Re: "concurrency" branch updated

[Ken Raeburn]

> It seems to me that in Emacs there is no need to be able to switch threads
> except when a thread is waiting.  That should make things much simpler.

Simpler, yes, but also more limiting.  Any large computational task needs to be 
written to surrender control now and then, if it might be used in an Emacs 
session that also talks to network servers that may time out and close 
connections if Emacs ignores them for too long.  I’ve had that happen.  Long 
delays waiting on a file system read operation (from NFS server or network 
hiccups) can have a similar effect, though we can probably arrange for some 
file operations to permit switching even if they’re normally quite fast.

I think preemptive thread switching (or real concurrent execution) is a better 
place to wind up, but cooperative thread switching is a good start.

Ken