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Search found 274 results on 11 pages for 'mutex'.

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• ReaderWriterLockSlim and Pulse/Wait

  - by Jono

  Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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• Equvalent c++0x program withought using boost threads..

  - by Eternal Learner

  I have the below simple program using boost threads, what would be the changes needed to do the same in c++0X #include<iostream> #include<boost/thread/thread.hpp> boost::mutex mutex; struct count { count(int i): id(i){} void operator()() { boost::mutex::scoped_lock lk(mutex); for(int i = 0 ; i < 10000 ; i++) { std::cout<<"Thread "<<id<<"has been called "<<i<<" Times"<<std::endl; } } private: int id; }; int main() { boost::thread thr1(count(1)); boost::thread thr2(count(2)); boost::thread thr3(count(3)); thr1.join(); thr2.join(); thr3.join(); return 0; }

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• Lua operations, that works in mutitheaded environment

  - by SBKarr

  My application uses Lua in multithreaded environment with global mutex. It implemented like this: Thread locks mutex, Call lua_newthread Perform some initialization on coroutine Run lua_resume on coroutine Unlocks mutex lua_lock/unlock is not implemented, GC is stopped, when lua works with coroutine. My question is, can I perform steps 2 and 3 without locking, if initialisation process does not requires any global Lua structs? Can i perform all this process without locking at all, if coroutine does not requires globals too? In what case I generally can use Lua functions without locking?

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• Simple Communication between 2 instances of application

  - by KyleGobel

  I have a WPF application that can take a few optional command line arguments. This application is also a single instance application (using a mutex to close any instances if one is already open). What I want for it to do though, is if something tries to open the application with some cmd line args, that the application will do what it's suppose to do with those (in my application it opens different dialogs based on the cmd line). What is the easiest way to achieve this? In psedo code here is what i'm looking for protected override void OnStartup(StartupEventArgs e) { bool mutexIsNew; using (System.Threading.Mutex m = new System.Threading.Mutex(true, "MyApplication", out mutexIsNew)) { //if this is not the first instance of the app if (!mutexIsNew) { //if there is some cmd line args if (e.Args.Length > 0) { //send the args to the older instance so it can handle them SendToOtherInstance(e.Args); //shutdown this new instance Application.Current.Shutdown(); } } } base.OnStartup(e); }

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• Virtual host is not working in Ubuntu 14 VPS using XAMPP 1.8.3

  - by viral4ever

  I am using XAMPP as server in ubuntu 14.04 VPS of digitalocean. I tried to setup virtual hosts. But it is not working and I am getting 403 error of access denied. I changed files too. My files with changes are /opt/lampp/etc/httpd.conf # # This is the main Apache HTTP server configuration file. It contains the # configuration directives that give the server its instructions. # See <URL:http://httpd.apache.org/docs/trunk/> for detailed information. # In particular, see # <URL:http://httpd.apache.org/docs/trunk/mod/directives.html> # for a discussion of each configuration directive. # # Do NOT simply read the instructions in here without understanding # what they do. They're here only as hints or reminders. If you are unsure # consult the online docs. You have been warned. # # Configuration and logfile names: If the filenames you specify for many # of the server's control files begin with "/" (or "drive:/" for Win32), the # server will use that explicit path. If the filenames do *not* begin # with "/", the value of ServerRoot is prepended -- so 'log/access_log' # with ServerRoot set to '/www' will be interpreted by the # server as '/www/log/access_log', where as '/log/access_log' will be # interpreted as '/log/access_log'. # # ServerRoot: The top of the directory tree under which the server's # configuration, error, and log files are kept. # # Do not add a slash at the end of the directory path. If you point # ServerRoot at a non-local disk, be sure to specify a local disk on the # Mutex directive, if file-based mutexes are used. If you wish to share the # same ServerRoot for multiple httpd daemons, you will need to change at # least PidFile. # ServerRoot "/opt/lampp" # # Mutex: Allows you to set the mutex mechanism and mutex file directory # for individual mutexes, or change the global defaults # # Uncomment and change the directory if mutexes are file-based and the default # mutex file directory is not on a local disk or is not appropriate for some # other reason. # # Mutex default:logs # # Listen: Allows you to bind Apache to specific IP addresses and/or # ports, instead of the default. See also the <VirtualHost> # directive. # # Change this to Listen on specific IP addresses as shown below to # prevent Apache from glomming onto all bound IP addresses. # #Listen 12.34.56.78:80 Listen 80 # # Dynamic Shared Object (DSO) Support # # To be able to use the functionality of a module which was built as a DSO you # have to place corresponding `LoadModule' lines at this location so the # directives contained in it are actually available _before_ they are used. # Statically compiled modules (those listed by `httpd -l') do not need # to be loaded here. # # Example: # LoadModule foo_module modules/mod_foo.so # LoadModule authn_file_module modules/mod_authn_file.so LoadModule authn_dbm_module modules/mod_authn_dbm.so LoadModule authn_anon_module modules/mod_authn_anon.so LoadModule authn_dbd_module modules/mod_authn_dbd.so LoadModule authn_socache_module modules/mod_authn_socache.so LoadModule authn_core_module modules/mod_authn_core.so LoadModule authz_host_module modules/mod_authz_host.so LoadModule authz_groupfile_module modules/mod_authz_groupfile.so LoadModule authz_user_module modules/mod_authz_user.so LoadModule authz_dbm_module modules/mod_authz_dbm.so LoadModule authz_owner_module modules/mod_authz_owner.so LoadModule authz_dbd_module modules/mod_authz_dbd.so LoadModule authz_core_module modules/mod_authz_core.so LoadModule authnz_ldap_module modules/mod_authnz_ldap.so LoadModule access_compat_module modules/mod_access_compat.so LoadModule auth_basic_module modules/mod_auth_basic.so LoadModule auth_form_module modules/mod_auth_form.so LoadModule auth_digest_module modules/mod_auth_digest.so LoadModule allowmethods_module modules/mod_allowmethods.so LoadModule file_cache_module modules/mod_file_cache.so LoadModule cache_module modules/mod_cache.so LoadModule cache_disk_module modules/mod_cache_disk.so LoadModule socache_shmcb_module modules/mod_socache_shmcb.so LoadModule socache_dbm_module modules/mod_socache_dbm.so LoadModule socache_memcache_module modules/mod_socache_memcache.so LoadModule dbd_module modules/mod_dbd.so LoadModule bucketeer_module modules/mod_bucketeer.so LoadModule dumpio_module modules/mod_dumpio.so LoadModule echo_module modules/mod_echo.so LoadModule case_filter_module modules/mod_case_filter.so LoadModule case_filter_in_module modules/mod_case_filter_in.so LoadModule buffer_module modules/mod_buffer.so LoadModule ratelimit_module modules/mod_ratelimit.so LoadModule reqtimeout_module modules/mod_reqtimeout.so LoadModule ext_filter_module modules/mod_ext_filter.so LoadModule request_module modules/mod_request.so LoadModule include_module modules/mod_include.so LoadModule filter_module modules/mod_filter.so LoadModule substitute_module modules/mod_substitute.so LoadModule sed_module modules/mod_sed.so LoadModule charset_lite_module modules/mod_charset_lite.so LoadModule deflate_module modules/mod_deflate.so LoadModule mime_module modules/mod_mime.so LoadModule ldap_module modules/mod_ldap.so LoadModule log_config_module modules/mod_log_config.so LoadModule log_debug_module modules/mod_log_debug.so LoadModule logio_module modules/mod_logio.so LoadModule env_module modules/mod_env.so LoadModule mime_magic_module modules/mod_mime_magic.so LoadModule cern_meta_module modules/mod_cern_meta.so LoadModule expires_module modules/mod_expires.so LoadModule headers_module modules/mod_headers.so LoadModule usertrack_module modules/mod_usertrack.so LoadModule unique_id_module modules/mod_unique_id.so LoadModule setenvif_module modules/mod_setenvif.so LoadModule version_module modules/mod_version.so LoadModule remoteip_module modules/mod_remoteip.so LoadModule proxy_module modules/mod_proxy.so LoadModule proxy_connect_module modules/mod_proxy_connect.so LoadModule proxy_ftp_module modules/mod_proxy_ftp.so LoadModule proxy_http_module modules/mod_proxy_http.so LoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so LoadModule proxy_scgi_module modules/mod_proxy_scgi.so LoadModule proxy_ajp_module modules/mod_proxy_ajp.so LoadModule proxy_balancer_module modules/mod_proxy_balancer.so LoadModule proxy_express_module modules/mod_proxy_express.so LoadModule session_module modules/mod_session.so LoadModule session_cookie_module modules/mod_session_cookie.so LoadModule session_dbd_module modules/mod_session_dbd.so LoadModule slotmem_shm_module modules/mod_slotmem_shm.so LoadModule ssl_module modules/mod_ssl.so LoadModule lbmethod_byrequests_module modules/mod_lbmethod_byrequests.so LoadModule lbmethod_bytraffic_module modules/mod_lbmethod_bytraffic.so LoadModule lbmethod_bybusyness_module modules/mod_lbmethod_bybusyness.so LoadModule lbmethod_heartbeat_module modules/mod_lbmethod_heartbeat.so LoadModule unixd_module modules/mod_unixd.so LoadModule dav_module modules/mod_dav.so LoadModule status_module modules/mod_status.so LoadModule autoindex_module modules/mod_autoindex.so LoadModule info_module modules/mod_info.so LoadModule suexec_module modules/mod_suexec.so LoadModule cgi_module modules/mod_cgi.so LoadModule cgid_module modules/mod_cgid.so LoadModule dav_fs_module modules/mod_dav_fs.so LoadModule vhost_alias_module modules/mod_vhost_alias.so LoadModule negotiation_module modules/mod_negotiation.so LoadModule dir_module modules/mod_dir.so LoadModule actions_module modules/mod_actions.so LoadModule speling_module modules/mod_speling.so LoadModule userdir_module modules/mod_userdir.so LoadModule alias_module modules/mod_alias.so LoadModule rewrite_module modules/mod_rewrite.so <IfDefine JUSTTOMAKEAPXSHAPPY> LoadModule php4_module modules/libphp4.so LoadModule php5_module modules/libphp5.so </IfDefine> <IfModule unixd_module> # # If you wish httpd to run as a different user or group, you must run # httpd as root initially and it will switch. # # User/Group: The name (or #number) of the user/group to run httpd as. # It is usually good practice to create a dedicated user and group for # running httpd, as with most system services. # User root Group www </IfModule> # 'Main' server configuration # # The directives in this section set up the values used by the 'main' # server, which responds to any requests that aren't handled by a # <VirtualHost> definition. These values also provide defaults for # any <VirtualHost> containers you may define later in the file. # # All of these directives may appear inside <VirtualHost> containers, # in which case these default settings will be overridden for the # virtual host being defined. # # # ServerAdmin: Your address, where problems with the server should be # e-mailed. This address appears on some server-generated pages, such # as error documents. e.g. [email protected] # ServerAdmin [email protected] # # ServerName gives the name and port that the server uses to identify itself. # This can often be determined automatically, but we recommend you specify # it explicitly to prevent problems during startup. # # If your host doesn't have a registered DNS name, enter its IP address here. # #ServerName www.example.com:@@Port@@ # XAMPP ServerName localhost # # Deny access to the entirety of your server's filesystem. You must # explicitly permit access to web content directories in other # <Directory> blocks below. # <Directory /> AllowOverride none Require all denied </Directory> # # Note that from this point forward you must specifically allow # particular features to be enabled - so if something's not working as # you might expect, make sure that you have specifically enabled it # below. # # # DocumentRoot: The directory out of which you will serve your # documents. By default, all requests are taken from this directory, but # symbolic links and aliases may be used to point to other locations. # DocumentRoot "/opt/lampp/htdocs" <Directory "/opt/lampp/htdocs"> # # Possible values for the Options directive are "None", "All", # or any combination of: # Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews # # Note that "MultiViews" must be named *explicitly* --- "Options All" # doesn't give it to you. # # The Options directive is both complicated and important. Please see # http://httpd.apache.org/docs/trunk/mod/core.html#options # for more information. # #Options Indexes FollowSymLinks # XAMPP Options Indexes FollowSymLinks ExecCGI Includes # # AllowOverride controls what directives may be placed in .htaccess files. # It can be "All", "None", or any combination of the keywords: # Options FileInfo AuthConfig Limit # #AllowOverride None # since XAMPP 1.4: AllowOverride All # # Controls who can get stuff from this server. # Require all granted </Directory> # # DirectoryIndex: sets the file that Apache will serve if a directory # is requested. # <IfModule dir_module> #DirectoryIndex index.html # XAMPP DirectoryIndex index.html index.html.var index.php index.php3 index.php4 </IfModule> # # The following lines prevent .htaccess and .htpasswd files from being # viewed by Web clients. # <Files ".ht*"> Require all denied </Files> # # ErrorLog: The location of the error log file. # If you do not specify an ErrorLog directive within a <VirtualHost> # container, error messages relating to that virtual host will be # logged here. If you *do* define an error logfile for a <VirtualHost> # container, that host's errors will be logged there and not here. # ErrorLog "logs/error_log" # # LogLevel: Control the number of messages logged to the error_log. # Possible values include: debug, info, notice, warn, error, crit, # alert, emerg. # LogLevel warn <IfModule log_config_module> # # The following directives define some format nicknames for use with # a CustomLog directive (see below). # LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined LogFormat "%h %l %u %t \"%r\" %>s %b" common <IfModule logio_module> # You need to enable mod_logio.c to use %I and %O LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" %I %O" combinedio </IfModule> # # The location and format of the access logfile (Common Logfile Format). # If you do not define any access logfiles within a <VirtualHost> # container, they will be logged here. Contrariwise, if you *do* # define per-<VirtualHost> access logfiles, transactions will be # logged therein and *not* in this file. # CustomLog "logs/access_log" common # # If you prefer a logfile with access, agent, and referer information # (Combined Logfile Format) you can use the following directive. # #CustomLog "logs/access_log" combined </IfModule> <IfModule alias_module> # # Redirect: Allows you to tell clients about documents that used to # exist in your server's namespace, but do not anymore. The client # will make a new request for the document at its new location. # Example: # Redirect permanent /foo http://www.example.com/bar # # Alias: Maps web paths into filesystem paths and is used to # access content that does not live under the DocumentRoot. # Example: # Alias /webpath /full/filesystem/path # # If you include a trailing / on /webpath then the server will # require it to be present in the URL. You will also likely # need to provide a <Directory> section to allow access to # the filesystem path. # # ScriptAlias: This controls which directories contain server scripts. # ScriptAliases are essentially the same as Aliases, except that # documents in the target directory are treated as applications and # run by the server when requested rather than as documents sent to the # client. The same rules about trailing "/" apply to ScriptAlias # directives as to Alias. # ScriptAlias /cgi-bin/ "/opt/lampp/cgi-bin/" </IfModule> <IfModule cgid_module> # # ScriptSock: On threaded servers, designate the path to the UNIX # socket used to communicate with the CGI daemon of mod_cgid. # #Scriptsock logs/cgisock </IfModule> # # "/opt/lampp/cgi-bin" should be changed to whatever your ScriptAliased # CGI directory exists, if you have that configured. # <Directory "/opt/lampp/cgi-bin"> AllowOverride None Options None Require all granted </Directory> <IfModule mime_module> # # TypesConfig points to the file containing the list of mappings from # filename extension to MIME-type. # TypesConfig etc/mime.types # # AddType allows you to add to or override the MIME configuration # file specified in TypesConfig for specific file types. # #AddType application/x-gzip .tgz # # AddEncoding allows you to have certain browsers uncompress # information on the fly. Note: Not all browsers support this. # #AddEncoding x-compress .Z #AddEncoding x-gzip .gz .tgz # # If the AddEncoding directives above are commented-out, then you # probably should define those extensions to indicate media types: # AddType application/x-compress .Z AddType application/x-gzip .gz .tgz # # AddHandler allows you to map certain file extensions to "handlers": # actions unrelated to filetype. These can be either built into the server # or added with the Action directive (see below) # # To use CGI scripts outside of ScriptAliased directories: # (You will also need to add "ExecCGI" to the "Options" directive.) # #AddHandler cgi-script .cgi # XAMPP, since LAMPP 0.9.8: AddHandler cgi-script .cgi .pl # For type maps (negotiated resources): #AddHandler type-map var # # Filters allow you to process content before it is sent to the client. # # To parse .shtml files for server-side includes (SSI): # (You will also need to add "Includes" to the "Options" directive.) # # XAMPP AddType text/html .shtml AddOutputFilter INCLUDES .shtml </IfModule> # # The mod_mime_magic module allows the server to use various hints from the # contents of the file itself to determine its type. The MIMEMagicFile # directive tells the module where the hint definitions are located. # #MIMEMagicFile etc/magic # # Customizable error responses come in three flavors: # 1) plain text 2) local redirects 3) external redirects # # Some examples: #ErrorDocument 500 "The server made a boo boo." #ErrorDocument 404 /missing.html #ErrorDocument 404 "/cgi-bin/missing_handler.pl" #ErrorDocument 402 http://www.example.com/subscription_info.html # # # MaxRanges: Maximum number of Ranges in a request before # returning the entire resource, or one of the special # values 'default', 'none' or 'unlimited'. # Default setting is to accept 200 Ranges. #MaxRanges unlimited # # EnableMMAP and EnableSendfile: On systems that support it, # memory-mapping or the sendfile syscall may be used to deliver # files. This usually improves server performance, but must # be turned off when serving from networked-mounted # filesystems or if support for these functions is otherwise # broken on your system. # Defaults: EnableMMAP On, EnableSendfile Off # EnableMMAP off EnableSendfile off # Supplemental configuration # # The configuration files in the etc/extra/ directory can be # included to add extra features or to modify the default configuration of # the server, or you may simply copy their contents here and change as # necessary. # Server-pool management (MPM specific) #Include etc/extra/httpd-mpm.conf # Multi-language error messages Include etc/extra/httpd-multilang-errordoc.conf # Fancy directory listings Include etc/extra/httpd-autoindex.conf # Language settings #Include etc/extra/httpd-languages.conf # User home directories #Include etc/extra/httpd-userdir.conf # Real-time info on requests and configuration #Include etc/extra/httpd-info.conf # Virtual hosts Include etc/extra/httpd-vhosts.conf # Local access to the Apache HTTP Server Manual #Include etc/extra/httpd-manual.conf # Distributed authoring and versioning (WebDAV) #Include etc/extra/httpd-dav.conf # Various default settings Include etc/extra/httpd-default.conf # Configure mod_proxy_html to understand HTML4/XHTML1 <IfModule proxy_html_module> Include etc/extra/proxy-html.conf </IfModule> # Secure (SSL/TLS) connections <IfModule ssl_module> # XAMPP <IfDefine SSL> Include etc/extra/httpd-ssl.conf </IfDefine> </IfModule> # # Note: The following must must be present to support # starting without SSL on platforms with no /dev/random equivalent # but a statically compiled-in mod_ssl. # <IfModule ssl_module> SSLRandomSeed startup builtin SSLRandomSeed connect builtin </IfModule> # XAMPP Include etc/extra/httpd-xampp.conf Include "/opt/lampp/apache2/conf/httpd.conf" I used command shown in this example. I used below lines to change and add group Add group "groupadd www" Add user to group "usermod -aG www root" Change htdocs group "chgrp -R www /opt/lampp/htdocs" Change sitedir group "chgrp -R www /opt/lampp/htdocs/mysite" Change htdocs chmod "chmod 2775 /opt/lampp/htdocs" Change sitedir chmod "chmod 2775 /opt/lampp/htdocs/mysite" And then I changed my vhosts.conf file # Virtual Hosts # # Required modules: mod_log_config # If you want to maintain multiple domains/hostnames on your # machine you can setup VirtualHost containers for them. Most configurations # use only name-based virtual hosts so the server doesn't need to worry about # IP addresses. This is indicated by the asterisks in the directives below. # # Please see the documentation at # <URL:http://httpd.apache.org/docs/2.4/vhosts/> # for further details before you try to setup virtual hosts. # # You may use the command line option '-S' to verify your virtual host # configuration. # # VirtualHost example: # Almost any Apache directive may go into a VirtualHost container. # The first VirtualHost section is used for all requests that do not # match a ServerName or ServerAlias in any <VirtualHost> block. # <VirtualHost *:80> ServerAdmin [email protected] DocumentRoot "/opt/lampp/docs/dummy-host.example.com" ServerName dummy-host.example.com ServerAlias www.dummy-host.example.com ErrorLog "logs/dummy-host.example.com-error_log" CustomLog "logs/dummy-host.example.com-access_log" common </VirtualHost> <VirtualHost *:80> ServerAdmin [email protected] DocumentRoot "/opt/lampp/docs/dummy-host2.example.com" ServerName dummy-host2.example.com ErrorLog "logs/dummy-host2.example.com-error_log" CustomLog "logs/dummy-host2.example.com-access_log" common </VirtualHost> NameVirtualHost * <VirtualHost *> ServerAdmin [email protected] DocumentRoot "/opt/lampp/htdocs/mysite" ServerName mysite.com ServerAlias mysite.com ErrorLog "/opt/lampp/htdocs/mysite/errorlogs" CustomLog "/opt/lampp/htdocs/mysite/customlog" common <Directory "/opt/lampp/htdocs/mysite"> Options Indexes FollowSymLinks Includes ExecCGI AllowOverride All Order Allow,Deny Allow from all Require all granted </Directory> </VirtualHost> but still its not working and I am getting 403 error on my ip and domain however I can access phpmyadmin. If anyone can help me, please help me.

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• Run the Windows .net Application in System Tray on System Startup

  - by Rajneesh Verma

  Hi, Today i have created a .net windows application which has following key points. 1. Run only one instance of the project: to achieve this i have change the code of Program.cs as: Code Snippet static class Program { /// <summary> /// The main entry point for the application. /// </summary> [ STAThread ] static void Main() { bool instanceCountOne = false ; using ( Mutex mtex = new Mutex ( true , "MyRunningApp" , out instanceCountOne)) { if (instanceCountOne) { Application ...(read more)

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• Processes to attach Windows Service to IDE and get control in onstart Event

  In this article we will see how to integrate IDE by using the .net built-in mutex logic using System.Diagnostics class.

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• Processes to attach Windows Service to IDE and get control in onstart Event

  In this article we will see how to integrate IDE by using the .net built-in mutex logic using System.Diagnostics class.

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• Using boost locks for RAII access to a semaphore

  - by dan

  Suppose I write a C++ semaphore class with an interface that models the boost Lockable concept (i.e. lock(); unlock(); try_lock(); etc.). Is it safe/recommended to use boost locks for RAII access to such an object? In other words, do boost locks (and/or other related parts of the boost thread library) assume that the Lockable concept will only be modeled by mutex-like objects which are locked and unlocked from the same thread? My guess is that it should be OK to use a semaphore as a model for Lockable. I've browsed through some of the boost source and it "seems" OK. The locks don't appear to store explicit references to this_thread or anything like that. Moreover, the Lockable concept doesn't have any function like whichThreadOwnsMe(). It also looks like I should even be able to pass a boost::unique_lock<MySemaphore> reference to boost::condition_variable_any::wait. However, the documentation is not explicitly clear about the requirements. To illustrate what I mean, consider a bare-bones binary semaphore class along these lines: class MySemaphore{ bool locked; boost::mutex mx; boost::condition_variable cv; public: void lock(){ boost::unique_lock<boost::mutex> lck(mx); while(locked) cv.wait(lck); locked=true; } void unlock(){ { boost::lock_guard<boost::mutex> lck(mx); if(!locked) error(); locked=false; } cv.notify_one(); } // bool try_lock(); void error(); etc. } Now suppose that somewhere, either on an object or globally, I have MySemaphore sem; I want to lock and unlock it using RAII. Also I want to be able to "pass" ownership of the lock from one thread to another. For example, in one thread I execute void doTask() { boost::unique_lock<MySemaphore> lock(sem); doSomeWorkWithSharedObject(); signalToSecondThread(); waitForSignalAck(); lock.release(); } While another thread is executing something like { waitForSignalFromFirstThread(); ackSignal(); boost::unique_lock<MySemaphore>(sem,boost::adopt_lock_t()); doMoreWorkWithSameSharedObject(); } The reason I am doing this is that I don't want anyone else to be able to get the lock on sem in between the time that the first thread executes doSomeWorkWithSharedObject() and the time the second executes doMoreWorkWithSameSharedObject(). Basically, I'm splitting one task into two parts. And the reason I'm splitting the task up is because (1) I want the first part of the task to get started as soon as possible, (2) I want to guarantee that the first part is complete before doTask() returns, and (3) I want the second, more time-consuming part of the task to be completed by another thread, possibly chosen from a pool of slave threads that are waiting around to finish tasks that have been started by master threads. NOTE: I recently posted this same question (sort of) here http://stackoverflow.com/questions/2754884/unlocking-a-mutex-from-a-different-thread-c but I confused mutexes with semaphores, and so the question about using boost locks didn't really get addressed.

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• Apache 2.4, Ubuntu 12.04 Forbidden Errors

  - by tubaguy50035

  I just installed Apache 2.4 today, and I'm having some issues getting vhost configuration to work correctly. Below is the vhost conf <VirtualHost *:80> ServerAdmin [email protected] DocumentRoot /hosting/Client/site.com/www ServerName site.com ServerAlias www.site.com <Directory "/hosting/Client/site.com/www"> Options +Indexes +FollowSymLinks Order allow,deny Allow from all </Directory> DirectoryIndex index.html </VirtualHost> There is an index.html file in /hosting/Client/site.com/www. When I go to the site, I receive a 403 forbidden error. The www-data group is the group on the www folder, which I've already given all permissions (r/w/x). I'm really at a loss as to why this is happening. Any thoughts? If I remove the vhost and go straight to the IP address, I get the default, "It works!" page. So I know that it's working. The error log says "client denied by server configuration". apache2ctl -S dump: nick@server:~$ apache2ctl -S /usr/sbin/apache2ctl: 87: ulimit: error setting limit (Operation not permitted) VirtualHost configuration: *:80 is a NameVirtualHost default server site.com (/etc/apache2/sites-enabled/site.com.conf:1) port 80 namevhost site.com (/etc/apache2/sites-enabled/site.com.conf:1) alias www.site.com port 80 namevhost site.com (/etc/apache2/sites-enabled/site.com.conf:1) alias www.site.com ServerRoot: "/etc/apache2" Main DocumentRoot: "/var/www" Main ErrorLog: "/var/log/apache2/error.log" Mutex watchdog-callback: using_defaults Mutex default: dir="/var/lock/apache2" mechanism=fcntl Mutex mpm-accept: using_defaults PidFile: "/var/run/apache2.pid" Define: DUMP_VHOSTS Define: DUMP_RUN_CFG Define: ENALBLE_USR_LIB_CGI_BIN User: name="www-data" id=33 not_used Group: name="www-data" id=33 not_used Ouput of namei -mo /hosting/Client/site/www/index.html f: /hosting/Client/site.com/www/index.html drwxr-xr-x root root / drwxr-xr-x root root hosting drwxr-xr-x root root Client drwxr-xr-x nick www-data site.com drwxr-xr-x nick www-data www -rw-rwxr-x nick www-data index.html

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• Storing objects in the array

  - by Ockonal

  Hello, I want to save boost signals objects in the map (association: signal name ? signal object). The signals signature is different, so the second type of map should be boost::any. map<string, any> mSignalAssociation; The question is how to store objects without defining type of new signal signature? typedef boost::signals2::signal<void (int KeyCode)> sigKeyPressed; mSignalAssociation.insert(make_pair("KeyPressed", sigKeyPressed())); // This is what I need: passing object without type definition mSignalAssociation["KeyPressed"] = (typename boost::signals2::signal<void (int KeyCode)>()); // One more trying which won't work. And I don't want use this sigKeyPressed mKeyPressed; mSignalAssociation["KeyPressed"] = mKeyPressed; All this tryings throw the error: /usr/include/boost/noncopyable.hpp: In copy constructor ‘boost::signals2::signal_base::signal_base(const boost::signals2::signal_base&)’: In file included from /usr/include/boost/signals2/detail/signals_common.hpp:17:0, /usr/include/boost/noncopyable.hpp:27:7: error: ‘boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)’ is private /usr/include/boost/signals2/signal_base.hpp:22:5: error: within this context ---------- /usr/include/boost/signals2/detail/signal_template.hpp: In copy constructor ‘boost::signals2::signal1<void, int&, boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void(int)>, boost::function<void(const boost::signals2::connection&, int)>, boost::signals2::mutex>::signal1(const boost::signals2::signal1<void, int, boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void(int)>, boost::function<void(const boost::signals2::connection&, int)>, boost::signals2::mutex>&)’: In file included from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52:0, /usr/include/boost/signals2/detail/signal_template.hpp:578:5: note: synthesized method ‘boost::signals2::signal_base::signal_base(const boost::signals2::signal_base&)’ first required here from /usr/include/boost/signals2.hpp:16, --------- /usr/include/boost/signals2/preprocessed_signal.hpp: In copy constructor ‘boost::signals2::signal<void(int)>::signal(const boost::signals2::signal<void(int)>&)’: In file included from /usr/include/boost/signals2/signal.hpp:36:0, /usr/include/boost/signals2/preprocessed_signal.hpp:42:5: note: synthesized method ‘boost::signals2::signal1<void, int, boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void(int)>, boost::function<void(const boost::signals2::connection&, int)>, boost::signals2::mutex>::signal1(const boost::signals2::signal1<void, int, boost::signals2::optional_last_value<void>, int, std::less<int>, boost::function<void(int)>, boost::function<void(const boost::signals2::connection&, int)>, boost::signals2::mutex>&)’ first required here from /home/ockonal/Workspace/Projects/Pseudoform-2/include/Core/Systems.hpp:6,

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• multi thread in c question

  - by REALFREE

  Does mutex guarantee to execute thread in order of arriving? that is, if, thread 2 and thread 3 arrive is waiting while thread 1 is in critical section what exactly happen after thread 1 exit critical section if thread 2 arrive at mutex lock before thread 3, thread 2 will be allowed to enter critical section before thread 3 ? or race condition will be occurred?

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• How to achieve syncronization in loadbalanced multiserver environment

  - by Anoop

  Hi, I have to create a .net web application which would run on more than one front end server which are load balanced. Now I have to use some third party api which is not thread safe so only one thread should call the API at a time so I have to some use syncronization machanism like lock or mutex which provide syncronisation within the process and across the process in machine.Now will lock or mutex work in loadbalanced multiserver environment correctly? If not then is there any mechanism using which I can syncronise all the threads in all the machines??

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• ACE_Mutex::acquire problem

  - by O. Askari

  Hi, I have a mutex in my class with the following definition: ACE_Mutex m_specsMutex; When i use the acquire() method that takes no parameters everything works just fine. But when i use it with a time value (as follows) it just immediately returns with -1 value. I'm sure that this mutex hasn't been acquired anywhere else so it shouldn't return -1. m_specsMutex.acquire(ACE_OS::gettimeofday() + ACE_Time_Value(30)) Am i doing anything wrong?

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• Fairness: Where can it be better handled?

  - by Srinivas Nayak

  Hi, I would like to share one of my practical experience with multiprogramming here. Yesterday I had written a multiprogram. Modifications to sharable resources were put under critical sections protected by P(mutex) and V(mutex) and those critical section code were put in a common library. The library will be used by concurrent applications (of my own). I had three applications that will use the common code from library and do their stuff independently. my library --------- work_on_shared_resource { P(mutex) get_shared_resource work_with_it V(mutex) } --------- my application ----------- application1 { *[ work_on_shared_resource do_something_else_non_ctitical ] } application2 { *[ work_on_shared_resource do_something_else_non_ctitical ] } application3 { *[ work_on_shared_resource ] } *[...] denote a loop. ------------ I had to run the applications on Linux OS. I had a thought in my mind, hanging over years, that, OS shall schedule all the processes running under him with all fairness. In other words, it will give all the processes, their pie of resource-usage equally well. When first two applications were put to work, they run perfectly well without deadlock. But when the third application started running, always the third one got the resources, but since it is not doing anything in its non-critical region, it gets the shared resource more often when other tasks are doing something else. So the other two applications were found almost totally halted. When the third application got terminated forcefully, the previous two applications resumed their work as before. I think, this is a case of starvation, first two applications had to starve. Now how can we ensure fairness? Now I started believing that OS scheduler is innocent and blind. It depends upon who won the race; he got the largest pie of CPU and resource. Shall we attempt to ensure fairness of resource users in the critical-section code in library? Or shall we leave it up to the applications to ensure fairness by being liberal, not greedy? To my knowledge, adding code to ensure fairness to the common library shall be an overwhelming task. On the other hand, believing on the applications will also never ensure 100% fairness. The application which does a very little task after working with shared resources shall win the race where as the application which does heavy processing after their work with shared resources shall always starve. What is the best practice in this case? Where we ensure fairness and how? Sincerely, Srinivas Nayak

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• Java threads not working correctly with linkedlist

  - by user69514

  Hi I am working on the sleeping barber problem. with the addition of having priority customer when they arrive they go in the front of the line and they are the next ones to get a haircut. I'm using a linkedlist and if I see a priority customer I put him in the beginning of the list, if the customer is not priority he goes to the end of the list. then I call the wantHaircut method getting the first element of the list. my problem is that the customer are being processed in the order they arrive, and the priority customer have to wait. here is the code where it all happens. any ideas what I am doing wrong? thanks public void arrivedBarbershop(Customer c){ if(waiting < numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - SITTING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting >= numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - STANDING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting < numChairs && !c.isPriority()){ waiting++; System.out.println("Customer " + c.getID() + ": arrived, sitting in the waiting room"); customer_list.addLast(c); customers.up(); // increment waiting customers } else if(waiting >= numChairs && !c.isPriority()) { System.out.println("Customer " + c.getID() + ": went to another barber because waiting room was full - " + waiting + " waiting"); mutex.up(); } if(!customer_list.isEmpty()){ this.wantHairCut(customer_list.removeFirst()); } } public void wantHairCut(Customer c) { mutex.up(); barber.down(); // waits for being allowed in barber chair System.out.println("Customer " + c.getID() + ": getting haircut"); try { /** haircut takes between 1 and 2 seconds **/ Thread.sleep(Barbershop.randomInt(1, 2) * 1000); } catch (InterruptedException e) { } System.out.println("Barber: finished cutting customer " + c.getID() + "'s hair"); c.gotHaircut = true; cutting.up(); // signals cutting has finished /** customer must pay now **/ this.wantToCashout(c); }

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• Boost thread synchronization in release build

  - by Joseph16

  Hi, when I try to run the following code in debug and release mode in VS2005. Each time I see different output in console and It doesn't seem like the multithreading is achieved in release mode. 1. #include <boost/thread.hpp> 2. #include <iostream> 3. 4. void wait(int seconds) 5. { 6. boost::this_thread::sleep(boost::posix_time::seconds(seconds)); 7. } 8. 9. boost::mutex mutex; 10. 11. void thread() 12. { 13. for (int i = 0; i < 5; ++i) 14. { 15. //wait(1); 16. mutex.lock(); 17. std::cout << "Thread " << boost::this_thread::get_id() << ": " << i << std::endl; 18. mutex.unlock(); 19. } 20. } 21. 22. int main() 23. { 24. boost::thread t1(thread); 25. boost::thread t2(thread); 26. t1.join(); 27. t2.join(); 28. } Debug Mode Thread 00153E60: 0 Thread 00153E90: 0 Thread 00153E60: 1 Thread 00153E90: 1 Thread 00153E90: 2 Thread 00153E60: 2 Thread 00153E90: 3 Thread 00153E60: 3 Thread 00153E60: 4 Thread 00153E90: 4 Press any key to continue . . . Release Mode Thread 00153D28: 0 Thread 00153D28: 1 Thread 00153D28: 2 Thread 00153D28: 3 Thread 00153D28: 4 Thread 00153D58: 0 Thread 00153D58: 1 Thread 00153D58: 2 Thread 00153D58: 3 Thread 00153D58: 4 Press any key to continue . . .

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• WDS 2008 R2 DHCP Error

  - by scampbell

  Im having a problem where I get the error 'An error occurred while obtaining an IP address from the DHCP server. Please check to ensure that there is an operational DHCP server on this network segment' when booting from a standard WDS boot.wim image taken from a Windows 7 DVD. I am using Server 2008 R2 and am adding the drivers to the boot using WDS, but also have the problem if the drivers are injected beforehand using DISM. When the error occurs I can shift + F10 and IPCONFIG and see it HAS picked up an internal IP from DHCP. Seems maybe it is timing out before it gets the IP? DHCP server is not on the WDS box but is in the same subnet. As per some fixes I have read I enabled RSTP on my switches but that didnt help. I have included the end of setupact.log to see if any of you have any ideas. Seems to be failing but as I say, the network IS initialized as I can see the internal IP assigned by DHCP when running IPCONFIG. I dont suppose theres any way of increasing the timeout? Thanks. 2011-04-11 17:26:31, Info [0x0b0022] WDS StartNetworking: Trying to start networking. 2011-04-11 17:26:31, Info WDS Network service dhcp not running or could not be queried: 264d00 1 1 2011-04-11 17:26:31, Info WDS Network service lmhosts not running or could not be queried: 264e18 1 1 2011-04-11 17:26:31, Info WDS Network service lanmanworkstation not running or could not be queried: 264d00 1 1 2011-04-11 17:26:31, Info WDS Network service bfe not running or could not be queried: 264e18 1 1 2011-04-11 17:26:31, Info WDS Network service ikeext not running or could not be queried: 264d00 1 1 2011-04-11 17:26:31, Info WDS Network service mpssvc not running or could not be queried: 264e18 1 1 2011-04-11 17:27:24, Info WDS Installing device pci\ven_14e4&dev_1691&subsys_04aa1028 X:\WINDOWS\INF\oem37.inf succeeded 2011-04-11 17:27:25, Info WDS No computer name specified, generating a random name. 2011-04-11 17:27:25, Info WDS Renaming computer to MININT-VN2P876. 2011-04-11 17:27:25, Info WDS Acquired profiling mutex 2011-04-11 17:27:25, Info WDS Service winmgmt disable: 0x00000000 2011-04-11 17:27:25, Info WDS Service winmgmt stop: 0x00000000 2011-04-11 17:27:25, Info WDS Service winmgmt enable: 0x00000000 2011-04-11 17:27:25, Info WDS Released profiling mutex 2011-04-11 17:27:25, Info WDS Acquired profiling mutex 2011-04-11 17:27:25, Info WDS Install MS_MSCLIENT: 0x0004a020 2011-04-11 17:27:25, Info WDS Install MS_NETBIOS: 0x0004a020 2011-04-11 17:27:25, Info WDS Install MS_SMB: 0x0004a020 2011-04-11 17:27:25, Info WDS Install MS_TCPIP6: 0x0004a020 2011-04-11 17:27:26, Info WDS Install MS_TCPIP: 0x0004a020 2011-04-11 17:27:26, Info WDS Service dhcp start: 0x00000000 2011-04-11 17:27:26, Info WDS Service lmhosts start: 0x00000000 2011-04-11 17:27:26, Info WDS Service ikeext start: 0x00000000 2011-04-11 17:27:26, Info WDS Service mpssvc start: 0x00000000 2011-04-11 17:27:26, Info WDS Released profiling mutex 2011-04-11 17:27:26, Info WDS Spent 967ms installing network components 2011-04-11 17:27:28, Info WDS Spent 2247ms installing network drivers 2011-04-11 17:27:38, Info WDS QueryAdapterStatus: no operational adapters found. 2011-04-11 17:27:38, Info WDS Spent 10140ms confirming network initialization; status 0x80004005 2011-04-11 17:27:38, Info WDS WaitForNetworkToInitialize failed; ignoring error 2011-04-11 17:27:38, Info WDS GetNetworkingInfo: WpeNetworkStatus returned [0x0]. Flags set: 2011-04-11 17:27:38, Error [0x0b003f] WDS StartNetworking: Failed to start networking. Error code [0x800704C6].[gle=0x000000cb] 2011-04-11 17:27:38, Info [0x0640ae] IBSLIB PublishMessage: Publishing message [WdsClient: An error occurred while obtaining an IP address from the DHCP server. Please check to ensure that there is an operational DHCP server on this network segment.]

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• C# 4: The Curious ConcurrentDictionary

  - by James Michael Hare

  In my previous post (here) I did a comparison of the new ConcurrentQueue versus the old standard of a System.Collections.Generic Queue with simple locking.  The results were exactly what I would have hoped, that the ConcurrentQueue was faster with multi-threading for most all situations.  In addition, concurrent collections have the added benefit that you can enumerate them even if they're being modified. So I set out to see what the improvements would be for the ConcurrentDictionary, would it have the same performance benefits as the ConcurrentQueue did?  Well, after running some tests and multiple tweaks and tunes, I have good and bad news. But first, let's look at the tests.  Obviously there's many things we can do with a dictionary.  One of the most notable uses, of course, in a multi-threaded environment is for a small, local in-memory cache.  So I set about to do a very simple simulation of a cache where I would create a test class that I'll just call an Accessor.  This accessor will attempt to look up a key in the dictionary, and if the key exists, it stops (i.e. a cache "hit").  However, if the lookup fails, it will then try to add the key and value to the dictionary (i.e. a cache "miss").  So here's the Accessor that will run the tests: 1: internal class Accessor 2: { 3: public int Hits { get; set; } 4: public int Misses { get; set; } 5: public Func<int, string> GetDelegate { get; set; } 6: public Action<int, string> AddDelegate { get; set; } 7: public int Iterations { get; set; } 8: public int MaxRange { get; set; } 9: public int Seed { get; set; } 10:  11: public void Access() 12: { 13: var randomGenerator = new Random(Seed); 14:  15: for (int i=0; i<Iterations; i++) 16: { 17: // give a wide spread so will have some duplicates and some unique 18: var target = randomGenerator.Next(1, MaxRange); 19:  20: // attempt to grab the item from the cache 21: var result = GetDelegate(target); 22:  23: // if the item doesn't exist, add it 24: if(result == null) 25: { 26: AddDelegate(target, target.ToString()); 27: Misses++; 28: } 29: else 30: { 31: Hits++; 32: } 33: } 34: } 35: } Note that so I could test different implementations, I defined a GetDelegate and AddDelegate that will call the appropriate dictionary methods to add or retrieve items in the cache using various techniques. So let's examine the three techniques I decided to test: Dictionary with mutex - Just your standard generic Dictionary with a simple lock construct on an internal object. Dictionary with ReaderWriterLockSlim - Same Dictionary, but now using a lock designed to let multiple readers access simultaneously and then locked when a writer needs access. ConcurrentDictionary - The new ConcurrentDictionary from System.Collections.Concurrent that is supposed to be optimized to allow multiple threads to access safely. So the approach to each of these is also fairly straight-forward.  Let's look at the GetDelegate and AddDelegate implementations for the Dictionary with mutex lock: 1: var addDelegate = (key,val) => 2: { 3: lock (_mutex) 4: { 5: _dictionary[key] = val; 6: } 7: }; 8: var getDelegate = (key) => 9: { 10: lock (_mutex) 11: { 12: string val; 13: return _dictionary.TryGetValue(key, out val) ? val : null; 14: } 15: }; Nothing new or fancy here, just your basic lock on a private object and then query/insert into the Dictionary. Now, for the Dictionary with ReadWriteLockSlim it's a little more complex: 1: var addDelegate = (key,val) => 2: { 3: _readerWriterLock.EnterWriteLock(); 4: _dictionary[key] = val; 5: _readerWriterLock.ExitWriteLock(); 6: }; 7: var getDelegate = (key) => 8: { 9: string val; 10: _readerWriterLock.EnterReadLock(); 11: if(!_dictionary.TryGetValue(key, out val)) 12: { 13: val = null; 14: } 15: _readerWriterLock.ExitReadLock(); 16: return val; 17: }; And finally, the ConcurrentDictionary, which since it does all it's own concurrency control, is remarkably elegant and simple: 1: var addDelegate = (key,val) => 2: { 3: _concurrentDictionary[key] = val; 4: }; 5: var getDelegate = (key) => 6: { 7: string s; 8: return _concurrentDictionary.TryGetValue(key, out s) ? s : null; 9: };                    Then, I set up a test harness that would simply ask the user for the number of concurrent Accessors to attempt to Access the cache (as specified in Accessor.Access() above) and then let them fly and see how long it took them all to complete.  Each of these tests was run with 10,000,000 cache accesses divided among the available Accessor instances.  All times are in milliseconds. 1: Dictionary with Mutex Locking 2: --------------------------------------------------- 3: Accessors Mostly Misses Mostly Hits 4: 1 7916 3285 5: 10 8293 3481 6: 100 8799 3532 7: 1000 8815 3584 8:  9:  10: Dictionary with ReaderWriterLockSlim Locking 11: --------------------------------------------------- 12: Accessors Mostly Misses Mostly Hits 13: 1 8445 3624 14: 10 11002 4119 15: 100 11076 3992 16: 1000 14794 4861 17:  18:  19: Concurrent Dictionary 20: --------------------------------------------------- 21: Accessors Mostly Misses Mostly Hits 22: 1 17443 3726 23: 10 14181 1897 24: 100 15141 1994 25: 1000 17209 2128 The first test I did across the board is the Mostly Misses category.  The mostly misses (more adds because data requested was not in the dictionary) shows an interesting trend.  In both cases the Dictionary with the simple mutex lock is much faster, and the ConcurrentDictionary is the slowest solution.  But this got me thinking, and a little research seemed to confirm it, maybe the ConcurrentDictionary is more optimized to concurrent "gets" than "adds".  So since the ratio of misses to hits were 2 to 1, I decided to reverse that and see the results. So I tweaked the data so that the number of keys were much smaller than the number of iterations to give me about a 2 to 1 ration of hits to misses (twice as likely to already find the item in the cache than to need to add it).  And yes, indeed here we see that the ConcurrentDictionary is indeed faster than the standard Dictionary here.  I have a strong feeling that as the ration of hits-to-misses gets higher and higher these number gets even better as well.  This makes sense since the ConcurrentDictionary is read-optimized. Also note that I tried the tests with capacity and concurrency hints on the ConcurrentDictionary but saw very little improvement, I think this is largely because on the 10,000,000 hit test it quickly ramped up to the correct capacity and concurrency and thus the impact was limited to the first few milliseconds of the run. So what does this tell us?  Well, as in all things, ConcurrentDictionary is not a panacea.  It won't solve all your woes and it shouldn't be the only Dictionary you ever use.  So when should we use each? Use System.Collections.Generic.Dictionary when: You need a single-threaded Dictionary (no locking needed). You need a multi-threaded Dictionary that is loaded only once at creation and never modified (no locking needed). You need a multi-threaded Dictionary to store items where writes are far more prevalent than reads (locking needed). And use System.Collections.Concurrent.ConcurrentDictionary when: You need a multi-threaded Dictionary where the writes are far more prevalent than reads. You need to be able to iterate over the collection without locking it even if its being modified. Both Dictionaries have their strong suits, I have a feeling this is just one where you need to know from design what you hope to use it for and make your decision based on that criteria.

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• Thread implemented as a Singleton

  - by rocknroll

  Hi all, I have a commercial application made with C,C++/Qt on Linux platform. The app collects data from different sensors and displays them on GUI. Each of the protocol for interfacing with sensors is implemented using singleton pattern and threads from Qt QThreads class. All the protocols except one work fine. Each protocol's run function for thread has following structure: void <ProtocolClassName>::run() { while(!mStop) //check whether screen is closed or not { mutex.lock() while(!waitcondition.wait(&mutex,5)) { if(mStop) return; } //Code for receiving and processing incoming data mutex.unlock(); } //end while } Hierarchy of GUI. 1.Login screen. 2. Screen of action. When a user logs in from login screen, we enter the action screen where all data is displayed and all the thread's for different sensors start. They wait on mStop variable in idle time and when data arrives they jump to receiving and processing data. Incoming data for the problem protocol is 117 bytes. In the main GUI threads there are timers which when timeout, grab the running instance of protocol using <ProtocolName>::instance() function Check the update variable of singleton class if its true and display the data. When the data display is done they reset the update variable in singleton class to false. The problematic protocol has the update time of 1 sec, which is also the frame rate of protocol. When I comment out the display function it runs fine. But when display is activated the application hangs consistently after 6-7 hours. I have asked this question on many forums but haven't received any worthwhile suggestions. I Hope that here I will get some help. Also, I have read a lot of literature on Singleton, multithreading, and found that people always discourage the use of singletons especially in C++. But in my application I can think of no other design for implementation. Thanks in advance A Hapless programmer

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• efficient thread-safe singleton in C++

  - by user168715

  The usual pattern for a singleton class is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) inst = new Foo(...); return *inst; } However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread. One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like static Foo &getInst() { static Foo *inst = NULL; if(inst == NULL) { pthread_mutex_lock(&mutex); if(inst == NULL) inst = new Foo(...); pthread_mutex_unlock(&mutex); } return *inst; } Is this the right way to do it, or are there any pitfalls I should be aware of? For instance, are there any static initialization order problems that might occur, i.e. is inst always guaranteed to be NULL the first time getInst is called?

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• How to synchronize access to many objects

  - by vividos

  I have a thread pool with some threads (e.g. as many as number of cores) that work on many objects, say thousands of objects. Normally I would give each object a mutex to protect access to its internals, lock it when I'm doing work, then release it. When two threads would try to access the same object, one of the threads has to wait. Now I want to save some resources and be scalable, as there may be thousands of objects, and still only a hand full of threads. I'm thinking about a class design where the thread has some sort of mutex or lock object, and assigns the lock to the object when the object should be accessed. This would save resources, as I only have as much lock objects as I have threads. Now comes the programming part, where I want to transfer this design into code, but don't know quite where to start. I'm programming in C++ and want to use Boost classes where possible, but self written classes that handle these special requirements are ok. How would I implement this? My first idea was to have a boost::mutex object per thread, and each object has a boost::shared_ptr that initially is unset (or NULL). Now when I want to access the object, I lock it by creating a scoped_lock object and assign it to the shared_ptr. When the shared_ptr is already set, I wait on the present lock. This idea sounds like a heap full of race conditions, so I sort of abandoned it. Is there another way to accomplish this design? A completely different way?

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• OpenGL multiple threads, variable handling [closed]

  - by toeplitz

  I have written an OpenGL program which runs in the following way: Main: - Initialize SDL - Create thread which has the OpenGL context: - Renderloop - Set camera (view) matrix with glUniform. - glDrawElements() .... etc. - Swapbuffers(); - Main SDL loop handling input events and such. - Update camera matrix of type glm::mat4. This is how I pass my camera object to the class that handles opengl. Camera *cam = new Camera(); gl.setCam(cam); where void setCam(Camera *camera) { this->camera = camera; } For rendering in the opengl context thread, this happens: glm::mat4 modelView = camera->view * model; glUniformMatrix4fv(shader->bindUniform("modelView"), 1, GL_FALSE, glm::value_ptr(modelView)); In the main program where my SDL and other things are handles I then recompute the view matrix. This his working fine without me using any mutex locks. Is this correct? On the other hand, I add objects to my scene by an "upload queue" and in this case I have to mutex lock my upload queue vector (vector class type) when adding items to it or else the program crashes. In summary: I recompute my matrix in a different thread and then use it in the opengl thread without any mutex lock. Why is this working? Edit: I think my question is similar to what was asked here: Should I lock a variable in one thread if I only need it's value in other threads, and why does it work if I don't?, only in my case it is even more simple with only one matrix being changed.

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• Error in loading component property (Swing GUI Forms)

  - by Christo Du Preez

  For no apparent reason all my Swing GUI forms using components linked to org.jdesktop.beansbinding.Converter started generating errors when trying to open the Design View: Error Error in loading component property: [JPanel]-filterTextField-converter. Cannot load property type class org.jdesktop.beansbinding.Converter. The property cannot be loaded. Errors occurred in loading... I'm currently using Netbeans 6.8. I opened my project in Netbeans 6.7.1 and all was fine but after a while the same thing happened. Looking at the .form and .java files and comparing it to previous backups, everything looks fine. Even my Netbeans tutorial project no longer works. What can cause this. Any suggestions would greatly be appreciated. After further investigation this is taken from my IDE's log : INFO: msg org.openide.ErrorManager$AnnException: msg at org.openide.ErrorManager$AnnException.findOrCreate(ErrorManager.java:867) at org.openide.ErrorManager$DelegatingErrorManager.annotate(ErrorManager.java:650) at org.netbeans.modules.form.GandalfPersistenceManager.annotateException(GandalfPersistenceManager.java:230) at org.netbeans.modules.form.GandalfPersistenceManager.annotateException(GandalfPersistenceManager.java:240) at org.netbeans.modules.form.GandalfPersistenceManager.getPropertyType(GandalfPersistenceManager.java:2362) at org.netbeans.modules.form.GandalfPersistenceManager.loadProperty(GandalfPersistenceManager.java:2041) at org.netbeans.modules.form.GandalfPersistenceManager.loadBindingProperties(GandalfPersistenceManager.java:2627) at org.netbeans.modules.form.GandalfPersistenceManager.loadComponent(GandalfPersistenceManager.java:900) at org.netbeans.modules.form.GandalfPersistenceManager.restoreComponent(GandalfPersistenceManager.java:845) at org.netbeans.modules.form.GandalfPersistenceManager.loadComponent(GandalfPersistenceManager.java:979) at org.netbeans.modules.form.GandalfPersistenceManager.restoreComponent(GandalfPersistenceManager.java:845) at org.netbeans.modules.form.GandalfPersistenceManager.loadNonVisuals(GandalfPersistenceManager.java:695) at org.netbeans.modules.form.GandalfPersistenceManager.loadForm(GandalfPersistenceManager.java:529) at org.netbeans.modules.form.GandalfPersistenceManager.loadForm(GandalfPersistenceManager.java:290) at org.netbeans.modules.form.FormEditor$3.run(FormEditor.java:339) at org.netbeans.modules.form.FormLAF$2.run(FormLAF.java:287) at org.openide.util.Mutex.doEventAccess(Mutex.java:1355) at org.openide.util.Mutex.readAccess(Mutex.java:317) at org.netbeans.modules.form.FormLAF.executeWithLookAndFeel(FormLAF.java:272) at org.netbeans.modules.form.FormEditor.loadFormData(FormEditor.java:337) at org.netbeans.modules.form.FormEditor.loadForm(FormEditor.java:266) at org.netbeans.modules.form.FormEditorSupport.loadForm(FormEditorSupport.java:306) at org.netbeans.modules.form.FormEditorSupport$3.run(FormEditorSupport.java:457) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209) at java.awt.EventQueue.dispatchEvent(EventQueue.java:597) at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:125) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) Caused by: java.lang.ClassNotFoundException: Will not load class org.jdesktop.beansbinding.Converter arbitrarily from one of ModuleCL@738d08[org.jdesktop.beansbinding] and ModuleCL@167e3a5[javax.beans.binding] starting from SystemClassLoader[556 modules]; see http://wiki.netbeans.org/DevFaqModuleCCE at org.netbeans.ProxyClassLoader.loadClass(ProxyClassLoader.java:241) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at org.netbeans.modules.form.project.FormClassLoader.findClass(FormClassLoader.java:83) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:247) at org.netbeans.modules.form.project.ClassPathUtils.loadClass(ClassPathUtils.java:95) at org.netbeans.modules.form.FormUtils.loadClass(FormUtils.java:1445) at org.netbeans.modules.form.PersistenceObjectRegistry.loadClass(PersistenceObjectRegistry.java:95) at org.netbeans.modules.form.GandalfPersistenceManager.getClassFromString(GandalfPersistenceManager.java:5516) at org.netbeans.modules.form.GandalfPersistenceManager.getPropertyType(GandalfPersistenceManager.java:2348) ... 27 more msg Error in loading component property: Other Components-mainPanel-jTextField1-converter Cannot load property type class org.jdesktop.beansbinding.Converter. The property cannot be loaded. Can someone please help me with this issue. This is still not resolved and not being able to edit my Forms or loosing binding properties every time I need to edit a Form is a real pain and time consuming! Any help would greatly be appreciated. Thanx.

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• How to use pthread_atfork() and pthread_once() to reinitialize mutexes in child processes

  - by Blair Zajac

  We have a C++ shared library that uses ZeroC's Ice library for RPC and unless we shut down Ice's runtime, we've observed child processes hanging on random mutexes. The Ice runtime starts threads, has many internal mutexes and keeps open file descriptors to servers. Additionally, we have a few of mutexes of our own to protect our internal state. Our shared library is used by hundreds of internal applications so we don't have control over when the process calls fork(), so we need a way to safely shutdown Ice and lock our mutexes while the process forks. Reading the POSIX standard on pthread_atfork() on handling mutexes and internal state: Alternatively, some libraries might have been able to supply just a child routine that reinitializes the mutexes in the library and all associated states to some known value (for example, what it was when the image was originally executed). This approach is not possible, though, because implementations are allowed to fail *_init() and *_destroy() calls for mutexes and locks if the mutex or lock is still locked. In this case, the child routine is not able to reinitialize the mutexes and locks. On Linux, the this test C program returns EPERM from pthread_mutex_unlock() in the child pthread_atfork() handler. Linux requires adding _NP to the PTHREAD_MUTEX_ERRORCHECK macro for it to compile. This program is linked from this good thread. Given that it's technically not safe or legal to unlock or destroy a mutex in the child, I'm thinking it's better to have pointers to mutexes and then have the child make new pthread_mutex_t on the heap and leave the parent's mutexes alone, thereby having a small memory leak. The only issue is how to reinitialize the state of the library and I'm thinking of reseting a pthread_once_t. Maybe because POSIX has an initializer for pthread_once_t that it can be reset to its initial state. #include <pthread.h> #include <stdlib.h> #include <string.h> static pthread_once_t once_control = PTHREAD_ONCE_INIT; static pthread_mutex_t *mutex_ptr = 0; static void setup_new_mutex() { mutex_ptr = malloc(sizeof(*mutex_ptr)); pthread_mutex_init(mutex_ptr, 0); } static void prepare() { pthread_mutex_lock(mutex_ptr); } static void parent() { pthread_mutex_unlock(mutex_ptr); } static void child() { // Reset the once control. pthread_once_t once = PTHREAD_ONCE_INIT; memcpy(&once_control, &once, sizeof(once_control)); setup_new_mutex(); } static void init() { setup_new_mutex(); pthread_atfork(&prepare, &parent, &child); } int my_library_call(int arg) { pthread_once(&once_control, &init); pthread_mutex_lock(mutex_ptr); // Do something here that requires the lock. int result = 2*arg; pthread_mutex_unlock(mutex_ptr); return result; } In the above sample in the child() I only reset the pthread_once_t by making a copy of a fresh pthread_once_t initialized with PTHREAD_ONCE_INIT. A new pthread_mutex_t is only created when the library function is invoked in the child process. This is hacky but maybe the best way of dealing with this skirting the standards. If the pthread_once_t contains a mutex then the system must have a way of initializing it from its PTHREAD_ONCE_INIT state. If it contains a pointer to a mutex allocated on the heap than it'll be forced to allocate a new one and set the address in the pthread_once_t. I'm hoping it doesn't use the address of the pthread_once_t for anything special which would defeat this. Searching comp.programming.threads group for pthread_atfork() shows a lot of good discussion and how little the POSIX standards really provides to solve this problem. There's also the issue that one should only call async-signal-safe functions from pthread_atfork() handlers, and it appears the most important one is the child handler, where only a memcpy() is done. Does this work? Is there a better way of dealing with the requirements of our shared library?

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