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  • how to split this label to get the specific value(free gold)

    - by Wolf
    Hello all i am having a fun filled irritating little problem which i am sure can be resolved in less than 5 seconds with the enlightened and combined minds of stack overflow users ok first off it seems i am having trouble communicating what my trouble is with the gentlemen and ladies who are trying to help me in earlier posts so i am going to make it very simple i need to get 337 and 229 out of this son of satan string that is constantly updating every 2 seconds now i dont know how to go about doing this i know i should probably use split but i dont know how to do it on this because i have very little experience with it Last login: Thu Jun 5 08:20:35 2014 from .** /*/*-..****.**///*-****.**.*/****/*/***status Virtual server [...] is UP. *: 337 bananas left ****(s)******: 229 bananas eaten(s) ** *. [* ] – i am tired and would like to finish this before i am gray or sentanced to prison for raving naked down my street please help and thanks in advance p.s dont really care if this gets down voted a bit tired and more than a little angry so enjoy

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  • How does lock(syncRoot) make sense on a static method?

    - by Rising Star
    The following code is excerpted from the (Windows Identity Foundation SDK) template that MS uses to create a new Security Token Service Web Site. public static CustomSecurityTokenServiceConfiguration Current { get { HttpApplicationState httpAppState = HttpContext.Current.Application; CustomSecurityTokenServiceConfiguration customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { lock ( syncRoot ) { customConfiguration = httpAppState.Get( CustomSecurityTokenServiceConfigurationKey ) as CustomSecurityTokenServiceConfiguration; if ( customConfiguration == null ) { customConfiguration = new CustomSecurityTokenServiceConfiguration(); httpAppState.Add( CustomSecurityTokenServiceConfigurationKey, customConfiguration ); } } } return customConfiguration; } } I'm relatively new to multi-threaded programming. I assume that the reason for the lock statement is to make this code thread-safe in the event that two web requests arrive at the web site at the same time. However, I would have thought that using lock (syncRoot) would not make sense because syncRoot refers to the current instance that this method is operating on... but this is a static method? How does this make sense?

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  • What is a good free ODBC viewer?

    - by wshato
    At my job I have to work with three different databases. One is a SQL Server 2008, for which I use SQL Server Management Studio, and another is MySQL, for which I use the MySQL tools. The third however is a Cache database that I can only access through a ODBC connection. Currently I use the SLIK software ODBC View tool to access it, but it is severely lacking when compared with the other two tools. Can anyone recommend a good tool for this type of work?

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  • A Plot Graph .NET WindowsForm Component Free

    - by user255946
    Hello All, I'm searching for a plot .NET component to plot a 2D line chart, given an array of data. It will be used with WindowsForm (C#) and It will be very helpful if it could be freeware. It is for a scientific application. This is my first asked question in stackoverflow, and excuse me for my terrible English written.

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  • Finding 'free' times in MySQL

    - by James Inman
    Hi, I've got a table as follows: mysql> DESCRIBE student_lectures; +------------------+----------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------+----------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | course_module_id | int(11) | YES | MUL | NULL | | | day | int(11) | YES | | NULL | | | start | datetime | YES | | NULL | | | end | datetime | YES | | NULL | | | cancelled_at | datetime | YES | | NULL | | | lecture_type_id | int(11) | YES | | NULL | | | lecture_id | int(11) | YES | | NULL | | | student_id | int(11) | YES | | NULL | | | created_at | datetime | YES | | NULL | | | updated_at | datetime | YES | | NULL | | +------------------+----------+------+-----+---------+----------------+ I'm essentially wanting to find times when a lecture doesn't happen - so to do this I'm thinking a query to group overlapping lectures together (so, for example, 9am-10am and 10am-11am lectures will be shown as a single 9am-11am lecture). There may be more than two lectures back-to-back. I've currently got this: SELECT l.start, l2.end FROM student_lectures l LEFT JOIN student_lectures l2 ON ( l2.start = l.end ) WHERE l.student_id = 1 AND l.start >= '2010-04-26 09:00:00' AND l.end <= '2010-04-30 19:00:00' AND l2.end IS NOT NULL AND l2.end != l.start GROUP BY l.start, l2.end ORDER BY l.start, l2.start Which returns: +---------------------+---------------------+ | start | end | +---------------------+---------------------+ | 2010-04-26 09:00:00 | 2010-04-26 11:00:00 | | 2010-04-26 10:00:00 | 2010-04-26 12:00:00 | | 2010-04-26 10:00:00 | 2010-04-26 13:00:00 | | 2010-04-26 13:15:00 | 2010-04-26 16:15:00 | | 2010-04-26 14:15:00 | 2010-04-26 16:15:00 | | 2010-04-26 15:15:00 | 2010-04-26 17:15:00 | | 2010-04-26 16:15:00 | 2010-04-26 18:15:00 | ...etc... The output I'm looking for from this would be: +---------------------+---------------------+ | start | end | +---------------------+---------------------+ | 2010-04-26 09:00:00 | 2010-04-26 13:00:00 | | 2010-04-26 13:15:00 | 2010-04-26 18:15:00 | Any help appreciated, thanks!

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  • Handling "other" option in dropdown select with free text input field

    - by ted776
    Hi, I'm trying to figure out the best way to handle a dropdown list where one of the options "other" shows a hidden text field (via jQuery), where the user can then enter text. Should both the dropdown and the input field be given the same "name" attribute, then server side code runs a check on the values of each in order to know what one is the active value - e.g if the value of the select box is "other", then check the value of the text input field - if this isn't the default value ("enter text"), then it's ok to use this value and save it to the database. Is this a messy approach to this problem?

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  • Suggestions on including free database products to include in an application - SQL Server Express or

    - by superartsy
    I am working on an enterprise level product that is designed around SQL Server Express and specifically its features (views, concurrent users, stored procedures, CASE and IF statements). Though we don't use any advanced SQL Server features, the database size limit of 4GB in the Express edition may up being a limitation. A work-around is that customers can move to more full-featured versions of SQL Server. The problem is that SQL Server Express deployment is not easy, and the installer size is huge. This is a major drawback for someone looking to try our product. You don't want end-users to not buy a product because the download is huge. Does anyone have any recommendations of a database that has a smaller footprint but all the features of Express and which can be migrated to express?

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  • strategy to allocate/free lots of small objects

    - by aaa
    hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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  • How to create "lock" (stop updating of cells) in Excel?

    - by Oozi
    My question is pretty simple, but one to which I can't really find a solution myself. I use Excel quite frequently, but rarely the fancy stuff. Anyway, to the point: How do I create a dropmenu that will lock certain cells, rows or columns? (by lock I mean unable to change via hand and stops updating itself). Example: A1 = 5 B1 = A1 * 100 Can I "lock" the B1-cell, so that changing A1 will have no effect on B1 (Will remain at value 500)? I would preferably want to be able to "unlock" the cell as well, instead of simply making function into value. Is this possible? Thanks in advance!

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  • 24+ Coda Alternatives for Windows and Linux

    - by Matt
    Coda plays an important role in designing layout on Mac. There are numerous coda alternatives for windows and Linux too. It is not possible to describe each and everyone so some of the coda alternatives, which work on both windows and Linux platforms, are discussed below. EditPlus $35.00 Good thing about EditPlus is that it highlights URLs and email addresses, activating them when you ‘crtl + double-click’. It also has a built in browser for previewing HTML, and FTP and SFTP support. Also supports Macros and RegEx find and replace. UltraEdit $49.99 It is another good coda alternative for windows and Linux. It is the best suited editor for text, HTML and HEX. It also plays an advanced PHP, Perl, Java and JavaScript editor for programmers. It supports disk-based 64-bit or standard file handling on 32-bit Windows platforms or window 2000 and later versions. HippoEdit $39.95 HippoEDIT has the best autocomplete it gives pop a ‘tooltip’ above your cursor as you type, suggesting words you’ve already typed. It does syntax highlighting for over 2 dozen language. Sublime Text $59.00 Sublime Text awesome ‘zoomed out’ view of the file lets you focus on the area you want. It lets you open a local file when you right-click on its link, and there are a few automation features, so this would make a solid choice of a text editor. Textpad $24.70 TextPad is simple editor with nifty features such as column select, drag-and-drop text between files, and hyperlink support. It also supports large files. Aptana Free Aptana Studio is one of the best editors working on both windows and Linux. It is a complete web development setting that has a nice blend of powerful authoring tools with a collection of online hosting and collaboration services. It is quite helpful as it support for PHP, CSS, FTP, and more. SciTE Free It is a SCIntilla based Text Editor. It has gradually developed as a generally useful editor. It provides for building and running programs. It is best to be used for jobs with simple configurations. SciTE is currently available for Intel Win32 and Linux compatible operating systems with GTK+. It has been run on Windows XP and on Fedora 8 and Ubuntu 7.10 with GTK+ 2.12 E Text Editor $34.96 E Text Editor is a new text editor for Windows, which also works on Linux as well. It has powerful editing features and also some unique abilities. It makes text manipulation quite fast and easy, and makes user focus on his writing as it automatically does all the manual work. It can be extend it in any language. It supports Text Mate bundles, thus allows the user to tap into a huge and active community. Editra Free Editra is an upcoming editor, with some fantastic features such as user profiles, auto-completion, session saving, and syntax highlighing for 60+ languages. Plugins can extend the feature set, offering an integrated python console, FTP client, file browser, and calculator, among others. PSPad Free PSPad is a good Template for writing CSS, as it an internal web browser, and a macro recorder to the table. It also supports hex editing, and some degree of code compiling. JEdit Free It is a mature programmer’s text editor and has taken a good deal of time to be developed as it is today. It is better than many costlier development tools due to its features and simplicity of use. It has been released as free software with full source code, provided under the terms of the GPL 2.0. Which also adds to its attractiveness. NEdit Free It is a multi-purpose text editor for the X Window System, which also works on Linux. It combines a standard, easy to use, graphical user interface with the full functionality and stability required by users who edit text for long period a day. It also provides for thorough support for development in various languages. It also facilitates the use of text processors, and other tools at the same time. It can be used productively by anyone who needs to edit text. It is quite a user-friendly tool. Its salient features include syntax highlighting with built in pattern, auto indent, tab emulation, block indentation adjustment etc. As of version 5.1, NEdit may be freely distributed under the terms of the GNU General Public License. MadEdit Free Mad Edit is an Open-Source and Cross-Platform Text/Hex Editor. It is written in C++ and wxWidgets. MadEdit can edit files in Text/Column/Hex modes. It also supports many useful functions, such as Syntax Highlighting, Word Wrap, Encoding for UTF8/16/32,and others. It also supports word count, which makes it quite a useful text editor for both windows and Linux. It has been recently modified on 10/09/2010. KompoZer Free Kompozer is a complete web authoring system that has a combination of web file management and easy-to-use WYSIWYG web page editing. KompoZer has been designed to be completely and extensively easy to use. It is thus an ideal tool for non-technical computer users who want to create an attractive, professional-looking web site without knowing HTML or web coding. It is based on the NVU source code. Vim Free Vim or “Vi IMproved” is an advanced text editor. Its salient features are syntax highlighting, word completion and it also has a huge amount of contributed content. Vim has several “modes” on offer for editing, which adds to the efficiency in editing. Thus it becomes a non-user-friendly application but it is also strength for its users. The normal mode binds alphanumeric keys to task-oriented commands. The visual mode highlights text. More tools for search & replace, defining functions, etc. are offered through command line mode. Vim comes with complete help. NotePad ++ Free One of the the best free text editor for Windows out there; with support for simple things—like syntax highlighting and folding—all the way up to FTP, Notepad++ should tick most of the boxes Notepad2 Free Notepad2 is also based on the Scintilla editing engine, but it’s much simpler than Notepad++. It bills itself as being fast, light-weight, and Notepad-like. Crimson Editor Free Crimson Editor has the ability to edit remote files, using a built-in FTP client; there’s also a spell checker. TotalEdit Free TotalEdit allows file comparison, RegEx search and replace, and has multiple options for file backup / versioning. For cleanup, it offers (X)HTML and XML customizable formatting, and a spell checker. In-Type Free ConTEXT Free SourceEdit Free SourceEdit includes features such as clipboard history, syntax highlighting and autocompletion for a decent set of languages. A hex editor and FTP client. RJ TextED Free RJ TextED supports integration with TopStyle Lite. Provides HTML validation and formatting. It includes an FTP client, a file browser, and a code browser, as well as a character map and support for email. GEDIT Free It is one of the best coda alternatives for windows and Linux. It has syntax highlighting and is best suitable for programming. It has many attractive features such as full support for UTF-8, undo/redo, and clipboard support, search and replace, configurable syntax highlighting for various languages and many more supportive features. It is extensible with plug ins. Other important coda alternatives for windows and Linux are Redcar, Bluefish Editor, NVU, Ruby Mine, Slick Edit, Geany, Editra, txt2html and CSSED. There are many more. Its up to user to decide which one suits best to his requirements. Related posts:10 Useful Text Editor For Developer Applications to Install & Run Windows on Linux Open Source WYSIWYG Text Editors

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  • C# async and actors

    - by Alex.Davies
    If you read my last post about async, you might be wondering what drove me to write such odd code in the first place. The short answer is that .NET Demon is written using NAct Actors. Actors are an old idea, which I believe deserve a renaissance under C# 5. The idea is to isolate each stateful object so that only one thread has access to its state at any point in time. That much should be familiar, it's equivalent to traditional lock-based synchronization. The different part is that actors pass "messages" to each other rather than calling a method and waiting for it to return. By doing that, each thread can only ever be holding one lock. This completely eliminates deadlocks, my least favourite concurrency problem. Most people who use actors take this quite literally, and there are plenty of frameworks which help you to create message classes and loops which can receive the messages, inspect what type of message they are, and process them accordingly. But I write C# for a reason. Do I really have to choose between using actors and everything I love about object orientation in C#? Type safety Interfaces Inheritance Generics As it turns out, no. You don't need to choose between messages and method calls. A method call makes a perfectly good message, as long as you don't wait for it to return. This is where asynchonous methods come in. I have used NAct for a while to wrap my objects in a proxy layer. As long as I followed the rule that methods must always return void, NAct queued up the call for later, and immediately released my thread. When I needed to get information out of other actors, I could use EventHandlers and callbacks (continuation passing style, for any CS geeks reading), and NAct would call me back in my isolated thread without blocking the actor that raised the event. Using callbacks looks horrible though. To remind you: m_BuildControl.FilterEnabledForBuilding(    projects,    enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(        enabledProjects,             newDirtyProjects =             {                 ....... Which is why I'm really happy that NAct now supports async methods. Now, methods are allowed to return Task rather than just void. I can await those methods, and C# 5 will turn the rest of my method into a continuation for me. NAct will run the other method in the other actor's context, but will make sure that when my method resumes, we're back in my context. Neither actor was ever blocked waiting for the other one. Apart from when they were actually busy doing something, they were responsive to concurrent messages from other sources. To be fair, you could use async methods with lock statements to achieve exactly the same thing, but it's ugly. Here's a realistic example of an object that has a queue of data that gets passed to another object to be processed: class QueueProcessor {    private readonly ItemProcessor m_ItemProcessor = ...     private readonly object m_Sync = new object();    private Queue<object> m_DataQueue = ...    private List<object> m_Results = ...     public async Task ProcessOne() {         object data = null;         lock (m_Sync)         {             data = m_DataQueue.Dequeue();         }         var processedData = await m_ItemProcessor.ProcessData(data); lock (m_Sync)         {             m_Results.Add(processedData);         }     } } We needed to write two lock blocks, one to get the data to process, one to store the result. The worrying part is how easily we could have forgotten one of the locks. Compare that to the version using NAct: class QueueProcessorActor : IActor { private readonly ItemProcessor m_ItemProcessor = ... private Queue<object> m_DataQueue = ... private List<object> m_Results = ... public async Task ProcessOne()     {         // We are an actor, it's always thread-safe to access our private fields         var data = m_DataQueue.Dequeue();         var processedData = await m_ItemProcessor.ProcessData(data);         m_Results.Add(processedData);     } } You don't have to explicitly lock anywhere, NAct ensures that your code will only ever run on one thread, because it's an actor. Either way, async is definitely better than traditional synchronous code. Here's a diagram of what a typical synchronous implementation might do: The left side shows what is running on the thread that has the lock required to access the QueueProcessor's data. The red section is where that lock is held, but doesn't need to be. Contrast that with the async version we wrote above: Here, the lock is released in the middle. The QueueProcessor is free to do something else. Most importantly, even if the ItemProcessor sometimes calls the QueueProcessor, they can never deadlock waiting for each other. So I thoroughly recommend you use async for all code that has to wait a while for things. And if you find yourself writing lots of lock statements, think about using actors as well. Using actors and async together really takes the misery out of concurrent programming.

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  • MacX DVD Ripper Pro is Free for How-To Geek Readers (Time Limited!)

    - by The Geek
    Want to rip a DVD to your hard drive, but don’t have a software package to do it? How-To Geek readers can get the normally non-free MacX DVD Ripper Pro for free, but only if you download your copy and install it before Saturday. Here’s how to get it. This time-limited offer is available to anybody for the next couple of days—just head to the download site, install the software package, and use the key provided. It’s as simple as that. Note: despite the confusion of the name, it’s available for both Mac and Windows. Latest Features How-To Geek ETC MacX DVD Ripper Pro is Free for How-To Geek Readers (Time Limited!) HTG Explains: What’s a Solid State Drive and What Do I Need to Know? How to Get Amazing Color from Photos in Photoshop, GIMP, and Paint.NET Learn To Adjust Contrast Like a Pro in Photoshop, GIMP, and Paint.NET Have You Ever Wondered How Your Operating System Got Its Name? Should You Delete Windows 7 Service Pack Backup Files to Save Space? Save Files Directly from Your Browser to the Cloud in Chrome and Iron The Steve Jobs Chronicles – Charlie and the Apple Factory [Video] Google Chrome Updates; Faster, Cleaner Menus, Encrypted Password Syncing, and More Glowing Chess Set Combines LEDs, Chess, and DIY Electronics Fun Peaceful Alpine River on a Sunny Day [Wallpaper] Fast Society Creates Mini and Mobile Temporary Social Networks

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  • FREE goodies if you are a UK based software house already live on the Windows Azure Platform

    - by Eric Nelson
    In the UK we have seen some fantastic take up around the Windows Azure Platform and we have lined up some great stuff in 2011 to help companies fully exploit the Cloud – but we need you to tell us what you are up to! Once you tell us about your plans around Windows Azure, you will get access to FREE benefits including email based developer support and free monthly allowance of Windows Azure, SQL Azure and AppFabric from Jan 2011 – and more! (This offer is referred to as Cloud Essentials and is explained here) And… we will be able to plan the right amount of activity to continue to help early adopters through 2011. Step 1: Sign up your company to Microsoft Platform Ready (you will need a windows live id to do this) Step 2: Add your applications For each application, state your intention around Windows Azure (and SQL etc if you so wish) Step 3: Verify your application works on the Windows Azure Platform Step 4 (Optional): Test your application works on the Windows Azure Platform Download the FREE test tool. Test your application with it and upload the successful results. Step 5: Revisit the MPR site in early January to get details of Cloud Essentials and other benefits P.S. You might want some background on the “fantastic take up” bit: We helped over 3000 UK companies deploy test applications during the beta phase of Windows Azure We directly trained over 1000 UK developers during 2010 We already have over 100 UK applications profiled on the Microsoft Platform Ready site And in a recent survey of UK ISVs you all look pretty excited around Cloud – 42% already offer their solution on the Cloud or plan to.

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  • Why would I get a bus error or segmentation fault when calling free() normally?

    - by chucknelson
    I have a very simple test program, running on Solaris 5.8: #include <stdio.h> #include <stdlib.h> int main(void) { char *paths; paths = getenv("PATH"); printf("Paths: %s\n", paths); free(paths); // this causes a bus error return 0; } If I don't call free() at the end, it displays the message fine and exits. If I include the free() call, it crashes with a bus error. I've had other calls to free(), in other programs, cause segmentation faults as well. Even if I allocate the memory for *paths myself, free() will cause a bus error. Is there some reason trying to free up the memory is causing a crash?

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  • Can I lock tables in an IF statement in MySQL?

    - by MalcomTucker
    This is throwing a syntax error - --from body of a stored proc IF (name = in_name) SET out_id = temp; ELSE LOCK TABLE People WRITE; INSERT INTO People (Name) VALUES (in_name); UNLOCK TABLE; SELECT LAST_INSERT_ID() INTO out_id END IF do I have to lock any tables I need at the start of the SP?

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  • dpkg stuck downloading font files

    - by Bob Bowles
    I have been reinstalling Ubuntu 12.04. The install from USB works fine, and I could update everything OK, but when I got to re-installing my application software I hit a snag. One of the packages I tried to re-install was ttf-mscorefonts-installer. dpkg stalled during this setup, downloading a font file (it had tried to download it all night). I stopped dpkg, and attempted to re-start downloading something else, but it would not let me. The commands I typed are as follows: bob@bobStudio:~$ sudo rm /var/lib/dpkg/lock This unlocks dpkg, but if I try to do something I get the following message (eg): bob@bobStudio:~$ sudo apt-get install synaptic E: dpgk was interrupted, you must manually run 'sudo dpkg --configure -a' to correct the problem So, I did just that: bob@bobStudio:~$ sudo dpkg --configure -a whereupon it started the previously failed download all over again. I went round the loop here a few times and each time after the configure command it re-started the failing download, but then I got this: bob@bobStudio:~$ sudo dpkg --configure -a Setting up update-notifier-common (0.119ubuntu8.4) ... ttf-mscorefonts-installer: downloading http://downloads.sourceforge.net/corefonts/andale32.exe Traceback (most recent call last): File "/usr/lib/update-notifier/package-data-downloader", line 234, in process_download_requests dest_file = urllib.urlretrieve(files[i])[0] File "/usr/lib/python2.7/urllib.py", line 93, in urlretrieve return _urlopener.retrieve(url, filename, reporthook, data) File "/usr/lib/python2.7/urllib.py", line 239, in retrieve fp = self.open(url, data) File "/usr/lib/python2.7/urllib.py", line 207, in open return getattr(self, name)(url) File "/usr/lib/python2.7/urllib.py", line 344, in open_http h.endheaders(data) File "/usr/lib/python2.7/httplib.py", line 954, in endheaders self._send_output(message_body) File "/usr/lib/python2.7/httplib.py", line 814, in _send_output self.send(msg) File "/usr/lib/python2.7/httplib.py", line 776, in send self.connect() File "/usr/lib/python2.7/httplib.py", line 757, in connect self.timeout, self.source_address) File "/usr/lib/python2.7/socket.py", line 553, in create_connection for res in getaddrinfo(host, port, 0, SOCK_STREAM): IOError: [Errno socket error] [Errno -2] Name or service not known Setting up ttf-mscorefonts-installer (3.4ubuntu3) ... bob@bobStudio:~$ sudo apt-get update E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable) E: Unable to lock directory /var/lib/apt/lists/ bob@bobStudio:~$ sudo rm /var/lib/dpkg/lock bob@bobStudio:~$ sudo apt-get update E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable) E: Unable to lock directory /var/lib/apt/lists/ The good news is that, once I sorted out the file locks, this seems to have permanently aborted the setup of the font package, so at least I can do something else with dpkg. That leaves two questions: 1) How could I have broken the loop without actually crashing out of dpkg? 2) How can I set up the ttf-mscorefonts-installer package in the future? Is this download really broken, or is it 'just' a bad Internet connection?

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  • SQL Server Table Polling by Multiple Subscribers

    - by Daniel Hester
    Background Designing Stored Procedures that are safe for multiple subscribers (to call simultaneously) can be challenging.  For example let’s say that you want multiple worker processes to poll a shared work queue that’s encapsulated as a SQL Table. This is a common scenario and through experience you’ll find that you want to use Table Hints to prevent unwanted locking when performing simultaneous queries on the same table. There are three table hints to consider: NOLOCK, READPAST and UPDLOCK. Both NOLOCK and READPAST table hints allow you to SELECT from a table without placing a LOCK on that table. However, SELECTs with the READPAST hint will ignore any records that are locked due to being updated/inserted (or otherwise “dirty”), whereas a SELECT with NOLOCK ignores all locks including dirty reads. For the initial update of the flag (that marks the record as available for subscription) I don’t use the NOLOCK Table Hint because I want to be sensitive to the “active” records in the table and I want to exclude them.  I use an Update Lock (UPDLOCK) in conjunction with a WHERE clause that uses a sub-select with a READPAST Table Hint in order to explicitly lock the records I’m updating (UPDLOCK) but not place a lock on the table when selecting the records that I’m going to update (READPAST). UPDATES should be allowed to lock the rows affected because we’re probably changing a flag on a record so that it is not included in a SELECT from another subscriber. On the UPDATE statement we should explicitly use the UPDLOCK to guard against lock escalation. A SELECT to check for the next record(s) to process can result in a shared read lock being held by more than one subscriber polling the shared work queue (SQL table). It is expected that more than one worker process (or server) might try to process the same new record(s) at the same time. When each process then tries to obtain the update lock, none of them can because another process has a shared read lock in place. Thus without the UPDLOCK hint the result would be a lock escalation deadlock; however with the UPDLOCK hint this condition is mitigated against. Note that using the READPAST table hint requires that you also set the ISOLATION LEVEL of the transaction to be READ COMMITTED (rather than the default of SERIALIZABLE). Guidance In the Stored Procedure that returns records to the multiple subscribers: Perform the UPDATE first. Change the flag that makes the record available to subscribers.  Additionally, you may want to update a LastUpdated datetime field in order to be able to check for records that “got stuck” in an intermediate state or for other auditing purposes. In the UPDATE statement use the (UPDLOCK) Table Hint on the UPDATE statement to prevent lock escalation. In the UPDATE statement also use a WHERE Clause that uses a sub-select with a (READPAST) Table Hint to select the records that you’re going to update. In the UPDATE statement use the OUTPUT clause in conjunction with a Temporary Table to isolate the record(s) that you’ve just updated and intend to return to the subscriber. This is the fastest way to update the record(s) and to get the records’ identifiers within the same operation. Finally do a set-based SELECT on the main Table (using the Temporary Table to identify the records in the set) with either a READPAST or NOLOCK table hint.  Use NOLOCK if there are other processes (besides the multiple subscribers) that might be changing the data that you want to return to the multiple subscribers; or use READPAST if you're sure there are no other processes (besides the multiple subscribers) that might be updating column data in the table for other purposes (e.g. changes to a person’s last name).  NOLOCK is generally the better fit in this part of the scenario. See the following as an example: CREATE PROCEDURE [dbo].[usp_NewCustomersSelect] AS BEGIN -- OVERRIDE THE DEFAULT ISOLATION LEVEL SET TRANSACTION ISOLATION LEVEL READ COMMITTED -- SET NOCOUNT ON SET NOCOUNT ON -- DECLARE TEMP TABLE -- Note that this example uses CustomerId as an identifier; -- you could just use the Identity column Id if that’s all you need. DECLARE @CustomersTempTable TABLE ( CustomerId NVARCHAR(255) ) -- PERFORM UPDATE FIRST -- [Customers] is the name of the table -- [Id] is the Identity Column on the table -- [CustomerId] is the business document key used to identify the -- record globally, i.e. in other systems or across SQL tables -- [Status] is INT or BIT field (if the status is a binary state) -- [LastUpdated] is a datetime field used to record the time of the -- last update UPDATE [Customers] WITH (UPDLOCK) SET [Status] = 1, [LastUpdated] = GETDATE() OUTPUT [INSERTED].[CustomerId] INTO @CustomersTempTable WHERE ([Id] = (SELECT TOP 100 [Id] FROM [Customers] WITH (READPAST) WHERE ([Status] = 0) ORDER BY [Id] ASC)) -- PERFORM SELECT FROM ENTITY TABLE SELECT [C].[CustomerId], [C].[FirstName], [C].[LastName], [C].[Address1], [C].[Address2], [C].[City], [C].[State], [C].[Zip], [C].[ShippingMethod], [C].[Id] FROM [Customers] AS [C] WITH (NOLOCK), @CustomersTempTable AS [TEMP] WHERE ([C].[CustomerId] = [TEMP].[CustomerId]) END In a system that has been designed to have multiple status values for records that need to be processed in the Work Queue it is necessary to have a “Watch Dog” process by which “stale” records in intermediate states (such as “In Progress”) are detected, i.e. a [Status] of 0 = New or Unprocessed; a [Status] of 1 = In Progress; a [Status] of 2 = Processed; etc.. Thus, if you have a business rule that states that the application should only process new records if all of the old records have been processed successfully (or marked as an error), then it will be necessary to build a monitoring process to detect stalled or stale records in the Work Queue, hence the use of the LastUpdated column in the example above. The Status field along with the LastUpdated field can be used as the criteria to detect stalled / stale records. It is possible to put this watchdog logic into the stored procedure above, but I would recommend making it a separate monitoring function. In writing the stored procedure that checks for stale records I would recommend using the same kind of lock semantics as suggested above. The example below looks for records that have been in the “In Progress” state ([Status] = 1) for greater than 60 seconds: CREATE PROCEDURE [dbo].[usp_NewCustomersWatchDog] AS BEGIN -- TO OVERRIDE THE DEFAULT ISOLATION LEVEL SET TRANSACTION ISOLATION LEVEL READ COMMITTED -- SET NOCOUNT ON SET NOCOUNT ON DECLARE @MaxWait int; SET @MaxWait = 60 IF EXISTS (SELECT 1 FROM [dbo].[Customers] WITH (READPAST) WHERE ([Status] = 1) AND (DATEDIFF(s, [LastUpdated], GETDATE()) > @MaxWait)) BEGIN SELECT 1 AS [IsWatchDogError] END ELSE BEGIN SELECT 0 AS [IsWatchDogError] END END Downloads The zip file below contains two SQL scripts: one to create a sample database with the above stored procedures and one to populate the sample database with 10,000 sample records.  I am very grateful to Red-Gate software for their excellent SQL Data Generator tool which enabled me to create these sample records in no time at all. References http://msdn.microsoft.com/en-us/library/ms187373.aspx http://www.techrepublic.com/article/using-nolock-and-readpast-table-hints-in-sql-server/6185492 http://geekswithblogs.net/gwiele/archive/2004/11/25/15974.aspx http://grounding.co.za/blogs/romiko/archive/2009/03/09/biztalk-sql-receive-location-deadlocks-dirty-reads-and-isolation-levels.aspx

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  • Are there cloud network drives that let users lock files or mark them as "in use"?

    - by Brandon Craig Rhodes
    Having spent several hours reading about the features and limitations of services like DropBox and Jungle Disk and the hundreds of competitors they seem to have (as though everyone with an AWS account these days goes ahead and writes a file sharing application just for fun), I have yet to find one that would let a team of people at a small business collaborate without stepping all over each other's toes. At a small business there are often many small documents per project — estimates, contracts, project plans, budgets — and team members frequently have to open and edit them, with all sorts of problems happening if two people edit a file at once. Even if a sharing service is smart enough to keep both versions of the file created, most small-business software (like word processors, spreadsheets, estimating software, or billing systems) has no way to compare — much less to merge! — the changes in two rival versions of a file that two people edited at the same time without each other's knowledge. So, my question: are their cloud-based file sharing solutions that not only provide a virtual network drive that people can access, but that also let users lock files — even if it's not a real lock but just a flag or indicator — that could possibly prevent remote workers from both editing the same file at once? Having one person wait for another person to finish editing is a very, very small inconvenience compared to the hour or more than it can take to compare two estimates by hand until you find and resolve the rival changes. Given this fact, I am surprised that almost none of the popular file sharing solutions seem to recognize this problem and provide some solution! Does anyone know of a service that does?

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  • Are there cloud network drives that let users lock files or mark them as "in use"?

    - by Brandon Craig Rhodes
    Having spent several hours reading about the features and limitations of services like DropBox and Jungle Disk and the hundreds of competitors they seem to have (as though everyone with an AWS account these days goes ahead and writes a file sharing application just for fun), I have yet to find one that would let a team of people at a small business collaborate without stepping all over each other's toes. At a small business there are often many small documents per project — estimates, contracts, project plans, budgets — and team members frequently have to open and edit them, with all sorts of problems happening if two people edit a file at once. Even if a sharing service is smart enough to keep both versions of the file created, most small-business software (like word processors, spreadsheets, estimating software, or billing systems) has no way to compare — much less to merge! — the changes in two rival versions of a file that two people edited at the same time without each other's knowledge. So, my question: are their cloud-based file sharing solutions that not only provide a virtual network drive that people can access, but that also let users lock files — even if it's not a real lock but just a flag or indicator — that could possibly prevent remote workers from both editing the same file at once? Having one person wait for another person to finish editing is a very, very small inconvenience compared to the hour or more than it can take to compare two estimates by hand until you find and resolve the rival changes. Given this fact, I am surprised that almost none of the popular file sharing solutions seem to recognize this problem and provide some solution! Does anyone know of a service that does?

    Read the article

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