The libunwind library version installed includes an rc number. The
latest released version of the `unwind-sys` crate doesn't handle this
properly, so rely on the latest commit in the upstream repository.
This is the start of the organization of types that are in their own
crates in order to break dependency cycles between other crates. The
idea here is that putting these packages into their own directory is the
first step toward cleaning them up. They have grown organically and it
is difficult to explain to new folks where to put new shared types. Many
of these crates contain more than traits or don't contain traits at all.
Notably, `script_traits` isn't touched because it is vendored from
Gecko. Eventually this will move to `third_party`.
This will ultimately make it simpler to update crate dependencies and
reduce duplicate when specifying requirements. Generally, this change
does not touch dependencies that are only used by a single crate. We
could consider moving them to workspace dependencies in the future.
> However, as it turns out, `crossbeam-channel`'s channels don't drop
> remaining messages until all associated senders *and* receivers are
> dropped. This means the exit signal won't be delivered as long as
> there's at least one `HangMonitorRegister` or
> `BackgroundHangMonitorChan` maintaining a copy of the sender. To work
> around this and guarantee a rapid delivery of the exit signal, the
> sender is wrapped in `Arc`, and only the worker thread maintains a
> strong reference, thus ensuring both the sender and receiver are
> dropped as soon as the worker thread exits.
> There's a race condition between the reception of
> `BackgroundHangMonitorControlMsg::Exit` and `MonitoredComponentMsg::
> Register`. When the worker receives `Exit`, it stops receiving
> messages, and any remaining messages (including the
> `MonitoredComponentMsg::Register` we sent) in the channel are dropped.
> Wrapping `exit_signal` with this RAII wrapper ensures the exit signal
> is delivered even in such cases.
This should (hopefully) eliminate the intermittent hang-ups in the test
case `test_hang_monitoring_exit_signal` for good.
Bound sampler buffer, add length feedback message, fix intermittence in test
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