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  • Task vs. process, is there really any difference?

    - by DASKAjA
    Hi there, I'm studying for my final exams in my CS major on the subject distributed systems and operating systems. I'm in the need for a good definition for the terms task, process and threads. So far I'm confident that a process is the representation of running (or suspended, but initiated) program with its own memory, program counter, registers, stack, etc (process control block). Processes can run threads which share memory, so that communication via shared memory is possible in contrast to processes which have to communicate via IPC. But what's the difference between tasks and process. I often read that they're interchangable and that the term task isn't used anymore. Is that really true?

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  • What is the difference between using $1 vs \1 in Perl regex substitutions?

    - by Mr Foo Bar
    I'm debugging some code and wondered if there is any practical difference between $1 and \1 in Perl regex substitutions For example: my $package_name = "Some::Package::ButNotThis"; $package_name =~ s{^(\w+::\w+)}{$1}; print $package_name; # Some::Package This following line seems functionally equivalent: $package_name =~ s{^(\w+::w+)}{\1}; Are there subtle differences between these two statements? Do they behave differently in different versions of Perl?

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  • Database table design vs. ease of use.

    - by Gastoni
    I have a table with 3 fields: color, fruit, date. I can pick 1 fruit and 1 color, but I can do this only once each day. examples: red, apple, monday red, mango, monday blue, apple, monday blue, mango, monday red, apple, tuesday The two ways in which I could build the table are: 1.- To have color, fruit and date be a composite primary key (PK). This makes it easy to insert data into the table because all the validation needed is done by the database. PK color PK fruit PK date 2.- Have and id column set as PK and then all the other fields. Many say thats the way it should be, because composite PKs are evil. For example, CakePHP does no support them. PK id color fruit date Both have advantages. Which would be the 'better' approach?

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  • For distributed applications, which to use, ASIO vs. MPI?

    - by Rhubarb
    I am a bit confused about this. If you're building a distributed application, which in some cases may perform parallel operations (although not necessarily mathematical), should you use ASIO or something like MPI? I take it MPI is a higher level than ASIO, but it's not clear where in the stack one would begin.

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  • PHP vs JSP Which is should I use/learn for my project?

    - by Jon
    I'm planning on making a fitness planning web application for my senior project at school. However, I don't know anything about either technology and my only experience with web development previously was with python and django. I was wondering what people might recommend to learn, what is most useful to learn for the job market, and what would be best for this project. If it matters, the programming languages I know are, C, C++, Java, and Python. My goal of the project is to learn technologies that will make me a more marketable person. Thanks

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  • NSNotification vs. Delegate Protocols?

    - by jr
    I have an iPhone application which basically is getting information from an API (in XML, but maybe JSON eventually). The result objects are typically displayed in view controllers (tables mainly). Here is the architecture right now. I have NSOperation classes which fetch the different objects from the remote server. Each of these NSOperation classes, will take a custom delegate method which will fire back the resulting objects as they are parsed, and then finally a method when no more results are available. So, the protocol for the delegates will be something like: (void) ObjectTypeResult:(ObjectType *)result; (void) ObjectTypeNoMoreResults; I think the solution works well, but I do end up with a bunch of delegate protocols around and then my view controllers have to implement all these delegate methods. I don't think its that bad, but I'm always on the lookout for a better design. So, I'm thinking about using NSNotifications to remove the use of the delegates. I could include the object in the userInfo part of the notification and just post objects as received, and then a final event when no more are available. Then I could just have one method in each view controller to receive all the data, even when using multiple objects in one controller.† So, can someone share with me some pros/cons of each approach. Should I consider refactoring my code to use Events rather then the delegates? Is one better then the other in certain situations? In my scenario I'm really not looking to receive notifications in multiple places, so maybe the protocol based delegates are the way to go. Thanks!

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  • Implementing a bitfield using java enums

    - by soappatrol
    Hello, I maintain a large document archive and I often use bit fields to record the status of my documents during processing or when validating them. My legacy code simply uses static int constants such as: static int DOCUMENT_STATUS_NO_STATE = 0 static int DOCUMENT_STATUS_OK = 1 static int DOCUMENT_STATUS_NO_TIF_FILE = 2 static int DOCUMENT_STATUS_NO_PDF_FILE = 4 This makes it pretty easy to indicate the state a document is in, by setting the appropriate flags. For example: status = DOCUMENT_STATUS_NO_TIF_FILE | DOCUMENT_STATUS_NO_PDF_FILE; Since the approach of using static constants is bad practice and because I would like to improve the code, I was looking to use Enums to achieve the same. There are a few requirements, one of them being the need to save the status into a database as a numeric type. So there is a need to transform the enumeration constants to a numeric value. Below is my first approach and I wonder if this is the correct way to go about this? class DocumentStatus{ public enum StatusFlag { DOCUMENT_STATUS_NOT_DEFINED(1<<0), DOCUMENT_STATUS_OK(1<<1), DOCUMENT_STATUS_MISSING_TID_DIR(1<<2), DOCUMENT_STATUS_MISSING_TIF_FILE(1<<3), DOCUMENT_STATUS_MISSING_PDF_FILE(1<<4), DOCUMENT_STATUS_MISSING_OCR_FILE(1<<5), DOCUMENT_STATUS_PAGE_COUNT_TIF(1<<6), DOCUMENT_STATUS_PAGE_COUNT_PDF(1<<7), DOCUMENT_STATUS_UNAVAILABLE(1<<8), private final long statusFlagValue; StatusFlag(long statusFlagValue) { this.statusFlagValue = statusFlagValue } public long getStatusFlagValue(){ return statusFlagValue } } /** * Translates a numeric status code into a Set of StatusFlag enums * @param numeric statusValue * @return EnumSet representing a documents status */ public EnumSet<StatusFlag> getStatusFlags(long statusValue) { EnumSet statusFlags = EnumSet.noneOf(StatusFlag.class) StatusFlag.each { statusFlag -> long flagValue = statusFlag.statusFlagValue if ( (flagValue&statusValue ) == flagValue ) { statusFlags.add(statusFlag) } } return statusFlags } /** * Translates a set of StatusFlag enums into a numeric status code * @param Set if statusFlags * @return numeric representation of the document status */ public long getStatusValue(Set<StatusFlag> flags) { long value=0 flags.each { statusFlag -> value|=statusFlag.getStatusFlagValue() } return value } public static void main(String[] args) { DocumentStatus ds = new DocumentStatus(); Set statusFlags = EnumSet.of( StatusFlag.DOCUMENT_STATUS_OK, StatusFlag.DOCUMENT_STATUS_UNAVAILABLE) assert ds.getStatusValue( statusFlags )==258 // 0000.0001|0000.0010 long numericStatusCode = 56 statusFlags = ds.getStatusFlags(numericStatusCode) assert !statusFlags.contains(StatusFlag.DOCUMENT_STATUS_OK) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_TIF_FILE) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_PDF_FILE) assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_OCR_FILE) } }

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  • delphi vs c# post returns different strings - utf problem?

    - by argh
    I'm posting two forms - one in c# and one in delphi. But the result string seems to be different: c# returns: ¤@@1@@@@1@@@@1@@xsm˱Â0Ð... delphi returns: #$1E'@@1@@@@1@@@@1@@x'#$009C... and sice both are compressed streams I'm getting errors while trying to decompress it... The C# is 'correct' - ie. extracts. I'm not an expert on delphi - I just need to convert some piece of code from c# to delphi. c# code: string GetData(Hashtable aParam, string ServerURL) { string Result = ""; WebRequest Request = HttpWebRequest.Create(ServerURL); Request.Method = "POST"; Request.ContentType = "application/x-www-form-urlencoded; charset=UTF-8"; UTF8Encoding encUTF8 = new System.Text.UTF8Encoding(false); StreamWriter writer = new StreamWriter(Request.GetRequestStream(), encUTF8); foreach (DictionaryEntry element in aParam) { writer.Write(element.Key + "=" + element.Value + "&"); } writer.Close(); writer.Dispose(); WebResponse Response = Request.GetResponse(); StreamReader Reader = new StreamReader(Response.GetResponseStream(), System.Text.Encoding.Default); Result = Reader.ReadToEnd(); Reader.Close(); Response.Close(); Reader.Dispose(); return Result; } delphi code: function GetData(aParam:TStringList; ServerURL:string):string; var req: TIdHTTP; res: string; begin req := TIdHTTP.Create(); with req do begin Request.ContentType := 'application/x-www-form-urlencoded; charset=UTF-8'; Request.Method := 'POST'; Request.CharSet := 'utf-8'; Request.AcceptCharSet := 'utf-8'; res := Post(ServerURL, aParam); end; Result := res; req.Free; end; -edit- I'm using delphi 2010

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  • Preprocessor "macro function" vs. function pointer - best practice?

    - by Dustin
    I recently started a small personal project (RGB value to BGR value conversion program) in C, and I realised that a function that converts from RGB to BGR can not only perform the conversion but also the inversion. Obviously that means I don't really need two functions rgb2bgr and bgr2rgb. However, does it matter whether I use a function pointer instead of a macro? For example: int rgb2bgr (const int rgb); /* * Should I do this because it allows the compiler to issue * appropriate error messages using the proper function name, * not to mention possible debugging benefits? */ int (*bgr2rgb) (const int bgr) = rgb2bgr; /* * Or should I do this since it is merely a convenience * and they're really the same function anyway? */ #define bgr2rgb(bgr) (rgb2bgr (bgr)) I'm not necessarily looking for a change in execution efficiency as it's more of a subjective question out of curiosity. I am well aware of the fact that type safety is neither lost nor gained using either method. Would the function pointer merely be a convenience or are there more practical benefits to be gained of which I am unaware?

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  • Prims vs Polys: what are the pros and cons of each?

    - by Richard Inglis
    I've noticed that most 3d gaming/rendering environments represent solids as a mesh of (usually triangular) 3d polygons. However some examples, such as Second Life, or PovRay use solids built from a set of 3d primitives (cube, sphere, cone, torus etc) on which various operations can be performed to create more complex shapes. So my question is: why choose one method over the other for representing 3d data? I can see there might be benefits for complex ray-tracing operations to be able to describe a surface as a single mathematical function (like PovRay does), but SL surely isn't attempting anything so ambitious with their rendering engine. Equally, I can imagine it might be more bandwidth-efficient to serve descriptions of generalised solids instead of arbitrary meshes, but is it really worth the downside that SL suffers from (ie modelling stuff is really hard, and usually the results are ugly) - was this just a bad decision made early in SL's development that they're now stuck with? Or is it an artefact of what's easiest to implement in OpenGL?

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  • Support clicking a link, but sending a POST (vs GET) to the server, without Ajax?

    - by xyld
    I'm thinking this isn't exactly possible, but maybe I'm wrong. I'm simply torn between those who believe that only POST requests should modify data on the server and people that relax the rule and allow GET requests to modify data. Take this situation. Say you have a table, each row is a row in the database. I'd like to allow them to delete the row via a fancy "X" icon as the very last <td></td> element in the row. AFAIK, the only way to send a POST to the server is via a form. But do I really stuff an entire form into the last <td></td> element just to do a POST? Or should I cheat and use an <a href=...></a> tag that sends a GET request? You may be thinking "Do both! Send a POST AND use the <a ...></a> tag! Use fancy javascript + xhr!" And I'll say, oh? And how will that degrade in a zero javascript environment? Maybe we've reached a point when it doesn't make sense to worry about gracefully degrading? I'm not sure. You tell me? I'm new to web development, but I understand most of the concepts involved.

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  • Decorators vs. classes in python web development.

    - by Tristan
    I've noticed three main ways Python web frameworks deal request handing: decorators, controller classes with methods for individual requests, and request classes with methods for GET/POST. I'm curious about the virtues of these three approaches. Are there major advantages or disadvantages to any of these approaches? To fix ideas, here are three examples. Bottle uses decorators: @route('/') def index(): return 'Hello World!' Pylons uses controller classes: class HelloController(BaseController): def index(self): return 'Hello World' Tornado uses request handler classes with methods for types: class MainHandler(tornado.web.RequestHandler): def get(self): self.write("Hello, world") Which style is the best practice?

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  • Not all symbols of an DLL-exported class is exported (VS9)

    - by mandrake
    I'm building a DLL from a group of static libraries and I'm having a problem where only parts of classes are exported. What I'm doing is declaring all symbols I want to export with a preprocessor definition like: #if defined(MYPROJ_BUILD_DLL) //Build as a DLL # define MY_API __declspec(dllexport) #elif defined(MYPROJ_USE_DLL) //Use as a DLL # define MY_API __declspec(dllimport) #else //Build or use as a static lib # define MY_API #endif For example: class MY_API Foo{ ... } I then build static library with MYPROJ_BUILD_DLL & MYPROJ_USE_DLL undefined causing a static library to be built. In another build I create a DLL from these static libraries. So I define MYPROJ_BUILD_DLL causing all symbols I want to export to be attributed with __declspec(dllexport) (this is done by including all static library headers in the DLL-project source file). Ok, so now to the problem. When I use this new DLL I get unresolved externals because not all symbols of a class is exported. For example in a class like this: class MY_API Foo{ public: Foo(char const* ); int bar(); private: Foo( char const*, char const* ); }; Only Foo::Foo( char const*, char const*); and int Foo::bar(); is exported. How can that be? I can understand if the entire class was missing, due to e.g. I forgot to include the header in the DLL-build. But it's only partial missing. Also, say if Foo::Foo( char const*) was not implemented; then the DLL build would have unresolved external errors. But the build is fine (I also double checked for declarations without implementation). Note: The combined size of the static libraries I'm combining is in the region of 30MB, and the resulting DLL is 1.2MB. I'm using Visual Studio 9.0 (2008) to build everything. And Depends to check for exported symbols.

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  • Modules vs. Classes and their influence on descendants of ActiveRecord::Base

    - by Chris
    Here's a Ruby OO head scratcher for ya, brought about by this Rails scenario: class Product < ActiveRecord::Base has_many(:prices) # define private helper methods end module PrintProduct attr_accessor(:isbn) # override methods in ActiveRecord::Base end class Book < Product include PrintProduct end Product is the base class of all products. Books are kept in the products table via STI. The PrintProduct module brings some common behavior and state to descendants of Product. Book is used inside fields_for blocks in views. This works for me, but I found some odd behavior: After form submission, inside my controller, if I call a method on a book that is defined in PrintProduct, and that method calls a helper method defined in Product, which in turn calls the prices method defined by has_many, I'll get an error complaining that Book#prices is not found. Why is that? Book is a direct descendant of Product! More interesting is the following.. As I developed this hierarchy PrintProduct started to become more of an abstract ActiveRecord::Base, so I thought it prudent to redefine everything as such: class Product < ActiveRecord::Base end class PrintProduct < Product end class Book < PrintProduct end All method definitions, etc. are the same. In this case, however, my web form won't load because the attributes defined by attr_accessor (which are "virtual attributes" referenced by the form but not persisted in the DB) aren't found. I'll get an error saying that there is no method Book#isbn. Why is that?? I can't see a reason why the attr_accessor attributes are not found inside my form's fields_for block when PrintProduct is a class, but they are found when PrintProduct is a Module. Any insight would be appreciated. I'm dying to know why these errors are occurring!

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