Changes the set of `default` feature flags to `[]`. By default, only
core traits are included without specifying feature flags. This makes it
easier for users to pick the components they need.
For convenience, a `full` feature flag is included that includes all
components.
Tests are configured to require the `full` feature. Testing individual
feature flags will need to be moved to a separate crate.
Closes#1791
* runtime: cleanup and add config options
This patch finishes the cleanup as part of the transition to Tokio 0.2.
A number of changes were made to take advantage of having all Tokio
types in a single crate. Also, fixes using Tokio types from
`spawn_blocking`.
* Many threads, one resource driver
Previously, in the threaded scheduler, a resource driver (mio::Poll /
timer combo) was created per thread. This was more or less fine, except
it required balancing across the available drivers. When using a
resource driver from **outside** of the thread pool, balancing is
tricky. The change was original done to avoid having a dedicated driver
thread.
Now, instead of creating many resource drivers, a single resource driver
is used. Each scheduler thread will attempt to "lock" the resource
driver before parking on it. If the resource driver is already locked,
the thread uses a condition variable to park. Contention should remain
low as, under load, the scheduler avoids using the drivers.
* Add configuration options to enable I/O / time
New configuration options are added to `runtime::Builder` to allow
enabling I/O and time drivers on a runtime instance basis. This is
useful when wanting to create lightweight runtime instances to execute
compute only tasks.
* Bug fixes
The condition variable parker is updated to the same algorithm used in
`std`. This is motivated by some potential deadlock cases discovered by
`loom`.
The basic scheduler is fixed to fairly schedule tasks. `push_front` was
accidentally used instead of `push_back`.
I/O, time, and spawning now work from within `spawn_blocking` closures.
* Misc cleanup
The threaded scheduler is no longer generic over `P :Park`. Instead, it
is hard coded to a specific parker. Tests, including loom tests, are
updated to use `Runtime` directly. This provides greater coverage.
The `blocking` module is moved back into `runtime` as all usage is
within `runtime` itself.
The I/O driver is made private and moved to `tokio::io::driver`. `Registration` is
moved to `tokio::io::Registration` and `PollEvented` is moved to `tokio::io::PollEvented`.
Additionally, the concurrent slab used by the I/O driver is cleaned up and extracted to
`tokio::util::slab`, allowing it to eventually be used by other types.
Carl Lerche