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• using a database and deploying the application

  - by evan

  I have a WPF application that stores a large amount of information in XML files and as the user uses the application they add more information to the XML files. It's basically using the XML files as a database. Since over the life of the program the XML files have gotten quite large, and I've been think about putting the data on a website, I've been looking into how to move all the information into an SQL database. I've used SQL databases with web applications (PHP, Ruby, and ASP.NET) but never with a Desktop application. Ideally I'd like to be able to keep all the information in one database file and distribute it along with the application without requiring the user to connect to a remote database (so they don't need an internet connection - though eventually it would be nice if could compare the local file's version with one online somewhere and update if necessary) and without making them install a local database server on their computer. Is this possible? I'd also like to use LINQ with any new database solution so switching to a database doesn't force to many changes (I read the XML with LINQ). I'm sure this question has been asked and that there are already some good tutorials on the subject but I just can't find them.

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• How do you get the viewport scale after pinch/zoom on an iPhone web app?

  - by Loktar

  Does anyone know how to get the size in pixels or scale value of the viewport after a user has pinched or double tapped to zoom in/out on a page in JavaScript? I've tried using window.innerWidth but I've had mixed results. Sometimes it seems to accurately give the number of pixels the viewport is showing, however, if I zoom way in on a page and then do a large pinch to zoom back out, window.innerWidth will be around 600-700 even though it is only showing ~200px of the page. The page is only 400px wide and it didn't show the checkered "you've gone too far" background you see when you zoom out beyond the page size. If I do small pinches to zoom in and out, window.innerWidth appears to work just fine. Unfortunately I can't rely on a user only making small pinch gestures :) I've also tried to use the scale property on the gesture event object, but I've found that unreliable because you don't always know the initial scale when you reload the page or use back/forward buttons to navigate to it even when using the meta tag to specify it. Ultimately, I'm trying to make an app that is aware of when a user is trying to zoom out beyond the maximum zoom level so if there is another way to do this I'm interested in hearing about it :) Here's the code I'm using to get the innerWidth: document.body.addEventListener('gestureend', function (evt) { console.log(window.innerWidth); // inaccurate when doing large pinch gestures }, false); Thanks!

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• Unboxing to unknown type

  - by Robert

  I'm trying to figure out syntax that supports unboxing an integral type (short/int/long) to its intrinsic type, when the type itself is unknown. Here is a completely contrived example that demonstrates the concept: // Just a simple container that returns values as objects struct DataStruct { public short ShortVale; public int IntValue; public long LongValue; public object GetBoxedShortValue() { return LongValue; } public object GetBoxedIntValue() { return LongValue; } public object GetBoxedLongValue() { return LongValue; } } static void Main( string[] args ) { DataStruct data; // Initialize data - any value will do data.LongValue = data.IntValue = data.ShortVale = 42; DataStruct newData; // This works if you know the type you are expecting! newData.ShortVale = (short)data.GetBoxedShortValue(); newData.IntValue = (int)data.GetBoxedIntValue(); newData.LongValue = (long)data.GetBoxedLongValue(); // But what about when you don't know? newData.ShortVale = data.GetBoxedShortValue(); // error newData.IntValue = data.GetBoxedIntValue(); // error newData.LongValue = data.GetBoxedLongValue(); // error } In each case, the integral types are consistent, so there should be some form of syntax that says "the object contains a simple type of X, return that as X (even though I don't know what X is)". Because the objects ultimately come from the same source, there really can't be a mismatch (short != long). I apologize for the contrived example, it seemed like the best way to demonstrate the syntax. Thanks.

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• Ruby ROXML - how to get an array to render its xml?

  - by Brian D.

  I'm trying to create a Messages object that inherits Array. The messages will gather a group of Message objects. I'm trying to create an xml output with ROXML that looks like this: <messages> <message> <type></type> <code></code> <body></body> </message> ... </messages> However, I can't figure out how to get the message objects in the Messages object to display in the xml. Here is the code I've been working with: require 'roxml' class Message include ROXML xml_accessor :type xml_accessor :code xml_accessor :body end class Messages < Array include ROXML # I think this is the problem - but how do I tell ROXML that # the messages are in this instance of array? xml_accessor :messages, :as => [Message] def add(message) self << message end end message = Message.new message.type = "error" message.code = "1234" message.body = "This is a test message." messages = Messages.new messages.add message puts messages.length puts messages.to_xml This outputs: 1 <messages/> So, the message object I added to messages isn't getting displayed. Anyone have any ideas? Or am I going about this the wrong way? Thanks for any help.

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• Using fields from an association (has_many) model with formtastic in rails

  - by pduersteler

  I searched and tried a lot, but I can't accomplish it as I want.. so here's my problem. class Moving < ActiveRecord::Base has_many :movingresources, :dependent => :destroy has_many :resources, :through => :movingresources end class Movingresource < ActiveRecord::Base belongs_to :moving belongs_to :resource end class Resource < ActiveRecord::Base has_many :movingresources has_many :movings, :through => :movingresources end Movingresources contains additional fields, like "quantity". We're working on the views for 'bill'. Thanks to formtastic to simplify the whole relationship thing by just writing <%= form.input :workers, :as => :check_boxes %> and i get a real nice checkbox list. But what I haven't found out so far is: How can i use the additional fields from 'movingresource', next or under each checkbox my desired fields from that model? I saw different approaches, mainly with manually looping through an array of objects and creating the appropriate forms, using :for in a form.inputs part, or not. But none of those solutions were clean (e.g. worked for the edit view but not for new because the required objects were not built or generated and generating them caused a mess). I want to know your solutions for this! :-)

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• Javascript function using "this = " gives "Invalid left-hand side in assignment"

  - by Brian M. Hunt

  I am trying to get a Javascript object to use the "this" assignments of another objects' constructor, as well as assume all that objects' prototype functions. Here's an example of what I'm attempting to accomplish: /* The base - contains assignments to 'this', and prototype functions */ function ObjX(a,b) { this.$a = a, $b = b; } ObjX.prototype.getB() { return this.$b; } function ObjY(a,b,c) { // here's what I'm thinking should work: this = ObjX(a, b * 12); /* and by 'work' I mean ObjY should have the following properties: * ObjY.$a == a, ObjY.$b == b * 12, * and ObjY.getB() == ObjX.prototype.getB() * ... unfortunately I get the error: * Uncaught ReferenceError: Invalid left-hand side in assignment */ this.$c = c; // just to further distinguish ObjY from ObjX. } I'd be grateful for your thoughts on how to have ObjY subsume ObjX's assignments to 'this' (i.e. not have to repeat all the this.$* = * assignments in ObjY's constructor) and have ObjY assume ObjX.prototype. My first thought is to try the following: function ObjY(a,b,c) { this.prototype = new ObjX(a,b*12); } Ideally I'd like to learn how to do this in a prototypal way (i.e. not have to use any of those 'classic' OOP substitutes like Base2). It may be noteworthy that ObjY will be anonymous (e.g. factory['ObjX'] = function(a,b,c) { this = ObjX(a,b*12); ... }) -- if I've the terminology right. Thank you.

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• Concurrent WCF calls via shared channel

  - by Kent Boogaart

  I have a web tier that forwards calls onto an application tier. The web tier uses a shared, cached channel to do so. The application tier services in question are stateless and have concurrency enabled. But they are not being called concurrently. If I alter the web tier to create a new channel on every call, then I do get concurrent calls onto the application tier. But I wanted to avoid that cost since it is functionally unnecessary for my scenario. I have no session state, and nor do I need to re-authenticate the caller each time. I understand that the creation of the channel factory is far more expensive than than the creation of the channels, but it is still a cost I'd like to avoid if possible. I found this article on MSDN that states: While channels and clients created by the channels are thread-safe, they might not support writing more than one message to the wire concurrently. If you are sending large messages, particularly if streaming, the send operation might block waiting for another send to complete. Firstly, I'm not sending large messages (just a lot of small ones since I'm doing load testing) but am still seeing the blocking behavior. Secondly, this is rather open-ended and unhelpful documentation. It says they "might not" support writing more than one message but doesn't explain the scenarios under which they would support concurrent messages. Can anyone shed some light on this?

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• smlnj rephrased question for listdir(filename, directoryname)

  - by czy1985

  i am a newbie learning sml and the question i am thrown with involves IO functions that i have no idea how it works even after reading it. Here is the 2 questions that i really need help with to get me started, please provide me with codings and some explaination, i will be able to trial and error with the code given for the other questions. Q1) listdir(filename,directoryname), which given the name of a directory, list its contents in a text file. The listing is in a form that makes it easy to seperate filenames, dates and sizes from each other. (similar to what msdos does with "dir" but instead of just listing it out, it places all the files and details into a text file. Q2) readlist(filename) which reads a list of filenames (each of which were produced by listdir in (Q1) and combines them into one large list. (reads from the text file in Q1 and then assigning the contents into 1 big list containing all the information) Thing is, i only learned from the lecturer in school on the introduction section, there isnt even a system input or output example shown, not even the "use file" function is taught. if anyone that knows sml sees this, please help. Thanks to anyone who took the effort helping me. Thanks for the reply, current I am using SMLNJ to try and do this. Basically, Q1 requires me to list the directory's files of the "directoryname" provided into a text file in "filename". The Q2 requires me to read from the "filename" text file and then place the contents into one large list. Duplicate of: smlnj listdir

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• Fast sketching tools for drawing C/C++ structs, pointers, etc...

  - by tomasorti

  Hi. I would like to know what do you use to sketch relations between different entities in C/C++. This can be a very broad issue, so I'll try to clarify a bit more my question and give an example. I'm looking for something that is simple enough as a user, and let me sketch easily containers, pointers, etc... in an informal way. The aim is to document some structs relations to pass them to junior developers. A look at the drawings is supposed to accelerate the understanding of the code. My solutions at this moment are to use: 1) Paper & pencil. 2) Microsoft PowerPoint/Word Autoshapes. 3) Freeware Dia. Other ones could be: 4) Microsoft Visio, but my company does not own licenses. 5) UML tools. I don't want to go this way. This is what I mean a more formal solution. I know tools like Rational Rose are great, and I tried boUML and violet and they are fine in some parts, but I prefer the flexibility of options 2) or 3). Finally, let me write down a more concrete example: Let's say I what to sketch a map that contains another map as the mapped value, and that one contains a struct as the mapped value, that holds a vector of pointers of a type and a pointer to other type. Also, there exist other structs that hold pointers to the objects pointed by the previous map, so there are objects pointed from different places. This is just one example I have, but you can easily come with one from you experience. What would you use to sketch this example or another similar you have dealt with? Best regards, Tomas.

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• FluentNHibernate mapping of composite foreign keys

  - by Faron

  I have an existing database schema and wish to replace the custom data access code with Fluent.NHibernate. The database schema cannot be changed since it already exists in a shipping product. And it is preferable if the domain objects did not change or only changed minimally. I am having trouble mapping one unusual schema construct illustrated with the following table structure: CREATE TABLE [Container] ( [ContainerId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_Container] PRIMARY KEY ( [ContainerId] ASC ) ) CREATE TABLE [Item] ( [ItemId] [uniqueidentifier] NOT NULL, [ContainerId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_Item] PRIMARY KEY ( [ContainerId] ASC, [ItemId] ASC ) ) CREATE TABLE [Property] ( [ContainerId] [uniqueidentifier] NOT NULL, [PropertyId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_Property] PRIMARY KEY ( [ContainerId] ASC, [PropertyId] ASC ) ) CREATE TABLE [Item_Property] ( [ContainerId] [uniqueidentifier] NOT NULL, [ItemId] [uniqueidentifier] NOT NULL, [PropertyId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_Item_Property] PRIMARY KEY ( [ContainerId] ASC, [ItemId] ASC, [PropertyId] ASC ) ) CREATE TABLE [Container_Property] ( [ContainerId] [uniqueidentifier] NOT NULL, [PropertyId] [uniqueidentifier] NOT NULL, CONSTRAINT [PK_Container_Property] PRIMARY KEY ( [ContainerId] ASC, [PropertyId] ASC ) ) The existing domain model has the following class structure: The Property class contains other members representing the property's name and value. The ContainerProperty and ItemProperty classes have no additional members. They exist only to identify the owner of the Property. The Container and Item classes have methods that return collections of ContainerProperty and ItemProperty respectively. Additionally, the Container class has a method that returns a collection of all of the Property objects in the object graph. My best guess is that this was either a convenience method or a legacy method that was never removed. The business logic mainly works with Item (as the aggregate root) and only works with a Container when adding or removing Items. I have tried several techniques for mapping this but none work so I won't include them here unless someone asks for them. How would you map this?

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• Reducing load time, or making the user think the load time is less

  - by Malfist

  I've been working on a website, and we've managed to reduce the total content for a page load from 13.7MiB's to 2.4, but the page still takes forever to load. It's a joomla site (ick), and it has a lot of redundant DOM elements (2000+ for the home page), and make 60+ HttpRequest's per page load, counting all the css, js, and image requests. Unlike drupal, joomla won't merge them all on the fly, and they have to be kept separate or else the joomla components will go nuts. What can I do to improve load time? Things I've done: Added colors to dom elements that have large images as their background so the color is loaded, then the image Reduced excessively large images to much smaller file sizes Reduced DOM elements to ~2000, from ~5000 Loading CSS at the start of the page, and javascript at the end Not totally possible, joomla injects it's own javascript and css and it does it at the header, always. Minified most javascript Setup caching and gziping on server Uncached size 2.4MB, cached is ~300KB, but even with so many dom elements, the page takes a good bit of time to render. What more can I do to improve the load time?

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• why is OOP hard for me?

  - by netrox

  I have trouble writing OOP in PHP... I understand the concept but I never create classes for my projects... mainly because it's often a small project and nothing complex. But when I read OOP, it seems more difficult to code than writing simple procedural statements. It also seems to take a lot of room as well with so many empty abstract classes and that can be easily lost in the land of objects... it's becoming like a junkyard to me. Also, I noticed that virtually all instructions on how to use OOP use "car" or "cat" or "dog" analogies. Hello... we're not dealing with animals or cars... we're dealing with windows or consoles. You can talk about analogies to death and I will never learn. What I want is see a code that's written to show how objects are created - not, "aCow-moo!" For example, I want to see a browser window object displaying say... three inputs. I want to see an "object" created to output a window with three inputs then I want to see how overriding works, like change the window object to display only two inputs instead of three inputs. I think that would make learning more easy, wouldn't it? Any recommended tutorials of that nature instead of quacks, moos, and woofs.

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• Thoughts on GoGrid vs EC2

  - by Jason

  I am currently hosting my SaaS application at GoGrid (Microsoft stack). Here's what I have: Database Server - physical box, 12 GB RAM, 2 X Quad Core CPU (2.13 GHz Xeon E5506) 2 Web / App servers - cloud servers, 2 GB RAM, 2 VCPUs 300 GB monthly bandwidth I am paying around $900 / month for this. My web / app servers are busting at the seams and need to be upgraded to 4 GB of RAM. I also need a firewall, and GoGrid just added this service for an additional $200. After the upgrade, I will be paying around $1,400. I started looking at Amazon EC2, specifically this config: Database server - "High Memory Double Extra Large Instance" - 34 GB RAM, 13 EC2 compute units 2 Web / App servers - "Large Instance" - 7.5 GB RAM, 4 EC2 compute units If I go with 1 year reserved instances, my upfront cost would be $4,500 and my monthly would be $700. This comes to $1,075 / month when amortized. Amazon also includes a firewall for free. Here are my questions: Do any of you have experience running a database (especially SQL Server) on an EC2 instance? How did it perform compared to a dedicated machine? One of my major concerns is with disk I/O. Amazon's description of a compute unit is fairly vague. Any ideas on how the CPU performance on the database servers would compare? I am hoping that the Amazon solution will provide significantly better performance than my current or even improved GoGrid setup. Having a virtual database server would also be nice in terms of availability. Right now I would be in serious trouble if I had any hardware issues. Thanks for any insight...

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• Py_INCREF/DECREF: When

  - by Izz ad-Din Ruhulessin

  Is one correct in stating the following: If a Python object is created in a C function, but the function doesn't return it, no INCREF is needed, but a DECREF is. [false]If the function does return it, you do need to INCREF, in the function that receives the return value.[/false] When assigning C typed variables as attributes, like double, int etc., to the Python object, no INCREF or DECREF is needed. Assigning Python objects as attributes to your other Python objects goes like this: PyObject *foo; foo = bar // A Python object tmp = self->foo; Py_INCREF(foo); self->foo = foo; Py_XDECREF(tmp); //taken from the manual, but it is unclear if this works in every situation EDIT: -- can I safely use this in every situation? (haven't run into one where it caused me problems) dealloc of a Python object needs to DECREF for every other Python object that it has as an attribute, but not for attributes that are C types. Edit With 'C type as an attribute I mean bar and baz: typedef struct { PyObject_HEAD PyObject *foo; int bar; double baz; } FooBarBaz;

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• Convert date to string upon saving a doctrine record

  - by takteek

  Hi, I'm trying to migrate one of my PHP projects to Doctrine. I've never used it before so there are a few things I don't understand. In my current code, I have a class similar to this: class ScheduleItem { private Date start; //A PEAR Date object. private Date end; public function getStart() { return $this-start; } public function setStart($val) { $this-start = $val; } public function getEnd() { return $this-end; } public function setEnd($val) { $this-end= $val; } } I have a ScheduleItemDAO class with methods like save(), getByID(), etc. When loading from and saving to the database, the DAO class converts the Date objects to and from strings so they can be stored in a timestamp field. In my attempt to move to Doctrine, I created a new class like this: class ScheduleItem extends Doctrine_Record { public function setTableDefinition() { $this-hasColumn('start', 'timestamp'); $this-hasColumn('end', 'timestamp'); } } I had hoped I would be able to use Date objects for the start and end times, and have them converted to strings when they are saved to the database. How can I accomplish this?

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• How can I strip Python logging calls without commenting them out?

  - by cdleary

  Today I was thinking about a Python project I wrote about a year back where I used logging pretty extensively. I remember having to comment out a lot of logging calls in inner-loop-like scenarios (the 90% code) because of the overhead (hotshot indicated it was one of my biggest bottlenecks). I wonder now if there's some canonical way to programmatically strip out logging calls in Python applications without commenting and uncommenting all the time. I'd think you could use inspection/recompilation or bytecode manipulation to do something like this and target only the code objects that are causing bottlenecks. This way, you could add a manipulator as a post-compilation step and use a centralized configuration file, like so: [Leave ERROR and above] my_module.SomeClass.method_with_lots_of_warn_calls [Leave WARN and above] my_module.SomeOtherClass.method_with_lots_of_info_calls [Leave INFO and above] my_module.SomeWeirdClass.method_with_lots_of_debug_calls Of course, you'd want to use it sparingly and probably with per-function granularity -- only for code objects that have shown logging to be a bottleneck. Anybody know of anything like this? Note: There are a few things that make this more difficult to do in a performant manner because of dynamic typing and late binding. For example, any calls to a method named debug may have to be wrapped with an if not isinstance(log, Logger). In any case, I'm assuming all of the minor details can be overcome, either by a gentleman's agreement or some run-time checking. :-)

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• jquery post and get request different on local intranet and live server

  - by nccsbim071

  Hi, I have been developing an asp.net mvc application where i need to make large amounts of jquery post and get request to call controller methods and get back json result. Everything is working fine. The problem is i had to write different jquery post and get request url on local intranet(deployed by making virtual directory) and live server. the current jquery request url is given as below: $.post("/ProjectsChat/GetMessages", { roomId: 24 },.......... now this format of url for jquery request works fine for live server but not for local intranet. Since on local intranet i have made a virtual directory. It only works when i append the name of the virtual directory like this "$.post("MyProjectVirutalDirName/ProjectsChat..................." I am sure most of you must have come across same problem. now i have made a full project, there are large number of jquery requests made, i want to test the application by deploying on local intranet and fix the bugs. Changing all the jquery requests for local intranet doesn't seem feasible solution to me, i am really in a big problem, i can't deploy the same project on live server just like that and test it there, client will kill me. I need some expert advice. Please help Thanks

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• How to organize and manage multiple database credentials in application?

  - by Polaris878

  Okay, so I'm designing a stand-alone web service (using RestLET as my framework). My application is divided in to 3 layers: Data Layer (just above the database, provides APIs for connecting to/querying database, and a database object) Object layer (responsible for serialization from the data layer... provides objects which the client layer can use without worrying about database) Client layer (This layer is the RestLET web service... basically just creates objects from the object layer and fulfills webservice request) Now, for each object I create in the object layer, I want to use different credentials (so I can sandbox each object...). The object layer should not know the exact credentials (IE the login/pw/DB URL etc). What would be the best way to manage this? I'm thinking that I should have a super class Database object in my data layer... and each subclass will contain the required log-in information... this way my object layer can just go Database db = new SubDatabase(); and then continue using that database. On the client level, they would just be able to go ItemCollection items = new ItemCollection(); and have no idea/control over the database that gets connected. I'm asking this because I am trying to make my platform extensible, so that others can easily create services off of my platform. If anyone has any experience with these architectural problems or how to manage this sort of thing I'd appreciate any insight or advice... Feel free to ask questions if this is confusing. Thanks! My platform is Java, the REST framework I'm using is RestLET, my database is MySQL.

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• Partially constructed object / Multi threading

  - by reto

  Heya! I'm using joda due to it's good reputation regarding multi threading. It goes great distances to make multi threaded date handling efficient, for example by making all Date/Time/DateTime objects immutable. But here's a situation where I'm not sure if Joda is really doing the right thing. It probably is correct, but I'd be very interested to see the explanation for it. When a toString() of a DateTime is being called Joda does the following: /* org.joda.time.base.AbstractInstant */ public String toString() { return ISODateTimeFormat.dateTime().print(this); } All formatters are thread safe, as they are as well ready-only. But what's about the formatter-factory: private static DateTimeFormatter dt; /* org.joda.time.format.ISODateTimeFormat */ public static DateTimeFormatter dateTime() { if (dt == null) { dt = new DateTimeFormatterBuilder() .append(date()) .append(tTime()) .toFormatter(); } return dt; } This is a common pattern in single threaded applications. I see the following dangers: Race condition during null check -- worst case: two objects get created. No Problem, as this is solely a helper object (unlike a normal singleton pattern situation), one gets saved in dt, the other is lost and will be garbage collected sooner or later. the static variable might point to a partially constructed object before the objec has been finished initialization (before calling me crazy, read about a similar situation in this Wikipedia article. So how does Joda ensure that not partially created formatter gets published in this static variable? Thanks for your explanations! Reto

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• Events and references pattern

  - by serhio

  In a project I have the following relation between BO and GUI By e.g. G could represent a graphic with time lines, C a TimeLine curve, P - points of that curve and T the time that represents each point. Each GUI object is associated with the BO corresponding object. When T changes GUI P captures the Changed event and changes its location. So, when G should be modified, it modifies internally its objects and as result T changes, P moves and the GuiG visually changes, everything is OK. But there is an inconvenient of this architecture... BO should not be recreated, because this will breack the link between BO and GUIO. In particular, GUI P should always have the same reference of T. If in a business logic I do by e.g. P1.T = new T(this.T + 10) GUI_P1 will not move anymore, because it wait an event from the reference of former P1.T object, that does not belongs to P1 anymore. So the solution was to always modify the existing objects, not to recreate it. But here is an other inconvenient: performance. Say I have a ready newC object that should replace the older one. Instead of doing G1.C = newC I should do foreach T in foreach P in C replace with T from P from newC. Is there an other more optimal way to do it?

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• Thread-safe data structure design

  - by Inso Reiges

  Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of "exists" call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? EDIT: I have a better example. Suppose that element retrieval returns either a reference or a pointer to the stored element and not it's copy. How can a caller be protected to safely use this pointer\reference after the call returns? If you think that not returning copies is a problem, then think about deep copies, i.e. objects that should also copy another objects they point to internally. Thank you.

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• Are there pitfalls to using static class/event as an application message bus

  - by Doug Clutter

  I have a static generic class that helps me move events around with very little overhead: public static class MessageBus<T> where T : EventArgs { public static event EventHandler<T> MessageReceived; public static void SendMessage(object sender, T message) { if (MessageReceived != null) MessageReceived(sender, message); } } To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information: class MyEventArgs : EventArgs { public string Message { get; set; } } Anywhere I'm interested in this event, I just wire up a handler: MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething(); Likewise, triggering the event is just as easy: MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"}); Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class". I have a couple questions: fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects. Are the listening objects being kept "alive" via the MessageReceived event? For instance, perhaps I have this code in a Form.Load event: MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload(); When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes: MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();

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• Implementing list position locator in C++?

  - by jfrazier

  I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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• Is Stream.Write thread-safe?

  - by Mike Spross

  I'm working on a client/server library for a legacy RPC implementation and was running into issues where the client would sometimes hang when waiting to a receive a response message to an RPC request message. It turns out the real problem was in my message framing code (I wasn't handling message boundaries correctly when reading data off the underlying NetworkStream), but it also made me suspicious of the code I was using to send data across the network, specifically in the case where the RPC server sends a large amount of data to a client as the result of a client RPC request. My send code uses a BinaryWriter to write a complete "message" to the underlying NetworkStream. The RPC protocol also implements a heartbeat algorithm, where the RPC server sends out PING messages every 15 seconds. The pings are sent out by a separate thread, so, at least in theory, a ping can be sent while the server is in the middle of streaming a large response back to a client. Suppose I have a Send method as follows, where stream is a NetworkStream: public void Send(Message message) { //Write the message to a temporary stream so we can send it all-at-once MemoryStream tempStream = new MemoryStream(); message.WriteToStream(tempStream); //Write the serialized message to the stream. //The BinaryWriter is a little redundant in this //simplified example, but here because //the production code uses it. byte[] data = tempStream.ToArray(); BinaryWriter bw = new BinaryWriter(stream); bw.Write(data, 0, data.Length); bw.Flush(); } So the question I have is, is the call to bw.Write (and by implication the call to the underlying Stream's Write method) atomic? That is, if a lengthy Write is still in progress on the sending thread, and the heartbeat thread kicks in and sends a PING message, will that thread block until the original Write call finishes, or do I have to add explicit synchronization to the Send method to prevent the two Send calls from clobbering the stream?

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• Is it important to dispose SolidBrush and Pen?

  - by Joe

  I recently came across this VerticalLabel control on CodeProject. I notice that the OnPaint method creates but doesn't dispose Pen and SolidBrush objects. Does this matter, and if so how can I demonstrate whatever problems it can cause? EDIT This isn't a question about the IDisposable pattern in general. I understand that callers should normally call Dispose on any class that implements IDisposable. What I want to know is what problems (if any) can be expected when GDI+ object are not disposed as in the above example. It's clear that, in the linked example, OnPaint may be called many times before the garbage collector kicks in, so there's the potential to run out of handles. However I suspect that GDI+ internally reuses handles in some circumstances (for example if you use a pen of a specific color from the Pens class, it is cached and reused). What I'm trying to understand is whether code like that in the linked example will be able to get away with neglecting to call Dispose. And if not, to see a sample that demonstrated what problems it can cause. I should add that I have very often (including the OnPaint documentation on MSDN) seen WinForms code samples that fail to dispose GDI+ objects.

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