Because in production stage the singleton are instantiated before the injector is returned where in development stage (default) the singleton (excepted the eager) are lazily instantiated. So in production mode we have (if I'm not wrong) a safety initialization.
Romain. Le mercredi 16 octobre 2013 06:55:38 UTC+2, Sam Berlin a écrit : > > What is it about production mode that makes you think it isn't necessary > (whereas it would be necessary with development mode)? > > sam > On Oct 16, 2013 12:27 AM, "Romain Gilles" <[email protected]<javascript:>> > wrote: > >> Hi all, >> I add a comment >> #19<https://code.google.com/p/google-guice/issues/detail?id=183#c19> on >> this issue since April. I would like to know if it's a stupid comment or >> not. In fact we fall in some case in a deadlock situation with the class >> level lock used by the Singleton scope. And I think in case of production >> stage the lock and event the volatile instance field are not required. For >> me only development mode require this kind of protection and we always >> create our Injector in production stage. >> Does it make sens for you? >> >> Here a code snippet of Singleton Scope (guice 3.0) : >> public static final Scope SINGLETON = new Scope() { >> public <T> Provider<T> scope(final Key<T> key, final Provider<T> >> creator) { >> return new Provider<T>() { >> /* >> * The lazily initialized singleton instance. Once set, this will >> either have type T or will >> * be equal to NULL. >> */ >> private volatile Object instance; >> >> // DCL on a volatile is safe as of Java 5, which we obviously >> require. >> @SuppressWarnings("DoubleCheckedLocking") >> public T get() { >> if (instance == null) { >> /* >> * Use a pretty coarse lock. We don't want to run into >> deadlocks >> * when two threads try to load circularly-dependent objects. >> * Maybe one of these days we will identify independent >> graphs of >> * objects and offer to load them in parallel. >> * >> * This block is re-entrant for circular dependencies. >> */ >> synchronized (InternalInjectorCreator.class) { >> if (instance == null) { >> T provided = creator.get(); >> >> // don't remember proxies; these exist only to serve >> circular dependencies >> if (provided instanceof CircularDependencyProxy) { >> return provided; >> } >> >> Object providedOrSentinel = (provided == null) ? NULL : >> provided; >> if (instance != null && instance != providedOrSentinel) { >> throw new ProvisionException( >> "Provider was reentrant while creating a >> singleton"); >> } >> >> instance = providedOrSentinel; >> } >> } >> } >> >> Object localInstance = instance; >> // This is safe because instance has type T or is equal to NULL >> @SuppressWarnings("unchecked") >> T returnedInstance = (localInstance != NULL) ? (T) >> localInstance : null; >> return returnedInstance; >> } >> >> Regards, >> >> Romain. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "google-guice" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To post to this group, send email to [email protected]<javascript:> >> . >> Visit this group at http://groups.google.com/group/google-guice. >> For more options, visit https://groups.google.com/groups/opt_out. >> > -- You received this message because you are subscribed to the Google Groups "google-guice" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-guice. For more options, visit https://groups.google.com/groups/opt_out.
