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• Multi-reader IPC solution?

  - by gct

  I'm working on a framework in C++ (just for fun for now), that lets the user write plugins that use a standard API to stream data between each other. There's going to be three basic transport mechanisms for the data: files, sockets, and some kind of IPC piping system. The system is set up so that for the non-file transport, each stream can have multiple readers. IE once a server socket it setup, multiple computers can connect and stream the data. I'm a little stuck at the multi-reader IPC system though. All my plugins run in threads so they live in the same address space, so some kind of shared memory system would work fine, I was thinking I'd write my own circular buffer with a write pointer and read pointers chassing it around the buffer, but I have my doubts that I can achieve the same performance as something like linux pipes. I'm curious what people would suggest for a multi-reader solution to something like this? Is the overhead for pipes or domain sockets low enough that I could just open a connection to each reader and issue separate writes to each reader? This is intended to be significant volumes of data (tens of mega-samples/sec), so performance is a must.

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• In threads, WaitForMultipleObjects never returns if set to INFINITE

  - by AKN

  Let say I have three thread handles HandleList[0] = hThread1; HandleList[1] = hThread2; HandleList[2] = hThread3; /*All the above are of type HANDLE*/ Before closing the application, I want the thread to get its task done. So I want to make app wait till thread completes. So I do, WaitForMultipleObjects(3, HandleList, TRUE, INFINITE ); By this I'm able to make the thread, complete its task. But control never move to next line after the call to WaitForMultileObjects irrespective of all thread completing its task. If I use, some seconds instead of INFINITE, it comes to next line after that many secs, irrspective of whether thread completes its task or not. WaitForMultipleObjects(3, HandleList, TRUE, 10000 ); My problem here is, I'm can't go for seconds, as I may not be sure whether the threads will complete its task with the given time. To list my problem in simple words, I want all my thread to finish the task, before I close my app. How can I achieve it using WaitForMultipleObjects API?

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• Syntax for documenting JSON structure

  - by Roman A. Taycher

  So I'm trying to document the format of the json returned by an api I am writing against and I'd like to know if there is any popular format for the documentation of json structure. Note I'm not trying to to test or validate anything, I'm just using this for documentation. Also some ways to add comments to non-constants(items always returned w/ the same value) would be nice. This the not totally thought out scheme I'm currently using: Plain names refer to identifiers or types. Some types have type-comment Strings that appear to be constant(always returned for that type of request) strings are "str" Constant Numbers would be just the number Constant null is null Booleans are true/false for constant booleans or Boolean otherwise [a,b,c] are lists with 3 items a,b,c [... ...] is a list of repeating elements of some types/constants/patterns {a:A,b:B,c:c} and {... ...} is the same for a dictionary. example: story := [header,footer] header := {"data":realHeader,"kind":"Listing"} realHeader := {"after": null, "before": null, "children": [{"data": realRealHeader, "kind": "t3"}], "modhash": ""} footer := {"data":AlmostComments,"kind":"Listing"} AlmostComments := {"data": {"after": null, "before": null, "children": comments, "modhash": ""}, "kind": "t1"} comments := [...{"data":comment, "kind":"t1"}...] realRealHeader := {"author": string, "clicked": boolean, "created": int, "created_utc": int, "domain": "code.reddit.com", "downs": int, "hidden": boolean, "id": string-id, "is_self": boolean, "levenshtein": null, "likes": null, "media": null, "media_embed": { }, "name": string-id, "num_comments": int, "over_18": false, "permalink": string-urlLinkToStoryStartingFrom/r, "saved": false, "score": int, "selftext": string, "selftext_html": string-html, "subreddit": string-subredditname, "subreddit_id": string-id, "thumbnail": "", "title": string, "ups": int, "url": "http://code.reddit.com/" } comments := { "author": string, "body": string-body_html-wout-html, "body_html": string-html-formated, "created": int, "created_utc": int, "downs": int, "id": string-id, "levenshtein": null, "likes": null, "link_id": string-id, "name": string-id", "parent_id": string-id, "replies": AlmostComments or null, "subreddit": string-subredditname, "subreddit_id": string-id, "ups": int }

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• LLVM: Passing a pointer to a struct, which holds a pointer to a function, to a JIT function

  - by Rusky

  I have an LLVM (version 2.7) module with a function that takes a pointer to a struct. That struct contains a function pointer to a C++ function. The module function is going to be JIT-compiled, and I need to build that struct in C++ using the LLVM API. I can't seem get the pointer to the function as an LLVM value, let alone pass a pointer to the ConstantStruct that I can't build. I'm not sure if I'm even on the track, but this is what I have so far: void print(char*); vector<Constant*> functions; functions.push_back(ConstantExpr::getIntToPtr( ConstantInt::get(Type::getInt32Ty(context), (int)print), /* function pointer type here, FunctionType::get(...) doesn't seem to work */ )); ConstantStruct* struct = cast<ConstantStruct>(ConstantStruct::get( cast<StructType>(m->getTypeByName("printer")), functions )); Function* main = m->getFunction("main"); vector<GenericValue> args; args[0].PointerVal = /* not sure what goes here */ ee->runFunction(main, args);

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• Connect Rails model to non-rails database

  - by the_snitch

  I'm creating a new web application (Rails 3 beta), of which pieces of it will access data from a legacy mysql database that a current php application is using. I do not wish to modify the legacy db schema, I just want to be able to read/write to it, as well as the rails application having it's own database using activerecord for the newer stuff. I'm using mysql for the rails app, so I have the adapter installed. How is the best way to do this? For example, I want contacts to come from the old database. Should I create a contacts controller, and manually call sql to get the variables for the views? Or should I create a Contact model, and define attributes that match the fields in the database, and am I able to use it like Contact.mail_address to have it call "SELECT mailaddr FROM contacts WHERE id=Contact.id". Sorry, I've never done much in Rails outside of the standard stuff that is documented well. I'm not sure of what the best approach would be. Ideally, I want the contacts to be presented to my rails application as native as possible, so that I can expose them RESTfully for API access. Any suggestions and code examples would be much appreciated

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• Simple App Engine Sessions Implementation

  - by raz0r

  Here is a very basic class for handling sessions on App Engine: """Lightweight implementation of cookie-based sessions for Google App Engine. Classes: Session """ import os import random import Cookie from google.appengine.api import memcache _COOKIE_NAME = 'app-sid' _COOKIE_PATH = '/' _SESSION_EXPIRE_TIME = 180 * 60 class Session(object): """Cookie-based session implementation using Memcached.""" def __init__(self): self.sid = None self.key = None self.session = None cookie_str = os.environ.get('HTTP_COOKIE', '') self.cookie = Cookie.SimpleCookie() self.cookie.load(cookie_str) if self.cookie.get(_COOKIE_NAME): self.sid = self.cookie[_COOKIE_NAME].value self.key = 'session-' + self.sid self.session = memcache.get(self.key) if self.session: self._update_memcache() else: self.sid = str(random.random())[5:] + str(random.random())[5:] self.key = 'session-' + self.sid self.session = dict() memcache.add(self.key, self.session, _SESSION_EXPIRE_TIME) self.cookie[_COOKIE_NAME] = self.sid self.cookie[_COOKIE_NAME]['path'] = _COOKIE_PATH print self.cookie def __len__(self): return len(self.session) def __getitem__(self, key): if key in self.session: return self.session[key] raise KeyError(str(key)) def __setitem__(self, key, value): self.session[key] = value self._update_memcache() def __delitem__(self, key): if key in self.session: del self.session[key] self._update_memcache() return None raise KeyError(str(key)) def __contains__(self, item): try: i = self.__getitem__(item) except KeyError: return False return True def _update_memcache(self): memcache.replace(self.key, self.session, _SESSION_EXPIRE_TIME) I would like some advices on how to improve the code for better security. Note: In the production version it will also save a copy of the session in the datastore. Note': I know there are much more complete implementations available online though I would like to learn more about this subject so please don't answer the question with "use that" or "use the other" library.

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• Memory management of objects returned by methods (iOS / Objective-C)

  - by iOSNewb

  I am learning Objective-C and iOS programming through the terrific iTunesU course posted by Stanford (http://www.stanford.edu/class/cs193p/cgi-bin/drupal/) Assignment 2 is to create a calculator with variable buttons. The chain of commands (e.g. 3+x-y) is stored in a NSMutableArray as "anExpression", and then we sub in random values for x and y based on an NSDictionary to get a solution. This part of the assignment is tripping me up: The final two [methods] “convert” anExpression to/from a property list: + (id)propertyListForExpression:(id)anExpression; + (id)expressionForPropertyList:(id)propertyList; You’ll remember from lecture that a property list is just any combination of NSArray, NSDictionary, NSString, NSNumber, etc., so why do we even need this method since anExpression is already a property list? (Since the expressions we build are NSMutableArrays that contain only NSString and NSNumber objects, they are, indeed, already property lists.) Well, because the caller of our API has no idea that anExpression is a property list. That’s an internal implementation detail we have chosen not to expose to callers. Even so, you may think, the implementation of these two methods is easy because anExpression is already a property list so we can just return the argument right back, right? Well, yes and no. The memory management on this one is a bit tricky. We’ll leave it up to you to figure out. Give it your best shot. Obviously, I am missing something with respect to memory management because I don't see why I can't just return the passed arguments right back. Thanks in advance for any answers!

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• How to call IronPython function from C#/F#?

  - by prosseek

  This is kind of follow up questions of http://stackoverflow.com/questions/2969194/integration-of-c-f-ironpython-and-ironruby In order to use C/C++ function from Python, SWIG is the easiest solution. The reverse way is also possible with Python C API, for example, if we have a python function as follows def add(x,y): return (x + 10*y) We can come up with the wrapper in C to use this python as follows. double Add(double a, double b) { PyObject *X, *Y, *pValue, *pArgs; double res; pArgs = PyTuple_New(2); X = Py_BuildValue("d", a); Y = Py_BuildValue("d", b); PyTuple_SetItem(pArgs, 0, X); PyTuple_SetItem(pArgs, 1, Y); pValue = PyEval_CallObject(pFunc, pArgs); res = PyFloat_AsDouble(pValue); Py_DECREF(X); Py_DECREF(Y); Py_DECREF(pArgs); return res; } How about the IronPython/C# or even F#? How to call the C#/F# function from IronPython? Or, is there any SWIG equivalent tool in IronPython/C#? How to call the IronPython function from C#/F#? I guess I could use "engine.CreateScriptSourceFromString" or similar, but I need to find a way to call IronPython function look like a C#/F# function.

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• Why does this tooltip appear *below* a transclucent form?

  - by Daniel Stutzbach

  I have an form with an Opacity less then 1.0. I have a tooltip associated with a label on the form. When I hover the mouse over the label, the tooltip shows up under the form instead of over the form. If I leave the Opacity at its default value of 1.0, the tooltip correctly appears over the form. However, my form is obviously no longer translucent. ;-) I'm testing on an XP system with .NET 3.5. If you don't see this problem on your system, let me know what operating system and version of .NET you have. I have tried manually adjusting the position of the ToolTip with SetWindowPos() and creating a ToolTip "by hand" using CreateWindowEx(), but the problem remains. This makes me suspect its a Win32 API problem, not a problem with the Windows Forms implementation that runs on top of Win32. Why does the tooltip appear under the form, and, more importantly, how can I get it to appear over the form where it should? Here is a minimal program to demonstrate the problem: using System; using System.Windows.Forms; public class Form1 : Form { private ToolTip toolTip1; private Label label1; [STAThread] static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } public Form1() { toolTip1 = new ToolTip(); label1 = new Label(); label1.Location = new System.Drawing.Point(105, 127); label1.Text = "Hover over me"; label1.AutoSize = true; toolTip1.SetToolTip(label1, "This is a moderately long string, " + "designed to be very long so that it will also be quite long."); ClientSize = new System.Drawing.Size(292, 268); Controls.Add(label1); Opacity = 0.8; } }

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• Is there a definitive reference document for Ruby syntax?

  - by JSW

  I'm searching for a definitive document on Ruby syntax. I know about the definitive documents for the core API and standard library, but what about the syntax itself? For instance, such a document should cover: reserved words, string literals syntax, naming rules for variables/classes/modules, all the conditional statements and their permutations, and so forth. I know there are many books and tutorials, yes, but every one of them is essentially a tutorial, each one having a range of different depth and focus. They will all, by necessity of brevity and narrative flow, omit certain details of the language that the author deems insignificant. For instance, did you know that you can use a case statement without an initial case value, and it will then execute the first true when clause? Any given Ruby book or tutorial may or may not cover that particular lesser-known functionality of the case syntax. It's not discussed in the section in "Programming Ruby" about case statements. But that is just one small example. So far the best documentation I've found is the rubyspec project, which appears to be an attempt to write a complete test suite for the language. That's not bad, but it's a bit hard to use from a practical standpoint as a developer working on my own projects. Am I just missing something or is there really no definitive readable document defining the whole of Ruby syntax?

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• Axis2 SOAP Envelope Header Information

  - by BigZig

  I'm consuming a web service that places an authentication token in the SOAP envelope header. It appears (through looking at the samples that came with the WS WSDL) that if the stub is generated in .NET, this header information is exposed through a member variable in the stub class. However, when I generate my Axis2 java stub using WSDL2Java it doesn't appear to be exposed anywhere. What is the correct way to extract this information from the SOAP envelope header? WSDL: http://www.vbar.com/zangelo/SecurityService.wsdl C# Sample: using System; using SignInSample.Security; // web service using SignInSample.Document; // web service namespace SignInSample { class SignInSampleClass { [STAThread] static void Main(string[] args) { // login to the Vault and set up the document service SecurityService secSvc = new SecurityService(); secSvc.Url = "http://localhost/AutodeskDM/Services/SecurityService.asmx"; secSvc.SecurityHeaderValue = new SignInSample.Security.SecurityHeader(); secSvc.SignIn("Administrator", "", "Vault"); DocumentServiceWse docSvc = new DocumentServiceWse(); docSvc.Url = "http://localhost/AutodeskDM/Services/DocumentService.asmx"; docSvc.SecurityHeaderValue = new SignInSample.Document.SecurityHeader(); docSvc.SecurityHeaderValue.Ticket = secSvc.SecurityHeaderValue.Ticket; docSvc.SecurityHeaderValue.UserId = secSvc.SecurityHeaderValue.UserId; } } } The sample illustrates what I'd like to do. Notice how the secSvc instance has a SecurityHeaderValue member variable that is populated after a successful secSvc.SignIn() invocation. Here's some relevant API documentation regarding the SignIn method: Although there is no return value, a successful sign in will populate the SecurityHeaderValue of the security service. The SecurityHeaderValue information is then used for other web service calls.

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• file upload in JSF using myfaces component

  - by prt

  Hi, all i am creating a JSF application where file uploading functionality is required.I have added all the required jar files in my /WEB-INF/lib folder. jsf-api.jar jsf-impl.jar jstl.jar standard.jar myfaces-extensions.jar commons-collections.jar commons-digester.jar commons-beanutils.jar commons-logging.jar commons-fileupload-1.0.jar but still when trying to deploy the application on apache 6.0.29 i am getting the following error. org.apache.catalina.core.StandardContext addApplicationListener INFO: The listener "com.sun.faces.config.ConfigureListener" is already configured for this context. The duplicate definition has been ignored. org.apache.catalina.core.StandardContext start SEVERE: Error listenerStart PM org.apache.catalina.core.StandardContext start SEVERE: Context [/jsfApplication] startup failed due to previous errors org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc The web application [/jsfApplication] registered the JBDC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered. org.apache.catalina.loader.WebappClassLoader clearReferencesThreads SEVERE: The web application [/jsfApplication] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. org.apache.catalina.loader.WebappClassLoader clearReferencesThreads SEVERE: The web application [/jsfApplication] appears to have started a thread named [MySQL Statement Cancellation Timer] but has failed to stop it. This is very likely to create a memory leak. log4j:ERROR LogMananger.repositorySelector was null likely due to error in class reloading, using NOPLoggerRepository. i am using also using hibernate and spring framework for this application. please help. thanks,

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• What are CAD apps written in, and how are they organized ?

  - by ldigas

  What are CAD applications (Rhino, Autocad) of today written in and how are they organized internally ? I gave as an example, Autocad and Rhino, although I would love to hear of other examples as well. I'm particularly interested in knowing what is their backend written in (multilanguage ?) and how is it organized, and how do they handle their frontend (GUI) in real time ? Do they use native windows API's or some libraries of their own, since I imagine, as good as may be, the open source solutions on today's market won't cut it. I may be wrong ... As most of you who have used them know, they handle amongs other things relatively complex rotational operations in realtime (shading is not interesting me). I've been doing some experiments with several packages recently, and for some larger models found that there is considerable difference in speed in, for example, programed rotation (big full ship models) amongst some of them (which I won't name). So I'm wondering about their internals ... Also, if someone knows of some book on the subject, I'd be interested to hear of it.

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• How to limit setAccessible to only "legitimate" uses?

  - by polygenelubricants

  The more I learned about the power of setAccessible, the more astonished I am at what it can do. This is adapted from my answer to the question (Using reflection to change static final File.separatorChar for unit testing). import java.lang.reflect.*; public class EverythingIsTrue { static void setFinalStatic(Field field, Object newValue) throws Exception { field.setAccessible(true); Field modifiersField = Field.class.getDeclaredField("modifiers"); modifiersField.setAccessible(true); modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL); field.set(null, newValue); } public static void main(String args[]) throws Exception { setFinalStatic(Boolean.class.getField("FALSE"), true); System.out.format("Everything is %s", false); // "Everything is true" } } You can do truly outrageous stuff: public class UltimateAnswerToEverything { static Integer[] ultimateAnswer() { Integer[] ret = new Integer[256]; java.util.Arrays.fill(ret, 42); return ret; } public static void main(String args[]) throws Exception { EverythingIsTrue.setFinalStatic( Class.forName("java.lang.Integer$IntegerCache") .getDeclaredField("cache"), ultimateAnswer() ); System.out.format("6 * 9 = %d", 6 * 9); // "6 * 9 = 42" } } Presumably the API designers realize how abusable setAccessible can be, but must have conceded that it has legitimate uses to provide it. So my questions are: What are the truly legitimate uses for setAccessible? Could Java has been designed as to NOT have this need in the first place? What would the negative consequences (if any) of such design be? Can you restrict setAccessible to legitimate uses only? Is it only through SecurityManager? How does it work? Whitelist/blacklist, granularity, etc? Is it common to have to configure it in your applications?

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• How to learn a C++ GUI library effectively?

  - by Chan

  Hello everyone, I have many options for GUI in my head while searching in stackoverflow, but these are what I chose among others: Qt gtkmm GTK+ I used GTK+ couple years ago, and I felt so painful when using C API without string object and containers. I prefer C++ style, I then switched to C++ gtkmm, but the documentation was bad at that time. I found no help when encountering an issue. Now I want to give a hard try for Qt4, but I really want to know how to learn a GUI librarie effectively. With core C++, I usually pick up a problem and try to solve it in different ways using that particular technique, functionality. On the other hand, after skimming through the documentation from Qt site, I don't think this way of studying is applicable, since the GUI classes and APIs are so much bigger. Plus I'm still in school, so I won't have much time to play all the day long with it. How do you guys learn GUI before? Can anyone share some experiences how they learn thing, that would be an invaluable input for me! Best regards, Chan Nguyen

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• Using nHibernate to map two different data models to one entity model

  - by Dan

  I have two different data models that map to the same Car entity. I needed to create a second entity called ParkedCar, which is identical to Car (and therefore inherits from it) in order to stop nhibernate complaining that two mappings exists for the same entity. public class Car { protected Car() { IsParked = false; } public virtual int Id { get; set; } public bool IsParked { get; internal set; } } public class ParkedCar : Car { public ParkedCar() { IsParked = true; } //no additional properties to car, merely exists to support mapping and signify the car is parked } The only issue is that when I come to retrieve a Car from the database using the Criteria API like so: SessionProvider.OpenSession.Session.CreateCriteria<Car>() .Add(Restrictions.Eq("Id", 123)) .List<Car>(); The query brings back Car Entities that are from the ParkedCar data model. Its as if nhibernate defaults to the specialised entity. And the mappings are defiantly looking in the right place: <class name="Car" xmlns="urn:nhibernate-mapping-2.2" table="tblCar"> <class name="ParkedCar" xmlns="urn:nhibernate-mapping-2.2" table="tblParkedCar" > How do I stop this?

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• How do I correct feature envy in this case?

  - by RMorrisey

  I have some code that looks like: class Parent { private Intermediate intermediateContainer; public Intermediate getIntermediate(); } class Intermediate { private Child child; public Child getChild() {...} public void intermediateOp(); } class Child { public void something(); public void somethingElse(); } class Client { private Parent parent; public void something() { parent.getIntermediate().getChild().something(); } public void somethingElse() { parent.getIntermediate().getChild().somethingElse(); } public void intermediate() { parent.getIntermediate().intermediateOp(); } } I understand that is an example of the "feature envy" code smell. The question is, what's the best way to fix it? My first instinct is to put the three methods on parent: parent.something(); parent.somethingElse(); parent.intermediateOp(); ...but I feel like this duplicates code, and clutters the API of the Parent class (which is already rather busy). Do I want to store the result of getIntermediate(), and/or getChild(), and keep my own references to these objects?

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• OpenCV. cvFnName() works, but cv::FunName() doesn't work

  - by Innuendo

  I'm using OpenCV to write a plugin for a simulator. I've made an OpenCV project (single - not a plugin) and it works fine. When I added OpenCV libs to the plugin project, I added all libs required. Visual Studio 2010 doesn't highlight any code line with red. All looks fine and compiles fine. But in execution, the program halts with a Runtime Error on any cv::function. For example: cv::imread, or cv::imwrite. But if I replace them with cvLoadImage() and cvSaveImage(), it works fine. Why does this happen? I don't want to rewrite the whole script in old-api-style (cvFnName). It means I should change all Mat objects to IplImages, and so on. UPDATE: // preparing template ifstream ifile(tmplfilename); if ( !FILE_LOADED && ifile ) { // loading template file Mat tmpl = cv::imread(tmplfilename, 1); // << here occurs error FILE_LOADED = true; } Mat src; Bmp2Mat(hDC, hBitmap, src); TargetDetector detector(src, tmpl); detector.detectTarget(); If I change to: if ( !FILE_LOADED && ifile ) { IplImage* tmpl = 0; tmpl = cvLoadImage(tmplfilename, 1); // no error occurs } And then no error occurs. Early it displayed some Runtime Error. Now, I wanted to copy exact message and it just crashes the application (simulator, what I am pluginning). It displays window error - to kill process or no. (I can't show exact message, because I'm using russian windows now)

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• Suggestions on writing a TCP IP messaging system (Client/Server) using Delphi 2010

  - by Shane

  I would like to write a messaging system using TCP IP in Delphi 2010. I would like to hear what my best options are for using the standard delphi 2010 components/indy components for doing this. I would like to write a server which does the listening and forwarding of messages to all machines on the network running a client. 1.) a.) clients can send a message to server to be forwarded to all other clients b.) clients listen for messages from other senders (via server) and displays messages. 2.) a.) Server can send a message to all clients b.) Server forwards any messages from clients to all other clients thanks for any suggestions NOTE: I am not writing a instant messaging or chat program. This is merely a system where users can send alerts/messages to other users - they can not reply to each other! NO commercial, shareware, etc links - please! I would like to hear about how you would go about writing this type of system and what approachs you would take, and possibly the TCP IP messaging architecture you would use. Whether it be straight Winows API, Indy components, etc, etc.

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• Accessing program information that gdb sees in C++

  - by anon

  I have a program written in C++, on Linux, compiled with -g. When I run it under gdb, I can 1) set breakpoints 2) at those breakpoints, print out variables 3) see the stackframe 4) given a variable that's a structure, print out parts of the structure (i.e. how ddd displays information). Now, given that my program is compiled with "-g" -- is there anyway that I can access this power within my program itself? I.e. given that my program is compiled with "-g", is there some std::vector<string> getStackFrame(); function I can call to get the current stackframe at the current point of execution? Given a pointer to an object and it's type ... can I do std::vector getClassMember(class_name); ? I realize the default answer is "no, C++ doesn't support that level of introspection" -- however, recall I'm on linux, my program is compiled with "-g", and gdb can do it, so clearly the inforamtion is there. Question is: is there some API for accessing it? EDIT: PS Naysers, I'd love to see a reason for closing this question.

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• I don't like Python functions that take two or more iterables. Is it a good idea?

  - by Xavier Ho

  This question came from looking at this question on Stackoverflow. def fringe8((px, py), (x1, y1, x2, y2)): Personally, it's been one of my pet peeves to see a function that takes two arguments with fixed-number iterables (like a tuple) or two or more dictionaries (Like in the Shotgun API). It's just hard to use, because of all the verbosity and double-bracketed enclosures. Wouldn't this be better: >>> class Point(object): ... def __init__(self, x, y): ... self.x = x ... self.y = y ... >>> class Rect(object): ... def __init__(self, x1, y1, x2, y2): ... self.x1 = x1 ... self.y1 = y1 ... self.x2 = x2 ... self.y2 = y2 ... >>> def fringe8(point, rect): ... # ... ... >>> >>> point = Point(2, 2) >>> rect = Rect(1, 1, 3, 3) >>> >>> fringe8(point, rect) Is there a situation where taking two or more iterable arguments is justified? Obviously the standard itertools Python library needs that, but I can't see it being pretty in maintainable, flexible code design.

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• How do i set the Transaction Isolation in EJB?

  - by Nitesh Panchal

  Hello, I am not able to find a way to set TransactionIsolation in ejb. Can anybody tell me how do i set it? I am using persistence. I have looked the following classes : EntityManager , EntityManagerFactory, UserTransaction. None of them seems to have any method like setTransactionIsolation or such. Do we need to change persistence.xml? I just read a book named Mastering EJB 3.0 4th edition. They gave a full 10 page theory about Isolation level that this problems occur and that occurs and such things but at the end they gave this paragraph :- "As we now know, the EJB standard does not deal with isolation levels directly, and rightly so. EJB is a component specification. It defines the behavior and contracts of a business component with clients and middleware infrastructure (containers) such that the component can be rendered as various middleware services properly. EJBs therefore are transactional components that interact with resource managers, such as the JDBC resource manager or JMS resource manager, via JTS, as part of a transaction. They are not, hence, resource components in themselves. Since isolation levels are very specific to the behavior and capabilities of the underlying resources, they should therefore be specified at the resource API levels. " What exactly does it mean? What is meant by resource level APIs? Please help me. If persistence has no way to set Isolation Level then why do they give such huge theory in an EJB book and make it heavy in weight unnecessarily :(

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• Set a datetime for next or previous sunday at specific time

  - by Marc

  I have an app where there is always a current contest (defined by start_date and end_date datetime). I have the following code in the application_controller.rb as a before_filter. def load_contest @contest_last = Contest.last @contest_last.present? ? @contest_leftover = (@contest_last.end_date.utc - Time.now.utc).to_i : @contest_leftover = 0 if @contest_last.nil? Contest.create(:start_date => Time.now.utc, :end_date => Time.now.utc + 10.minutes) elsif @contest_leftover < 0 @winner = Organization.order('votes_count DESC').first @contest_last.update_attributes!(:organization_id => @winner.id, :winner_votes => @winner.votes_count) if @winner.present? Organization.update_all(:votes_count => 0) Contest.create(:start_date => @contest_last.end_date.utc, :end_date => Time.now.utc + 10.minutes) end end My questions: 1) I would like to change the :end_date to something that signifies next Sunday at a certain time (eg. next Sunday at 8pm). Similarly, I could then set the :start_date to to the previous Sunday at a certain time. I saw that there is a sunday() class (http://api.rubyonrails.org/classes/Time.html#method-i-sunday), but not sure how to specify a certain time on that day. 2) For this situation of always wanting the current contest, is there a better way of loading it in the app? Would caching it be better and then reloading if a new one is created? Not sure how this would be done, but seems to be more efficient. Thanks!

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• Automatically restarting Erlang applications

  - by Nick

  I recently ran into a bug where an entire Erlang application died, yielding a log message that looked like this: =INFO REPORT==== 11-Jun-2010::11:07:25 === application: myapp exited: shutdown type: temporary I have no idea what triggered this shutdown, but the real problem I have is that it didn't restart itself. Instead, the now-empty Erlang VM just sat there doing nothing. Now, from the research I've done, it looks like there are other "start types" you can give an application: 'transient' and 'permanent'. If I start a Supervisor within an application, I can tell it to make a particular process transient or permanent, and it will automatically restart it for me. However, according to the documentation, if I make an application transient or permanent, it doesn't restart it when it dies, but rather it kills all the other applications as well. What I really want to do is somehow tell the Erlang VM that a particular application should always be running, and if it goes down, restart it. Is this possible to do? (I'm not talking about implementing a supervisor on top of my application, because then it's a catch 22: what if my supervisor process crashes? I'm looking for some sort of API or setting that I can use to have Erlang monitor and restart my application for me.) Thanks!

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• Function returning a class containing a function returning a class

  - by Scott

  I'm working on an object-oriented Excel add-in to retrieve information from our ERP system's database. Here is an example of a function call: itemDescription = Macola.Item("12345").Description Macola is an instance of a class which takes care of database access. Item() is a function of the Macola class which returns an instance of an ItemMaster class. Description() is a function of the ItemMaster class. This is all working correctly. Items can be be stored in more than one location, so my next step is to do this: quantityOnHand = Macola.Item("12345").Location("A1").QuantityOnHand Location() is a function of the ItemMaster class which returns an instance of the ItemLocation class (well, in theory anyway). QuantityOnHand() is a function of the ItemLocation class. But for some reason, the ItemLocation class is not even being intialized. Public Function Location(inventoryLocation As String) As ItemLocation Set Location = New ItemLocation Location.Item = item_no Location.Code = inventoryLocation End Function In the above sample, the variable item_no is a member variable of the ItemMaster class. Oddly enough, I can successfully instantiate the ItemLocation class outside of the ItemMaster class in a non-class module. Dim test As New ItemLocation test.Item = "12345" test.Code = "A1" quantityOnHand = test.QuantityOnHand Is there some way to make this work the way I want? I'm trying to keep the API as simple as possible. So that it only takes one line of code to retrieve a value.

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