15 files changed, 334 insertions, 223 deletions

diff --git a/src/libgreen/sched.rs b/src/libgreen/sched.rs
index 4b1c4e3b425..ad32ba7ba6d 100644
--- a/src/libgreen/sched.rs
+++ b/src/libgreen/sched.rs
@@ -15,7 +15,7 @@ use std::rt::rtio::{RemoteCallback, PausableIdleCallback, Callback, EventLoop};
 use std::rt::task::BlockedTask;
 use std::rt::task::Task;
 use std::sync::deque;
-use std::unstable::mutex::Mutex;
+use std::unstable::mutex::NativeMutex;
 use std::unstable::raw;
 
 use TaskState;
@@ -669,8 +669,7 @@ impl Scheduler {
         // is acquired here. This is the resumption points and the "bounce"
         // that it is referring to.
         unsafe {
-            current_task.nasty_deschedule_lock.lock();
-            current_task.nasty_deschedule_lock.unlock();
+            let _guard = current_task.nasty_deschedule_lock.lock();
         }
         return current_task;
     }
@@ -765,10 +764,11 @@ impl Scheduler {
         // to it, but we're guaranteed that the task won't exit until we've
         // unlocked the lock so there's no worry of this memory going away.
         let cur = self.change_task_context(cur, next, |sched, mut task| {
-            let lock: *mut Mutex = &mut task.nasty_deschedule_lock;
-            unsafe { (*lock).lock() }
-            f(sched, BlockedTask::block(task.swap()));
-            unsafe { (*lock).unlock() }
+            let lock: *mut NativeMutex = &mut task.nasty_deschedule_lock;
+            unsafe {
+                let _guard = (*lock).lock();
+                f(sched, BlockedTask::block(task.swap()));
+            }
         });
         cur.put();
     }
@@ -1453,8 +1453,8 @@ mod test {
 
     #[test]
     fn test_spawn_sched_blocking() {
-        use std::unstable::mutex::{Mutex, MUTEX_INIT};
-        static mut LOCK: Mutex = MUTEX_INIT;
+        use std::unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
+        static mut LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
 
         // Testing that a task in one scheduler can block in foreign code
         // without affecting other schedulers
@@ -1466,12 +1466,11 @@ mod test {
             let mut handle = pool.spawn_sched();
             handle.send(PinnedTask(pool.task(TaskOpts::new(), proc() {
                 unsafe {
-                    LOCK.lock();
+                    let mut guard = LOCK.lock();
 
                     start_ch.send(());
-                    LOCK.wait();   // block the scheduler thread
-                    LOCK.signal(); // let them know we have the lock
-                    LOCK.unlock();
+                    guard.wait();   // block the scheduler thread
+                    guard.signal(); // let them know we have the lock
                 }
 
                 fin_ch.send(());
@@ -1503,10 +1502,9 @@ mod test {
                 child_ch.send(20);
                 pingpong(&parent_po, &child_ch);
                 unsafe {
-                    LOCK.lock();
-                    LOCK.signal();   // wakeup waiting scheduler
-                    LOCK.wait();     // wait for them to grab the lock
-                    LOCK.unlock();
+                    let mut guard = LOCK.lock();
+                    guard.signal();   // wakeup waiting scheduler
+                    guard.wait();     // wait for them to grab the lock
                 }
             })));
             drop(handle);
diff --git a/src/libgreen/simple.rs b/src/libgreen/simple.rs
index 8db95f55d18..297c22e2cd6 100644
--- a/src/libgreen/simple.rs
+++ b/src/libgreen/simple.rs
@@ -17,10 +17,10 @@ use std::rt::local::Local;
 use std::rt::rtio;
 use std::rt::task::{Task, BlockedTask};
 use std::task::TaskOpts;
-use std::unstable::sync::LittleLock;
+use std::unstable::mutex::NativeMutex;
 
 struct SimpleTask {
-    lock: LittleLock,
+    lock: NativeMutex,
     awoken: bool,
 }
 
@@ -59,9 +59,9 @@ impl Runtime for SimpleTask {
         to_wake.put_runtime(self as ~Runtime);
         unsafe {
             cast::forget(to_wake);
-            let _l = (*me).lock.lock();
+            let mut guard = (*me).lock.lock();
             (*me).awoken = true;
-            (*me).lock.signal();
+            guard.signal();
         }
     }
 
@@ -83,7 +83,7 @@ impl Runtime for SimpleTask {
 pub fn task() -> ~Task {
     let mut task = ~Task::new();
     task.put_runtime(~SimpleTask {
-        lock: LittleLock::new(),
+        lock: unsafe {NativeMutex::new()},
         awoken: false,
     } as ~Runtime);
     return task;
diff --git a/src/libgreen/task.rs b/src/libgreen/task.rs
index 2aca72e35f1..74d93b4b2db 100644
--- a/src/libgreen/task.rs
+++ b/src/libgreen/task.rs
@@ -25,7 +25,7 @@ use std::rt::local::Local;
 use std::rt::rtio;
 use std::rt::task::{Task, BlockedTask, SendMessage};
 use std::task::TaskOpts;
-use std::unstable::mutex::Mutex;
+use std::unstable::mutex::NativeMutex;
 use std::unstable::raw;
 
 use context::Context;
@@ -65,7 +65,7 @@ pub struct GreenTask {
     pool_id: uint,
 
     // See the comments in the scheduler about why this is necessary
-    nasty_deschedule_lock: Mutex,
+    nasty_deschedule_lock: NativeMutex,
 }
 
 pub enum TaskType {
@@ -163,7 +163,7 @@ impl GreenTask {
             task_type: task_type,
             sched: None,
             handle: None,
-            nasty_deschedule_lock: unsafe { Mutex::new() },
+            nasty_deschedule_lock: unsafe { NativeMutex::new() },
             task: Some(~Task::new()),
         }
     }
@@ -322,11 +322,10 @@ impl GreenTask {
     // uncontended except for when the task is rescheduled).
     fn reawaken_remotely(mut ~self) {
         unsafe {
-            let mtx = &mut self.nasty_deschedule_lock as *mut Mutex;
+            let mtx = &mut self.nasty_deschedule_lock as *mut NativeMutex;
             let handle = self.handle.get_mut_ref() as *mut SchedHandle;
-            (*mtx).lock();
+            let _guard = (*mtx).lock();
             (*handle).send(RunOnce(self));
-            (*mtx).unlock();
         }
     }
 }
@@ -479,12 +478,6 @@ impl Runtime for GreenTask {
     fn wrap(~self) -> ~Any { self as ~Any }
 }
 
-impl Drop for GreenTask {
-    fn drop(&mut self) {
-        unsafe { self.nasty_deschedule_lock.destroy(); }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use std::rt::Runtime;
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;
diff --git a/src/librustuv/queue.rs b/src/librustuv/queue.rs
index 5b697e0d73d..da502ca72de 100644
--- a/src/librustuv/queue.rs
+++ b/src/librustuv/queue.rs
@@ -23,7 +23,7 @@
 use std::cast;
 use std::libc::{c_void, c_int};
 use std::rt::task::BlockedTask;
-use std::unstable::sync::LittleLock;
+use std::unstable::mutex::NativeMutex;
 use std::sync::arc::UnsafeArc;
 use mpsc = std::sync::mpsc_queue;
 
@@ -39,7 +39,7 @@ enum Message {
 
 struct State {
     handle: *uvll::uv_async_t,
-    lock: LittleLock, // see comments in async_cb for why this is needed
+    lock: NativeMutex, // see comments in async_cb for why this is needed
     queue: mpsc::Queue<Message>,
 }
 
@@ -112,7 +112,7 @@ impl QueuePool {
         let handle = UvHandle::alloc(None::<AsyncWatcher>, uvll::UV_ASYNC);
         let state = UnsafeArc::new(State {
             handle: handle,
-            lock: LittleLock::new(),
+            lock: unsafe {NativeMutex::new()},
             queue: mpsc::Queue::new(),
         });
         let q = ~QueuePool {
diff --git a/src/libstd/comm/shared.rs b/src/libstd/comm/shared.rs
index 77bf2d7a68d..031ce991ba4 100644
--- a/src/libstd/comm/shared.rs
+++ b/src/libstd/comm/shared.rs
@@ -28,7 +28,7 @@ use rt::local::Local;
 use rt::task::{Task, BlockedTask};
 use rt::thread::Thread;
 use sync::atomics;
-use unstable::mutex::Mutex;
+use unstable::mutex::NativeMutex;
 use vec::OwnedVector;
 
 use mpsc = sync::mpsc_queue;
@@ -53,7 +53,7 @@ pub struct Packet<T> {
 
     // this lock protects various portions of this implementation during
     // select()
-    select_lock: Mutex,
+    select_lock: NativeMutex,
 }
 
 pub enum Failure {
@@ -72,10 +72,10 @@ impl<T: Send> Packet<T> {
             channels: atomics::AtomicInt::new(2),
             port_dropped: atomics::AtomicBool::new(false),
             sender_drain: atomics::AtomicInt::new(0),
-            select_lock: unsafe { Mutex::new() },
+            select_lock: unsafe { NativeMutex::new() },
         };
         // see comments in inherit_blocker about why we grab this lock
-        unsafe { p.select_lock.lock() }
+        unsafe { p.select_lock.lock_noguard() }
         return p;
     }
 
@@ -124,7 +124,7 @@ impl<T: Send> Packet<T> {
         // interfere with this method. After we unlock this lock, we're
         // signifying that we're done modifying self.cnt and self.to_wake and
         // the port is ready for the world to continue using it.
-        unsafe { self.select_lock.unlock() }
+        unsafe { self.select_lock.unlock_noguard() }
     }
 
     pub fn send(&mut self, t: T) -> bool {
@@ -438,8 +438,7 @@ impl<T: Send> Packet<T> {
         // about looking at and dealing with to_wake. Once we have acquired the
         // lock, we are guaranteed that inherit_blocker is done.
         unsafe {
-            self.select_lock.lock();
-            self.select_lock.unlock();
+            let _guard = self.select_lock.lock();
         }
 
         // Like the stream implementation, we want to make sure that the count
@@ -487,7 +486,6 @@ impl<T: Send> Drop for Packet<T> {
             assert_eq!(self.cnt.load(atomics::SeqCst), DISCONNECTED);
             assert_eq!(self.to_wake.load(atomics::SeqCst), 0);
             assert_eq!(self.channels.load(atomics::SeqCst), 0);
-            self.select_lock.destroy();
         }
     }
 }
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 20d1ae2f3e2..719ed62d03d 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -44,7 +44,6 @@ use ptr;
 use str;
 use str::{Str, StrSlice};
 use fmt;
-use unstable::finally::Finally;
 use sync::atomics::{AtomicInt, INIT_ATOMIC_INT, SeqCst};
 use path::{Path, GenericPath};
 use iter::Iterator;
@@ -145,16 +144,13 @@ Accessing environment variables is not generally threadsafe.
 Serialize access through a global lock.
 */
 fn with_env_lock<T>(f: || -> T) -> T {
-    use unstable::mutex::{Mutex, MUTEX_INIT};
-    use unstable::finally::Finally;
+    use unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
 
-    static mut lock: Mutex = MUTEX_INIT;
+    static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
 
     unsafe {
-        return (|| {
-            lock.lock();
-            f()
-        }).finally(|| lock.unlock());
+        let _guard = lock.lock();
+        f()
     }
 }
 
diff --git a/src/libstd/rt/args.rs b/src/libstd/rt/args.rs
index c417ea375fd..6f73265978b 100644
--- a/src/libstd/rt/args.rs
+++ b/src/libstd/rt/args.rs
@@ -68,12 +68,11 @@ mod imp {
     use option::{Option, Some, None};
     use ptr::RawPtr;
     use iter::Iterator;
-    use unstable::finally::Finally;
-    use unstable::mutex::{Mutex, MUTEX_INIT};
+    use unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
     use mem;
 
     static mut global_args_ptr: uint = 0;
-    static mut lock: Mutex = MUTEX_INIT;
+    static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
 
     #[cfg(not(test))]
     pub unsafe fn init(argc: int, argv: **u8) {
@@ -111,16 +110,10 @@ mod imp {
     }
 
     fn with_lock<T>(f: || -> T) -> T {
-        (|| {
-            unsafe {
-                lock.lock();
-                f()
-            }
-        }).finally(|| {
-            unsafe {
-                lock.unlock();
-            }
-        })
+        unsafe {
+            let _guard = lock.lock();
+            f()
+        }
     }
 
     fn get_global_ptr() -> *mut Option<~~[~[u8]]> {
diff --git a/src/libstd/unstable/dynamic_lib.rs b/src/libstd/unstable/dynamic_lib.rs
index 8529b69c6eb..84fa528ebf1 100644
--- a/src/libstd/unstable/dynamic_lib.rs
+++ b/src/libstd/unstable/dynamic_lib.rs
@@ -152,12 +152,12 @@ pub mod dl {
     }
 
     pub fn check_for_errors_in<T>(f: || -> T) -> Result<T, ~str> {
-        use unstable::mutex::{Mutex, MUTEX_INIT};
-        static mut lock: Mutex = MUTEX_INIT;
+        use unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
+        static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
         unsafe {
             // dlerror isn't thread safe, so we need to lock around this entire
             // sequence
-            lock.lock();
+            let _guard = lock.lock();
             let _old_error = dlerror();
 
             let result = f();
@@ -168,7 +168,7 @@ pub mod dl {
             } else {
                 Err(str::raw::from_c_str(last_error))
             };
-            lock.unlock();
+
             ret
         }
     }
diff --git a/src/libstd/unstable/mutex.rs b/src/libstd/unstable/mutex.rs
index 3122e925e82..34ddee46d35 100644
--- a/src/libstd/unstable/mutex.rs
+++ b/src/libstd/unstable/mutex.rs
@@ -8,78 +8,157 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! A native mutex and condition variable type
+//! A native mutex and condition variable type.
 //!
 //! This module contains bindings to the platform's native mutex/condition
-//! variable primitives. It provides a single type, `Mutex`, which can be
-//! statically initialized via the `MUTEX_INIT` value. This object serves as both a
-//! mutex and a condition variable simultaneously.
+//! variable primitives. It provides two types: `StaticNativeMutex`, which can
+//! be statically initialized via the `NATIVE_MUTEX_INIT` value, and a simple
+//! wrapper `NativeMutex` that has a destructor to clean up after itself. These
+//! objects serve as both mutexes and condition variables simultaneously.
 //!
-//! The lock is lazily initialized, but it can only be unsafely destroyed. A
-//! statically initialized lock doesn't necessarily have a time at which it can
-//! get deallocated. For this reason, there is no `Drop` implementation of the
-//! mutex, but rather the `destroy()` method must be invoked manually if
-//! destruction of the mutex is desired.
+//! The static lock is lazily initialized, but it can only be unsafely
+//! destroyed. A statically initialized lock doesn't necessarily have a time at
+//! which it can get deallocated. For this reason, there is no `Drop`
+//! implementation of the static mutex, but rather the `destroy()` method must
+//! be invoked manually if destruction of the mutex is desired.
 //!
-//! It is not recommended to use this type for idiomatic rust use. This type is
-//! appropriate where no other options are available, but other rust concurrency
-//! primitives should be used before this type.
+//! The non-static `NativeMutex` type does have a destructor, but cannot be
+//! statically initialized.
+//!
+//! It is not recommended to use this type for idiomatic rust use. These types
+//! are appropriate where no other options are available, but other rust
+//! concurrency primitives should be used before them: the `sync` crate defines
+//! `StaticMutex` and `Mutex` types.
 //!
 //! # Example
 //!
-//!     use std::unstable::mutex::{Mutex, MUTEX_INIT};
+//! ```rust
+//! use std::unstable::mutex::{NativeMutex, StaticNativeMutex, NATIVE_MUTEX_INIT};
+//!
+//! // Use a statically initialized mutex
+//! static mut LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
+//!
+//! unsafe {
+//!     let _guard = LOCK.lock();
+//! } // automatically unlocked here
 //!
-//!     // Use a statically initialized mutex
-//!     static mut lock: Mutex = MUTEX_INIT;
+//! // Use a normally initialized mutex
+//! unsafe {
+//!     let mut lock = NativeMutex::new();
 //!
-//!     unsafe {
-//!         lock.lock();
-//!         lock.unlock();
-//!     }
+//!     {
+//!         let _guard = lock.lock();
+//!     } // unlocked here
 //!
-//!     // Use a normally initialized mutex
-//!     let mut lock = Mutex::new();
-//!     unsafe {
-//!         lock.lock();
-//!         lock.unlock();
-//!         lock.destroy();
-//!     }
+//!     // sometimes the RAII guard isn't appropriate
+//!     lock.lock_noguard();
+//!     lock.unlock_noguard();
+//! } // `lock` is deallocated here
+//! ```
 
 #[allow(non_camel_case_types)];
 
-pub struct Mutex {
+use option::{Option, None, Some};
+use ops::Drop;
+
+/// A native mutex suitable for storing in statics (that is, it has
+/// the `destroy` method rather than a destructor).
+///
+/// Prefer the `NativeMutex` type where possible, since that does not
+/// require manual deallocation.
+pub struct StaticNativeMutex {
     priv inner: imp::Mutex,
 }
 
-pub static MUTEX_INIT: Mutex = Mutex {
+/// A native mutex with a destructor for clean-up.
+///
+/// See `StaticNativeMutex` for a version that is suitable for storing in
+/// statics.
+pub struct NativeMutex {
+    priv inner: StaticNativeMutex
+}
+
+/// Automatically unlocks the mutex that it was created from on
+/// destruction.
+///
+/// Using this makes lock-based code resilient to unwinding/task
+/// failure, because the lock will be automatically unlocked even
+/// then.
+#[must_use]
+pub struct LockGuard<'a> {
+    priv lock: &'a mut StaticNativeMutex
+}
+
+pub static NATIVE_MUTEX_INIT: StaticNativeMutex = StaticNativeMutex {
     inner: imp::MUTEX_INIT,
 };
 
-impl Mutex {
-    /// Creates a new mutex
-    pub unsafe fn new() -> Mutex {
-        Mutex { inner: imp::Mutex::new() }
+impl StaticNativeMutex {
+    /// Creates a new mutex.
+    ///
+    /// Note that a mutex created in this way needs to be explicit
+    /// freed with a call to `destroy` or it will leak.
+    pub unsafe fn new() -> StaticNativeMutex {
+        StaticNativeMutex { inner: imp::Mutex::new() }
     }
 
     /// Acquires this lock. This assumes that the current thread does not
     /// already hold the lock.
-    pub unsafe fn lock(&mut self) { self.inner.lock() }
+    ///
+    /// # Example
+    /// ```rust
+    /// use std::unstable::mutex::{StaticNativeMutex, NATIVE_MUTEX_INIT};
+    /// static mut LOCK: StaticNativeMutex = NATIVE_MUTEX_INIT;
+    /// unsafe {
+    ///     let _guard = LOCK.lock();
+    ///     // critical section...
+    /// } // automatically unlocked in `_guard`'s destructor
+    /// ```
+    pub unsafe fn lock<'a>(&'a mut self) -> LockGuard<'a> {
+        self.inner.lock();
+
+        LockGuard { lock: self }
+    }
+
+    /// Attempts to acquire the lock. The value returned is `Some` if
+    /// the attempt succeeded.
+    pub unsafe fn trylock<'a>(&'a mut self) -> Option<LockGuard<'a>> {
+        if self.inner.trylock() {
+            Some(LockGuard { lock: self })
+        } else {
+            None
+        }
+    }
 
-    /// Attempts to acquire the lock. The value returned is whether the lock was
-    /// acquired or not
-    pub unsafe fn trylock(&mut self) -> bool { self.inner.trylock() }
+    /// Acquire the lock without creating a `LockGuard`.
+    ///
+    /// These needs to be paired with a call to `.unlock_noguard`. Prefer using
+    /// `.lock`.
+    pub unsafe fn lock_noguard(&mut self) { self.inner.lock() }
+
+    /// Attempts to acquire the lock without creating a
+    /// `LockGuard`. The value returned is whether the lock was
+    /// acquired or not.
+    ///
+    /// If `true` is returned, this needs to be paired with a call to
+    /// `.unlock_noguard`. Prefer using `.trylock`.
+    pub unsafe fn trylock_noguard(&mut self) -> bool {
+        self.inner.trylock()
+    }
 
     /// Unlocks the lock. This assumes that the current thread already holds the
     /// lock.
-    pub unsafe fn unlock(&mut self) { self.inner.unlock() }
+    pub unsafe fn unlock_noguard(&mut self) { self.inner.unlock() }
 
     /// Block on the internal condition variable.
     ///
-    /// This function assumes that the lock is already held
-    pub unsafe fn wait(&mut self) { self.inner.wait() }
+    /// This function assumes that the lock is already held. Prefer
+    /// using `LockGuard.wait` since that guarantees that the lock is
+    /// held.
+    pub unsafe fn wait_noguard(&mut self) { self.inner.wait() }
 
     /// Signals a thread in `wait` to wake up
-    pub unsafe fn signal(&mut self) { self.inner.signal() }
+    pub unsafe fn signal_noguard(&mut self) { self.inner.signal() }
 
     /// This function is especially unsafe because there are no guarantees made
     /// that no other thread is currently holding the lock or waiting on the
@@ -87,6 +166,96 @@ impl Mutex {
     pub unsafe fn destroy(&mut self) { self.inner.destroy() }
 }
 
+impl NativeMutex {
+    /// Creates a new mutex.
+    ///
+    /// The user must be careful to ensure the mutex is not locked when its is
+    /// being destroyed.
+    pub unsafe fn new() -> NativeMutex {
+        NativeMutex { inner: StaticNativeMutex::new() }
+    }
+
+    /// Acquires this lock. This assumes that the current thread does not
+    /// already hold the lock.
+    ///
+    /// # Example
+    /// ```rust
+    /// use std::unstable::mutex::NativeMutex;
+    /// unsafe {
+    ///     let mut lock = NativeMutex::new();
+    ///
+    ///     {
+    ///         let _guard = lock.lock();
+    ///         // critical section...
+    ///     } // automatically unlocked in `_guard`'s destructor
+    /// }
+    /// ```
+    pub unsafe fn lock<'a>(&'a mut self) -> LockGuard<'a> {
+        self.inner.lock()
+    }
+
+    /// Attempts to acquire the lock. The value returned is `Some` if
+    /// the attempt succeeded.
+    pub unsafe fn trylock<'a>(&'a mut self) -> Option<LockGuard<'a>> {
+        self.inner.trylock()
+    }
+
+    /// Acquire the lock without creating a `LockGuard`.
+    ///
+    /// These needs to be paired with a call to `.unlock_noguard`. Prefer using
+    /// `.lock`.
+    pub unsafe fn lock_noguard(&mut self) { self.inner.lock_noguard() }
+
+    /// Attempts to acquire the lock without creating a
+    /// `LockGuard`. The value returned is whether the lock was
+    /// acquired or not.
+    ///
+    /// If `true` is returned, this needs to be paired with a call to
+    /// `.unlock_noguard`. Prefer using `.trylock`.
+    pub unsafe fn trylock_noguard(&mut self) -> bool {
+        self.inner.trylock_noguard()
+    }
+
+    /// Unlocks the lock. This assumes that the current thread already holds the
+    /// lock.
+    pub unsafe fn unlock_noguard(&mut self) { self.inner.unlock_noguard() }
+
+    /// Block on the internal condition variable.
+    ///
+    /// This function assumes that the lock is already held. Prefer
+    /// using `LockGuard.wait` since that guarantees that the lock is
+    /// held.
+    pub unsafe fn wait_noguard(&mut self) { self.inner.wait_noguard() }
+
+    /// Signals a thread in `wait` to wake up
+    pub unsafe fn signal_noguard(&mut self) { self.inner.signal_noguard() }
+}
+
+impl Drop for NativeMutex {
+    fn drop(&mut self) {
+        unsafe {self.inner.destroy()}
+    }
+}
+
+impl<'a> LockGuard<'a> {
+    /// Block on the internal condition variable.
+    pub unsafe fn wait(&mut self) {
+        self.lock.wait_noguard()
+    }
+
+    /// Signals a thread in `wait` to wake up.
+    pub unsafe fn signal(&mut self) {
+        self.lock.signal_noguard()
+    }
+}
+
+#[unsafe_destructor]
+impl<'a> Drop for LockGuard<'a> {
+    fn drop(&mut self) {
+        unsafe {self.lock.unlock_noguard()}
+    }
+}
+
 #[cfg(unix)]
 mod imp {
     use libc;
@@ -382,30 +551,56 @@ mod imp {
 mod test {
     use prelude::*;
 
-    use super::{Mutex, MUTEX_INIT};
+    use mem::drop;
+    use super::{StaticNativeMutex, NATIVE_MUTEX_INIT};
     use rt::thread::Thread;
 
     #[test]
-    fn somke_lock() {
-        static mut lock: Mutex = MUTEX_INIT;
+    fn smoke_lock() {
+        static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
         unsafe {
-            lock.lock();
-            lock.unlock();
+            let _guard = lock.lock();
         }
     }
 
     #[test]
-    fn somke_cond() {
-        static mut lock: Mutex = MUTEX_INIT;
+    fn smoke_cond() {
+        static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
         unsafe {
-            lock.lock();
+            let mut guard = lock.lock();
             let t = Thread::start(proc() {
-                lock.lock();
-                lock.signal();
-                lock.unlock();
+                let mut guard = lock.lock();
+                guard.signal();
             });
-            lock.wait();
-            lock.unlock();
+            guard.wait();
+            drop(guard);
+
+            t.join();
+        }
+    }
+
+    #[test]
+    fn smoke_lock_noguard() {
+        static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
+        unsafe {
+            lock.lock_noguard();
+            lock.unlock_noguard();
+        }
+    }
+
+    #[test]
+    fn smoke_cond_noguard() {
+        static mut lock: StaticNativeMutex = NATIVE_MUTEX_INIT;
+        unsafe {
+            lock.lock_noguard();
+            let t = Thread::start(proc() {
+                lock.lock_noguard();
+                lock.signal_noguard();
+                lock.unlock_noguard();
+            });
+            lock.wait_noguard();
+            lock.unlock_noguard();
+
             t.join();
         }
     }
@@ -413,7 +608,7 @@ mod test {
     #[test]
     fn destroy_immediately() {
         unsafe {
-            let mut m = Mutex::new();
+            let mut m = StaticNativeMutex::new();
             m.destroy();
         }
     }
diff --git a/src/libstd/unstable/sync.rs b/src/libstd/unstable/sync.rs
index c2fa168a478..93322977bc1 100644
--- a/src/libstd/unstable/sync.rs
+++ b/src/libstd/unstable/sync.rs
@@ -10,63 +10,11 @@
 
 use clone::Clone;
 use kinds::Send;
-use ops::Drop;
-use option::{Option,Some,None};
 use sync::arc::UnsafeArc;
-use unstable::mutex::Mutex;
-
-pub struct LittleLock {
-    priv l: Mutex,
-}
-
-pub struct LittleGuard<'a> {
-    priv l: &'a mut Mutex,
-}
-
-impl Drop for LittleLock {
-    fn drop(&mut self) {
-        unsafe { self.l.destroy(); }
-    }
-}
-
-#[unsafe_destructor]
-impl<'a> Drop for LittleGuard<'a> {
-    fn drop(&mut self) {
-        unsafe { self.l.unlock(); }
-    }
-}
-
-impl LittleLock {
-    pub fn new() -> LittleLock {
-        unsafe { LittleLock { l: Mutex::new() } }
-    }
-
-    pub unsafe fn lock<'a>(&'a mut self) -> LittleGuard<'a> {
-        self.l.lock();
-        LittleGuard { l: &mut self.l }
-    }
-
-    pub unsafe fn try_lock<'a>(&'a mut self) -> Option<LittleGuard<'a>> {
-        if self.l.trylock() {
-            Some(LittleGuard { l: &mut self.l })
-        } else {
-            None
-        }
-    }
-
-    pub unsafe fn signal(&mut self) {
-        self.l.signal();
-    }
-}
-
-impl<'a> LittleGuard<'a> {
-    pub unsafe fn wait(&mut self) {
-        self.l.wait();
-    }
-}
+use unstable::mutex::NativeMutex;
 
 struct ExData<T> {
-    lock: LittleLock,
+    lock: NativeMutex,
     failed: bool,
     data: T,
 }
@@ -95,7 +43,7 @@ impl<T:Send> Clone for Exclusive<T> {
 impl<T:Send> Exclusive<T> {
     pub fn new(user_data: T) -> Exclusive<T> {
         let data = ExData {
-            lock: LittleLock::new(),
+            lock: unsafe {NativeMutex::new()},
             failed: false,
             data: user_data
         };
@@ -104,8 +52,8 @@ impl<T:Send> Exclusive<T> {
         }
     }
 
-    // Exactly like std::arc::MutexArc,access(), but with the LittleLock
-    // instead of a proper mutex. Same reason for being unsafe.
+    // Exactly like sync::MutexArc.access(). Same reason for being
+    // unsafe.
     //
     // Currently, scheduling operations (i.e., descheduling, receiving on a pipe,
     // accessing the provided condition variable) are prohibited while inside
@@ -131,14 +79,14 @@ impl<T:Send> Exclusive<T> {
     #[inline]
     pub unsafe fn hold_and_signal(&self, f: |x: &mut T|) {
         let rec = self.x.get();
-        let _l = (*rec).lock.lock();
+        let mut guard = (*rec).lock.lock();
         if (*rec).failed {
             fail!("Poisoned Exclusive::new - another task failed inside!");
         }
         (*rec).failed = true;
         f(&mut (*rec).data);
         (*rec).failed = false;
-        (*rec).lock.signal();
+        guard.signal();
     }
 
     #[inline]
diff --git a/src/libsync/sync/mutex.rs b/src/libsync/sync/mutex.rs
index 8489773bd88..9ca2f1fd7ff 100644
--- a/src/libsync/sync/mutex.rs
+++ b/src/libsync/sync/mutex.rs
@@ -133,7 +133,7 @@ pub struct StaticMutex {
     /// uint-cast of the native thread waiting for this mutex
     priv native_blocker: uint,
     /// an OS mutex used by native threads
-    priv lock: mutex::Mutex,
+    priv lock: mutex::StaticNativeMutex,
 
     /// A concurrent mpsc queue used by green threads, along with a count used
     /// to figure out when to dequeue and enqueue.
@@ -143,6 +143,7 @@ pub struct StaticMutex {
 
 /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
 /// dropped (falls out of scope), the lock will be unlocked.
+#[must_use]
 pub struct Guard<'a> {
     priv lock: &'a mut StaticMutex,
 }
@@ -150,7 +151,7 @@ pub struct Guard<'a> {
 /// Static initialization of a mutex. This constant can be used to initialize
 /// other mutex constants.
 pub static MUTEX_INIT: StaticMutex = StaticMutex {
-    lock: mutex::MUTEX_INIT,
+    lock: mutex::NATIVE_MUTEX_INIT,
     state: atomics::INIT_ATOMIC_UINT,
     flavor: Unlocked,
     green_blocker: 0,
@@ -288,11 +289,11 @@ impl StaticMutex {
     // `lock()` function on an OS mutex
     fn native_lock(&mut self, t: ~Task) {
         Local::put(t);
-        unsafe { self.lock.lock(); }
+        unsafe { self.lock.lock_noguard(); }
     }
 
     fn native_unlock(&mut self) {
-        unsafe { self.lock.unlock(); }
+        unsafe { self.lock.unlock_noguard(); }
     }
 
     fn green_lock(&mut self, t: ~Task) {
@@ -441,7 +442,7 @@ impl Mutex {
                 native_blocker: 0,
                 green_cnt: atomics::AtomicUint::new(0),
                 q: q::Queue::new(),
-                lock: unsafe { mutex::Mutex::new() },
+                lock: unsafe { mutex::StaticNativeMutex::new() },
             }
         }
     }