Re: [v3] default linux allocator

[Dhruv Matani <dhruvbird at gmx dot net>]

On Tue, 2004-07-13 at 23:38, Benjamin Kosnik wrote:
> Yo dudes... this switches this default allocator for linux to
> mt_allocator. I'd like to try this out on mainline, and then possibly
> move this to the gcc-3_4-branch after a review of gcc-testresults.
> 
> Sound like a good idea? Barring objections, I'll do this tomorrow.

No objections, but there is this little thing about the synchronization
that I had mentioned a few months ago, and it seems to have been
forgotten!

On line 470:

	  // Return this block to our list and update counters and
	  // owner id as needed.
	  --__bin._M_used[__block->_M_thread_id]; //THIS LINE.

	  __block->_M_next = __bin._M_first[__thread_id];
	  __bin._M_first[__thread_id] = __block;

The line marked THIS LINE seems to be faulty to me. What I suspect might
happen is that because the access to
__bin._M_used[__block->_M_thread_id] if __block->_M_thread_id !=
__thread_id is that some other thread might be accessing that variable,
so the update will not be an atomic one, and it might lead to data
corruption! So, the suggested way to go would be to use one of the
__atomic_decrement() functions or something to that effect to ensure
data consistency. Also, other places in the allocate will have to update
their variables atomically.




> 
> There also seemed to be interest in making this this default on solaris,
> and perhaps others. I think these can be separate patches.
> 
> -benjamin
-- 
        -Dhruv Matani.
http://www.geocities.com/dhruvbird/

As a rule, man is a fool. When it's hot, he wants it cold. 
When it's cold he wants it hot. He always wants what is not.
	-Anon.