Re: local vs global object IDs

[Ludovic Courtès]

Hi,

On Tue, Jun 03, 2003 at 02:39:55PM +0200, Marcus Brinkmann wrote:
> Note that this would also eliminate the problem of reusing object ids while
> there are still tasks referring to it.  Instead the local ID entry for that
> task and object can be set to denote a dead name.  In fact, using local IDs
> would mean that we make one step in direction of the Mach IPC system
> conceptually.  Coupled with clever memory management this can potentially
> lead to a situation where all costs associated with a task's references to
> objects, except the object itself (which might be shared anyway), are
> directly attributed to the task.

Note that global IDs may cause troubles if they are used within a
persistent task as we discussed it some time ago [1].  Also, a Fluke
paper [2] addresses the issue of using local references vs. global
references (see section 3.1.3, "Relativity of References").  Basically,
it states that checkpointing global references such as thread IDs in L3
(and the same goes for L4) is bad since these references may become
invalid upon restart, whereas persistance of local references *can* be
guaranteed.

Hope this is relevant,
Ludovic.

[1] http://mail.gnu.org/archive/html/l4-hurd/2003-01/msg00002.html
[2] "Microkernels Meet Recursive Virtual Machines",
    http://www.cs.utah.edu/flux/papers/fluke-rvm-abs.html