Re: "concurrency" branch updated

[Tom Tromey <tom@tromey.com>]

John> Upgrading to preemptive switching could happen later, once we've
John> had more experience with writing cooperative code. I hope at that
John> point it would be a fairly seamless upgrade, and we'd have mature
John> facilities in place to accommodate it (i.e., the ability to
John> "stack" backtraces, to inspect the environment of inactive
John> threads, a messaging facility between threads to avoid global
John> mutation, etc).

I don't understand what stacking backtraces is.

Messaging is already on the branch; or rather, locks and condition
variables are on the branch, and it's simple to build thread-safe pipes
and queues and whatnot using those.

John> What I want most is to make deadlocks and race conditions
John> naturally hard to write -- if not impossible. The rise of
John> Heisenbugs could make our job as maintainers much more
John> difficult. All the worst bugs in my programming career were
John> related to preemptive threading in some way.

Race-free-ness will not come from this branch.  It takes a traditional
threads-and-locks approach.

Tom