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  • Don&rsquo;t Kill the Password

    - by Anthony Trudeau
    A week ago Mr. Honan from Wired.com penned an article on security he titled “Kill the Password: Why a String of Characters Can’t Protect Us Anymore.” He asserts that the password is not effective and a new solution is needed. Unfortunately, Mr. Honan was a victim of hacking. As a result he has a victim’s vendetta. His conclusion is ill conceived even though there are smatterings of truth and good advice. The password is a security barrier much like a lock on your door. In of itself it’s not guaranteeing protection. You can have a good password akin to a steel reinforced door with the best lock money can buy, or you can have a poor password like “password” which is like a sliding lock like on a bathroom stall. But, just like in the real world a lock isn’t always enough. You can have a lock, security system, video cameras, guard dogs, and even armed security guards; but none of that guarantees your protection. Even top secret government agencies can be breached by someone who is just that good (as dramatized in movies like Mission Impossible). And that’s the crux of it. There are real hackers out there that are that good. Killer coding ninja monkeys do exist! We still have locks on our doors, because they still serve their role. Passwords are no different. Security doesn’t end with the password. Most people would agree that stuffing your mattress with your life savings isn’t a good idea even if you have the best locks and security system. Most people agree its safest to have the money in a bank. Essentially this is compartmentalization. Compartmentalization extends to the online world as well. You’re at risk if your online banking accounts are linked to the same account as your social networks. This is especially true if you’re lackadaisical about linking those social networks to outside sources including apps. The object here is to minimize the damage that can be done. An attacker should not be able to get into your bank account, because they breached your Twitter account. It’s time to prioritize once you’ve compartmentalized. This simply means deciding how much security you want for the different compartments which I’ll call security zones. Social networking applications like Facebook provide a lot of security features. However, security features are almost always a compromise with privacy and convenience. It’s similar to an engineering adage, but in this case it’s security, convenience, and privacy – pick two. For example, you might use a safe instead of bank to store your money, because the convenience of having your money closer or the privacy of not having the bank records is more important than the added security. The following are lists of security do’s and don’ts (these aren’t meant to be exhaustive and each could be an article in of themselves): Security Do’s: Use strong passwords based on a phrase Use encryption whenever you can (e.g. HTTPS in Facebook) Use a firewall (and learn to use it properly) Configure security on your router (including port blocking) Keep your operating system patched Make routine backups of important files Realize that if you’re not paying for it, you’re the product Security Don’ts Link accounts if at all possible Reuse passwords across your security zones Use real answers for security questions (e.g. mother’s maiden name) Trust anything you download Ignore message boxes shown by your system or browser Forget to test your backups Share your primary email indiscriminately Only you can decide your comfort level between convenience, privacy, and security. Attackers are going to find exploits in software. Software is complex and depends on other software. The exploits are the responsibility of the software company. But your security is always your responsibility. Complete security is an illusion. But, there is plenty you can do to minimize the risk online just like you do in the physical world. Be safe and enjoy what the Internet has to offer. I expect passwords to be necessary just as long as locks.

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  • Java Cloud Service Integration to REST Service

    - by Jani Rautiainen
    Service (JCS) provides a platform to develop and deploy business applications in the cloud. In Fusion Applications Cloud deployments customers do not have the option to deploy custom applications developed with JDeveloper to ensure the integrity and supportability of the hosted application service. Instead the custom applications can be deployed to the JCS and integrated to the Fusion Application Cloud instance. This series of articles will go through the features of JCS, provide end-to-end examples on how to develop and deploy applications on JCS and how to integrate them with the Fusion Applications instance. In this article a custom application integrating with REST service will be implemented. We will use REST services provided by Taleo as an example; however the same approach will work with any REST service. In this example the data from the REST service is used to populate a dynamic table. Pre-requisites Access to Cloud instance In order to deploy the application access to a JCS instance is needed, a free trial JCS instance can be obtained from Oracle Cloud site. To register you will need a credit card even if the credit card will not be charged. To register simply click "Try it" and choose the "Java" option. The confirmation email will contain the connection details. See this video for example of the registration.Once the request is processed you will be assigned 2 service instances; Java and Database. Applications deployed to the JCS must use Oracle Database Cloud Service as their underlying database. So when JCS instance is created a database instance is associated with it using a JDBC data source.The cloud services can be monitored and managed through the web UI. For details refer to Getting Started with Oracle Cloud. JDeveloper JDeveloper contains Cloud specific features related to e.g. connection and deployment. To use these features download the JDeveloper from JDeveloper download site by clicking the "Download JDeveloper 11.1.1.7.1 for ADF deployment on Oracle Cloud" link, this version of JDeveloper will have the JCS integration features that will be used in this article. For versions that do not include the Cloud integration features the Oracle Java Cloud Service SDK or the JCS Java Console can be used for deployment. For details on installing and configuring the JDeveloper refer to the installation guideFor details on SDK refer to Using the Command-Line Interface to Monitor Oracle Java Cloud Service and Using the Command-Line Interface to Manage Oracle Java Cloud Service. Access to a local database The database associated with the JCS instance cannot be connected to with JDBC.  Since creating ADFbc business component requires a JDBC connection we will need access to a local database. 3rd party libraries This example will use some 3rd party libraries for implementing the REST service call and processing the input / output content. Other libraries may also be used, however these are tested to work. Jersey 1.x Jersey library will be used as a client to make the call to the REST service. JCS documentation for supported specifications states: Java API for RESTful Web Services (JAX-RS) 1.1 So Jersey 1.x will be used. Download the single-JAR Jersey bundle; in this example Jersey 1.18 JAR bundle is used. Json-simple Jjson-simple library will be used to process the json objects. Download the  JAR file; in this example json-simple-1.1.1.jar is used. Accessing data in Taleo Before implementing the application it is beneficial to familiarize oneself with the data in Taleo. Easiest way to do this is by using a RESTClient on your browser. Once added to the browser you can access the UI: The client can be used to call the REST services to test the URLs and data before adding them into the application. First derive the base URL for the service this can be done with: Method: GET URL: https://tbe.taleo.net/MANAGER/dispatcher/api/v1/serviceUrl/<company name> The response will contain the base URL to be used for the service calls for the company. Next obtain authentication token with: Method: POST URL: https://ch.tbe.taleo.net/CH07/ats/api/v1/login?orgCode=<company>&userName=<user name>&password=<password> The response includes an authentication token that can be used for few hours to authenticate with the service: {   "response": {     "authToken": "webapi26419680747505890557"   },   "status": {     "detail": {},     "success": true   } } To authenticate the service calls navigate to "Headers -> Custom Header": And add a new request header with: Name: Cookie Value: authToken=webapi26419680747505890557 Once authentication token is defined the tool can be used to invoke REST services; for example: Method: GET URL: https://ch.tbe.taleo.net/CH07/ats/api/v1/object/candidate/search.xml?status=16 This data will be used on the application to be created. For details on the Taleo REST services refer to the Taleo Business Edition REST API Guide. Create Application First Fusion Web Application is created and configured. Start JDeveloper and click "New Application": Application Name: JcsRestDemo Application Package Prefix: oracle.apps.jcs.test Application Template: Fusion Web Application (ADF) Configure Local Cloud Connection Follow the steps documented in the "Java Cloud Service ADF Web Application" article to configure a local database connection needed to create the ADFbc objects. Configure Libraries Add the 3rd party libraries into the class path. Create the following directory and copy the jar files into it: <JDEV_USER_HOME>/JcsRestDemo/lib  Select the "Model" project, navigate "Application -> Project Properties -> Libraries and Classpath -> Add JAR / Directory" and add the 2 3rd party libraries: Accessing Data from Taleo To access data from Taleo using the REST service the 3rd party libraries will be used. 2 Java classes are implemented, one representing the Candidate object and another for accessing the Taleo repository Candidate Candidate object is a POJO object used to represent the candidate data obtained from the Taleo repository. The data obtained will be used to populate the ADFbc object used to display the data on the UI. The candidate object contains simply the variables we obtain using the REST services and the getters / setters for them: Navigate "New -> General -> Java -> Java Class", enter "Candidate" as the name and create it in the package "oracle.apps.jcs.test.model".  Copy / paste the following as the content: import oracle.jbo.domain.Number; public class Candidate { private Number candId; private String firstName; private String lastName; public Candidate() { super(); } public Candidate(Number candId, String firstName, String lastName) { super(); this.candId = candId; this.firstName = firstName; this.lastName = lastName; } public void setCandId(Number candId) { this.candId = candId; } public Number getCandId() { return candId; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getFirstName() { return firstName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getLastName() { return lastName; } } Taleo Repository Taleo repository class will interact with the Taleo REST services. The logic will query data from Taleo and populate Candidate objects with the data. The Candidate object will then be used to populate the ADFbc object used to display data on the UI. Navigate "New -> General -> Java -> Java Class", enter "TaleoRepository" as the name and create it in the package "oracle.apps.jcs.test.model".  Copy / paste the following as the content (for details of the implementation refer to the documentation in the code): import com.sun.jersey.api.client.Client; import com.sun.jersey.api.client.ClientResponse; import com.sun.jersey.api.client.WebResource; import com.sun.jersey.core.util.MultivaluedMapImpl; import java.io.StringReader; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.Map; import javax.ws.rs.core.MediaType; import javax.ws.rs.core.MultivaluedMap; import oracle.jbo.domain.Number; import org.json.simple.JSONArray; import org.json.simple.JSONObject; import org.json.simple.parser.JSONParser; /** * This class interacts with the Taleo REST services */ public class TaleoRepository { /** * Connection information needed to access the Taleo services */ String _company = null; String _userName = null; String _password = null; /** * Jersey client used to access the REST services */ Client _client = null; /** * Parser for processing the JSON objects used as * input / output for the services */ JSONParser _parser = null; /** * The base url for constructing the REST URLs. This is obtained * from Taleo with a service call */ String _baseUrl = null; /** * Authentication token obtained from Taleo using a service call. * The token can be used to authenticate on subsequent * service calls. The token will expire in 4 hours */ String _authToken = null; /** * Static url that can be used to obtain the url used to construct * service calls for a given company */ private static String _taleoUrl = "https://tbe.taleo.net/MANAGER/dispatcher/api/v1/serviceUrl/"; /** * Default constructor for the repository * Authentication details are passed as parameters and used to generate * authentication token. Note that each service call will * generate its own token. This is done to avoid dealing with the expiry * of the token. Also only 20 tokens are allowed per user simultaneously. * So instead for each call there is login / logout. * * @param company the company for which the service calls are made * @param userName the user name to authenticate with * @param password the password to authenticate with. */ public TaleoRepository(String company, String userName, String password) { super(); _company = company; _userName = userName; _password = password; _client = Client.create(); _parser = new JSONParser(); _baseUrl = getBaseUrl(); } /** * This obtains the base url for a company to be used * to construct the urls for service calls * @return base url for the service calls */ private String getBaseUrl() { String result = null; if (null != _baseUrl) { result = _baseUrl; } else { try { String company = _company; WebResource resource = _client.resource(_taleoUrl + company); ClientResponse response = resource.type(MediaType.APPLICATION_FORM_URLENCODED_TYPE).get(ClientResponse.class); String entity = response.getEntity(String.class); JSONObject jsonObject = (JSONObject)_parser.parse(new StringReader(entity)); JSONObject jsonResponse = (JSONObject)jsonObject.get("response"); result = (String)jsonResponse.get("URL"); } catch (Exception ex) { ex.printStackTrace(); } } return result; } /** * Generates authentication token, that can be used to authenticate on * subsequent service calls. Note that each service call will * generate its own token. This is done to avoid dealing with the expiry * of the token. Also only 20 tokens are allowed per user simultaneously. * So instead for each call there is login / logout. * @return authentication token that can be used to authenticate on * subsequent service calls */ private String login() { String result = null; try { MultivaluedMap<String, String> formData = new MultivaluedMapImpl(); formData.add("orgCode", _company); formData.add("userName", _userName); formData.add("password", _password); WebResource resource = _client.resource(_baseUrl + "login"); ClientResponse response = resource.type(MediaType.APPLICATION_FORM_URLENCODED_TYPE).post(ClientResponse.class, formData); String entity = response.getEntity(String.class); JSONObject jsonObject = (JSONObject)_parser.parse(new StringReader(entity)); JSONObject jsonResponse = (JSONObject)jsonObject.get("response"); result = (String)jsonResponse.get("authToken"); } catch (Exception ex) { throw new RuntimeException("Unable to login ", ex); } if (null == result) throw new RuntimeException("Unable to login "); return result; } /** * Releases a authentication token. Each call to login must be followed * by call to logout after the processing is done. This is required as * the tokens are limited to 20 per user and if not released the tokens * will only expire after 4 hours. * @param authToken */ private void logout(String authToken) { WebResource resource = _client.resource(_baseUrl + "logout"); resource.header("cookie", "authToken=" + authToken).post(ClientResponse.class); } /** * This method is used to obtain a list of candidates using a REST * service call. At this example the query is hard coded to query * based on status. The url constructed to access the service is: * <_baseUrl>/object/candidate/search.xml?status=16 * @return List of candidates obtained with the service call */ public List<Candidate> getCandidates() { List<Candidate> result = new ArrayList<Candidate>(); try { // First login, note that in finally block we must have logout _authToken = "authToken=" + login(); /** * Construct the URL, the resulting url will be: * <_baseUrl>/object/candidate/search.xml?status=16 */ MultivaluedMap<String, String> formData = new MultivaluedMapImpl(); formData.add("status", "16"); JSONArray searchResults = (JSONArray)getTaleoResource("object/candidate/search", "searchResults", formData); /** * Process the results, the resulting JSON object is something like * this (simplified for readability): * * { * "response": * { * "searchResults": * [ * { * "candidate": * { * "candId": 211, * "firstName": "Mary", * "lastName": "Stochi", * logic here will find the candidate object(s), obtain the desired * data from them, construct a Candidate object based on the data * and add it to the results. */ for (Object object : searchResults) { JSONObject temp = (JSONObject)object; JSONObject candidate = (JSONObject)findObject(temp, "candidate"); Long candIdTemp = (Long)candidate.get("candId"); Number candId = (null == candIdTemp ? null : new Number(candIdTemp)); String firstName = (String)candidate.get("firstName"); String lastName = (String)candidate.get("lastName"); result.add(new Candidate(candId, firstName, lastName)); } } catch (Exception ex) { ex.printStackTrace(); } finally { if (null != _authToken) logout(_authToken); } return result; } /** * Convenience method to construct url for the service call, invoke the * service and obtain a resource from the response * @param path the path for the service to be invoked. This is combined * with the base url to construct a url for the service * @param resource the key for the object in the response that will be * obtained * @param parameters any parameters used for the service call. The call * is slightly different depending whether parameters exist or not. * @return the resource from the response for the service call */ private Object getTaleoResource(String path, String resource, MultivaluedMap<String, String> parameters) { Object result = null; try { WebResource webResource = _client.resource(_baseUrl + path); ClientResponse response = null; if (null == parameters) response = webResource.header("cookie", _authToken).get(ClientResponse.class); else response = webResource.queryParams(parameters).header("cookie", _authToken).get(ClientResponse.class); String entity = response.getEntity(String.class); JSONObject jsonObject = (JSONObject)_parser.parse(new StringReader(entity)); result = findObject(jsonObject, resource); } catch (Exception ex) { ex.printStackTrace(); } return result; } /** * Convenience method to recursively find a object with an key * traversing down from a given root object. This will traverse a * JSONObject / JSONArray recursively to find a matching key, if found * the object with the key is returned. * @param root root object which contains the key searched for * @param key the key for the object to search for * @return the object matching the key */ private Object findObject(Object root, String key) { Object result = null; if (root instanceof JSONObject) { JSONObject rootJSON = (JSONObject)root; if (rootJSON.containsKey(key)) { result = rootJSON.get(key); } else { Iterator children = rootJSON.entrySet().iterator(); while (children.hasNext()) { Map.Entry entry = (Map.Entry)children.next(); Object child = entry.getValue(); if (child instanceof JSONObject || child instanceof JSONArray) { result = findObject(child, key); if (null != result) break; } } } } else if (root instanceof JSONArray) { JSONArray rootJSON = (JSONArray)root; for (Object child : rootJSON) { if (child instanceof JSONObject || child instanceof JSONArray) { result = findObject(child, key); if (null != result) break; } } } return result; } }   Creating Business Objects While JCS application can be created without a local database, the local database is required when using ADFbc objects even if database objects are not referred. For this example we will create a "Transient" view object that will be programmatically populated based the data obtained from Taleo REST services. Creating ADFbc objects Choose the "Model" project and navigate "New -> Business Tier : ADF Business Components : View Object". On the "Initialize Business Components Project" choose the local database connection created in previous step. On Step 1 enter "JcsRestDemoVO" on the "Name" and choose "Rows populated programmatically, not based on query": On step 2 create the following attributes: CandId Type: Number Updatable: Always Key Attribute: checked Name Type: String Updatable: Always On steps 3 and 4 accept defaults and click "Next".  On step 5 check the "Application Module" checkbox and enter "JcsRestDemoAM" as the name: Click "Finish" to generate the objects. Populating the VO To display the data on the UI the "transient VO" is populated programmatically based on the data obtained from the Taleo REST services. Open the "JcsRestDemoVOImpl.java". Copy / paste the following as the content (for details of the implementation refer to the documentation in the code): import java.sql.ResultSet; import java.util.List; import java.util.ListIterator; import oracle.jbo.server.ViewObjectImpl; import oracle.jbo.server.ViewRowImpl; import oracle.jbo.server.ViewRowSetImpl; // --------------------------------------------------------------------- // --- File generated by Oracle ADF Business Components Design Time. // --- Tue Feb 18 09:40:25 PST 2014 // --- Custom code may be added to this class. // --- Warning: Do not modify method signatures of generated methods. // --------------------------------------------------------------------- public class JcsRestDemoVOImpl extends ViewObjectImpl { /** * This is the default constructor (do not remove). */ public JcsRestDemoVOImpl() { } @Override public void executeQuery() { /** * For some reason we need to reset everything, otherwise * 2nd entry to the UI screen may fail with * "java.util.NoSuchElementException" in createRowFromResultSet * call to "candidates.next()". I am not sure why this is happening * as the Iterator is new and "hasNext" is true at the point * of the execution. My theory is that since the iterator object is * exactly the same the VO cache somehow reuses the iterator including * the pointer that has already exhausted the iterable elements on the * previous run. Working around the issue * here by cleaning out everything on the VO every time before query * is executed on the VO. */ getViewDef().setQuery(null); getViewDef().setSelectClause(null); setQuery(null); this.reset(); this.clearCache(); super.executeQuery(); } /** * executeQueryForCollection - overridden for custom java data source support. */ protected void executeQueryForCollection(Object qc, Object[] params, int noUserParams) { /** * Integrate with the Taleo REST services using TaleoRepository class. * A list of candidates matching a hard coded query is obtained. */ TaleoRepository repository = new TaleoRepository(<company>, <username>, <password>); List<Candidate> candidates = repository.getCandidates(); /** * Store iterator for the candidates as user data on the collection. * This will be used in createRowFromResultSet to create rows based on * the custom iterator. */ ListIterator<Candidate> candidatescIterator = candidates.listIterator(); setUserDataForCollection(qc, candidatescIterator); super.executeQueryForCollection(qc, params, noUserParams); } /** * hasNextForCollection - overridden for custom java data source support. */ protected boolean hasNextForCollection(Object qc) { boolean result = false; /** * Determines whether there are candidates for which to create a row */ ListIterator<Candidate> candidates = (ListIterator<Candidate>)getUserDataForCollection(qc); result = candidates.hasNext(); /** * If all candidates to be created indicate that processing is done */ if (!result) { setFetchCompleteForCollection(qc, true); } return result; } /** * createRowFromResultSet - overridden for custom java data source support. */ protected ViewRowImpl createRowFromResultSet(Object qc, ResultSet resultSet) { /** * Obtain the next candidate from the collection and create a row * for it. */ ListIterator<Candidate> candidates = (ListIterator<Candidate>)getUserDataForCollection(qc); ViewRowImpl row = createNewRowForCollection(qc); try { Candidate candidate = candidates.next(); row.setAttribute("CandId", candidate.getCandId()); row.setAttribute("Name", candidate.getFirstName() + " " + candidate.getLastName()); } catch (Exception e) { e.printStackTrace(); } return row; } /** * getQueryHitCount - overridden for custom java data source support. */ public long getQueryHitCount(ViewRowSetImpl viewRowSet) { /** * For this example this is not implemented rather we always return 0. */ return 0; } } Creating UI Choose the "ViewController" project and navigate "New -> Web Tier : JSF : JSF Page". On the "Create JSF Page" enter "JcsRestDemo" as name and ensure that the "Create as XML document (*.jspx)" is checked.  Open "JcsRestDemo.jspx" and navigate to "Data Controls -> JcsRestDemoAMDataControl -> JcsRestDemoVO1" and drag & drop the VO to the "<af:form> " as a "ADF Read-only Table": Accept the defaults in "Edit Table Columns". To execute the query navigate to to "Data Controls -> JcsRestDemoAMDataControl -> JcsRestDemoVO1 -> Operations -> Execute" and drag & drop the operation to the "<af:form> " as a "Button": Deploying to JCS Follow the same steps as documented in previous article"Java Cloud Service ADF Web Application". Once deployed the application can be accessed with URL: https://java-[identity domain].java.[data center].oraclecloudapps.com/JcsRestDemo-ViewController-context-root/faces/JcsRestDemo.jspx The UI displays a list of candidates obtained from the Taleo REST Services: Summary In this article we learned how to integrate with REST services using Jersey library in JCS. In future articles various other integration techniques will be covered.

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  • CLR via C# 3rd Edition is out

    - by Abhijeet Patel
    Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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  • MySQL Connector/Net 6.5.5 Maintenance Release has been released

    - by fernando
    MySQL Connector/Net 6.5.5, a new maintenance release of our 6.5 series, has been released.  This release is GA quality and is appropriate for use in production environments.  Please note that 6.6 is our latest driver series and is the recommended product for development. It is now available in source and binary form from http://dev.mysql.com/downloads/connector/net/#downloads and mirror sites (note that not all mirror sites may be up to date at this point-if you can't find this version on some mirror, please try again later or choose another download site.) The 6.5.5 version of MySQL Connector/Net brings the following fixes: - Fix for ArgumentNull exception when using Take().Count() in a LINQ to Entities query (bug MySql #64749, Oracle bug #13913047). - Fix for type varchar changed to bit when saving in Table Designer (Oracle bug #13916560). - Fix for error when trying to change the name of an Index on the Indexes/Keys editor; along with this fix now users can change the Index type of a new Index which could not be done   in previous versions, and when changing the Index name the change is reflected on the list view at the left side of the Index/Keys editor (Oracle bug #13613801). - Fix for stored procedure call using only its name with EF code first (MySql bug #64999, Oracle bug #14008699). - Fix for List.Contains generates a bunch of ORs instead of more efficient IN clause in   LINQ to Entities (Oracle bug #14016344, MySql bug #64934). - Fix for performance issue in generated EF query: .NET StartsWith/Contains/EndsWith produces MySql's locate instead of Like (MySql bug #64935, Oracle bug #14009363). - Fix for script generated for code first contains wrong alter table and wrong declaration for byte[] (MySql bug #64216, Oracle bug #13900091). - Fix and code contribution for bug Timed out sessions are removed without notification which allow to enable the Expired CallBack when Session Provider times out any session (bug MySql #62266 Oracle bug # 13354935) - Fix for Exception thrown when using cascade delete in an EDM Model-First in Entity Framework (Oracle bug #14008752, MySql bug #64779). - Fix for Session locking issue with MySqlSessionStateStore (MySql bug #63997, Oracble bug #13733054). - Fixed deleting a user profile using Profile provider (MySQL bug #64470, Oracle bug #13790123) - Fix for bug Cannot Create an Entity with a Key of Type String (MySQL bug #65289, Oracle bug #14540202). This fix checks if the type has a FixedLength facet set in order to create a char otherwise should create varchar, mediumtext or longtext types when using a String CLR type in Code First or Model First also tested in Database First. Unit tests added for Code First and ProviderManifest. - Fix for bug "CacheServerProperties can cause 'Packet too large' error". The issue was due to a missing reading of Max_allowed_packet server property when CacheServerProperties is in true, since the value was read only in the first connection but the following pooled connections had a wrong value causing a Packet too large error. Including also a unit test for this scenario. All unit test passed. MySQL Bug #66578 Orabug #14593547. - Fix for handling unnamed parameter in MySQLCommand. This fix allows the mysqlcommand to handle parameters without requiring naming (e.g. INSERT INTO Test (id,name) VALUES (?, ?) ) (MySQL Bug #66060, Oracle bug #14499549). - Fixed inheritance on Entity Framework Code First scenarios. Discriminator column is created using its correct type as varchar(128) (MySql bug #63920 and Oracle bug #13582335). - Fixed "Trying to customize column precision in Code First does not work" (MySql bug #65001, Oracle bug #14469048). - Fixed bug ASP.NET Membership database fails on MySql database UTF32 (MySQL bug #65144, Oracle bug #14495292). - Fix for MySqlCommand.LastInsertedId holding only 32 bit values (MySql bug #65452, Oracle bug #14171960) by changing   several internal declaration of lastinsertid from int to long. - Fixed "Decimal type should have digits at right of decimal point", now default is 2, but user's changes in   EDM designer are recognized (MySql bug #65127, Oracle bug #14474342). - Fix for NullReferenceException when saving an uninitialized row in Entity Framework (MySql bug #66066, Oracle bug #14479715). - Fix for error when calling RoleProvider.RemoveUserFromRole(): causes an exception due to a wrong table being used (MySql bug #65805, Oracle bug #14405338). - Fix for "Memory Leak on MySql.Data.MySqlClient.MySqlCommand", too many MemoryStream's instances created (MySql bug #65696, Oracle bug #14468204). - Added ANTLR attribution notice (Oracle bug #14379162). - Fixed Entity Framework + mysql connector/net in partial trust throws exceptions (MySql bug #65036, Oracle bug #14668820). - Added support in Parser for Datetime and Time types with precision when using Server 5.6 (No bug Number). - Small improvement on MySqlPoolManager CleanIdleConnections for better mysqlpoolmanager idlecleanuptimer at startup (MySql bug #66472 and Oracle bug #14652624). - Fix for bug TIMESTAMP values are mistakenly represented as DateTime with Kind = Local (Mysql bug #66964, Oracle bug #14740705). - Fix for bug Keyword not supported. Parameter name: AttachDbFilename (Mysql bug #66880, Oracle bug #14733472). - Added support to MySql script file to retrieve data when using "SHOW" statements. - Fix for Package Load Failure in Visual Studio 2005 (MySql bug #63073, Oracle bug #13491674). - Fix for bug "Unable to connect using IPv6 connections" (MySQL bug #67253, Oracle bug #14835718). - Added auto-generated values for Guid identity columns (MySql bug #67450, Oracle bug #15834176). - Fix for method FirstOrDefault not supported in some LINQ to Entities queries (MySql bug #67377, Oracle bug #15856964). The release is available to download at http://dev.mysql.com/downloads/connector/net/6.5.html Documentation ------------------------------------- You can view current Connector/Net documentation at http://dev.mysql.com/doc/refman/5.5/en/connector-net.html You can find our team blog at http://blogs.oracle.com/MySQLOnWindows. You can also post questions on our forums at http://forums.mysql.com/. Enjoy and thanks for the support! 

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  • Get and Set property accessors are ‘actually’ methods

    - by nmarun
    Well, they are ‘special’ methods, but they indeed are methods. See the class below: 1: public class Person 2: { 3: private string _name; 4:  5: public string Name 6: { 7: get 8: { 9: return _name; 10: } 11: set 12: { 13: if (value == "aaa") 14: { 15: throw new ArgumentException("Invalid Name"); 16: } 17: _name = value; 18: } 19: } 20:  21: public void Save() 22: { 23: Console.WriteLine("Saving..."); 24: } 25: } Ok, so a class with a field, a property with the get and set accessors and a method. Now my calling code says: 1: static void Main() 2: { 3: try 4: { 5: Person person1 = new Person 6: { 7: Name = "aaa", 8: }; 9:  10: } 11: catch (Exception ex) 12: { 13: Console.WriteLine(ex.Message); 14: Console.WriteLine(ex.StackTrace); 15: Console.WriteLine("--------------------"); 16: } 17: } When the code is run, you’ll get the following exception message displayed: Now, you see the first line of the stack trace where it says that the exception was thrown in the method set_Name(String value). Wait a minute, we have not declared any method with that name in our Person class. Oh no, we actually have. When you create a property, this is what happens behind the screen. The CLR creates two methods for each get and set property accessor. Let’s look at the signature once again: set_Name(String value) This also tells you where the ‘value’ keyword comes from in our set property accessor. You’re actually wiring up a method parameter to a field. 1: set 2: { 3: if (value == "aaa") 4: { 5: throw new ArgumentException("Invalid Name"); 6: } 7: _name = value; 8: } Digging deeper on this, I ran the ILDasm tool and this is what I see: We see the ‘free’ constructor (named .ctor) that the compiler gives us, the _name field, the Name property and the Save method. We also see the get_Name and set_Name methods. In order to compare the Save and the set_Name methods, I double-clicked on the two methods and this is what I see: The ‘.method’ keyword tells that both Save and set_Name are both methods (no guessing there!). Seeing the set_Name method as a public method did kinda surprise me. So I said, why can’t I do a person1.set_Name(“abc”) since it is declared as public. This cannot be done because the get_Name and set_Name methods have an extra attribute called ‘specialname’. This attribute is used to identify an IL (Intermediate Language) token that can be treated with special care by the .net language. So the thumb-rule is that any method with the ‘specialname’ attribute cannot be generally called / invoked by the user (a simple test using intellisense proves this). Their functionality is exposed through other ways. In our case, this is done through the property itself. The same concept gets extended to constructors as well making them special methods too. These so-called ‘special’ methods can be identified through reflection. 1: static void ReflectOnPerson() 2: { 3: Type personType = typeof(Person); 4:  5: MethodInfo[] methods = personType.GetMethods(); 6:  7: for (int i = 0; i < methods.Length; i++) 8: { 9: Console.Write("Method: {0}", methods[i].Name); 10: // Determine whether or not each method is a special name. 11: if (methods[i].IsSpecialName) 12: { 13: Console.Write(" has 'SpecialName' attribute"); 14: } 15: Console.WriteLine(); 16: } 17: } Line 11 shows the ‘IsSpecialName’ boolean property. So a method with a ‘specialname’ attribute gets mapped to the IsSpecialName property. The output is displayed as: Wuhuuu! There they are.. our special guests / methods. Verdict: Getting to know the internals… helps!

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  • regarding the Windows Phone 7 series, XNA and Visual Basic

    - by Chris Williams
    as long as we're talking about VB... I figured I would share this as well. Hi everyone, I'm about to express a sentiment that might ruffle a few feathers, but I think most of you know me well enough to know I love like accept VB for what it is and that what I'm about to say is with good intentions. (The rest of you, who don't know me, please take my word for it.) The world is full of VB developers, I was one of them for a long time. I think it's safe to assume that none of us are ignorant people who require handholding. We're working professionals, making a living by using our skills as developers. I'm also willing to bet that quite a few of us are fluent in C# as well as VB. It may not be your preferred language, but many of you can do it and you prove that nearly every day. Honestly, I don't know ANY developers or consultants that have only known ONE language ever. So it pains me greatly when I see the word "CAN'T" being tossed around like a crutch... as in "we CAN'T develop for the windows phone or we CAN'T develop XNA games." At MIX, Microsoft hath decreed that C# is the language of choice for developing for the Windows Phone 7. I think it's a safe bet that you won't see VB support if it isn't there already. (Just like XNA... which is up to version 4.0 by now.)  So what? (Yeah... I said it.) I think everyone here can agree that actual coding is only one part of software design and development. There is nothing stopping ANY of you from beginning the process of designing your killer phone app, writing up specs, requirements, doing UI design, workflow, mockups, storyboards, art, etc.... None of these things are language dependent. IF by the time you've got that stuff out of the way, and there's still no VB support, then start doing some rapid prototyping of your app in C# (I know, I know... heresy!)  You still have to spend time learning how the phone does things, what UI tricks do what, what paradigms make sense, how to use to accelerometer and the tilt and the multitouch functionality. I can guarantee you that time spent doing this is a great investment, no matter WHAT extension your code files have. Eventually, you may have a working prototype. IF by this time, there's STILL no VB support... fret not, you've made significant progress on your app. You've designed it, prototyped it, figured out how to use the phone specific features... so you might as well finish it and pat yourself on the back for learning something new... and possibly being first to market with your new app. I'll be happy to argue any and all of these points online or off with anyone who cares to do so, but there is one undeniable point that you simply can't argue:  Your potential customers do not care AT ALL what programming language you used to write the app they are about to purchase. They care that it works. If your biggest concern is being first to market, than stop complaining and get busy because you're running out of time and the 3000+ people who were at MIX certainly aren't waiting for you. They've already started working on their apps.

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  • Using Delegates in C# (Part 1)

    - by rajbk
    This post provides a very basic introduction of delegates in C#. Part 2 of this post can be read here. A delegate is a class that is derived from System.Delegate.  It contains a list of one or more methods called an invocation list. When a delegate instance is “invoked” with the arguments as defined in the signature of the delegate, each of the methods in the invocation list gets invoked with the arguments. The code below shows example with static and instance methods respectively: Static Methods 1: using System; 2: using System.Linq; 3: using System.Collections.Generic; 4: 5: public delegate void SayName(string name); 6: 7: public class Program 8: { 9: [STAThread] 10: static void Main(string[] args) 11: { 12: SayName englishDelegate = new SayName(SayNameInEnglish); 13: SayName frenchDelegate = new SayName(SayNameInFrench); 14: SayName combinedDelegate =(SayName)Delegate.Combine(englishDelegate, frenchDelegate); 15: 16: combinedDelegate.Invoke("Tom"); 17: Console.ReadLine(); 18: } 19: 20: static void SayNameInFrench(string name) { 21: Console.WriteLine("J'ai m'appelle " + name); 22: } 23: 24: static void SayNameInEnglish(string name) { 25: Console.WriteLine("My name is " + name); 26: } 27: } We have declared a delegate of type SayName with return type of void and taking an input parameter of name of type string. On line 12, we create a new instance of this delegate which refers to a static method - SayNameInEnglish.  SayNameInEnglish has the same return type and parameter list as the delegate declaration.  Once a delegate is instantiated, the instance will always refer to the same target. Delegates are immutable. On line 13, we create a new instance of the delegate but point to a different static method. As you may recall, a delegate instance encapsulates an invocation list. You create an invocation list by combining delegates using the Delegate.Combine method (there is an easier syntax as you will see later). When two non null delegate instances are combined, their invocation lists get combined to form a new invocation list. This is done in line 14.  On line 16, we invoke the delegate with the Invoke method and pass in the required string parameter. Since the delegate has an invocation list with two entries, each of the method in the invocation list is invoked. If an unhandled exception occurs during the invocation of one of these methods, the exception gets bubbled up to the line where the invocation was made (line 16). If a delegate is null and you try to invoke it, you will get a System.NullReferenceException. We see the following output when the method is run: My name is TomJ'ai m'apelle Tom Instance Methods The code below outputs the same results as before. The only difference here is we are creating delegates that point to a target object (an instance of Translator) and instance methods which have the same signature as the delegate type. The target object can never be null. We also use the short cut syntax += to combine the delegates instead of Delegate.Combine. 1: public delegate void SayName(string name); 2: 3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Translator translator = new Translator(); 9: SayName combinedDelegate = new SayName(translator.SayNameInEnglish); 10: combinedDelegate += new SayName(translator.SayNameInFrench); 11:  12: combinedDelegate.Invoke("Tom"); 13: Console.ReadLine(); 14: } 15: } 16: 17: public class Translator { 18: public void SayNameInFrench(string name) { 19: Console.WriteLine("J'ai m'appelle " + name); 20: } 21: 22: public void SayNameInEnglish(string name) { 23: Console.WriteLine("My name is " + name); 24: } 25: } A delegate can be removed from a combination of delegates by using the –= operator. Removing a delegate from an empty list or removing a delegate that does not exist in a non empty list will not result in an exception. Delegates are invoked synchronously using the Invoke method. We can also invoke them asynchronously using the BeginInvoke and EndInvoke methods which are compiler generated.

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  • Oracle Employees Support New World Record for IYF Children's Hour

    - by Maria Sandu
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 960 students ‘crouched’, ‘touched’ and ‘set’ under the watchful eye of International Rugby Referee Alain Roland, and supported by Oracle employees, to successfully set a new world record for the World’s Largest Scrum to raise funds and awareness for the Irish Youth Foundation. Last year Oracle Employees supported the Irish Youth Foundation by donating funds from their payroll through the Giving Tree Appeal. We were the largest corporate donor to the IYF by raising €3075. To acknowledge our generosity the IYF asked Oracle Leadership in Society team members to participate in their most recent campaign which was to break the Guinness Book of Records by forming the World’s Largest Rugby Scrum. This was a wonderful opportunity for Oracle’s Leadership in Society to promote the charity, support education and to make a mark in the Corporate Social Responsibility field. The students who formed the scrum also gave up their lunch money and raised a total of €3000. This year we hope Oracle Employees will once again support the IYF with the challenge to match that amount. On the 24th of October the sun shone down on the streaming lines of students entering the field. 480 students were decked out in bright red Oracle T-Shirts against the other 480 in blue and white jerseys - all ready to form a striking scrum. Ryan Tubridy the host of the event made the opening announcement and with the blow of a whistle the Scum began. 960 students locked tight together with the Leinster players also at each side. Leinster Manager Matt O’Connor was there along with presenters Ryan Tubridy and George Hook to assist with getting the boys in line and keeping the shape of the scrum. In accordance with Guinness Book of Records rules, the ball was fed into the scrum properly by Ireland and Leinster scrum-half, Eoin Reddan, and was then passed out the line to his Leinster team mates including Ian Madigan, Brendan Macken and Jordi Murphy, also proudly sporting the Oracle T-Shirt. The new World Record was made, everyone gave a big cheer and thankfully nobody got injured! Thank you to everyone in Oracle who donated last year through the Giving Tree Appeal. Your generosity has gone a long way to support local groups both. Last year’s donation was so substantial that the IYF were able to spread it across two youth groups: The first being Ballybough Youth Project in Dublin. The funding gave them the chance to give 24 young people from their project the chance to get away from the inner city and the problems and issues they face in their daily life by taking a trip to the Cavan Centre to spend a weekend away in a safe and comfortable environment; a very rare holiday in these young people’s lives. The Rahoon Family Centre. Used the money to help secure the long term sustainability of their project. They act as an educational/social/fun project that has been working with disadvantaged children for the past 16 years. Their aim is to change young people’s future with fun /social education and supporting them so they can maximize their creativity and potential. We hope you can help support this worthy cause again this year, so keep an eye out for the Children’s Hour and Giving Tree Appeal! About the Irish Youth Foundation The IYF provides opportunities for marginalised children and young people facing difficult and extreme conditions to experience success in their lives. It passionately believes that achievement starts with opportunity. The IYF’s strategy is based on providing safe places where children can go after school; to grow, to learn and to play; and providing opportunities for teenagers from under-served communities to succeed and excel in their lives. The IYF supports innovative grassroots projects operated by dedicated professionals who understand young people and care about them. This allows the IYF to focus on supporting young people at risk of dropping out of school and, in particular, on the critical transition from primary to secondary school; and empowering teenagers from disadvantaged neighborhoods to become engaged in their local communities. Find out more here www.iyf.ie

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  • Writing an ASP.Net Web based TFS Client

    - by Glav
    So one of the things I needed to do was write an ASP.Net MVC based application for our senior execs to manage a set of arbitrary attributes against stories, bugs etc to be able to attribute whether the item was related to Research and Development, and if so, what kind. We are using TFS Azure and don’t have the option of custom templates. I have decided on using a string based field within the template that is not very visible and which we don’t use to write a small set of custom which will determine the research and development association. However, this string munging on the field is not very user friendly so we need a simple tool that can display attributes against items in a simple dropdown list or something similar. Enter a custom web app that accesses our TFS items in Azure (Note: We are also using Visual Studio 2012) Now TFS Azure uses your Live ID and it is not really possible to easily do this in a server based app where no interaction is available. Even if you capture the Live ID credentials yourself and try to submit them to TFS Azure, it wont work. Bottom line is that it is not straightforward nor obvious what you have to do. In fact, it is a real pain to find and there are some answers out there which don’t appear to be answers at all given they didn’t work in my scenario. So for anyone else who wants to do this, here is a simple breakdown on what you have to do: Go here and get the “TFS Service Credential Viewer”. Install it, run it and connect to your TFS instance in azure and create a service account. Note the username and password exactly as it presents it to you. This is the magic identity that will allow unattended, programmatic access. Without this step, don’t bother trying to do anything else. In your MVC app, reference the following assemblies from “C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\ReferenceAssemblies\v2.0”: Microsoft.TeamFoundation.Client.dll Microsoft.TeamFoundation.Common.dll Microsoft.TeamFoundation.VersionControl.Client.dll Microsoft.TeamFoundation.VersionControl.Common.dll Microsoft.TeamFoundation.WorkItemTracking.Client.DataStoreLoader.dll Microsoft.TeamFoundation.WorkItemTracking.Client.dll Microsoft.TeamFoundation.WorkItemTracking.Common.dll If hosting this in Internet Information Server, for the application pool this app runs under, you will need to enable 32 Bit support. You also have to allow the TFS client assemblies to store a cache of files on your system. If you don’t do this, you will authenticate fine, but then get an exception saying that it is unable to access the cache at some directory path when you query work items. You can set this up by adding the following to your web.config, in the <appSettings> element as shown below: <appSettings> <!-- Add reference to TFS Client Cache --> <add key="WorkItemTrackingCacheRoot" value="C:\windows\temp" /> </appSettings> With all that in place, you can write the following code: var token = new Microsoft.TeamFoundation.Client.SimpleWebTokenCredential("{you-service-account-name", "{your-service-acct-password}"); var clientCreds = new Microsoft.TeamFoundation.Client.TfsClientCredentials(token); var currentCollection = new TfsTeamProjectCollection(new Uri(“https://{yourdomain}.visualstudio.com/defaultcollection”), clientCreds); TfsConfigurationServercurrentCollection.EnsureAuthenticated(); In the above code, not the URL contains the “defaultcollection” at the end of the URL. Obviously replace {yourdomain} with whatever is defined for your TFS in Azure instance. In addition, make sure the service user account and password that was generated in the first step is substituted in here. Note: If something is not right, the “EnsureAuthenticated()” call will throw an exception with the message being you are not authorised. If you forget the “defaultcollection” on the URL, it will still fail but with a message saying you are not authorised. That is, a similar but different exception message. And that is it. You can then query the collection using something like: var service = currentCollection.GetService<WorkItemStore>(); var proj = service.Projects[0]; var allQueries = proj.StoredQueries; for (int qcnt = 0; qcnt < allQueries.Count; qcnt++) {     var query = allQueries[qcnt];     var queryDesc = string.format(“Query found named: {0}”,query.Name); } You get the idea. If you search around, you will find references to the ServiceIdentityCredentialProvider which is referenced in this article. I had no luck with this method and it all looked too hard since it required an extra KB article and other magic sauce. So I hope that helps. This article certainly would have helped me save a boat load of time and frustration.

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  • WebSocket API 1.1 released!

    - by Pavel Bucek
    Its my please to announce that JSR 356 – Java API for WebSocket maintenance release ballot vote finished with majority of “yes” votes (actually, only one eligible voter did not vote, all other votes were “yeses”). New release is maintenance release and it addresses only one issue:  WEBSOCKET_SPEC-226. What changed in the 1.1? Version 1.1 is fully backwards compatible with version 1.0, there are only two methods added to javax.websocket.Session: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 /** * Register to handle to incoming messages in this conversation. A maximum of one message handler per * native websocket message type (text, binary, pong) may be added to each Session. I.e. a maximum * of one message handler to handle incoming text messages a maximum of one message handler for * handling incoming binary messages, and a maximum of one for handling incoming pong * messages. For further details of which message handlers handle which of the native websocket * message types please see {@link MessageHandler.Whole} and {@link MessageHandler.Partial}. * Adding more than one of any one type will result in a runtime exception. * * @param clazz   type of the message processed by message handler to be registered. * @param handler whole message handler to be added. * @throws IllegalStateException if there is already a MessageHandler registered for the same native *                               websocket message type as this handler. */ public void addMessageHandler(Class<T> clazz, MessageHandler.Whole<T> handler); /** * Register to handle to incoming messages in this conversation. A maximum of one message handler per * native websocket message type (text, binary, pong) may be added to each Session. I.e. a maximum * of one message handler to handle incoming text messages a maximum of one message handler for * handling incoming binary messages, and a maximum of one for handling incoming pong * messages. For further details of which message handlers handle which of the native websocket * message types please see {@link MessageHandler.Whole} and {@link MessageHandler.Partial}. * Adding more than one of any one type will result in a runtime exception. * * * @param clazz   type of the message processed by message handler to be registered. * @param handler partial message handler to be added. * @throws IllegalStateException if there is already a MessageHandler registered for the same native *                               websocket message type as this handler. */ public void addMessageHandler(Class<T> clazz, MessageHandler.Partial<T> handler); Why do we need to add those methods? Short and not precise version: to support Lambda expressions as MessageHandlers. Longer and slightly more precise explanation: old Session#addMessageHandler method (which is still there and works as it worked till now) does rely on getting the generic parameter during the runtime, which is not (always) possible. The unfortunate part is that it works for some common cases and the expert group did not catch this issue before 1.0 release because of that. The issue is really clearly visible when Lambdas are used as message handlers: 1 2 3 session.addMessageHandler(message -> { System.out.println("### Received: " + message); }); There is no way for the JSR 356 implementation to get the type of the used Lambda expression, thus this call will always result in an exception. Since all modern IDEs do recommend to use Lambda expressions when possible and MessageHandler interfaces are single method interfaces, it basically just scream “use Lambdas” all over the place but when you do that, the application will fail during runtime. Only solution we currently have is to explicitly provide the type of registered MessageHandler. (There might be another sometime in the future when generic type reification is introduced, but that is not going to happen soon enough). So the example above will then be: 1 2 3 session.addMessageHandler(String.class, message -> { System.out.println("### Received: " + message); }); and voila, it works. There are some limitations – you cannot do 1 List<String>.class , so you will need to encapsulate these types when you want to use them in MessageHandler implementation (something like “class MyType extends ArrayList<String>”). There is no better way how to solve this issue, because Java currently does not provide good way how to describe generic types. The api itself is available on maven central, look for javax.websocket:javax.websocket-api:1.1. The reference implementation is project Tyrus, which implements WebSocket API 1.1 from version 1.8.

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  • Thread.Interrupt Is Evil

    - by Alois Kraus
    Recently I have found an interesting issue with Thread.Interrupt during application shutdown. Some application was crashing once a week and we had not really a clue what was the issue. Since it happened not very often it was left as is until we have got some memory dumps during the crash. A memory dump usually means WindDbg which I really like to use (I know I am one of the very few fans of it).  After a quick analysis I did find that the main thread already had exited and the thread with the crash was stuck in a Monitor.Wait. Strange Indeed. Running the application a few thousand times under the debugger would potentially not have shown me what the reason was so I decided to what I call constructive debugging. I did create a simple Console application project and try to simulate the exact circumstances when the crash did happen from the information I have via memory dump and source code reading. The thread that was  crashing was actually MS code from an old version of the Microsoft Caching Application Block. From reading the code I could conclude that the main thread did call the Dispose method on the CacheManger class which did call Thread.Interrupt on the cache scavenger thread which was just waiting for work to do. My first version of the repro looked like this   static void Main(string[] args) { Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); } static void ThreadFunc() { while (true) { object value = Dequeue(); // block until unblocked or awaken via ThreadInterruptedException } } static object WaitObject = new object(); static object Dequeue() { object lret = "got value"; try { lock (WaitObject) { } } catch (ThreadInterruptedException) { Console.WriteLine("Got ThreadInterruptException"); lret = null; } return lret; } I do start a background thread and call Thread.Interrupt on it and then directly let the application terminate. The thread in the meantime does plenty of Monitor.Enter/Leave calls to simulate work on it. This first version did not crash. So I need to dig deeper. From the memory dump I did know that the finalizer thread was doing just some critical finalizers which were closing file handles. Ok lets add some long running finalizers to the sample. class FinalizableObject : CriticalFinalizerObject { ~FinalizableObject() { Console.WriteLine("Hi we are waiting to finalize now and block the finalizer thread for 5s."); Thread.Sleep(5000); } } class Program { static void Main(string[] args) { FinalizableObject fin = new FinalizableObject(); Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); GC.KeepAlive(fin); // prevent finalizing it too early // After leaving main the other thread is woken up via Thread.Abort // while we are finalizing. This causes a stackoverflow in the CLR ThreadAbortException handling at this time. } With this changed Main method and a blocking critical finalizer I did get my crash just like the real application. The funny thing is that this is actually a CLR bug. When the main method is left the CLR does suspend all threads except the finalizer thread and declares all objects as garbage. After the normal finalizers were called the critical finalizers are executed to e.g. free OS handles (usually). Remember that I did call Thread.Interrupt as one of the last methods in the Main method. The Interrupt method is actually asynchronous and does wake a thread up and throws a ThreadInterruptedException only once unlike Thread.Abort which does rethrow the exception when an exception handling clause is left. It seems that the CLR does not expect that a frozen thread does wake up again while the critical finalizers are executed. While trying to raise a ThreadInterrupedException the CLR goes down with an stack overflow. Ups not so nice. Why has this nobody noticed for years is my next question. As it turned out this error does only happen on the CLR for .NET 4.0 (x86 and x64). It does not show up in earlier or later versions of the CLR. I have reported this issue on connect here but so far it was not confirmed as a CLR bug. But I would be surprised if my console application was to blame for a stack overflow in my test thread in a Monitor.Wait call. What is the moral of this story? Thread.Abort is evil but Thread.Interrupt is too. It is so evil that even the CLR of .NET 4.0 contains a race condition during the CLR shutdown. When the CLR gurus can get it wrong the chances are high that you get it wrong too when you use this constructs. If you do not believe me see what Patrick Smacchia does blog about Thread.Abort and List.Sort. Not only the CLR creators can get it wrong. The BCL writers do sometimes have a hard time with correct exception handling as well. If you do tell me that you use Thread.Abort frequently and never had problems with it I do suspect that you do not have looked deep enough into your application to find such sporadic errors.

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  • Feynman's inbox

    - by user12607414
    Here is Richard Feynman writing on the ease of criticizing theories, and the difficulty of forming them: The problem is not just to say something might be wrong, but to replace it by something — and that is not so easy. As soon as any really definite idea is substituted it becomes almost immediately apparent that it does not work. The second difficulty is that there is an infinite number of possibilities of these simple types. It is something like this. You are sitting working very hard, you have worked for a long time trying to open a safe. Then some Joe comes along who knows nothing about what you are doing, except that you are trying to open the safe. He says ‘Why don’t you try the combination 10:20:30?’ Because you are busy, you have tried a lot of things, maybe you have already tried 10:20:30. Maybe you know already that the middle number is 32 not 20. Maybe you know as a matter of fact that it is a five digit combination… So please do not send me any letters trying to tell me how the thing is going to work. I read them — I always read them to make sure that I have not already thought of what is suggested — but it takes too long to answer them, because they are usually in the class ‘try 10:20:30’. (“Seeking New Laws”, page 161 in The Character of Physical Law.) As a sometime designer (and longtime critic) of widely used computer systems, I have seen similar difficulties appear when anyone undertakes to publicly design a piece of software that may be used by many thousands of customers. (I have been on both sides of the fence, of course.) The design possibilities are endless, but the deep design problems are usually hidden beneath a mass of superfluous detail. The sheer numbers can be daunting. Even if only one customer out of a thousand feels a need to express a passionately held idea, it can take a long time to read all the mail. And it is a fact of life that many of those strong suggestions are only weakly supported by reason or evidence. Opinions are plentiful, but substantive research is time-consuming, and hence rare. A related phenomenon commonly seen with software is bike-shedding, where interlocutors focus on surface details like naming and syntax… or (come to think of it) like lock combinations. On the other hand, software is easier than quantum physics, and the population of people able to make substantial suggestions about software systems is several orders of magnitude bigger than Feynman’s circle of colleagues. My own work would be poorer without contributions — sometimes unsolicited, sometimes passionately urged on me — from the open source community. If a Nobel prize winner thought it was worthwhile to read his mail on the faint chance of learning a good idea, I am certainly not going to throw mine away. (In case anyone is still reading this, and is wondering what provoked a meditation on the quality of one’s inbox contents, I’ll simply point out that the volume has been very high, for many months, on the Lambda-Dev mailing list, where the next version of the Java language is being discussed. Bravo to those of my colleagues who are surfing that wave.) I started this note thinking there was an odd parallel between the life of the physicist and that of a software designer. On second thought, I’ll bet that is the story for anybody who works in public on something requiring special training. (And that would be pretty much anything worth doing.) In any case, Feynman saw it clearly and said it well.

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  • RemoveHandler Issues with Custom Events

    - by Jeff Certain
    This is a case of things being more complicated that I thought they should be. Since it took a while to figure this one out, I thought it was worth explaining and putting all of the pieces to the answer in one spot. Let me set the stage. Architecturally, I have the notion of generic producers and consumers. These put items onto, and remove items from, a queue. This provides a generic, thread-safe mechanism to load balance the creation and processing of work items in our application. Part of the IProducer(Of T) interface is: 1: Public Interface IProducer(Of T) 2: Event ItemProduced(ByVal sender As IProducer(Of T), ByVal item As T) 3: Event ProductionComplete(ByVal sender As IProducer(Of T)) 4: End Interface Nothing sinister there, is there? In order to simplify our developers’ lives, I wrapped the queue with some functionality to manage the produces and consumers. Since the developer can specify the number of producers and consumers that are spun up, the queue code manages adding event handlers as the producers and consumers are instantiated. Now, we’ve been having some memory leaks and, in order to eliminate the possibility that this was caused by weak references to event handles, I wanted to remove them. This is where it got dicey. My first attempt looked like this: 1: For Each producer As P In Producers 2: RemoveHandler producer.ItemProduced, AddressOf ItemProducedHandler 3: RemoveHandler producer.ProductionComplete, AddressOf ProductionCompleteHandler 4: producer.Dispose() 5: Next What you can’t see in my posted code are the warnings this caused. The 'AddressOf' expression has no effect in this context because the method argument to 'AddressOf' requires a relaxed conversion to the delegate type of the event. Assign the 'AddressOf' expression to a variable, and use the variable to add or remove the method as the handler.  Now, what on earth does that mean? Well, a quick Bing search uncovered a whole bunch of talk about delegates. The first solution I found just changed all parameters in the event handler to Object. Sorry, but no. I used generics precisely because I wanted type safety, not because I wanted to use Object. More searching. Eventually, I found this forum post, where Jeff Shan revealed a missing piece of the puzzle. The other revelation came from Lian_ZA in this post. However, these two only hinted at the solution. Trying some of what they suggested led to finally getting an invalid cast exception that revealed the existence of ItemProducedEventHandler. Hold on a minute! I didn’t create that delegate. There’s nothing even close to that name in my code… except the ItemProduced event in the interface. Could it be? Naaaaah. Hmmm…. Well, as it turns out, there is a delegate created by the compiler for each event. By explicitly creating a delegate that refers to the method in question, implicitly cast to the generated delegate type, I was able to remove the handlers: 1: For Each producer As P In Producers 2: Dim _itemProducedHandler As IProducer(Of T).ItemProducedEventHandler = AddressOf ItemProducedHandler 3: RemoveHandler producer.ItemProduced, _itemProducedHandler 4:  5: Dim _productionCompleteHandler As IProducer(Of T).ProductionCompleteEventHandler = AddressOf ProductionCompleteHandler 6: RemoveHandler producer.ProductionComplete, _productionCompleteHandler 7: producer.Dispose() 8: Next That’s “all” it took to finally be able to remove the event handlers and maintain type-safe code. Hopefully, this will save you the same challenges I had in trying to figure out how to fix this issue!

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  • WMemoryProfiler is Released

    - by Alois Kraus
    What is it? WMemoryProfiler is a managed profiling Api to aid integration testing. This free library can get managed heap statistics and memory usage for your own process (remember testing) and other processes as well. The best thing is that it does work from .NET 2.0 up to .NET 4.5 in x86 and x64. To make it more interesting it can attach to any running .NET process. The reason why I do mention this is that commercial profilers do support this functionality only for their professional editions. An normally only since .NET 4.0 since the profiling API only since then does support attaching to a running process. This thing does differ in many aspects from “normal” profilers because while profiling yourself you can get all objects from all managed heaps back as an object array. If you ever wanted to change the state of an object which does only exist a method local in another thread you can get your hands on it now … Enough theory. Show me some code /// <summary> /// Show feature to not only get statisics out of a process but also the newly allocated /// instances since the last call to MarkCurrentObjects. /// GetNewObjects does return the newly allocated objects as object array /// </summary> static void InstanceTracking() { using (var dumper = new MemoryDumper()) // if you have problems use to see the debugger windows true,true)) { dumper.MarkCurrentObjects(); Allocate(); ILookup<Type, object> newObjects = dumper.GetNewObjects() .ToLookup( x => x.GetType() ); Console.WriteLine("New Strings:"); foreach (var newStr in newObjects[typeof(string)] ) { Console.WriteLine("Str: {0}", newStr); } } } … New Strings: Str: qqd Str: String data: Str: String data: 0 Str: String data: 1 … This is really hot stuff. Not only you can get heap statistics but you can directly examine the new objects and make queries upon them. When I do find more time I can reconstruct the object root graph from it from my own process. It this cool or what? You can also peek into the Finalization Queue to check if you did accidentally forget to dispose a whole bunch of objects … /// <summary> /// .NET 4.0 or above only. Get all finalizable objects which are ready for finalization and have no other object roots anymore. /// </summary> static void NotYetFinalizedObjects() { using (var dumper = new MemoryDumper()) { object[] finalizable = dumper.GetObjectsReadyForFinalization(); Console.WriteLine("Currently {0} objects of types {1} are ready for finalization. Consider disposing them before.", finalizable.Length, String.Join(",", finalizable.ToLookup( x=> x.GetType() ) .Select( x=> x.Key.Name)) ); } } How does it work? The W of WMemoryProfiler is a good hint. It does employ Windbg and SOS dll to do the heavy lifting and concentrates on an easy to use Api which does hide completely Windbg. If you do not want to see Windbg you will never see it. In my experience the most complex thing is actually to download Windbg from the Windows 8 Stanalone SDK. This is described in the Readme and the exception you are greeted with if it is missing in much greater detail. So I will not go into this here.   What Next? Depending on the feedback I do get I can imagine some features which might be useful as well Calculate first order GC Roots from the actual object graph Identify global statics in Types in object graph Support read out of finalization queue of .NET 2.0 as well. Support Memory Dump analysis (again a feature only supported by commercial profilers in their professional editions if it is supported at all) Deserialize objects from a memory dump into a live process back (this would need some more investigation but it is doable) The last item needs some explanation. Why on earth would you want to do that? The basic idea is to store in your live process some logging/tracing data which can become quite big but since it is never written to it is very fast to generate. When your process crashes with a memory dump you could transfer this data structure back into a live viewer which can then nicely display your program state at the point it did crash. This is an advanced trouble shooting technique I have not seen anywhere yet but it could be quite useful. You can have here a look at the current feature list of WMemoryProfiler with some examples.   How To Get Started? First I would download the released source package (it is tiny). And compile the complete project. Then you can compile the Example project (it has this name) and uncomment in the main method the scenario you want to check out. If you are greeted with an exception it is time to install the Windows 8 Standalone SDK which is described in great detail in the exception text. Thats it for the first round. I have seen something more limited in the Java world some years ago (now I cannot find the link anymore) but anyway. Now we have something much better.

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  • ConcurrentDictionary<TKey,TValue> used with Lazy<T>

    - by Reed
    In a recent thread on the MSDN forum for the TPL, Stephen Toub suggested mixing ConcurrentDictionary<T,U> with Lazy<T>.  This provides a fantastic model for creating a thread safe dictionary of values where the construction of the value type is expensive.  This is an incredibly useful pattern for many operations, such as value caches. The ConcurrentDictionary<TKey, TValue> class was added in .NET 4, and provides a thread-safe, lock free collection of key value pairs.  While this is a fantastic replacement for Dictionary<TKey, TValue>, it has a potential flaw when used with values where construction of the value class is expensive. The typical way this is used is to call a method such as GetOrAdd to fetch or add a value to the dictionary.  It handles all of the thread safety for you, but as a result, if two threads call this simultaneously, two instances of TValue can easily be constructed. If TValue is very expensive to construct, or worse, has side effects if constructed too often, this is less than desirable.  While you can easily work around this with locking, Stephen Toub provided a very clever alternative – using Lazy<TValue> as the value in the dictionary instead. This looks like the following.  Instead of calling: MyValue value = dictionary.GetOrAdd( key, () => new MyValue(key)); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would instead use a ConcurrentDictionary<TKey, Lazy<TValue>>, and write: MyValue value = dictionary.GetOrAdd( key, () => new Lazy<MyValue>( () => new MyValue(key))) .Value; This simple change dramatically changes how the operation works.  Now, if two threads call this simultaneously, instead of constructing two MyValue instances, we construct two Lazy<MyValue> instances. However, the Lazy<T> class is very cheap to construct.  Unlike “MyValue”, we can safely afford to construct this twice and “throw away” one of the instances. We then call Lazy<T>.Value at the end to fetch our “MyValue” instance.  At this point, GetOrAdd will always return the same instance of Lazy<MyValue>.  Since Lazy<T> doesn’t construct the MyValue instance until requested, the actual MyClass instance returned is only constructed once.

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  • Creating a voxel world with 3D arrays using threads

    - by Sean M.
    I am making a voxel game (a bit like Minecraft) in C++(11), and I've come across an issue with creating a world efficiently. In my program, I have a World class, which holds a 3D array of Region class pointers. When I initialize the world, I give it a width, height, and depth so it knows how large of a world to create. Each Region is split up into a 32x32x32 area of blocks, so as you may guess, it takes a while to initialize the world once the world gets to be above 8x4x8 Regions. In order to alleviate this issue, I thought that using threads to generate different levels of the world concurrently would make it go faster. Having not used threads much before this, and being still relatively new to C++, I'm not entirely sure how to go about implementing one thread per level (level being a xz plane with a height of 1), when there is a variable number of levels. I tried this: for(int i = 0; i < height; i++) { std::thread th(std::bind(&World::load, this, width, height, depth)); th.join(); } Where load() just loads all Regions at height "height". But that executes the threads one at a time (which makes sense, looking back), and that of course takes as long as generating all Regions in one loop. I then tried: std::thread t1(std::bind(&World::load, this, w, h1, h2 - 1, d)); std::thread t2(std::bind(&World::load, this, w, h2, h3 - 1, d)); std::thread t3(std::bind(&World::load, this, w, h3, h4 - 1, d)); std::thread t4(std::bind(&World::load, this, w, h4, h - 1, d)); t1.join(); t2.join(); t3.join(); t4.join(); This works in that the world loads about 3-3.5 times faster, but this forces the height to be a multiple of 4, and it also gives the same exact VAO object to every single Region, which need individual VAOs in order to render properly. The VAO of each Region is set in the constructor, so I'm assuming that somehow the VAO number is not thread safe or something (again, unfamiliar with threads). So basically, my question is two one-part: How to I implement a variable number of threads that all execute at the same time, and force the main thread to wait for them using join() without stopping the other threads? How do I make the VAO objects thread safe, so when a bunch of Regions are being created at the same time across multiple threads, they don't all get the exact same VAO? Turns out it has to do with GL contexts not working across multiple threads. I moved the VAO/VBO creation back to the main thread. Fixed! Here is the code for block.h/.cpp, region.h/.cpp, and CVBObject.h/.cpp which controls VBOs and VAOs, in case you need it. If you need to see anything else just ask. EDIT: Also, I'd prefer not to have answers that are like "you should have used boost". I'm trying to do this without boost to get used to threads before moving onto other libraries.

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  • Upgrade to Xubuntu 13.10 - Saucy Salamander

    As a common 'fashion' it is possible to upgrade an existing installation of Ubuntu or one of its derivates every six months. Of course, you might opt-in for the adventure and directly keep your system always on the latest version (including alphas and betas), or you might like to play safe and stay on the long-term support (LTS) versions which are updated every two years only. As for me, I'd like to jump from release to release on my main desktop machine. And since 17th October Saucy Salamander or also known as Ubuntu 13.10 has been released for general use. The following paragraphs document the steps I went in order to upgrade my system to the recent version. Don't worry about the fact that I'm actually using Xubuntu. It's mainly a flavoured version of Ubuntu running Xfce 4.10 as default X Window manager. Well, I have Gnome and LXDE on the same system... just out of couriosity. Preparing the system Before you think about upgrading you have to ensure that your current system is running on the latest packages. This can be done easily via a terminal like so: $ sudo apt-get update && sudo apt-get -y dist-upgrade --fix-missing Next, we are going to initiate the upgrade itself: $ sudo update-manager As a result the graphical Software Updater should inform you that a newer version of Ubuntu is available for installation. Ubuntu's Software Updater informs you whether an upgrade is available Running the upgrade After clicking 'Upgrade...' you will be presented with information about the new version. Details about Ubuntu 13.10 (Saucy Salamander) Simply continue with the procedure and your system will be analysed for the next steps. Analysing the existing system and preparing the actual upgrade to 13.10 Next, we are at the point of no return. Last confirmation dialog before having a coffee break while your machine is occupied to download the necessary packages. Not the best bandwidth at hand after all... yours might be faster. Are you really sure that you want to start the upgrade? Let's go and have fun! Anyway, bye bye Raring Ringtail and Welcome Saucy Salamander! In case that you added any additional repositories like Medibuntu or PPAs you will be informed that they are going to be disabled during the upgrade and they might require some manual intervention after completion. Ubuntu is playing safe and third party repositories are disabled during the upgrade Well, depending on your internet bandwidth this might take something between a couple of minutes and some hours to download all the packages and then trigger the actual installation process. In my case I left my PC unattended during the night. Time to reboot Finally, it's time to restart your system and see what's going to happen... In my case absolutely nothing unexpected. The system booted the new kernel 3.11.0 as usual and I was greeted by a new login screen. Honestly, 'same' system as before - which is good and I love that fact of consistency - and I can continue to work productively. And also Software Updater confirms that we just had a painless upgrade: System is running Ubuntu 13.10 - Saucy Salamander - and up to date See you in six months again... ;-) Post-scriptum In case that you would to upgrade to the latest development version of Ubuntu, run the following command in a console: $ sudo update-manager -d And repeat all steps as described above.

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  • c# display DB table structure

    - by user3529643
    I have a question. My code is the following : public partial class Form1 : Form { public OleDbConnection datCon; public string MyDataFile; public ArrayList tblArray; public ArrayList fldArray; public Form1() { InitializeComponent(); lvData.Clear(); lvData.View = View.Details; lvData.LabelEdit = false; lvData.FullRowSelect = true; lvData.GridLines = true; } private void DataConnection() { MyDataFile = Application.StartupPath + @"\studenti.mdb"; string MyCon = @"provider=microsoft.jet.oledb.4.0;data source=" + MyDataFile; try { datCon = new OleDbConnection(MyCon); } catch (Exception ex) { MessageBox.Show(ex.Message); } FillTreeView(); } private void GetTables(OleDbConnection cnn) { try { cnn.Open(); DataTable schTable = cnn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, new Object[] { null, null, null, "TABLE" }); tblArray = new ArrayList(); foreach (DataRow datrow in schTable.Rows) { tblArray.Add(datrow["TABLE_NAME"].ToString()); } cnn.Close(); } catch (Exception ex) { MessageBox.Show(ex.Message); } } private void GetFields(OleDbConnection cnn, string tabNode) { string tabName; try { tabName = tabNode; cnn.Open(); DataTable schTable = cnn.GetOleDbSchemaTable(OleDbSchemaGuid.Columns, new Object[] { null, null, tabName }); fldArray = new ArrayList(); foreach (DataRow datRow in schTable.Rows) { fldArray.Add(datRow["COLUMN_NAME"].ToString()); } cnn.Close(); } catch (Exception ex) { MessageBox.Show(ex.Message); } } private void FillTreeView() { tvData.Nodes.Clear(); tvData.Nodes.Add("Database"); tvData.Nodes[0].Tag = "RootDB"; GetTables(datCon); // add table node for (int i = 0; i < tblArray.Count; i++) { tvData.Nodes[0].Nodes.Add(tblArray[i].ToString()); tvData.Nodes[0].Nodes[i].Tag = "Tables"; } // add field node for (int i = 0; i < tblArray.Count; i++) { GetFields(datCon, tblArray[i].ToString()); for (int j = 0; j < fldArray.Count; j++) { tvData.Nodes[0].Nodes[i].Nodes.Add(fldArray[j].ToString()); tvData.Nodes[0].Nodes[i].Nodes[j].Tag = "Fields"; } } this.tvData.ContextMenuStrip = contextMenuStrip1; contextMenuStrip1.ItemClicked +=contextMenuStrip1_ItemClicked; } public void FillListView(OleDbConnection cnn, string tabName) { OleDbCommand cmdRead; OleDbDataReader datReader; string strField; lblTableName.Text = tabName; strField = "SELECT * FROM [" + tabName + "]"; // Initi cmdRead obiect cmdRead = new OleDbCommand(strField, cnn); cnn.Open(); datReader = cmdRead.ExecuteReader(); // fill ListView while (datReader.Read()) { ListViewItem objListItem = new ListViewItem(datReader.GetValue(0).ToString()); for (int c = 1; c < datReader.FieldCount; c++) { objListItem.SubItems.Add(datReader.GetValue(c).ToString()); } lvData.Items.Add(objListItem); } datReader.Close(); cnn.Close(); } private void ViewToolStripMenuItem_Click(object sender, EventArgs e) { DataConnection(); } public void tvData_AfterExpand(object sender, System.Windows.Forms.TreeViewEventArgs e) { string tabName; int fldCount; if (e.Node.Tag.ToString() == "Tables") { fldCount = e.Node.GetNodeCount(false); //column headers. int n = lvData.Width; double wid = n / fldCount; // width columnn for (int c = 0; c < fldCount; c++) { lvData.Columns.Add(e.Node.Nodes[c].Text, (int)wid, HorizontalAlignment.Left); } // gett table name tabName = e.Node.Text; FillListView(datCon, tabName); } } public void button1_Click(object sender, EventArgs e) { //TO DO?? } } I have a treeview populated with tables (nodes) from my database, and a listview which is populated with the data from my tables when I click on a table. As you can see I have a button1 on my form. When I click it I want it to display to me the structure of the table I selected in my treeview (a treeview node). Not too many details, just the name of the columns in my table, type of columns, primary keys. I've tried to follow many tutorials but I can t seem to manage it.

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  • Core Data managed object context thread synchronisation

    - by Ben Reeves
    I'm have an issue where i'm updating a many-to-many relationship in a background thread, which works fine in that threa, but when I send the object back to the main thread the changes do not show. If I close the app and reopen the data is saved fine and the changes show on the main thread. Also using [context lock] instead of a different managed object context works fine. I have tried NSManagedObjectContext: - (BOOL)save:(NSError **)error; - (void)refreshObject:(NSManagedObject *)object mergeChanges:(BOOL)flag; at different stages throughout the process but it doesn't seem to help. My core data code uses the following getter to ensure any operations are thread safe: - (NSManagedObjectContext *) managedObjectContext { NSThread * thisThread = [NSThread currentThread]; if (thisThread == [NSThread mainThread]) { //Main thread just return default context return managedObjectContext; } else { //Thread safe trickery NSManagedObjectContext * threadManagedObjectContext = [[thisThread threadDictionary] objectForKey:CONTEXT_KEY]; if (threadManagedObjectContext == nil) { threadManagedObjectContext = [[[NSManagedObjectContext alloc] init] autorelease]; [threadManagedObjectContext setPersistentStoreCoordinator: [self persistentStoreCoordinator]]; [[thisThread threadDictionary] setObject:threadManagedObjectContext forKey:CONTEXT_KEY]; } return threadManagedObjectContext; } } and when I pass object between threads i'm using -(NSManagedObject*)makeSafe:(NSManagedObject*)object { if ([object managedObjectContext] != [self managedObjectContext]) { NSError * error = nil; object = [[self managedObjectContext] existingObjectWithID:[object objectID] error:&error]; if (error) { NSLog(@"Error makeSafe: %@", error); } } return object; } Any help appreciated

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  • Synchronizing Asynchronous request handlers in Silverlight environment

    - by Eric Lifka
    For our senior design project my group is making a Silverlight application that utilizes graph theory concepts and stores the data in a database on the back end. We have a situation where we add a link between two nodes in the graph and upon doing so we run analysis to re-categorize our clusters of nodes. The problem is that this re-categorization is quite complex and involves multiple queries and updates to the database so if multiple instances of it run at once it quickly garbles data and breaks (by trying to re-insert already used primary keys). Essentially it's not thread safe, and we're trying to make it safe, and that's where we're failing and need help :). The create link function looks like this: private Semaphore dblock = new Semaphore(1, 1); // This function is on our service reference and gets called // by the client code. public int addNeed(int nodeOne, int nodeTwo) { dblock.WaitOne(); submitNewNeed(createNewNeed(nodeOne, nodeTwo)); verifyClusters(nodeOne, nodeTwo); dblock.Release(); return 0; } private void verifyClusters(int nodeOne, int nodeTwo) { // Run analysis of nodeOne and nodeTwo in graph } All copies of addNeed should wait for the first one that comes in to finish before another can execute. But instead they all seem to be running and conflicting with each other in the verifyClusters method. One solution would be to force our front end calls to be made synchronously. And in fact, when we do that everything works fine, so the code logic isn't broken. But when it's launched our application will be deployed within a business setting and used by internal IT staff (or at least that's the plan) so we'll have the same problem. We can't force all clients to submit data at different times, so we really need to get it synchronized on the back end. Thanks for any help you can give, I'd be glad to supply any additional information that you could need!

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  • In Java Concurrency In Practice by Brian Goetz, why is the Memoizer class not annotated with @ThreadSafe?

    - by dig_dug
    Java Concurrency In Practice by Brian Goetz provides an example of a efficient scalable cache for concurrent use. The final version of the example showing the implementation for class Memoizer (pg 108) shows such a cache. I am wondering why the class is not annotated with @ThreadSafe? The client, class Factorizer, of the cache is properly annotated with @ThreadSafe. The appendix states that if a class is not annotated with either @ThreadSafe or @Immutable that it should be assumed that it isn't thread safe. Memoizer seems thread-safe though. Here is the code for Memoizer: public class Memoizer<A, V> implements Computable<A, V> { private final ConcurrentMap<A, Future<V>> cache = new ConcurrentHashMap<A, Future<V>>(); private final Computable<A, V> c; public Memoizer(Computable<A, V> c) { this.c = c; } public V compute(final A arg) throws InterruptedException { while (true) { Future<V> f = cache.get(arg); if (f == null) { Callable<V> eval = new Callable<V>() { public V call() throws InterruptedException { return c.compute(arg); } }; FutureTask<V> ft = new FutureTask<V>(eval); f = cache.putIfAbsent(arg, ft); if (f == null) { f = ft; ft.run(); } } try { return f.get(); } catch (CancellationException e) { cache.remove(arg, f); } catch (ExecutionException e) { throw launderThrowable(e.getCause()); } } } }

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  • Singletons, thread safety and structuremap

    - by Ben
    Hi, Currently I have the following class: public class PluginManager { private static bool s_initialized; private static object s_lock = new object(); public static void Initialize() { if (!s_initialized) { lock (s_lock) { if (!s_initialized) { // initialize s_initialized = true; } } } } } The important thing here is that Initialize() should only be executed once whilst the application is running. I thought that I would refactor this into a singleton class since this would be more thread safe?: public sealed class PluginService { static PluginService() { } private static PluginService _instance = new PluginService(); public static PluginService Instance { get { return _instance; } } private bool s_initialized; public void Initialize() { if (!s_initialized) { // initialize s_initialized = true; } } } Question one, is it still necessary to have the lock here (I have removed it) since we will only ever be working on the same instance? Finally, I want to use DI and structure map to initialize my servcices so I have refactored as below: public interface IPluginService { void Initialize(); } public class NewPluginService : IPluginService { private bool s_initialized; public void Initialize() { if (!s_initialized) { // initialize s_initialized = true; } } } And in my registry: ForRequestedType<IPluginService>() .TheDefaultIsConcreteType<NewPluginService>().AsSingletons(); This works as expected (singleton returning true in the following code): var instance1 = ObjectFactory.GetInstance<IPluginService>(); var instance2 = ObjectFactory.GetInstance<IPluginService>(); bool singleton = (instance1 == instance2); So my next question, is the structure map solution as thread safe as the singleton class (second example). The only downside is that this would still allow NewPluginService to be instantiated directly (if not using structure map). Many thanks, Ben

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  • g++ C++0x enum class Compiler Warnings

    - by Travis G
    I've been refactoring my horrible mess of C++ type-safe psuedo-enums to the new C++0x type-safe enums because they're way more readable. Anyway, I use them in exported classes, so I explicitly mark them to be exported: enum class __attribute__((visibility("default"))) MyEnum : unsigned int { One = 1, Two = 2 }; Compiling this with g++ yields the following warning: type attributes ignored after type is already defined This seems very strange, since, as far as I know, that warning is meant to prevent actual mistakes like: class __attribute__((visibility("default"))) MyClass { }; class __attribute__((visibility("hidden"))) MyClass; Of course, I'm clearly not doing that, since I have only marked the visibility attributes at the definition of the enum class and I'm not re-defining or declaring it anywhere else (I can duplicate this error with a single file). Ultimately, I can't make this bit of code actually cause a problem, save for the fact that, if I change a value and re-compile the consumer without re-compiling the shared library, the consumer passes the new values and the shared library has no idea what to do with them (although I wouldn't expect that to work in the first place). Am I being way too pedantic? Can this be safely ignored? I suspect so, but at the same time, having this error prevents me from compiling with Werror, which makes me uncomfortable. I would really like to see this problem go away.

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  • Is it possible to use Indy 10.5.8.0 with Delphi XE?

    - by jachguate
    The case I'm trying to update the INDY to the latest version for my Delphi XE (Update 1), so I downloaded the latest INDY10 file (Indy_4545.zip) from indy.fulgan.com/ZIP. The packages compiles successfully and I can now even see the new version 10.5.8.0 on the about box dialog, but after a IDE restart I got a message saying: No se encuentra el punto de entrada del procedimiento @Idhttp@TIdCustomHTTP@GetRequestHeaders$qqrv en la biblioteca de vínculos dinámicos IndyProtocols150.bpl. My free translation to English: Entry point not found for procedure @Idhttp@TIdCustomHTTP@GetRequestHeaders$qqrv not found on the dynamic link library IndyProtocols150.bpl. After a quick comparision of old and new IdHTTP.pas I found a lot of changes on the TIdCustomHttp class, including the rename of some methods GetResponseHeaders to GetResponse GetRequestHeaders to GetRequest SetRequestHeaders to SetRequest Along with changed public/published method firms in this and other and classes interfaces. After the update, I got a lot of packages failing to load, including dclcxPivotGridOLAPD15.bpl, which in turns depends on dclDataSnapServer150.bpl which encounters the missing method on the bpl. AFAIK I can't recompile the dclDataSnapServer150.bpl (and maybe other failing packages, I just stopped here). DataSnap and DevExpress support on the IDE is a must for my day to day so The questions Is there a safe pre-established path to update to the newest INDY for Delphi XE? If not, am I on the safe side by just parching the source code by creating the old public methods and call the new ones on the implementation part? am I missing something else or am I really stuck with INDY 10.5.7 until the next Delphi minor/major release?

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  • perl multiple tasks problem

    - by Alice Wozownik
    I have finished my earlier multithreaded program that uses perl threads and it works on my system. The problem is that on some systems that it needs to run on, thread support is not compiled into perl and I cannot install additional packages. I therefore need to use something other than threads, and I am moving my code to using fork(). This works on my windows system in starting the subtasks. A few problems: How to determine when the child process exits? I created new threads when the thread count was below a certain value, I need to keep track of how many threads are running. For processes, how do I know when one exits so I can keep track of how many exist at the time, incrementing a counter when one is created and decrementing when one exits? Is file I/O using handles obtained with OPEN when opened by the parent process safe in the child process? I need to append to a file for each of the child processes, is this safe on unix as well. Is there any alternative to fork and threads? I tried use Parallel::ForkManager, but that isn't installed on my system (use Parallel::ForkManager; gave an error) and I absolutely require that my perl script work on all unix/windows systems without installing any additional modules.

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