src/libstd/sync/rwlock.rs - rust - Git at Google

 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 use prelude::v1::*;

 use cell::UnsafeCell;
 use marker;
 use ops::{Deref, DerefMut};
 use sync::poison::{self, LockResult, TryLockError, TryLockResult};
 use sys_common::rwlock as sys;

 /// A reader-writer lock
 ///
 /// This type of lock allows a number of readers or at most one writer at any
 /// point in time. The write portion of this lock typically allows modification
 /// of the underlying data (exclusive access) and the read portion of this lock
 /// typically allows for read-only access (shared access).
 ///
 /// The type parameter `T` represents the data that this lock protects. It is
 /// required that `T` satisfies `Send` to be shared across tasks and `Sync` to
 /// allow concurrent access through readers. The RAII guards returned from the
 /// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
 /// to allow access to the contained of the lock.
 ///
 /// # Poisoning
 ///
 /// RwLocks, like Mutexes, will become poisoned on panics. Note, however, that
 /// an RwLock may only be poisoned if a panic occurs while it is locked
 /// exclusively (write mode). If a panic occurs in any reader, then the lock
 /// will not be poisoned.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::sync::RwLock;
 ///
 /// let lock = RwLock::new(5i);
 ///
 /// // many reader locks can be held at once
 /// {
 ///     let r1 = lock.read().unwrap();
 ///     let r2 = lock.read().unwrap();
 ///     assert_eq!(*r1, 5);
 ///     assert_eq!(*r2, 5);
 /// } // read locks are dropped at this point
 ///
 /// // only one write lock may be held, however
 /// {
 ///     let mut w = lock.write().unwrap();
 ///     *w += 1;
 ///     assert_eq!(*w, 6);
 /// } // write lock is dropped here
 /// ```
 #[stable]
 pub struct RwLock<T> {
     inner: Box<StaticRwLock>,
     data: UnsafeCell<T>,
 }

 unsafe impl<T:'static+Send> Send for RwLock<T> {}
 unsafe impl<T> Sync for RwLock<T> {}

 /// Structure representing a statically allocated RwLock.
 ///
 /// This structure is intended to be used inside of a `static` and will provide
 /// automatic global access as well as lazy initialization. The internal
 /// resources of this RwLock, however, must be manually deallocated.
 ///
 /// # Example
 ///
 /// ```
 /// use std::sync::{StaticRwLock, RW_LOCK_INIT};
 ///
 /// static LOCK: StaticRwLock = RW_LOCK_INIT;
 ///
 /// {
 ///     let _g = LOCK.read().unwrap();
 ///     // ... shared read access
 /// }
 /// {
 ///     let _g = LOCK.write().unwrap();
 ///     // ... exclusive write access
 /// }
 /// unsafe { LOCK.destroy() } // free all resources
 /// ```
 #[unstable = "may be merged with RwLock in the future"]
 pub struct StaticRwLock {
     lock: sys::RWLock,
     poison: poison::Flag,
 }

 unsafe impl Send for StaticRwLock {}
 unsafe impl Sync for StaticRwLock {}

 /// Constant initialization for a statically-initialized rwlock.
 #[unstable = "may be merged with RwLock in the future"]
 pub const RW_LOCK_INIT: StaticRwLock = StaticRwLock {
     lock: sys::RWLOCK_INIT,
     poison: poison::FLAG_INIT,
 };

 /// RAII structure used to release the shared read access of a lock when
 /// dropped.
 #[must_use]
 #[stable]
 pub struct RwLockReadGuard<'a, T: 'a> {
     __lock: &'a StaticRwLock,
     __data: &'a UnsafeCell<T>,
     __marker: marker::NoSend,
 }

 /// RAII structure used to release the exclusive write access of a lock when
 /// dropped.
 #[must_use]
 #[stable]
 pub struct RwLockWriteGuard<'a, T: 'a> {
     __lock: &'a StaticRwLock,
     __data: &'a UnsafeCell<T>,
     __poison: poison::Guard,
     __marker: marker::NoSend,
 }

 impl<T: Send + Sync> RwLock<T> {
     /// Creates a new instance of an RwLock which is unlocked and read to go.
     #[stable]
     pub fn new(t: T) -> RwLock<T> {
         RwLock { inner: box RW_LOCK_INIT, data: UnsafeCell::new(t) }
     }

     /// Locks this rwlock with shared read access, blocking the current thread
     /// until it can be acquired.
     ///
     /// The calling thread will be blocked until there are no more writers which
     /// hold the lock. There may be other readers currently inside the lock when
     /// this method returns. This method does not provide any guarantees with
     /// respect to the ordering of whether contentious readers or writers will
     /// acquire the lock first.
     ///
     /// Returns an RAII guard which will release this thread's shared access
     /// once it is dropped.
     ///
     /// # Failure
     ///
     /// This function will return an error if the RwLock is poisoned. An RwLock
     /// is poisoned whenever a writer panics while holding an exclusive lock.
     /// The failure will occur immediately after the lock has been acquired.
     #[inline]
     #[stable]
     pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
         unsafe { self.inner.lock.read() }
         RwLockReadGuard::new(&*self.inner, &self.data)
     }

     /// Attempt to acquire this lock with shared read access.
     ///
     /// This function will never block and will return immediately if `read`
     /// would otherwise succeed. Returns `Some` of an RAII guard which will
     /// release the shared access of this thread when dropped, or `None` if the
     /// access could not be granted. This method does not provide any
     /// guarantees with respect to the ordering of whether contentious readers
     /// or writers will acquire the lock first.
     ///
     /// # Failure
     ///
     /// This function will return an error if the RwLock is poisoned. An RwLock
     /// is poisoned whenever a writer panics while holding an exclusive lock. An
     /// error will only be returned if the lock would have otherwise been
     /// acquired.
     #[inline]
     #[stable]
     pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
         if unsafe { self.inner.lock.try_read() } {
             Ok(try!(RwLockReadGuard::new(&*self.inner, &self.data)))
         } else {
             Err(TryLockError::WouldBlock)
         }
     }

     /// Lock this rwlock with exclusive write access, blocking the current
     /// thread until it can be acquired.
     ///
     /// This function will not return while other writers or other readers
     /// currently have access to the lock.
     ///
     /// Returns an RAII guard which will drop the write access of this rwlock
     /// when dropped.
     ///
     /// # Failure
     ///
     /// This function will return an error if the RwLock is poisoned. An RwLock
     /// is poisoned whenever a writer panics while holding an exclusive lock.
     /// An error will be returned when the lock is acquired.
     #[inline]
     #[stable]
     pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
         unsafe { self.inner.lock.write() }
         RwLockWriteGuard::new(&*self.inner, &self.data)
     }

     /// Attempt to lock this rwlock with exclusive write access.
     ///
     /// This function does not ever block, and it will return `None` if a call
     /// to `write` would otherwise block. If successful, an RAII guard is
     /// returned.
     ///
     /// # Failure
     ///
     /// This function will return an error if the RwLock is poisoned. An RwLock
     /// is poisoned whenever a writer panics while holding an exclusive lock. An
     /// error will only be returned if the lock would have otherwise been
     /// acquired.
     #[inline]
     #[stable]
     pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
         if unsafe { self.inner.lock.try_read() } {
             Ok(try!(RwLockWriteGuard::new(&*self.inner, &self.data)))
         } else {
             Err(TryLockError::WouldBlock)
         }
     }
 }

 #[unsafe_destructor]
 #[stable]
 impl<T> Drop for RwLock<T> {
     fn drop(&mut self) {
         unsafe { self.inner.lock.destroy() }
     }
 }

 struct Dummy(UnsafeCell<()>);
 unsafe impl Sync for Dummy {}
 static DUMMY: Dummy = Dummy(UnsafeCell { value: () });

 impl StaticRwLock {
     /// Locks this rwlock with shared read access, blocking the current thread
     /// until it can be acquired.
     ///
     /// See `RwLock::read`.
     #[inline]
     #[unstable = "may be merged with RwLock in the future"]
     pub fn read(&'static self) -> LockResult<RwLockReadGuard<'static, ()>> {
         unsafe { self.lock.read() }
         RwLockReadGuard::new(self, &DUMMY.0)
     }

     /// Attempt to acquire this lock with shared read access.
     ///
     /// See `RwLock::try_read`.
     #[inline]
     #[unstable = "may be merged with RwLock in the future"]
     pub fn try_read(&'static self)
                     -> TryLockResult<RwLockReadGuard<'static, ()>> {
         if unsafe { self.lock.try_read() } {
             Ok(try!(RwLockReadGuard::new(self, &DUMMY.0)))
         } else {
             Err(TryLockError::WouldBlock)
         }
     }

     /// Lock this rwlock with exclusive write access, blocking the current
     /// thread until it can be acquired.
     ///
     /// See `RwLock::write`.
     #[inline]
     #[unstable = "may be merged with RwLock in the future"]
     pub fn write(&'static self) -> LockResult<RwLockWriteGuard<'static, ()>> {
         unsafe { self.lock.write() }
         RwLockWriteGuard::new(self, &DUMMY.0)
     }

     /// Attempt to lock this rwlock with exclusive write access.
     ///
     /// See `RwLock::try_write`.
     #[inline]
     #[unstable = "may be merged with RwLock in the future"]
     pub fn try_write(&'static self)
                      -> TryLockResult<RwLockWriteGuard<'static, ()>> {
         if unsafe { self.lock.try_write() } {
             Ok(try!(RwLockWriteGuard::new(self, &DUMMY.0)))
         } else {
             Err(TryLockError::WouldBlock)
         }
     }

     /// Deallocate all resources associated with this static lock.
     ///
     /// This method is unsafe to call as there is no guarantee that there are no
     /// active users of the lock, and this also doesn't prevent any future users
     /// of this lock. This method is required to be called to not leak memory on
     /// all platforms.
     #[unstable = "may be merged with RwLock in the future"]
     pub unsafe fn destroy(&'static self) {
         self.lock.destroy()
     }
 }

 impl<'rwlock, T> RwLockReadGuard<'rwlock, T> {
     fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
            -> LockResult<RwLockReadGuard<'rwlock, T>> {
         poison::map_result(lock.poison.borrow(), |_| {
             RwLockReadGuard {
                 __lock: lock,
                 __data: data,
                 __marker: marker::NoSend,
             }
         })
     }
 }
 impl<'rwlock, T> RwLockWriteGuard<'rwlock, T> {
     fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
            -> LockResult<RwLockWriteGuard<'rwlock, T>> {
         poison::map_result(lock.poison.borrow(), |guard| {
             RwLockWriteGuard {
                 __lock: lock,
                 __data: data,
                 __poison: guard,
                 __marker: marker::NoSend,
             }
         })
     }
 }

 #[stable]
 impl<'rwlock, T> Deref for RwLockReadGuard<'rwlock, T> {
     type Target = T;

     fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
 }
 #[stable]
 impl<'rwlock, T> Deref for RwLockWriteGuard<'rwlock, T> {
     type Target = T;

     fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
 }
 #[stable]
 impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T> {
     fn deref_mut(&mut self) -> &mut T {
         unsafe { &mut *self.__data.get() }
     }
 }

 #[unsafe_destructor]
 #[stable]
 impl<'a, T> Drop for RwLockReadGuard<'a, T> {
     fn drop(&mut self) {
         unsafe { self.__lock.lock.read_unlock(); }
     }
 }

 #[unsafe_destructor]
 #[stable]
 impl<'a, T> Drop for RwLockWriteGuard<'a, T> {
     fn drop(&mut self) {
         self.__lock.poison.done(&self.__poison);
         unsafe { self.__lock.lock.write_unlock(); }
     }
 }

 #[cfg(test)]
 mod tests {
     use prelude::v1::*;

     use rand::{self, Rng};
     use sync::mpsc::channel;
     use thread::Thread;
     use sync::{Arc, RwLock, StaticRwLock, RW_LOCK_INIT};

     #[test]
     fn smoke() {
         let l = RwLock::new(());
         drop(l.read().unwrap());
         drop(l.write().unwrap());
         drop((l.read().unwrap(), l.read().unwrap()));
         drop(l.write().unwrap());
     }

     #[test]
     fn static_smoke() {
         static R: StaticRwLock = RW_LOCK_INIT;
         drop(R.read().unwrap());
         drop(R.write().unwrap());
         drop((R.read().unwrap(), R.read().unwrap()));
         drop(R.write().unwrap());
         unsafe { R.destroy(); }
     }

     #[test]
     fn frob() {
         static R: StaticRwLock = RW_LOCK_INIT;
         static N: uint = 10;
         static M: uint = 1000;

         let (tx, rx) = channel::<()>();
         for _ in range(0, N) {
             let tx = tx.clone();
             Thread::spawn(move|| {
                 let mut rng = rand::thread_rng();
                 for _ in range(0, M) {
                     if rng.gen_weighted_bool(N) {
                         drop(R.write().unwrap());
                     } else {
                         drop(R.read().unwrap());
                     }
                 }
                 drop(tx);
             });
         }
         drop(tx);
         let _ = rx.recv();
         unsafe { R.destroy(); }
     }

     #[test]
     fn test_rw_arc_poison_wr() {
         let arc = Arc::new(RwLock::new(1i));
         let arc2 = arc.clone();
         let _: Result<uint, _> = Thread::scoped(move|| {
             let _lock = arc2.write().unwrap();
             panic!();
         }).join();
         assert!(arc.read().is_err());
     }

     #[test]
     fn test_rw_arc_poison_ww() {
         let arc = Arc::new(RwLock::new(1i));
         let arc2 = arc.clone();
         let _: Result<uint, _> = Thread::scoped(move|| {
             let _lock = arc2.write().unwrap();
             panic!();
         }).join();
         assert!(arc.write().is_err());
     }

     #[test]
     fn test_rw_arc_no_poison_rr() {
         let arc = Arc::new(RwLock::new(1i));
         let arc2 = arc.clone();
         let _: Result<uint, _> = Thread::scoped(move|| {
             let _lock = arc2.read().unwrap();
             panic!();
         }).join();
         let lock = arc.read().unwrap();
         assert_eq!(*lock, 1);
     }
     #[test]
     fn test_rw_arc_no_poison_rw() {
         let arc = Arc::new(RwLock::new(1i));
         let arc2 = arc.clone();
         let _: Result<uint, _> = Thread::scoped(move|| {
             let _lock = arc2.read().unwrap();
             panic!()
         }).join();
         let lock = arc.write().unwrap();
         assert_eq!(*lock, 1);
     }

     #[test]
     fn test_rw_arc() {
         let arc = Arc::new(RwLock::new(0i));
         let arc2 = arc.clone();
         let (tx, rx) = channel();

         Thread::spawn(move|| {
             let mut lock = arc2.write().unwrap();
             for _ in range(0u, 10) {
                 let tmp = *lock;
                 *lock = -1;
                 Thread::yield_now();
                 *lock = tmp + 1;
             }
             tx.send(()).unwrap();
         });

         // Readers try to catch the writer in the act
         let mut children = Vec::new();
         for _ in range(0u, 5) {
             let arc3 = arc.clone();
             children.push(Thread::scoped(move|| {
                 let lock = arc3.read().unwrap();
                 assert!(*lock >= 0);
             }));
         }

         // Wait for children to pass their asserts
         for r in children.into_iter() {
             assert!(r.join().is_ok());
         }

         // Wait for writer to finish
         rx.recv().unwrap();
         let lock = arc.read().unwrap();
         assert_eq!(*lock, 10);
     }

     #[test]
     fn test_rw_arc_access_in_unwind() {
         let arc = Arc::new(RwLock::new(1i));
         let arc2 = arc.clone();
         let _ = Thread::scoped(move|| -> () {
             struct Unwinder {
                 i: Arc<RwLock<int>>,
             }
             impl Drop for Unwinder {
                 fn drop(&mut self) {
                     let mut lock = self.i.write().unwrap();
                     *lock += 1;
                 }
             }
             let _u = Unwinder { i: arc2 };
             panic!();
         }).join();
         let lock = arc.read().unwrap();
         assert_eq!(*lock, 2);
     }
 }
	// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
	// file at the top-level directory of this distribution and at
	// http://rust-lang.org/COPYRIGHT.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.

	use prelude::v1::*;

	use cell::UnsafeCell;
	use marker;
	use ops::{Deref, DerefMut};
	use sync::poison::{self, LockResult, TryLockError, TryLockResult};
	use sys_common::rwlock as sys;

	/// A reader-writer lock
	///
	/// This type of lock allows a number of readers or at most one writer at any
	/// point in time. The write portion of this lock typically allows modification
	/// of the underlying data (exclusive access) and the read portion of this lock
	/// typically allows for read-only access (shared access).
	///
	/// The type parameter `T` represents the data that this lock protects. It is
	/// required that `T` satisfies `Send` to be shared across tasks and `Sync` to
	/// allow concurrent access through readers. The RAII guards returned from the
	/// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
	/// to allow access to the contained of the lock.
	///
	/// # Poisoning
	///
	/// RwLocks, like Mutexes, will become poisoned on panics. Note, however, that
	/// an RwLock may only be poisoned if a panic occurs while it is locked
	/// exclusively (write mode). If a panic occurs in any reader, then the lock
	/// will not be poisoned.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::RwLock;
	///
	/// let lock = RwLock::new(5i);
	///
	/// // many reader locks can be held at once
	/// {
	/// let r1 = lock.read().unwrap();
	/// let r2 = lock.read().unwrap();
	/// assert_eq!(*r1, 5);
	/// assert_eq!(*r2, 5);
	/// } // read locks are dropped at this point
	///
	/// // only one write lock may be held, however
	/// {
	/// let mut w = lock.write().unwrap();
	/// *w += 1;
	/// assert_eq!(*w, 6);
	/// } // write lock is dropped here
	/// ```
	#[stable]
	pub struct RwLock<T> {
	inner: Box<StaticRwLock>,
	data: UnsafeCell<T>,
	}

	unsafe impl<T:'static+Send> Send for RwLock<T> {}
	unsafe impl<T> Sync for RwLock<T> {}

	/// Structure representing a statically allocated RwLock.
	///
	/// This structure is intended to be used inside of a `static` and will provide
	/// automatic global access as well as lazy initialization. The internal
	/// resources of this RwLock, however, must be manually deallocated.
	///
	/// # Example
	///
	/// ```
	/// use std::sync::{StaticRwLock, RW_LOCK_INIT};
	///
	/// static LOCK: StaticRwLock = RW_LOCK_INIT;
	///
	/// {
	/// let _g = LOCK.read().unwrap();
	/// // ... shared read access
	/// }
	/// {
	/// let _g = LOCK.write().unwrap();
	/// // ... exclusive write access
	/// }
	/// unsafe { LOCK.destroy() } // free all resources
	/// ```
	#[unstable = "may be merged with RwLock in the future"]
	pub struct StaticRwLock {
	lock: sys::RWLock,
	poison: poison::Flag,
	}

	unsafe impl Send for StaticRwLock {}
	unsafe impl Sync for StaticRwLock {}

	/// Constant initialization for a statically-initialized rwlock.
	#[unstable = "may be merged with RwLock in the future"]
	pub const RW_LOCK_INIT: StaticRwLock = StaticRwLock {
	lock: sys::RWLOCK_INIT,
	poison: poison::FLAG_INIT,
	};

	/// RAII structure used to release the shared read access of a lock when
	/// dropped.
	#[must_use]
	#[stable]
	pub struct RwLockReadGuard<'a, T: 'a> {
	__lock: &'a StaticRwLock,
	__data: &'a UnsafeCell<T>,
	__marker: marker::NoSend,
	}

	/// RAII structure used to release the exclusive write access of a lock when
	/// dropped.
	#[must_use]
	#[stable]
	pub struct RwLockWriteGuard<'a, T: 'a> {
	__lock: &'a StaticRwLock,
	__data: &'a UnsafeCell<T>,
	__poison: poison::Guard,
	__marker: marker::NoSend,
	}

	impl<T: Send + Sync> RwLock<T> {
	/// Creates a new instance of an RwLock which is unlocked and read to go.
	#[stable]
	pub fn new(t: T) -> RwLock<T> {
	RwLock { inner: box RW_LOCK_INIT, data: UnsafeCell::new(t) }
	}

	/// Locks this rwlock with shared read access, blocking the current thread
	/// until it can be acquired.
	///
	/// The calling thread will be blocked until there are no more writers which
	/// hold the lock. There may be other readers currently inside the lock when
	/// this method returns. This method does not provide any guarantees with
	/// respect to the ordering of whether contentious readers or writers will
	/// acquire the lock first.
	///
	/// Returns an RAII guard which will release this thread's shared access
	/// once it is dropped.
	///
	/// # Failure
	///
	/// This function will return an error if the RwLock is poisoned. An RwLock
	/// is poisoned whenever a writer panics while holding an exclusive lock.
	/// The failure will occur immediately after the lock has been acquired.
	#[inline]
	#[stable]
	pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
	unsafe { self.inner.lock.read() }
	RwLockReadGuard::new(&*self.inner, &self.data)
	}

	/// Attempt to acquire this lock with shared read access.
	///
	/// This function will never block and will return immediately if `read`
	/// would otherwise succeed. Returns `Some` of an RAII guard which will
	/// release the shared access of this thread when dropped, or `None` if the
	/// access could not be granted. This method does not provide any
	/// guarantees with respect to the ordering of whether contentious readers
	/// or writers will acquire the lock first.
	///
	/// # Failure
	///
	/// This function will return an error if the RwLock is poisoned. An RwLock
	/// is poisoned whenever a writer panics while holding an exclusive lock. An
	/// error will only be returned if the lock would have otherwise been
	/// acquired.
	#[inline]
	#[stable]
	pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
	if unsafe { self.inner.lock.try_read() } {
	Ok(try!(RwLockReadGuard::new(&*self.inner, &self.data)))
	} else {
	Err(TryLockError::WouldBlock)
	}
	}

	/// Lock this rwlock with exclusive write access, blocking the current
	/// thread until it can be acquired.
	///
	/// This function will not return while other writers or other readers
	/// currently have access to the lock.
	///
	/// Returns an RAII guard which will drop the write access of this rwlock
	/// when dropped.
	///
	/// # Failure
	///
	/// This function will return an error if the RwLock is poisoned. An RwLock
	/// is poisoned whenever a writer panics while holding an exclusive lock.
	/// An error will be returned when the lock is acquired.
	#[inline]
	#[stable]
	pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
	unsafe { self.inner.lock.write() }
	RwLockWriteGuard::new(&*self.inner, &self.data)
	}

	/// Attempt to lock this rwlock with exclusive write access.
	///
	/// This function does not ever block, and it will return `None` if a call
	/// to `write` would otherwise block. If successful, an RAII guard is
	/// returned.
	///
	/// # Failure
	///
	/// This function will return an error if the RwLock is poisoned. An RwLock
	/// is poisoned whenever a writer panics while holding an exclusive lock. An
	/// error will only be returned if the lock would have otherwise been
	/// acquired.
	#[inline]
	#[stable]
	pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
	if unsafe { self.inner.lock.try_read() } {
	Ok(try!(RwLockWriteGuard::new(&*self.inner, &self.data)))
	} else {
	Err(TryLockError::WouldBlock)
	}
	}
	}

	#[unsafe_destructor]
	#[stable]
	impl<T> Drop for RwLock<T> {
	fn drop(&mut self) {
	unsafe { self.inner.lock.destroy() }
	}
	}

	struct Dummy(UnsafeCell<()>);
	unsafe impl Sync for Dummy {}
	static DUMMY: Dummy = Dummy(UnsafeCell { value: () });

	impl StaticRwLock {
	/// Locks this rwlock with shared read access, blocking the current thread
	/// until it can be acquired.
	///
	/// See `RwLock::read`.
	#[inline]
	#[unstable = "may be merged with RwLock in the future"]
	pub fn read(&'static self) -> LockResult<RwLockReadGuard<'static, ()>> {
	unsafe { self.lock.read() }
	RwLockReadGuard::new(self, &DUMMY.0)
	}

	/// Attempt to acquire this lock with shared read access.
	///
	/// See `RwLock::try_read`.
	#[inline]
	#[unstable = "may be merged with RwLock in the future"]
	pub fn try_read(&'static self)
	-> TryLockResult<RwLockReadGuard<'static, ()>> {
	if unsafe { self.lock.try_read() } {
	Ok(try!(RwLockReadGuard::new(self, &DUMMY.0)))
	} else {
	Err(TryLockError::WouldBlock)
	}
	}

	/// Lock this rwlock with exclusive write access, blocking the current
	/// thread until it can be acquired.
	///
	/// See `RwLock::write`.
	#[inline]
	#[unstable = "may be merged with RwLock in the future"]
	pub fn write(&'static self) -> LockResult<RwLockWriteGuard<'static, ()>> {
	unsafe { self.lock.write() }
	RwLockWriteGuard::new(self, &DUMMY.0)
	}

	/// Attempt to lock this rwlock with exclusive write access.
	///
	/// See `RwLock::try_write`.
	#[inline]
	#[unstable = "may be merged with RwLock in the future"]
	pub fn try_write(&'static self)
	-> TryLockResult<RwLockWriteGuard<'static, ()>> {
	if unsafe { self.lock.try_write() } {
	Ok(try!(RwLockWriteGuard::new(self, &DUMMY.0)))
	} else {
	Err(TryLockError::WouldBlock)
	}
	}

	/// Deallocate all resources associated with this static lock.
	///
	/// This method is unsafe to call as there is no guarantee that there are no
	/// active users of the lock, and this also doesn't prevent any future users
	/// of this lock. This method is required to be called to not leak memory on
	/// all platforms.
	#[unstable = "may be merged with RwLock in the future"]
	pub unsafe fn destroy(&'static self) {
	self.lock.destroy()
	}
	}

	impl<'rwlock, T> RwLockReadGuard<'rwlock, T> {
	fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
	-> LockResult<RwLockReadGuard<'rwlock, T>> {
	poison::map_result(lock.poison.borrow(), \|_\| {
	RwLockReadGuard {
	__lock: lock,
	__data: data,
	__marker: marker::NoSend,
	}
	})
	}
	}
	impl<'rwlock, T> RwLockWriteGuard<'rwlock, T> {
	fn new(lock: &'rwlock StaticRwLock, data: &'rwlock UnsafeCell<T>)
	-> LockResult<RwLockWriteGuard<'rwlock, T>> {
	poison::map_result(lock.poison.borrow(), \|guard\| {
	RwLockWriteGuard {
	__lock: lock,
	__data: data,
	__poison: guard,
	__marker: marker::NoSend,
	}
	})
	}
	}

	#[stable]
	impl<'rwlock, T> Deref for RwLockReadGuard<'rwlock, T> {
	type Target = T;

	fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
	}
	#[stable]
	impl<'rwlock, T> Deref for RwLockWriteGuard<'rwlock, T> {
	type Target = T;

	fn deref(&self) -> &T { unsafe { &*self.__data.get() } }
	}
	#[stable]
	impl<'rwlock, T> DerefMut for RwLockWriteGuard<'rwlock, T> {
	fn deref_mut(&mut self) -> &mut T {
	unsafe { &mut *self.__data.get() }
	}
	}

	#[unsafe_destructor]
	#[stable]
	impl<'a, T> Drop for RwLockReadGuard<'a, T> {
	fn drop(&mut self) {
	unsafe { self.__lock.lock.read_unlock(); }
	}
	}

	#[unsafe_destructor]
	#[stable]
	impl<'a, T> Drop for RwLockWriteGuard<'a, T> {
	fn drop(&mut self) {
	self.__lock.poison.done(&self.__poison);
	unsafe { self.__lock.lock.write_unlock(); }
	}
	}

	#[cfg(test)]
	mod tests {
	use prelude::v1::*;

	use rand::{self, Rng};
	use sync::mpsc::channel;
	use thread::Thread;
	use sync::{Arc, RwLock, StaticRwLock, RW_LOCK_INIT};

	#[test]
	fn smoke() {
	let l = RwLock::new(());
	drop(l.read().unwrap());
	drop(l.write().unwrap());
	drop((l.read().unwrap(), l.read().unwrap()));
	drop(l.write().unwrap());
	}

	#[test]
	fn static_smoke() {
	static R: StaticRwLock = RW_LOCK_INIT;
	drop(R.read().unwrap());
	drop(R.write().unwrap());
	drop((R.read().unwrap(), R.read().unwrap()));
	drop(R.write().unwrap());
	unsafe { R.destroy(); }
	}

	#[test]
	fn frob() {
	static R: StaticRwLock = RW_LOCK_INIT;
	static N: uint = 10;
	static M: uint = 1000;

	let (tx, rx) = channel::<()>();
	for _ in range(0, N) {
	let tx = tx.clone();
	Thread::spawn(move\|\| {
	let mut rng = rand::thread_rng();
	for _ in range(0, M) {
	if rng.gen_weighted_bool(N) {
	drop(R.write().unwrap());
	} else {
	drop(R.read().unwrap());
	}
	}
	drop(tx);
	});
	}
	drop(tx);
	let _ = rx.recv();
	unsafe { R.destroy(); }
	}

	#[test]
	fn test_rw_arc_poison_wr() {
	let arc = Arc::new(RwLock::new(1i));
	let arc2 = arc.clone();
	let _: Result<uint, _> = Thread::scoped(move\|\| {
	let _lock = arc2.write().unwrap();
	panic!();
	}).join();
	assert!(arc.read().is_err());
	}

	#[test]
	fn test_rw_arc_poison_ww() {
	let arc = Arc::new(RwLock::new(1i));
	let arc2 = arc.clone();
	let _: Result<uint, _> = Thread::scoped(move\|\| {
	let _lock = arc2.write().unwrap();
	panic!();
	}).join();
	assert!(arc.write().is_err());
	}

	#[test]
	fn test_rw_arc_no_poison_rr() {
	let arc = Arc::new(RwLock::new(1i));
	let arc2 = arc.clone();
	let _: Result<uint, _> = Thread::scoped(move\|\| {
	let _lock = arc2.read().unwrap();
	panic!();
	}).join();
	let lock = arc.read().unwrap();
	assert_eq!(*lock, 1);
	}
	#[test]
	fn test_rw_arc_no_poison_rw() {
	let arc = Arc::new(RwLock::new(1i));
	let arc2 = arc.clone();
	let _: Result<uint, _> = Thread::scoped(move\|\| {
	let _lock = arc2.read().unwrap();
	panic!()
	}).join();
	let lock = arc.write().unwrap();
	assert_eq!(*lock, 1);
	}

	#[test]
	fn test_rw_arc() {
	let arc = Arc::new(RwLock::new(0i));
	let arc2 = arc.clone();
	let (tx, rx) = channel();

	Thread::spawn(move\|\| {
	let mut lock = arc2.write().unwrap();
	for _ in range(0u, 10) {
	let tmp = *lock;
	*lock = -1;
	Thread::yield_now();
	*lock = tmp + 1;
	}
	tx.send(()).unwrap();
	});

	// Readers try to catch the writer in the act
	let mut children = Vec::new();
	for _ in range(0u, 5) {
	let arc3 = arc.clone();
	children.push(Thread::scoped(move\|\| {
	let lock = arc3.read().unwrap();
	assert!(*lock >= 0);
	}));
	}

	// Wait for children to pass their asserts
	for r in children.into_iter() {
	assert!(r.join().is_ok());
	}

	// Wait for writer to finish
	rx.recv().unwrap();
	let lock = arc.read().unwrap();
	assert_eq!(*lock, 10);
	}

	#[test]
	fn test_rw_arc_access_in_unwind() {
	let arc = Arc::new(RwLock::new(1i));
	let arc2 = arc.clone();
	let _ = Thread::scoped(move\|\| -> () {
	struct Unwinder {
	i: Arc<RwLock<int>>,
	}
	impl Drop for Unwinder {
	fn drop(&mut self) {
	let mut lock = self.i.write().unwrap();
	*lock += 1;
	}
	}
	let _u = Unwinder { i: arc2 };
	panic!();
	}).join();
	let lock = arc.read().unwrap();
	assert_eq!(*lock, 2);
	}
	}