- Use `Handle::default` over `Handle::current` for consistent semantics
- Make all `windows::Event` constructors lazily invoke `global_init`
so they can be safely constructed off-task
- Don't assume the reactor is alive and event registration will be done
when calling `global_init`
Add windows regression tests. Unfortunately, Windows doesn't have a
reliable way of programmatically sending CTRL_C or CTRL_BREAK events
to a progress, so the tests can only exercise our internal machinery by
invoking the handler that we register with the OS
Fixes#999
* Minimize allocation needed for channels
* Use a newtype for signal ids
* We can just cast the raw pointer to a `usize` and still perform a
simple identity check, without incurring any implications of storing a
raw pointer (e.g. previously Signal was !Sync and had an unsafe impl of
Send, and now it is naturally Sync+Send)
* Broadcast with `try_send` instead of `start_send`
The `Stream::start_send` method uses backpressure and schedules the
current task to be notified whenever the channel has additional room,
which means we'll generate a lot of unnecessary wakeups whenever a
channel gets full
By changing to `try_send` and handling any errors, we ensure the
Driver's task won't get woken up when a Signal finally consumes its
notification, since we're coalescing things anyway
Ivan Petkov