On Tue, 11 Dec 2007, Linus Torvalds wrote:

quoted text
> That said, I suspect there are a few things fighting you:
> 
>  - threading is hard. I haven't looked a lot at the changes Nico did to do 
>    a threaded object packer, but what I've seen does not convince me it is 
>    correct. The "trg_entry" accesses are *mostly* protected with 
>    "cache_lock", but nothing else really seems to be, so quite frankly, I 
>    wouldn't trust the threaded version very much. It's off by default, and 
>    for a good reason, I think.

I beg to differ (of course, since I always know precisely what I do, and 
like you, my code never has bugs).

Seriously though, the trg_entry has not to be protected at all.  Why? 
Simply because each thread has its own exclusive set of objects which no 
other threads ever mess with.  They never overlap.

quoted text
>    For example: the packing code does this:
> 
> 	if (!src->data) {
> 		read_lock();
> 		src->data = read_sha1_file(src_entry->idx.sha1, &type, &sz);
> 		read_unlock();
> 		...
> 
>    and that's racy. If two threads come in at roughly the same time and 
>    see a NULL src->data, they