On Fri, Jan 9, 2009 at 11:31 AM, Leslie P. Polzer
> it should be enough to lock a hash table shared between
> multiple threads when a write is in progress.
In practice this is currently true, yes, but this is not in any way
guaranteed: implementation details may change, and that can mean that
concurrent reads are future-proof safe.
> Using a mutex however would make readers block each
> other, too.
> How can I block only when a write is in progress?
You need to roll a read-write lock. (Yes, it would be nice for SBCL to