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• How can I share an entity framework model across website users

  - by richardmoss

  Hello, Currently my website is based around MVC and the Entity Framework running against a SQL Server 2005 database. So far, it has all been running very smoothly, and I really enjoy MVC and its slimmer more concise code (and no huge viewstates or soul destroying postbacks ;)) Recently I was working on upgrading the site to use a simple forum system, and this is where I started running into problems. When I was testing the site using two different browsers, if I created or replied to a post in one browser, the other browser couldn't see the post. At the moment, each visitor to the site gets their own copy of the entity model, which I store in their session data. Obviously this is the problem as updates to one model aren't getting carried to the other. As a test, I tried storing a single copy of the model which all visitors would access by assigning the model to a static variable. This worked, and both browsers could see each others modifications. However, it had its side effects. For example, if I fired up both browsers at the same time and the model was initialized, one browser would crash, and the other would work fine, despite me using a locking object so in theory one of them should have been delayed until the model was ready (of course I could have implemented this wrong ;)). Also, originally this site did use one model for all visitors and when it was live, it frequently shut down - killing the IIS application pool while it did. Now I'm not sure if this was related, but I don't really want to reintroduce whatever bug I had that caused this shut down. So, my question is a simple one really - what is the best way of either using the same model for all website users so they all see updates, or if they do have separate copies (which I imagine will have a performance impact in time) how can the models detect changes in the database and update themselves according. Thanks in advance for any advice! Regards; Richard Moss

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• Python optimization problem?

  - by user342079

  Alright, i had this homework recently (don't worry, i've already done it, but in c++) but I got curious how i could do it in python. The problem is about 2 light sources that emit light. I won't get into details tho. Here's the code (that I've managed to optimize a bit in the latter part): import math, array import numpy as np from PIL import Image size = (800,800) width, height = size s1x = width * 1./8 s1y = height * 1./8 s2x = width * 7./8 s2y = height * 7./8 r,g,b = (255,255,255) arr = np.zeros((width,height,3)) hy = math.hypot print 'computing distances (%s by %s)'%size, for i in xrange(width): if i%(width/10)==0: print i, if i%20==0: print '.', for j in xrange(height): d1 = hy(i-s1x,j-s1y) d2 = hy(i-s2x,j-s2y) arr[i][j] = abs(d1-d2) print '' arr2 = np.zeros((width,height,3),dtype="uint8") for ld in [200,116,100,84,68,52,36,20,8,4,2]: print 'now computing image for ld = '+str(ld) arr2 *= 0 arr2 += abs(arr%ld-ld/2)*(r,g,b)/(ld/2) print 'saving image...' ar2img = Image.fromarray(arr2) ar2img.save('ld'+str(ld).rjust(4,'0')+'.png') print 'saved as ld'+str(ld).rjust(4,'0')+'.png' I have managed to optimize most of it, but there's still a huge performance gap in the part with the 2 for-s, and I can't seem to think of a way to bypass that using common array operations... I'm open to suggestions :D

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• Doing coding in Linux through a virtual machine on Windows VS partitioning

  - by ihaveitnow

  I already have experience with setting up virtual machines, running them and other minor tasks. Im a gamer, so I wont get rid of windows (for now at least...) but I do want to be a great programmer and to be involved with the Open-Source community. Id like to know if its a good idea to do my programming in linux through a virtual machine, vs giving it a partitioned section of the HDD. Id like to know about performance pros and cons and functionality. All responses are appreciated, thanks in advance. The type of programming I intend to dive into : Android Dev, Web Dev, Desktop Dev...More Android and Web right now though. So im looking at C#,C,C++,Java,PHP,HTML,MySQL...Off the top of the dome. I do web designing as well, so dreamweaver is added as an "essential". But im sure I can do dreamweaver files and upload them to the server after programming in Linux...Right? And any info on IDE's in Linux for the above mentioned are appreciated, but i would prefer going the coding route and understanding the essence of whats happening "under the covers" Thanks to all for reading, I appreciate it. Hope this isnt confusing :S

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• Possible to capture all events in a web browser?

  - by David

  I am working on a pet project and am at the research stage. Quick summary I am trying to intercept all form submits, onclick, and every single keydown. My library of choice is either jquery, or jquery + prototypejs. I figure I can batch up the events into a queue/stack and send it back to the server in time interval batches to keep performance relatively stable. Concerns Form submits and change's would be relatively simple.. Something like $("form :inputs").bind("change", function() { ... record event... }); But how to ensure I get precedence over the applications handlers as I have a habit of putting return false on a lot of my form handlers when there is a validation issue. As I understand it, that effectively stops the event in its tracks. My project For my smaller remote clients I will put their products onto a VPS or run it in my home data center. Currently I use a basic authentication system, given a username/password they see the website and then hopefully send me somewhat sane notes on what is broken or should be tweaked. As a better solution, I've written a simple proxy web server that does the above but allows me to have one DNS entry and then depending on credentials it makes an internal request relaying headers and re-writing URLS as needed. Every single html/text or application/* request is compressed and shoved into a sqlite table so I can partially replay what they've done. Now I am shifting to the frontend and would like to capture clicks, keydown's, and submits on everything on the page.

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• How to efficiently convert String, integer, double, datetime to binary and vica versa?

  - by Ben

  Hi, I'm quite new to C# (I'm using .NET 4.0) so please bear with me. I need to save some object properties (their properties are int, double, String, boolean, datetime) to a file. But I want to encrypt the files using my own encryption, so I can't use FileStream to convert to binary. Also I don't want to use object serialization, because of performance issues. The idea is simple, first I need to somehow convert objects (their properties) to binary (array), then encrypt (some sort of xor) the array and append it to the end of the file. When reading first decrypt the array and then somehow convert the binary array back to object properties (from which I'll generate objects). I know (roughly =) ) how to convert these things by hand and I could code it, but it would be useless (too slow). I think the best way would be just to get properties' representation in memory and save that. But I don't know how to do it using C# (maybe using pointers?). Also I though about using MemoryStream but again I think it would be inefficient. I am thinking about class Converter, but it does not support toByte(datetime) (documentation says it always throws exception). For converting back I think the only options is class Converter. Note: I know the structure of objects and they will not change, also the maximum String length is also known. Thank you for all your ideas and time. EDIT: I will be storing only parts of objects, in some cases also parts of different objects (a couple of properties from one object type and a couple from another), thus I think that serialization is not an option for me.

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• Pump Messages During Long Operations + C#

  - by Newbie

  Hi I have a web service that is doing huge computation and is taking more than a minute. I have generated the proxy file of the web service and then from my client end I am using the dll(of course I generated the proxy dll). My client side code is TimeSeries3D t = new TimeSeries3D(); int portfolioId = 4387919; string[] str = new string[2]; str[0] = "MKT_CAP"; DateRange dr = new DateRange(); dr.mStartDate = DateTime.Today; dr.mEndDate = DateTime.Today; Service1 sc = new Service1(); t = sc.GetAttributesForPortfolio(portfolioId, true, str, dr); But since it is taking to much time for the server to compute, after 1 minute I am receiving an error message The CLR has been unable to transition from COM context 0x33caf30 to COM context 0x33cb0a0 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. Kindly guide me what to do? Thanks

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• Flex web application: prevent framerate drop when window is invisible

  - by JayPea

  So there's been a new "feature" in the flash player since version 10.1, which reduces the player's framerate to 2 fps when the application window is out of view. This is good news for performance, but it can break some functionality, such as the Timer class. I have an application which uses a Timer to display a countdown. Given the nature of the application, it is required for the Timer to complete its countdown even if the user is not there to see it. Imagine that you need to give the user only 10 seconds to perform a task. If the user minimizes the window halfway through the counter, they can take as much time as they want and still have 5 seconds left when they return to the window. This apparently can not be avoided with the newer flash players. In Air applications there is the backgroundFrameRate property which can be set to prevent this behavior, but this is part of the WindowedApplication class, so it seems that it is not available in a web application. Does anyone know a way to keep a constant frame rate even when the window is not visible? Thanks

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• How do repos (SVN, GIT) work?

  - by masfenix

  I read SO nearly everyday and mostly there is a thread about source control. I have a few questions. I am going to use SVN as example. 1) There is a team (small, large dosnt matter). In the morning everyone checks out the code to start working. At noon Person A commits, while person B still works on it. What happens when person B commits? how will person B know that there is an updated file? 2) I am assuming the answer to the first question is "run an update command which tells you", ok so person B finds out that the file they have been working on all morning in changed. When they see the udpated file, it seems like person A has REWRITTEN the file for better performance. What does person B do? Seems like there whole day was a waste of time. Or if they commit their version then its a waste of person A's time? 3) What are branches? thanks, and if anyone knows a laymen terms pdf or something that explains it that would be awesome.

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• Optimizing an embedded SELECT query in mySQL

  - by Crazy Serb

  Ok, here's a query that I am running right now on a table that has 45,000 records and is 65MB in size... and is just about to get bigger and bigger (so I gotta think of the future performance as well here): SELECT count(payment_id) as signup_count, sum(amount) as signup_amount FROM payments p WHERE tm_completed BETWEEN '2009-05-01' AND '2009-05-30' AND completed > 0 AND tm_completed IS NOT NULL AND member_id NOT IN (SELECT p2.member_id FROM payments p2 WHERE p2.completed=1 AND p2.tm_completed < '2009-05-01' AND p2.tm_completed IS NOT NULL GROUP BY p2.member_id) And as you might or might not imagine - it chokes the mysql server to a standstill... What it does is - it simply pulls the number of new users who signed up, have at least one "completed" payment, tm_completed is not empty (as it is only populated for completed payments), and (the embedded Select) that member has never had a "completed" payment before - meaning he's a new member (just because the system does rebills and whatnot, and this is the only way to sort of differentiate between an existing member who just got rebilled and a new member who got billed for the first time). Now, is there any possible way to optimize this query to use less resources or something, and to stop taking my mysql resources down on their knees...? Am I missing any info to clarify this any further? Let me know... EDIT: Here are the indexes already on that table: PRIMARY PRIMARY 46757 payment_id member_id INDEX 23378 member_id payer_id INDEX 11689 payer_id coupon_id INDEX 1 coupon_id tm_added INDEX 46757 tm_added, product_id tm_completed INDEX 46757 tm_completed, product_id

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• Caching issue with javascript and asp.net

  - by Ed Woodcock

  Hi guys: I asked a question a while back on here regarding caching data for a calendar/scheduling web app, and got some good responses. However, I have now decided to change my approach and stat caching the data in javascript. I am directly caching the HTML for each day's column in the calendar grid inside the $('body').data() object, which gives very fast page load times (almost unnoticable). However, problems start to arise when the user requests data that is not yet in the cache. This data is created by the server using an ajax call, so it's asynchronous, and takes about 0.2s per week's data. My current approach is simply to block for 0.5s when the user requests information from the server, and cache 4 weeks either side in the inital page load (and 1 extra week per page change request), however I doubt this is the optimal method. Does anyone have a suggestion as to how to improve the situation? To summarise: Each week takes 0.2s to retrieve from the server, asynchronously. Performance must be as close to real-time as possible. (however the data is not needed to be fully real-time: most appointments are added by the user and so we can re-cache after this) Currently 4 weeks are cached on either side of the inial week loaded: this is not enough. to cache 1 year takes ~ 21s, this is too slow for an initial load.

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• How can I optimize the SELECT statement running on an Oracle database?

  - by Elvis Lou

  I have a SELECT statement in ORACLE: SELECT COUNT(DISTINCT ds1.endpoint_msisdn) multiple30, dss1.service, dss1.endpoint_provisioning_id, dss1.company_scope, Nvl(x.subscription_status, dss1.subscription_status) subscription_status FROM daily_summary ds1 join daily_summary ds2 ON ds1.endpoint_msisdn = ds2.endpoint_msisdn, daily_summary_static dss1, daily_summary_static dss2, (SELECT NULL subscription_status FROM dual UNION ALL SELECT -2 subscription_status FROM dual) x WHERE ds1.summary_ts >= To_date('10-04-2012', 'dd-mm-yyyy') - 30 AND ds1.summary_ts <= To_date('10-04-2012', 'dd-mm-yyyy') AND dss1.last_active >= To_date('10-04-2012', 'dd-mm-yyyy') - 30 AND dss1.last_active <= To_date('10-04-2012', 'dd-mm-yyyy') AND dss2.last_active >= To_date('10-04-2012', 'dd-mm-yyyy') - 30 AND dss2.last_active <= To_date('10-04-2012', 'dd-mm-yyyy') AND dss1.service <> dss2.service AND ( dss1.company_scope = 2 OR dss1.company_scope = 5 ) AND ( dss2.company_scope = 2 OR dss2.company_scope = 5 ) AND dss1.company_scope = dss2.company_scope AND ds1.endpoint_noc_id = dss1.endpoint_noc_id AND ds1.endpoint_host_id = dss1.endpoint_host_id AND ds1.endpoint_instance_id = dss1.endpoint_instance_id AND ds2.endpoint_noc_id = dss2.endpoint_noc_id AND ds2.endpoint_host_id = dss2.endpoint_host_id AND ds2.endpoint_instance_id = dss2.endpoint_instance_id AND dss1.endpoint_provisioning_id = dss2.endpoint_provisioning_id AND Least(1, ds1.total_actions) = 1 AND Least(1, ds2.total_actions) = 1 GROUP BY dss1.service, dss1.endpoint_provisioning_id, dss1.company_scope, Nvl(x.subscription_status, dss1.subscription_status); This query took about 26 minutes to return in my environment, but if I remove the section: dss1.last_active >= to_date('10-04-2012','dd-mm-yyyy') - 30 AND dss1.last_active <= to_date('10-04-2012','dd-mm-yyyy') AND dss2.last_active >= to_date('10-04-2012','dd-mm-yyyy') - 30 AND dss2.last_active <= to_date('10-04-2012','dd-mm-yyyy') AND it only took 20 seconds to run. We have index on the column last_active, I don't know why the section slow down the performance so much? any ideas?

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• Unable to get data from a WCF client

  - by Scott

  I am developing a DLL that will provide sychronized time stamps to multiple applications running on the same machine. The timestamps are altered in a thread that uses a high performance timer and a scalar to provide the appearance of moving faster than real-time. For obvious reasons I want only 1 instance of this time library, and I thought I could use WCF for the other processes to connect to this and poll for timestamps whenever they want. When I connect however I never get a valid time stamp, just an empty DateTime. I should point out that the library does work. The original implementation was a single DLL that each application incorporated and each one was synced using windows messages. I'm fairly sure it has something to do with how I'm setting up the WCF stuff, to which I am still pretty new. Here are the contract definitions: public interface ITimerCallbacks { [OperationContract(IsOneWay = true)] void TimerElapsed(String id); } [ServiceContract(SessionMode = SessionMode.Required, CallbackContract = typeof(ITimerCallbacks))] public interface ISimTime { [OperationContract] DateTime GetTime(); } Here is my class definition: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)] public class SimTimeServer: ISimTime The host setup: // set up WCF interprocess comms host = new ServiceHost(typeof(SimTimeServer), new Uri[] { new Uri("net.pipe://localhost") }); host.AddServiceEndpoint(typeof(ISimTime), new NetNamedPipeBinding(), "SimTime"); host.Open(); and the implementation of the interface function server-side: public DateTime GetTime() { if (ThreadMutex.WaitOne(20)) { RetTime = CurrentTime; ThreadMutex.ReleaseMutex(); } return RetTime; } Lastly the client-side implementation: Callbacks myCallbacks = new Callbacks(); DuplexChannelFactory pipeFactory = new DuplexChannelFactory(myCallbacks, new NetNamedPipeBinding(), new EndpointAddress("net.pipe://localhost/SimTime")); ISimTime pipeProxy = pipeFactory.CreateChannel(); while (true) { string str = Console.ReadLine(); if (str.ToLower().Contains("get")) Console.WriteLine(pipeProxy.GetTime().ToString()); else if (str.ToLower().Contains("exit")) break; }

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• Undefined Web.config error in VS 2008

  - by user1066050

  I'm working on a web app using VS 2008, .Net 3.5 and C#. Most of the projects in the solution are either classic asp.net pages with some MVC 1 in the mix, the rest is shared libraries. The solution is one that is some 5 years old and has gone through a variety of developers working on it and clearly has some performance and architectural issues. Previously, I've been working on the project using VS 2008 on a Win XP machine, but have just transitioned over to a new box using Win 7 Ultimate. To do so, I've installed VS 2008, asp.net 3.5. To support future work on the solution I've also installed VS 2010 and asp.net 4.0. Opening the solution on the new box with VS 2008 works fine, and it builds without error. However, when I attempt to run it with the debugger, I get the following message: "There is an error in web.config. Please correct before proceeding. (You might rename the current web.config and add a new one.)" I think it's clear that there is some sort of environmental issue regarding web.config on the new machine, but the error message is not "helpful". Adding a new web.config is not an option as the existing one is quite long and involved (too much to post here). I'm hoping someone has a suggestion or two about where I might look for missing elements or changed configurations that might produce such an error message. Lacking that, I'll revisit this post and provide the web.config in the hope that will elicit further help. Thanks to all in advance for taking a look at this. The StackOverflow community has helped me many times in the past with pertinent answers although this is my first posting. Jeff

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• Thread-safety of read-only memory access

  - by Edmund

  I've implemented the Barnes-Hut gravity algorithm in C as follows: Build a tree of clustered stars. For each star, traverse the tree and apply the gravitational forces from each applicable node. Update the star velocities and positions. Stage 2 is the most expensive stage, and so is implemented in parallel by dividing the set of stars. E.g. with 1000 stars and 2 threads, I have one thread processing the first 500 stars and the second thread processing the second 500. In practice this works: it speeds the computation by about 30% with two threads on a two-core machine, compared to the non-threaded version. Additionally, it yields the same numerical results as the original non-threaded version. My concern is that the two threads are accessing the same resource (namely, the tree) simultaneously. I have not added any synchronisation to the thread workers, so it's likely they will attempt to read from the same location at some point. Although access to the tree is strictly read-only I am not 100% sure it's safe. It has worked when I've tested it but I know this is no guarantee of correctness! Questions Do I need to make a private copy of the tree for each thread? Even if it is safe, are there performance problems of accessing the same memory from multiple threads?

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• Handling form from different view and passing form validation through session in django

  - by Mo J. Mughrabi

  I have a requirement here to build a comment-like app in my django project, the app has a view to receive a submitted form process it and return the errors to where ever it came from. I finally managed to get it to work, but I have doubt for the way am using it might be wrong since am passing the entire validated form in the session. below is the code comment/templatetags/comment.py @register.inclusion_tag('comment/form.html', takes_context=True) def comment_form(context, model, object_id, next): """ comment_form() is responsible for rendering the comment form """ # clear sessions from variable incase it was found content_type = ContentType.objects.get_for_model(model) try: request = context['request'] if request.session.get('comment_form', False): form = CommentForm(request.session['comment_form']) form.fields['content_type'].initial = 15 form.fields['object_id'].initial = 2 form.fields['next'].initial = next else: form = CommentForm(initial={ 'content_type' : content_type.id, 'object_id' : object_id, 'next' : next }) except Exception as e: logging.error(str(e)) form = None return { 'form' : form } comment/view.py def save_comment(request): """ save_comment: """ if request.method == 'POST': # clear sessions from variable incase it was found if request.session.get('comment_form', False): del request.session['comment_form'] form = CommentForm(request.POST) if form.is_valid(): obj = form.save(commit=False) if request.user.is_authenticated(): obj.created_by = request.user obj.save() messages.info(request, _('Your comment has been posted.')) return redirect(form.data.get('next')) else: request.session['comment_form'] = request.POST return redirect(form.data.get('next')) else: raise Http404 the usage is by loading the template tag and firing {% comment_form article article.id article.get_absolute_url %} my doubt is if am doing the correct approach or not by passing the validated form to the session. Would that be a problem? security risk? performance issues? Please advise Update In response to Pol question. The reason why I went with this approach is because comment form is handled in a separate app. In my scenario, I render objects such as article and all I do is invoke the templatetag to render the form. What would be an alternative approach for my case? You also shared with me the django comment app, which am aware of but the client am working with requires a lot of complex work to be done in the comment app thats why am working on a new one.

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• Heavy Mysql operation & Time Constraints [closed]

  - by Rahul Jha

  There is a performance issue where that I have stuck with my application which is based on PHP & MySql. The application is for Data Migration where data has to be uploaded and after various processes (Cleaning from foreign characters, duplicate check, id generation) it has to be inserted into one central table and then to 5 different tables. There, an id is generated and that id has to be updated to central table. There are different sets of records and validation rules. The problem I am facing is that when I insert say(4K) rows file (containing 20 columns) it is working fine within 15 min it gets inserted everywhere. But, when I insert the same records again then at this time it is taking one hour to insert (ideally it should get inserted by marking earlier inserted data as duplicate). After going through the log file, I noticed is that there is a Mysql select statement where I am checking the duplicates and getting ID which are duplicates. Then I am calling a function inside for loop which is basically inserting records into 5 tables and updates id to central table. This Calling function is major time of whole process. P.S. The records has to be inserted record by record.. Kindly Suggest some solution.. //This is that sample code $query=mysql_query("SELECT DISTINCT p1.ID FROM table1 p1, table2 p2, table3 a WHERE p2.datatype =0 AND (p1.datatype =1 || p1.datatype=2) AND p2.ID =0 AND p1.ID = a.ID AND p1.coulmn1 = p2.column1 AND p1.coulmn2 = p2.coulmn2 AND a.coulmn3 = p2.column3"); $num=mysql_num_rows($query); for($i=0;$i<$num;$i++) { $f=mysql_result($query,$i,"ID"); //calling function RecordInsert($f); }

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• How would I go about sharing variables in a C++ class with Lua?

  - by Nicholas Flynt

  I'm fairly new to Lua, I've been working on trying to implement Lua scripting for logic in a Game Engine I'm putting together. I've had no trouble so far getting Lua up and running through the engine, and I'm able to call Lua functions from C and C functions from Lua. The way the engine works now, each Object class contains a set of variables that the engine can quickly iterate over to draw or process for physics. While game objects all need to access and manipulate these variables in order for the Game Engine itself to see any changes, they are free to create their own variables, a Lua is exceedingly flexible about this so I don't forsee any issues. Anyway, currently the Game Engine side of things are sitting in C land, and I really want them to stay there for performance reasons. So in an ideal world, when spawning a new game object, I'd need to be able to give Lua read/write access to this standard set of variables as part of the Lua object's base class, which its game logic could then proceed to run wild with. So far, I'm keeping two separate tables of objects in place-- Lua spawns a new game object which adds itself to a numerically indexed global table of objects, and then proceeds to call a C++ function, which creates a new GameObject class and registers the Lua index (an int) with the class. So far so good, C++ functions can now see the Lua object and easily perform operations or call functions in Lua land using dostring. What I need to do now is take the C++ variables, part of the GameObject class, and expose them to Lua, and this is where google is failing me. I've encountered a very nice method here which details the process using tags, but I've read that this method is deprecated in favor of metatables. What is the ideal way to accomplish this? Is it worth the hassle of learning how to pass class definitions around using libBind or some equivalent method, or is there a simple way I can just register each variable (once, at spawn time) with the global lua object? What's the "current" best way to do this, as of Lua 5.1.4?

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• Is it a good idea to use MySQL and Neo4j together?

  - by Sanoj

  I will make an application with a lot of similar items (millions), and I would like to store them in a MySQL database, because I would like to do a lot of statistics and search on specific values for specific columns. But at the same time, I will store relations between all the items, that are related in many connected binary-tree-like structures (transitive closure), and relation databases are not good at that kind of structures, so I would like to store all relations in Neo4j which have good performance for this kind of data. My plan is to have all data except the relations in the MySQL database and all relations with item_id stored in the Neo4j database. When I want to lookup a tree, I first search the Neo4j for all the item_id:s in the tree, then I search the MySQL-database for all the specified items in a query that would look like: SELECT * FROM items WHERE item_id = 45 OR item_id = 345435 OR item_id = 343 OR item_id = 78 OR item_id = 4522 OR item_id = 676 OR item_id = 443 OR item_id = 4255 OR item_id = 4345 Is this a good idea, or am I very wrong? I haven't used graph-databases before. Are there any better approaches to my problem? How would the MySQL-query perform in this case?

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• Two radically different queries against 4 mil records execute in the same time - one uses brute force.

  - by IanC

  I'm using SQL Server 2008. I have a table with over 3 million records, which is related to another table with a million records. I have spent a few days experimenting with different ways of querying these tables. I have it down to two radically different queries, both of which take 6s to execute on my laptop. The first query uses a brute force method of evaluating possibly likely matches, and removes incorrect matches via aggregate summation calculations. The second gets all possibly likely matches, then removes incorrect matches via an EXCEPT query that uses two dedicated indexes to find the low and high mismatches. Logically, one would expect the brute force to be slow and the indexes one to be fast. Not so. And I have experimented heavily with indexes until I got the best speed. Further, the brute force query doesn't require as many indexes, which means that technically it would yield better overall system performance. Below are the two execution plans. If you can't see them, please let me know and I'll re-post then in landscape orientation / mail them to you. Brute-force query: Index-based exception query: My question is, based on the execution plans, which one look more efficient? I realize that thing may change as my data grows.

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• ReaderWriterLockSlim and Pulse/Wait

  - by Jono

  Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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• HTML5 audio object doesn't play on iPad (when called from a setTimeout)

  - by Dan Halliday

  I have a page with a hidden <audio> object which is being started and stopped using a custom button via javascript. (The reason being I want to customise the button, and that drawing an audio player seems to destroy rendering performance on iPad anyway). A simplified example (in coffeescript): // Works fine on all browsers constructor: (@_button, @_audio) -> @_button.on 'click', @_play // Bind button's click event with jQuery _play: (e) => @_audio[0].play() // Call play() on audio element The audio plays fine when triggered from a function bound to a click event, but I actually want an animation to complete before the file plays so I put .play() inside a setTimeout. However I just can't get this to work: // Will not play on iPad constructor: (@_button, @_audio) -> @_button.on 'click', @_play // Bind button's click event with jQuery _play: (e) => setTimeout (=> // Declare a 300ms timeout @_audio[0].play() // Call play() on audio element ), 300 I've checked that @_audio (this._audio) is in scope and that its play() method exists. Why doesn't this work on iPad?

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• What hash algorithms are paralellizable? Optimizing the hashing of large files utilizing on mult-co

  - by DanO

  I'm interested in optimizing the hashing of some large files (optimizing wall clock time). The I/O has been optimized well enough already and the I/O device (local SSD) is only tapped at about 25% of capacity, while one of the CPU cores is completely maxed-out. I have more cores available, and in the future will likely have even more cores. So far I've only been able to tap into more cores if I happen to need multiple hashes of the same file, say an MD5 AND a SHA256 at the same time. I can use the same I/O stream to feed two or more hash algorithms, and I get the faster algorithms done for free (as far as wall clock time). As I understand most hash algorithms, each new bit changes the entire result, and it is inherently challenging/impossible to do in parallel. Are any of the mainstream hash algorithms parallelizable? Are there any non-mainstream hashes that are parallelizable (and that have at least a sample implementation available)? As future CPUs will trend toward more cores and a leveling off in clock speed, is there any way to improve the performance of file hashing? (other than liquid nitrogen cooled overclocking?) or is it inherently non-parallelizable?

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• Start with remoting or with WCF

  - by Sheldon

  Hi. I'm just starting with distributed application development. I need to create (all by myself) an enterprise application for document management. That application will run on an intranet (within the firewall, no internet access is required now, BUT is probably that will be later). The application needs to manage images that will be stored within MySQL Server (as blobs) and those images will be then recovered by the app and eventually one or more of them will be converted to PDF. Performance is the most important non-functional requirement. I have a couple of doubts. What do you suggest to use, .NET Remoting or WCF over TCP-IP (I think second one is the best for the moment I need to expose the business logic over internet, changing the protocol). Where do you suggest to make the transformation of the images to pdf files, I'm using iText. (I have thought to have the business logic stored within the IIS and exposed via WCF, and that business logic to be responsible of getting the images and transforming them to PDF, that because the IIS and the MySQL Server are the same physical machine). I ask about where to do the transformation because the app must be accessible from multiple devices, and for example, for mobile devices, the pdf maybe is not necessary. Thank you very much in advance.

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• How to justify using a scripting language as part of a project

  - by sylvanaar

  I have a specific project in which I want to use either a scripting language + C, or as an alternative a 100% Java solution. The program adapts a legacy system for use with other moderns systems. Basically, I have few choices as to what language I can use. I have C/C++, Java 1.4, and I have also compiled the Lua for this environment. The program does 'screen scraping' and has to deal with alot of strings. That part of the code is highly variable. Most of the developers at my company use C, so - my original design was to write some portions in C, and use Lua for the part that dealt with strings and changed freqently. I was told 'You have to justify your use of the scripting language.' So i reworked my design using 100% Java, and was told - Java wont have enough performance. You should do the whole thing in C. I'm not controlling lasers or doing image processing - just some screen scraping. I still have to provide justification for using anything but C - so what justification can I provide?

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• LINQ to SQL: Reusable expression for property?

  - by coenvdwel

  Pardon me for being unable to phrase the title more exact. Basically, I have three LINQ objects linked to tables. One is Product, the other is Company and the last is a mapping table Mapping to store what Company sells which products and by which ID this Company refers to this Product. I am now retrieving a list of products as follows: var options = new DataLoadOptions(); options.LoadWith<Product>(p => p.Mappings); context.LoadOptions = options; var products = ( from p in context.Products select new { ProductID = p.ProductID, //BackendProductID = p.BackendProductID, BackendProductID = (p.Mappings.Count == 0) ? "None" : (p.Mappings.Count > 1) ? "Multiple" : p.Mappings.First().BackendProductID, Description = p.Description } ).ToList(); This does a single query retrieving the information I want. But I want to be able to move the logic behind the BackendProductID into the LINQ object so I can use the commented line instead of the annoyingly nested ternary operator statements for neatness and re-usability. So I added the following property to the Product object: public string BackendProductID { get { if (Mappings.Count == 0) return "None"; if (Mappings.Count > 1) return "Multiple"; return Mappings.First().BackendProductID; } } The list is still the same, but it now does a query for every single Product to get it's BackendProductID. The code is neater and re-usable, but the performance now is terrible. What I need is some kind of Expression or Delegate but I couldn't get my head around writing one. It always ended up querying for every single product, still. Any help would be appreciated!

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