runtime: cleanup and add config options (#1807)

* 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.

1 files changed, 2 insertions, 0 deletions

diff --git a/tokio-macros/src/lib.rs b/tokio-macros/src/lib.rs
index 62c8d94b..65c8fdee 100644
--- a/tokio-macros/src/lib.rs
+++ b/tokio-macros/src/lib.rs
@@ -110,6 +110,7 @@ pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
             fn #name(#inputs) #ret {
                 tokio::runtime::Builder::new()
                     .basic_scheduler()
+                    .enable_all()
                     .build()
                     .unwrap()
                     .block_on(async { #body })
@@ -211,6 +212,7 @@ pub fn test(args: TokenStream, item: TokenStream) -> TokenStream {
             fn #name() #ret {
                 tokio::runtime::Builder::new()
                     .basic_scheduler()
+                    .enable_all()
                     .build()
                     .unwrap()
                     .block_on(async { #body })