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• Is the design notion of layers contrived?

  - by Bruce

  Hi all I'm reading through Eric Evans' awesome work, Domain-Driven Design. However, I can't help feeling that the 'layers' model is contrived. To expand on that statement, it seems as if it tries to shoe-horn various concepts into a specific, neat model, that of layers talking to each other. It seems to me that the layers model is too simplified to actually capture the way that (good) software works. To expand further: Evans says: "Partition a complex program into layers. Develop a design within each layer that is cohesive and that depends only on the layers below. Follow standard architectural patterns to provide loose coupling to the layers above." Maybe I'm misunderstanding what 'depends' means, but as far as I can see, it can either mean a) Class X (in the UI for example) has a reference to a concrete class Y (in the main application) or b) Class X has a reference to a class Y-ish object providing class Y-ish services (ie a reference held as an interface). If it means (a), then this is clearly a bad thing, since it defeats re-using the UI as a front-end to some other application that provides Y-ish functionality. But if it means (b), then how is the UI any more dependent on the application, than the application is dependent on the UI? Both are decoupled from each other as much as they can be while still talking to each other. Evans' layer model of dependencies going one way seems too neat. First, isn't it more accurate to say that each area of the design provides a module that is pretty much an island to itself, and that ideally all communication is through interfaces, in a contract-driven/responsibility-driven paradigm? (ie, the 'dependency only on lower layers' is contrived). Likewise with the domain layer talking to the database - the domain layer is as decoupled (through DAO etc) from the database as the database is from the domain layer. Neither is dependent on the other, both can be swapped out. Second, the idea of a conceptual straight line (as in from one layer to the next) is artificial - isn't there more a network of intercommunicating but separate modules, including external services, utility services and so on, branching off at different angles? Thanks all - hoping that your responses can clarify my understanding on this..

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• XML Parsing Error - C#

  - by Indebi

  My code is having an XML parsing error at line 7 position 32 and I'm not really sure why Exact Error Dump 5/1/2010 10:21:42 AM System.Xml.XmlException: An error occurred while parsing EntityName. Line 7, position 32. at System.Xml.XmlTextReaderImpl.Throw(Exception e) at System.Xml.XmlTextReaderImpl.Throw(String res, Int32 lineNo, Int32 linePos) at System.Xml.XmlTextReaderImpl.HandleEntityReference(Boolean isInAttributeValue, EntityExpandType expandType, Int32& charRefEndPos) at System.Xml.XmlTextReaderImpl.ParseAttributeValueSlow(Int32 curPos, Char quoteChar, NodeData attr) at System.Xml.XmlTextReaderImpl.ParseAttributes() at System.Xml.XmlTextReaderImpl.ParseElement() at System.Xml.XmlTextReaderImpl.ParseElementContent() at System.Xml.XmlTextReaderImpl.Read() at System.Xml.XmlLoader.LoadNode(Boolean skipOverWhitespace) at System.Xml.XmlLoader.LoadDocSequence(XmlDocument parentDoc) at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace) at System.Xml.XmlDocument.Load(XmlReader reader) at System.Xml.XmlDocument.Load(String filename) at Lookoa.LoadingPackages.LoadingPackages_Load(Object sender, EventArgs e) in C:\Users\Administrator\Documents\Visual Studio 2010\Projects\Lookoa\Lookoa\LoadingPackages.cs:line 30 Xml File, please note this is just a sample because I want the program to work before I begin to fill this repository <repo> <Packages> <TheFirstPackage id="00001" longname="Mozilla Firefox" appver="3.6.3" pkgver="0.01" description="Mozilla Firefox is a free and open source web browser descended from the Mozilla Application Suite and managed by Mozilla Corporation. A Net Applications statistic put Firefox at 24.52% of the recorded usage share of web browsers as of March 2010[update], making it the second most popular browser in terms of current use worldwide after Microsoft's Internet Explorer." cat="WWW" rlsdate="4/8/10" pkgloc="http://google.com"/> </Packages> <categories> <WWW longname="World Wide Web" description="Software that's focus is communication or primarily uses the web for any particular reason."> </WWW> <Fun longname="Entertainment & Other" description="Music Players, Video Players, Games, or anything that doesn't fit in any of the other categories."> </Fun> <Work longname="Productivity" description="Application's commonly used for occupational needs or, stuff you work on"> </Work> <Advanced longname="System & Security" description="Applications that protect the computer from malware, clean the computer, and other utilities."> </Advanced> </categories> </repo> Small part of C# Code //Loading the Package and Category lists //The info from them is gonna populate the listboxes for Category and Packages Repository.Load("repo.info"); XmlNodeList Categories = Repository.GetElementsByTagName("categories"); foreach (XmlNode Category in Categories) { CategoryNumber++; CategoryNames[CategoryNumber] = Category.Name; MessageBox.Show(CategoryNames[CategoryNumber]); } The Messagebox.Show() is just to make sure it's getting the correct results

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• What is the best workaround for the WCF client `using` block issue?

  - by Eric King

  I like instantiating my WCF service clients within a using block as it's pretty much the standard way to use resources that implement IDisposable: using (var client = new SomeWCFServiceClient()) { //Do something with the client } But, as noted in this MSDN article, wrapping a WCF client in a using block could mask any errors that result in the client being left in a faulted state (like a timeout or communication problem). Long story short, when Dispose() is called, the client's Close() method fires, but throws and error because it's in a faulted state. The original exception is then masked by the second exception. Not good. The suggested workaround in the MSDN article is to completely avoid using a using block, and to instead instantiate your clients and use them something like this: try { ... client.Close(); } catch (CommunicationException e) { ... client.Abort(); } catch (TimeoutException e) { ... client.Abort(); } catch (Exception e) { ... client.Abort(); throw; } Compared to the using block, I think that's ugly. And a lot of code to write each time you need a client. Luckily, I found a few other workarounds, such as this one on IServiceOriented. You start with: public delegate void UseServiceDelegate<T>(T proxy); public static class Service<T> { public static ChannelFactory<T> _channelFactory = new ChannelFactory<T>(""); public static void Use(UseServiceDelegate<T> codeBlock) { IClientChannel proxy = (IClientChannel)_channelFactory.CreateChannel(); bool success = false; try { codeBlock((T)proxy); proxy.Close(); success = true; } finally { if (!success) { proxy.Abort(); } } } } Which then allows: Service<IOrderService>.Use(orderService => { orderService.PlaceOrder(request); } That's not bad, but I don't think it's as expressive and easily understandable as the using block. The workaround I'm currently trying to use I first read about on blog.davidbarret.net. Basically you override the client's Dispose() method wherever you use it. Something like: public partial class SomeWCFServiceClient : IDisposable { void IDisposable.Dispose() { if (this.State == CommunicationState.Faulted) { this.Abort(); } else { this.Close(); } } } This appears to be able to allow the using block again without the danger of masking a faulted state exception. So, are there any other gotchas I have to look out for using these workarounds? Has anybody come up with anything better?

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• not sure if this is my mistake ~~ vs2010 Add Service Reference fails

  - by gerryLowry

  https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter the above is from Taleo's API guide. I'm trying to create a WCF Client (e.g.: " Creating Your First WCF Client" http://channel9.msdn.com/shows/Endpoint/Endpoint-Screencasts-Creating-Your-First-WCF-Client/ ) The tbe.taleo... link is from Taleo's API documentation. Likely my understanding is flawed. My assumption is that when the link from Taleo is entered into the vs2010 "Add Service Reference" dialog and GO is clicked, then vs2010 should retrieve a proper WSDL/SOAP envelope back from the Taleo link. That does not happen; instead an error occurs. Fiddler2 (http://fiddler2.com) displays the status code 500 "HTTP/1.1 500 Internal Server Error". [FULL DETAILS BELOW] "WcfTestClient.exe" gives a similar error: [WcfTestClient DETAILS BELOW] QUESTION: is it me, or is the Taleo link flawed? Thank you, Gerry [FULL DETAILS "Add Service Reference"] The HTML document does not contain Web service discovery information. Metadata contains a reference that cannot be resolved: 'https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter'. The content type text/xml;charset=utf-8 of the response message does not match the content type of the binding (application/soap+xml; charset=utf-8). If using a custom encoder, be sure that the IsContentTypeSupported method is implemented properly. The first 544 bytes of the response were: ' SOAP-ENV:Protocol Unsupported content type "application/soap+xml; charset=utf-8", must be: "text/xml". /MANAGER/dispatcher/servlet/rpcrouter '. The remote server returned an error: (500) Internal Server Error. If the service is defined in the current solution, try building the solution and adding the service reference again. [WcfTestClient DETAILS] Error: Cannot obtain Metadata from https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter If this is a Windows (R) Communication Foundation service to which you have access, please check that you have enabled metadata publishing at the specified address. For help enabling metadata publishing, please refer to the MSDN documentation at http://go.microsoft.com/fwlink/?LinkId=65455.WS-Metadata Exchange Error URI: https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter Metadata contains a reference that cannot be resolved: 'https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter'. The content type text/xml;charset=utf-8 of the response message does not match the content type of the binding (application/soap+xml; charset=utf-8). If using a custom encoder, be sure that the IsContentTypeSupported method is implemented properly. The first 544 bytes of the response were: 'SOAP-ENV:ProtocolUnsupported content type "application/soap+xml; charset=utf-8", must be: "text/xml"./MANAGER/dispatcher/servlet/rpcrouter'. The remote server returned an error: (500) Internal Server Error.HTTP GET Error URI: https://tbe.taleo.net/MANAGER/dispatcher/servlet/rpcrouter The HTML document does not contain Web service discovery information.

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• How to use CFNetwork to get byte array from sockets?

  - by Vic

  Hi, I'm working in a project for the iPad, it is a small program and I need it to communicate with another software that runs on windows and act like a server; so the application that I'm creating for the iPad will be the client. I'm using CFNetwork to do sockets communication, this is the way I'm establishing the connection: char ip[] = "192.168.0.244"; NSString *ipAddress = [[NSString alloc] initWithCString:ip]; /* Build our socket context; this ties an instance of self to the socket */ CFSocketContext CTX = { 0, self, NULL, NULL, NULL }; /* Create the server socket as a TCP IPv4 socket and set a callback */ /* for calls to the socket's lower-level connect() function */ TCPClient = CFSocketCreate(NULL, PF_INET, SOCK_STREAM, IPPROTO_TCP, kCFSocketDataCallBack, (CFSocketCallBack)ConnectCallBack, &CTX); if (TCPClient == NULL) return; /* Set the port and address we want to listen on */ struct sockaddr_in addr; memset(&addr, 0, sizeof(addr)); addr.sin_len = sizeof(addr); addr.sin_family = AF_INET; addr.sin_port = htons(PORT); addr.sin_addr.s_addr = inet_addr([ipAddress UTF8String]); CFDataRef connectAddr = CFDataCreate(NULL, (unsigned char *)&addr, sizeof(addr)); CFSocketConnectToAddress(TCPClient, connectAddr, -1); CFRunLoopSourceRef sourceRef = CFSocketCreateRunLoopSource(kCFAllocatorDefault, TCPClient, 0); CFRunLoopAddSource(CFRunLoopGetCurrent(), sourceRef, kCFRunLoopCommonModes); CFRelease(sourceRef); CFRunLoopRun(); And this is the way I sent the data, which basically is a byte array /* The native socket, used for various operations */ // TCPClient is a CFSocketRef member variable CFSocketNativeHandle sock = CFSocketGetNative(TCPClient); Byte byteData[3]; byteData[0] = 0; byteData[1] = 4; byteData[2] = 0; send(sock, byteData, strlen(byteData)+1, 0); Finally, as you may have noticed, when I create the server socket, I registered a callback for the kCFSocketDataCallBack type, this is the code. void ConnectCallBack(CFSocketRef socket, CFSocketCallBackType type, CFDataRef address, const void *data, void *info) { // SocketsViewController is the class that contains all the methods SocketsViewController *obj = (SocketsViewController*)info; UInt8 *unsignedData = (UInt8 *) CFDataGetBytePtr(data); char *value = (char*)unsignedData; NSString *text = [[NSString alloc]initWithCString:value length:strlen(value)]; [obj writeToTextView:text]; [text release]; } Actually, this callback is being invoked in my code, the problem is that I don't know how can I get the data that the windows client sent me, I'm expecting to receive an array of bytes, but I don't know how can I get those bytes from the data param. If anyone can help me to find a way to do this, or maybe me point me to another way to get the data from the server in my client application I would really appreciate it. Thanks.

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• Where to put a glossary of important terms and patterns in documentation?

  - by Tetha

  Greetings. I want to document certain patterns in the code in order to build up a consistent terminology (in order to easen communication about the software). I am, however, unsure, where to define the terms given. In order to get on the same level, an example: I have a code generator. This code generator receives a certain InputStructure from the Parser (yes, the name InputStructure might be less than ideal). This InputStructure is then transformed into various subsequent datastructures (like an abstract description of the validation process). Each of these datastructures can be either transformed into another value of the same datastructure or it can be transformed into the next datastructure. This should sound like Pipes and Filters to some degree. Given this, I call an operation which takes a datastructures and constructs a value of the same datastructure a transformation, while I call an operation which takes a datastructure and produces a different follow-up datastructure a derivation. The final step of deriving a string containing code is called emitting. (So, overall, the codegenerator takes the input-structure and transforms, transforms, derives, transforms, derives and finally emits). I think emphasizing these terms will be benefitial in communications, because then it is easy to talk about things. If you hear "transformation", you know "Ok, I only need to think about these two datastructures", if you hear "emitting", you know "Ok, I only need to know this datastructure and the target language.". However, where do I document these patterns? The current code base uses visitors and offers classes called like ValidatorTransformationBase<ResultType> (or InputStructureTransformationBase<ResultType>, and so one and so on). I do not really want to add the definition of such terms to the interfaces, because in that case, I'd have to repeat myself on each and every interface, which clearly violates DRY. I am considering to emphasize the distinction between Transformations and Derivations by adding further interfaces (I would have to think about a better name for the TransformationBase-classes, but then I could do thinks like ValidatorTransformation extends ValidatorTransformationBase<Validator>, or ValidatorDerivationFromInputStructure extends InputStructureTransformation<Validator>). I also think I should add a custom page to the doxygen documentation already existing, as in "Glossary" or "Architecture Principles", which contains such principles. The only disadvantage of this would be that a contributor will need to find this page in order to actually learn about this. Am I missing possibilities or am I judging something wrong here in your opinion? -- Regards, Tetha

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• A Question about using jython when run a receving socket in python

  - by abusemind

  Hi, I have not a lot of knowledge of python and network programming. Currently I am trying to implement a simple application which can receive a text message sent by the user, fetch some information from the google search api, and return the results via text message to the user. This application will continue to listening to the users messages and reply immediately. How I get the text short message sent by the user? It's a program named fetion from the mobile supplier in China. The client side fetion, just like a instant communication tool, can send/receive messages to/from other people who are using mobile to receive/send SMS. I am using a open source python program that simulates the fetion program. So basically I can use this python program to communate with others who using cell phone via SMS. My core program is based on java, so I need to take this python program into java environment. I am using jython, and now I am available to send messages to users by some lines of java codes. But the real question is the process of receving from users via SMS. In python code, a new thread is created to continuously listen to the user. It should be OK in Python, but when I run the similar process in Jython, the following exception occurs: Exception in thread Thread:Traceback (most recent call last): File "D:\jython2.5.1\Lib\threading.py", line 178, in _Thread__bootstrap self.run() File "<iostream>", line 1389, in run File "<iostream>", line 1207, in receive File "<iostream>", line 1207, in receive File "<iostream>", line 150, in recv File "D:\jython2.5.1\Lib\select.py", line 223, in native_select pobj.register(fd, POLLIN) File "D:\jython2.5.1\Lib\select.py", line 104, in register raise _map_exception(jlx) error: (20000, 'socket must be in non-blocking mode') The line 150 in the python code is as follows: def recv(self,timeout=False): if self.login_type == "HTTP": time.sleep(10) return self.get_offline_msg() pass else: if timeout: infd,outfd,errfd = select([self.__sock,],[],[],timeout)//<---line 150 here else: infd,outfd,errfd = select([self.__sock,],[],[]) if len(infd) != 0: ret = self.__tcp_recv() num = len(ret) d_print(('num',),locals()) if num == 0: return ret if num == 1: return ret[0] for r in ret: self.queue.put(r) d_print(('r',),locals()) if not self.queue.empty(): return self.queue.get() else: return "TimeOut" Because of I am not very familiar with python, especially the socket part, and also new in Jython use, I really need your help or only advice or explanation. Thank you very much!

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• Hibernate Communications Link Failure in Hibernate Based Java Servlet application powered by MySQL

  - by Vatsala

  Let me describe my question - I have a Java application - Hibernate as the DB interfacing layer over MySQL. I get the communications link failure error in my application. The occurence of this error is a very specific case. I get this error , When I leave mysql server unattended for more than approximately 6 hours (i.e. when there are no queries issued to MySQL for more than approximately 6 hours). I am pasting a top 'exception' level description below, and adding a pastebin link for a detailed stacktrace description. javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: java.net.ConnectException: Connection refused: connect the link to the pastebin for further investigation - http://pastebin.com/4KujAmgD What I understand from these exception statements is that MySQL is refusing to take in any connections after a period of idle/nil activity. I have been reading up a bit about this via google search, and came to know that one of the possible ways to overcome this is to set values for c3p0 properties as c3p0 comes bundled with Hibernate. Specifically, I read from here http://www.mchange.com/projects/c3p0/index.html that setting two properties idleConnectionTestPeriod and preferredTestQuery will solve this for me. But these values dont seem to have had an effect. Is this the correct approach to fixing this? If not, what is the right way to get over this? The following are related Communications Link Failure questions at stackoverflow.com, but I've not found a satisfactory answer in their answers. http://stackoverflow.com/questions/2121829/java-db-communications-link-failure http://stackoverflow.com/questions/298988/how-to-handle-communication-link-failure Note 1 - i dont get this error when I am using my application continuosly. Note 2 - I use JPA with Hibernate and hence my hibernate.dialect,etc hibernate properties reside within the persistence.xml in the META-INF folder (does that prevent the c3p0 properties from working?) edit - Here are the c3p0 parameters I tried out - select 1; 2

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• How to force VS 2010 to skip "builds" of projects which haven't changed?

  - by Ladislav Mrnka

  Our product's solution has more than 100+ projects (500+ksloc of production code). Most of them are C# projects but we also have few using C++/CLI to bridge communication with native code. Rebuilding the whole solution takes several minutes. That's fine. If I want to rebuilt the solution I expect that it will really take some time. What is not fine is time needed to build solution after full rebuild. Imagine I used full rebuild and know without doing any changes to to the solution I press Build (F6 or Ctrl+Shift+B). Why it takes 35s if there was no change? In output I see that it started "building" of each project - it doesn't perform real build but it does something which consumes significant amount of time. That 35s delay is pain in the ass. Yes I can improve the time by not using build solution but only build project (Shift+F6). If I run build project on particular test project I'm currently working on it will take "only" 8+s. It requires me to run project build on correct project (the test project to ensure dependent tested code is build as well). At least ReSharper test runner correctly recognizes that only this single project must be build and rerunning test usually contains only 8+s compilation. My current coding Kata is: don't touch Ctrl+Shift+B. The test project build will take 8s even if I don't do any changes. The reason why it takes 8s is because it also "builds" dependencies = in my case it "builds" more than 20 projects but I made changes only to unit test or single dependency! I don't want it to touch other projects. Is there a way to simply tell VS to build only projects where some changes were done and projects which are dependent on changed ones (preferably this part as another build option)? I worry you will tell me that it is exactly what VS is doing but in MS way ... I want to improve my TDD experience and reduce the time of compilation (in TDD the compilation can happen twice per minute). To make this even more frustrated I'm working in a team where most of developers used to work on Java projects prior to joining this one. So you can imagine how they are pissed off when they must use VS in contrast to full incremental compilation in Java. I don't require incremental compilation of classes. I expect working incremental compilation of solutions. Especially in product like VS 2010 Ultimate which costs several thousands dollars. I really don't want to get answers like: Make a separate solution Unload projects you don't need etc. I can read those answers here. Those are not acceptable solutions. We're not paying for VS to do such compromises.

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• Choosing the right .NET architecture. WCF? WPF/Forms, ASP.NET (MVC)?

  - by Tommy Jakobsen

  I’m in the situation that I have to design and implement a rather big system from the bottom. I’m having some (a lot actually) questions about the architecture that I would like your comments and thoughts on. I don’t hope that I’ve written too much here, but I wanted to give you all an idea of what the system is. Quick info about the applications, read if you want: I can’t share much detail about the project, but basically it’s a system where we offer our customer a service to manage their users. We have a hotline where the users call and our hotline uses an (windows) application (intranet) to manage the user’s data, etc. The customer also has a web application where they can see reports, information about their business and users, and the ability to modify their data. Modifying data is not just user data like address and so, but also information about the products/services the user has, which can be complicated. The applications will be built on Microsoft .NET Framework 4, with a MS SQL Server 2008 database. There will be a few applications that have to access this database, such as: Intranet application (used by us and our hotline) Customer web application type 1 Customer web application type 2 Customer web application type n different applications) … Now my big problem is what .NET parts I should use for such a system. For the “backend” I’ve considered using Windows Communication Foundation: Would WCF be a good choice? The intranet application will be an application that has to edit lots of records in the database. It has to be easy to navigate using the keyboard (fast to work with). Has a feature such as “find customer, find that, lookup this, choose this and update that”. What would be the best choice to develop this application in? Would it be WPF or good old Windows Forms? I don’t need all of the fancy graphics features in WPF, like 3D, but the application has to look nice (maybe something like the new Visual Studio/Office tools). And the same question goes for the web pages. They have much the same work to do, but not as many features as the intranet application, and not the same amount of data (much less). That is my questions for now. I’m hoping to get a discussion going that will open my eyes to some of these technologies, helping me decide architecture to go with. I would like to say thanks in advance, and let you all know that any thoughts will be much appreciated.

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• How to initiate chatting between two clients and two clients only, using applets and servlets?

  - by mithun1538

  Hello everyone, I first need to apologize for my earlier questions. (You can check my profile for them)They seemed to ask more questions than give answers. Hence, I am laying down the actual question that started all them absurd questions. I am trying to design a chat applet. Till now, I have coded the applet, servlet and communication between the applet and the servlet. The code in the servlet side is such that I was able to establish chatting between clients using the applets, but the code was more like a broadcast all feature, i.e. all clients would be chatting with each other. That was my first objective when I started designing the chat applet. The second step is chatting between only two specific users, much like any other chat application we have. So this was my idea for it: I create an instance of the servlet that has the 'broadcast-all' code. I then pass the address of this instance to the respective clients. 2 client applets use the address to then chat. Technically the code is 'broadcast-all', but since only 2 clients are connected to it, it gives the chatting between two clients feature. Thus, groups of 2 clients have different instances of the same servlet, and each instance handles chatting between two clients at a max. However, as predicted, the idea didn't materialize! I tried to create an instance of the servlet but the only solution for that was using sessions on the servlet side, and I don't know how to use this session for later communications. I then tried to modify my broadcast-all code. In that code, I was using classes that implemented Observer and Observable interfaces. So the next idea that I got was: Create a new object of the Observable class(say class_1). This object be common to 2 clients. 2 clients that wish to chat will use same object of the class_1. 2 other clients will use a different object of class_1. But the problem here lies with the class that implements the Observer interface(say class_2). Since this has observers monitoring the same type of class, namely class_1, how do I establish an observer monitoring one object of class_1 and another observer monitoring another object of the same class class_1 (Because notifyObservers() would notify all the observers and I can't assign a particular observer to a particular object)? I first decided to ask individual problems, like how to create instances of servlets, using objects of observable and observer and so on in stackoverflow... but I got confused even more. Can anyone give me an idea how to establish chatting between two clients only?(I am using Http and not sockets or RMI). Regards, Mithun. P.S. Thanks to all who replied to my previous (absurd) queries. I should have stated the purpose earlier so that you guys could help me better.

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• PHP max_execution_time not timing out

  - by Joey Ezekiel

  This is not one of the regular questions if sleep is counted for timeout or stuff like that. Ok, here's the problem: I've set the max_execution_time for PHP as 15 seconds and ideally this should time out when it crosses the set limit, but it doesn't. Apache has been restarted after the change to the php.ini file and an ini_get('max_execution_time') is all fine. Sometimes the script runs for upto 200 seconds which is crazy. I have no database communication whatsoever. All the script does is looking for files on the unix filesystem and in some cases re-directing to another JSP page. There is no sleep() on the script. I calculate the total execution time of the PHP script like this: At the start of the script I set : $_mtime = microtime(); $_mtime = explode(" ",$_mtime); $_mtime = $_mtime[1] + $_mtime[0]; $_gStartTime = $_mtime; and the end time($_gEndTime) is calculated similarly. The total time is calculated in a shutdown function that I've registered: register_shutdown_function('shutdown'); ............. function shutdown() { .............. .............. $_total_time = $_gEndTime - $_gStartTime; .............. switch (connection_status ()) { case CONNECTION_NORMAL: .... break; .... case CONNECTION_TIMEOUT: .... break; ...... } } Note: I cannot use $_SERVER['REQUEST_TIME'] because my PHP version is incompatible. That sucks - I know. 1) Well, my first question obviously is is why is my PHP script executing even after the set timeout limit? 2) Apache has the Timeout directive which is 300 seconds but the PHP binary does not read the Apache config and this should not be a problem. 3) Is there a possibility that something is sending PHP into a sleep mode? 4) Am I calculating the execution time in a wrong way? Is there a better way to do this? I'm stumped at this point. PHP Wizards - please help.

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• Decrypting data from a secure socket

  - by Ronald

  I'm working on a server application in Java. I've successfully got past the handshake portion of the communication process, but how do I go about decrypting my input stream? Here is how I set up my server: import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; import java.util.ArrayList; import java.util.HashMap; import javax.net.ServerSocketFactory; import javax.net.ssl.SSLServerSocket; import javax.net.ssl.SSLServerSocketFactory; import org.json.me.JSONException; import dictionary.Dictionary; public class Server { private static int port = 1234; public static void main(String[] args) throws JSONException { System.setProperty("javax.net.ssl.keyStore", "src/my.keystore"); System.setProperty("javax.net.ssl.keyStorePassword", "test123"); System.out.println("Starting server on port: " + port); HashMap<String, Game> games = new HashMap<String, Game>(); final String[] enabledCipherSuites = { "SSL_RSA_WITH_RC4_128_SHA" }; try{ SSLServerSocketFactory socketFactory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault(); SSLServerSocket listener = (SSLServerSocket) socketFactory.createServerSocket(port); listener.setEnabledCipherSuites(enabledCipherSuites); Socket server; Dictionary dict = new Dictionary(); Game game = new Game(dict); //for testing, creates 1 global game. while(true){ server = listener.accept(); ClientConnection conn = new ClientConnection(server, game, "User"); Thread t = new Thread(conn); t.start(); } } catch(IOException e){ System.out.println("Failed setting up on port: " + port); e.printStackTrace(); } } } I used a BufferedReader to get the data send from the client: BufferedReader d = new BufferedReader(new InputStreamReader(socket.getInputStream())); After the handshake is complete it appears like I'm getting encrypted data. I did some research online and it seems like I might need to use a Cipher, but I'm not sure. Any ideas?

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• Modular GWT design concerns

  - by GlGuru

  Hi, I have a couple of questions regarding a modular GWT based application framework. I have some ideas about them but being new to the field of web development I feel they are far from ideal. I'd appreciate a few comments and suggestions in this regard. Here are my questions: I am developing a framework which will allow third parties to embed GWT applications into our website and do some communication with them using simple iFrame postMessage. All these third party modules are going to use our SDK which is also GWT based. The problem arises that even though all the modules will be using the same codebase there is going to be a massive overheard in the amount of duplicate Javascript code (i.e. our common SDK code base which is quite large) being downloaded on the client's machine. This is highly redundant and problematic, not only due to the sheer size of duplicate code but, also due to the fact that subsequent updates of the SDK would require the modules to be recompiled which is going to create a DLL hell kind of scenario in the long run. What is the best way of doing this kind of thing? Is there a way where I can have some static GWT code (i.e. the SDK) and the dynamic GWT module refers to it (even if lies on a different domain) and it all work happily? The other part of the problem lies in providing robust scripting front end to the SDK. At first it appears to be trivial since Javascript itself is a scripting language. However, I do not know how to load and call a piece of pure Javascript code at runtime? I am willing to put restrictions on the target Javascript (i.e. having a function main and unique namespace or something). Furthermore the Javascript will come as a string from a database and not as a full URL. If its doable in Javascript how does one get this right in GWT i.e. forcing the compiler to emit a certain function in the generated Javascript? This I believe can be lesser of a problem by having a stub Javascript with all the right requirements which just loads up a GWT generated Javascript. Is any of this possible at all? I generally hate to be this verbose but I hope to find a quick solution to the problem as its holding up my progress. I'd highly appreciate any comments, suggestions and experiences.

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• Access violation when running native C++ application that uses a /clr built DLL

  - by doobop

  I'm reorganzing a legacy mixed (managed and unmanaged DLLs) application so that the main application segment is unmanaged MFC and that will call a C++ DLL compiled with /clr flag that will bridge the communication between the managed (C# DLLs) and unmanaged code. Unfortuantely, my changed have resulted in an Access violation that occurs before the application InitInstance() is called. This makes it very difficult to debug. The only information I get is the following stack trace. > 64006108() ntdll.dll!_ZwCreateMutant@16() + 0xc bytes kernel32.dll!_CreateMutexW@12() + 0x7a bytes So, here are some sceanrios I've tried. - Turned on Exceptions-Win32 Exceptions-c0000005 Access Violation to break when Thrown. Still the most detail I get is from the above stack trace. I've tried the application with F10, but it fails before any breakpoints are hit and fails with the above stack trace. - I've stubbed out the bridge DLL so that it only has one method that returns a bool and that method is coded to just return false (no C# code called). bool DllPassthrough::IsFailed() { return false; } If the stubbed out DLL is compiled with the /clr flag, the application fails. If it is compiled without the /clr flag, the application runs. - I've created a stub MFC application using the Visual Studio wizard for multidocument applications and call DllPassthrough::IsFailed(). This succeeds even with the /clr flag used to compile the DLL. - I've tried doing a manual LoadLibrary on winmm.lib as outlined in the following note Access violation when using c++/cli. The application still fails. So, my questions are how to solve the problem? Any hints, strategies, or previous incidents. And, failing that, how can I get more information on what code segment or library is causing the access exception? If I try more involved workarounds like doing LoadLibrary calls, I'd like to narrow it to the failing libraries. Thanks. BTW, we are using Visual Studio 2008 and the project is being built against the .NET 2.0 framework for the managed sections.

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• Basic shared memory program in C

  - by nicopuri

  Hi, I want to make a basic chat application in C using Shared memory. I am working in Linux. The application consist in writing the client and the server can read, and if the server write the client can read the message. I tried to do this, but I can't achieve the communication between client and server. The code is the following: Server.c int main(int argc, char **argv) { char *msg; static char buf[SIZE]; int n; msg = getmem(); memset(msg, 0, SIZE); initmutex(); while ( true ) { if( (n = read(0, buf, sizeof buf)) 0 ) { enter(); sprintf(msg, "%.*s", n, buf); printf("Servidor escribe: %s", msg); leave(); }else{ enter(); if ( strcmp(buf, msg) ) { printf("Servidor lee: %s", msg); strcpy(buf, msg); } leave(); sleep(1); } } return 0; } Client.c int main(int argc, char **argv) { char *msg; static char buf[SIZE-1]; int n; msg = getmem(); initmutex(); while(true) { if ( (n = read(0, buf, sizeof buf)) 0 ) { enter(); sprintf(msg, "%.*s", n, buf); printf("Cliente escribe: %s", msg); leave(); }else{ enter(); if ( strcmp(buf, msg) ) { printf("Cliente lee: %s", msg); strcpy(buf, msg); } leave(); sleep(1); } } printf("Cliente termina\n"); return 0; } The shared memory module is the folowing: #include "common.h" void fatal(char *s) { perror(s); exit(1); } char * getmem(void) { int fd; char *mem; if ( (fd = shm_open("/message", O_RDWR|O_CREAT, 0666)) == -1 ) fatal("sh_open"); ftruncate(fd, SIZE); if ( !(mem = mmap(NULL, SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) ) fatal("mmap"); close(fd); return mem; } static sem_t *sd; void initmutex(void) { if ( !(sd = sem_open("/mutex", O_RDWR|O_CREAT, 0666, 1)) ) fatal("sem_open"); } void enter(void) { sem_wait(sd); } void leave(void) { sem_post(sd); }

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• Converting C source to C++

  - by Barry Kelly

  How would you go about converting a reasonably large (300K), fairly mature C codebase to C++? The kind of C I have in mind is split into files roughly corresponding to modules (i.e. less granular than a typical OO class-based decomposition), using internal linkage in lieu private functions and data, and external linkage for public functions and data. Global variables are used extensively for communication between the modules. There is a very extensive integration test suite available, but no unit (i.e. module) level tests. I have in mind a general strategy: Compile everything in C++'s C subset and get that working. Convert modules into huge classes, so that all the cross-references are scoped by a class name, but leaving all functions and data as static members, and get that working. Convert huge classes into instances with appropriate constructors and initialized cross-references; replace static member accesses with indirect accesses as appropriate; and get that working. Now, approach the project as an ill-factored OO application, and write unit tests where dependencies are tractable, and decompose into separate classes where they are not; the goal here would be to move from one working program to another at each transformation. Obviously, this would be quite a bit of work. Are there any case studies / war stories out there on this kind of translation? Alternative strategies? Other useful advice? Note 1: the program is a compiler, and probably millions of other programs rely on its behaviour not changing, so wholesale rewriting is pretty much not an option. Note 2: the source is nearly 20 years old, and has perhaps 30% code churn (lines modified + added / previous total lines) per year. It is heavily maintained and extended, in other words. Thus, one of the goals would be to increase mantainability. [For the sake of the question, assume that translation into C++ is mandatory, and that leaving it in C is not an option. The point of adding this condition is to weed out the "leave it in C" answers.]

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• Multi-threaded Pooled Allocators

  - by Darren Engwirda

  I'm having some issues using pooled memory allocators for std::list objects in a multi-threaded application. The part of the code I'm concerned with runs each thread function in isolation (i.e. there is no communication or synchronization between threads) and therefore I'd like to setup separate memory pools for each thread, where each pool is not thread-safe (and hence fast). I've tried using a shared thread-safe singleton memory pool and found the performance to be poor, as expected. This is a heavily simplified version of the type of thing I'm trying to do. A lot has been included in a pseudo-code kind of way, sorry if it's confusing. /* The thread functor - one instance of MAKE_QUADTREE created for each thread */ class make_quadtree { private: /* A non-thread-safe memory pool for int linked list items, let's say that it's * something along the lines of BOOST::OBJECT_POOL */ pooled_allocator<int> item_pool; /* The problem! - a local class that would be constructed within each std::list as the * allocator but really just delegates to ITEM_POOL */ class local_alloc { public : //!! I understand that I can't access ITEM_POOL from within a nested class like //!! this, that's really my question - can I get something along these lines to //!! work?? pointer allocate (size_t n) { return ( item_pool.allocate(n) ); } }; public : make_quadtree (): item_pool() // only construct 1 instance of ITEM_POOL per // MAKE_QUADTREE object { /* The kind of data structures - vectors of linked lists * The idea is that all of the linked lists should share a local pooled allocator */ std::vector<std::list<int, local_alloc>> lists; /* The actual operations - too complicated to show, but in general: * * - The vector LISTS is grown as a quadtree is built, it's size is the number of * quadtree "boxes" * * - Each element of LISTS (each linked list) represents the ID's of items * contained within each quadtree box (say they're xy points), as the quadtree * is grown a lot of ID pop/push-ing between lists occurs, hence the memory pool * is important for performance */ } }; So really my problem is that I'd like to have one memory pool instance per thread functor instance, but within each thread functor share the pool between multiple std::list objects.

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• Which network protocol to use for lightweight notification of remote apps?

  - by Chris Thornton

  I have this situation.... Client-initiated SOAP 1.1 communication between one server and let's say, tens of thousands of clients. Clients are external, coming in through our firewall, authenticated by certificate, https, etc.. They can be anywhere, and usually have their own firewalls, NAT routers, etc... They're truely external, not just remote corporate offices. They could be in a corporate/campus network, DSL/Cable, even Dialup. Client uses Delphi (2005 + SOAP fixes from 2007), and the server is C#, but from an architecture/design standpoint, that shouldn't matter. Currently, clients push new data to the server and pull new data from the server on 15-minute polling loop. The server currently does not push data - the client hits the "messagecount" method, to see if there is new data to pull. If 0, it sleeps for another 15 min and checks again. We're trying to get that down to 7 seconds. If this were an internal app, with one or just a few dozen clients, we'd write a cilent "listener" soap service, and would push data to it. But since they're external, sit behind their own firewalls, and sometimes private networks behind NAT routers, this is not practical. So we're left with polling on a much quicker loop. 10K clients, each checking their messagecount every 10 seconds, is going to be 1000/sec messages that will mostly just waste bandwidth, server, firewall, and authenticator resources. So I'm trying to design something better than what would amount to a self-inflicted DoS attack. I don't think it's practical to have the server send soap messages to the client (push) as this would require too much configuration at the client end. But I think there are alternatives that I don't know about. Such as: 1) Is there a way for the client to make a request for GetMessageCount() via Soap 1.1, and get the response, and then perhaps, "stay on the line" for perhaps 5-10 minutes to get additional responses in case new data arrives? i.e the server says "0", then a minute later in response to some SQL trigger (the server is C# on Sql Server, btw), knows that this client is still "on the line" and sends the updated message count of "5"? 2) Is there some other protocol that we could use to "ping" the client, using information gathered from their last GetMessageCount() request? 3) I don't even know. I guess I'm looking for some magic protocol where the client can send a GetMessageCount() request, which would include info for "oh by the way, in case the answer changes in the next hour, ping me at this address...". Also, I'm assuming that any of these "keep the line open" schemes would seriously impact the server sizing, as it would need to keep many thousands of connections open, simultaneously. That would likely impact the firewalls too, I think. Is there anything out there like that? Or am I pretty much stuck with polling? TIA, Chris

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• Multi-tier applications using L2S, WCF and Base Class

  - by Gena Verdel

  Hi all. One day I decided to build this nice multi-tier application using L2S and WCF. The simplified model is : DataBase-L2S-Wrapper(DTO)-Client Application. The communication between Client and Database is achieved by using Data Transfer Objects which contain entity objects as their properties. abstract public class BaseObject { public virtual IccSystem.iccObjectTypes ObjectICC_Type { get { return IccSystem.iccObjectTypes.unknownType; } } [global::System.Data.Linq.Mapping.ColumnAttribute(Storage = "_ID", AutoSync = AutoSync.OnInsert, DbType = "BigInt NOT NULL IDENTITY", IsPrimaryKey = true, IsDbGenerated = true)] [global::System.Runtime.Serialization.DataMemberAttribute(Order = 1)] public virtual long ID { //get; //set; get { return _ID; } set { _ID = value; } } } [DataContract] public class BaseObjectWrapper<T> where T : BaseObject { #region Fields private T _DBObject; #endregion #region Properties [DataMember] public T Entity { get { return _DBObject; } set { _DBObject = value; } } #endregion } Pretty simple, isn't it?. Here's the catch. Each one of the mapped classes contains ID property itself so I decided to override it like this [global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.Divisions")] [global::System.Runtime.Serialization.DataContractAttribute()] public partial class Division : INotifyPropertyChanging, INotifyPropertyChanged { [global::System.Data.Linq.Mapping.ColumnAttribute(Storage="_ID", AutoSync=AutoSync.OnInsert, DbType="BigInt NOT NULL IDENTITY", IsPrimaryKey=true, IsDbGenerated=true)] [global::System.Runtime.Serialization.DataMemberAttribute(Order=1)] public override long ID { get { return this._ID; } set { if ((this._ID != value)) { this.OnIDChanging(value); this.SendPropertyChanging(); this._ID = value; this.SendPropertyChanged("ID"); this.OnIDChanged(); } } } } Wrapper for division is pretty straightforward as well: public class DivisionWrapper : BaseObjectWrapper<Division> { } It worked pretty well as long as I kept ID values at mapped class and its BaseObject class the same(that's not very good approach, I know, but still) but then this happened: private CentralDC _dc; public bool UpdateDivision(ref DivisionWrapper division) { DivisionWrapper tempWrapper = division; if (division.Entity == null) { return false; } try { Table<Division> table = _dc.Divisions; var q = table.Where(o => o.ID == tempWrapper.Entity.ID); if (q.Count() == 0) { division.Entity._errorMessage = "Unable to locate entity with id " + division.Entity.ID.ToString(); return false; } var realEntity = q.First(); realEntity = division.Entity; _dc.SubmitChanges(); return true; } catch (Exception ex) { division.Entity._errorMessage = ex.Message; return false; } } When trying to enumerate over the in-memory query the following exception occurred: Class member BaseObject.ID is unmapped. Although I'm stating the type and overriding the ID property L2S fails to work. Any suggestions?

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• Hibernate Communications Link Failure in Restlet-Hibernate Based Java application powered by MySQL

  - by Vatsala

  Let me describe my question - I have a Java application - Hibernate as the DB interfacing layer over MySQL. I get the communications link failure error in my application. The occurence of this error is a very specific case. I get this error , When I leave mysql server unattended for more than approximately 6 hours (i.e. when there are no queries issued to MySQL for more than approximately 6 hours). I am pasting a top 'exception' level description below, and adding a pastebin link for a detailed stacktrace description. javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: org.hibernate.exception.JDBCConnectionException: Cannot open connection - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure - The last packet successfully received from the server was 1,274,868,181,212 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago. - Caused by: java.net.ConnectException: Connection refused: connect the link to the pastebin for further investigation - http://pastebin.com/4KujAmgD What I understand from these exception statements is that MySQL is refusing to take in any connections after a period of idle/nil activity. I have been reading up a bit about this via google search, and came to know that one of the possible ways to overcome this is to set values for c3p0 properties as c3p0 comes bundled with Hibernate. Specifically, I read from here http://www.mchange.com/projects/c3p0/index.html that setting two properties idleConnectionTestPeriod and preferredTestQuery will solve this for me. But these values dont seem to have had an effect. Is this the correct approach to fixing this? If not, what is the right way to get over this? The following are related Communications Link Failure questions at stackoverflow.com, but I've not found a satisfactory answer in their answers. http://stackoverflow.com/questions/2121829/java-db-communications-link-failure http://stackoverflow.com/questions/298988/how-to-handle-communication-link-failure Note 1 - i dont get this error when I am using my application continuosly. Note 2 - I use JPA with Hibernate and hence my hibernate.dialect,etc hibernate properties reside within the persistence.xml in the META-INF folder (does that prevent the c3p0 properties from working?)

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• Supporting multiple instances of a plugin DLL with global data

  - by Bruno De Fraine

  Context: I converted a legacy standalone engine into a plugin component for a composition tool. Technically, this means that I compiled the engine code base to a C DLL which I invoke from a .NET wrapper using P/Invoke; the wrapper implements an interface defined by the composition tool. This works quite well, but now I receive the request to load multiple instances of the engine, for different projects. Since the engine keeps the project data in a set of global variables, and since the DLL with the engine code base is loaded only once, loading multiple projects means that the project data is overwritten. I can see a number of solutions, but they all have some disadvantages: You can create multiple DLLs with the same code, which are seen as different DLLs by Windows, so their code is not shared. Probably this already works if you have multiple copies of the engine DLL with different names. However, the engine is invoked from the wrapper using DllImport attributes and I think the name of the engine DLL needs to be known when compiling the wrapper. Obviously, if I have to compile different versions of the wrapper for each project, this is quite cumbersome. The engine could run as a separate process. This means that the wrapper would launch a separate process for the engine when it loads a project, and it would use some form of IPC to communicate with this process. While this is a relatively clean solution, it requires some effort to get working, I don't now which IPC technology would be best to set-up this kind of construction. There may also be a significant overhead of the communication: the engine needs to frequently exchange arrays of floating-point numbers. The engine could be adapted to support multiple projects. This means that the global variables should be put into a project structure, and every reference to the globals should be converted to a corresponding reference that is relative to a particular project. There are about 20-30 global variables, but as you can imagine, these global variables are referenced from all over the code base, so this conversion would need to be done in some automatic manner. A related problem is that you should be able to reference the "current" project structure in all places, but passing this along as an extra argument in each and every function signature is also cumbersome. Does there exist a technique (in C) to consider the current call stack and find the nearest enclosing instance of a relevant data value there? Can the stackoverflow community give some advice on these (or other) solutions?

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• How do I call the methods in a model via controller? Zend Framework

  - by Joel

  Hi guys, I've been searching for tutorials to better understand this, but I'm having no luck. Please forgive the lengthy explination, but I want make sure I explain myself well. First, I'm quite new to the MVC structure, though I have been doing tutorials and learning as best I can. I have been moving over a live site into the Zend Framework model. So far, I have all the views within views/scripts/index/example.phtml. So therefore I'm using one IndexController and I have the code in each Action method for each page: IE public function exampleAction() Because I didn't know how to interact with a model, I put all the methods at the bottom of the controller (a fat controller). So basically, I had a working site by using a View and Controller and no model. ... Now I'm trying to learn how to incorporate the Model. So I created a View at: view/scripts/calendar/index.phtml I created a new Controller at: controller/CalendarControllers.php and a new model at: model/Calendar.php The problem is I think I'm not correctly communication with the model (I'm still new to OOP). Can you look over my controller and model and tell me if you see a problem. I'm needing to return an array from runCalendarScript(), but I'm not sure if I can return an array into the object like I'm trying to? I don't really understand how to "run" the runCalendarScript() from the controller? Thanks for any help! I'm stripping out most of the guts of the methods for the sake of brevity: controller: <?php class CalendarController extends Zend_Controller_Action { public function indexAction() { $finishedFeedArray = new Application_Model_Calendar(); $this->view->googleArray = $finishedFeedArray; } } model: <?php class Application_Model_Calendar { public function _runCalendarScript(){ $gcal = $this->_validateCalendarConnection(); $uncleanedFeedArray = $this->_getCalendarFeed($gcal); $finishedFeedArray = $this->_cleanFeed($uncleanedFeedArray); return $finishedFeedArray; } //Validate Google Calendar connection public function _validateCalendarConnection() { ... return $gcal; } //extracts googles calendar object into the $feed object public function _getCalendarFeed($gcal) { ... return $feed; } //cleans the feed to just text, etc protected function _cleanFeed($uncleanedFeedArray) { $contentText = $this->_cleanupText($event); $eventData = $this->_filterEventDetails($contentText); return $cleanedArray; } //Cleans up all formatting of text from Calendar feed public function _cleanupText($event) { ... return $contentText; } //filterEventDetails protected function _filterEventDetails($contentText) { ... return $data; } }

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• Chrome extension - Localstorage not working

  - by Bjarki Jonasson

  I'm writing a Chrome extension that uses a content script to modify certain parts of a website. The content script worked fine until I tried to add an options page to my extension. Right now I'm using an options.html file to save user preferences to localstorage, as you can see here: <html> <head><title>Options</title></head> <script type="text/javascript"> function save_options() { var select = document.getElementById("width"); var width = select.children[select.selectedIndex].value; localStorage["site_width"] = width; } function restore_options() { var fwidth = localStorage["site_width"]; if (!fwidth) { return; } var select = document.getElementById("width"); for (var i = 0; i < select.children.length; i++) { var child = select.children[i]; if (child.value == fwidth) { child.selected = "true"; break; } } } </script> <body onload="restore_options()"> Width: <select id="width"> <option value="100%">100%</option> <option value="90%">90%</option> <option value="80%">80%</option> <option value="70%">70%</option> </select> <br> <button onclick="save_options()">Save</button> </body> </html> I also have a background.html file to handle the communication between the content script and the localstorage: <html> <script type="text/javascript"> chrome.extension.onRequest.addListener(function(request, sender, sendResponse) { if (request.method == "siteWidth") sendResponse({status: localStorage["site_width"]}); else sendResponse({}); }); </script> </html> Then there's the actual content script that looks like this: var Width; chrome.extension.sendRequest({method: "siteWidth"}, function(response) { width = response.status; }); None of that code actually works. It looks solid enough to me but I'm not a very experienced programmer so I might be wrong. Could someone explain localstorage to me in layman's terms?

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• Several client waiting for the same event

  - by ff8mania

  I'm developing a communication API to be used by a lot of generic clients to communicate with a proprietary system. This proprietary system exposes an API, and I use a particular classes to send and wait messages from this system: obviously the system alert me that a message is ready using an event. The event is named OnMessageArrived. My idea is to expose a simple SendSyncMessage(message) method that helps the user/client to simply send a message and the method returns the response. The client: using ( Communicator c = new Communicator() ) { response = c.SendSync(message); } The communicator class is done in this way: public class Communicator : IDisposable { // Proprietary system object ExternalSystem c; String currentRespone; Guid currentGUID; private readonly ManualResetEvent _manualResetEvent; private ManualResetEvent _manualResetEvent2; String systemName = "system"; String ServerName = "server"; public Communicator() { _manualResetEvent = new ManualResetEvent(false); //This methods are from the proprietary system API c = SystemInstance.CreateInstance(); c.Connect(systemName , ServerName); } private void ConnectionStarter( object data ) { c.OnMessageArrivedEvent += c_OnMessageArrivedEvent; _manualResetEvent.WaitOne(); c.OnMessageArrivedEvent-= c_OnMessageArrivedEvent; } public String SendSync( String Message ) { Thread _internalThread = new Thread(ConnectionStarter); _internalThread.Start(c); _manualResetEvent2 = new ManualResetEvent(false); String toRet; int messageID; currentGUID = Guid.NewGuid(); c.SendMessage(Message, "Request", currentGUID.ToString()); _manualResetEvent2.WaitOne(); toRet = currentRespone; return toRet; } void c_OnMessageArrivedEvent( int Id, string root, string guid, int TimeOut, out int ReturnCode ) { if ( !guid.Equals(currentGUID.ToString()) ) { _manualResetEvent2.Set(); ReturnCode = 0; return; } object newMessage; c.FetchMessage(Id, 7, out newMessage); currentRespone = newMessage.ToString(); ReturnCode = 0; _manualResetEvent2.Set(); } } I'm really noob in using waithandle, but my idea was to create an instance that sends the message and waits for an event. As soon as the event arrived, checks if the message is the one I expect (checking the unique guid), otherwise continues to wait for the next event. This because could be (and usually is in this way) a lot of clients working concurrently, and I want them to work parallel. As I implemented my stuff, at the moment if I run client 1, client 2 and client 3, client 2 starts sending message as soon as client 1 has finished, and client 3 as client 2 has finished: not what I'm trying to do. Can you help me to fix my code and get my target? Thanks!

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