> > Right, except each thread gets its own binding. So it's not necessarily > that you'll get the value of the last binding up the call stack. This will > only be true if you are in the same thread also.
The last binding up in the call stack implies that you are in the same thread, but I think I know what you mean, which brings up the limitation of implementing dynamically scoped vars with ThreadLocal: It would be reasonable to expect that the bindings of dynamic vars propagate to all code inside the same function, even if executed by a different thread. > ThreadLocal is an object, and so is a Clojure Var. > A Clojure var is not only an object, it is a language construct. And when you make it dynamic, you can bind and re-bind it with different values as your functions are invoked within each other. This is something a ThreadLocal can't do, and it makes the dynamic var a different kind of beast, used for different purposes. A dynamic var emulates a local var that you don't need to pass as a parameter to functions down the stack. > In both, you'll probably want to store the instance through a globally > accessible name, like with def in Clojure or a static in Java. You don't > have too, but I don't see the use case for a local reference to the > ThreadLocal or the Var. > Dynamic vars are required to be global in Clojure, because Clojure will check that your symbols have been defined, but they wouldn't need to. ThreadLocals don't need to be global either, you can define them in the smaller scope where they are used. > Then there's the details, like Vars have a default global scope value, > while ThreadLocal has a default init method if you get before a set. > This is not unimportant, and indicates that vars and ThreadLocals are meant for different purposes. A ThreadLocal will guarantee a new, different value for each thread. For Vars, you need to manually do that at thread creation, and it may be tricky for threads that you don't create, if possible. Regression: The reason that I brought up this discussion is that I didn't understand why clojure.tools.logging uses a dynamic var for enforcing the use of a specific *logger-factory*. Does anybody have an explanation for that? Thanks, Ernesto > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
