rt: Implement ThreadPerCore scheduling mode

Fixes #3465.

src/libcore/task.rs

@@ -1403,11 +1403,9 @@ fn spawn_raw(+opts: TaskOpts, +f: fn~()) {
 
         let num_threads = match opts.mode {
           SingleThreaded => 1u,
-          ThreadPerCore => {
+          ThreadPerCore => rustrt::rust_num_threads(),
-            fail ~"thread_per_core scheduling mode unimplemented"
-          }
           ThreadPerTask => {
-            fail ~"thread_per_task scheduling mode unimplemented"
+            fail ~"ThreadPerTask scheduling mode unimplemented"
           }
           ManualThreads(threads) => {
             if threads == 0u {
@@ -1657,6 +1655,8 @@ extern mod rustrt {
 
     fn rust_get_sched_id() -> sched_id;
     fn rust_new_sched(num_threads: libc::uintptr_t) -> sched_id;
+    fn sched_threads() -> libc::size_t;
+    fn rust_num_threads() -> libc::uintptr_t;
 
     fn get_task_id() -> task_id;
     #[rust_stack]
@@ -2422,3 +2422,13 @@ fn test_tls_cleanup_on_failure() unsafe {
     local_data_set(int_key, @31337);
     fail;
 }
+
+#[test]
+fn test_sched_thread_per_core() {
+    let cores = rustrt::rust_num_threads();
+    let mut reported_threads = 0u;
+    do spawn_sched(ThreadPerCore) {
+        reported_threads = rustrt::sched_threads();
+    }
+    assert(cores == reported_threads);
+}

src/rt/rust_builtin.cpp

@@ -572,6 +572,12 @@ rust_get_sched_id() {
     return task->sched->get_id();
 }
 
+extern "C" CDECL uintptr_t
+rust_num_threads() {
+    rust_task *task = rust_get_current_task();
+    return task->kernel->env->num_sched_threads;
+}
+
 extern "C" CDECL rust_sched_id
 rust_new_sched(uintptr_t threads) {
     rust_task *task = rust_get_current_task();
@@ -620,7 +626,7 @@ start_task(rust_task *target, fn_env_pair *f) {
     target->start(f->f, f->env, NULL);
 }
 
-extern "C" CDECL int
+extern "C" CDECL size_t
 sched_threads() {
     rust_task *task = rust_get_current_task();
     return task->sched->number_of_threads();

src/rt/rustrt.def.in

@@ -32,6 +32,7 @@ rand_seed
 rust_get_sched_id
 rust_new_sched
 rust_new_task_in_sched
+rust_num_threads
 rust_path_is_dir
 rust_path_exists
 rust_getcwd