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• Why is my Python OpenGL render2DTexture function so slow?

  - by Barakat

  SOLVED: The problem was actually using time.time() every CPU cycle to see whether the next frame should be drawn or not. The time it takes to execute time.time() was having an impact on the FPS. I made this function for drawing 2D textures as images in a 2D view in my OpenGL application. After doing some testing I found that it takes up 1-2 fps per texture. I know I am probably doing something wrong in this code. Any ideas? I am limiting the FPS to 60. Edit: When I disable the texture rendering it adds about 15% fps back. When I disabled text rendering it adds about 15% fps back. When i disable both barely any fps is consumed anymore. IE: 20 out of 60 fps with both on. 30 out of 60 when one is disabled. 58 out of 60 when both are disabled. When rendering the text on a button ( the control I'm using to test this ), it only "prepares" the text when the button label is set. Updated code, still running at the same speed but still works the same: def render2DTexture( self, texture, rect, texrect ): glEnable( GL_TEXTURE_2D ) glBindTexture( GL_TEXTURE_2D, texture ) glBegin( GL_QUADS ) glTexCoord2f( texrect.left, texrect.bottom ) glVertex2i( rect.left, self.windowSize[1] - rect.top ) glTexCoord2f( texrect.right, texrect.bottom ) glVertex2i( rect.left + rect.right, self.windowSize[1] - rect.top ) glTexCoord2f( texrect.right, texrect.top ) glVertex2i( rect.left + rect.right, self.windowSize[1] - ( rect.top + rect.bottom ) ) glTexCoord2f( texrect.left, texrect.top ) glVertex2i( rect.left, self.windowSize[1] - ( rect.top + rect.bottom ) ) glEnd() glDisable( GL_TEXTURE_2D ) def prepareText( self, text, fontFace, color ): self.loadFont( fontFace ) bmp = self.fonts[ fontFace ].render( text, 1, color ) return ( pygame.image.tostring( bmp, 'RGBA', 1 ), bmp.get_width(), bmp.get_height() ) def renderText( self, pText, position ): glRasterPos2i( position[0], self.windowSize[1] - ( position[1] + pText[2] ) ) glDrawPixels( pText[1], pText[2], GL_RGBA, GL_UNSIGNED_BYTE, pText[0] )

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• Binary search in a sorted (memory-mapped ?) file in Java

  - by sds

  I am struggling to port a Perl program to Java, and learning Java as I go. A central component of the original program is a Perl module that does string prefix lookups in a +500 GB sorted text file using binary search (essentially, "seek" to a byte offset in the middle of the file, backtrack to nearest newline, compare line prefix with the search string, "seek" to half/double that byte offset, repeat until found...) I have experimented with several database solutions but found that nothing beats this in sheer lookup speed with data sets of this size. Do you know of any existing Java library that implements such functionality? Failing that, could you point me to some idiomatic example code that does random access reads in text files? Alternatively, I am not familiar with the new (?) Java I/O libraries but would it be an option to memory-map the 500 GB text file (I'm on a 64-bit machine with memory to spare) and do binary search on the memory-mapped byte array? I would be very interested to hear any experiences you have to share about this and similar problems.

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• Polymorphic Numerics on .Net and In C#

  - by Bent Rasmussen

  It's a real shame that in .Net there is no polymorphism for numbers, i.e. no INumeric interface that unifies the different kinds of numerical types such as bool, byte, uint, int, etc. In the extreme one would like a complete package of abstract algebra types. Joe Duffy has an article about the issue: http://www.bluebytesoftware.com/blog/CommentView,guid,14b37ade-3110-4596-9d6e-bacdcd75baa8.aspx How would you express this in C#, in order to retrofit it, without having influence over .Net or C#? I have one idea that involves first defining one or more abstract types (interfaces such as INumeric - or more abstract than that) and then defining structs that implement these and wrap types such as int while providing operations that return the new type (e.g. Integer32 : INumeric; where addition would be defined as public Integer32 Add(Integer32 other) { return Return(Value + other.Value); } I am somewhat afraid of the execution speed of this code but at least it is abstract. No operator overloading goodness... Any other ideas? .Net doesn't look like a viable long-term platform if it cannot have this kind of abstraction I think - and be efficient about it. Abstraction is reuse.

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• Problem calling web service from within JBOSS EJB Service

  - by Rob Goodwin

  I have a simple web service sitting on our internal network. I used SOAPUI to do a bit of testing, generated the service classes from the WSDL , and wrote some java code to access the service. All went as expected as I was able to create the service proxy classes and make calls. Pretty simple stuff. The only speed bump was getting java to trust the certificate from the machine providing the web service. That was not a technical problem, but rather my lack of experience with SSL based web services. Now onto my problem. I coded up a simple EJB service and deployed it into JBoss Application Server 4.3 and now get the following error in the code that previously worked. 12:21:50,235 WARN [ServiceDelegateImpl] Cannot access wsdlURL: https://WS-Test/TestService/v2/TestService?wsdl I can access the wsdl file from a web browser running on the same machine as the application server using the URL in the error message. I am at a loss as to where to go from here. I turned on the debug logs in JBOSS and got nothing more than what I showed above. I have done some searching on the net and found the same error in some questions, but those questions had no answers. The web services classes where generated with JAX-WS 2.2 using the wsimport ant task and placed in a jar that is included in the ejb package. JBoss is deployed in RHEL 5.4, where the standalone testing was done on Windows XP.

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• WPF, C# - Making Intellisense/Autocomplete list, fastest way to filter list of strings

  - by user559548

  Hello everyone, I'm writing an Intellisense/Autocomplete like the one you find in Visual Studio. It's all fine up until when the list contains probably 2000+ items. I'm using a simple LINQ statement for doing the filtering: var filterCollection = from s in listCollection where s.FilterValue.IndexOf(currentWord, StringComparison.OrdinalIgnoreCase) >= 0 orderby s.FilterValue select s; I then assign this collection to a WPF Listbox's ItemSource, and that's the end of it, works fine. Noting that, the Listbox is also virtualised as well, so there will only be at most 7-8 visual elements in memory and in the visual tree. However the caveat right now is that, when the user types extremely fast in the richtextbox, and on every key up I execute the filtering + binding, there's this semi-race condition, or out of sync filtering, like the first key stroke's filtering could still be doing it's filtering or binding work, while the fourth key stroke is also doing the same. I know I could put in a delay before applying the filter, but I'm trying to achieve a seamless filtering much like the one in Visual Studio. I'm not sure where my problem exactly lies, so I'm also attributing it to IndexOf's string operation, or perhaps my list of string's could be optimised in some kind of index, that could speed up searching. Any suggestions of code samples are much welcomed. Thanks.

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• A better python property decorator

  - by leChuck

  I've inherited some python code that contains a rather cryptic decorator. This decorator sets properties in classes all over the project. The problem is that this I have traced my debugging problems to this decorator. Seems it "fubars" all debuggers I've tried and trying to speed up the code with psyco breaks everthing. (Seems psyco and this decorator dont play nice). I think it would be best to change it. def Property(function): """Allow readable properties""" keys = 'fget', 'fset', 'fdel' func_locals = {'doc':function.__doc__} def probeFunc(frame, event, arg): if event == 'return': locals = frame.f_locals func_locals.update(dict((k,locals.get(k)) for k in keys)) sys.settrace(None) return probeFunc sys.settrace(probeFunc) function() return property(**func_locals) Used like so: class A(object): @Property def prop(): def fget(self): return self.__prop def fset(self, value): self.__prop = value ... ect The errors I get say the problems are because of sys.settrace. (Perhaps this is abuse of settrace ?) My question: Is the same decorator achievable without sys.settrace. If not I'm in for some heavy rewrites.

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• Optimize Use of Ramdisk for Eclipse Development

  - by Eric J.

  We're developing Java/SpringSource applications with Eclipse on 32-bit Vista machines with 4GB RAM. The OS exposes roughly 3.3GB of RAM due to reservations for hardware etc. in the virtual address space. I came across several Ramdisk drivers that can create a virtual disk from the OS-hidden RAM and am looking for suggestions how best to use the 740MB virtual disk to speed development in our environment. The slowest part of development for us is compiling as well as launching SpringSource dm Server. One option is to configure Vista to swap to the Ramdisk. That works, and noticeably speeds up development in low memory situations. However, the 3.3GB available to the OS is often sufficient and there are many situations where we do not use the swap file(s) much. Another option is to use the Ramdisk as a location for temporary files. Using the Vista mklink command, I created a hard link from where the SpringSource dm Server's work area normally resides to the Ramdisk. That significantly improves server startup times but does nothing for compile times. There are roughly 500MB still free on the Ramdisk when the work directory is fully utilized, so room for plenty more. What other files/directories might be candidates to place on the Ramdisk? Eclipse-related files? (Parts of) the JDK? Is there a free/open source tool for Vista that will show me which files are used most frequently during a period of time to reduce the guesswork?

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• [Doxygen] How to documenting global dependencies for functions?

  - by Thomas Matthews

  I've got some C code from a 3rd party vendor (for an embedded platform) that uses global variables (for speed & space optimizations). I'm documenting the code, converting to Doxygen format. How do I put a note in the function documentation that the function requires on global variables and functions? Doxygen has special commands for annotating parameters and return values as describe here: Doxygen Special Commands. I did not see any commands for global variables. Example C code: extern unsigned char data_buffer[]; //!< Global variable. /*! Returns the next available data byte. * \return Next data byte. */ unsigned char Get_Byte(void) { static unsigned int index = 0; return data_buffer[index++]; //!< Uses global variable. } In the above code, I would like to add Doxygen comments that the function depends on the global variable data_buffer.

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• learning to type - tips for programmers?

  - by OrbMan

  After hunting and pecking for about 35 years, I have decided to learn to type. I am learning QWERTY and have learned about 2/3 of the letters so far. While learning, I have noticed how asymmeterical the keyboard is, which really bothers me. (I will probably switch to a symmetrical keyboard eventually, but for now am trying to do everything as standard and "correct" as possible.) Although I am not there yet in my lessons, it seems that many of the keys I am going to use as a C# web developer are supposed to be typed by the pinky of my right hand. Are there any typing patterns you have developed that are more ergonomic (or faster) when typing large volumes of code rife with braces, colons, semi-colons and quotes? Or, should I just accept the fact that every other key is going to be hit with my right pinky? It is not that speed is such a huge concern, as much as that it seems so inefficient to rely on one finger so much... As an example, some of the conventions I use as a hunt and pecker, like typing open and close braces right away with my index and middle finger, and then hitting the left arrow key to fill in the inner content, don't seem to work as well with just a pinky. What are some typing patterns using a standard QWERTY keyboard that work really well for you as a programmer?

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• Link checker ; how to avoid false positives

  - by Burnzy

  I'm working a on a link checker/broken link finder and I am getting many false positives, after double checking I noticed that many error codes were returning webexceptions but they were actually downloadable, but in some other cases the statuscode is 404 and i can access the page from the browse. So here is the code, its pretty ugly, and id like to have something more, id say practical. All the status codes are in that big if are used to filter the ones i dont want to add to brokenlink because they are valid links ( i tested them all ). What i need to fix is the structure (if possible) and how to not get false 404. Thank you! try { HttpWebRequest request = ( HttpWebRequest ) WebRequest.Create ( uri ); request.Method = "Head"; request.MaximumResponseHeadersLength = 32; // FOR IE SLOW SPEED request.AllowAutoRedirect = true; using ( HttpWebResponse response = ( HttpWebResponse ) request.GetResponse() ) { request.Abort(); } /* WebClient wc = new WebClient(); wc.DownloadString( uri ); */ _validlinks.Add ( strUri ); } catch ( WebException wex ) { if ( !wex.Message.Contains ( "The remote name could not be resolved:" ) && wex.Status != WebExceptionStatus.ServerProtocolViolation ) { if ( wex.Status != WebExceptionStatus.Timeout ) { HttpStatusCode code = ( ( HttpWebResponse ) wex.Response ).StatusCode; if ( code != HttpStatusCode.OK && code != HttpStatusCode.BadRequest && code != HttpStatusCode.Accepted && code != HttpStatusCode.InternalServerError && code != HttpStatusCode.Forbidden && code != HttpStatusCode.Redirect && code != HttpStatusCode.Found ) { _brokenlinks.Add ( new Href ( new Uri ( strUri , UriKind.RelativeOrAbsolute ) , UrlType.External ) ); } else _validlinks.Add ( strUri ); } else _brokenlinks.Add ( new Href ( new Uri ( strUri , UriKind.RelativeOrAbsolute ) , UrlType.External ) ); } else _validlinks.Add ( strUri ); }

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• Why is curl in Ruby slower than command-line curl?

  - by Stiivi

  I am trying to download more than 1m pages (URLs ending by a sequence ID). I have implemented kind of multi-purpose download manager with configurable number of download threads and one processing thread. The downloader downloads files in batches: curl = Curl::Easy.new batch_urls.each { |url_info| curl.url = url_info[:url] curl.perform file = File.new(url_info[:file], "wb") file << curl.body_str file.close # ... some other stuff } I have tried to download 8000 pages sample. When using the code above, I get 1000 in 2 minutes. When I write all URLs into a file and do in shell: cat list | xargs curl I gen all 8000 pages in two minutes. Thing is, I need it to have it in ruby code, because there is other monitoring and processing code. I have tried: Curl::Multi - it is somehow faster, but misses 50-90% of files (does not download them and gives no reason/code) multiple threads with Curl::Easy - around the same speed as single threaded Why is reused Curl::Easy slower than subsequent command line curl calls and how can I make it faster? Or what I am doing wrong? I would prefer to fix my download manager code than to make downloading for this case in a different way. Before this, I was calling command-line wget which I provided with a file with list of URLs. Howerver, not all errors were handled, also it was not possible to specify output file for each URL separately when using URL list. Now it seems to me that the best way would be to use multiple threads with system call to 'curl' command. But why when I can use directly Curl in Ruby? Code for the download manager is here, if it might help: Download Manager (I have played with timeouts, from not-setting it to various values, it did not seem help) Any hints appreciated.

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• Dragging an UIView inside UIScrollView

  - by Sergey Mikhanov

  Hello community! I am trying to solve a basic problem with drag and drop on iPhone. Here's my setup: I have a UIScrollView which has one large content subview (I'm able to scroll and zoom it) Content subview has several small tiles as subviews that should be dragged around inside it. My UIScrollView subclass has this method: - (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event { UIView *tile = [contentView pointInsideTiles:[self convertPoint:point toView:contentView] withEvent:event]; if (tile) { return tile; } else { return [super hitTest:point withEvent:event]; } } Content subview has this method: - (UIView *)pointInsideTiles:(CGPoint)point withEvent:(UIEvent *)event { for (TileView *tile in tiles) { if ([tile pointInside:[self convertPoint:point toView:tile] withEvent:event]) return tile; } return nil; } And tile view has this method: - (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event { UITouch *touch = [touches anyObject]; CGPoint location = [touch locationInView:self.superview]; self.center = location; } This works, but not fully correct: the tile sometimes "falls down" during the drag process. More precisely, it stops receiving touchesMoved: invocations, and scroll view starts scrolling instead. I noticed that this depends on the drag speed: the faster I drag, the quicker the tile "falls". Any ideas on how to keep the tile glued to the dragging finger? Thanks in advance!

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• SQL Server insert performance

  - by Jose

  I have an insert query that gets generated like this INSERT INTO InvoiceDetail (LegacyId,InvoiceId,DetailTypeId,Fee,FeeTax,Investigatorid,SalespersonId,CreateDate,CreatedById,IsChargeBack,Expense,RepoAgentId,PayeeName,ExpensePaymentId,AdjustDetailId) VALUES(1,1,2,1500.0000,0.0000,163,1002,'11/30/2001 12:00:00 AM',1116,0,550.0000,850,NULL,@ExpensePay1,NULL); DECLARE @InvDetail1 INT; SET @InvDetail1 = (SELECT @@IDENTITY); This query is generated for only 110K rows. It takes 30 minutes for all of these query's to execute I checked the query plan and the largest % nodes are A Clustered Index Insert at 57% query cost which has a long xml that I don't want to post. A Table Spool which is 38% query cost <RelOp AvgRowSize="35" EstimateCPU="5.01038E-05" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Eager Spool" NodeId="80" Parallel="false" PhysicalOp="Table Spool" EstimatedTotalSubtreeCost="0.0466109"> <OutputList> <ColumnReference Database="[SkipPro]" Schema="[dbo]" Table="[InvoiceDetail]" Column="InvoiceId" /> <ColumnReference Database="[SkipPro]" Schema="[dbo]" Table="[InvoiceDetail]" Column="InvestigatorId" /> <ColumnReference Column="Expr1054" /> <ColumnReference Column="Expr1055" /> </OutputList> <Spool PrimaryNodeId="3" /> </RelOp> So my question is what is there that I can do to improve the speed of this thing? I already run ALTER TABLE TABLENAME NOCHECK CONSTRAINTS ALL Before the queries and then ALTER TABLE TABLENAME NOCHECK CONSTRAINTS ALL after the queries. And that didn't shave off hardly anything off of the time. Know I am running these queries in a .NET application that uses a SqlCommand object to send the query. I then tried to output the sql commands to a file and then execute it using sqlcmd, but I wasn't getting any updates on how it was doing, so I gave up on that. Any ideas or hints or help?

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• Fastest way to generate delimited string from 1d numpy array

  - by Abiel

  I have a program which needs to turn many large one-dimensional numpy arrays of floats into delimited strings. I am finding this operation quite slow relative to the mathematical operations in my program and am wondering if there is a way to speed it up. For example, consider the following loop, which takes 100,000 random numbers in a numpy array and joins each array into a comma-delimited string. import numpy as np x = np.random.randn(100000) for i in range(100): ",".join(map(str, x)) This loop takes about 20 seconds to complete (total, not each cycle). In contrast, consider that 100 cycles of something like elementwise multiplication (x*x) would take than one 1/10 of a second to complete. Clearly the string join operation creates a large performance bottleneck; in my actual application it will dominate total runtime. This makes me wonder, is there a faster way than ",".join(map(str, x))? Since map() is where almost all the processing time occurs, this comes down to the question of whether there a faster to way convert a very large number of numbers to strings.

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• DAL Layer : EF 4.0 or Normal Data access layer with Stored Procedure

  - by Harryboy

  Hello Experts, Application : I am working on one mid-large size application which will be used as a product, we need to decide on our DAL layer. Application UI is in Silverlight and DAL layer is going to be behind service layer. We are also moving ahead with domain model, so our DB tables and domain classes are not having same structure. So patterns like Data Mapper and Repository will definitely come into picture. I need to design DAL Layer considering below mentioned factors in priority manner Speed of Development with above average performance Maintenance Future support and stability of the technology Performance Limitation : 1) As we need to strictly go ahead with microsoft, we can not use NHibernate or any other ORM except EF 4.0 2) We can use any code generation tool (Should be Open source or very cheap) but it should only generate code in .Net, so there would not be any licensing issue on per copy basis. Questions I read so many articles about EF 4.0, on outset it looks like that it is still lacking in features from NHibernate but it is considerably better then EF 1.0 So, Do you people feel that we should go ahead with EF 4.0 or we should stick to ADO .Net and use any code geneartion tool like code smith or any other you feel best Also i need to answer questions like what time it will take to port application from EF 4.0 to ADO .Net if in future we stuck up with EF 4.0 for some features or we are having serious performance issue. In reverse case if we go ahead and choose ADO .Net then what time it will take to swith to EF 4.0 Lastly..as i was going through the article i found the code only approach (with POCO classes) seems to be best suited for our requirement as switching is really easy from one technology to other. Please share your thoughts on the same and please guide on the above questions

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• Use a vector to index a matrix without linear index

  - by David_G

  G'day, I'm trying to find a way to use a vector of [x,y] points to index from a large matrix in MATLAB. Usually, I would convert the subscript points to the linear index of the matrix.(for eg. Use a vector as an index to a matrix in MATLab) However, the matrix is 4-dimensional, and I want to take all of the elements of the 3rd and 4th dimensions that have the same 1st and 2nd dimension. Let me hopefully demonstrate with an example: Matrix = nan(4,4,2,2); % where the dimensions are (x,y,depth,time) Matrix(1,2,:,:) = 999; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(3,4,:,:) = 888; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(4,4,:,:) = 124; Now, I want to be able to index with the subscripts (1,2) and (3,4), etc and return not only the 999 and 888 which exist in Matrix(:,:,1,1) but the contents which exist at Matrix(:,:,1,2),Matrix(:,:,2,1) and Matrix(:,:,2,2), and so on (IRL, the dimensions of Matrix might be more like size(Matrix) = (300 250 30 200) I don't want to use linear indices because I would like the results to be in a similar vector fashion. For example, I would like a result which is something like: ans(time=1) 999 888 124 999 888 124 ans(time=2) etc etc etc etc etc etc I'd also like to add that due to the size of the matrix I'm dealing with, speed is an issue here - thus why I'd like to use subscript indices to index to the data. I should also mention that (unlike this question: Accessing values using subscripts without using sub2ind) since I want all the information stored in the extra dimensions, 3 and 4, of the i and jth indices, I don't think that a slightly faster version of sub2ind still would not cut it..

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• Best Practice - Removing item from generic collection in C#

  - by Matt Davis

  I'm using C# in Visual Studio 2008 with .NET 3.5. I have a generic dictionary that maps types of events to a generic list of subscribers. A subscriber can be subscribed to more than one event. private static Dictionary<EventType, List<ISubscriber>> _subscriptions; To remove a subscriber from the subscription list, I can use either of these two options. Option 1: ISubscriber subscriber; // defined elsewhere foreach (EventType event in _subscriptions.Keys) { if (_subscriptions[event].Contains(subscriber)) { _subscriptions[event].Remove(subscriber); } } Option 2: ISubscriber subscriber; // defined elsewhere foreach (EventType event in _subscriptions.Keys) { _subscriptions[event].Remove(subscriber); } I have two questions. First, notice that Option 1 checks for existence before removing the item, while Option 2 uses a brute force removal since Remove() does not throw an exception. Of these two, which is the preferred, "best-practice" way to do this? Second, is there another, "cleaner," more elegant way to do this, perhaps with a lambda expression or using a LINQ extension? I'm still getting acclimated to these two features. Thanks. EDIT Just to clarify, I realize that the choice between Options 1 and 2 is a choice of speed (Option 2) versus maintainability (Option 1). In this particular case, I'm not necessarily trying to optimize the code, although that is certainly a worthy consideration. What I'm trying to understand is if there is a generally well-established practice for doing this. If not, which option would you use in your own code?

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• C# WinForms MultiThreading in Loop

  - by Goober

  Scenario I have a background worker in my application that runs off and does a bunch of processing. I specifically used this implementation so as to keep my User Interface fluid and prevent it from freezing up. I want to keep the background worker, but inside that thread, spawn off ONLY 3 MORE threads - making them share the processing (currently the worker thread just loops through and processes each asset one-by-one. However I would like to speed this up but using only a limited number of threads. Question Given the code below, how can I get the loop to choose a thread that is free, and then essentially wait if there isn't one free before it continues. CODE foreach (KeyValuePair<int, LiveAsset> kvp in laToHaganise) { Haganise h = new Haganise(kvp.Value, busDate, inputMktSet, outputMktSet, prodType, noOfAssets, bulkSaving); h.DoWork(); } Thoughts I'm guessing that I would have to start off by creating 3 new threads, but my concern is that if I'm instantiating a new Haganise object each time - how can I pass the correct "h" object to the correct thread..... Thread firstThread = new Thread(new ThreadStart(h.DoWork)); Thread secondThread =new Thread(new ThreadStart(h.DoWork)); Thread thirdThread = new Thread(new ThreadStart(h.DoWork)); Help greatly appreciated.

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• Which is the best jQuery-powered site?

  - by Reigel

  This "Top 10 JavaScript (jQuery) Powered Sites", posted about 2 years ago, was the one that invites me(after seeing the list) to use jQuery. All the sites in that list made me realize how cool it is to build sites powered by jQuery. And now more and more sites are being powered by jQuery. More and more developers are learning jQuery. Two years have past now but I still do a search to google for best sites and still got me to that link and which the link is not updated from the first time I have looked at it. Here at stackoverflow, there are lots of jQuery user. I was thinking if we can here show some of the sites that you know that is powered by jQuery which you think is best. If you can, please make it one site one answer, so that we can make a vote if it's really best jQuery powered site. We will take a look if it is really well implemented ( the way the codes are written, fast speed site, etc...) and deserves to be the best. Lot's of viewers will benefit from it. Like, we can view and have an idea of how we will make our next project cooler, faster, and powerful.

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• Haskell math performance

  - by Travis Brown

  I'm in the middle of porting David Blei's original C implementation of Latent Dirichlet Allocation to Haskell, and I'm trying to decide whether to leave some of the low-level stuff in C. The following function is one example—it's an approximation of the second derivative of lgamma: double trigamma(double x) { double p; int i; x=x+6; p=1/(x*x); p=(((((0.075757575757576*p-0.033333333333333)*p+0.0238095238095238) *p-0.033333333333333)*p+0.166666666666667)*p+1)/x+0.5*p; for (i=0; i<6 ;i++) { x=x-1; p=1/(x*x)+p; } return(p); } I've translated this into more or less idiomatic Haskell as follows: trigamma :: Double -> Double trigamma x = snd $ last $ take 7 $ iterate next (x' - 1, p') where x' = x + 6 p = 1 / x' ^ 2 p' = p / 2 + c / x' c = foldr1 (\a b -> (a + b * p)) [1, 1/6, -1/30, 1/42, -1/30, 5/66] next (x, p) = (x - 1, 1 / x ^ 2 + p) The problem is that when I run both through Criterion, my Haskell version is six or seven times slower (I'm compiling with -O2 on GHC 6.12.1). Some similar functions are even worse. I know practically nothing about Haskell performance, and I'm not terribly interested in digging through Core or anything like that, since I can always just call the handful of math-intensive C functions through FFI. But I'm curious about whether there's low-hanging fruit that I'm missing—some kind of extension or library or annotation that I could use to speed up this numeric stuff without making it too ugly.

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• PHP / C++ space calculations for parcel packing

  - by Andrew Willis

  I am working on a shopping cart project which requires a 'postage calculator' based on items that the person has in their cart. Obviously I will be storing the item's dimensions incl. weight and padding in a database and will also store the parcel (box) size and weight that the items will go in to, incl. box padding. Figuring the weight of the parcels will be easy but I was wondering how to go about figuring how to pack the box via PHP, that is, I would like the code to 'play tetris' with the items to make sure they get the best possible fit, giving accurate postage costs. Does anybody have any ideas on how best to achieve this or does anybody know of a PHP Class or function that can do this? EDIT: When I said 'best possible fit' maybe I was being optimistic! Having the script try every possible combination of package distribution within the parcel would be over the top, however I could improve the speed by writing the algoritm in C++ and running the program in PHP when the user 'checks out', the return value being an array with the parcel size and weight (which are all that are needed to calculate postage costs)

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• is mysql index useful on column 'state' when only doing bit-operations on the column?

  - by Geert-Jan

  I have a lot of domain entities (stored in mysql) which undergo lots of different operations. Each operation is executed from a different program. I need to keep (flow)-state for these entities which I implemented in as a long field 'flowstate' used as a bitset. to query mysql for entities which have undergone a certain operation I do something like: select * from entities where state >> 7 & 1 = 1 Indicating bit 7 (cooresponding to operation 7) has run. (<-- simplified) Anyway, I really didn't pay attention to the performance implications of this setup in the beginning, and I think I'm in a bit of trouble since queries as the above run pretty slow. What I'd like to know: Does an mysql index on 'flowstate' help at all? After all it's not a single value Mysql can quickly find using a binary sort or whatever. If it doesn't, are there any other things I could do to speed things up? . Are there special 'mask-indices' for fields with use-cases as the above? TIA, Geert-jan

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• Can Haskell's Parsec library be used to implement a recursive descent parser with backup?

  - by Thor Thurn

  I've been considering using Haskell's Parsec parsing library to parse a subset of Java as a recursive descent parser as an alternative to more traditional parser-generator solutions like Happy. Parsec seems very easy to use, and parse speed is definitely not a factor for me. I'm wondering, though, if it's possible to implement "backup" with Parsec, a technique which finds the correct production to use by trying each one in turn. For a simple example, consider the very start of the JLS Java grammar: Literal: IntegerLiteral FloatingPointLiteral I'd like a way to not have to figure out how I should order these two rules to get the parse to succeed. As it stands, a naive implementation like this: literal = do { x <- try (do { v <- integer; return (IntLiteral v)}) <|> (do { v <- float; return (FPLiteral v)}); return(Literal x) } Will not work... inputs like "15.2" will cause the integer parser to succeed first, and then the whole thing will choke on the "." symbol. In this case, of course, it's obvious that you can solve the problem by re-ordering the two productions. In the general case, though, finding things like this is going to be a nightmare, and it's very likely that I'll miss some cases. Ideally, I'd like a way to have Parsec figure out stuff like this for me. Is this possible, or am I simply trying to do too much with the library? The Parsec documentation claims that it can "parse context-sensitive, infinite look-ahead grammars", so it seems like something like I should be able to do something here.

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• Self-describing file format for gigapixel images?

  - by Adam Goode

  In medical imaging, there appears to be two ways of storing huge gigapixel images: Use lots of JPEG images (either packed into files or individually) and cook up some bizarre index format to describe what goes where. Tack on some metadata in some other format. Use TIFF's tile and multi-image support to cleanly store the images as a single file, and provide downsampled versions for zooming speed. Then abuse various TIFF tags to store metadata in non-standard ways. Also, store tiles with overlapping boundaries that must be individually translated later. In both cases, the reader must understand the format well enough to understand how to draw things and read the metadata. Is there a better way to store these images? Is TIFF (or BigTIFF) still the right format for this? Does XMP solve the problem of metadata? The main issues are: Storing images in a way that allows for rapid random access (tiling) Storing downsampled images for rapid zooming (pyramid) Handling cases where tiles are overlapping or sparse (scanners often work by moving a camera over a slide in 2D and capturing only where there is something to image) Storing important metadata, including associated images like a slide's label and thumbnail Support for lossy storage What kind of (hopefully non-proprietary) formats do people use to store large aerial photographs or maps? These images have similar properties.

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• Python Turtle Graphics, how to plot functions over an interval?

  - by TheDragonAce

  I need to plot a function over a specified interval. The function is f1, which is shown below in the code, and the interval is [-7, -3]; [-1, 1]; [3, 7] with a step of .01. When I execute the program, nothing is drawn. Any ideas? import turtle from math import sqrt wn = turtle.Screen() wn.bgcolor("white") wn.title("Plotting") mypen = turtle.Turtle() mypen.shape("classic") mypen.color("black") mypen.speed(10) while True: try: def f1(x): return 2 * sqrt((-abs(abs(x)-1)) * abs(3 - abs(x))/((abs(x)-1)*(3-abs(x)))) * \ (1 + abs(abs(x)-3)/(abs(x)-3))*sqrt(1-(x/7)**2)+(5+0.97*(abs(x-0.5)+abs(x+0.5))-\ 3*(abs(x-0.75)+abs(x+0.75)))*(1+abs(1-abs(x))/(1-abs(x))) mypen.penup() step=.01 startf11=-7 stopf11=-3 startf12=-1 stopf12=1 startf13=3 stopf13=7 def f11 (startf11,stopf11,step): rc=[] y = f1(startf11) while y<=stopf11: rc.append(startf11) #y+=step mypen.setpos(f1(startf11)*25,y*25) mypen.dot() def f12 (startf12,stopf12,step): rc=[] y = f1(startf12) while y<=stopf12: rc.append(startf12) #y+=step mypen.setpos(f1(startf12)*25, y*25) mypen.dot() def f13 (startf13,stopf13,step): rc=[] y = f1(startf13) while y<=stopf13: rc.append(startf13) #y+=step mypen.setpos(f1(startf13)*25, y*25) mypen.dot() f11(startf11,stopf11,step) f12(startf12,stopf12,step) f13(startf13,stopf13,step) except ZeroDivisionError: continue

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