Revamp TaskBuilder API

This patch consolidates and cleans up the task spawning APIs:

* Removes the problematic `future_result` method from `std::task::TaskBuilder`,
  and adds a `try_future` that both spawns the task and returns a future
  representing its eventual result (or failure).

* Removes the public `opts` field from `TaskBuilder`, instead adding appropriate
  builder methods to configure the task.

* Adds extension traits to libgreen and libnative that add methods to
  `TaskBuilder` for spawning the task as a green or native thread.

Previously, there was no way to benefit from the `TaskBuilder` functionality and
also set the scheduler to spawn within.

With this change, all task spawning scenarios are supported through the
`TaskBuilder` interface.

Closes #3725.

[breaking-change]

2 files changed, 41 insertions, 3 deletions

diff --git a/src/libnative/lib.rs b/src/libnative/lib.rs
index f04dfac80cc..40b99c5bbdb 100644
--- a/src/libnative/lib.rs
+++ b/src/libnative/lib.rs
@@ -32,10 +32,13 @@
 //! ```rust
 //! extern crate native;
 //!
+//! use std::task::TaskBuilder;
+//! use native::NativeTaskBuilder;
+//!
 //! fn main() {
 //!     // We're not sure whether this main function is run in 1:1 or M:N mode.
 //!
-//!     native::task::spawn(proc() {
+//!     TaskBuilder::new().native().spawn(proc() {
 //!         // this code is guaranteed to be run on a native thread
 //!     });
 //! }
@@ -50,7 +53,8 @@
        html_root_url = "http://doc.rust-lang.org/")]
 #![deny(unused_result, unused_must_use)]
 #![allow(non_camel_case_types)]
-#![feature(macro_rules)]
+#![allow(deprecated)]
+#![feature(default_type_params)]
 
 // NB this crate explicitly does *not* allow glob imports, please seriously
 //    consider whether they're needed before adding that feature here (the
@@ -65,6 +69,8 @@ use std::os;
 use std::rt;
 use std::str;
 
+pub use task::NativeTaskBuilder;
+
 pub mod io;
 pub mod task;
 
diff --git a/src/libnative/task.rs b/src/libnative/task.rs
index b073c2c7fbf..88e581a4791 100644
--- a/src/libnative/task.rs
+++ b/src/libnative/task.rs
@@ -27,6 +27,7 @@ use std::rt;
 
 use io;
 use task;
+use std::task::{TaskBuilder, Spawner};
 
 /// Creates a new Task which is ready to execute as a 1:1 task.
 pub fn new(stack_bounds: (uint, uint)) -> Box<Task> {
@@ -48,12 +49,14 @@ fn ops() -> Box<Ops> {
 }
 
 /// Spawns a function with the default configuration
+#[deprecated = "use the native method of NativeTaskBuilder instead"]
 pub fn spawn(f: proc():Send) {
     spawn_opts(TaskOpts { name: None, stack_size: None, on_exit: None }, f)
 }
 
 /// Spawns a new task given the configuration options and a procedure to run
 /// inside the task.
+#[deprecated = "use the native method of NativeTaskBuilder instead"]
 pub fn spawn_opts(opts: TaskOpts, f: proc():Send) {
     let TaskOpts { name, stack_size, on_exit } = opts;
 
@@ -95,6 +98,26 @@ pub fn spawn_opts(opts: TaskOpts, f: proc():Send) {
     })
 }
 
+/// A spawner for native tasks
+pub struct NativeSpawner;
+
+impl Spawner for NativeSpawner {
+    fn spawn(self, opts: TaskOpts, f: proc():Send) {
+        spawn_opts(opts, f)
+    }
+}
+
+/// An extension trait adding a `native` configuration method to `TaskBuilder`.
+pub trait NativeTaskBuilder {
+    fn native(self) -> TaskBuilder<NativeSpawner>;
+}
+
+impl<S: Spawner> NativeTaskBuilder for TaskBuilder<S> {
+    fn native(self) -> TaskBuilder<NativeSpawner> {
+        self.spawner(NativeSpawner)
+    }
+}
+
 // This structure is the glue between channels and the 1:1 scheduling mode. This
 // structure is allocated once per task.
 struct Ops {
@@ -259,7 +282,8 @@ mod tests {
     use std::rt::local::Local;
     use std::rt::task::{Task, TaskOpts};
     use std::task;
-    use super::{spawn, spawn_opts, Ops};
+    use std::task::TaskBuilder;
+    use super::{spawn, spawn_opts, Ops, NativeTaskBuilder};
 
     #[test]
     fn smoke() {
@@ -347,4 +371,12 @@ mod tests {
         });
         rx.recv();
     }
+
+    #[test]
+    fn test_native_builder() {
+        let res = TaskBuilder::new().native().try(proc() {
+            "Success!".to_string()
+        });
+        assert_eq!(res.ok().unwrap(), "Success!".to_string());
+    }
 }