auto merge of #12235 : huonw/rust/raii-lock, r=alexcrichton

- adds a `LockGuard` type returned by `.lock` and `.trylock` that unlocks the mutex in the destructor
- renames `mutex::Mutex` to `StaticNativeMutex` 
- adds a `NativeMutex` type with a destructor
- removes `LittleLock`
- adds `#[must_use]` to `sync::mutex::Guard` to remind people to use it

4 files changed, 24 insertions, 35 deletions

diff --git a/src/libnative/bookkeeping.rs b/src/libnative/bookkeeping.rs
index 868586b3691..b1addc5cda5 100644
--- a/src/libnative/bookkeeping.rs
+++ b/src/libnative/bookkeeping.rs
@@ -17,10 +17,10 @@
 //! The green counterpart for this is bookkeeping on sched pools.
 
 use std::sync::atomics;
-use std::unstable::mutex::{Mutex, MUTEX_INIT};
+use std::unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
 
 static mut TASK_COUNT: atomics::AtomicUint = atomics::INIT_ATOMIC_UINT;
-static mut TASK_LOCK: Mutex = MUTEX_INIT;
+static mut TASK_LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
 
 pub fn increment() {
     let _ = unsafe { TASK_COUNT.fetch_add(1, atomics::SeqCst) };
@@ -29,9 +29,8 @@ pub fn increment() {
 pub fn decrement() {
     unsafe {
         if TASK_COUNT.fetch_sub(1, atomics::SeqCst) == 1 {
-            TASK_LOCK.lock();
-            TASK_LOCK.signal();
-            TASK_LOCK.unlock();
+            let mut guard = TASK_LOCK.lock();
+            guard.signal();
         }
     }
 }
@@ -40,11 +39,12 @@ pub fn decrement() {
 /// the entry points of native programs
 pub fn wait_for_other_tasks() {
     unsafe {
-        TASK_LOCK.lock();
-        while TASK_COUNT.load(atomics::SeqCst) > 0 {
-            TASK_LOCK.wait();
+        {
+            let mut guard = TASK_LOCK.lock();
+            while TASK_COUNT.load(atomics::SeqCst) > 0 {
+                guard.wait();
+            }
         }
-        TASK_LOCK.unlock();
         TASK_LOCK.destroy();
     }
 }
diff --git a/src/libnative/io/net.rs b/src/libnative/io/net.rs
index ec6a5c5cb9b..b33b54862dc 100644
--- a/src/libnative/io/net.rs
+++ b/src/libnative/io/net.rs
@@ -218,11 +218,11 @@ pub fn init() {
     }
 
     unsafe {
-        use std::unstable::mutex::{Mutex, MUTEX_INIT};
+        use std::unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
         static mut INITIALIZED: bool = false;
-        static mut LOCK: Mutex = MUTEX_INIT;
+        static mut LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
 
-        LOCK.lock();
+        let _guard = LOCK.lock();
         if !INITIALIZED {
             let mut data: WSADATA = mem::init();
             let ret = WSAStartup(0x202,      // version 2.2
@@ -230,7 +230,6 @@ pub fn init() {
             assert_eq!(ret, 0);
             INITIALIZED = true;
         }
-        LOCK.unlock();
     }
 }
 
diff --git a/src/libnative/io/timer_helper.rs b/src/libnative/io/timer_helper.rs
index 2c976e67d25..004cd6f3114 100644
--- a/src/libnative/io/timer_helper.rs
+++ b/src/libnative/io/timer_helper.rs
@@ -22,7 +22,7 @@
 
 use std::cast;
 use std::rt;
-use std::unstable::mutex::{Mutex, MUTEX_INIT};
+use std::unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
 
 use bookkeeping;
 use io::timer::{Req, Shutdown};
@@ -37,11 +37,11 @@ static mut HELPER_CHAN: *mut Chan<Req> = 0 as *mut Chan<Req>;
 static mut HELPER_SIGNAL: imp::signal = 0 as imp::signal;
 
 pub fn boot(helper: fn(imp::signal, Port<Req>)) {
-    static mut LOCK: Mutex = MUTEX_INIT;
+    static mut LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
     static mut INITIALIZED: bool = false;
 
     unsafe {
-        LOCK.lock();
+        let mut _guard = LOCK.lock();
         if !INITIALIZED {
             let (msgp, msgc) = Chan::new();
             // promote this to a shared channel
@@ -58,7 +58,6 @@ pub fn boot(helper: fn(imp::signal, Port<Req>)) {
             rt::at_exit(proc() { shutdown() });
             INITIALIZED = true;
         }
-        LOCK.unlock();
     }
 }
 
diff --git a/src/libnative/task.rs b/src/libnative/task.rs
index a9c3afbbb16..d8f410834f2 100644
--- a/src/libnative/task.rs
+++ b/src/libnative/task.rs
@@ -22,7 +22,7 @@ use std::rt::task::{Task, BlockedTask, SendMessage};
 use std::rt::thread::Thread;
 use std::rt;
 use std::task::TaskOpts;
-use std::unstable::mutex::Mutex;
+use std::unstable::mutex::NativeMutex;
 use std::unstable::stack;
 
 use io;
@@ -40,7 +40,7 @@ pub fn new(stack_bounds: (uint, uint)) -> ~Task {
 
 fn ops() -> ~Ops {
     ~Ops {
-        lock: unsafe { Mutex::new() },
+        lock: unsafe { NativeMutex::new() },
         awoken: false,
         io: io::IoFactory::new(),
         // these *should* get overwritten
@@ -109,7 +109,7 @@ pub fn spawn_opts(opts: TaskOpts, f: proc()) {
 // This structure is the glue between channels and the 1:1 scheduling mode. This
 // structure is allocated once per task.
 struct Ops {
-    lock: Mutex,       // native synchronization
+    lock: NativeMutex,       // native synchronization
     awoken: bool,      // used to prevent spurious wakeups
     io: io::IoFactory, // local I/O factory
 
@@ -191,20 +191,19 @@ impl rt::Runtime for Ops {
             let task = BlockedTask::block(cur_task);
 
             if times == 1 {
-                (*me).lock.lock();
+                let mut guard = (*me).lock.lock();
                 (*me).awoken = false;
                 match f(task) {
                     Ok(()) => {
                         while !(*me).awoken {
-                            (*me).lock.wait();
+                            guard.wait();
                         }
                     }
                     Err(task) => { cast::forget(task.wake()); }
                 }
-                (*me).lock.unlock();
             } else {
                 let mut iter = task.make_selectable(times);
-                (*me).lock.lock();
+                let mut guard = (*me).lock.lock();
                 (*me).awoken = false;
                 let success = iter.all(|task| {
                     match f(task) {
@@ -216,9 +215,8 @@ impl rt::Runtime for Ops {
                     }
                 });
                 while success && !(*me).awoken {
-                    (*me).lock.wait();
+                    guard.wait();
                 }
-                (*me).lock.unlock();
             }
             // re-acquire ownership of the task
             cur_task = cast::transmute::<uint, ~Task>(cur_task_dupe);
@@ -235,10 +233,9 @@ impl rt::Runtime for Ops {
             let me = &mut *self as *mut Ops;
             to_wake.put_runtime(self as ~rt::Runtime);
             cast::forget(to_wake);
-            (*me).lock.lock();
+            let mut guard = (*me).lock.lock();
             (*me).awoken = true;
-            (*me).lock.signal();
-            (*me).lock.unlock();
+            guard.signal();
         }
     }
 
@@ -254,12 +251,6 @@ impl rt::Runtime for Ops {
     }
 }
 
-impl Drop for Ops {
-    fn drop(&mut self) {
-        unsafe { self.lock.destroy() }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::rt::Runtime;