vm: release cached bindings that become unbound.

When a function binding is removed using fmakunbound, virtual
machine descriptions hang on to the previously cached binding
in the ftab. When the symbol is newly bound, virtual machine
descriptions keep pointing to the old function.

To solve this, we put the vm_desc structures into a global
list and provide a function that fmakunbound calls to scrub
all the VM descriptors of that binding.

* eval.c (makunbound, fmakunbound): Call new
vm_invalidate_binding function.

* vm.c (struct vm_desc_links): New structure.
(struct vm_desc): New member lnk, with links.
(vmd_list): New static variable: circular list of all VM
descriptors.
(vm_make_desc): Insert new VM descriptor into list.
(vm_desc_destroy): Remove VM descriptor from list.
(vm_invalidate_binding): New function.

* vm.h (vm_invalidate_binding): Declared.

1 files changed, 1 insertions, 0 deletions

diff --git a/vm.h b/vm.h
index da2fab08..30720d0d 100644
--- a/vm.h
+++ b/vm.h
@@ -31,4 +31,5 @@ val vm_make_desc(val nlevels, val nregs, val bytecode,
                  val datavec, val funvec);
 val vm_execute_toplevel(val desc);
 val vm_execute_closure(val fun, struct args *);
+void vm_invalidate_binding(val sym);
 void vm_init(void);