C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Singleton in a multithreaded app          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Jeremy Godfrey Guest Posted: Wed Sep 24, 2003 11:41 am    Post subject: Singleton in a multithreaded app Hi, "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? Jeremy Godfrey [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alexander Terekhov Guest Posted: Wed Sep 24, 2003 10:28 pm    Post subject: Re: Singleton in a multithreaded app Jeremy Godfrey wrote: Quote: Hi, "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. regards, alexander. -- typedef std::aligned_storage<std::mutex> pthread_mutex_t; [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Andrei Alexandrescu (See Guest Posted: Wed Sep 24, 2003 10:42 pm    Post subject: Re: Singleton in a multithreaded app "Jeremy Godfrey" <nospam (AT) nospam (DOT) com> wrote Quote: Hi, "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? A once function is a good way to go. Absent that, you can rely on an atomic integer. Andrei [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Joe Seigh Guest Posted: Thu Sep 25, 2003 9:19 pm    Post subject: Re: Singleton in a multithreaded app Alexander Terekhov wrote: Quote: Jeremy Godfrey wrote: Hi, "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. Statically intialized in C, correct? I assume you can't assume that static inialization of C++ objects will work correctly or that there is even such a thing? Joe Seigh [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top WW Guest Posted: Fri Sep 26, 2003 10:35 am    Post subject: Re: Singleton in a multithreaded app Joe Seigh wrote: Quote: Alexander Terekhov wrote: [SNIP] Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. Statically intialized in C, correct? I assume you can't assume that static inialization of C++ objects will work correctly or that there is even such a thing? "pthread_mutex_t POD" he says and "magic" "PTHREAD_MUTEX_INITIALIZER" he says. AFAIK static initialization of PODs works the same way in C++ as in C. Please correct me if I am wrong. And please do it so by standard quotes. -- WW aka Attila [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alexander Terekhov Guest Posted: Fri Sep 26, 2003 10:37 am    Post subject: Re: Singleton in a multithreaded app Joe Seigh wrote: [...] Quote: Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. Statically intialized in C, correct? I assume you can't assume that static inialization of C++ objects will work correctly or that there is even such a thing? typedef std::aligned_storage<std::mutex> pthread_mutex_t; // POD #define PTHREAD_MUTEX_INITIALIZER { /* magic */ } regards, alexander. P.S. std::pthread_mutex_t * mutex::c_mutex() throw(); -- extern "C" int pthread_mutex_destroy(pthread_mutex_t * m) throw() { m->object().~object(); // "may fail" shall be caught in the std::unexpected() handler return 0; } [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Joe Seigh Guest Posted: Sat Sep 27, 2003 1:47 am    Post subject: Re: Singleton in a multithreaded app WW wrote: Quote: Joe Seigh wrote: Alexander Terekhov wrote: [SNIP] Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. Statically intialized in C, correct? I assume you can't assume that static inialization of C++ objects will work correctly or that there is even such a thing? "pthread_mutex_t POD" he says and "magic" "PTHREAD_MUTEX_INITIALIZER" he says. AFAIK static initialization of PODs works the same way in C++ as in C. Please correct me if I am wrong. And please do it so by standard quotes. Sorry, I don't have a copy of the standard. That's why I was asking the question. In C++, if you had class Something { int x; int y; public: Something() : x(0), y(0) {} }; then static Something z; would initialize the same as doing the following in C struct something_t { int x; int y; }; static struct something_t z = {0, 0}; For thread safety, you want static initialization done before "main" is called when there is supposedly only one thread running. I don't know if POD initializers in C++ ctors have to work that way. It may work in some implementations but since C++ says nothing with respect to threads, you may have to imbed some stuff in C just on general principle. Joe Seigh [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Sat Sep 27, 2003 10:16 am    Post subject: Re: Singleton in a multithreaded app Joe Seigh <jseigh_01 (AT) xemaps (DOT) com> wrote Quote: Alexander Terekhov wrote: Jeremy Godfrey wrote: "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. Statically intialized in C, correct? I assume you can't assume that static inialization of C++ objects will work correctly or that there is even such a thing? Static initialization in C++ works just like it does in C. And pthread_mutex_t is a C struct. C compatibility in C++ is there for a purpose. -- James Kanze GABI Software mailto:kanze (AT) gabi-soft (DOT) fr Conseils en informatique orientée objet/ http://www.gabi-soft.fr Beratung in objektorientierter Datenverarbeitung 11 rue de Rambouillet, 78460 Chevreuse, France, +33 (0)1 30 23 45 16 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Sat Sep 27, 2003 2:45 pm    Post subject: Re: Singleton in a multithreaded app In article <3F742BB7.647F74A4 (AT) xemaps (DOT) com>, Joe Seigh <jseigh_01 (AT) xemaps (DOT) com> writes Quote: Sorry, I don't have a copy of the standard. That's why I was asking the question. In C++, if you had class Something { int x; int y; public: Something() : x(0), y(0) {} }; then static Something z; would initialize the same as doing the following in C struct something_t { int x; int y; }; static struct something_t z = {0, 0}; For thread safety, you want static initialization done before "main" is called when there is supposedly only one thread running. I don't know if POD initializers in C++ ctors have to work that way. They do, but as you provide a ctor something_t will be statically zero initialised (much as for C, and in this case exactly as for C) and dynamically initialised by calling the ctor. The latter, might be optimised away in this case). Quote: It may work in some implementations but since C++ says nothing with respect to threads, you may have to imbed some stuff in C just on general principle. But C says nothing about threads either. Globals must be ctored before their point of first use (and before any function in the same TU is used.) -- Francis Glassborow ACCU If you are not using up-to-date virus protection you should not be reading this. Viruses do not just hurt the infected but the hole community. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Raoul Gough Guest Posted: Mon Sep 29, 2003 9:33 pm    Post subject: Re: Singleton in a multithreaded app Alexander Terekhov <terekhov (AT) web (DOT) de> writes: Quote: Jeremy Godfrey wrote: Hi, "Modern C++ Design" talks about safely creating singletons in a multithreaded app by using a mutex object but seems to overlook how to safely create the mutex object. What thoughts do people have on this? Is boost::call_once() the best way to safely create the mutex in a portable way? Don't use boost::call_once() for that (its sort of "funny" impl and its applicability for other things aside for a moment). You can use pthread_mutex_t POD and the magic of PTHREAD_MUTEX_INITIALIZER to initialize statically allocated mutex. That won't be as portable as boost::call_once, though. Do you think call_once is actually wrong for managing singletons (or even just singleton mutexes)? -- Raoul Gough. (setq dabbrev-case-fold-search nil) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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