Re: thread cancellation, take 2

[Julian Graham]

> I find it more elegant to use closures to that end.  I.e., when
> installing a handler, you'd write something like this:
>
>   (let ((cleanup (thread-cleanup-procedure (current-thread))))
>     (set-thread-cleanup-procedure! (current-thread)
>                                    (lambda ()
>                                      ;; invoke previous handler
>                                      (if (procedure? cleanup)
>                                          (cleanup))
>                                      ;; clean up...
>                                      )))
>
> There's a race here in case multiple threads try to change the cleanup
> procedure associated with that particular thread at the same time, but I
> suppose it is not an issue in practice.

Fair enough, re: closures.  But why should callers outside the current
thread be able to access that thread's cleanup handler procedure?
Maybe this isn't a realistic issue, but you could use this to "inject"
arbitrary code into a separate thread by setting the cleanup procedure
and immediately canceling the thread.  Why not treat the handler as
thread-specific data?