I have an application that models events as objects. They are frequently allocated and deallocated. It occurred to me that this class might be a canidate for a custom allocator that allocates objects from a simple pool.
I found this article (from 2010) https://www.mikeash.com/pyblog/friday-qa-2010-12-17-custom-object-allocators-in-objective-c.html that describes my situation. - objects allocated and deallocated on same thread - not subclassed - direct subclass of NSObject The gist of it is to override allocWithZone: to retrieve objects from a 'cache' (it could be pre-allocated, in my application). There is a line that sets the ISA Pointer of the new object to the class. I looked through the source code to NSObject.m and libobjc2/runtime.c and it looks like his idea doesn't violate any assumptions. But I've been wondering a couple of things about this in the context of ARC and a 64-bit implementation. + (id)allocWithZone: (NSZone *)zone { id obj = GetObjectFromCache(); if(obj) *(Class *)obj = self; // set the ISA pointer to the CLASS else obj = [super allocWithZone: zone]; return obj; } 1. Is the assignment of the ISA pointer (the first slot in the object) to the CLASS still valid in 2018? With 64-bit pointers I think some bits are used for refcounts and other things. Maybe this assignment isn't safe. This article https://sectionfive.net/blog/2015/03/31/arc-in-depth-part-i/ says that with "tagged pointers" you need to use a function object_setClass(). Is that the right thing for libobjc2 and GNUstep. 2. Will this work with ARC? It seems like keeping reference counts of references to instances is independent of alloc/dealloc of objects, so it shouldn't matter. Thanks for any information or pointers! -Tom _______________________________________________ Discuss-gnustep mailing list Discuss-gnustep@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnustep
