Subj : membar's for double-linked list /w lock-free reads...
To   : comp.programming.threads
From : Chris Thomasson
Date : Mon May 02 2005 08:22 pm

I have implemented some basic list operations that can be used with 
lock-free reads, but I am not "totally" sure which membars are required. I 
believe all that I need is a store barrier and classic release semantics. 
Something like this:


// push into double list

1. allocate new_node and initialize it.

2. lock list mutex.

3. read list back pointer /w dependant load into lback.

4. point new_node->prev to lback.

5. Make new_node visible by pointing lback->next to new_node /w release 
barrier.

6. point the list back pointer to new_node /w release barrier.

7. unlock list mutex.


I was wondering if that was sufficient. As you can see, step 5 makes 
new_node visible to readers. It seems that the release barrier in step 5 
should ensure that new_node is fully visible before a reader can access it 
with a dependant load barrier. Any thoughts?




Here is the actual code in question:

http://appcore.home.comcast.net/appcore/include/ac_dlist_h.html
( all the memory barriers functions are prefixed with ac_mb_ and are located 
in about the middle of the file )




Thank you for your time.

.