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• Parallelism in .NET – Part 13, Introducing the Task class

  - by Reed

  Once we’ve used a task-based decomposition to decompose a problem, we need a clean abstraction usable to implement the resulting decomposition.  Given that task decomposition is founded upon defining discrete tasks, .NET 4 has introduced a new API for dealing with task related issues, the aptly named Task class. The Task class is a wrapper for a delegate representing a single, discrete task within your decomposition.  We will go into various methods of construction for tasks later, but, when reduced to its fundamentals, an instance of a Task is nothing more than a wrapper around a delegate with some utility functionality added.  In order to fully understand the Task class within the new Task Parallel Library, it is important to realize that a task really is just a delegate – nothing more.  In particular, note that I never mentioned threading or parallelism in my description of a Task.  Although the Task class exists in the new System.Threading.Tasks namespace: Tasks are not directly related to threads or multithreading. Of course, Task instances will typically be used in our implementation of concurrency within an application, but the Task class itself does not provide the concurrency used.  The Task API supports using Tasks in an entirely single threaded, synchronous manner. Tasks are very much like standard delegates.  You can execute a task synchronously via Task.RunSynchronously(), or you can use Task.Start() to schedule a task to run, typically asynchronously.  This is very similar to using delegate.Invoke to execute a delegate synchronously, or using delegate.BeginInvoke to execute it asynchronously. The Task class adds some nice functionality on top of a standard delegate which improves usability in both synchronous and multithreaded environments. The first addition provided by Task is a means of handling cancellation via the new unified cancellation mechanism of .NET 4.  If the wrapped delegate within a Task raises an OperationCanceledException during it’s operation, which is typically generated via calling ThrowIfCancellationRequested on a CancellationToken, or if the CancellationToken used to construct a Task instance is flagged as canceled, the Task’s IsCanceled property will be set to true automatically.  This provides a clean way to determine whether a Task has been canceled, often without requiring specific exception handling. Tasks also provide a clean API which can be used for waiting on a task.  Although the Task class explicitly implements IAsyncResult, Tasks provide a nicer usage model than the traditional .NET Asynchronous Programming Model.  Instead of needing to track an IAsyncResult handle, you can just directly call Task.Wait() to block until a Task has completed.  Overloads exist for providing a timeout, a CancellationToken, or both to prevent waiting indefinitely.  In addition, the Task class provides static methods for waiting on multiple tasks – Task.WaitAll and Task.WaitAny, again with overloads providing time out options.  This provides a very simple, clean API for waiting on single or multiple tasks. Finally, Tasks provide a much nicer model for Exception handling.  If the delegate wrapped within a Task raises an exception, the exception will automatically get wrapped into an AggregateException and exposed via the Task.Exception property.  This exception is stored with the Task directly, and does not tear down the application.  Later, when Task.Wait() (or Task.WaitAll or Task.WaitAny) is called on this task, an AggregateException will be raised at that point if any of the tasks raised an exception.  For example, suppose we have the following code: Task taskOne = new Task( () => { throw new ApplicationException("Random Exception!"); }); Task taskTwo = new Task( () => { throw new ArgumentException("Different exception here"); }); // Start the tasks taskOne.Start(); taskTwo.Start(); try { Task.WaitAll(new[] { taskOne, taskTwo }); } catch (AggregateException e) { Console.WriteLine(e.InnerExceptions.Count); foreach (var inner in e.InnerExceptions) Console.WriteLine(inner.Message); } .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; } Here, our routine will print: 2 Different exception here Random Exception! Note that we had two separate tasks, each of which raised two distinctly different types of exceptions.  We can handle this cleanly, with very little code, in a much nicer manner than the Asynchronous Programming API.  We no longer need to handle TargetInvocationException or worry about implementing the Event-based Asynchronous Pattern properly by setting the AsyncCompletedEventArgs.Error property.  Instead, we just raise our exception as normal, and handle AggregateException in a single location in our calling code.

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• How to render partial.js in rails 3

  - by julian-mann

  Using rails3 - I have a project with many tasks. I want to use javascript to build the UI for each task. I figured I could display those tasks on the projects show page by rendering a javascript partial for each. I can't get 'tasks/show' to see tasks/show.js.erb Any ideas? In projects/show.html.erb <div id="tasks"> <%= render(:partial => "tasks/show", :collection => @project.tasks) %> </div> tasks/show.js.erb $("tasks").append(new TaskWidget(task.id)) I get the errors ActionView::MissingTemplate in Projects#show Missing partial tasks/show with {:handlers=>[:erb, :rjs, :builder, :rhtml, :rxml], :formats=>[:html], :locale=>[:en, :en]} in view paths .... around line #13 Thanks

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• Simple task framework - building software from reusable pieces

  - by RuslanD

  I'm writing a web service with several APIs, and they will be sharing some of the implementation code. In order not to copy-paste, I would like to ideally implement each API call as a series of tasks, which are executed in a sequence determined by the business logic. One obvious question is whether that's the best strategy for code reuse, or whether I can look at it in a different way. But assuming I want to go with tasks, several issues arise: What's a good task interface to use? How do I pass data computed in one task to another task in the sequence that might need it? In the past, I've worked with task interfaces like: interface Task<T, U> { U execute(T input); } Then I also had sort of a "task context" object which had getters and setters for any kind of data my tasks needed to produce or consume, and it gets passed to all tasks. I'm aware that this suffers from a host of problems. So I wanted to figure out a better way to implement it this time around. My current idea is to have a TaskContext object which is a type-safe heterogeneous container (as described in Effective Java). Each task can ask for an item from this container (task input), or add an item to the container (task output). That way, tasks don't need to know about each other directly, and I don't have to write a class with dozens of methods for each data item. There are, however, several drawbacks: Each item in this TaskContext container should be a complex type that wraps around the actual item data. If task A uses a String for some purpose, and task B uses a String for something entirely different, then just storing a mapping between String.class and some object doesn't work for both tasks. The other reason is that I can't use that kind of container for generic collections directly, so they need to be wrapped in another object. This means that, based on how many tasks I define, I would need to also define a number of classes for the task items that may be consumed or produced, which may lead to code bloat and duplication. For instance, if a task takes some Long value as input and produces another Long value as output, I would have to have two classes that simply wrap around a Long, which IMO can spiral out of control pretty quickly as the codebase evolves. I briefly looked at workflow engine libraries, but they kind of seem like a heavy hammer for this particular nail. How would you go about writing a simple task framework with the following requirements: Tasks should be as self-contained as possible, so they can be composed in different ways to create different workflows. That being said, some tasks may perform expensive computations that are prerequisites for other tasks. We want to have a way of storing the results of intermediate computations done by tasks so that other tasks can use those results for free. The task framework should be light, i.e. growing the code doesn't involve introducing many new types just to plug into the framework.

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• Techniques for modeling a dynamic dataflow with Java concurrency API

  - by Maian

  Is there an elegant way to model a dynamic dataflow in Java? By dataflow, I mean there are various types of tasks, and these tasks can be "connected" arbitrarily, such that when a task finishes, successor tasks are executed in parallel using the finished tasks output as input, or when multiple tasks finish, their output is aggregated in a successor task (see flow-based programming). By dynamic, I mean that the type and number of successors tasks when a task finishes depends on the output of that finished task, so for example, task A may spawn task B if it has a certain output, but may spawn task C if has a different output. Another way of putting it is that each task (or set of tasks) is responsible for determining what the next tasks are. Sample dataflow for rendering a webpage: I have as task types: file downloader, HTML/CSS renderer, HTML parser/DOM builder, image renderer, JavaScript parser, JavaScript interpreter. File downloader task for HTML file HTML parser/DOM builder task File downloader task for each embedded file/link If image, image renderer If external JavaScript, JavaScript parser JavaScript interpreter Otherwise, just store in some var/field in HTML parser task JavaScript parser for each embedded script JavaScript interpreter Wait for above tasks to finish, then HTML/CSS renderer (obviously not optimal or perfectly correct, but this is simple) I'm not saying the solution needs to be some comprehensive framework (in fact, the closer to the JDK API, the better), and I absolutely don't want something as heavyweight is say Spring Web Flow or some declarative markup or other DSL. To be more specific, I'm trying to think of a good way to model this in Java with Callables, Executors, ExecutorCompletionServices, and perhaps various synchronizer classes (like Semaphore or CountDownLatch). There are a couple use cases and requirements: Don't make any assumptions on what executor(s) the tasks will run on. In fact, to simplify, just assume there's only one executor. It can be a fixed thread pool executor, so a naive implementation can result in deadlocks (e.g. imagine a task that submits another task and then blocks until that subtask is finished, and now imagine several of these tasks using up all the threads). To simplify, assume that the data is not streamed between tasks (task output-succeeding task input) - the finishing task and succeeding task won't exist together, so the input data to the succeeding task will not be changed by the preceeding task (since it's already done). There are only a couple operations that the dataflow "engine" should be able to handle: A mechanism where a task can queue more tasks A mechanism whereby a successor task is not queued until all the required input tasks are finished A mechanism whereby the main thread (or other threads not managed by the executor) blocks until the flow is finished A mechanism whereby the main thread (or other threads not managed by the executor) blocks until certain tasks have finished Since the dataflow is dynamic (depends on input/state of the task), the activation of these mechanisms should occur within the task code, e.g. the code in a Callable is itself responsible for queueing more Callables. The dataflow "internals" should not be exposed to the tasks (Callables) themselves - only the operations listed above should be available to the task. Note that the type of the data is not necessarily the same for all tasks, e.g. a file download task may accept a File as input but will output a String. If a task throws an uncaught exception (indicating some fatal error requiring all dataflow processing to stop), it must propagate up to the thread that initiated the dataflow as quickly as possible and cancel all tasks (or something fancier like a fatal error handler). Tasks should be launched as soon as possible. This along with the previous requirement should preclude simple Future polling + Thread.sleep(). As a bonus, I would like to dataflow engine itself to perform some action (like logging) every time task is finished or when no has finished in X time since last task has finished. Something like: ExecutorCompletionService<T> ecs; while (hasTasks()) { Future<T> future = ecs.poll(1 minute); some_action_like_logging(); if (future != null) { future.get() ... } ... } Are there straightforward ways to do all this with Java concurrency API? Or if it's going to complex no matter what with what's available in the JDK, is there a lightweight library that satisfies the requirements? I already have a partial solution that fits my particular use case (it cheats in a way, since I'm using two executors, and just so you know, it's not related at all to the web browser example I gave above), but I'd like to see a more general purpose and elegant solution.

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• Find the order among tasks in a company by using prolog?

  - by Cem

  First of all,I wish a happy new year for everyone.I searched more and worked a lot but I could not solve this question.I am quite a new in prolog and I must do this homework. In my homework,the question is like this: Write a prolog program that determines a valid order for the tasks to be carried out in a company. The prolog program will consist of a set of "before" predicates which denotes the order between task pairs. Here is an example; before(a,b). before(a,e). before(d,c). before(b,c). before(c,e). Here, task a should be carried before tasks b and e, d before c and so on. Hence a valid ordering of the tasks would be [a, b, d, c, e]. The order predicate in your program will be queried as follows. ?- order([a,b,c,d,e],X). X = [a, b, d, c, e] ; X = [a, d, b, c, e] ; X = [d, a, b, c, e] ; false. Hint: Try to generate different orders for the tasks (permutation) and then check if the order is consistent with the "before" relationships given. Even if you can generate a single valid order, you will get reasonable partial credits.

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• Why does Celery work in Python shell, but not in my Django views? (import problem)

  - by TIMEX

  I installed Celery (latest stable version.) I have a directory called /home/myuser/fable/jobs. Inside this directory, I have a file called tasks.py: from celery.decorators import task from celery.task import Task class Submitter(Task): def run(self, post, **kwargs): return "Yes, it works!!!!!!" Inside this directory, I also have a file called celeryconfig.py: BROKER_HOST = "localhost" BROKER_PORT = 5672 BROKER_USER = "abc" BROKER_PASSWORD = "xyz" BROKER_VHOST = "fablemq" CELERY_RESULT_BACKEND = "amqp" CELERY_IMPORTS = ("tasks", ) In my /etc/profile, I have these set as my PYTHONPATH: PYTHONPATH=/home/myuser/fable:/home/myuser/fable/jobs So I run my Celery worker using the console ($ celeryd --loglevel=INFO), and I try it out. I open the Python console and import the tasks. Then, I run the Submitter. >>> import fable.jobs.tasks as tasks >>> s = tasks.Submitter() >>> s.delay("abc") <AsyncResult: d70d9732-fb07-4cca-82be-d7912124a987> Everything works, as you can see in my console [2011-01-09 17:30:05,766: INFO/MainProcess] Task tasks.Submitter[d70d9732-fb07-4cca-82be-d7912124a987] succeeded in 0.0398268699646s: But when I go into my Django's views.py and run the exact 3 lines of code as above, I get this: [2011-01-09 17:25:20,298: ERROR/MainProcess] Unknown task ignored: "Task of kind 'fable.jobs.tasks.Submitter' is not registered, please make sure it's imported.": {'retries': 0, 'task': 'fable.jobs.tasks.Submitter', 'args': ('abc',), 'expires': None, 'eta': None, 'kwargs': {}, 'id': 'eb5c65b4-f352-45c6-96f1-05d3a5329d53'} Traceback (most recent call last): File "/home/myuser/mysite-env/lib/python2.6/site-packages/celery/worker/listener.py", line 321, in receive_message eventer=self.event_dispatcher) File "/home/myuser/mysite-env/lib/python2.6/site-packages/celery/worker/job.py", line 299, in from_message eta=eta, expires=expires) File "/home/myuser/mysite-env/lib/python2.6/site-packages/celery/worker/job.py", line 243, in __init__ self.task = tasks[self.task_name] File "/home/myuser/mysite-env/lib/python2.6/site-packages/celery/registry.py", line 63, in __getitem__ raise self.NotRegistered(str(exc)) NotRegistered: "Task of kind 'fable.jobs.tasks.Submitter' is not registered, please make sure it's imported." It's weird, because the celeryd client does show that it's registered, when I launch it. [2011-01-09 17:38:27,446: WARNING/MainProcess] Configuration -> . broker -> amqp://GOGOme@localhost:5672/fablemq . queues -> . celery -> exchange:celery (direct) binding:celery . concurrency -> 1 . loader -> celery.loaders.default.Loader . logfile -> [stderr]@INFO . events -> OFF . beat -> OFF . tasks -> . tasks.Decayer . tasks.Submitter Can someone help?

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• Class hierarchy problem (with generic's variance!)

  - by devoured elysium

  The problem: class StatesChain : IState, IHasStateList { private TasksChain tasks = new TasksChain(); ... public IList<IState> States { get { return _taskChain.Tasks; } } IList<ITask> IHasTasksCollection.Tasks { get { return _taskChain.Tasks; } <-- ERROR! You can't do this in C#! I want to return an IList<ITask> from an IList<IStates>. } } Assuming the IList returned will be read-only, I know that what I'm trying to achieve is safe (or is it not?). Is there any way I can accomplish what I'm trying? I wouldn't want to try to implement myself the TasksChain algorithm (again!), as it would be error prone and would lead to code duplication. Maybe I could just define an abstract Chain and then implement both TasksChain and StatesChain from there? Or maybe implementing a Chain<T> class? How would you approach this situation? The Details: I have defined an ITask interface: public interface ITask { bool Run(); ITask FailureTask { get; } } and a IState interface that inherits from ITask: public interface IState : ITask { IState FailureState { get; } } I have also defined an IHasTasksList interface: interface IHasTasksList { List<Tasks> Tasks { get; } } and an IHasStatesList: interface IHasTasksList { List<Tasks> States { get; } } Now, I have defined a TasksChain, that is a class that has some code logic that will manipulate a chain of tasks (beware that TasksChain is itself a kind of ITask!): class TasksChain : ITask, IHasTasksList { IList<ITask> tasks = new List<ITask>(); ... public List<ITask> Tasks { get { return _tasks; } } ... } I am implementing a State the following way: public class State : IState { private readonly TaskChain _taskChain = new TaskChain(); public State(Precondition precondition, Execution execution) { _taskChain.Tasks.Add(precondition); _taskChain.Tasks.Add(execution); } public bool Run() { return _taskChain.Run(); } public IState FailureState { get { return (IState)_taskChain.Tasks[0].FailureTask; } } ITask ITask.FailureTask { get { return FailureState; } } } which, as you can see, makes use of explicit interface implementations to "hide" FailureTask and instead show FailureState property. The problem comes from the fact that I also want to define a StatesChain, that inherits both from IState and IHasStateList (and that also imples ITask and IHasTaskList, implemented as explicit interfaces) and I want it to also hide IHasTaskList's Tasks and only show IHasStateList's States. (What is contained in "The problem" section should really be after this, but I thought puting it first would be way more reader friendly). (pff..long text) Thanks!

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• Can I override task :environment in test_helper.rb to test rake tasks?

  - by Michael Barton

  I have a series of rake tasks in a Rakefile which I'd like to test as part of my specs etc. Each task is defined in the form: task :do_somthing => :environment do # Do something with the database here end Where the :environment task sets up an ActiveRecord/DataMapper database connection and classes. I'm not using this as part of Rails but I have a series of tests which I like to run as part of BDD. This snippet illustrates how I'm trying to test the rake tasks. def setup @rake = Rake::Application.new Rake.application = @rake load File.dirname(__FILE__) + '/../../tasks/do_something.rake' end should "import data" do @rake["do_something"].invoke assert something_in_the_database end So my request for help - is it possible to over-ride the :environment task in my test_helper.rb file so I my rake testing interacts with the my test database, rather than production? I've tried redefining the task in the helper file, but this doesn't work. Any help for a solution would be great, as I've been stuck on this for the past week.

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• How to get import custom tasks more than once without warning message?

  - by Nam Gi VU

  I'm using some custom tasks from MSBuild Extension Pack (MEP). My projects are splitted among many files. In those files I import the MEP tasks using (twice or three times in two/three files). I receive the warning message when doing this like: ... warning MSB4011: "C:\Program Files\MSBuild\ExtensionPack\MSBuild.ExtensionPack.tasks" cannot be imported again. It was already imported at "D:...\Tasker.proj (5,3)". This is most likely a build authoring error. This subsequent import will be ignored. Does anyone know how to get rid of this warning message? Please help!

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• Can a rake task know about the other tasks in the invocation chain?

  - by andrewdotnich

  Rake (like make) is able to have many targets/tasks specified on invocation. Is it possible for a rake task to access the list of tasks the user invoked, in order to do its job? Scenario: Consider a Rake-based build tool. A help task would like to know what tasks were also specified in order to print their usage and halt the build process. The benefit of this as opposed to rake-style parameter passing are cleaner syntax (rake help build instead of rake help task=build) and chaining (rake help build run_tests would print usage for both).

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• Cruise control: should deployment be in tasks or publishers?

  - by Aligma

  I'm setting up a Cruise Control configuration for one project. I have an <msbuild> task under <tasks>. It seems that I have the option of putting my file deployment under either <tasks> or <publishers>. Logically I would think it should reside under <publishers> but none of the examples I have seen online work this way. Should deployment happen within in <tasks> or <publishers>?

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• Various roles in an Organization and their respective tasks.

  - by balu

  In various organizations(Software Company) there would be various designations having different roles. I would like to know the Industry accepted & followed trend in the organization hierarchy(..Like DBA,System Architect,Project Manager,Senior Developer,Developer,QA,Design Team,Delivery Manager etc..).And the various roles played by each of them in the various stages of the Software Development Life Cycle.Who all could possibly be sharing the responsibility mutually?

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• Should Developers Perform All Tasks or Should They Specialize?

  - by Bob Horn

  Disclaimer: The intent of this question isn't to discern what is better for the individual developer, but for the system as a whole. I've worked in environments where small teams managed certain areas. For example, there would be a small team for every one of these functions: UI Framework code Business/application logic Database I've also worked on teams where the developers were responsible for all of these areas and more (QA, analsyt, etc...). My current environment promotes agile development (specifically scrum) and everyone has their hands in every area mentioned above. While there are pros and cons to each approach, I'd be curious to know if there are more pros and cons than I list below, and also what the generally feeling is about which approach is better. Devs Do It All Pros 1. Developers may be more well-rounded 2. Developers know more of the system Cons 1. Everyone has their hands in all areas, increasing the probability of creating less-than-optimal results in that area 2. It can take longer to do something with which you are unfamiliar (jack of all trades, master of none) Devs Specialize Pros 1. Developers can create policies and procedures for their area of expertise and more easily enforce them 2. Developers have more of a chance to become deeply knowledgeable about their specific area and make it the best it can be 3. Other developers don't cross boundaries and degrade another area Cons 1. As one colleague put it: "Why would you want to pigeon-hole yourself like that?" (Meaning some developers won't get a chance to work in certain areas.) It's easy to say how wonderful agile is, and that we should do it all, but I'm somewhat of a fan of having areas of expertise. Without that expertise, I've seen code degrade, database schemas become difficult to manage, hack UI code, etc... Let's face it, some people make careers out of doing just UI work, or just database work. It's not that easy to just fill in and do as good of a job as an expert in that area.

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• What are some tasks you might ask a potential ruby developer hire to complete?

  - by opensourcechris

  I would like to start a career path as a developer. As my first Language I chose Ruby to learn. What are some types of coding I might be asked to do as part of an evaluation at a potential employer? For example on my interview... Employer: "So, you think you can be a programer!" Me: "Why yes sir, I believe I would be a fitting addition to your team" Employer: "Well that remains to be seen! To demonstrate your basic knowledge please code insert evaluation project here What would you have me do to demonstrate my skills?

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• 5 year old ubuntu system, always dist-upgraded => ok. however some tasks remain

  - by knb

  I have a PC with a current ubuntu distribution installed. I've upgraded many times since 5.10. It always went well, however some tools or features were kindof left behind in a unsatisfactory state: grub to grub2 - is it an really necessary to switch the boot loader some time to grub2. Upgrading this scares me abit. I still have ext3 devices - is it worth upgrading to ext4? should I wait for btrfs? hibernation and suspend- it only worked in 5.10, since 6.04 it was messed up. Should I really care? Any chance to repair this myself? Simply by cleanup or hacking config files. It is a desktop PC after all. So energy saving functionality is not really needed. I am using vmware workstation 6.5 and the latest kernel that supports it is 2.6.32. This is my default kernel now, ignoring 2.6.35. Am I missing anything important in the new kernel now?

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• Many user stories share the same technical tasks: what to do?

  - by d3prok

  A little introduction to my case: As part of a bigger product, my team is asked to realize a small IDE for a DSL. The user of this product will be able to make function calls in the code and we are also asked to provide some useful function libraries. The team, together with the PO, put on the wall a certain number of user stories regarding the various libraries for the IDE user. When estimating the first of those stories, the team decided that the function call mechanism would have been an engaging but not completely obvious task, so the estimate for that user story raised up from a simple 3 to a more dangerous 5. Coming to the problem: The team then moved to the user stories regarding the other libraries, actually 10 stories, and added those 2 points of "function call mechanism" thing to each of those user story. This immediately raised up the total points for the product of 20 points! Everyone in the team knows that each user story could be picked up by the PO for the next iteration at any time, so we shouldn't isolate that part in one user story, but those 20 points feel so awfully unrealistic! I've proposed a solution, but I'm absolutely not satisfied: We created a "Design story" and put those annoying 2 points over it. However when we came to realize and demonstrate it to our customers, we were unable to show something really valuable for them about that story! Here the problem is whether we should ignore the principle of having isolated user stories (without any dependency between them). What would you do, or even better what have you done, in situations like this? (a small foot-note: following a suggestion I've moved this question from stackoverflow)

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• Rails OpenID Authentication Plugin No Longer Installs Rake Tasks?

  - by Rich Apodaca

  I'm following the Railscasts tutorial on using OpenID with AuthLogic. This command: $ script/plugin install git://github.com/rails/open_id_authentication.git installs the plugin, but I don't see any OpenID Rake tasks (rake -T). In particular, I can no longer run the task: $ rake open_id_authentication:db:create With previous applications, the Rake tasks were installed without a problem, so what's changed with the plugin? Which version of the plugin do I need to get the behavior I'm looking for? Using Rails 2.3.5.

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• In Rails, how should I implement a Status field for a Tasks app - integer or enum?

  - by Doug

  For a Rails 3.0 Todo app, I have a Tasks model with a Status field. What's the best way to store the Status field data (field type) and still display a human-readable version in a view (HTML table)? Status can be: 0 = Normal 1 = Active 2 = Completed Right now I have this: Rails Schema Here: create_table "tasks", :force = true do |t| t.integer "status", :limit = 1, :default = 0, :null = false Rails Model Here: class Task < ActiveRecord::Base validates_inclusion_of :status, :in => 0..2, :message => "{{value}} must be 0, 1, or 2" Rails View Here: <h1>Listing tasks</h1> <table> <tr> <th>Status</th> <th>Name</th> <th></th> <th></th> <th></th> </tr> <% @tasks.each do |task| %> <tr> <td><%= task.status %></td> <td><%= task.name %></td> <td><%= link_to 'Show', task %></td> <td><%= link_to 'Edit', edit_task_path(task) %></td> <td><%= link_to 'Delete', task, :confirm => 'Are you sure?', :method => :delete %></td> </tr> <% end %> </table> Requirements Store a Task's status in the db such that the values are easily localizable, i.e. I'm not sure I want to store "normal", "active", "completed" as a string field. Solution must work with Rails 3.0. Questions: Should I store the field as an integer (see above)? If so, how do I display the correct human readable status in an HTML table in my Rails view, e.g. show "Active" instead of "1" in the HTML table. Should I use an enum? If so, is this easy to localize later? Should I use straight strings, e.g. "Normal", "Active", "Completed" Can you provide a quick code sample of the view helper, controller or view code to make this work?

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• Is it possible to use in a Rakefile tasks from another one?

  - by Geo

  I have some Rake tasks I'd like to use in my Rakefiles. Is it possible to include tasks defined in one rakefile from another rakefile?

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• UppercuT &ndash; Custom Extensions Now With PowerShell and Ruby

  - by Robz / Fervent Coder

  Arguably, one of the most powerful features of UppercuT (UC) is the ability to extend any step of the build process with a pre, post, or replace hook. This customization is done in a separate location from the build so you can upgrade without wondering if you broke the build. There is a hook before each step of the build has run. There is a hook after. And back to power again, there is a replacement hook. If you don’t like what the step is doing and/or you want to replace it’s entire functionality, you just drop a custom replacement extension and UppercuT will perform the custom step instead. Up until recently all custom hooks had to be written in NAnt. Now they are a little sweeter because you no longer need to use NAnt to extend UC if you don’t want to. You can use PowerShell. Or Ruby.   Let that sink in for a moment. You don’t have to even need to interact with NAnt at all now. Extension Points On the wiki, all of the extension points are shown. The basic idea is that you would put whatever customization you are doing in a separate folder named build.custom. Each step Let’s take a look at all we can customize: The start point is default.build. It calls build.custom/default.pre.build if it exists, then it runs build/default.build (normal tasks) OR build.custom/default.replace.build if it exists, and finally build.custom/default.post.build if it exists. Every step below runs with the same extension points but changes on the file name it is looking for. NOTE: If you include default.replace.build, nothing else will run because everything is called from default.build.    * policyChecks.step    * versionBuilder.step NOTE: If you include build.custom/versionBuilder.replace.step, the items below will not run.      - svn.step, tfs.step, or git.step (the custom tasks for these need to go in build.custom/versioners)    * generateBuildInfo.step    * compile.step    * environmentBuilder.step    * analyze.step NOTE: If you include build.custom/analyze.replace.step, the items below will not run.      - test.step (the custom tasks for this need to go in build.custom/analyzers) NOTE: If you include build.custom/analyzers/test.replace.step, the items below will not run.        + mbunit2.step, gallio.step, or nunit.step (the custom tasks for these need to go in build.custom/analyzers)      - ncover.step (the custom tasks for this need to go in build.custom/analyzers)      - ndepend.step (the custom tasks for this need to go in build.custom/analyzers)      - moma.step (the custom tasks for this need to go in build.custom/analyzers)    * package.step NOTE: If you include build.custom/package.replace.step, the items below will not run.      - deploymentBuilder.step Customize UppercuT Builds With PowerShell UppercuT can now be extended with PowerShell (PS). To customize any extension point with PS, just add .ps1 to the end of the file name and write your custom tasks in PowerShell. If you are not signing your scripts you will need to change a setting in the UppercuT.config file. This does impose a security risk, because this allows PS to now run any PS script. This setting stays that way on ANY machine that runs the build until manually changed by someone. I’m not responsible if you mess up your machine or anyone else’s by doing this. You’ve been warned. Now that you are fully aware of any security holes you may open and are okay with that, let’s move on. Let’s create a file called default.replace.build.ps1 in the build.custom folder. Open that file in notepad and let’s add this to it: write-host "hello - I'm a custom task written in Powershell!" Now, let’s run build.bat. You could get some PSake action going here. I won’t dive into that in this post though. Customize UppercuT Builds With Ruby If you want to customize any extension point with Ruby, just add .rb to the end of the file name and write your custom tasks in Ruby.  Let’s write a custom ruby task for UC. If you were thinking it would be the same as the one we just wrote for PS, you’d be right! In the build.custom folder, lets create a file called default.replace.build.rb. Open that file in notepad and let’s put this in there: puts "I'm a custom ruby task!" Now, let’s run build.bat again. That’s chunky bacon. UppercuT and Albacore.NET Just for fun, I wanted to see if I could replace the compile.step with a Rake task. Not just any rake task, Albacore’s msbuild task. Albacore is a suite of rake tasks brought about by Derick Bailey to make building .NET with Rake easier. It has quite a bit of support with developers that are using Rake to build code. In my build.custom folder, I drop a compile.replace.step.rb. I also put in a separate file that will contain my Albacore rake task and I call that compile.rb. What are the contents of compile.replace.step.rb? rake = 'rake' arguments= '-f ' + Dir.pwd + '/../build.custom/compile.rb' #puts "Calling #{rake} " + arguments system("#{rake} " + arguments) Since the custom extensions call ruby, we have to shell back out and call rake. That’s what we are doing here. We also realize that ruby is called from the build folder, so we need to back out and dive into the build.custom folder to find the file that is technically next to us. What are the contents of compile.rb? require 'rubygems' require 'fileutils' require 'albacore' task :default => [:compile] puts "Using Ruby to compile UppercuT with Albacore Tasks" desc 'Compile the source' msbuild :compile do |msb| msb.properties = { :configuration => :Release, :outputpath => '../../build_output/UppercuT' } msb.targets [:clean, :build] msb.verbosity = "quiet" msb.path_to_command = 'c:/Windows/Microsoft.NET/Framework/v3.5/MSBuild.exe' msb.solution = '../uppercut.sln' end We are using the msbuild task here. We change the output path to the build_output/UppercuT folder. The output path has “../../” because this is based on every project. We could grab the current directory and then point the task specifically to a folder if we have projects that are at different levels. We want the verbosity to be quiet so we set that as well. So what kind of output do you get for this? Let’s run build.bat custom_tasks_replace:      [echo] Running custom tasks instead of normal tasks if C:\code\uppercut\build\..\build.custom\compile.replace.step exists.      [exec] (in C:/code/uppercut/build)      [exec] Using Ruby to compile UppercuT with Albacore Tasks      [exec] Microsoft (R) Build Engine Version 3.5.30729.4926      [exec] [Microsoft .NET Framework, Version 2.0.50727.4927]      [exec] Copyright (C) Microsoft Corporation 2007. All rights reserved. If you think this is awesome, you’d be right!   With this knowledge you shall build.

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• Extract 2 numbers preceded with two different strings in a paragrapf using TCL Regular Expression

  - by Madhu

  Hi, I need to extract two different numbers preceded by two different strings. Employee Id-- Employee16(I need 16) and Employee links-- Employee links:2 (I need 2). Source String looks like following: Employee16, Employee name is QueenRose Working for 46w0d Billing is Distributed 65537 assigned tasks, 0 reordered, 0 unassigned 0 discarded, 0 lost received, 5/255 load received sequence unavailable, 0xC2E7 sent sequence Employee links: 2 active, 0 inactive (max not set, min not set) Dt3/5/10:0, since 46w0d, no tasks pending Dt3/5/10:10, since 21w0d, no tasks rcvd Employee is currently working in Hardware section. Employee19, Employee name is Edward11 Working for 48w4d Billing is Distributed 206801498 assigned tasks, 0 reordered, 0 unassigned 655372 discarded, 0 lost received, 9/255 load received sequence unavailable, 0x23CA sent sequence Employee links: 7 active, 0 inactive (max not set, min not set) Dt3/5/10:0, since 47w2d, tasks pending Dt3/5/10:10, since 28w6d, no tasks pending Dt3/5/10:11, since 18w4d, no tasks pending Dt3/5/10:12, since 18w4d, no tasks pending Dt3/5/10:13, since 18w4d, no tasks pending Dt3/5/10:14, since 18w4d, no tasks pending Dt3/5/10:15, since 7w2d, no tasks pending Employee is currently working in Hardware sectione. Employee6 (inactive) Employee links: 2 Dt3/5/10:0 (inactive) Dt3/5/10:10 (inactive) Employee7 (inactive) Employee links: 2 Dt3/5/10:0 (inactive) Dt3/5/10:10 (inactive) Tried with the following: Multilink(\d+)[^\n\r]*[^M]*Member links:\s+(\d+) But is not listing all the Ids and links. Can anybody help me getting this? Thanks in advance, Madhu.

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• Can I use Google Apps for mail but Exchange for calendar, tasks & contacts?

  - by RexE

  My parents' domain is registered with Google Apps (standard edition). Currently, the only service they are using is email (which they access via IMAP in Outlook). I'd like to register this same domain with a hosted Exchange service so that they can sync their Exchange calendar, tasks, and contacts with Outlook as well. I'd like to keep their email on Google for a couple of reasons. Is this possible?

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• Scrum in 5 Minutes

  - by Stephen.Walther

  The goal of this blog entry is to explain the basic concepts of Scrum in less than five minutes. You learn how Scrum can help a team of developers to successfully complete a complex software project. Product Backlog and the Product Owner Imagine that you are part of a team which needs to create a new website – for example, an e-commerce website. You have an overwhelming amount of work to do. You need to build (or possibly buy) a shopping cart, install an SSL certificate, create a product catalog, create a Facebook page, and at least a hundred other things that you have not thought of yet. According to Scrum, the first thing you should do is create a list. Place the highest priority items at the top of the list and the lower priority items lower in the list. For example, creating the shopping cart and buying the domain name might be high priority items and creating a Facebook page might be a lower priority item. In Scrum, this list is called the Product Backlog. How do you prioritize the items in the Product Backlog? Different stakeholders in the project might have different priorities. Gary, your division VP, thinks that it is crucial that the e-commerce site has a mobile app. Sally, your direct manager, thinks taking advantage of new HTML5 features is much more important. Multiple people are pulling you in different directions. According to Scrum, it is important that you always designate one person, and only one person, as the Product Owner. The Product Owner is the person who decides what items should be added to the Product Backlog and the priority of the items in the Product Backlog. The Product Owner could be the customer who is paying the bills, the project manager who is responsible for delivering the project, or a customer representative. The critical point is that the Product Owner must always be a single person and that single person has absolute authority over the Product Backlog. Sprints and the Sprint Backlog So now the developer team has a prioritized list of items and they can start work. The team starts implementing the first item in the Backlog — the shopping cart — and the team is making good progress. Unfortunately, however, half-way through the work of implementing the shopping cart, the Product Owner changes his mind. The Product Owner decides that it is much more important to create the product catalog before the shopping cart. With some frustration, the team switches their developmental efforts to focus on implementing the product catalog. However, part way through completing this work, once again the Product Owner changes his mind about the highest priority item. Getting work done when priorities are constantly shifting is frustrating for the developer team and it results in lower productivity. At the same time, however, the Product Owner needs to have absolute authority over the priority of the items which need to get done. Scrum solves this conflict with the concept of Sprints. In Scrum, a developer team works in Sprints. At the beginning of a Sprint the developers and the Product Owner agree on the items from the backlog which they will complete during the Sprint. This subset of items from the Product Backlog becomes the Sprint Backlog. During the Sprint, the Product Owner is not allowed to change the items in the Sprint Backlog. In other words, the Product Owner cannot shift priorities on the developer team during the Sprint. Different teams use Sprints of different lengths such as one month Sprints, two-week Sprints, and one week Sprints. For high-stress, time critical projects, teams typically choose shorter sprints such as one week sprints. For more mature projects, longer one month sprints might be more appropriate. A team can pick whatever Sprint length makes sense for them just as long as the team is consistent. You should pick a Sprint length and stick with it. Daily Scrum During a Sprint, the developer team needs to have meetings to coordinate their work on completing the items in the Sprint Backlog. For example, the team needs to discuss who is working on what and whether any blocking issues have been discovered. Developers hate meetings (well, sane developers hate meetings). Meetings take developers away from their work of actually implementing stuff as opposed to talking about implementing stuff. However, a developer team which never has meetings and never coordinates their work also has problems. For example, Fred might get stuck on a programming problem for days and never reach out for help even though Tom (who sits in the cubicle next to him) has already solved the very same problem. Or, both Ted and Fred might have started working on the same item from the Sprint Backlog at the same time. In Scrum, these conflicting needs – limiting meetings but enabling team coordination – are resolved with the idea of the Daily Scrum. The Daily Scrum is a meeting for coordinating the work of the developer team which happens once a day. To keep the meeting short, each developer answers only the following three questions: 1. What have you done since yesterday? 2. What do you plan to do today? 3. Any impediments in your way? During the Daily Scrum, developers are not allowed to talk about issues with their cat, do demos of their latest work, or tell heroic stories of programming problems overcome. The meeting must be kept short — typically about 15 minutes. Issues which come up during the Daily Scrum should be discussed in separate meetings which do not involve the whole developer team. Stories and Tasks Items in the Product or Sprint Backlog – such as building a shopping cart or creating a Facebook page – are often referred to as User Stories or Stories. The Stories are created by the Product Owner and should represent some business need. Unlike the Product Owner, the developer team needs to think about how a Story should be implemented. At the beginning of a Sprint, the developer team takes the Stories from the Sprint Backlog and breaks the stories into tasks. For example, the developer team might take the Create a Shopping Cart story and break it into the following tasks: · Enable users to add and remote items from shopping cart · Persist the shopping cart to database between visits · Redirect user to checkout page when Checkout button is clicked During the Daily Scrum, members of the developer team volunteer to complete the tasks required to implement the next Story in the Sprint Backlog. When a developer talks about what he did yesterday or plans to do tomorrow then the developer should be referring to a task. Stories are owned by the Product Owner and a story is all about business value. In contrast, the tasks are owned by the developer team and a task is all about implementation details. A story might take several days or weeks to complete. A task is something which a developer can complete in less than a day. Some teams get lazy about breaking stories into tasks. Neglecting to break stories into tasks can lead to “Never Ending Stories” If you don’t break a story into tasks, then you can’t know how much of a story has actually been completed because you don’t have a clear idea about the implementation steps required to complete the story. Scrumboard During the Daily Scrum, the developer team uses a Scrumboard to coordinate their work. A Scrumboard contains a list of the stories for the current Sprint, the tasks associated with each Story, and the state of each task. The developer team uses the Scrumboard so everyone on the team can see, at a glance, what everyone is working on. As a developer works on a task, the task moves from state to state and the state of the task is updated on the Scrumboard. Common task states are ToDo, In Progress, and Done. Some teams include additional task states such as Needs Review or Needs Testing. Some teams use a physical Scrumboard. In that case, you use index cards to represent the stories and the tasks and you tack the index cards onto a physical board. Using a physical Scrumboard has several disadvantages. A physical Scrumboard does not work well with a distributed team – for example, it is hard to share the same physical Scrumboard between Boston and Seattle. Also, generating reports from a physical Scrumboard is more difficult than generating reports from an online Scrumboard. Estimating Stories and Tasks Stakeholders in a project, the people investing in a project, need to have an idea of how a project is progressing and when the project will be completed. For example, if you are investing in creating an e-commerce site, you need to know when the site can be launched. It is not enough to just say that “the project will be done when it is done” because the stakeholders almost certainly have a limited budget to devote to the project. The people investing in the project cannot determine the business value of the project unless they can have an estimate of how long it will take to complete the project. Developers hate to give estimates. The reason that developers hate to give estimates is that the estimates are almost always completely made up. For example, you really don’t know how long it takes to build a shopping cart until you finish building a shopping cart, and at that point, the estimate is no longer useful. The problem is that writing code is much more like Finding a Cure for Cancer than Building a Brick Wall. Building a brick wall is very straightforward. After you learn how to add one brick to a wall, you understand everything that is involved in adding a brick to a wall. There is no additional research required and no surprises. If, on the other hand, I assembled a team of scientists and asked them to find a cure for cancer, and estimate exactly how long it will take, they would have no idea. The problem is that there are too many unknowns. I don’t know how to cure cancer, I need to do a lot of research here, so I cannot even begin to estimate how long it will take. So developers hate to provide estimates, but the Product Owner and other product stakeholders, have a legitimate need for estimates. Scrum resolves this conflict by using the idea of Story Points. Different teams use different units to represent Story Points. For example, some teams use shirt sizes such as Small, Medium, Large, and X-Large. Some teams prefer to use Coffee Cup sizes such as Tall, Short, and Grande. Finally, some teams like to use numbers from the Fibonacci series. These alternative units are converted into a Story Point value. Regardless of the type of unit which you use to represent Story Points, the goal is the same. Instead of attempting to estimate a Story in hours (which is doomed to failure), you use a much less fine-grained measure of work. A developer team is much more likely to be able to estimate that a Story is Small or X-Large than the exact number of hours required to complete the story. So you can think of Story Points as a compromise between the needs of the Product Owner and the developer team. When a Sprint starts, the developer team devotes more time to thinking about the Stories in a Sprint and the developer team breaks the Stories into Tasks. In Scrum, you estimate the work required to complete a Story by using Story Points and you estimate the work required to complete a task by using hours. The difference between Stories and Tasks is that you don’t create a task until you are just about ready to start working on a task. A task is something that you should be able to create within a day, so you have a much better chance of providing an accurate estimate of the work required to complete a task than a story. Burndown Charts In Scrum, you use Burndown charts to represent the remaining work on a project. You use Release Burndown charts to represent the overall remaining work for a project and you use Sprint Burndown charts to represent the overall remaining work for a particular Sprint. You create a Release Burndown chart by calculating the remaining number of uncompleted Story Points for the entire Product Backlog every day. The vertical axis represents Story Points and the horizontal axis represents time. A Sprint Burndown chart is similar to a Release Burndown chart, but it focuses on the remaining work for a particular Sprint. There are two different types of Sprint Burndown charts. You can either represent the remaining work in a Sprint with Story Points or with task hours (the following image, taken from Wikipedia, uses hours). When each Product Backlog Story is completed, the Release Burndown chart slopes down. When each Story or task is completed, the Sprint Burndown chart slopes down. Burndown charts typically do not always slope down over time. As new work is added to the Product Backlog, the Release Burndown chart slopes up. If new tasks are discovered during a Sprint, the Sprint Burndown chart will also slope up. The purpose of a Burndown chart is to give you a way to track team progress over time. If, halfway through a Sprint, the Sprint Burndown chart is still climbing a hill then you know that you are in trouble. Team Velocity Stakeholders in a project always want more work done faster. For example, the Product Owner for the e-commerce site wants the website to launch before tomorrow. Developers tend to be overly optimistic. Rarely do developers acknowledge the physical limitations of reality. So Project stakeholders and the developer team often collude to delude themselves about how much work can be done and how quickly. Too many software projects begin in a state of optimism and end in frustration as deadlines zoom by. In Scrum, this problem is overcome by calculating a number called the Team Velocity. The Team Velocity is a measure of the average number of Story Points which a team has completed in previous Sprints. Knowing the Team Velocity is important during the Sprint Planning meeting when the Product Owner and the developer team work together to determine the number of stories which can be completed in the next Sprint. If you know the Team Velocity then you can avoid committing to do more work than the team has been able to accomplish in the past, and your team is much more likely to complete all of the work required for the next Sprint. Scrum Master There are three roles in Scrum: the Product Owner, the developer team, and the Scrum Master. I’v e already discussed the Product Owner. The Product Owner is the one and only person who maintains the Product Backlog and prioritizes the stories. I’ve also described the role of the developer team. The members of the developer team do the work of implementing the stories by breaking the stories into tasks. The final role, which I have not discussed, is the role of the Scrum Master. The Scrum Master is responsible for ensuring that the team is following the Scrum process. For example, the Scrum Master is responsible for making sure that there is a Daily Scrum meeting and that everyone answers the standard three questions. The Scrum Master is also responsible for removing (non-technical) impediments which the team might encounter. For example, if the team cannot start work until everyone installs the latest version of Microsoft Visual Studio then the Scrum Master has the responsibility of working with management to get the latest version of Visual Studio as quickly as possible. The Scrum Master can be a member of the developer team. Furthermore, different people can take on the role of the Scrum Master over time. The Scrum Master, however, cannot be the same person as the Product Owner. Using SonicAgile SonicAgile (SonicAgile.com) is an online tool which you can use to manage your projects using Scrum. You can use the SonicAgile Product Backlog to create a prioritized list of stories. You can estimate the size of the Stories using different Story Point units such as Shirt Sizes and Coffee Cup sizes. You can use SonicAgile during the Sprint Planning meeting to select the Stories that you want to complete during a particular Sprint. You can configure Sprints to be any length of time. SonicAgile calculates Team Velocity automatically and displays a warning when you add too many stories to a Sprint. In other words, it warns you when it thinks you are overcommitting in a Sprint. SonicAgile also includes a Scrumboard which displays the list of Stories selected for a Sprint and the tasks associated with each story. You can drag tasks from one task state to another. Finally, SonicAgile enables you to generate Release Burndown and Sprint Burndown charts. You can use these charts to view the progress of your team. To learn more about SonicAgile, visit SonicAgile.com. Summary In this post, I described many of the basic concepts of Scrum. You learned how a Product Owner uses a Product Backlog to create a prioritized list of tasks. I explained why work is completed in Sprints so the developer team can be more productive. I also explained how a developer team uses the daily scrum to coordinate their work. You learned how the developer team uses a Scrumboard to see, at a glance, who is working on what and the state of each task. I also discussed Burndown charts. You learned how you can use both Release and Sprint Burndown charts to track team progress in completing a project. Finally, I described the crucial role of the Scrum Master – the person who is responsible for ensuring that the rules of Scrum are being followed. My goal was not to describe all of the concepts of Scrum. This post was intended to be an introductory overview. For a comprehensive explanation of Scrum, I recommend reading Ken Schwaber’s book Agile Project Management with Scrum: http://www.amazon.com/Agile-Project-Management-Microsoft-Professional/dp/073561993X/ref=la_B001H6ODMC_1_1?ie=UTF8&qid=1345224000&sr=1-1

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• A Method for Reducing Contention and Overhead in Worker Queues for Multithreaded Java Applications

  - by Janice J. Heiss

  A java.net article, rich in practical resources, by IBM India Labs’ Sathiskumar Palaniappan, Kavitha Varadarajan, and Jayashree Viswanathan, explores the challenge of writing code in a way that that effectively makes use of the resources of modern multicore processors and multiprocessor servers.As the article states: “Many server applications, such as Web servers, application servers, database servers, file servers, and mail servers, maintain worker queues and thread pools to handle large numbers of short tasks that arrive from remote sources. In general, a ‘worker queue’ holds all the short tasks that need to be executed, and the threads in the thread pool retrieve the tasks from the worker queue and complete the tasks. Since multiple threads act on the worker queue, adding tasks to and deleting tasks from the worker queue needs to be synchronized, which introduces contention in the worker queue.” The article goes on to explain ways that developers can reduce contention by maintaining one queue per thread. It also demonstrates a work-stealing technique that helps in effectively utilizing the CPU in multicore systems. Read the rest of the article here.

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• What happens differently when you add a task Asynchronously on GAE?

  - by Ben Grunfeld

  Google's doc on async tasks assumes knowledge of the difference between regular and asynchronously added tasks. add_async(task, transactional=False, rpc=None) Asynchronously add a Task or a list of Tasks to this Queue. How is adding tasks asynchronously different to adding them regularly. I.e. what is the difference between using add(task, transactional=False) and add_async(task, transactional=False, rpc=None) I've heard that adding tasks regularly blocks certain things. Any explanation of what it blocks and how, and how async tasks don't block would be greatly appreciated.

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