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• Returning large collections from WCF Serivce

  - by Nate Bross

  I'm trying to determine the best approach for building a WCF Service, and the area I'm struggling with most is returning lists of objects. The built-in maxMessageSize of 64k seems pretty high, and I really don't want to bump it up (quick googling finds 100s of places bumping the maxMessageSize up to multi-gigabyte range which seems foolish). But, when I'm returning a collection of objects (~150 items) I am exceeding the default 64k. I'm almost to the point of returning my own class which inherits IEnumerable and has properties for hasNext, hasPrevious and PageSize so that I can implement paging on the client side -- this seems like alot of code. The other option is to jackup the maxMessageSize and hope for the best, but that feels wrong. All other aspects of my service are working great, its just returning large collectiosn where I'm having issues. For background, there are two types of consumers of this service, UI applications which will be primarly web and/or wpf applications, and data processing applications, .NET console apps, and maybe some other non-UI apps. For the UI applications, I would like to keep them responsive and keep the messageSize low, on the console apps it doesn't matter as much as they are just pulling data down to do processing and push it back up to the service.

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• Cant' cast a class with multiple inheritance

  - by Jay S.

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

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• How to generate lots of redundant ajax elements like checkboxes and pulldowns in Django?

  - by iJames

  Hello folks. I've been getting lots of answers from stackoverflow now that I'm in Django just be searching. Now I hope my question will also create some value for everybody. In choosing Django, I was hoping there was some similar mechanism to the way you can do partials in ROR. This was going to help me in two ways. One was in generating repeating indexed forms or form elements, and also in rendering only a piece of the page on the round trip. I've done a little bit of that by using taconite with a simple URL click but now I'm trying to get more advanced. This will focus on the form issue which boils down to how to iterate over a secondary object. If I have a list of photo instances, each of which has a couple of parameters, let's say a size and a quantity. I want to generate form elements for each photo instance separately. But then I have two lists I want to iterate on at the same time. Context: photos : Photo.objects.all() and forms = {} for photo in photos: forms[photo.id] = PhotoForm() In other words we've got a list of photo objects and a dict of forms based on the photo.id. Here's an abstraction of the template: {% for photo in photos %} {% include "photoview.html" %} {% comment %} So here I want to use the photo.id as an index to get the correct form. So that each photo has its own form. I would want to have a different action and each form field would be unique. Is that possible? How can I iterate on that? Thanks! {% endcomment %} Quantity: {{ oi.quantity }} {{ form.quantity }} Dimensions: {{ oi.size }} {{ form.size }} {% endfor %} What can I do about this simple case. And how can I make it where every control is automatically updating the server instead of using a form at all? Thanks! James

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• Rails: generating URLs for actions in JSON response

  - by Chris Butler

  In a view I am generating an HTML canvas of figures based on model data in an app. In the view I am preloading JSON model data in the page like this (to avoid an initial request back): <script type="text/javascript" charset="utf-8"> <% ActiveRecord::Base.include_root_in_json = false -%> var objects = <%= @objects.to_json(:include => :other_objects) %>; ... Based on mouse (or touch) interaction I want to redirect to other parts of my app that are model specific (such as view, edit, delete, etc.). Rather than hard code the URLs in my JavaScript I want to generate them from Rails (which means it always adapts the latest routes). It seems like I have one of three options: Add an empty attr to the model that the controller fills in with the appropriate URL (we don't want to use routes in the model) before the JSON is generated Generate custom JSON where I add the different URLs manually Generate the URL as a template from Rails and replace the IDs in JavaScript as appropriate I am starting to lean towards #1 for ease of implementation and maintainability. Are there any other options that I am missing? Is #1 not the best? Thanks! Chris

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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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• Serializing QGraphicsScene contents

  - by Rob

  I am using the Qt QGraphicsScene class, adding pre-defined items such as QGraphicsRectItem, QGraphicsLineItem, etc. and I want to serialize the scene contents to disk. However, the base QGraphicsItem class (that the other items I use derive from) doesn't support serialization so I need to roll my own code. The problem is that all access to these objects is via a base QGraphicsItem pointer, so the serialization code I have is horrible: QGraphicsScene* scene = new QGraphicsScene; scene->addRect(QRectF(0, 0, 100, 100)); scene->addLine(QLineF(0, 0, 100, 100)); ... QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { if (item->type() == QGraphicsRectItem::Type) { QGraphicsRectItem* rect = qgraphicsitem_cast<QGraphicsRectItem*>(item); // Access QGraphicsRectItem members here } else if (item->type() == QGraphicsLineItem::Type) { QGraphicsLineItem* line = qgraphicsitem_cast<QGraphicsLineItem*>(item); // Access QGraphicsLineItem members here } ... } This is not good code IMHO. So, instead I could create an ABC class like this: class Item { public: virtual void serialize(QDataStream& strm, int version) = 0; }; class Rect : public QGraphicsRectItem, public Item { public: void serialize(QDataStream& strm, int version) { // Serialize this object } ... }; I can then add Rect objects using QGraphicsScene::addItem(new Rect(,,,)); But this doesn't really help me as the following will crash: QList<QGraphicsItem*> list = scene->items(); foreach (QGraphicsItem* item, items) { Item* myitem = reinterpret_class<Item*>(item); myitem->serialize(...) // FAIL } Any way I can make this work?

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• What would be the light way to render a JSP page without an App/Web Server

  - by kolrie

  First, some background: I will have to work on code for a JSP that will demand a lot of code fixing and testing. This JSP will receive a structure of given objects, and render it according to a couple of rules. What I would like to do, is to write a "Test Server" that would read some mock data out of a fixtures file, and mock those objects into a factory that would be used by the JSP in question. The target App Server is WebSphere and I would like to code, change, code in order to test appropriate HTML rendering. I have done something similar on the past, but the JSP part was just calling a method on a rendering object, so I created an Ad Hoc HTTP server that would read the fixture files, parse it and render HTML. All I had to do was run it inside RAD, change the HTML code and hit F5. So question pretty much goes down to: Is there any stand alone library or lightweight server (I thought of Jetty) that would take a JSP, and given the correct contexts (Request, Response, Session, etc.) render the proper HTML?

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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• Which source control paradigm and solution to embed in a custom editor application?

  - by Greg Harman

  I am building an application that manages a number of custom objects, which may be edited concurrently by multiple users (using different instances of the application). These objects have an underlying serialized representation, and my plan is to persist them (through my application UI) in an external source control system. Of course this implies that my application can check the current version of an object for updates, a merging interface for each object, etc. My question is what source control paradigm(s) and specific solution(s) to support and why. The way I (perhaps naively) see the source control world is three general paradigms: Single-repository, locked access (MS SourceSafe) Single-repository, concurrent access (CVS/SVN) Distributed (Mercurial, Git) I haven't heard of anyone using #1 for quite a number of years, so I am planning to disregard this case altogether (unless I get a compelling argument otherwise). However, I'm at a loss as to whether to support #2 or #3, and which specific implementations. I'm concerned that the use paradigms are subtly different enough that I can't adequately capture basic operations in a single UI. The last bit of information I should convey is that this application is intended to be deployed in a commercial setting, where a source control system may already be in use. I would prefer not to support more than one solution unless it's really a deal-breaker, so wide adoption in a corporate setting is a plus.

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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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• 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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• Recursive Iterators

  - by soandos

  I am having some trouble making an iterator that can traverse the following type of data structure. I have a class called Expression, which has one data member, a List<object>. This list can have any number of children, and some of those children might be other Expression objects. I want to traverse this structure, and print out every non-list object (but I do want to print out the elements of the list of course), but before entering a list, I want to return "begin nest" and after I just exited a list, I want to return "end nest". I was able to do this if I ignored the class wherever possible, and just had List<object> objects with List<object> items if I wanted a subExpression, but I would rather do away with this, and instead have an Expressions as the sublists (it would make it easier to do operations on the object. I am aware that I could use extension methods on the List<object> but it would not be appropriate (who wants an Evaluate method on their list that takes no arguments?). The code that I used to generate the origonal iterator (that works) is: public IEnumerator GetEnumerator(){ return theIterator(expr).GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is List<object>)){ yield return " begin nest "; foreach (var item in (List<object>)root){ foreach (var item2 in theIterator(item)){ yield return item2; } } yield return " end nest "; } else yield return root; } A type swap of List<object> for expression did not work, and lead to a stackOverflow error. How should the iterator be implemented? Update: Here is the swapped code: public IEnumerator GetEnumerator() { return this.GetEnumerator(); } private IEnumerable theIterator(object root) { if ((root is Expression)) { yield return " begin nest "; foreach (var item in (Expression)root) { foreach (var item2 in theIterator(item)) yield return item2; } yield return " end nest "; } else yield return root; }

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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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