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• Need help running Python app as service in Ubuntu with Upstart

  - by GreeenGuru

  I have written a logging application in Python that is meant to start at boot, but I've been unable to start the app with Ubuntu's Upstart init daemon. When run from the terminal with sudo /usr/local/greeenlog/main.pyw, the application works perfectly. Here is what I've tried for the Upstart job: /etc/init/greeenlog.conf # greeenlog description "I log stuff." start on startup stop on shutdown script exec /usr/local/greeenlog/main.pyw end script My application starts one child thread, in case that is important. I've tried the job with the expect fork stanza without any change in the results. I've also tried this with sudo and without the script statements (just a lone exec statement). In all cases, after boot, running status greeenlog returns greeenlog stop/waiting and running start greeenlog returns: start: Rejected send message, 1 matched rules; type="method_call", sender=":1.61" (uid=1000 pid=2496 comm="start) interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply=0 destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")) Can anyone see what I'm doing wrong? I appreciate any help you can give. Thanks.

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• Why ntp settle time toe long?

  - by fercis

  I simply try to set-up NTP to my system. Both server and clients will run on my computer which are linked together with local link. One of them will have the reference clock. Both the server and Client are linux Ubuntu. I install ntp daemon to both sides. In clients, I enter the ip address of the server to /etc/ntp.conf. Everything works fine. However, the setting of the time to correct time in client side takes too long time (around 17 minutes). Is it possible to gather correct time just at startup. I write some code that regularly calls "ntpdate " by system call and the problem is solved but there has to be something that allows me to decrease the poll time of the client to 1-2 minutes. There are some settings as maxpoll - minpoll in ntp.conf, but I couldn't manage to understand their function, because with the best configuration (minpoll 4? 16 seconds?) I also cannot see that client side corrects its time before 10 minutes. In addition, in some cases my client is an embedded system (ARM - IGEP board) and it always opens with an irrelevant date (2-3 years ago). So the time that takes to correct the time should not depend on the time difference also.

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• Suppressing PostSharp Multicast with Attribute

  - by Dan Bryant

  I've recently started experimenting with PostSharp and I found a particularly helpful aspect to automate implementation of INotifyPropertyChanged. You can see the example here. The basic functionality is excellent (all properties will be notified), but there are cases where I might want to suppress notification. For instance, I might know that a particular property is set once in the constructor and will never change again. As such, there is no need to emit the code for NotifyPropertyChanged. The overhead is minimal when classes are not frequently instantiated and I can prevent the problem by switching from an automatically generated property to a field-backed property and writing to the field. However, as I'm learning this new tool, it would be helpful to know if there is a way to tag a property with an attribute to suppress the code generation. I'd like to be able to do something like this: [NotifyPropertyChanged] public class MyClass { public double SomeValue { get; set; } public double ModifiedValue { get; private set; } [SuppressNotify] public double OnlySetOnce { get; private set; } public MyClass() { OnlySetOnce = 1.0; } }

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• using an alternative string quotation syntax in python

  - by Cawas

  Just wondering... I find using escape characters too distracting. I'd rather do something like this: print ^'Let's begin and end with sets of unlikely 2 chars and bingo!'^ Let's begin and end with sets of unlikely 2 chars and bingo! Note the ' inside the string, and how this syntax would have no issue with it, or whatever else inside for basically all cases. Too bad markdown can't properly colorize it (yet), so I decided to <pre> it. Sure, the ^ could be any other char, I'm not sure what would look/work better. That sounds good enough to me, tho. Probably some other language already have a similar solution. And, just maybe, Python already have such a feature and I overlooked it. I hope this is the case. But if it isn't, would it be too hard to, somehow, change Python's interpreter and be able to select an arbitrary (or even standardized) syntax for notating the strings? I realize there are many ways to change statements and the whole syntax in general by using pre-compilators, but this is far more specific. And going any of those routes is what I call "too hard". I'm not really needing to do this so, again, I'm just wondering.

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• Image resizing - sometimes very poor quality?!

  - by eWolf

  I'm resizing some images to the screen resolution of the user; if the aspect ratio is wrong, the image should be cut. My code looks like this: protected void ConvertToBitmap(string filename) { var origImg = System.Drawing.Image.FromFile(filename); var widthDivisor = (double)origImg.Width / (double)System.Windows.Forms.Screen.PrimaryScreen.Bounds.Width; var heightDivisor = (double)origImg.Height / (double)System.Windows.Forms.Screen.PrimaryScreen.Bounds.Height; int newWidth, newHeight; if (widthDivisor < heightDivisor) { newWidth = (int)((double)origImg.Width / widthDivisor); newHeight = (int)((double)origImg.Height / widthDivisor); } else { newWidth = (int)((double)origImg.Width / heightDivisor); newHeight = (int)((double)origImg.Height / heightDivisor); } var newImg = origImg.GetThumbnailImage(newWidth, newHeight, null, IntPtr.Zero); newImg.Save(this.GetBitmapPath(filename), System.Drawing.Imaging.ImageFormat.Bmp); } In most cases, this works fine. But for some images, the result has an extremely poor quality. It looks like the would have been resized to something very small (thumbnail size) and enlarged again.. But the resolution of the image is correct. What can I do? Example orig image: Example resized image: Note: I have a WPF application but I use the WinForms function for resizing because it's easier and because I already need a reference to System.Windows.Forms for a tray icon.

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• How to find Tomcat's PID and kill it in python?

  - by 4herpsand7derpsago

  Normally, one shuts down Apache Tomcat by running its shutdown.sh script (or batch file). In some cases, such as when Tomcat's web container is hosting a web app that does some crazy things with multi-threading, running shutdown.sh gracefully shuts down some parts of Tomcat (as I can see more available memory returning to the system), but the Tomcat process keeps running. I'm trying to write a simple Python script that: Calls shutdown.sh Runs ps -aef | grep tomcat to find any process with Tomcat referenced If applicable, kills the process with kill -9 <PID> Here's what I've got so far (as a prototype - I'm brand new to Python BTW): #!/usr/bin/python # Imports import sys import subprocess # Load from imported module. if __init__ == "__main__": main() # Main entry point. def main(): # Shutdown Tomcat shutdownCmd = "sh ${TOMCAT_HOME}/bin/shutdown.sh" subprocess.call([shutdownCmd], shell=true) # Check for PID grepCmd = "ps -aef | grep tomcat" grepResults = subprocess.call([grepCmd], shell=true) if(grepResult.length > 1): # Get PID and kill it. pid = ??? killPidCmd = "kill -9 $pid" subprocess.call([killPidCmd], shell=true) # Exit. sys.exit() I'm struggling with the middle part - with obtaining the grep results, checking to see if their size is greater than 1 (since grep always returns a reference to itself, at least 1 result will always be returned, methinks), and then parsing that returned PID and passing it into the killPidCmd. Thanks in advance!

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• Web development: Haskell or Scheme

  - by Robert E. Lester

  I would like to to choose one of these languages for building web applications. I'm not interested in framework per say, but have the following needs: Rapid development. Easy to scale. Strong community for the web. Quick and easy to deploy. I'm very familiar with Haskell, and have some familiarity with scheme (in particular PLT). Scheme appeals to me as good candidate for web development due to it's simple syntax which is homogenous across libraries. I state this despite my subjective opinion that Haskell is a 'cleaner' language. Haskell web apps seem to require learning and building a patchwork of different combinator libraries. On the plus side, I realise this can be quite expressive, although I'd prefer to eliminate impedance mismatches where possible. While scheme-plt looks to be a good fit, I can find but one example of it being used in the "real world". Haskell doesn't seem to fair too much better here, but there seems to be a bigger community behind the web side. Please help me make up my mind. For the most part I'm interested in real-world use cases.

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• questions about name mangling in C++

  - by Tim

  I am trying to learn and understand name mangling in C++. Here are some questions: (1) From devx When a global function is overloaded, the generated mangled name for each overloaded version is unique. Name mangling is also applied to variables. Thus, a local variable and a global variable with the same user-given name still get distinct mangled names. Are there other examples that are using name mangling, besides overloading functions and same-name global and local variables ? (2) From Wiki The need arises where the language allows different entities to be named with the same identifier as long as they occupy a different namespace (where a namespace is typically defined by a module, class, or explicit namespace directive). I don't quite understand why name mangling is only applied to the cases when the identifiers belong to different namespaces, since overloading functions can be in the same namespace and same-name global and local variables can also be in the same space. How to understand this? Do variables with same name but in different scopes also use name mangling? (3) Does C have name mangling? If it does not, how can it deal with the case when some global and local variables have the same name? C does not have overloading functions, right? Thanks and regards!

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• A monkey could do this better - Access to and availability of private member functions in C++

  - by David

  I am wandering the desert of my brain. I'm trying to write something like the following: class MyClass { // Peripherally Related Stuff public: void TakeAnAction(int oneThing, int anotherThing) { switch(oneThing){ case THING_A: TakeThisActionWith(anotherThing); break; //cases THINGS_NOT_A: }; private: void TakeThisActionWith(int thing) { string outcome = new string; outcome = LookUpOutcome(thing); // Do some stuff based on outcome return; } string LookUpOutcome(int key) { string oc = new string; oc = MyPrivateMap[key]; return oc; } map<int, string> MyPrivateMap; Then in the .cc file where I am actually using these things, while compiling the TakeAnAction section, it [CC, the solaris compiler] throws an an error: 'The function LookUpOutcome must have a prototype' and bombs out. In my header file, I have declared 'string LookUpOutcome(int key);' in the private section of the class. I have tried all sorts of variations. I tried to use 'this' for a little while, and it gave me 'Can only use this in non-static member function.' Sadly, I haven't declared anything static and these are all, putatively, member functions. I tried it [on TakeAnAction and LookUp] when I got the error, but I got something like, 'Can't access MyPrivateMap from LookUp'. MyPrivateMap could be made public and I could refer to it directly, I guess, but my sensibility says that is not the right way to go about this [that means that namespace scoped helper functions are out, I think]. I also guess I could just inline the lookup and subsequent other stuff, but my line-o-meter goes on tilt. I'm trying desperately not to kludge it.

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• Is extending a base class with non-virtual destructor dangerous in C++

  - by Akusete

  Take the following code class A { }; class B : public A { }; class C : public A { int x; }; int main (int argc, char** argv) { A* b = new B(); A* c = new C(); //in both cases, only ~A() is called, not ~B() or ~C() delete b; //is this ok? delete c; //does this line leak memory? return 0; } when calling delete on a class with a non-virtual destructor with member functions (like class C), can the memory allocator tell what the proper size of the object is? If not, is memory leaked? Secondly, if the class has no member functions, and no explicit destructor behaviour (like class B), is everything ok? I ask this because I wanted to create a class to extend std::string, (which I know is not recommended, but for the sake of the discussion just bear with it), and overload the +=,+ operator. -Weffc++ gives me a warning because std::string has a non virtual destructor, but does it matter if the sub-class has no members and does not need to do anything in its destructor? -- FYI the += overload was to do proper file path formatting, so the path class could be used like class path : public std::string { //... overload, +=, + //... add last_path_component, remove_path_component, ext, etc... }; path foo = "/some/file/path"; foo = foo + "filename.txt"; //and so on... I just wanted to make sure someone doing this path* foo = new path(); std::string* bar = foo; delete bar; would not cause any problems with memory allocation

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• JUnit Test method with randomized nature

  - by Peter

  Hey, I'm working on a small project for myself at the moment and I'm using it as an opportunity to get acquainted with unit testing and maintaining proper documentation. I have a Deck class with represents a deck of cards (it's very simple and, to be honest, I can be sure that it works without a unit test, but like I said I'm getting used to using unit tests) and it has a shuffle() method which changes the order of the cards in the deck. The implementation is very simple and will certainly work: public void shuffle() { Collections.shuffle(this.cards); } But, how could I implement a unit test for this method. My first thought was to check if the top card of the deck was different after calling shuffle() but there is of course the possibility that it would be the same. My second thought was to check if the entire order of cards has changed, but again they could possibly be in the same order. So, how could I write a test that ensures this method works in all cases? And, in general, how can you unit test methods for which the outcome depends on some randomness? Cheers, Pete

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• Different Scala Actor Implementations Overview

  - by Stefan K.

  I'm trying to find the 'right' actor implementation for my thesis. I realized there is a bunch of them and it's a bit confusing to pick one. Personally I'm especially interested in remote actors, but I guess a complete overview would be helpful to many others. This is a pretty general question, so feel free to answer just for the implementation you know about. I know about the following Scala Actor implementations (SAI). Please add the missing ones. Scala 2.7 (difference to) Scala 2.8 Akka (http://www.akkasource.org/) Lift (http://liftweb.net/) Scalaz (http://code.google.com/p/scalaz/) What are the target use-cases for these SAIs (lightweight vs. "heavy" enterprise framework)? do they support remote actors? What shortcomings do remote actors have in the SAIs? How is their performace? How active is there community? How easy are they to get started? How good is the documentation? How easy are they to extend? How stable are they? Which projects are using them? What are their shortcomings? What are their design principles? Are they thread based or event based (receive/ react) or both? Nested receiveS hotswapping the Actor’s message loop

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• With a browser, how do I know which decimal separator does the client use?

  - by Quassnoi

  I'm developing a web application. I need to display some decimal data correctly so that it can be copied and pasted into a certain GUI application that is not under my control. The GUI application is locale sensitive and it accepts only the correct decimal separator which is set in the system. I can guess the decimal separator from Accept-Language and the guess will be correct in 95% cases, but sometimes it fails. Is there any way to do it on server side (preferably, so that I can collect statistics), or on client side? Update: The whole point of the task is doing it automatically. In fact, this webapp is a kind of online interface to a legacy GUI which helps to fill the forms correctly. The kind of users that use it mostly have no idea on what a decimal separator is. The Accept-Language solution is implemented and works, but I'd like to improve it. Update2: I need to retrive a very specific setting: decimal separator set in Control Panel / Regional and Language Options / Regional Options / Customize. I deal with four kinds of operating systems: Russian Windows with a comma as a DS (80%). English Windows with a period as a DS (15%). Russian Windows with a period as a DS to make poorly written English applications work (4%). English Windows with a comma as a DS to make poorly written Russian applications work (1%). All 100% of clients are in Russia and the legacy application deals with Russian goverment-issued forms, so asking for a country will yield 100% of Russian Federation, and GeoIP will yield 80% of Russian Federation and 20% of other, incorrect answers.

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• Rails running multiple delayed_job - lock tables

  - by pepernik

  Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

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• Are document-oriented databases any more suitable than relational ones for persisting objects?

  - by Owen Fraser-Green

  In terms of database usage, the last decade was the age of the ORM with hundreds competing to persist our object graphs in plain old-fashioned RMDBS. Now we seem to be witnessing the coming of age of document-oriented databases. These databases are highly optimized for schema-free documents but are also very attractive for their ability to scale out and query a cluster in parallel. Document-oriented databases also hold a couple of advantages over RDBMS's for persisting data models in object-oriented designs. As the tables are schema-free, one can store objects belonging to different classes in an inheritance hierarchy side-by-side. Also, as the domain model changes, so long as the code can cope with getting back objects from an old version of the domain classes, one can avoid having to migrate the whole database at every change. On the other hand, the performance benefits of document-oriented databases mainly appear to come about when storing deeper documents. In object-oriented terms, classes which are composed of other classes, for example, a blog post and its comments. In most of the examples of this I can come up with though, such as the blog one, the gain in read access would appear to be offset by the penalty in having to write the whole blog post "document" every time a new comment is added. It looks to me as though document-oriented databases can bring significant benefits to object-oriented systems if one takes extreme care to organize the objects in deep graphs optimized for the way the data will be read and written but this means knowing the use cases up front. In the real world, we often don't know until we actually have a live implementation we can profile. So is the case of relational vs. document-oriented databases one of swings and roundabouts? I'm interested in people's opinions and advice, in particular if anyone has built any significant applications on a document-oriented database.

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• how to conditional display a control in asp wizard based on the radiobutton click in a particular st

  - by Pramod

  Hi, I've been stuck with this problem where there are 3 steps in an asp wizard control. The first step has a radiobutton (yes and no) and based on the radio button input chosen by the user, i would need to hide or show a label in the second wizardstep. Example: Step 1: Choose 1 among the two options: Yes No (radStep1) Step 2: if the radiobutton option in the previous step was yes.. then display a label(lblStep2) in this step.. Else hide the label. I've been handling this through the jquery as i want the functionality in the aspx page itself... The jquery code goes like this... $("#<%=radStep1.ClientID %> input").click(function() { if($("#<%= radStep1.ClientID %> input").index(this) == 0) { $("#<%=lblStep2.ClientID %>").show(); } else if($("#<%= radStep1.ClientID %> input").index(this) == 1) { $("#<%=lblStep2.ClientID %>").hide(); } However, in both the cases, the label is getting displayed.. Could you please help me out if there is anything that i'm missing? I'm guessing that the label is getting hidden at first and then getting shown again once i click on the next button... Thanks a ton in advance....

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• Does SetFileBandwidthReservation affect memory-mapped file performance?

  - by Ghostrider

  Does this function affect Memory-mapped file performance? Here's the problem I need to solve: I have two applications competing for disk access: "reader" and "updater". Whole system runs on Windows Server 2008 R2 x64 "Updater" constantly accesses disk in a linear manner, updating data. They system is set up in such a way that updater always has infinite data to update. Consider that it is constantly approximating a solution of a huge set of equations that takes up entire 2TB disk drive. Updater uses ReadFile and WriteFile to process data in a linear fashion. "Reader" is occasionally invoked by user to get some pieces of data. Usually user would read several 4kb blocks from the drive and stop. Occasionally user needs to read up to 100mb sequentially. In exceptional cases up to several gigabytes. Reader maps files to memory to get data it needs. What I would like to achieve is for "reader" to have absolute priority so that "updater" would completely stop if needed so that "reader" could get the data user needs ASAP. Is this problem solvable by using SetPriorityClass and SetFileBandwidthReservation calls? I would really hate to put synchronization login in "reader" and "updater" and rather have the OS take care of priorities.

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• m2eclipse: How to set Eclipse project settings when importing a maven project?

  - by Marius Andreiana

  Using m2eclipse Eclipse plugin, everybody on the dev team should be able to checkout source code, import Maven project in Eclipse and be good to go. I saw m2eclipse is being merged into Eclipse 3.7, and maven-eclipse-plugin won't be maintained any longer, so I'm looking for a m2eclipse-based solution (without running "mvn eclipse:clean eclipse:eclipse" before project import, which is what maven-eclipse-plugin does). maven-eclipse-plugin allows this in pom.xml <additionalConfig> <file> <name>.settings/com.google.gdt.eclipse.core.prefs</name> <content><![CDATA[ eclipse.preferences.version=2 jarsExcludedFromWebInfLib= warSrcDir=${project.build.directory}/${project.build.finalName} warSrcDirIsOutput=true ]]> </content> </file> The more general question is How would m2eclipse do something similar? For some cases, just saving the eclipse .settings/prefs file works (e.g. org.eclipse.jdt.ui.prefs), but in this case, com.google.gdt.eclipse.core.prefs is always overwritten on m2eclipse project import. A specific question is asked here, with no reply. Thanks! UPDATE: Not possible now, see request

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• When software problems reported are not really software problems

  - by AndyUK

  Hi Apologies if this has already been covered or you think it really belongs on wiki. I am a software developer at a company that manufactures microarray printing machines for the biosciences industry. I am primarily involved in interfacing with various bits of hardware (pneumatics, hydraulics, stepper motors, sensors etc) via GUI development in C++ to aspirate and print samples onto microarray slides. On joining the company I noticed that whenever there was a hardware-related problem this would cause the whole setup to freeze, with nobody being any the wiser as to what the specific problem was - hardware / software / misuse etc. Since then I have improved things somewhat by introducing software timeouts and exception handling to better identify and deal with any hardware-related problems that arise eg PLC commands not successfully completed, inappropriate FPGA response commands, and various other deadlock type conditions etc. In addition, the software will now log a summary of the specific problem, inform the user and exit the thread gracefully. This software is not embedded, just interfacing using serial ports. In spite of what has been achieved, non-software guys still do not fully appreciate that in these cases, the 'software' problem they are reporting to me is not really a software problem, rather the software is reporting a problem, but not causing it. Don't get me wrong, there is nothing I enjoy more than to come down on software bugs like a ton of bricks, and looking at ways of improving robustness in any way. I know the system well enough now that I almost have a sixth sense for these things. No matter how many times I try to explain this point to people, it does not really penetrate. They still report what are essentially hardware problems (which eventually get fixed) as software ones. I would like to hear from any others that have endured similar finger-pointing experiences and what methods they used to deal with them.

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• Cant' cast a class with multiple inheritance

  - by Jay S.

  I am trying to refactor some code while leaving existing functionality in tact. I'm having trouble casting a pointer to an object into a base interface and then getting the derived class out later. The program uses a factory object to create instances of these objects in certain cases. Here are some examples of the classes I'm working with. // This is the one I'm working with now that is causing all the trouble. // Some, but not all methods in NewAbstract and OldAbstract overlap, so I // used virtual inheritance. class MyObject : virtual public NewAbstract, virtual public OldAbstract { ... } // This is what it looked like before class MyObject : public OldAbstract { ... } // This is an example of most other classes that use the base interface class NormalObject : public ISerializable // The two abstract classes. They inherit from the same object. class NewAbstract : public ISerializable { ... } class OldAbstract : public ISerializable { ... } // A factory object used to create instances of ISerializable objects. template<class T> class Factory { public: ... virtual ISerializable* createObject() const { return static_cast<ISerializable*>(new T()); // current factory code } ... } This question has good information on what the different types of casting do, but it's not helping me figure out this situation. Using static_cast and regular casting give me error C2594: 'static_cast': ambiguous conversions from 'MyObject *' to 'ISerializable *'. Using dynamic_cast causes createObject() to return NULL. The NormalObject style classes and the old version of MyObject work with the existing static_cast in the factory. Is there a way to make this cast work? It seems like it should be possible.

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• Overlapping template partial specialization when wanting an "override" case: how to avoid the error?

  - by user173342

  I'm dealing with a pretty simple template struct that has an enum value set by whether its 2 template parameters are the same type or not. template<typename T, typename U> struct is_same { enum { value = 0 }; }; template<typename T> struct is_same<T, T> { enum { value = 1 }; }; This is part of a library (Eigen), so I can't alter this design without breaking it. When value == 0, a static assert aborts compilation. So I have a special numerical templated class SpecialCase that can do ops with different specializations of itself. So I set up an override like this: template<typename T> struct SpecialCase { ... }; template<typename LT, typename RT> struct is_same<SpecialCase<LT>, SpecialCase<RT>> { enum { value = 1 }; }; However, this throws the error: more than one partial specialization matches the template argument list Now, I understand why. It's the case where LT == RT, which steps on the toes of is_same<T, T>. What I don't know is how to keep my SpecialCase override and get rid of the error. Is there a trick to get around this? edit: To clarify, I need all cases where LT != RT to also be considered the same (have value 1). Not just LT == RT.

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• Inner join on 2 arrays?

  - by russ

  I'm trying to find a solution to the following (I'm thinking with Linq) to the following: I need to pull down certain files from a larger list of files on an ftp server that have a similar file name. For example, we send an order file to some company for processing then they return a response file that we can download. So, I could send them the files "order_123.txt" and "order_456.txt". After a certain amount of time I need to go look for and download the responses for those files that will be named "order_123.resp" and "order_456.resp". The kicker is that in some cases I can have multiple responses in which case they would create "order_123-1.resp" and "order_123-2.resp" and also the files don't get removed from the server. I know this can be accomplished by looping through the files I know I need responses to then loop through all the files on the server until I find files that match but I'm hoping that I don't have to loop through the files on the server more than once. This example may help clarify: I've sent "order_222.txt" and "order_333.txt" they processed them and the ftp server contains: "order_111-1.resp" "order_001.resp" "order_222-1.resp" "order_222-2.resp" "order_333.resp" I need to download the 3rd, 4th, and 5th file. Thanks.

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• Prototypal inheritance should save memory, right?

  - by Techpriester

  Hi Folks, I've been wondering: Using prototypes in JavaScript should be more memory efficient than attaching every member of an object directly to it for the following reasons: The prototype is just one single object. The instances hold only references to their prototype. Versus: Every instance holds a copy of all the members and methods that are defined by the constructor. I started a little experiment with this: var TestObjectFat = function() { this.number = 42; this.text = randomString(1000); } var TestObjectThin = function() { this.number = 42; } TestObjectThin.prototype.text = randomString(1000); randomString(x) just produces a, well, random String of length x. I then instantiated the objects in large quantities like this: var arr = new Array(); for (var i = 0; i < 1000; i++) { arr.push(new TestObjectFat()); // or new TestObjectThin() } ... and checked the memory usage of the browser process (Google Chrome). I know, that's not very exact... However, in both cases the memory usage went up significantly as expected (about 30MB for TestObjectFat), but the prototype variant used not much less memory (about 26MB for TestObjectThin). I also checked: The TestObjectThin instances contain the same string in their "text" property, so they are really using the property of the prototype. Now, I'm not so sure what to think about this. The prototyping doesn't seem to be the big memory saver at all. I know that prototyping is a great idea for many other reasons, but I'm specifically concerned with memory usage here. Any explanations why the prototype variant uses almost the same amount of memory? Am I missing something?

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• Accelerometer gravity components

  - by Dvd

  Hi, I know this question is definitely solved somewhere many times already, please enlighten me if you know of their existence, thanks. Quick rundown: I want to compute from a 3 axis accelerometer the gravity component on each of these 3 axes. I have used 2 axes free body diagrams to work out the accelerometer's gravity component in the world X-Z, Y-Z and X-Y axes. But the solution seems slightly off, it's acceptable for extreme cases when only 1 accelerometer axis is exposed to gravity, but for a pitch and roll of both 45 degrees, the combined total magnitude is greater than gravity (obtained by Xa^2+Ya^2+Za^2=g^2; Xa, Ya and Za are accelerometer readings in its X, Y and Z axis). More detail: The device is a Nexus One, and have a magnetic field sensor for azimuth, pitch and roll in addition to the 3-axis accelerometer. In the world's axis (with Z in the same direction as gravity, and either X or Y points to the north pole, don't think this matters much?), I assumed my device has a pitch (P) on the Y-Z axis, and a roll (R) on the X-Z axis. With that I used simple trig to get: Sin(R)=Ax/Gxz Cos(R)=Az/Gxz Tan(R)=Ax/Az There is another set for pitch, P. Now I defined gravity to have 3 components in the world's axis, a Gxz that is measurable only in the X-Z axis, a Gyz for Y-Z, and a Gxy for X-Y axis. Gxz^2+Gyz^2+Gxy^2=2*G^2 the 2G is because gravity is effectively included twice in this definition. Oh and the X-Y axis produce something more exotic... I'll explain if required later. From these equations I obtained a formula for Az, and removed the tan operations because I don't know how to handle tan90 calculations (it's infinity?). So my question is, anyone know whether I did this right/wrong or able to point me to the right direction? Thanks! Dvd

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• C standard addressing simplification inconsistency

  - by Chris Lutz

  Section §6.5.3.2 "Address and indirection operators" ¶3 says (relevant section only): The unary & operator returns the address of its operand. ... If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. ... This means that this: int *i = NULL; printf("%p", (void *) (&*i) ); printf("%p", (void *) (&i[10]) ); Should be perfectly legal, printing the null pointer (probably 0) and the null pointer plus 10 (probably 10). The standard seems very clear that both of those cases are required to be optimized. However, it doesn't seem to require the following to be optimized: struct { int a; short b; } *s = 0; printf("%p", (void *) (&s->b) ); This seems awfully inconsistent. I can see no reason that the above code shouldn't print the null pointer plus sizeof(int) (possibly 4). Simplifying a &-> expression is going to be the same conceptually (IMHO) as &[], a simple address-plus-offset. It's even an offset that's going to be determinable at compile time, rather than potentially runtime with the [] operator. Is there anything in the rationale about why this is so seemingly inconsistent?

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