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

Author: bors

Diff for: 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 for: 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 for: 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 for: 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 for: src/libnative/io/net.rs

@@ -218,19 +218,18 @@ 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
                                  &mut data);
             assert_eq!(ret, 0);
             INITIALIZED = true;
         }
-        LOCK.unlock();
     }
 }
 

Diff for: 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 for: 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 for: 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 {