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  • EF4 generates invalid script

    - by Jaxidian
    When I right-click in a .EDMX file and click Generate Database From Model, the resulting script is obviously wrong because of the table names. What it generates is the following script. Note the table names in the DROP TABLE part versus the CREATE TABLE part. Why is this inconsistent? This is obviously not a reusable script. What I created was an Entity named "Address" and an Entity named "Company", etc (all singular). The EntitySet names are pluralized. The "Pluralize New Objects" boolean does not change this either. So what's the deal? For what it's worth, I originally generated the EDMX by pointing it to a database that had tables with non-pluralized names and now that I've made some changes, I want to go back the other way. I'd like to have the option to go back and forth as neither the db-first nor the model-first model is ideal in all scenarios, and I have the control to ensure that there will be no merging issues from multiple people going both ways at the same time. -- -------------------------------------------------- -- Dropping existing FOREIGN KEY constraints -- NOTE: if the constraint does not exist, an ignorable error will be reported. -- -------------------------------------------------- ALTER TABLE [Address] DROP CONSTRAINT [FK_Address_StateID-State_ID]; GO ALTER TABLE [Company] DROP CONSTRAINT [FK_Company_AddressID-Address_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_BossEmployeeID-Employee_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_CompanyID-Company_ID]; GO ALTER TABLE [Employee] DROP CONSTRAINT [FK_Employee_PersonID-Person_ID]; GO ALTER TABLE [Person] DROP CONSTRAINT [FK_Person_AddressID-Address_ID]; GO -- -------------------------------------------------- -- Dropping existing tables -- NOTE: if the table does not exist, an ignorable error will be reported. -- -------------------------------------------------- DROP TABLE [Address]; GO DROP TABLE [Company]; GO DROP TABLE [Employee]; GO DROP TABLE [Person]; GO DROP TABLE [State]; GO -- -------------------------------------------------- -- Creating all tables -- -------------------------------------------------- -- Creating table 'Addresses' CREATE TABLE [Addresses] ( [ID] int IDENTITY(1,1) NOT NULL, [StreetAddress] nvarchar(100) NOT NULL, [City] nvarchar(100) NOT NULL, [StateID] int NOT NULL, [Zip] nvarchar(10) NOT NULL ); GO -- Creating table 'Companies' CREATE TABLE [Companies] ( [ID] int IDENTITY(1,1) NOT NULL, [Name] nvarchar(100) NOT NULL, [AddressID] int NOT NULL ); GO -- Creating table 'People' CREATE TABLE [People] ( [ID] int IDENTITY(1,1) NOT NULL, [FirstName] nvarchar(100) NOT NULL, [LastName] nvarchar(100) NOT NULL, [AddressID] int NOT NULL ); GO -- Creating table 'States' CREATE TABLE [States] ( [ID] int IDENTITY(1,1) NOT NULL, [Name] nvarchar(100) NOT NULL, [Abbreviation] nvarchar(2) NOT NULL ); GO -- Creating table 'Employees' CREATE TABLE [Employees] ( [ID] int IDENTITY(1,1) NOT NULL, [PersonID] int NOT NULL, [CompanyID] int NOT NULL, [Position] nvarchar(100) NOT NULL, [BossEmployeeID] int NULL ); GO -- -------------------------------------------------- -- Creating all PRIMARY KEY constraints -- -------------------------------------------------- -- Creating primary key on [ID] in table 'Addresses' ALTER TABLE [Addresses] ADD CONSTRAINT [PK_Addresses] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'Companies' ALTER TABLE [Companies] ADD CONSTRAINT [PK_Companies] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'People' ALTER TABLE [People] ADD CONSTRAINT [PK_People] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'States' ALTER TABLE [States] ADD CONSTRAINT [PK_States] PRIMARY KEY ([ID] ); GO -- Creating primary key on [ID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [PK_Employees] PRIMARY KEY ([ID] ); GO -- -------------------------------------------------- -- Creating all FOREIGN KEY constraints -- -------------------------------------------------- -- Creating foreign key on [StateID] in table 'Addresses' ALTER TABLE [Addresses] ADD CONSTRAINT [FK_Address_StateID_State_ID] FOREIGN KEY ([StateID]) REFERENCES [States] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Address_StateID_State_ID' CREATE INDEX [IX_FK_Address_StateID_State_ID] ON [Addresses] ([StateID]); GO -- Creating foreign key on [AddressID] in table 'Companies' ALTER TABLE [Companies] ADD CONSTRAINT [FK_Company_AddressID_Address_ID] FOREIGN KEY ([AddressID]) REFERENCES [Addresses] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Company_AddressID_Address_ID' CREATE INDEX [IX_FK_Company_AddressID_Address_ID] ON [Companies] ([AddressID]); GO -- Creating foreign key on [AddressID] in table 'People' ALTER TABLE [People] ADD CONSTRAINT [FK_Person_AddressID_Address_ID] FOREIGN KEY ([AddressID]) REFERENCES [Addresses] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Person_AddressID_Address_ID' CREATE INDEX [IX_FK_Person_AddressID_Address_ID] ON [People] ([AddressID]); GO -- Creating foreign key on [CompanyID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_CompanyID_Company_ID] FOREIGN KEY ([CompanyID]) REFERENCES [Companies] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_CompanyID_Company_ID' CREATE INDEX [IX_FK_Employee_CompanyID_Company_ID] ON [Employees] ([CompanyID]); GO -- Creating foreign key on [BossEmployeeID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_BossEmployeeID_Employee_ID] FOREIGN KEY ([BossEmployeeID]) REFERENCES [Employees] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_BossEmployeeID_Employee_ID' CREATE INDEX [IX_FK_Employee_BossEmployeeID_Employee_ID] ON [Employees] ([BossEmployeeID]); GO -- Creating foreign key on [PersonID] in table 'Employees' ALTER TABLE [Employees] ADD CONSTRAINT [FK_Employee_PersonID_Person_ID] FOREIGN KEY ([PersonID]) REFERENCES [People] ([ID]) ON DELETE NO ACTION ON UPDATE NO ACTION; -- Creating non-clustered index for FOREIGN KEY 'FK_Employee_PersonID_Person_ID' CREATE INDEX [IX_FK_Employee_PersonID_Person_ID] ON [Employees] ([PersonID]); GO -- -------------------------------------------------- -- Script has ended -- --------------------------------------------------

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  • What's the better user experience: Waiting once at startup for a long time or waiting frequently for a short time?

    - by Roflcoptr
    I'm currently design an application that involves a lot of calculation. Now I have generally two possibilities which I have both tested: 1) During startup of the application I calculated only the most important values and these values that consume a lot of time. So the user has to wait approximately 15 seconds during startup. But on the other hand a lot of user interactions require recalculation so that the user often has to wait 2-3 seconds after clicking somewhere until the application has calculated and loaded all values 2) I load everything during startup. This takes from 90 to 120 seconds... This is quite a long time, but the big advantage is that all the user interactions are executed immediately. So what would you generally consider the better approach? Loading all time-consuming operations during startup or when needed?

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  • C#: Handling Notifications: inheritance, events, or delegates?

    - by James Michael Hare
    Often times as developers we have to design a class where we get notification when certain things happen. In older object-oriented code this would often be implemented by overriding methods -- with events, delegates, and interfaces, however, we have far more elegant options. So, when should you use each of these methods and what are their strengths and weaknesses? Now, for the purposes of this article when I say notification, I'm just talking about ways for a class to let a user know that something has occurred. This can be through any programmatic means such as inheritance, events, delegates, etc. So let's build some context. I'm sitting here thinking about a provider neutral messaging layer for the place I work, and I got to the point where I needed to design the message subscriber which will receive messages from the message bus. Basically, what we want is to be able to create a message listener and have it be called whenever a new message arrives. Now, back before the flood we would have done this via inheritance and an abstract class: 1:  2: // using inheritance - omitting argument null checks and halt logic 3: public abstract class MessageListener 4: { 5: private ISubscriber _subscriber; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber) 11: { 12: _subscriber = subscriber; 13: _messageThread = new Thread(MessageLoop); 14: _messageThread.Start(); 15: } 16:  17: // user will override this to process their messages 18: protected abstract void OnMessageReceived(Message msg); 19:  20: // handle the looping in the thread 21: private void MessageLoop() 22: { 23: while(!_isHalted) 24: { 25: // as long as processing, wait 1 second for message 26: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 27: if(msg != null) 28: { 29: OnMessageReceived(msg); 30: } 31: } 32: } 33: ... 34: } It seems so odd to write this kind of code now. Does it feel odd to you? Maybe it's just because I've gotten so used to delegation that I really don't like the feel of this. To me it is akin to saying that if I want to drive my car I need to derive a new instance of it just to put myself in the driver's seat. And yet, unquestionably, five years ago I would have probably written the code as you see above. To me, inheritance is a flawed approach for notifications due to several reasons: Inheritance is one of the HIGHEST forms of coupling. You can't seal the listener class because it depends on sub-classing to work. Because C# does not allow multiple-inheritance, I've spent my one inheritance implementing this class. Every time you need to listen to a bus, you have to derive a class which leads to lots of trivial sub-classes. The act of consuming a message should be a separate responsibility than the act of listening for a message (SRP). Inheritance is such a strong statement (this IS-A that) that it should only be used in building type hierarchies and not for overriding use-specific behaviors and notifications. Chances are, if a class needs to be inherited to be used, it most likely is not designed as well as it could be in today's modern programming languages. So lets look at the other tools available to us for getting notified instead. Here's a few other choices to consider. Have the listener expose a MessageReceived event. Have the listener accept a new IMessageHandler interface instance. Have the listener accept an Action<Message> delegate. Really, all of these are different forms of delegation. Now, .NET events are a bit heavier than the other types of delegates in terms of run-time execution, but they are a great way to allow others using your class to subscribe to your events: 1: // using event - ommiting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private bool _isHalted = false; 6: private Thread _messageThread; 7:  8: // assign the subscriber and start the messaging loop 9: public MessageListener(ISubscriber subscriber) 10: { 11: _subscriber = subscriber; 12: _messageThread = new Thread(MessageLoop); 13: _messageThread.Start(); 14: } 15:  16: // user will override this to process their messages 17: public event Action<Message> MessageReceived; 18:  19: // handle the looping in the thread 20: private void MessageLoop() 21: { 22: while(!_isHalted) 23: { 24: // as long as processing, wait 1 second for message 25: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 26: if(msg != null && MessageReceived != null) 27: { 28: MessageReceived(msg); 29: } 30: } 31: } 32: } Note, now we can seal the class to avoid changes and the user just needs to provide a message handling method: 1: theListener.MessageReceived += CustomReceiveMethod; However, personally I don't think events hold up as well in this case because events are largely optional. To me, what is the point of a listener if you create one with no event listeners? So in my mind, use events when handling the notification is optional. So how about the delegation via interface? I personally like this method quite a bit. Basically what it does is similar to inheritance method mentioned first, but better because it makes it easy to split the part of the class that doesn't change (the base listener behavior) from the part that does change (the user-specified action after receiving a message). So assuming we had an interface like: 1: public interface IMessageHandler 2: { 3: void OnMessageReceived(Message receivedMessage); 4: } Our listener would look like this: 1: // using delegation via interface - omitting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private IMessageHandler _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, IMessageHandler handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // handle the looping in the thread 19: private void MessageLoop() 20: { 21: while(!_isHalted) 22: { 23: // as long as processing, wait 1 second for message 24: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 25: if(msg != null) 26: { 27: _handler.OnMessageReceived(msg); 28: } 29: } 30: } 31: } And they would call it by creating a class that implements IMessageHandler and pass that instance into the constructor of the listener. I like that this alleviates the issues of inheritance and essentially forces you to provide a handler (as opposed to events) on construction. Well, this is good, but personally I think we could go one step further. While I like this better than events or inheritance, it still forces you to implement a specific method name. What if that name collides? Furthermore if you have lots of these you end up either with large classes inheriting multiple interfaces to implement one method, or lots of small classes. Also, if you had one class that wanted to manage messages from two different subscribers differently, it wouldn't be able to because the interface can't be overloaded. This brings me to using delegates directly. In general, every time I think about creating an interface for something, and if that interface contains only one method, I start thinking a delegate is a better approach. Now, that said delegates don't accomplish everything an interface can. Obviously having the interface allows you to refer to the classes that implement the interface which can be very handy. In this case, though, really all you want is a method to handle the messages. So let's look at a method delegate: 1: // using delegation via delegate - omitting argument null checks and halt logic 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private Action<Message> _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, Action<Message> handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // handle the looping in the thread 19: private void MessageLoop() 20: { 21: while(!_isHalted) 22: { 23: // as long as processing, wait 1 second for message 24: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 25: if(msg != null) 26: { 27: _handler(msg); 28: } 29: } 30: } 31: } Here the MessageListener now takes an Action<Message>.  For those of you unfamiliar with the pre-defined delegate types in .NET, that is a method with the signature: void SomeMethodName(Message). The great thing about delegates is it gives you a lot of power. You could create an anonymous delegate, a lambda, or specify any other method as long as it satisfies the Action<Message> signature. This way, you don't need to define an arbitrary helper class or name the method a specific thing. Incidentally, we could combine both the interface and delegate approach to allow maximum flexibility. Doing this, the user could either pass in a delegate, or specify a delegate interface: 1: // using delegation - give users choice of interface or delegate 2: public sealed class MessageListener 3: { 4: private ISubscriber _subscriber; 5: private Action<Message> _handler; 6: private bool _isHalted = false; 7: private Thread _messageThread; 8:  9: // assign the subscriber and start the messaging loop 10: public MessageListener(ISubscriber subscriber, Action<Message> handler) 11: { 12: _subscriber = subscriber; 13: _handler = handler; 14: _messageThread = new Thread(MessageLoop); 15: _messageThread.Start(); 16: } 17:  18: // passes the interface method as a delegate using method group 19: public MessageListener(ISubscriber subscriber, IMessageHandler handler) 20: : this(subscriber, handler.OnMessageReceived) 21: { 22: } 23:  24: // handle the looping in the thread 25: private void MessageLoop() 26: { 27: while(!_isHalted) 28: { 29: // as long as processing, wait 1 second for message 30: Message msg = _subscriber.Receive(TimeSpan.FromSeconds(1)); 31: if(msg != null) 32: { 33: _handler(msg); 34: } 35: } 36: } 37: } } This is the method I tend to prefer because it allows the user of the class to choose which method works best for them. You may be curious about the actual performance of these different methods. 1: Enter iterations: 2: 1000000 3:  4: Inheritance took 4 ms. 5: Events took 7 ms. 6: Interface delegation took 4 ms. 7: Lambda delegate took 5 ms. Before you get too caught up in the numbers, however, keep in mind that this is performance over over 1,000,000 iterations. Since they are all < 10 ms which boils down to fractions of a micro-second per iteration so really any of them are a fine choice performance wise. As such, I think the choice of what to do really boils down to what you're trying to do. Here's my guidelines: Inheritance should be used only when defining a collection of related types with implementation specific behaviors, it should not be used as a hook for users to add their own functionality. Events should be used when subscription is optional or multi-cast is desired. Interface delegation should be used when you wish to refer to implementing classes by the interface type or if the type requires several methods to be implemented. Delegate method delegation should be used when you only need to provide one method and do not need to refer to implementers by the interface name.

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  • Downloading large files hangs system

    - by Igor
    When Im trying to download large files, i.e. 1gb or more under FireFox, first of all it starts with very big download speed and in few seconds in almost get up to max (~11 MBps). It is downloading very fast, but when downloaded size becomes near 700-800mb and more, my system almost completely hangs, so I can do nothing - I just have to wait until it finishes downloading. Also when it hangs, I can't see the download progress - it looks like it completely hangs. Sometimes, however, if the file size is near 1gb, the system comes back from hang, finishing download, but sometimes I just cant wait before system comes back and have to kill FF from top (it takes me 2 minutes to do this, because of very slow system performance). I use Firefox as primary browser. If I use wget with direct link to file - everything is fine. Speed at max, no performance decrease. So what can I do?

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  • SQL SERVER – Weekly Series – Memory Lane – #007

    - by pinaldave
    Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2006 Find Stored Procedure Related to Table in Database – Search in All Stored Procedure In 2006 I wrote a small script which will help user  find all the Stored Procedures (SP) which are related to one or more specific tables. This was quite a popular script however, in SQL Server 2012 the same can be achieved using new DMV sys.sql-expression_dependencies. I recently blogged about it over Find Referenced or Referencing Object in SQL Server using sys.sql_expression_dependencies. 2007 SQL SERVER – Versions, CodeNames, Year of Release 1993 – SQL Server 4.21 for Windows NT 1995 – SQL Server 6.0, codenamed SQL95 1996 – SQL Server 6.5, codenamed Hydra 1999 – SQL Server 7.0, codenamed Sphinx 1999 – SQL Server 7.0 OLAP, codenamed Plato 2000 – SQL Server 2000 32-bit, codenamed Shiloh (version 8.0) 2003 – SQL Server 2000 64-bit, codenamed Liberty 2005 – SQL Server 2005, codenamed Yukon (version 9.0) 2008 – SQL Server 2008, codenamed Katmai (version 10.0) 2011 – SQL Server 2008, codenamed Denali (version 11.0) Search String in Stored Procedure Searching sting in the stored procedure is one of the most frequent task developer do. They might be searching for a table, view or any other details. I have written a script to do the same in SQL Server 2000 and SQL Server 2005. This is worth bookmarking blog post. There is an alternative way to do the same as well here is the example. 2008 SQL SERVER – Refresh Database Using T-SQL NO! Some of the questions have a single answer NO! You may want to read the question in the original blog post. I had a great time saying No! SQL SERVER – Delete Backup History – Cleanup Backup History SQL Server stores history of all the taken backup forever. History of all the backup is stored in the msdb database. Many times older history is no more required. Following Stored Procedure can be executed with a parameter which takes days of history to keep. In the following example 30 is passed to keep a history of month. 2009 Stored Procedure are Compiled on First Run – SP taking Longer to Run First Time Is stored procedure pre-compiled? Why the Stored Procedure takes a long time to run for the first time?  This is a very common questions often discussed by developers and DBAs. There is an absolutely definite answer but the question has been discussed forever. There is a misconception that stored procedures are pre-compiled. They are not pre-compiled, but compiled only during the first run. For every subsequent runs, it is for sure pre-compiled. Read the entire article for example and demonstration. Removing Key Lookup – Seek Predicate – Predicate – An Interesting Observation Related to Datatypes This is one of the most important performance tuning lesson on my blog. I suggest this weekend you spend time reading them and let me know what you think about the concepts which I have demonstrated in the four part series. Part 1 | Part 2 | Part 3 | Part 4 Seek Predicate is the operation that describes the b-tree portion of the Seek. Predicate is the operation that describes the additional filter using non-key columns. Based on the description, it is very clear that Seek Predicate is better than Predicate as it searches indexes whereas in Predicate, the search is on non-key columns – which implies that the search is on the data in page files itself. Policy Based Management – Create, Evaluate and Fix Policies This article will cover the most spectacular feature of SQL Server – Policy-based management and how the configuration of SQL Server with policy-based management architecture can make a powerful difference. Policy based management is loaded with several advantages. It can help you implement various policies for reliable configuration of the system. It also provides additional administration assistance to DBAs and helps them effortlessly manage various tasks of SQL Server across the enterprise. 2010 Recycle Error Log – Create New Log file without Server Restart Once I observed a DBA to restaring the SQL Server when he needed new error log file. This was funny and sad both at the same time. There is no need to restart the server to create a new log file or recycle the log file. You can run sp_cycle_errorlog and achieve the same result. Get Database Backup History for a Single Database Simple but effective script! Reducing CXPACKET Wait Stats for High Transactional Database The subject is very complex and I have done my best to simplify the concept. In simpler words, when a parallel operation is created for SQL Query, there are multiple threads for a single query. Each query deals with a different set of the data (or rows). Due to some reasons, one or more of the threads lag behind, creating the CXPACKET Wait Stat. Threads which came first have to wait for the slower thread to finish. The Wait by a specific completed thread is called CXPACKET Wait Stat. Information Related to DATETIME and DATETIME2 There are quite a lot of confusion with DATETIME and DATETIME2. DATETIME2 is also one of the underutilized datatype of SQL Server.  In this blog post I have written a follow up of the my earlier datetime series where I clarify a few of the concepts related to datetime. Difference Between GETDATE and SYSDATETIME Difference Between DATETIME and DATETIME2 – WITH GETDATE Difference Between DATETIME and DATETIME2 2011 Introduction to CUME_DIST – Analytic Functions Introduced in SQL Server 2012 SQL Server 2012 introduces new analytical function CUME_DIST(). This function provides cumulative distribution value. It will be very difficult to explain this in words so I will attempt small example to explain you this function. Instead of creating new table, I will be using AdventureWorks sample database as most of the developer uses that for experiment. Introduction to FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012 SQL Server 2012 introduces new analytical functions FIRST_VALUE() and LAST_VALUE(). This function returns first and last value from the list. It will be very difficult to explain this in words so I’d like to attempt to explain its function through a brief example. Instead of creating a new table, I will be using the AdventureWorks sample database as most developers use that for experiment purposes. OVER clause with FIRST _VALUE and LAST_VALUE – Analytic Functions Introduced in SQL Server 2012 – ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING “Don’t you think there is bug in your first example where FIRST_VALUE is remain same but the LAST_VALUE is changing every line. I think the LAST_VALUE should be the highest value in the windows or set of result.” Puzzle – Functions FIRST_VALUE and LAST_VALUE with OVER clause and ORDER BY You can see that row number 2, 3, 4, and 5 has same SalesOrderID = 43667. The FIRST_VALUE is 78 and LAST_VALUE is 77. Now if these function was working on maximum and minimum value they should have given answer as 77 and 80 respectively instead of 78 and 77. Also the value of FIRST_VALUE is greater than LAST_VALUE 77. Why? Explain in detail. Introduction to LEAD and LAG – Analytic Functions Introduced in SQL Server 2012 SQL Server 2012 introduces new analytical function LEAD() and LAG(). This functions accesses data from a subsequent row (for lead) and previous row (for lag) in the same result set without the use of a self-join . It will be very difficult to explain this in words so I will attempt small example to explain you this function. Instead of creating new table, I will be using AdventureWorks sample database as most of the developer uses that for experiment. A Real Story of Book Getting ‘Out of Stock’ to A 25% Discount Story Available Our book was out of stock in 48 hours of it was arrived in stock! We got call from the online store with a request for more copies within 12 hours. But we had printed only as many as we had sent them. There were no extra copies. We finally talked to the printer to get more copies. However, due to festivals and holidays the copies could not be shipped to the online retailer for two days. We knew for sure that they were going to be out of the book for 48 hours. This is the story of how we overcame that situation! Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Are there deprecated practices for multithread and multiprocessor programming that I should no longer use?

    - by DeveloperDon
    In the early days of FORTRAN and BASIC, essentially all programs were written with GOTO statements. The result was spaghetti code and the solution was structured programming. Similarly, pointers can have difficult to control characteristics in our programs. C++ started with plenty of pointers, but use of references are recommended. Libraries like STL can reduce some of our dependency. There are also idioms to create smart pointers that have better characteristics, and some version of C++ permit references and managed code. Programming practices like inheritance and polymorphism use a lot of pointers behind the scenes (just as for, while, do structured programming generates code filled with branch instructions). Languages like Java eliminate pointers and use garbage collection to manage dynamically allocated data instead of depending on programmers to match all their new and delete statements. In my reading, I have seen examples of multi-process and multi-thread programming that don't seem to use semaphores. Do they use the same thing with different names or do they have new ways of structuring protection of resources from concurrent use? For example, a specific example of a system for multithread programming with multicore processors is OpenMP. It represents a critical region as follows, without the use of semaphores, which seem not to be included in the environment. th_id = omp_get_thread_num(); #pragma omp critical { cout << "Hello World from thread " << th_id << '\n'; } This example is an excerpt from: http://en.wikipedia.org/wiki/OpenMP Alternatively, similar protection of threads from each other using semaphores with functions wait() and signal() might look like this: wait(sem); th_id = get_thread_num(); cout << "Hello World from thread " << th_id << '\n'; signal(sem); In this example, things are pretty simple, and just a simple review is enough to show the wait() and signal() calls are matched and even with a lot of concurrency, thread safety is provided. But other algorithms are more complicated and use multiple semaphores (both binary and counting) spread across multiple functions with complex conditions that can be called by many threads. The consequences of creating deadlock or failing to make things thread safe can be hard to manage. Do these systems like OpenMP eliminate the problems with semaphores? Do they move the problem somewhere else? How do I transform my favorite semaphore using algorithm to not use semaphores anymore?

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  • Should tests be in the same ruby file or in separeted ruby files?

    - by Junior Mayhé
    While using Selenium and Ruby to do some functional tests, I am worried with the performance. So is it better to add all test methods in the same ruby file, or I should put each one in separated code files? Below a sample with all tests in the same file: # encoding: utf-8 require "selenium-webdriver" require "test/unit" class Tests < Test::Unit::TestCase def setup @driver = Selenium::WebDriver.for :firefox @base_url = "http://mysite" @driver.manage.timeouts.implicit_wait = 30 @verification_errors = [] @wait = Selenium::WebDriver::Wait.new :timeout => 10 end def teardown @driver.quit assert_equal [], @verification_errors end def element_present?(how, what) @driver.find_element(how, what) true rescue Selenium::WebDriver::Error::NoSuchElementError false end def verify(&blk) yield rescue Test::Unit::AssertionFailedError => ex @verification_errors << ex end def test_1 @driver.get(@base_url + "/") # a huge test here end def test_2 @driver.get(@base_url + "/") # a huge test here end def test_3 @driver.get(@base_url + "/") # a huge test here end def test_4 @driver.get(@base_url + "/") # a huge test here end def test_5 @driver.get(@base_url + "/") # a huge test here end end

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  • Temporary dimming of desktop in 12.04

    - by deshmukh
    I am running Ubuntu 12.04 (almost default install regularly updated) Unity interface on ASUS X53U (AMD Brazos Dual Core C60 with 2GB RAM). On launching Thunderbird and Firefox, the application dims and the cursor changes to wait mode. In case of Thunderbird, this is most pronounced with the wait time of up to a minute. Memory status checked with free indicates around 500MB of free memory on such occasions. The OS is stable and I can switch to a different work-space, etc. What could this be? Is this something normal?

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  • Wubi 12.04 boot error message

    - by Leandro
    Im having a boot problem with my Wubi 12.04 system. When Ubuntu starts to boot up, a message will appear in my screen and it's something like: T#s..... does not exist Sorry, I couldn't read all the message. Then another message pop-out after Ubuntu loading screen this time the message is this: Gave up waiting for root device. Common problems: -Boot args (cat /proc/cmdline) -check rootdelay= (did the system wait long enough?) -check root= (did the system wait for the right device?) -missing module (cat /proc/module: ls /dev) ALERT! /dev/disk/by/by_uuid/EODC2345DC231576 does not exist. Dropping to a shell

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  • 12.04 64 bit: Keybord not responding for about 20 seconds at startup/beginning of session

    - by Danilo
    I am running Ubuntu 12.04 64bit. When I get at the login screen and try to type the password for my user, I cannot type anything for about 20 seconds. After that, the keyboard starts responding and everything works fine. Mouse is responding normally as well as all buttons of the login interface (time/calendar, session selection (Unity/Unity 2D), etc.). What could be the reason for this behavior? How can I solve this temporary freeze of the keyboard so that I can type my password immediately without having to wait each time? Thanks for your time. EDIT: I tried auto login, but the problem is still there: the Desktop loads but even there, if I try to type something in the dash or anywhere else, I must wait about 20 seconds before I can actually start typing. Can the issue be related to some keyboard modules that get loaded little bit "too late"?

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  • When was sys.dm_os_wait_stats last cleared?

    - by SQLOS Team
    The sys.dm_os_wait_stats DMV provides essential metrics for diagnosing SQL Server performance problems. Returning incrementally accumulating information about all the completed waits encountered by executing threads it is a useful way to identify bottlenecks such as IO latency issues or waits on locks. The counters are reset each time SQL server is restarted, or when the following command is run: DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR); To make sense out of these wait values you need to know how they change over time. Suppose you are asked to troubleshoot a system and you don't know when the wait stats were last zeroed. Is there any way to find the elapsed time since this happened? If the wait stats were not cleared using the DBCC SQLPERF command then you can simply correlate the stats with the time SQL Server was started using the sqlserver_start_time column introduced in SQL Server 2008 R2: SELECT sqlserver_start_time from sys.dm_os_sys_info However how do you tell if someone has run DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR) since the server was started, and if they did, when? Without this information the initial, or historical, wait_stats have less value until you can measure deltas over time. There is a way to at least estimate when the stats were last cleared, by using the wait stats themselves and choosing a thread that spends most of its time sleeping. A good candidate is the SQL Trace incremental flush task, which mostly sleeps (in 4 second intervals) and in between it attempts to flush (if there are new events – which is rare when only default trace is running) – so it pretty much sleeps all the time. Hence the time it has spent waiting is very close to the elapsed time since the counter was reset. Credit goes to Ivan Penkov in the SQLOS dev team for suggesting this. Here's an example (excuse formatting): 144 seconds after the server was started: select top 10 wait_type, wait_time_ms from sys.dm_os_wait_stats order by wait_time_ms desc wait_type                                                               wait_time_ms--------------------------------------------------------------------------------------------------------------- XE_DISPATCHER_WAIT                                      242273LAZYWRITER_SLEEP                                          146010LOGMGR_QUEUE                                                145412DIRTY_PAGE_POLL                                             145411XE_TIMER_EVENT                                               145216REQUEST_FOR_DEADLOCK_SEARCH             145194SQLTRACE_INCREMENTAL_FLUSH_SLEEP    144325SLEEP_TASK                                                        73359BROKER_TO_FLUSH                                           73113PREEMPTIVE_OS_AUTHENTICATIONOPS       143 (10 rows affected) Reset: DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR)" DBCC execution completed. If DBCC printed error messages, contact your system administrator. After 8 seconds: select top 10 wait_type, wait_time_ms from sys.dm_os_wait_stats order by wait_time_ms desc wait_type                                                                 wait_time_ms--------------------------------------------------------------------------------------------------------------------- REQUEST_FOR_DEADLOCK_SEARCH              10013LAZYWRITER_SLEEP                                           8124SQLTRACE_INCREMENTAL_FLUSH_SLEEP     8017LOGMGR_QUEUE                                                 7579DIRTY_PAGE_POLL                                              7532XE_TIMER_EVENT                                                5007BROKER_TO_FLUSH                                            4118SLEEP_TASK                                                         3089PREEMPTIVE_OS_AUTHENTICATIONOPS        28SOS_SCHEDULER_YIELD                                   27 (10 rows affected)   After 12 seconds: select top 10 wait_type, wait_time_ms from sys.dm_os_wait_stats order by wait_time_ms desc wait_type                                                                  wait_time_ms------------------------------------------------------------------------------------------------------ REQUEST_FOR_DEADLOCK_SEARCH               15020LAZYWRITER_SLEEP                                            14206LOGMGR_QUEUE                                                  14036DIRTY_PAGE_POLL                                               13973SQLTRACE_INCREMENTAL_FLUSH_SLEEP      12026XE_TIMER_EVENT                                                 10014SLEEP_TASK                                                          7207BROKER_TO_FLUSH                                             7207PREEMPTIVE_OS_AUTHENTICATIONOPS         57SOS_SCHEDULER_YIELD                                     28 (10 rows affected) It may not be accurate to the millisecond, but it can provide a useful data point, and give an indication whether the wait stats were manually cleared after startup, and if so approximately when. - Guy     Originally posted at http://blogs.msdn.com/b/sqlosteam/

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  • wireless driver error after install

    - by James
    after following this command to update wifi drivers:1- Boot into Ubuntu 2- Open a terminal by pressing Ctrl+Alt+T 3- Type in the following (verbatim!) sudo apt-get update && sudo apt-get upgrade press Enter, the command will prompt for your password (the one you use to login into Ubuntu), type it and press Enter. Wait for it to finish updating your system. Now type: sudo apt-get remove bcmwl-kernel-source sudo apt-get install firmware-b43-installer Wait for the command to finish installing the driver, when done restart your computer. i get a message after the first command when installing has done saying not enough space so it aborts! what do i do to fix this

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  • Should tests be in the same Ruby file or in separated Ruby files?

    - by Junior Mayhé
    While using Selenium and Ruby to do some functional tests, I am worried with the performance. So is it better to add all test methods in the same Ruby file, or I should put each one in separated code files? Below a sample with all tests in the same file: # encoding: utf-8 require "selenium-webdriver" require "test/unit" class Tests < Test::Unit::TestCase def setup @driver = Selenium::WebDriver.for :firefox @base_url = "http://mysite" @driver.manage.timeouts.implicit_wait = 30 @verification_errors = [] @wait = Selenium::WebDriver::Wait.new :timeout => 10 end def teardown @driver.quit assert_equal [], @verification_errors end def element_present?(how, what) @driver.find_element(how, what) true rescue Selenium::WebDriver::Error::NoSuchElementError false end def verify(&blk) yield rescue Test::Unit::AssertionFailedError => ex @verification_errors << ex end def test_1 @driver.get(@base_url + "/") # a huge test here end def test_2 @driver.get(@base_url + "/") # a huge test here end def test_3 @driver.get(@base_url + "/") # a huge test here end def test_4 @driver.get(@base_url + "/") # a huge test here end def test_5 @driver.get(@base_url + "/") # a huge test here end end

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  • SQL Azure Security: DoS Part II

    - by Herve Roggero
    Ah!  When you shoot yourself in the foot... a few times... it hurts! That's what I did on Sunday, to learn more about the behavior of the SQL Azure Denial Of Service prevention feature. This article is a short follow up to my last post on this feature. In this post, I will outline some of the lessons learned that were the result of testing the behavior of SQL Azure from two machines. From the standpoint of SQL Azure, they look like one machine since they are behind a NAT. All logins affected The first thing to note is that all the logins are affected. If you lock yourself out to a specific database, none of the logins will work on that database. In fact the database size becomes "--" in the SQL Azure Portal.   Less than 100 sessions I was able to see 50+ sessions being made in SQL Azure (by looking at sys.dm_exec_sessions) before being locked out. The the DoS feature appears to be triggered in part by the number of open sessions. I could not determine if the lockout is triggered by the speed at which connection requests are made however.   Other Databases Unaffected This was interesting... the DoS feature works at the database level. Other databases were available for me to use.   Just Wait Initially I thought that going through SQL Azure and connecting from there would reset the database and allow me to connect again. Unfortunately this doesn't seem to be the case. You will have to wait. And the more you lock yourself out, the more you will have to wait... The first time the database became available again within 30 seconds or so; the second time within 2-3 minutes and the third time... within 2-3 hours...   Successful Logins The DoS feature appears to engage only for valid logins. If you have a login failure, it doesn't seem to count. I ran a test with over 100 login failures without being locked.

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  • Identifying which pattern fits better.

    - by Daniel Grillo
    I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern. Edit I'll try to explain better taking in count the given comments and answers. I've already done this software and now I'm trying to refactoring it. I'm trying to use patterns, even if it is not necessary because I'm taking advantage of this little software to learn about some patterns. Despite I think that one (or more) pattern fits here and it could improve my code. When I want to read version of the software of my device, I don't have to assembly the command with parameters. It is fixed. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. To read a portion of the memory (maximum of 256 bytes), I have to assembly the command using the parameters Len and Address. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. To write a portion in the memory (maximum of 256 bytes), I have to assembly the command using the parameters Len, Address and Data. So I have to send it. After wait for response. If there is a response, treat (or parse) it and returns. I think that I could use Template Method because I have almost the same algorithm for all. But the problem is some commands are fixes, others have 2 or 3 parameters. I think that parameters should be passed on the constructor of the class. But each class will have a constructor overriding the abstract class constructor. Is this a problem for the template method? Should I use other pattern?

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  • Desktop dims when Thunderbird and Firefox are launched

    - by deshmukh
    I am running Ubuntu 12.04 (almost default install regularly updated) Unity interface on ASUS X53U (AMD Brazos Dual Core C60 with 2GB RAM). On launching Thunderbird and Firefox, the application dims and the cursor changes to wait mode. In case of Thunderbird, this is most pronounced with the wait time of up to a minute. Memory status checked with free indicates around 500MB of free memory on such occasions. The OS is stable and I can switch to a different work-space, etc. What could this be? Is this something normal?

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  • Plans for Java 7 and E-Business Suite Certification

    - by Steven Chan (Oracle Development)
    As of June 2012, Java 7 has not been certified yet with Oracle E-Business Suite.  EBS customers should continue to run JRE 6 on their Windows end-user desktops, and JDK 6 on their EBS servers. If a search engine has brought you to this article, please check the Certifications summary for our latest certified Java release. Our plans for certifying Java 7 for the E-Business Suite We plan on releasing the Java 7 certification for E-Business Suite customers in two phases: Phase 1: Certify JRE 7 for Windows end-user desktops Phase 2: Certify JDK 7 for server-based components When will Java 7 be certified with EBS? We're working on the first phase now. As usual, I cannot discuss release dates here, but you can monitor or subscribe to this blog for updates. Current known issues with JRE 7 in EBS environments Our current testing shows that there are known incompatibilities between JRE 7 and the Forms-invocation process in EBS environments.  We have been working directly with the Java division on this for a while now.  In the meantime, EBS customers should not deploy JRE 7 to their end-user Windows desktop clients. You should stick with JRE 1.6 for now.  But wait, you previously said... Older JRE certification announcements stated: Our standard policy is that all E-Business Suite customers can apply all JRE updates to end-user desktops from JRE 1.6.0_03 and higher.  We test all new JRE releases in parallel with the JRE development process, so all JRE releases are considered certified with the E-Business Suite on the same day that they're released by our Java team.  You do not need to wait for a certification announcement before applying new JRE releases to your EBS users' desktops. Yes, this is true.  This standard boilerplate text was written before JRE 7 was released, so there was no possibility of misunderstanding.  With the availability of JRE 7, that boilerplate needs to be revised to read: Our standard policy is that all E-Business Suite customers can apply all JRE updates to end-user desktops from JRE 1.6.0_03 and later updates on the 1.6 codeline.  We test all new JRE 1.6 releases in parallel with the JRE development process, so all new JRE 1.6 releases are considered certified with the E-Business Suite on the same day that they're released by our Java team.  You do not need to wait for a certification announcement before applying new JRE 1.6 releases to your EBS users' desktops. References Recommended Browsers for Oracle Applications 11i (Metalink Note 285218.1) Upgrading Sun JRE (Native Plug-in) with Oracle Applications 11i for Windows Clients (Metalink Note 290807.1) Recommended Browsers for Oracle Applications 12 (MetaLink Note 389422.1) Upgrading JRE Plugin with Oracle Applications R12 (MetaLink Note 393931.1) Related Articles Mismanaged Session Cookie Issue Fixed for EBS in JRE 1.6.0_23 Roundup: Oracle JInitiator 1.3 Desupported for EBS Customers in July 2009

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  • Partners - There's a Virtual Seat Awaiting You

    - by Get_Specialized!
    That's right; no need to book travel, wait in airport lines or deal with expenses afterwards! Leave the luggage at home and just log on. Attend the LIVE Oracle FY13 PartnerNetwork Kickoff June 26th/27th. from your own location. Why wait, it just takes a moment to register for your region: NAS  - Tuesday, June 26 @ 8:30 am PT  EMEA - Tuesday, June 26 @ 2:00 pm BST LAD - Tuesday, June 26 @ 2:00pm EDT (Miami) / 3:00pm BRT (Sao Paulo) Japan - Wednesday, June 27 @ 10:00 am JST APAC - Wednesday, June 27 @ 8:30 am IST (Bangalore) / 11:00 am SGT (Singapore), 1:00 pm AEST (Sydney) Your further invited to interact in the conversation and bring forth questions to the Oracle PartnerNetwork on Twitter

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  • Kernel panic when booting from USB

    - by maaartinus
    I downloaded ubuntu-11.04-desktop-amd64.iso and used Universal-USB-Installer-1.8.6.3.exe to format my USB stick und put the ISO on it. When I tried to install from it, I've got a kernel panic just like here, except for the version number (mine was 2.6.38-8-generic #42-ubuntu). My ISO image seems to work, as I installed it into a VMWare player without problems. Booting Linux from USB works surely too, as I did it some time ago with an older Ubuntu version. I can imagine things to try out, e.g., write the image again, try another version, pray, look for patches, etc. However, I'm looking for a time-efficient solution, something what most probably works. An advice of the sort "wait two weeks until it's surely fixed, then download again" is acceptable, I'm determined to switch to Linux, but it can wait a bit.

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  • Ubuntu doesn't start and I can't login

    - by Meph00
    My ubuntu 13.04 doesn't boot anymore. Eternal black screen. If I press ALT+CTRL+F1 I see that it's stucked on "Checking battery state [OK]." I'd like to try to go with sudo apt-get install gdm but I can't login on terminal tty2, tty3 etc. They correctly ask for my nickname, then they make me wait a lot, ask for password and make me wait again. After a lot of time (... a lot) the best I could achieve was visualizing "Documentantion https://help.ubuntu.com". I can never reach the point where I can give commands. Plus, during the long pauses, every 2 minutes it gives a messagge like this: INFO: task XXX blocked for more than 120 seconds. Any suggestion? Sorry for my bad english and thanks everyone for the attention.

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  • Checking timeouts made more readable

    - by Markus
    I have several situations where I need to control timeouts in a technical application. Either in a loop or as a simple check. Of course – handling this is really easy, but none of these is looking cute. To clarify, here is some C# (Pseudo) code: private DateTime girlWentIntoBathroom; girlWentIntoBathroom = DateTime.Now; do { // do something } while (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now); or if (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); Now I was inspired by something a saw in Ruby on StackOverflow: Now I’m wondering if this construct can be made more readable using extension methods. My goal is something that can be read like “If girlWentIntoBathroom is more than 10 seconds ago” 1st attempt if (girlWentIntoBathroom > (10).Seconds().Ago()) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); So I wrote an extension for integer that converts the integer into a TimeSpan public static TimeSpan Seconds(this int amount) { return new TimeSpan(0, 0, amount); } After that, I wrote an extension for TimeSpan like this: public static DateTime Ago(this TimeSpan diff) { return DateTime.Now.Add(-diff); } This works fine so far, but has a great disadvantage. The logic is inverted! Since girlWentIntoBathroom is a timestamp in the past, the right side of the equation needs to count backwards: impossible. Just inverting the equation is no solution, because it will invert the read sentence as well. 2nd attempt So I tried something new: if (girlWentIntoBathroom.IsMoreThan(10).SecondsAgo()) MessageBox.Show("Knock louder"); else MessageBox.Show("Wait a little longer"); IsMoreThan() needs to transport the past timestamp as well as the span for the extension SecondsAgo(). It could be: public static DateWithIntegerSpan IsMoreThan(this DateTime baseTime, int span) { return new DateWithIntegerSpan() { Date = baseTime, Span = span }; } Where DateWithIntegerSpan is simply: public class DateWithIntegerSpan { public DateTime Date {get; set;} public int Span { get; set; } } And SecondsAgo() is public static bool SecondsAgo(this DateWithIntegerSpan dateAndSpan) { return dateAndSpan.Date.Add(new TimeSpan(0, 0, dateAndSpan.Span)) < DateTime.Now; } Using this approach, the English sentence matches the expected behavior. But the disadvantage is, that I need a helping class (DateWithIntegerSpan). Has anyone an idea to make checking timeouts look more cute and closer to a readable sentence? Am I a little too insane thinking about something minor like this?

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  • WinRAR extracting file before checking password? [closed]

    - by opatachibueze
    I tried extracting an encrypted rar file today, and I discovered that I had to wait the same amount of time I'll wait before a file is extracted (extraction reaches 99% completion) for WinRAR to conclude it's the wrong password (winrar message: "CRC failed wrong password or corrupt file?") . My guess is that this file is somewhere on the Computer just before the detection, - it has to be and then gets deleted after it's verified that the password is not the same? Is there anyway I can forcefully get this file from the PC? Thanks.

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  • Synchronous communication using NSOperationQueue

    - by chip_munks
    I am new to Objective C programming. I have created two threads called add and display using the NSInvocationOperation and added it on to the NSOperationQueue. I make the display thread to run first and then run the add thread. The display thread after printing the "Welcome to display" has to wait for the results to print from the add method. So i have set the waitUntilFinished method. Both the Operations are on the same queue. If i use waitUntilFinished for operations on the same queue there may be a situation for deadlock to happen(from apples developer documentation). Is it so? To wait for particular time interval there is a method called waitUntilDate: But if i need to like this wait(min(100,dmax)); let dmax = 20; How to do i wait for these conditions? It would be much helpful if anyone can explain with an example. EDITED: threadss.h ------------ #import <Foundation/Foundation.h> @interface threadss : NSObject { BOOL m_bRunThread; int a,b,c; NSOperationQueue* queue; NSInvocationOperation* operation; NSInvocationOperation* operation1; NSConditionLock* theConditionLock; } -(void)Thread; -(void)add; -(void)display; @end threadss.m ------------ #import "threadss.h" @implementation threadss -(id)init { if (self = [super init]) { queue = [[NSOperationQueue alloc]init]; operation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(display) object:nil]; operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(add) object:nil]; theConditionLock = [[NSConditionLock alloc]init]; } return self; } -(void)Thread { m_bRunThread = YES; //[operation addDependency:operation1]; if (m_bRunThread) { [queue addOperation:operation]; } //[operation addDependency:operation1]; [queue addOperation:operation1]; //[self performSelectorOnMainThread:@selector(display) withObject:nil waitUntilDone:YES]; //NSLog(@"I'm going to do the asynchronous communication btwn the threads!!"); //[self add]; //[operation addDependency:self]; sleep(1); [queue release]; [operation release]; //[operation1 release]; } -(void)add { NSLog(@"Going to add a and b!!"); a=1; b=2; c = a + b; NSLog(@"Finished adding!!"); } -(void)display { NSLog(@"Into the display method"); [operation1 waitUntilFinished]; NSLog(@"The Result is:%d",c); } @end main.m ------- #import <Foundation/Foundation.h> #import "threadss.h" int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; threadss* thread = [[threadss alloc]init]; [thread Thread]; [pool drain]; return 0; } This is what i have tried with a sample program. output 2011-06-03 19:40:47.898 threads_NSOperationQueue[3812:1503] Going to add a and b!! 2011-06-03 19:40:47.898 threads_NSOperationQueue[3812:1303] Into the display method 2011-06-03 19:40:47.902 threads_NSOperationQueue[3812:1503] Finished adding!! 2011-06-03 19:40:47.904 threads_NSOperationQueue[3812:1303] The Result is:3 Is the way of invoking the thread is correct. 1.Will there be any deadlock condition? 2.How to do wait(min(100,dmax)) where dmax = 50.

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