[Linux-cluster] Some GDLM questions

[Jeff]

Monday, July 5, 2004, 5:31:35 AM, Patrick Caulfield wrote:

> On Sat, Jul 03, 2004 at 10:33:56AM -0400, Jeff wrote:
>> These are from reviewing http://people.redhat.com/~teigland/sca.pdf
>> and the CVS copy of cluster/dlm/doc/libdlm.txt.
>> ------------------------------------------------------------------
>> 
>> If a program requests a lock on the AST side can it wait for
>> the lock to complete without returning from the original AST
>> routine?  Would it use the poll/select mechanism to do this?

> In kernel space you shouldn't wait or do much work in the AST routine or
> you can block the kernel's AST delivery thread. You can call dlm_lock() in an
> AST routine though.

> In userspace you can do pretty much what you like in the AST routine as (by
> default) they run in a seperate thread - see libdlm for more details on this.

Thanks for the answers. One more question about acquiring locks in
the worker thread.

Assuming I'm using pthreads if I want to call dlm_lock() in the worker
thread (AST routine) and I need to wait for that dlm_lock() call to complete
would I call dlm_get_fd() and loop calling dlm_dispatch() until I see that
the lock completes? This involves dlm_dispatch() calling itself
recursively which I assume is going to be ok.

Can you call dlm_pthread_init() more than once to start multiple
service threads? I have some routines which are called
both by the mainline code and as an AST routine. I'm wondering if I
need them to be aware of how they're called or whether they can
always simply open the fd and use dlm_dispatch if they need to
issue a 'blocking' dlm_lock() call.