task safe linked list?

task safe linked list?

[Tom Moran]

Is there a good way to use Protected Types to make a task safe linked
list?  I'd like to add/remove things on a dynamice set of lists with a
protected object to ensure serialized access to the links.  But where
could the protected object go?  Not in any one node because
insert/remove is a three-node operation.  Not in any one list root
because these lists are not rooted, but are linked groups, ie, objects
a,b,c are linked together as are d and e and I might add f to a,b,c or
to d,e, or remove b from the former and add it to the latter.  It
appears I must use a single global lock on "any fiddling with any
links in any list'.  Any other suggestions? 

Re: task safe linked list?

[Geert Bosch]

Tom Moran <tmoran@bix.com> wrote:
   Is there a good way to use Protected Types to make a task safe linked
   list?  I'd like to add/remove things on a dynamice set of lists with a
   protected object to ensure serialized access to the links.  But where
   could the protected object go?  Not in any one node because
   insert/remove is a three-node operation.  Not in any one list root
   because these lists are not rooted, but are linked groups, ie, objects
   a,b,c are linked together as are d and e and I might add f to a,b,c or
   to d,e, or remove b from the former and add it to the latter.  It
   appears I must use a single global lock on "any fiddling with any
   links in any list'.  Any other suggestions? 

I would use a List_Manager protected type with all necessary tree operations.
Then you just call Some_Manager.Insert (New_Node, List) for example.

It is a good idea to make the Node_Type a limited private type and 
put it in a generic package with the List_Manager, so you can be 
sure the list is only accessed through the List_Manager. 

Then you can use multiple instantiations of the package to create
lists that can be accessed concurrently. Since a new instantiation
will create a new node type, you cannot accidently mix nodes.

Have fun!

   Geert