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  • Get Compiz working on x1300 ati

    - by wdkrnls
    Hi, I have Ubuntu 10.10 installed on a thinkpad T60 with an ati mobile x1300. Ubuntu isn't loading any proprietary drivers and compiz doesn't work. A google search turned up nothing. Sure, some people reported "bad performance", but I'm not getting any "performance" with compiz and these post were all for previous editions. I'm new to messing with ati drivers. Is there a way to make sure xorg-video-ati is loaded? Do I have to add any voodoo lines somewhere in /etc/X11/? Did anyone else have this problem? Thanks for your help!

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  • Googling query from anywhere

    - by Shagun
    Some times when I am trying out stuff on my terminal, I get some blockade or some error to resolve which I have to copy the error or last message then open my browser and then Google the query. Is it possible for me that I select the message via mouse and when I right click I get a Google it option as I get when I select some text on a browser? PS : I am not asking how to do Google search via terminal or how to browse web via terminal.These were the results I got when I goggled my question. what I want is something more general. Whenever I select a piece of text I should get a "Google me" option with the right click of my mouse(or maybe with pressing of a key or something). I would prefer that the query takes place in a browser and not in a terminal.

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  • Generating CMakeLists.txt

    - by vanna
    I got a bunch of C++ sources files and headers. They may use external libraries such as Boost e.g. I am interested in the process of building binaries for Windows and *nix. Makefiles (*nix) and .vcproj (Windows) call compilers with some specifications such as the order of compilation, compilation options and stuff. CMakeLists.txt can be used by CMake to build either makefiles or .vcproj and use very helpful commands such as recursive search of files, automatic linkage with known libraries, installers, variables that can be used in source files... Is there any existing tool that would generate a CMakeLists.txt from specified options ? Options could be like : scan this folder and make a library out of it, then scan this other folder and make an executable and automatically link both with Boost as well along with a user friendly installer with generated INSTALL.txt and README.txt. Something very powerful like that.

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  • Why would urls submitted in google webmaster tools drop to 0?

    - by ambient
    Why would urls submitted in google webmaster tools drop to 0? It's a small site, only like 20 pages, I submitted the xml sitemap and for about a week it said 20 urls submitted. A day or so ago it indexed about 17 of the pages, but today when looking it not only says that 0 are indexed but also 0 have been submitted. I did a site search on google and found clearly that pages are indexed, is this just an error on google webmaster tools? Any help or thoughts would be appreciated. Thanks!

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  • Is Google indexing pages that has no connection with other pages? [duplicate]

    - by Grkmksk
    This question already has an answer here: How did Google find my unlinked newly created pages? 3 answers I am working on a web project that has nearly 100 thousand instant users and there is a webpage that we are using for test cases. There are no links pointing to it from other pages. It shouldn't be indexed by Google or any other search engines. "noindex" can be used in this situation, I know but I wonder if Google (or any others) indexes this page, if I don't do anything to prevent it.

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  • Does a large (hidden) submenu count towards site content in tems of determining page similarities?

    - by Name
    Basically, I have this site that recently lost a lot of traffic after I optimized the html, the exact reasons to which are uncertain. The graph of impressions (times a page appears on search listings) is continuously going down like an e^-x function. Because the content, previously occupying five pages of tables, now fits within a few paragraph tags, the menu now occupies about 80% of the live html code and I am starting to have doubts wherether this affects the "similar pages" factor that Google punishes. Questions: As far as I know, Google ignores invisible material and the submenus are only visible when hovered over. Has anything at all changed in this area? If I ajax in the submenus, leaving only the main eight menu items to load, will I be punished for "hiding" information? Is the idea worth testing or is it frankly retarded?

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  • Windows 8 : Google sort son application de recherche pour contrer Bing et prépare le terrain à ses services concurrents de Microsoft

    Windows 8 : Google sort son application de recherche Pour contrer Bing et préparer le terrain pour ses services concurrents de Microsoft La recherche par défaut de Windows 8 est bien évidemment Bing. On ne sait pas si la justice décidera de s'attaquer à cette application, comme elle l'a fait pour Internet Explorer ou le Media Player, mais on sait une chose : Google a déjà réagi. Et de la meilleure manière qui soit : pas devant les tribunaux donc, mais avec une application maison. Tout comme pour la version iOS, Google Search for Windows 8 est gratuit, propose la recherche vocale et tous les raccourcis vers les services hébergés de Google. Dont Gmail, Calendar , Maps ...

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  • Off-Page SEO - The Ethos of Backlinking

    I want to delve under the bonnet more regarding off-page, so let's get to it! How do we get backlinks to our site? It may seem easy and what springs to mind for many is to ask someone to link to your site while in return you link back to theirs. In general this is a very fair and sensible undertaking, it really is. However, in Google's eyes and perhaps in the other two big search engines too now, its not counted as a valuable link any longer.

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  • type of application form in Visual Studio 2013 [on hold]

    - by Lyhour Chhay
    I wanna ask all of you about the type of application form which can developed by using Visual Studio . I know only 2 , there are windows application form and web application form . So i wanna know more because my teacher told me that there 4 more application forms . I try to search on Google or Wikipedia but still can't find the best answer for me . I hope that you all of you can help me. Best Regard !! thx in advance.

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  • Where can I get the 10k common English dictionary words which Stack overflow uses in related question? [migrated]

    - by itpian.com
    Where can I get the 10k common English dictionary words which Stack overflow uses in related question? Here in SE podcast - http://blog.stackoverflow.com/2008/12/podcast-32/ One of our major performance optimizations for the “related questions” query is removing the top 10,000 most common English dictionary words (as determined by Google search) before submitting the query to the SQL Server 2008 full text engine. It’s shocking how little is left of most posts once you remove the top 10k English dictionary words. This helps limit and narrow the returned results, which makes the query dramatically faster.

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  • CMS/platform/portal for personnel placement/recruiting [closed]

    - by mezzanine
    Possible Duplicate: Which Content Management System (CMS)/Wiki should I use? I am interested in building a platform where I can match specialists/experts in a certain profession with potential customers/clients. Therefore, the professionals should be able to register with information about them and their area of expertise, and customers should be able to search for them and contact them via my website. Bonus would be some kind of feedback or rating functionality. Examples for other areas are http://www.lawyers.com/ for lawyers and http://sortfolio.com/ for web designers. Is there some kind of platform which already provides this functionality and could be customized?

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  • TexturePacker ignores extensions

    - by The Oddler
    I'm using TexturePacker in one of my games, though when packing a bunch of textures their extension is kept in the data file. So when I want to find a texture I need to search for "image.png" instead of just "image". Is there an option to let texture packer ignore the extensions of my source images in the data file? Solved: So if anyone else wants this, here's the exported I made: https://www.box.com/s/bf12q1i1yc9jr2c5yehd Just extract it into "C:\Program Files (x86)\CodeAndWeb\TexturePacker\bin\exporters\UIToolkit No Extensions" (or something similar) and it should show op as an exporter.

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  • Domain name similar to an other existing one, bad for SEO?

    - by qqfr2507
    I am in the process of choosing a domain name for a personal project. I have found a very good one (let's say it is "myproject.com") but it is very close to another existing domain name ("smyproject.com"). Only the first letter is different. This website has a very different activity from mine. My question is: is it bad for SEO? When someone will type "myproject" in a search engine, is there a risk that the first result will be "smyproject.com" if this website has better SEO than mine? Thanks for your help!

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  • Building a simple web app with database? [on hold]

    - by Zooce
    I'm building a simple airline reservation system (web app) for a class. I'm trying to find out where to start learning about implementing and integrating a sql database. User's should be able to search for available flights based on destination and departure cities and the like. A good example would be Google Flights. I'd like to access a data base with all of the flight information and display it within tables on the web page. Admins should be able to modify the databases as well. I've tried to learn about things like Node.js, PHP, and AJAX, but most of the tutorials that I've found have been difficult to understand. Any suggestions would be really appreciated, thanks!

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  • Should I install programs from a source tarball (`.tar.gz`), from the Ubuntu Software Centre, or from elsewhere?

    - by Flimm
    There are several ways to install an application in Ubuntu: You can download a source tarball (generally a .tar.gz or a .tar.bz2 file) and install it manually. (See How to install a .tar.gz (or .tar.bz2) file?) You can download a .deb file and install it manually, using dpkg or the Software Centre. You can search for the application in the Ubuntu Software Centre and install it there, or use apt with the official Ubuntu repositories. You can find a PPA or a third-party repo, and install it from there. What are the pros and cons of each method? Please discuss security implications, frequency of updates and program reliability of each method in your answer.

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  • Activity and View [closed]

    - by CYB
    Now, I'm going to create an app that can reserve something. There's three function like menu, reserve, and search. However, I don't know that I should create them as three Activities or just use three views as the function. I want to switch to other function by onclicklistener. Below is my onClickListener, private OnClickListener listener = new OnClickListener(){ public void onClick(View v) { switch(v.getId()){ case R.id.fuiButton1: break; case R.id.fuiButton2: break; case R.id.fuiButton3: break; } } }; Which is the best choice ?

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  • FTP client says directory permissions are 0000

    - by nnnmmm
    I encountered a problem that appears to be related to permissions (same as this one). When I looked at the permissions of various directories in FireFTP, they all were 0000, which is obviously nonsense, since all the other pages are served without any problems. I only have ftp access, and I think it’s a Windows server (The header says "Server: Microsoft-IIS/7.5"). I’ve tried a different ftp client, with the same result. Changing the permissions results in a "'SITE CHMOD 764 [directory]': command not understood" error. A search on Google and SO for "permissions windows 0000" and similar queries didn’t turn up anything. How can I view and change the actual permissions?

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  • How can I find the closest vector to another in a specific direction?

    - by Sniper
    Perhaps I am not phrasing it incorrectly in my searches, but I can not find anything on this. I have a vector3 with a specific direction that it is facing, I want to get the closest object to that position in that specific direction. Basically I want to get the object that is being aimed at. I have thought about finding all objects within a box and then finding the closest object to my vector from them results, but I am sure that there is a more efficient way. The Z axis is optional, the objects are most likely within a few meters of the search vector. http://i.stack.imgur.com/FafAu.jpg

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  • Need some help fixing fonts (11.04 Alpha 3)

    - by Spacecraft
    Hi I changed my Application Font and Window Font to something much better looking but it has a few problems. The font is Umpush Light. It's doing this in the software center: http://img851.imageshack.us/img851/8307/workspace1004.png If I increase the font size from 11 to 12, that problem goes away, but then everything is too large. When I increase it this also happens: http://img819.imageshack.us/img819/6231/workspace1006e.png It starts moving the text in the search box up, and the "All Applications" drop down gets messed up too. It seems like there is too much padding around the font or something. Anyone have any ideas on how I can fix this?

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  • Difference between "/" at end of URL and without "/" [closed]

    - by user702325
    Possible Duplicate: Does it make a difference if your url ends in a trailing slash or not? Why treat these as different URLs? I am doing a 301 redirect in my WP application using .htaccess and have mapped some of the URLs which have either been removed from the new domain or the URL structure has been changed. While doing I got a doubt I have following URL structure in my .htaccess file RewriteCond %{HTTP_HOST} ^old.com$ [OR] RewriteCond %{HTTP_HOST} ^www.old.com$ RewriteRule ^tag/waiting$ http://www.new.com/tag/relationships [R=301,L] while checking this i found that at some places URL is like http://www.new.com/tag/relationships while at others its like http://www.new.com/tag/relationships/, while both refer to the same location but not sure if this will make any difference to SEO and search engines. Please suggest if the way i am doing mapping is correct or do i need to modify it to handle both UR

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  • Spurious resets on Ubuntu

    - by boone2048
    I have a PC running Ubuntu 13.04 64bit, and I do weekly updates, so everything should be up-to-date. Everything is running fine, but sometimes, once-twice a week a complete reset happens. I think it must be software or hardware (perhaps Videocard) related, but I can't figure out what could be wrong. Can anybody suggest some ways, log files, where I could continue to search? By looking just at dmesg/dmesg.0 and Xorg.0.log I got nowhere. I cant find even a user application segfault. Any help is really appreciated.

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  • 4oD (UK) - Can't stream

    - by lordqwerty
    I'm using the most up-to-date version of firefox and flash player. When I go on 4oD and press play I used to get the loading screen showing forever with nothing playing. I then had a search and someone suggested to turn off Ad-Block. So I did and it plays the advertisements. Once the last ad has played it does nothing. Has anyone else got this problem? Has anyone managed to fix it? Any help would be appreciated. Thanks.

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  • Difficult to replicate objects (object Customer) on the list? [migrated]

    - by gandolf
    I wrote a program that does work with files like delete and update, store, and search And all customers But I have a problem with the method is LoadAll Once the data are read from the file and then Deserialize the object becomes But when I want to save the list of objects in the list are repeated. How can I prevent the duplication in this code? var customerStr = File.ReadAllLines (address); The code is written in CustomerDataAccess class DataAccess Layer. Project File The main problem with the method LoadAll Code: public ICollection<Customer> LoadAll() { var alldata = File.ReadAllLines(address); List<Customer> lst = new List<Customer>(); foreach (var s in alldata) { var objCustomer = customerSerializer.Deserialize(s); lst.Add(objCustomer); } return lst; }

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  • postfix 5.7.1 Relay access denied when sending mail with cron

    - by zensys
    Reluctant to ask because there is so much here about 'postfix relay access denied' but I cannot find my case: I use php (Zend Framework) to send emails outside my network using the Google mail server because I could not send mail outside my server (user: web). However when I sent out an email via cron (user: root, I believe), still using ZF, using the same mail config/credentials, I get the message: '5.7.1 Relay access denied' I guess I need to know one of two things: 1. How can I use the google smtp server from cron 2. What do I need to change in my config to send mail using my own server instead of google Though the answer to 2. is the more structural solution I assume, I am quite happy with an answer to 1. as well because I think Google is better at server maintaince (security/spam) than I am. Below my ZF application.ini mail section, main.cf and master.cf: application.ini: resources.mail.transport.type = smtp resources.mail.transport.auth = login resources.mail.transport.host = "smtp.gmail.com" resources.mail.transport.ssl = tls resources.mail.transport.port = 587 resources.mail.transport.username = [email protected] resources.mail.transport.password = xxxxxxx resources.mail.defaultFrom.email = [email protected] resources.mail.defaultFrom.name = "my company" main.cf: # Debian specific: Specifying a file name will cause the first # line of that file to be used as the name. The Debian default # is /etc/mailname. #myorigin = /etc/mailname smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) biff = no # appending .domain is the MUA's job. append_dot_mydomain = no # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h readme_directory = /usr/share/doc/postfix # TLS parameters smtpd_tls_cert_file = /etc/postfix/smtpd.cert smtpd_tls_key_file = /etc/postfix/smtpd.key smtpd_use_tls = yes smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for # information on enabling SSL in the smtp client. myhostname = mail.second-start.nl mydomain = second-start.nl alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases myorigin = /etc/mailname mydestination = relayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 mailbox_command = procmail -a "$EXTENSION" mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all html_directory = /usr/share/doc/postfix/html message_size_limit = 30720000 virtual_alias_domains = virtual_alias_maps = proxy:mysql:/etc/postfix/mysql-virtual_forwardings.cf, mysql:/etc/postfix/mysql-virtual_email2email.cf virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql-virtual_domains.cf virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailboxes.cf virtual_mailbox_base = /home/vmail virtual_uid_maps = static:5000 virtual_gid_maps = static:5000 smtpd_sasl_auth_enable = yes broken_sasl_auth_clients = yes smtpd_sasl_authenticated_header = yes # see under Spam smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks $virtual_mailbox_limit_maps virtual_transport = dovecot dovecot_destination_recipient_limit = 1 # Spam disable_vrfy_command = yes smtpd_delay_reject = yes smtpd_helo_required = yes smtpd_helo_restrictions = permit_mynetworks, check_helo_access hash:/etc/postfix/helo_access, reject_non_fqdn_hostname, reject_invalid_hostname, permit smtpd_recipient_restrictions = permit_sasl_authenticated, reject_unauth_destination, reject_invalid_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unknown_sender_domain, reject_unknown_recipient_domain, permit_mynetworks, reject_non_fqdn_hostname, reject_rbl_client sbl.spamhaus.org, reject_rbl_client zen.spamhaus.org, reject_rbl_client cbl.abuseat.org, reject_rbl_client bl.spamcop.net, permit smtpd_error_sleep_time = 1s smtpd_soft_error_limit = 10 smtpd_hard_error_limit = 20 master.cf: # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (yes) (never) (100) # ========================================================================== smtp inet n - - - - smtpd #smtp inet n - - - 1 postscreen #smtpd pass - - - - - smtpd #dnsblog unix - - - - 0 dnsblog #tlsproxy unix - - - - 0 tlsproxy #submission inet n - - - - smtpd # -o smtpd_tls_security_level=encrypt # -o smtpd_sasl_auth_enable=yes # -o smtpd_client_restrictions=permit_sasl_authenticated,reject # -o milter_macro_daemon_name=ORIGINATING #smtps inet n - - - - smtpd # -o smtpd_tls_wrappermode=yes # -o smtpd_sasl_auth_enable=yes # -o smtpd_client_restrictions=permit_sasl_authenticated,reject # -o milter_macro_daemon_name=ORIGINATING #628 inet n - - - - qmqpd pickup fifo n - - 60 1 pickup cleanup unix n - - - 0 cleanup qmgr fifo n - n 300 1 qmgr #qmgr fifo n - - 300 1 oqmgr tlsmgr unix - - - 1000? 1 tlsmgr rewrite unix - - - - - trivial-rewrite bounce unix - - - - 0 bounce defer unix - - - - 0 bounce trace unix - - - - 0 bounce verify unix - - - - 1 verify flush unix n - - 1000? 0 flush proxymap unix - - n - - proxymap proxywrite unix - - n - 1 proxymap smtp unix - - - - - smtp # When relaying mail as backup MX, disable fallback_relay to avoid MX loops relay unix - - - - - smtp -o smtp_fallback_relay= # -o smtp_helo_timeout=5 -o smtp_connect_timeout=5 showq unix n - - - - showq error unix - - - - - error retry unix - - - - - error discard unix - - - - - discard local unix - n n - - local virtual unix - n n - - virtual lmtp unix - - - - - lmtp anvil unix - - - - 1 anvil scache unix - - - - 1 scache # # ==================================================================== # Interfaces to non-Postfix software. Be sure to examine the manual # pages of the non-Postfix software to find out what options it wants. # # Many of the following services use the Postfix pipe(8) delivery # agent. See the pipe(8) man page for information about ${recipient} # and other message envelope options. # ==================================================================== # # maildrop. See the Postfix MAILDROP_README file for details. # Also specify in main.cf: maildrop_destination_recipient_limit=1 # maildrop unix - n n - - pipe flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient} # # ==================================================================== # # Recent Cyrus versions can use the existing "lmtp" master.cf entry. # # Specify in cyrus.conf: # lmtp cmd="lmtpd -a" listen="localhost:lmtp" proto=tcp4 # # Specify in main.cf one or more of the following: # mailbox_transport = lmtp:inet:localhost # virtual_transport = lmtp:inet:localhost # # ==================================================================== # # Cyrus 2.1.5 (Amos Gouaux) # Also specify in main.cf: cyrus_destination_recipient_limit=1 # #cyrus unix - n n - - pipe # user=cyrus argv=/cyrus/bin/deliver -e -r ${sender} -m ${extension} ${user} # # ==================================================================== # Old example of delivery via Cyrus. # #old-cyrus unix - n n - - pipe # flags=R user=cyrus argv=/cyrus/bin/deliver -e -m ${extension} ${user} # # ==================================================================== # # See the Postfix UUCP_README file for configuration details. # uucp unix - n n - - pipe flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient) # # Other external delivery methods. # ifmail unix - n n - - pipe flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient) bsmtp unix - n n - - pipe flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipient scalemail-backend unix - n n - 2 pipe flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension} mailman unix - n n - - pipe flags=FR user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py ${nexthop} ${user} dovecot unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/deliver -d ${recipient}

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  • Inside the Concurrent Collections: ConcurrentBag

    - by Simon Cooper
    Unlike the other concurrent collections, ConcurrentBag does not really have a non-concurrent analogy. As stated in the MSDN documentation, ConcurrentBag is optimised for the situation where the same thread is both producing and consuming items from the collection. We'll see how this is the case as we take a closer look. Again, I recommend you have ConcurrentBag open in a decompiler for reference. Thread Statics ConcurrentBag makes heavy use of thread statics - static variables marked with ThreadStaticAttribute. This is a special attribute that instructs the CLR to scope any values assigned to or read from the variable to the executing thread, not globally within the AppDomain. This means that if two different threads assign two different values to the same thread static variable, one value will not overwrite the other, and each thread will see the value they assigned to the variable, separately to any other thread. This is a very useful function that allows for ConcurrentBag's concurrency properties. You can think of a thread static variable: [ThreadStatic] private static int m_Value; as doing the same as: private static Dictionary<Thread, int> m_Values; where the executing thread's identity is used to automatically set and retrieve the corresponding value in the dictionary. In .NET 4, this usage of ThreadStaticAttribute is encapsulated in the ThreadLocal class. Lists of lists ConcurrentBag, at its core, operates as a linked list of linked lists: Each outer list node is an instance of ThreadLocalList, and each inner list node is an instance of Node. Each outer ThreadLocalList is owned by a particular thread, accessible through the thread local m_locals variable: private ThreadLocal<ThreadLocalList<T>> m_locals It is important to note that, although the m_locals variable is thread-local, that only applies to accesses through that variable. The objects referenced by the thread (each instance of the ThreadLocalList object) are normal heap objects that are not specific to any thread. Thinking back to the Dictionary analogy above, if each value stored in the dictionary could be accessed by other means, then any thread could access the value belonging to other threads using that mechanism. Only reads and writes to the variable defined as thread-local are re-routed by the CLR according to the executing thread's identity. So, although m_locals is defined as thread-local, the m_headList, m_nextList and m_tailList variables aren't. This means that any thread can access all the thread local lists in the collection by doing a linear search through the outer linked list defined by these variables. Adding items So, onto the collection operations. First, adding items. This one's pretty simple. If the current thread doesn't already own an instance of ThreadLocalList, then one is created (or, if there are lists owned by threads that have stopped, it takes control of one of those). Then the item is added to the head of that thread's list. That's it. Don't worry, it'll get more complicated when we account for the other operations on the list! Taking & Peeking items This is where it gets tricky. If the current thread's list has items in it, then it peeks or removes the head item (not the tail item) from the local list and returns that. However, if the local list is empty, it has to go and steal another item from another list, belonging to a different thread. It iterates through all the thread local lists in the collection using the m_headList and m_nextList variables until it finds one that has items in it, and it steals one item from that list. Up to this point, the two threads had been operating completely independently. To steal an item from another thread's list, the stealing thread has to do it in such a way as to not step on the owning thread's toes. Recall how adding and removing items both operate on the head of the thread's linked list? That gives us an easy way out - a thread trying to steal items from another thread can pop in round the back of another thread's list using the m_tail variable, and steal an item from the back without the owning thread knowing anything about it. The owning thread can carry on completely independently, unaware that one of its items has been nicked. However, this only works when there are at least 3 items in the list, as that guarantees there will be at least one node between the owning thread performing operations on the list head and the thread stealing items from the tail - there's no chance of the two threads operating on the same node at the same time and causing a race condition. If there's less than three items in the list, then there does need to be some synchronization between the two threads. In this case, the lock on the ThreadLocalList object is used to mediate access to a thread's list when there's the possibility of contention. Thread synchronization In ConcurrentBag, this is done using several mechanisms: Operations performed by the owner thread only take out the lock when there are less than three items in the collection. With three or greater items, there won't be any conflict with a stealing thread operating on the tail of the list. If a lock isn't taken out, the owning thread sets the list's m_currentOp variable to a non-zero value for the duration of the operation. This indicates to all other threads that there is a non-locked operation currently occuring on that list. The stealing thread always takes out the lock, to prevent two threads trying to steal from the same list at the same time. After taking out the lock, the stealing thread spinwaits until m_currentOp has been set to zero before actually performing the steal. This ensures there won't be a conflict with the owning thread when the number of items in the list is on the 2-3 item borderline. If any add or remove operations are started in the meantime, and the list is below 3 items, those operations try to take out the list's lock and are blocked until the stealing thread has finished. This allows a thread to steal an item from another thread's list without corrupting it. What about synchronization in the collection as a whole? Collection synchronization Any thread that operates on the collection's global structure (accessing anything outside the thread local lists) has to take out the collection's global lock - m_globalListsLock. This single lock is sufficient when adding a new thread local list, as the items inside each thread's list are unaffected. However, what about operations (such as Count or ToArray) that need to access every item in the collection? In order to ensure a consistent view, all operations on the collection are stopped while the count or ToArray is performed. This is done by freezing the bag at the start, performing the global operation, and unfreezing at the end: The global lock is taken out, to prevent structural alterations to the collection. m_needSync is set to true. This notifies all the threads that they need to take out their list's lock irregardless of what operation they're doing. All the list locks are taken out in order. This blocks all locking operations on the lists. The freezing thread waits for all current lockless operations to finish by spinwaiting on each m_currentOp field. The global operation can then be performed while the bag is frozen, but no other operations can take place at the same time, as all other threads are blocked on a list's lock. Then, once the global operation has finished, the locks are released, m_needSync is unset, and normal concurrent operation resumes. Concurrent principles That's the essence of how ConcurrentBag operates. Each thread operates independently on its own local list, except when they have to steal items from another list. When stealing, only the stealing thread is forced to take out the lock; the owning thread only has to when there is the possibility of contention. And a global lock controls accesses to the structure of the collection outside the thread lists. Operations affecting the entire collection take out all locks in the collection to freeze the contents at a single point in time. So, what principles can we extract here? Threads operate independently Thread-static variables and ThreadLocal makes this easy. Threads operate entirely concurrently on their own structures; only when they need to grab data from another thread is there any thread contention. Minimised lock-taking Even when two threads need to operate on the same data structures (one thread stealing from another), they do so in such a way such that the probability of actually blocking on a lock is minimised; the owning thread always operates on the head of the list, and the stealing thread always operates on the tail. Management of lockless operations Any operations that don't take out a lock still have a 'hook' to force them to lock when necessary. This allows all operations on the collection to be stopped temporarily while a global snapshot is taken. Hopefully, such operations will be short-lived and infrequent. That's all the concurrent collections covered. I hope you've found it as informative and interesting as I have. Next, I'll be taking a closer look at ThreadLocal, which I came across while analyzing ConcurrentBag. As you'll see, the operation of this class deserves a much closer look.

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