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• Database design for credit based purchases

  - by FreshCode

  I need an elegant way to implement credit-based purchases for an online store with a small variety of products which can be purchased using virtual credit or real currency. Alternatively, products could only be priced in credits. Previous work I have implemented credit-based purchasing before using different product types (eg. Credit, Voucher or Music) with post-order processing to assign purchased credit to users in the form of real currency, which could subsequently be used to discount future orders' charge totals. This worked fairly well as a makeshift solution, but did not succeed in disconnecting the virtual currency from the real currency, which is what I'd like to do, since spending credits is psychologically easier for customers than spending real currency. Design I need guidance on designing the database correctly with support for the simultaneous bulk purchase of credits at a discount along with real currency products. Alternatively, should all products be priced in credits and only credit have a real currency value? Existing Database Design Partial Products table: ProductId Title Type UnitPrice SalePrice Partial Orders table: OrderId UserId (related to Users table, not shown) Status Value Total Partial OrderItems table (similar to CartItems table): OrderItemId OrderId (related to Orders table) ProductId (related to Products table) Quantity UnitPrice SalePrice Prospective UserCredits table: CreditId UserId (related to Users table, not shown) Value (+/- value. Summed over time to determine saldo.) Date I'm using ASP.NET MVC and LINQ-to-SQL on a SQL Server database.

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• Django form linking 2 models by many to many field.

  - by Ed

  I have two models: class Actor(models.Model): name = models.CharField(max_length=30, unique = True) event = models.ManyToManyField(Event, blank=True, null=True) class Event(models.Model): name = models.CharField(max_length=30, unique = True) long_description = models.TextField(blank=True, null=True) I want to create a form that allows me to identify the link between the two models when I add a new entry. This works: class ActorForm(forms.ModelForm): class Meta: model = Actor The form includes both name and event, allowing me to create a new Actor and simultaneous link it to an existing Event. On the flipside, class EventForm(forms.ModelForm): class Meta: model = Event This form does not include an actor association. So I am only able to create a new Event. I can't simultaneously link it to an existing Actor. I tried to create an inline formset: EventFormSet = forms.models.inlineformset_factory(Event, Actor, can_delete = False, extra = 2, form = ActorForm) but I get an error <'class ctg.dtb.models.Actor'> has no ForeignKey to <'class ctg.dtb.models.Event'> This isn't too surprising. The inlineformset worked for another set of models I had, but this is a different example. I think I'm going about it entirely wrong. Overall question: How can I create a form that allows me to create a new Event and link it to an existing Actor?

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• Servlet requests are executed sequentially for no apparent reason in Glassfish v3

  - by Fabien Benoit

  Hi, I'm using Glassfish 3 Web profile and can't get http workers to execute concurrently requests on a servlet. This is how i observed the problem. I've made a very simple servlet, that writes the current thread name to the standard output and sleep for 10 seconds : protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println(Thread.currentThread().getName()); try { Thread.sleep(10000); // 10 sec } catch (InterruptedException ex) {} } } And when i'm running several simultaneous requests, I clearly see in the logs that the requests are sequentially executed (one trace every 10 seconds). INFO: http-thread-pool-8080-(2) (10 seconds later...) INFO: http-thread-pool-8080-(1) (10 seconds later...) INFO: http-thread-pool-8080-(2) etc. All my GF settings are untouched - it's the out-of-the-box config (the default thread pool is 2 threads min, 5 max if I recall properly). ...I really don't understand why the sleep() block all the others worker threads. Any insight would be greatly appreciated ! Thanks, Fabien

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• Why does output of fltk-config truncate arguments to gcc?

  - by James Morris

  I'm trying to build an application I've downloaded which uses the SCONS "make replacement" and the Fast Light Tool Kit Gui. The SConstruct code to detect the presence of fltk is: guienv = Environment(CPPFLAGS = '') guiconf = Configure(guienv) if not guiconf.CheckLibWithHeader('lo', 'lo/lo.h','c'): print 'Did not find liblo for OSC, exiting!' Exit(1) if not guiconf.CheckLibWithHeader('fltk', 'FL/Fl.H','c++'): print 'Did not find FLTK for the gui, exiting!' Exit(1) Unfortunately, on my (Gentoo Linux) system, and many others (Linux distributions) this can be quite troublesome if the package manager allows the simultaneous install of FLTK-1 and FLTK-2. I have attempted to modify the SConstruct file to use fltk-config --cflags and fltk-config --ldflags (or fltk-config --libs might be better than ldflags) by adding them like so: guienv.Append(CPPPATH = os.popen('fltk-config --cflags').read()) guienv.Append(LIBPATH = os.popen('fltk-config --ldflags').read()) But this causes the test for liblo to fail! Looking in config.log shows how it failed: scons: Configure: Checking for C library lo... gcc -o .sconf_temp/conftest_4.o -c "-I/usr/include/fltk-1.1 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_THREAD_SAFE -D_REENTRANT" gcc: no input files scons: Configure: no How should this really be done? And to complete my answer, how do I remove the quotes from the result of os.popen( 'command').read()? EDIT The real question here is why does appending the output of fltk-config cause gcc to not receive the filename argument it is supposed to compile?

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• File transfer eating alot of CPU

  - by Dan C.

  I'm trying to transfer a file over a IHttpHandler, the code is pretty simple. However when i start a single transfer it uses about 20% of the CPU. If i were to scale this to 20 simultaneous transfers the CPU is very high. Is there a better way I can be doing this to keep the CPU lower? the client code just sends over chunks of the file 64KB at a time. public void ProcessRequest(HttpContext context) { if (context.Request.Params["secretKey"] == null) { } else { accessCode = context.Request.Params["secretKey"].ToString(); } if (accessCode == "test") { string fileName = context.Request.Params["fileName"].ToString(); byte[] buffer = Convert.FromBase64String(context.Request.Form["data"]); string fileGuid = context.Request.Params["smGuid"].ToString(); string user = context.Request.Params["user"].ToString(); SaveFile(fileName, buffer, user); } } public void SaveFile(string fileName, byte[] buffer, string user) { string DirPath = @"E:\Filestorage\" + user + @"\"; if (!Directory.Exists(DirPath)) { Directory.CreateDirectory(DirPath); } string FilePath = @"E:\Filestorage\" + user + @"\" + fileName; FileStream writer = new FileStream(FilePath, File.Exists(FilePath) ? FileMode.Append : FileMode.Create, FileAccess.Write, FileShare.ReadWrite); writer.Write(buffer, 0, buffer.Length); writer.Close(); }

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• Can a large transaction log cause cpu hikes to occur

  - by Simon Rigby

  Hello all, I have a client with a very large database on Sql Server 2005. The total space allocated to the db is 15Gb with roughly 5Gb to the db and 10 Gb to the transaction log. Just recently a web application that is connecting to that db is timing out. I have traced the actions on the web page and examined the queries that execute whilst these web operation are performed. There is nothing untoward in the execution plan. The query itself used multiple joins but completes very quickly. However, the db server's CPU hikes to 100% for a few seconds. The issue occurs when several simultaneous users are working on the system (when I say multiple .. read about 5). Under this timeouts start to occur. I suppose my question is, can a large transaction log cause issues with CPU performance? There is about 12Gb of free space on the disk currently. The configuration is a little out of my hands but the db and log are both on the same physical disk. I appreciate that the log file is massive and needs attending to, but I'm just looking for a heads up as to whether this may cause CPU spikes (ie trying to find the correlation). The timeouts are a recent thing and this app has been responsive for a few years (ie its a recent manifestation). Many Thanks,

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• Collecting high-volume video viewing data

  - by DanK

  I want to add tracking to our Flash-based media player so that we can provide analytics that show what sections of videos are being watched (at the moment, we just register a view when a video starts playing) For example, if a viewer watches the first 30 seconds of a video and then clicks away to something else, we want the data to reflect that. Likewise, if someone watches the first 10 seconds, then scrubs the timeline to the last minute of the video and watches that, we want to register viewing on the parts watched and not the middle section. My first thought was to collect up the viewing data in the player and send it all to the server at the end of a viewing session. Unfortunately, Flash does not seem to have an event that you can hook into when a viewer clicks away from the page the movie is on (probably a good thing - it would be open to abuse) So, it looks like we're going to have to make regular requests to the server as the video is playing. This is obviously going to lead to a high volume of requests when there are large numbers of simultaneous viewers. The simple approach of dumping all these 'heartbeat' events from clients to a database feels like it will quickly become unmanageable so I'm wondering whether I should be taking an approach where viewing sessions are cached in memory and flushed to database when they become inactive (based on a timeout). That way, the data could be stored as time spans rather than individual heartbeats. So, to the question - what is the best way to approach dealing with this kind of high-volume viewing data? Are there any good existing architectures/patterns? Thanks, Dan.

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• PulpCore OGG music playback - can't loop as soon as I animate the musicVolume property

  - by Peter Perhác

  I have been experimenting with PulpCore for about a week or so and I am enjoying it very much but today I ran into a problem that I can't quite figure out. Sound bgMusic = Sound.load("music/music.ogg"); Playback musicPlayback; ... musicVolume = new Fixed(0.75); musicPlayback = bgMusic.loop(musicVolume); //TODO figure out why it's NOT looping when volume is animated // musicVolume.animate(0, musicVolume.get(), FADE_IN_TIME); This code, for as long as the last line is commented out, plays the music.ogg again and again in an endless loop (which I can stop by calling stop on the Playback object returned from loop(). However, I would like the music to fade in smoothly, so following the advice of the PulpCore API docs, I added the last line which will create the fade-in but the music will only play once and then stop. I wonder why is that? Here is a bit of the documentation: Playback pulpcore.sound.Sound.loop(Fixed level) Loops this sound clip with the specified volume level (0.0 to 1.0). The level may have a property animation attached. Parameters: level Returns: a Playback object for this unique sound playback (one Sound can have many simultaneous Playback objects) or null if the sound could not be played. So what could be the problem? I repeat, with the last line, the sound fades in but doesn't loop, without it it loops but starts with the specified 0.75 volume level.

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• Commercial Website architecture question

  - by Maxime ARNSTAMM

  Hello everyone, I have to write an architecture case study but there are some things that i don't know, so i'd like some pointers on the following : The website must handle 5k simultaneous users. The backend is composed by a commercial software, some webservices, some message queues, and a database. I want to recommend to use Spring for the backend, to deal with the different elements, and to expose some Rest services. I also want to recommend wicket for the front (not the point here). What i don't know is : must i install the front and the back on the same tomcat server or two different ? and i am tempted to put two servers for the front, with a load balancer (no need for session replication in this case). But if i have two front servers, must i have two back servers ? i don't want to create some kind of bottleneck. Based on what i read on this blog a really huge charge is handle by one tomcat only for the first website mentionned. But i cannot find any info on this, so i can't tell if it seems plausible. If you can enlight me, so i can go on in my case study, that would be really helpful. Thanks :)

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• How do I correctly detect presence of FLTK using SCONS?

  - by James Morris

  I'm trying to build an application I've downloaded which uses the SCONS "make replacement" and the Fast Light Tool Kit Gui. The SConstruct code to detect the presence of fltk is: guienv = Environment(CPPFLAGS = '') guiconf = Configure(guienv) if not guiconf.CheckLibWithHeader('lo', 'lo/lo.h','c'): print 'Did not find liblo for OSC, exiting!' Exit(1) if not guiconf.CheckLibWithHeader('fltk', 'FL/Fl.H','c++'): print 'Did not find FLTK for the gui, exiting!' Exit(1) Unfortunately, on my (Gentoo Linux) system, and many others (Linux distributions) this can be quite troublesome if the package manager allows the simultaneous install of FLTK-1 and FLTK-2. Being Idealistic, I attempted to modify the SConstruct file to use fltk-config --cflags and fltk-config --ldflags (or fltk-config --libs might be better than ldflags) by adding them like so: guienv.Append(CPPPATH = os.popen('fltk-config --cflags').read()) guienv.Append(LIBPATH = os.popen('fltk-config --ldflags').read()) But this causes the test for liblo to fail! Looking in config.log shows how it failed: scons: Configure: Checking for C library lo... gcc -o .sconf_temp/conftest_4.o -c "-I/usr/include/fltk-1.1 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_THREAD_SAFE -D_REENTRANT" gcc: no input files scons: Configure: no How should this really be done?

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• How can I make an even more random number in ActionScript 2.0

  - by Theo

  I write a piece of software that runs inside banner ads which generates millions of session IDs every day. For a long time I've known that the random number generator in Flash is't random enough to generate sufficiently unique IDs, so I've employed a number of tricks to get even more random numbers. However, in ActionScript 2.0 it's not easy, and I'm seeing more and more collisions, so I wonder if there is something I've overlooked. As far as I can tell the problem with Math.random() is that it's seeded by the system time, and when you have sufficient numbers of simultaneous attempts you're bound to see collisions. In ActionScript 3.0 I use the System.totalMemory, but there's no equivalent in ActionScript 2.0. AS3 also has Font.enumerateFonts, and a few other things that are different from system to system. On the server side I also add the IP address to the session ID, but even that isn't enough (for example, many large companies use a single proxy server and that means that thousands of people all have the same IP -- and since they tend to look at the same sites, with the same ads, roughly at the same time, there are many session ID collisions). What I need isn't something perfectly random, just something that is random enough to dilute the randomness I get from Math.random(). Think of it this way: there is a certain chance that two people will generate the same random number sequence using only Math.random(), but the chance of two people generating the same sequence and having, say, the exact same list of fonts is significantly lower. I cannot rely on having sufficient script access to use ExternalInterface to get hold of things like the user agent, or the URL of the page. I don't need suggestions of how to do it in AS3, or any other system, only AS2 -- using only what's available in the standard APIs. The best I've come up with so far is to use the list of microphones (Microphone.names), but I've also tried to make some fingerprinting using some of the properties in System.capabilities, I'm not sure how much randomness I can get out of that though so I'm not using that at the moment. I hope I've overlooked something.

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• Which apache worker to use with passenger and how?

  - by Millisami

  I've this config in my apache2.conf <IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 150 MaxRequestsPerChild 0 </IfModule> # worker MPM # StartServers: initial number of server processes to start # MaxClients: maximum number of simultaneous client connections # MinSpareThreads: minimum number of worker threads which are kept spare # MaxSpareThreads: maximum number of worker threads which are kept spare # ThreadsPerChild: constant number of worker threads in each server process # MaxRequestsPerChild: maximum number of requests a server process serves <IfModule mpm_worker_module> StartServers 2 MaxClients 15 MinSpareThreads 4 MaxSpareThreads 5 ThreadsPerChild 15 MaxRequestsPerChild 50000 </IfModule> Now I'm confused here. Which module gets loaded on which conditions? The phusion guys have suggested to use the worker module. Since both are present in apache conf file, do I have to comment the mpm_prefork_module or leave it as it is? Following is my passenger conf file for apache: LoadModule passenger_module /usr/lib/ruby/gems/1.8/gems/passenger-2.2.4/ext/apache2/mod_passenger.so PassengerRoot /usr/lib/ruby/gems/1.8/gems/passenger-2.2.4 PassengerRuby /usr/bin/ruby1.8 PassengerMaxPoolSize 3 PassengerPoolIdleTime 999999 RailsFrameworkSpawnerIdleTime 0 RailsAppSpawnerIdleTime 0 I'm running just a single Rails 2.3.2 app on 256MB slice at slicehost. I'm not quite satisfied with the performance yet. Are the settings above are any good??

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• ASP.NET Memory Usage in IIS is FAR greater than in DevEnv. Is this normal?

  - by Tom

  Greetings! I have an ASP.NET app that scrapes data from a handful of external pages, parses the relevant bits and displays them in a table. Total data retrieved is 3-4MB and the resulting page is about 1MB. I am using synchronous WebRequest GetResponse for the retrieval, but the same problem existed using an asynchronous BeginGetResponse/EndGetResponse process. There is no database access, no session storage, no caching, but an in-memory list of about 100 objects (total 1MB of data), plus a good amount of AJAX (AjaxControlToolkit). This issue appears on the very first run of the app, even if I have restarted IIS. The issue: When I run the app on my dev computer, the maximum commit charge is about 1.5GB. The biggest user, measured by Task Manager's VM Size, is WebDev.WebServer.exe (600MB). The app runs perfectly. When I run it on my rent-a-server (IIS 7.5, 1GB RAM), the maximum commit charge is over 3.8GB. The biggest user is w3wp.exe at 2.7GB. IIS grinds to a halt and spits out a timed-out error page. Given my limited server budget and the hope of having multiple simultaneous users, I'm kind of in a panic. Is this normal? If I bump the server RAM up to 4GB, will that be enough? Will multiple users require even more memory? Could the culprit be AJAX or the list of objects? Thanks for any insight you can provide.

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• How to increase the performance of a loop which runs for every 'n' minutes.

  - by GustlyWind

  Hi Giving small background to my requirement and what i had accomplished so far: There are 18 Scheduler tasks run at regular intervals (least being 30 mins) takes input of nearly 5000 eligible employees run into a static method for iteration and generates a mail content for that employee and mails. An average task takes about 9 min multiplied by 18 will be roughly 162 mins meanwhile there would be next tasks which will be in queue (I assume). So my plan is something like the below loop try { // Handle Arraylist of alerts eligible employees Iterator employee = empIDs.iterator(); while (employee.hasNext()) { ScheduledImplementation.getInstance().sendAlertInfoToEmpForGivenAlertType((Long)employee.next(), configType,schedType); } } catch (Exception vEx) { _log.error("Exception Caught During sending " + configType + " messages:" + configType, vEx); } Since I know how many employees would come to my method I will divide the while loop into two and perform simultaneous operations on two or three employees at a time. Is this possible. Or is there any other ways I can improve the performance. Some of the things I had implemented so far 1.Wherever possible made methods static and variables too Didn't bother to catch exceptions and send back because these are background tasks. (And I assume this improves performance) Get the DB values in one query instead of multiple hits. If am successful in optimizing the while loop I think i can save couple of mins. Thanks

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• Java OO design confusion: how to handle actions modified by states modified by actions...

  - by Arvanem

  Hi folks, Given an entity, whose action is potentially modified by states (of the entity and other entities) in turn potentially modified by other actions (of the entity and other entities) , what is the best way to code or design to handle the potential existence of the modifiers? Speaking metaphorically, I am coding a Java application representing a piano. As you know a piano has keys (which, when pressed, emit sound) and pedals (which, when pressed, modify the keys' sounds). My base class structure is as follows: Entity (for keys and pedals) State (this holds each entity's states, e.g. name such as "soft pedal", and boolean "Pressed"), Action (this holds each entity's actions, e.g. play sound when pressed, or modify others sounds). By composition, the Entity class has a copy of each of State and Action inside it. e.g.: public class Entity { State entityState = new State(); Action entityAction = new Action(); Thus I have coded a "C-Sharp" key Entity. When I "press" that entity (set its "Pressed" state to true), its action plays a "C-Sharp" sound and then sets its "Pressed" state to false. At the same time, if the "C-Sharp" key entity is not "tuned", its sound deviates from "C-Sharp". Meanwhile I have coded a "soft pedal" Entity. When that entity is "pressed", no sound plays but its action is to make softer the sound of the "C-Sharp" and other key entities. I have also coded a "sustain pedal" Entity. When that entity is "pressed", no sound plays but its action is to enable reverberation of the sound of the "C-Sharp" and other key entities. Both the "soft" and "sustain pedals" can be pressed at the same time with the result that keys entities become both softened and reverberating. In short, I do not understand how to make this simultaneous series of states and actions modify each other in a sensible OO way. I am wary of coding a massive series of "if" statements or "switches". Thanks in advance for any help or links you can offer.

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• Browser performance when combining image resizing with animated movement

  - by Steve Reichgut

  I have been tasked with the job of converting a Flash animation into HTML. The animation is rather complex and requires the need to move multiple images (9) from location (x,y) to location (x2,y2) while simultaneously increasing the image size from 215px wide to 930px wide. While doing some initial testing of this animation with just 1-2 images, I noticed a lot of choppiness in FF handling of this animation. To try and isolate the problem, I removed the dynamic resizing of the animation and just moved it from point A to point B. What was interesting was that I saw the same behavior when simply moving a 930px image that was resized down to 215px (via the CSS width or inline width properties). When I try the same animation with a different image that is actually 215px wide, it performed smoothly. I then tried the same animation with the original 930px wide image (with no resizing) and it performed well also. This makes me wonder if the browser is having to "resize" the image down to 215px each time it is moved which is causing the choppiness. Is this a correct assumption? If so, is there any other way to optimize the animation to allow for simultaneous image resizing and image movement? Notes: 1) One optimization I have done is to position the images absolutely in order to minimize the reflow process. 2) I have tested the animation using both jQuery and the fX animation framework.

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• How to find an embedded platform?

  - by gmagana

  I am new to the locating hardware side of embedded programming and so after being completely overwhelmed with all the choices out there (pc104, custom boards, a zillion option for each board, volume discounts, devel kits, ahhh!!) I am asking here for some direction. Basically, I must find a new motherboard and (most likely) re-implement the program logic. Rewriting this in C/C++/Java/C#/Pascal/BASIC is not a problem for me. so my real problem is finding the hardware. This motherboard will have several other devices attached to it. Here is a summary of what I need to do: Required: 2 RS232 serial ports (one used all the time for primary UI, the second one not continuous) 1 modem (9600+ baud ok) [Modem will be in simultaneous use with only one of the serial port devices, so interrupt sharing with one serial port is OK, but not both] Minimum permanent/long term storage: Whatever O/S requires + 1 MB (executable) + 512 KB (Data files) RAM: Minimal, whatever the O/S requires plus maybe 1MB for executable. Nice to have: USB port(s) Ethernet network port Wireless network Implementation languages (any O/S I will adapt to): First choice Java/C# (Mono ok) Second choice is C/Pascal Third is BASIC Ok, given all this, I am having a lot of trouble finding hardware that will support this that is low in cost. Every manufacturer site I visit has a lot of options, and it's difficult to see if their offering will even satisfy my must-have requirements (for example they sometimes list 3 "serial ports", but it appears that only one of the three is RS232, for example, and don't mention what the other two are). The #1 constraint is cost, #2 is size. Can anyone help me with this? This little task has left me thinking I should have gone for EE and not CS :-). EDIT: A bit of background: This is a system currently in production, but the original programmer passed away, and the current hardware manufacturer cannot find hardware to run the (currently) DOS system, so I need to reimplement this in a modern platform. I can only change the programming and the motherboard hardware.

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• Handling Application Logic in Multiple AsyncTask onPostExecute()s

  - by stormin986

  I have three simultaneous instances of an AsyncTask for download three files. When two particular ones finish, at the end of onPostExecute() I check a flag set by each, and if both are true, I call startActivity() for the next Activity. I am currently seeing the activity called twice, or something that resembles this type of behavior. Since the screen does that 'swipe left' kind of transition to the next activity, it sometimes does it twice (and when I hit back, it goes back to the same activity). It's obvious two versions of the activity that SHOULD only get called once are being put on the Activity stack. The only way I can find that this is possible is if both AsyncTasks' onPostExecute() executed SO simultaneously that they were virtually running the same lines at the same time, since I set the 'itemXdownloaded' flag to true right before I check for both and call startActivity(). But this is happening enough that it's very hard for me to believe that both downloads are finishing precisely at the same time and having their onPostExecute()s so close together... Any thoughts on what could be going on here? General gist of code (details removed, ignore any syntactical errors I may have edited in): // In onPostExecute() switch (downloadID) { case DL1: dl1complete = true; break; case DL2: dl2complete = true; break; case DL3: dl3complete = true; break; } // If 1 and 2 are done, move on (DL3 still going in background) if ( downloadID != DL3 && dl1complete && dl2complete) { ParentClass.this.startActivity(new Intent(ParentClass.this, NextActivity.class)); }

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• multi-shop orders table and sequential order numbers based on shop

  - by imanc

  Hey, I am looking at building a shop solution that needs to be scalable. Currently it retrieves 1-2000 orders on average per day across multiple country based shops (e.g. uk, us, de, dk, es etc.) but this order could be 10x this amount in two years. I am looking at either using separate country-shop databases to store the orders tables, or looking to combine all into one order table. If all orders exist in one table with a global ID (auto num) and country ID (e.g uk,de,dk etc.), each countries orders would also need to have sequential ordering. So in essence, we'd have to have a global ID and a country order ID, with the country order ID being sequential for countries only, e.g. global ID = 1000, country = UK, country order ID = 1000 global ID = 1001, country = DE, country order ID = 1000 global ID = 1002, country = DE, country order ID = 1001 global ID = 1003, country = DE, country order ID = 1002 global ID = 1004, country = UK, country order ID = 1001 THe global ID would be DB generated and not something I would need to worry about. But I am thinking that I'd have to do a query to get the current country order based ID+1 to find the next sequential number. Two things concern me about this: 1) query times when the table has potentially millions of rows of data and I'm doing a read before a write, 2) the potential for ID number clashes due to simultaneous writes/reads. With a MyISAM table the entire table could be locked whilst the last country order + 1 is retrieved, to prevent ID number clashes. I am wondering if anyone knows of a more elegant solution? Cheers, imanc

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• [C++][OpenMP] Proper use of "atomic directive" to lock STL container

  - by conradlee

  I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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• How do I handle the messages for a simple web-based live chat, on the server side?

  - by Carson Myers

  I'm building a simple live chat into a web application running on Django, but one thing I'm confused about is how I should store the messages between users. The chat will support multiple users, and a chat "session" is composed of users connected to one user that is the "host." The application is a sort of online document collaboration thing, so user X has a document, and users Y and Z would connect to user X to talk about the document, and that would be one chat session. If user Y disconnected for five minutes, and then signed back in and reconnected to user X, he should not get any of the messages shared between users X and Z while he was away. if users X, Y, and Z can have a chat session about user X's document, then users X and Y can connect to a simultaneous, but separate discussion about user Z's document. How should I handle this? Should I keep each message in the database? Each message would have an owner user and a target user (the host), and a separate table would be used to connect users with messages (which messages are visible to what users). Or should I store each session as an HTML file on the server, which messages get appended to? The problem is, I can't just send messages directly between clients. They have to be sent to the server in a POST request, and then each client has to periodically check for the messages in a GET request. Except I can't just have each message cleared after a client fetches it, because there could be multiple clients. How should I set this up? Any suggestions?

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• XMLHttpRequest leak

  - by Raja

  Hi everyone, Below is my javascript code snippet. Its not running as expected, please help me with this. <script type="text/javascript"> function getCurrentLocation() { console.log("inside location"); navigator.geolocation.getCurrentPosition(function(position) { insert_coord(new google.maps.LatLng(position.coords.latitude,position.coords.longitude)); }); } function insert_coord(loc) { var request = new XMLHttpRequest(); request.open("POST","start.php",true); request.onreadystatechange = function() { callback(request); }; request.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); request.send("lat=" + encodeURIComponent(loc.lat()) + "&lng=" + encodeURIComponent(loc.lng())); return request; } function callback(req) { console.log("inside callback"); if(req.readyState == 4) if(req.status == 200) { document.getElementById("scratch").innerHTML = "callback success"; //window.setTimeout("getCurrentLocation()",5000); setTimeout(getCurrentLocation,5000); } } getCurrentLocation(); //called on body load </script> What i'm trying to achieve is to send my current location to the php page every 5 seconds or so. i can see few of the coordinates in my database but after sometime it gets weird. Firebug show very weird logs like simultaneous POST's at irregular intervals. Here's the firebug screenshot: IS there a leak in the program. please help. EDIT: The expected outcome in the firebug console should be like this :- inside location POST .... inside callback /* 5 secs later */ inside location POST ... inside callback /* keep repeating */

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• How many users are sufficient to make a heavy load for web application

  - by galymzhan

  I have a web application, which has been suffering high load recent days. The application runs on single server which has 8-core Intel CPU and 4gb of RAM. Software: Drupal 5 (Apache 2, PHP5, MySQL5) running on Debian. After reaching 500 authenticated and 200 anonymous users (simultaneous), the application drastically decreases its performance up to total failure. The biggest load comes from authenticated users, who perform activities, causing insert/update/deletes on db. I think mysql is a bottleneck. Is it normal to slow down on such number of users? EDIT: I forgot to mention that I did some kind of profiling. I runned commands top, htop and they showed me that all memory was being used by MySQL! After some time MySQL starts to perform terribly slow, site goes down, and we have to restart/stop apache to reduce load. Administrators said that there was about 200 active mysql connections at that moment. The worst point is that we need to solve this ASAP, I can't do deep profiling analysis/code refactoring, so I'm considering 2 ways: my tables are MyIsam, I heard they use table-level locking which is very slow, is it right? could I change it to Innodb without worry? what if I take MySQL, and move it to dedicated machine with a lot of RAM?

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• Tracking down slow managed DLL loading

  - by Alex K

  I am faced with the following issue and at this point I feel like I'm severely lacking some sort of tool, I just don't know what that tool is, or what exactly it should be doing. Here is the setup: I have a 3rd party DLL that has to be registered in GAC. This all works fine and good on pretty much every machine our software was deployed on before. But now we got 2 machines, seemingly identical to the ones we know work (they are cloned from the same image and stuffed with the same hardware, so pretty much the only difference is software settings, over which I went over and over, and they seem fine). Now the problem, the DLL in GAC takes a very long time to load. At least I believe this is the issue, what I can say definitively is that instantiating a single class from that DLL is the slow part. Once it is loaded, thing fly as they always have. But while on known-good machines the DLL loads so fast that a timestamp in the log doesn't even change, on these 2 machines it take over 1min to load. Knowns: I have no access to the source, so I can't debug through the DLL. Our app is the only one that uses it (so shouldn't be simultaneous access issues). There is only one version of this DLL in existance, so it shouldn't be a matter of version conflict. The GAC reference is being used (if I uninstall the DLL from GAC, an exception will be thrown about the missing GAC reference). Could someone with a greater skill in debug-fu suggest what I can do to track down the root cause of this issue?

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• Continuous build infrastructure recommendations for primarily C++; GreenHills Integrity

  - by andersoj

  I need your recommendations for continuous build products for a large (1-2MLOC) software development project. Characteristics: ClearCase revision control Approx 80% C++; 15% Java; 5% script or low-level Compiles for Green Hills Integrity OS, but also some windows and JVM chunks Mostly an embedded system; also includes some UI pieces and some development support (simulation tools, config tools, etc...) Each notional "version" of the deliverable includes deployment images for a number of boards, UI machines, etc... (~10 separate images; 5 distinct operating systems) Need to maintain/track many simultaneous versions which, notably, are built for a variety of different board support packages Build cycle time is a major issue on the project, need support for whatever features help address this (mostly need to manage a large farm of build machines, I guess..) Operates in a secure environment (this is a gov't program) (Edited to add: This is a classified program; outsourcing the build infrastructure is a non-starter.) Interested in any best practices or peripheral guidance you might offer. The build automation issues is one of several overlapping best practices that appear to be missing on the program, but try to keep your answers focused on build infrastructure piece and observations directly related. Cost is not an object. Scalability and ease of retrofitting onto an existing infrastructure are key. JA

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