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• Today's Links (6/17/2011)

  - by Bob Rhubart

  Call for Nominations: Oracle Eco-Enterprise Innovation Awards Is your organization using Oracle products to reduce your environmental footprint while reducing costs? If so, submit your nomination for Oracle's Eco-Enterprise Innovation award. These awards will be presented to select customers and their partners who are using any of Oracle's products to not only take an environmental lead, but also to reduce their costs and improve their business efficiencies by using green business practices. Beyond The Data Grid: Coherence, Normalization, Joins, and Linear Scalability | Ben Stopford Ben Stopford presents ODC, a highly distributed in-memory normalized NoSQL datastore designed for scalability, based on normalized data, Snowflake Schema, and Connected Replication pattern. Upgrading ALSB services to OSB | John Chin-a-Woeng John Chin-a-Woeng walks you through the upgrade from Aqualogic Service Bus (ALSB 3.0) to Oracle Service Bus (OSB 10.3). SOA & Middleware: Pinning tasks to a user in BPM 11g | Niall Commiskey Commiskey illustrates a scenario. JDeveloper 11gR2: New option Test WebService in WSDL editor | Lucas Jellema The "Test WebService" button in the WSDL Editor in JDeveloper 11gr2 is "just a little feature addition," says Oracle ACE Director Lucas Jellema. "But it can be quite useful all the same." Enterprise Business Intelligence 11g Seminar with Mark Rittman Oracle ACE Director Mark Rittman conducts a two-day course for Oracle University, in Dublin, IE, July 4-5, 2011. Data Integration Webcast Series Join Oracle experts for a series covering our data integration solutions. You’ll get invaluable information to help boost your data infrastructure so that you can accelerate your business.

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• Technical Questions for Java Experts

  - by Tori Wieldt

  The "Oracle Technology Network" (meaning me) will be at Devoxx next week doing interviews with Java experts. Do you have technical questions about Project Jigsaw, JavaFX or Java on MacOS? Take a look at the list below of experts and topics. Leave your questions as a comment on this blog and I'll do my best to include them. Most of the interviews happen Tuesday, so get you questions in quickly. Thanks! Interviewee InterviewTopic Arun Gupta and Alexis Moussine-Pouchkine Java EE Mark Reinhold OpenJDK Mark Reinhold Project Jigsaw Jasper Potts JavaFX Scott Kovatch Java on Mac OS Brian Goetz & Mark Reinhold JDK 8 Brian Goetz Project Lambda Steven Chin JavaFX Marek Potociar JAX-RS Claude Falguiere Dev for Tablets Alan Bateman NIO2 Regina ten Bruggencate JDuchess Martijn Verburg Adopt a JSR Note: This is different than the call for questions for the Fireside chat on Tuesday afternoon, Devoxx conference keynote speakers (Henrik Ståhl, senior director of product management for the Java platform at Oracle, and Cameron Purdy, VP of development for the Java EE platform) and the technical discussion panel on Friday morning. Leave (and vote on) those questions here. 

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• How to Get AirVideo Features in Android for Free

  - by Zainul Franciscus

  AirVideo makes it possible for iPhone, iPad, or iPod Touch users to stream any video format on their devices. If you’re an Android user, then you are in luck, because you can get AirVideo’s features for free with VLC-Share. In today’s tutorial, we will start off by giving you an instruction on how to install VLC-Share, followed by configuring firewall and port forwarding, and we complete the tutorial with a walk through of VLC-Share features. Wallpaper available from our Naruto Customization set. Latest Features How-To Geek ETC How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Ask How-To Geek: How Can I Monitor My Bandwidth Usage? Internet Explorer 9 RC Now Available: Here’s the Most Interesting New Stuff Smart Taskbar Is a Thumb Friendly Android Task Launcher Comix is an Awesome Comics Archive Viewer for Linux Get the MakeUseOf eBook Guide to Speeding Up Windows for Free Need Tech Support? Call the Star Wars Help Desk! [Video Classic] Reclaim Vertical UI Space by Adding a Toolbar to the Left or Right Side of Firefox Androidify Turns You into an Android-style Avatar

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• Windows 2008 IIS 7 PHP Caching / Blank Page Problems?

  - by darkAsPitch

  I don't even know how to explain this. The only thing I can think is 'why am I working with a windows server?' I am renting a dedicated 1and1 server - I installed PHP myself - with fast CGI and caching (pretty sure I checked OK on something about dynamic caching for PHP when I installed it.) Every few hours of intensive php processing - my pages start locking up - usually just showing blank pages - with no errors whatsoever. Just now, I checked a page - let's call it a.php - and it was showing the results of b.php - I thought I had been hacked! Simply restarting the IIS server however, fixes the problem. Any ideas / help / knowledge on similar problems with windows 2008?

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• juju bootstrap key error?

  - by mxdog

  I followed the guides the best as i could. there is some information missing like do as root or as regular user ..formatting, quotes no quotes..what the password or paraphrase for ssh should be ..couple other trivial things. that im sure add up to where im at (stuck!) so i have a working mass server on mx-nas-01 and 3 nodes and have been trying to get juju to start. I have tried this as both root and my regular account, sudo no-sudo and here is the output i get from juju bootstrap (however i try it) I don't know if this could be a host,domain,account issue or what i will mention i did have to shut off my dhcp server and install masq (all defaults) to get the maas pxe to work for the nodes mxdog@mx-nas-01:/$ juju bootstrap Traceback (most recent call last): File "/usr/bin/juju", line 8, in main(sys.argv[1:]) File "/usr/lib/python2.7/dist-packages/juju/control/init.py", line 183, in main env_config.load_or_write_sample() File "/usr/lib/python2.7/dist-packages/juju/environment/config.py", line 229, in load_or_write_sample self.load() File "/usr/lib/python2.7/dist-packages/juju/environment/config.py", line 115, in load self.parse(file.read(), path) File "/usr/lib/python2.7/dist-packages/juju/environment/config.py", line 138, in parse config = SCHEMA.coerce(config, []) File "/usr/lib/python2.7/dist-packages/juju/lib/schema.py", line 266, in coerce new_dict[k] = self.schema[k].coerce(v, path) File "/usr/lib/python2.7/dist-packages/juju/lib/schema.py", line 233, in coerce new_subvalue = self.value_schema.coerce(subvalue, value_path) File "/usr/lib/python2.7/dist-packages/juju/lib/schema.py", line 301, in coerce return self.schemas[selected].coerce(value, path) KeyError: 'mass' environments: maas: type: mass mass-server: http://192.168.0.30:80/MAAS mass-oauth: tDRdtJeEKVARBh93eT:N5dK5HSZBsA45cBdx9:S8wMNrfkT9PeYvQN9YrnbHGxmKARv8vb admin-secret: ########## default-series: precise

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• Implementing the transport layer for a SIP UAC

  - by Jonathan Henson

  I have a somewhat simple, but specific, question about implementing the transport layer for a SIP UAC. Do I expect the response to a request on the same socket that I sent the request on, or do I let the UDP or TCP listener pick up the response and then route it to the correct transaction from there? The RFC does not seem to say anything on the matter. It seems that especially using UDP, which is connection-less, that I should just let the listeners pick up the response, but that seems sort of counter intuitive. Particularly, I have seen plenty of UAC implementations which do not depend on having a Listener in the transport layer. Also, most implementations I have looked at do not have the UAS receiving loop responding on the socket at all. This would tend to indicate that the client should not be expecting a reply on the socket that it sent the request on. For clarification: Suppose my transport layer consists of the following elements: TCPClient (Sends Requests for a UAC via TCP) UDPClient (Sends Requests for a UAC vid UDP) TCPSever (Loop receiving Requests and dispatching to transaction layer via TCP) UDPServer (Loop receiving Requests and dispatching to transaction layer via UDP) Obviously, the *Client sends my Requests. The question is, what receives the Response? The *Client waiting on a recv or recvfrom call on the socket it used to send the request, or the *Server? Conversely, the *Server receives my requests, What sends the Response? The *Client? doesn't this break the roles of each member a bit?

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• What is the difference between Callback<T> and Java 8's Supplier<T>?

  - by Dan Pantry

  I've been switching over to Java from C# after some recommendations from some over at CodeReview. So, when I was looking into LWJGL, one thing I remembered was that every call to Display must be executed on the same thread that the Display.create() method was invoked on. Remembering this, I whipped up a class that looks a bit like this. public class LwjglDisplayWindow implements DisplayWindow { private final static int TargetFramesPerSecond = 60; private final Scheduler _scheduler; public LwjglDisplayWindow(Scheduler displayScheduler, DisplayMode displayMode) throws LWJGLException { _scheduler = displayScheduler; Display.setDisplayMode(displayMode); Display.create(); } public void dispose() { Display.destroy(); } @Override public int getTargetFramesPerSecond() { return TargetFramesPerSecond; } @Override public Future<Boolean> isClosed() { return _scheduler.schedule(() -> Display.isCloseRequested()); } } While writing this class you'll notice that I created a method called isClosed() that returns a Future<Boolean>. This dispatches a function to my Scheduler interface (which is nothing more than a wrapper around an ScheduledExecutorService. While writing the schedule method on the Scheduler I noticed that I could either use a Supplier<T> argument or a Callable<T> argument to represent the function that is passed in. ScheduledExecutorService didn't contain an override for Supplier<T> but I noticed that the lambda expression () -> Display.isCloseRequested() is actually type compatible with both Callable<bool> and Supplier<bool>. My question is, is there a difference between those two, semantically or otherwise - and if so, what is it, so I can adhere to it?

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• Does it make sense to write a build scripts in C++?

  - by Klaim

  I'm using CMake to generate my projects IDE/makefiles, but I still need to call custom "scripts" to manipulate my compiled files or even generate code. In previous projects I've been using Python and it was OK, but now I'm having serious trouble managing a lot of dependencies in two very big projects I'm working on so I want to minimize the dependencies everywhere. Someone suggested to me to use C++ to write my build scripts instead of adding a language dependency just for that. The projects themeselves already use C++ so there are several advantages that I can see: to build the whole project, only a C++ compiler and CMake would be necessary, nothing else (all the other dependencies are C or C++); C++ type safety (when using modern C++) makes everything easier to get "correct"; it's also the language I know the better so I'm more at ease with it even if I'm able to write some good Python code; potential gain in execution speed (but i don't think it will really be perceptible); However, I think there might be some drawbacks and I'm not sure of the real impact as I didn't try yet: might be longer to write the code (that said I'm not sure because I'm efficient enough in C++ to write something that work quickly, so maybe for this system it wouldn't be so long to write) (compilation time shouldn't be a problem for this case); I must assume that all the text files I'll read as input are in UTF-8, I'm not sure it can be easilly checked at runtime in C++ and the language will not check it for you; libraries in C++ are harder to manage than in scripting languages; I lack experience and forsight so maybe I'm missing advantages and drawbacks. So the question is: does it make sense to use C++ for this? do you have experiences to report and do you see advantages and disadvantages that might be important?

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• Finding throuput of CPU and Hardrive on Solaris

  - by Jim

  How do i find the throughput of a CPU and the Hardisk on an open solaris machine. Using MPstat or iostat. I'm having a hard time identifying the throughput if it is given at all in the commands output. Eg. in mpstat there is very little explanation as to what the columns mean http://docs.sun.com/app/docs/doc/816-5166/mpstat-1m?l=en&a=view&q=syscl+mpstat I've been using the syscl column divided by time interval to find the throughput but to be honest i have no idea what a system call truelly is. I'm trying to to analyze a hardrive and CPU while writing a file to the hardisk and when at rest Thanks in advance. Jim

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• How do I download photos tagged of me from Facebook?

  - by Keith

  I want to be able to download (and back up) photos tagged of me in Facebook. I'm specifically not interested in my own photo albums - I uploaded them and therefore have them already in better quality than FB. What I want are the photos other have uploaded that have me in them. I have a couple of hundred of these now, and don't much fancy three hours of right-click save-as... There seem to be a couple of utilities that pop up with a quick search, but (call me paranoid) I'm wary about giving some random freeware app my login and password. Social safe looked promising, but as it doesn't support this feature at the moment it's kinda pointless. Can anyone recommend one that they've actually used? I'd consider an open source one - I'm a programmer and don't mind digging through to check that it doesn't do anything nasty.

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• Connection two wireless ADSL routers to share IPs

  - by user35218

  I have two wireless ADSL routers sitting right next to each other, each with his own internet connection. I'd like to be able to connect to a computer that is connected to router A from a computer that is connected to router B, while keeping both routers internet connection individually. i.e. If computer A is connected to router A, it will use router A internet connection, and a second computer, call it B, will be connected to router B, and will use router B internet connection. Is this possible?

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• How to add command line arguments to command line arguments in Windows shortcut?

  - by Pawin

  I know I can add a command line argument/option to a shortcut this way; for example: "C:\Program Files\Internet Explorer\iexplore.exe" www.a.com So IE will connect to a.com when it starts up. What I would like to do is to get IE connecting to a.com when I call it through another program like the following: C:\Windows\SysWOW64\ForceBindIP.exe 192.168.1.151 "C:\Program Files\Internet Explorer\iexplore.exe" www.a.com This does not work. IE starts up but doesn't go to a.com. It seems like the argument is either ignored or is understood as an argument of ForceBindIP instead (I'm not sure). What I am trying to do is to create 2 IE shortcuts such each of them binds one IE window to one NIC and one particular website. So adding the www.a.com etc in its startup list won't help. OS is Windows 8. Apologize if this has been asked and answered before. Please suggest keywords for searching if that's the case.

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• Make own dial-up ISP using broadband connection [on hold]

  - by SkylarMT

  So, I see no reason why this wouldn't be possible. I have a Linux server (a Raspberry Pi to be exact) connected via Ethernet to a broadband ISP. I want to be able to dial a number, have it go through the normal telephone network, onto the Internet via a VoIP provider (I know you can call a Skype user from a landline), to my Raspberry Pi, and then have the Pi connect me to the Internet. I've found guides on making your own ISP, but they all involve a dedicated phone line on the server end. Is there a way to do this with no modem on the server end? I live in an area with a lot of people still on dialup, and if I pull this off I could make some extra money. Thanks!

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• Send one invalid email response to sender

  - by Kafuka

  I discovered that my postfix/dovecot configuration isn't rejecting emails. If a person sends an email to an invalid email-address, it just drops it. I am fine with this behavior since I think it discourages spammers from mining emails (I have had some success). Recently a person I did not want to talk to emailed an address I cut off and didn't receive a response back. It would have saved me some problems if they knew to call me instead of sending 50+ emails. How would I configure Dovecot/postfix to send a message back to a sender of an email address and then limit this 1 per domain or unique email. Debian Stable Linux 3.6.5-linode47 Dovecot 1.2.15 Postfix 2.7.1 PSQL - backend if that matters

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• Paranoid Encryption

  - by Lord Jaguar

  Call me paranoid, but I really like to keep my stuff secret, but readily available on the cloud. So, asking this question. How safe and reliable is encryption software (e.g., truecrypt)? The reason I ask is that, what is I encrypt my data today with this software and after a couple of years, the software is gone ! What happens to my encrypted data? Is it equally safe to AES encrypt using 7-zip? Will it provide the same level or equivalent level of encryption as truecrypt or other encryption software? (I agree truecrypt will be better because of the container encryption it gives.) And what happens if 7-zip shuts down after 5 years? I am sorry if I am sounding paranoid, but I am coming back to my original question... Is there any application/software independent encryption? Meaning, can I encrypt with one software and decrypt with another so that I will not be dependent on just one vendor? I want my encryption to depend ONLY on the password and NOT on the encryption program/software? The next question, can I write my own program that does AES/stronger encryption when I give it a passphrase, so that I don't need to depend on third party software for encryption? If yes, which language supports the same? Can someone give me a heads up as to where to look for in case of writing my own encryption program?

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• ArchBeat Link-o-Rama for 2012-06-27

  - by Bob Rhubart

  Resource Kit: Oracle Exadata for the Communications industry In addition to several customer case studies, in video and white paper formats, this resource kit also includes a technical overview of Oracle Exadata Database Machine and a product datasheet. Registration is required for those who don't already have a free Oracle.com membership account. Call for Nominations: Oracle Fusion Middleware Innovation Awards 2012 - Win a free pass to #OOW12 These awards honor customers for their cutting-edge solutions using Oracle Fusion Middleware. Either a customer, their partner, or an Oracle representative can submit the nomination form on behalf of the customer. Submission deadline: July 17. Winners receive a free pass to Oracle OpenWorld 2012 in San Francisco. BPM – Disable DBMS job to refresh B2B Materialized View | Mark Nelson "If you are running BPM and you are not using B2B, you might want to disable the DBMS job that refreshes the B2B materialized view," says Fusion Middleware A-Team blogger Mark Nelson. Learn how in his short post. A Universal JMX Client for Weblogic –Part 1: Monitoring BPEL Thread Pools in SOA 11g | Stefan Koser A concise how-to from Oracle Fusion Middleware A-Team blogger Stefan Koser. Thought for the Day "There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult." — C. A. R. Hoare Source: SoftwareQuotes.com/

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• SQL ADO.NET shortcut extensions (old school!)

  - by Jeff

  As much as I love me some ORM's (I've used LINQ to SQL quite a bit, and for the MSDN/TechNet Profile and Forums we're using NHibernate more and more), there are times when it's appropriate, and in some ways more simple, to just throw up so old school ADO.NET connections, commands, readers and such. It still feels like a pain though to new up all the stuff, make sure it's closed, blah blah blah. It's pretty much the least favorite task of writing data access code. To minimize the pain, I have a set of extension methods that I like to use that drastically reduce the code you have to write. Here they are... public static void Using(this SqlConnection connection, Action<SqlConnection> action) {     connection.Open();     action(connection);     connection.Close(); } public static SqlCommand Command(this SqlConnection connection, string sql){    var command = new SqlCommand(sql, connection);    return command;}public static SqlCommand AddParameter(this SqlCommand command, string parameterName, object value){    command.Parameters.AddWithValue(parameterName, value);    return command;}public static object ExecuteAndReturnIdentity(this SqlCommand command){    if (command.Connection == null)        throw new Exception("SqlCommand has no connection.");    command.ExecuteNonQuery();    command.Parameters.Clear();    command.CommandText = "SELECT @@IDENTITY";    var result = command.ExecuteScalar();    return result;}public static SqlDataReader ReadOne(this SqlDataReader reader, Action<SqlDataReader> action){    if (reader.Read())        action(reader);    reader.Close();    return reader;}public static SqlDataReader ReadAll(this SqlDataReader reader, Action<SqlDataReader> action){    while (reader.Read())        action(reader);    reader.Close();    return reader;} It has been awhile since I've really revisited these, so you will likely find opportunity for further optimization. The bottom line here is that you can chain together a bunch of these methods to make a much more concise database call, in terms of the code on your screen, anyway. Here are some examples: public Dictionary<string, string> Get(){    var dictionary = new Dictionary<string, string>();    _sqlHelper.GetConnection().Using(connection =>        connection.Command("SELECT Setting, [Value] FROM Settings")            .ExecuteReader()            .ReadAll(r => dictionary.Add(r.GetString(0), r.GetString(1))));    return dictionary;} or... public void ChangeName(User user, string newName){    _sqlHelper.GetConnection().Using(connection =>         connection.Command("UPDATE Users SET Name = @Name WHERE UserID = @UserID")            .AddParameter("@Name", newName)            .AddParameter("@UserID", user.UserID)            .ExecuteNonQuery());} The _sqlHelper.GetConnection() is just some other code that gets a connection object for you. You might have an even cleaner way to take that step out entirely. This looks more fluent, and the real magic sauce for me is the reader bits where you can put any kind of arbitrary method in there to iterate over the results.

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• Search SSIS packages for table/column references

  - by Nigel Rivett

  A lot of companies now use TFS or some other system and keep all their packages in a single project. This means that a copy of all the packages will end up on your local disk. There is major failing with SSIS that it is sometimes quite difficult to find what a package is actually doing, what it accesses and what it affects. This is a simple dos script which will search through all packages in a folder for a string and write the names of found packages to an output file. Just copy the text to a .bat file (I use aaSearch.bat) in the folder with all the package scripts Change the output filename (twice), change the find string value and run it in a dos window. It works on any text file type so you can also search store procedure scripts – but there are easier ways of doing that. echo. > aaSearch_factSales.txt for /f “delims=” %%a in (‘dir /B /s *.dtsx’) do call :subr “%%a” goto:EOF :subr findstr “factSales” %1 if %ERRORLEVEL% NEQ 1 echo %1 >> aaSearch_factSales.txt goto:EOF

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• Sprites rendering blurry with velocity

  - by ashes999

  After adding velocity to my game, I feel like my textures are twitching. I thought it was just my eyes, until I finally captured it in a screenshot: The one on the left is what renders in my game; the one on the right is the original sprite, pasted over. (This is a screenshot from Photoshop, zoomed in 6x.) Notice the edges are aliasing -- it looks almost like sub-pixel rendering. In fact, if I had not forced my sprites (which have position and velocity as ints) to draw using integer values, I would swear that MonoGame is drawing with floating point values. But it isn't. What could be the cause of these things appearing blurry? It doesn't happen without velocity applied. To be precise, my SpriteComponent class has a Vector2 Position field. When I call Draw, I essentially use new Vector2((int)Math.Round(this.Position.X), (int)Math.Round(this.Position.Y)) for the position. I had a bug before where even stationary objects would jitter -- that was due to me using the straight Position vector and not rounding the values to ints. If I use Floor/Ceiling instead of round, the sprite sinks/hovers (one pixel difference either way) but still draws blurry.

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• How do I set up an sftp user to login with a password to an EC2 ubuntu server ?

  - by Doron

  Hello, I have an Ubuntu Server running on an EC2 instance. To login to that server I use a certificate file without any password. I've installed and configured vsftpd and created a user (let's call him "testuser") for which I've set a /bin/false ssh terminal so it will only be able to connect via sftp and upload/access files on his home directory. However - when I try to connect to the server from my computer, running sftp testuser@my-ec2-server I get Permission denied (publickey). Connection closed messages so I can't log in. How can I remove the certificate requirement for this user only (meaning, the "ubuntu" user will still have to use the certificate file to login via ssh), so normal sftp clients will be able to connect using a username and a password ? Thank you. PS Using Ubuntu Server 10.10 official AMI from canonical, 64bit on a micro instance.

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• Problem with gmailfs

  - by user35529

  Hello(????????????) I've got a little with gmailfs. I'm trying to mount gmail accout as a local file system on my Debian Lenny using the following command. mount -t gmailfs none /mnt/gmail -o [email protected],password=mypassword,fsname=SixSixSix But it gives my garbage like this Ignored option :rw Traceback (most recent call last): File "/sbin/mount.gmailfs", line 166, in <module> main(mountpoint, namedOptions, useEncfs) File "/sbin/mount.gmailfs", line 92, in main gmailfs.main(mountpoint, namedOptions) File "/usr/lib/python2.5/site-packages/gmailfs.py", line 1175, in main server = Gmailfs(namedOptions,mountpoint,version="gmailfs 0.8.0",usage='',dash_s_do='setsingle') File "/usr/lib/python2.5/site-packages/gmailfs.py", line 611, in __init__ self.ga.login() File "/usr/lib/python2.5/site-packages/libgmail.py", line 316, in login raise GmailLoginFailure("Login failed. (Wrong username/password?)") libgmail.GmailLoginFailure: 'Login failed. (Wrong username/password?)' Username and Password are totally correct.

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• Domain and TS migration

  - by Windex

  The migration steps outlined by Microsoft in the ts migration seem to deal with moving TS to a different server on the same domain and call for adding the licensing service to another system, move the licenses and then put TS on whatever server you want. However with migrating the domain as well I don't have any place to move the TS server to. So my thought was to simply re-activate my licenses on the new server using the same method as a new TS setup. My question is essentially will this work the way I think it will or will the MS activation clearing house deny the new server? Is there a procedure to follow that "deactivates" the licenses on a server so that the clearing house knows there are some free? (FWIW I can look up the license information through the eopen website and have access to the original license doc.)

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• Rails: Law of Demeter Confusion

  - by user2158382

  I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. EDIT I completely understand and agree that this is still a violation and I need to create a method in Wallet called withdraw that handles the payment for me and that I should call that method inside the Customer class. What I don't get is that according to this process, my first example still violates the Law of Demeter because Invoice is still reaching directly into Customer to get the street. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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• Why isn't there a typeclass for functions?

  - by Steve314

  I already tried this on Reddit, but there's no sign of a response - maybe it's the wrong place, maybe I'm too impatient. Anyway... In a learning problem I've been messing around with, I realised I needed a typeclass for functions with operations for applying, composing etc. Reasons... It can be convenient to treat a representation of a function as if it were the function itself, so that applying the function implicitly uses an interpreter, and composing functions derives a new description. Once you have a typeclass for functions, you can have derived typeclasses for special kinds of functions - in my case, I want invertible functions. For example, functions that apply integer offsets could be represented by an ADT containing an integer. Applying those functions just means adding the integer. Composition is implemented by adding the wrapped integers. The inverse function has the integer negated. The identity function wraps zero. The constant function cannot be provided because there's no suitable representation for it. Of course it doesn't need to spell things as if it the values were genuine Haskell functions, but once I had the idea, I thought a library like that must already exist and maybe even using the standard spellings. But I can't find such a typeclass in the Haskell library. I found the Data.Function module, but there's no typeclass - just some common functions that are also available from the Prelude. So - why isn't there a typeclass for functions? Is it "just because there isn't" or "because it's not so useful as you think"? Or maybe there's a fundamental problem with the idea? The biggest possible problem I've thought of so far is that function application on actual functions would probably have to be special-cased by the compiler to avoid a looping problem - in order to apply this function I need to apply the function application function, and to do that I need to call the function application function, and to do that...

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• JUnit Testing in Multithread Application

  - by e2bady

  This is a problem me and my team faces in almost all of the projects. Testing certain parts of the application with JUnit is not easy and you need to start early and to stick to it, but that's not the question I'm asking. The actual problem is that with n-Threads, locking, possible exceptions within the threads and shared objects the task of testing is not as simple as testing the class, but testing them under endless possible situations within threading. To be more precise, let me tell you about the design of one of our applications: When a user makes a request several threads are started that each analyse a part of the data to complete the analysis, these threads run a certain time depending on the size of the chunk of data (which are endless and of uncertain quality) to analyse, or they may fail if the data was insufficient/lacking quality. After each completed its analysis they call upon a handler which decides after each thread terminates if the collected analysis-data is sufficient to deliver an answer to the request. All of these analysers share certain parts of the applications (some parts because the instances are very big and only a certain number can be loaded into memory and those instances are reusable, some parts because they have a standing connection, where connecting takes time, ex.gr. sql connections) so locking is very common (done with reentrant-locks). While the applications runs very efficient and fast, it's not very easy to test it under real-world conditions. What we do right now is test each class and it's predefined conditions, but there are no automated tests for interlocking and synchronization, which in my opionion is not very good for quality insurances. Given this example how would you handle testing the threading, interlocking and synchronization?

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