff at the binding office use his ruler to show it is less than 1 inch. How to adjust the margins in LaTex then? Thanks!

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Precision of cos(atan2(y,x)) versus using complex <double>, C++

- by Ivan

Hi all, I'm writing some coordinate transformations (more specifically the Joukoswky Transform, Wikipedia Joukowsky Transform), and I'm interested in performance, but of course precision. I'm trying to do the coordinate transformations in two ways: 1) Calculating the real and complex parts in separate, using double precision, as below: double r2 = chi.x*chi.x + chi.y*chi.y; //double sq = pow(r2,-0.5*n) + pow(r2,0.5*n); //slow!!! double sq = sqrt(r2); //way faster! double co = cos(atan2(chi.y,chi.x)); double si = sin(atan2(chi.y,chi.x)); Z.x = 0.5*(co*sq + co/sq); Z.y = 0.5*si*sq; where chi and Z are simple structures with double x and y as members. 2) Using complex : Z = 0.5 * (chi + (1.0 / chi)); Where Z and chi are complex . There interesting part is that indeed the case 1) is faster (about 20%), but the precision is bad, giving error in the third decimal number after the comma after the inverse transform, while the complex gives back the exact number. So, the problem is on the cos(atan2), sin(atan2)? But if it is, how the complex handles that? Thanks!

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Simulating O_NOFOLLOW (2): Is this other approach safe?

- by Daniel Trebbien

As a follow-up question to this one, I thought of another approach which builds off of @caf's answer for the case where I want to append to file name and create it if it does not exist. Here is what I came up with: Create a temporary directory with mode 0700 in a system temporary directory on the same filesystem as file name. Create an empty, temporary, regular file (temp_name) in the temporary directory (only serves as placeholder). Open file name for reading only, just to create it if it does not exist. The OS may follow name if it is a symbolic link; I don't care at this point. Make a hard link to name at temp_name (overwriting the placeholder file). If the link call fails, then exit. (Maybe someone has come along and removed the file at name, who knows?) Use lstat on temp_name (now a hard link). If S_ISLNK(lst.st_mode), then exit. open temp_name for writing, append (O_WRONLY | O_APPEND). Write everything out. Close the file descriptor. unlink the hard link. Remove the temporary directory. (All of this, by the way, is for an open source project that I am working on. You can view the source of my implementation of this approach here.) Is this procedure safe against symbolic link attacks? For example, is it possible for a malicious process to ensure that the inode for name represents a regular file for the duration of the lstat check, then make the inode a symbolic link with the temp_name hard link now pointing to the new, symbolic link? I am assuming that a malicious process cannot affect temp_name.

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Orthogonal projection and texture coordinates in opengl

- by knuck

I'm writing a 2D game in Opengl. I already set up the orthogonal projection so I can easily know where a quad will end up on screen. The problem is, I also want to be able to map pixels directly to texture coords, so I also applied an orthogonal transformation (using gluOrtho2d) to the texture. Now I can map pixels directly using integers and glTexCoord2i. The thing is, after googling/reading/asking, I found out no one really knows (apparently) the behavior of glTexCoord2i, but it works just fine the way I'm using. Some sample test code I wrote follows: glBegin(GL_QUADS); glTexCoord2i(16,0); glVertex2f(X, Y); glTexCoord2i(16,16); glVertex2f(X, Y+32); glTexCoord2i(32, 16); glVertex2f(X+32, Y+32); glTexCoord2i(32, 0); glVertex2f(X+32, Y); glEnd(); So, is there any problem with what I'm doing, or is what I'm doing correct?

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TeamCity + HG. Only pull (push?) passing builds

- by ColoradoMatt

Feels like with the popularity of continuous integration this one should be a piece of cake but I am stumped. I am setting up TeamCity with HG. I want to be able to push changesets up to a repository that TeamCity watches and runs builds on changes. That's easy. Next, if a build passes, I want that changeset to be pulled into a "clean" repository... one that contains only passing changesets. Should be easy but... TeamCity 6 supports multiple build steps and if any step fails, the rest don't run. My thought was to put a build step at the end that does a pull (or optionally a push?) to get the passing changeset into the clean repository. I am trying to use PsExec to run hg on the box with the repositories. If I try to run just a plain 'hg pull' it can't find the hg.exe even though it is set in the path and I have used the -w flag. I have tried putting a .bat file in the clean repository that takes a revision parameter and it works fine... locally. When I try to run the .bat file remotely (using PsExec) it runs everything fine but it tries to run it on the build agent. Even if I set the -w argument it runs the .bat file there but tries to run the contents on the build agent box. Am I just WAY off in my approach? Seems like this is a pretty obvious thing to do so either my Google skills are waning or no one thinks this is worthy of writing about. Either way, I am stuck in SVN land trying to get out so I would appreciate some help!

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Controlling the order of PicoContainer startup

- by Trejkaz

I have been tasked with doing some refactoring work on how we start up applications. Basically we have a bunch of console apps which were depending on the GUI application startup code, causing bogus dependencies which have kick-on effects for which libraries we need to ship, and which dependencies other modules need to declare. So I have written a simple startup framework where I basically just throw a bunch of Runnable objects into a list and then run them in order - and it works. But I was thinking - we already have PicoContainer in our project, so all these things that need to be run on startup could potentially be thrown into a PicoContainer, and if they implement Startable they will start... But in some cases we want to specify the ordering between them. For example, I don't want any other component writing to the log before we write a header into the log indicating that the application is starting up. I know I can introduce ordering by introducing injection dependencies, but this feels like a hack in this case - I would need to add the log header writer as a dependency for every other component which might write to the log, which isn't great at all. Nonetheless it seems like it would be nice to control the order of PicoContainer startup, so is there perhaps some other way? Alternatively I could just keep it simple and stick to my list of Runnable. It does, after all, work.

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Executing sequential stored procedures; works in query analyzer, doesn't in my .NET application

- by evanmortland

Hello, I have an audit record table that I am writing to. I am connecting to MyDb, which has a stored procedure called 'CreateAudit', which is a passthrough stored procedure to another database on the same machine called MyOther DB with a stored procedure called 'CreatedAudit' as well. In other words in MyDB I have CreateAudit, which does the following EXEC dbo.MyOtherDB.CreateAudit. I call the MyDb CreateAudit stored procedure from my application, using subsonic as the DAL. The first time I call it, I call it with the following (pseudocode): Result = CreateAudit(recordId, "Opened") One line after that, I call: Result2 = CreateAudit(recordId, "Closed") In my second stored procedure it is supposed to mark the record that was created by the CreateAudit(recordId, "Opened") with a status of closed. It works great if I run them independently of one another, but when they run in sequence in the application, the record is not marked as "Closed". When I run SQL profiler I see that both queries ran, and if I copy the queries out and run them from query analyzer the record gets marked as closed 100% of the time! When I run it from the application, about once every 20 times or so, the record is successfully marked closed - the other 19 times nothing happens, but I do not get an error! Is it possible for the .NET app to skip over the ouput from the first stored procedure and start executing the second stored procedure before the record in the first is created? When I add a "WAITFOR DELAY '00:00:00:003'" to the top of my stored procedure, the record is also closed 100% of the time. My head is spinning, any ideas why this is happening! Thanks for any responses, very interested in hearing how this can happen.

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Putting a C++ Vector as a Member in a Class that Uses a Memory Pool

- by Deep-B

Hey, I've been writing a multi-threaded DLL for database access using ADO/ODBC for use with a legacy application. I need to keep multiple database connections for each thread, so I've put the ADO objects for each connection in an object and thinking of keeping an array of them inside a custom threadInfo object. Obviously a vector would serve better here - I need to delete/rearrange objects on the go and a vector would simplify that. Problem is, I'm allocating a heap for each thread to avoid heap contention and stuff and allocating all my memory from there. So my question is: how do I make the vector allocate from the thread-specific heap? (Or would it know internally to allocate memory from the same heap as its wrapper class - sounds unlikely, but I'm not a C++ guy) I've googled a bit and it looks like I might need to write an allocator or something - which looks like so much of work I don't want. Is there any other way? I've heard vector uses placement-new for all its stuff inside, so can overloading operator new be worked into it? My scant knowledge of the insides of C++ doesn't help, seeing as I'm mainly a C programmer (even that - relatively). It's very possible I'm missing something elementary somewhere. If nothing easier comes up - I might just go and do the array thing, but hopefully it won't come to that. I'm using MS-VC++ 6.0 (hey, it's rude to laugh! :-P ). Any/all help will be much appreciated.

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SQL: script to create country, state tables

- by pcampbell

Consider writing an application that requires registration for an entity, and the schema has been defined to require the country, state/prov/county data to be normalized. This is fairly typical stuff here. Naming also is important to reflect. Each country has a different name for this entity: USA = states Australia = states + territories Canada = provinces + territories Mexico = states Brazil = states Sweden = provinces UK = counties, principalities, and perhaps more! Most times when approaching this problem, I have to scratch together a list of good countries, and the states/prov/counties of each. The app may be concerned with a few countries and not others. The process is full of pain. It typically involves one of two approaches: opening up some previous DB and creating a CREATE script based on those tables. Run that script in the context of the new system. creating a DTS package from database1 to database2, with all the DDL and data included in the transfer. My goal now is to script the creation and insert of the countries that I'd be concerned with in the app of the day. When I want to roll out Countries X/Y/Z, I'll open CountryX.sql, and load its states into the ProvState table. Question: do you have a set of scripts in your toolset to create schema and data for countries and state/province/county? If so, would you share your scripts here? (U.K. citizens, please feel free to correct me by way of a comment in the use of counties.)

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Swing: what to do when a JTree update takes too long and freezes other GUI elements?

- by java.is.for.desktop

Hello, everyone! I know that GUI code in Java Swing must be put inside SwingUtilities.invokeAndWait or SwingUtilities.invokeLater. This way threading works fine. Sadly, in my situation, the GUI update it that thing which takes much longer than background thread(s). More specific: I update a JTree with about just 400 entries, nesting depth is maximum 4, so should be nothing scary, right? But it takes sometimes one second! I need to ensure that the user is able to type in a JTextPane without delays. Well, guess what, the slow JTree updates do cause delays for JTextPane during input. It refreshes only as soon as the tree gets updated. I am using Netbeans and know empirically that a Java app can update lots of information without freezing the rest of the UI. How can it be done? NOTE 1: All those DefaultMutableTreeNodes are prepared outside the invokeAndWait. NOTE 2: When I replace invokeAndWait with invokeLater the tree doesn't get updated. NOTE 3: Fond out that recursive tree expansion takes far the most time. NOTE 4: I'm using custom tree cell renderer, will try without and report. NOTE 4a: My tree cell renderer uses a map to cache and reuse created JTextComponents, depending on tree node (as a key). CLUE 1: Wow! Without setting custom cell renderer it's 10 times faster. I think, I'll need few good tutorials on writing custom tree cell renderers.

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write html content from javascript

- by Nikita Rybak

There's one thing I want to do with javascript, but don't know how. In a perfect world it would look like this: <p>My very cool page!</p> <script type="text/javascript"> document.write('<div>some content</div>'); </script> And this script would insert <div>some content</div> right before (or after, or instead of) script tag. But in the real world, document.write starts writing html anew, removing any static content in the page (<p> tag, in this case). This is simplified example, but should give you the idea. I know that I can statically put <div id="some_id"></div> before script tag and insert html in it from js, but I wanna be able to use multiple instances of this snippet without changing it (generating random id manually) each time. I'm ok to use jquery or any other existing library as well. Is there any way to achieve this? Thanks!

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How can I write System preferences with Java? Can I invoke UAC?

- by Jonas

How can I write system preferences with Java, using Preferences.systemRoot()? I tried with: Preferences preferences = Preferences.systemRoot(); preferences.put("/myapplication/databasepath", pathToDatabase); But I got this error message: 2010-maj-29 19:02:50 java.util.prefs.WindowsPreferences openKey VARNING: Could not open windows registry node Software\JavaSoft\Prefs at root 0x80000002. Windows RegOpenKey(...) returned error code 5. Exception in thread "AWT-EventQueue-0" java.lang.SecurityException: Could not open windows registry node Software\JavaSoft\Prefs at root 0x80000002: Access denied at java.util.prefs.WindowsPreferences.openKey(Unknown Source) at java.util.prefs.WindowsPreferences.openKey(Unknown Source) at java.util.prefs.WindowsPreferences.openKey(Unknown Source) at java.util.prefs.WindowsPreferences.putSpi(Unknown Source) at java.util.prefs.AbstractPreferences.put(Unknown Source) at biz.accountia.pos.install.Setup$2.actionPerformed(Setup.java:43) I would like to do this, because I want to install an embedded JavaDB database, and let multiple users on the computer to use the same database with the application. How to solve this? Can I invoke UAC and do this as Administrator from Java? And if I log in as Administrator when writing, can I read the values with my Java application if I'm logged in as a User?

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How to distinguish between two different UDP clients on the same IP address?

- by Ricket

I'm writing a UDP server, which is a first for me; I've only done a bit of TCP communications. And I'm having trouble figuring out exactly how to distinguish which user is which, since UDP deals only with packets rather than connections and I therefore cannot tell exactly who I'm communicating with. Here is pseudocode of my current server loop: DatagramPacket p; socket.receive(p); // now p contains the user's IP and port, and the data int key = getKey(p); if(key == 0) { // connection request key = makeKey(p); clients.add(key, p.ip); send(p.ip, p.port, key); // give the user his key } else { // user has a key // verify key belongs to that IP address // lookup the user's session data based on the key // react to the packet in the context of the session } When designing this, I kept in mind these points: Multiple users may exist on the same IP address, due to the presence of routers, therefore users must have a separate identification key. Packets can be spoofed, so the key should be checked against its original IP address and ignored if a different IP tries to use the key. The outbound port on the client side might change among packets. Is that third assumption correct, or can I simply assume that one user = one IP+port combination? Is this commonly done, or should I continue to create a special key like I am currently doing? I'm not completely clear on how TCP negotiates a connection so if you think I should model it off of TCP then please link me to a good tutorial or something on TCP's SYN/SYNACK/ACK mess. Also note, I do have a provision to resend a key, if an IP sends a 0 and that IP already has a pending key; I omitted it to keep the snippet simple. I understand that UDP is not guaranteed to arrive, and I plan to add reliability to the main packet handling code later as well.

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Display post data !

- by Comii

I am trying to post data from vb.net application to web service asmx that is located on server! For posting data from vb.net application I am using this code: Public Function Post(ByVal url As String, ByVal data As String) As String Dim vystup As String = Nothing Try 'Our postvars Dim buffer As Byte() = Encoding.ASCII.GetBytes(data) 'Initialisation, we use localhost, change if appliable Dim WebReq As HttpWebRequest = DirectCast(WebRequest.Create(url), HttpWebRequest) 'Our method is post, otherwise the buffer (postvars) would be useless WebReq.Method = "POST" 'We use form contentType, for the postvars. WebReq.ContentType = "application/x-www-form-urlencoded" 'The length of the buffer (postvars) is used as contentlength. WebReq.ContentLength = buffer.Length 'We open a stream for writing the postvars Dim PostData As Stream = WebReq.GetRequestStream() 'Now we write, and afterwards, we close. Closing is always important! PostData.Write(buffer, 0, buffer.Length) PostData.Close() 'Get the response handle, we have no true response yet! Dim WebResp As HttpWebResponse = DirectCast(WebReq.GetResponse(), HttpWebResponse) 'Let's show some information about the response Console.WriteLine(WebResp.StatusCode) Console.WriteLine(WebResp.Server) 'Now, we read the response (the string), and output it. Dim Answer As Stream = WebResp.GetResponseStream() Dim _Answer As New StreamReader(Answer) 'Congratulations, you just requested your first POST page, you 'can now start logging into most login forms, with your application 'Or other examples. vystup = _Answer.ReadToEnd() Catch ex As Exception MessageBox.Show(ex.Message) End Try Return vystup.Trim() & vbLf End Function Now how i can retrieve this data in asmx service?

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What is the best way to auto-generate INSERT statements for a SQL Server table?

- by JosephStyons

We are writing a new application, and while testing, we will need a bunch of dummy data. I've added that data by using MS Access to dump excel files into the relevant tables. Every so often, we want to "refresh" the relevant tables, which means dropping them all, re-creating them, and running a saved MS Access append query. The first part (dropping & re-creating) is an easy sql script, but the last part makes me cringe. I want a single setup script that has a bunch of INSERTs to regenerate the dummy data. I have the data in the tables now. What is the best way to automatically generate a big list of INSERT statements from that dataset? I'm thinking of something like in TOAD (for Oracle) where you can right-click on a grid and click Save As-Insert Statements, and it will just dump a big sql script wherever you want. The only way I can think of doing it is to save the table to an excel sheet and then write an excel formula to create an INSERT for every row, which is surely not the best way. I'm using the 2008 Management Studio to connect to a SQL Server 2005 database.

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Optimizing processing and management of large Java data arrays

- by mikera

I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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Perf4J Graph Output from Log File

- by manyxcxi

I currently have a long running process that I am trying to analyze with Perf4J. I currently have it writing results in CSV format to its own log file using the AsyncCoalescingStatisticsAppender and a StatisticsCsvLayout on the file appender. My question is; when I try and use the --graph option from the command line (using the perf4j jar) it isn't populating the data points- it isn't populating anything. Are my appenders set incorrectly? The log file contains hundreds (sometimes thousands) of data points of about 10 different tag names. <appender name="perfAppender" class="org.apache.log4j.FileAppender"> <param name="File" value="perfStats.log"/> <layout class="org.perf4j.log4j.StatisticsCsvLayout"> </layout> </appender> <appender name="CoalescingStatistics" class="org.perf4j.log4j.AsyncCoalescingStatisticsAppender">  <param name="TimeSlice" value="10000"/> <appender-ref ref="ConsoleAppender"/> <appender-ref ref="CompositeRollingFileAppender"/> <appender-ref ref="perfAppender"/> </appender>

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How to exit an if clause

- by Roman Stolper

What sorts of methods exist for prematurely exiting an if clause? There are times when I'm writing code and want to put a break statement inside of an if clause, only to remember that those can only be used for loops. Lets take the following code as an example: if some_condition: ... if condition_a: # do something # and then exit the outer if block ... if condition_b: # do something # and then exit the outer if block # more code here I can think of one way to do this: assuming the exit cases happen within nested if statements, wrap the remaining code in a big else block. Example: if some_condition: ... if condition_a: # do something # and then exit the outer if block else: ... if condition_b: # do something # and then exit the outer if block else: # more code here The problem with this is that more exit locations mean more nesting/indented code. Alternatively, I could write my code to have the if clauses be as small as possible and not require any exits. Does anyone know of a good/better way to exit an if clause? If there are any associated else-if and else clauses, I figure that exiting would skip over them.

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Reasons for & against a Database

- by dbemerlin

Hi, i had a discussion with a coworker about the architecture of a program i'm writing and i'd like some more opinions. The Situation: The Program should update at near-realtime (+/- 1 Minute). It involves the movement of objects on a coordinate system. There are some events that occur at regular intervals (i.e. creation of the objects). Movements can change at any time through user input. My solution was: Build a server that runs continously and stores the data internally. The server dumps a state-of-the-program at regular intervals to protect against powerfailures and/or crashes. He argued that the program requires a Database and i should use cronjobs to update the data. I can store movement information by storing startpoint, endpoint and speed and update the position in the cronjob (and calculate collisions with other objects there) by calculating direction and speed. His reasons: Requires more CPU & Memory because it runs constantly. Powerfailures/Crashes might destroy data. Databases are faster. My reasons against this are mostly: Not very precise as events can only occur at full minutes (wouldn't be that bad though). Requires (possibly costly) transformation of data on every run from relational data to objects. RDBMS are a general solution for a specialized problem so a specialized solution should be more efficient. Powerfailures (or other crashes) can leave the Data in an undefined state with only partially updated data unless (possibly costly) precautions (like transactions) are taken. What are your opinions about that? Which arguments can you add for any side?

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Best practices for managing updating a database with a complex set of changes

- by Sarge

I am writing an application where I have some publicly available information in a database which I want the users to be able to edit. The information is not textual like a wiki but is similar in concept because the edits bring the public information increasingly closer to the truth. The changes will affect multiple tables and the update needs to be automatically checked before affecting the public tables. I'm working on the design and I'm wondering if there are any best practices that might help with some particular issues. I want to provide undo capability. I want to show the user the combined result of all their changes. When the user says they're done, I need to check the underlying public data to make sure it hasn't been changed by somebody else. My current plan is to have the user work in a set of tables setup to be a private working area. Once they're ready they can kick off a process to check everything and update the public tables. Undo can be recorded using Command pattern saving to a table. Are there any techniques I might have missed or useful papers or patterns? Thanks in advance!

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