make Context::new take a stack, instead of creating one

benches/context_new.rs

@@ -1,14 +1,16 @@
 #![feature(test)]
 extern crate test;
 extern crate lwkt;
-use lwkt::Context;
+use lwkt::{Context, StackSource};
 
 static mut ctx_slot: *mut Context = 0 as *mut Context;
 
 #[bench]
 fn context_new(b: &mut test::Bencher) {
   b.iter(|| unsafe {
-    let mut ctx = Context::new(move || {
+    let stack = lwkt::os::StackSource::get_stack(4 << 20);
+
+    let mut ctx = Context::new(stack, move || {
       let ctx_ptr = ctx_slot;
       loop {
         (*ctx_ptr).swap()

benches/swap.rs

@@ -1,14 +1,16 @@
 #![feature(test)]
 extern crate test;
 extern crate lwkt;
-use lwkt::Context;
+use lwkt::{Context, StackSource};
 
 static mut ctx_slot: *mut Context = 0 as *mut Context;
 
 #[bench]
 fn swap(b: &mut test::Bencher) {
   unsafe {
-    let mut ctx = Context::new(move || {
+    let stack = lwkt::os::StackSource::get_stack(4 << 20);
+
+    let mut ctx = Context::new(stack, move || {
       let ctx_ptr = ctx_slot;
       loop {
         (*ctx_ptr).swap()

examples/basic.rs

@@ -1,13 +1,15 @@
 #![feature(thread_local)]
 extern crate lwkt;
-use lwkt::Context;
+use lwkt::{Context, StackSource};
 
 #[thread_local]
 static mut ctx_slot: *mut Context = 0 as *mut Context;
 
 fn main() {
   unsafe {
-    let mut ctx = Context::new(move || {
+    let stack = lwkt::os::StackSource::get_stack(4 << 20);
+
+    let mut ctx = Context::new(stack, move || {
       println!("it's alive!");
       (*ctx_slot).swap();
     });

src/context.rs

@@ -1,7 +1,5 @@
 use core::prelude::*;
-use stack::StackSource;
 use arch::Registers;
-use stack::Stack;
 use os;
 
 pub struct Context {
@@ -11,8 +9,7 @@ pub struct Context {
 
 impl Context {
   #[inline]
-  pub unsafe fn new<F>(f: F) -> Context where F: FnOnce() + Send + 'static {
-    let mut stack = os::StackSource::get_stack(4 << 20);
+  pub unsafe fn new<F>(mut stack: os::Stack, f: F) -> Context where F: FnOnce() + Send + 'static {
     let regs = Registers::new(&mut stack, f);
     Context {
       regs: regs,

src/lib.rs

@@ -20,4 +20,4 @@ pub mod context;
 pub mod stack;
 
 mod arch;
-mod os;
+pub mod os;