Comment by NeillC

The lock in unfair. We are unfair because you get better performance by not allowing the lock hold time to be extended by context swap. As a result, we always unconditionally release a lock when an exclusive acquire is release or the last shared guy releases. Then we go find people to wake. In this gap the lock can be stollen. The threads that steal all look like exclusive guys. My overall rule of thumb is that in the presence of any exclusive acquires you can never assume a shared acquire is compatible with any other shared acquire. A second shared acquire might wait for the first acquire to exit. We do this for example, so a stream of readers don't starve a writer. This is another case like that but somewhat less obvious. I have no idea if the owners will attempt to fix or take the view that you're trying to assume something we don't guarantee. I'll admit that this is a kind of strange case. You could obviously queue a wait block and the in progress waker will sort this out. Could well get a performance impact from that. I tried to explain this general rule of thumb to you this morning when you contacted me. I could not understand much of what you said.