src/libstd/sync/rwlock.rs - third_party/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 fmt;
 use marker;
 use mem;
 use ops::{Deref, DerefMut};
 use ptr;
 use sys_common::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 priority policy of the lock is dependent on the underlying operating
 /// system's implementation, and this type does not guarantee that any
 /// particular policy will be used.
 ///
 /// The type parameter `T` represents the data that this lock protects. It is
 /// required that `T` satisfies `Send` to be shared across threads 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
 ///
 /// An `RwLock`, like `Mutex`, will become poisoned on a panic. 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(5);
 ///
 /// // 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(feature = "rust1", since = "1.0.0")]
 pub struct RwLock<T: ?Sized> {
     inner: Box<sys::RWLock>,
     poison: poison::Flag,
     data: UnsafeCell<T>,
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized + Send + Sync> Send for RwLock<T> {}
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}

 /// RAII structure used to release the shared read access of a lock when
 /// dropped.
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
     __lock: &'a RwLock<T>,
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: ?Sized> !marker::Send for RwLockReadGuard<'a, T> {}

 /// RAII structure used to release the exclusive write access of a lock when
 /// dropped.
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
     __lock: &'a RwLock<T>,
     __poison: poison::Guard,
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: ?Sized> !marker::Send for RwLockWriteGuard<'a, T> {}

 impl<T> RwLock<T> {
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::RwLock;
     ///
     /// let lock = RwLock::new(5);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(t: T) -> RwLock<T> {
         RwLock {
             inner: box sys::RWLock::new(),
             poison: poison::Flag::new(),
             data: UnsafeCell::new(t),
         }
     }
 }

 impl<T: ?Sized> RwLock<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.
     ///
     /// # Errors
     ///
     /// 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(feature = "rust1", since = "1.0.0")]
     pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
         unsafe {
             self.inner.read();
             RwLockReadGuard::new(self)
         }
     }

     /// Attempts to acquire this rwlock with shared read access.
     ///
     /// If the access could not be granted at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the shared access
     /// when it is dropped.
     ///
     /// This function does not block.
     ///
     /// This function does not provide any guarantees with respect to the ordering
     /// of whether contentious readers or writers will acquire the lock first.
     ///
     /// # Errors
     ///
     /// 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(feature = "rust1", since = "1.0.0")]
     pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
         unsafe {
             if self.inner.try_read() {
                 Ok(RwLockReadGuard::new(self)?)
             } else {
                 Err(TryLockError::WouldBlock)
             }
         }
     }

     /// Locks 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.
     ///
     /// # Errors
     ///
     /// 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(feature = "rust1", since = "1.0.0")]
     pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
         unsafe {
             self.inner.write();
             RwLockWriteGuard::new(self)
         }
     }

     /// Attempts to lock this rwlock with exclusive write access.
     ///
     /// If the lock could not be acquired at this time, then `Err` is returned.
     /// Otherwise, an RAII guard is returned which will release the lock when
     /// it is dropped.
     ///
     /// This function does not block.
     ///
     /// This function does not provide any guarantees with respect to the ordering
     /// of whether contentious readers or writers will acquire the lock first.
     ///
     /// # Errors
     ///
     /// 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(feature = "rust1", since = "1.0.0")]
     pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
         unsafe {
             if self.inner.try_write() {
                 Ok(RwLockWriteGuard::new(self)?)
             } else {
                 Err(TryLockError::WouldBlock)
             }
         }
     }

     /// Determines whether the lock is poisoned.
     ///
     /// If another thread is active, the lock can still become poisoned at any
     /// time.  You should not trust a `false` value for program correctness
     /// without additional synchronization.
     #[inline]
     #[stable(feature = "sync_poison", since = "1.2.0")]
     pub fn is_poisoned(&self) -> bool {
         self.poison.get()
     }

     /// Consumes this `RwLock`, returning the underlying data.
     ///
     /// # Errors
     ///
     /// 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.
     #[stable(feature = "rwlock_into_inner", since = "1.6.0")]
     pub fn into_inner(self) -> LockResult<T> where T: Sized {
         // We know statically that there are no outstanding references to
         // `self` so there's no need to lock the inner lock.
         //
         // To get the inner value, we'd like to call `data.into_inner()`,
         // but because `RwLock` impl-s `Drop`, we can't move out of it, so
         // we'll have to destructure it manually instead.
         unsafe {
             // Like `let RwLock { inner, poison, data } = self`.
             let (inner, poison, data) = {
                 let RwLock { ref inner, ref poison, ref data } = self;
                 (ptr::read(inner), ptr::read(poison), ptr::read(data))
             };
             mem::forget(self);
             inner.destroy();  // Keep in sync with the `Drop` impl.
             drop(inner);

             poison::map_result(poison.borrow(), |_| data.into_inner())
         }
     }

     /// Returns a mutable reference to the underlying data.
     ///
     /// Since this call borrows the `RwLock` mutably, no actual locking needs to
     /// take place---the mutable borrow statically guarantees no locks exist.
     ///
     /// # Errors
     ///
     /// 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.
     #[stable(feature = "rwlock_get_mut", since = "1.6.0")]
     pub fn get_mut(&mut self) -> LockResult<&mut T> {
         // We know statically that there are no other references to `self`, so
         // there's no need to lock the inner lock.
         let data = unsafe { &mut *self.data.get() };
         poison::map_result(self.poison.borrow(), |_| data)
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> Drop for RwLock<T> {
     #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         // IMPORTANT: This code needs to be kept in sync with `RwLock::into_inner`.
         unsafe { self.inner.destroy() }
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_read() {
             Ok(guard) => write!(f, "RwLock {{ data: {:?} }}", &*guard),
             Err(TryLockError::Poisoned(err)) => {
                 write!(f, "RwLock {{ data: Poisoned({:?}) }}", &**err.get_ref())
             },
             Err(TryLockError::WouldBlock) => write!(f, "RwLock {{ <locked> }}")
         }
     }
 }

 #[stable(feature = "rw_lock_default", since = "1.9.0")]
 impl<T: Default> Default for RwLock<T> {
     fn default() -> RwLock<T> {
         RwLock::new(Default::default())
     }
 }

 impl<'rwlock, T: ?Sized> RwLockReadGuard<'rwlock, T> {
     unsafe fn new(lock: &'rwlock RwLock<T>)
                   -> LockResult<RwLockReadGuard<'rwlock, T>> {
         poison::map_result(lock.poison.borrow(), |_| {
             RwLockReadGuard {
                 __lock: lock,
             }
         })
     }
 }

 impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
     unsafe fn new(lock: &'rwlock RwLock<T>)
                   -> LockResult<RwLockWriteGuard<'rwlock, T>> {
         poison::map_result(lock.poison.borrow(), |guard| {
             RwLockWriteGuard {
                 __lock: lock,
                 __poison: guard,
             }
         })
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
     type Target = T;

     fn deref(&self) -> &T {
         unsafe { &*self.__lock.data.get() }
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
     type Target = T;

     fn deref(&self) -> &T {
         unsafe { &*self.__lock.data.get() }
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'rwlock, T: ?Sized> DerefMut for RwLockWriteGuard<'rwlock, T> {
     fn deref_mut(&mut self) -> &mut T {
         unsafe { &mut *self.__lock.data.get() }
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
     fn drop(&mut self) {
         unsafe { self.__lock.inner.read_unlock(); }
     }
 }

 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
     fn drop(&mut self) {
         self.__lock.poison.done(&self.__poison);
         unsafe { self.__lock.inner.write_unlock(); }
     }
 }

 #[cfg(test)]
 mod tests {
     #![allow(deprecated)] // rand

     use prelude::v1::*;

     use rand::{self, Rng};
     use sync::mpsc::channel;
     use thread;
     use sync::{Arc, RwLock, TryLockError};
     use sync::atomic::{AtomicUsize, Ordering};

     #[derive(Eq, PartialEq, Debug)]
     struct NonCopy(i32);

     #[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 frob() {
         const N: usize = 10;
         const M: usize = 1000;

         let r = Arc::new(RwLock::new(()));

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

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

     #[test]
     fn test_rw_arc_no_poison_rr() {
         let arc = Arc::new(RwLock::new(1));
         let arc2 = arc.clone();
         let _: Result<(), _> = thread::spawn(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(1));
         let arc2 = arc.clone();
         let _: Result<(), _> = thread::spawn(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(0));
         let arc2 = arc.clone();
         let (tx, rx) = channel();

         thread::spawn(move|| {
             let mut lock = arc2.write().unwrap();
             for _ in 0..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 0..5 {
             let arc3 = arc.clone();
             children.push(thread::spawn(move|| {
                 let lock = arc3.read().unwrap();
                 assert!(*lock >= 0);
             }));
         }

         // Wait for children to pass their asserts
         for r in children {
             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(1));
         let arc2 = arc.clone();
         let _ = thread::spawn(move|| -> () {
             struct Unwinder {
                 i: Arc<RwLock<isize>>,
             }
             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);
     }

     #[test]
     fn test_rwlock_unsized() {
         let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
         {
             let b = &mut *rw.write().unwrap();
             b[0] = 4;
             b[2] = 5;
         }
         let comp: &[i32] = &[4, 2, 5];
         assert_eq!(&*rw.read().unwrap(), comp);
     }

     #[test]
     fn test_rwlock_try_write() {
         use mem::drop;

         let lock = RwLock::new(0isize);
         let read_guard = lock.read().unwrap();

         let write_result = lock.try_write();
         match write_result {
             Err(TryLockError::WouldBlock) => (),
             Ok(_) => assert!(false, "try_write should not succeed while read_guard is in scope"),
             Err(_) => assert!(false, "unexpected error"),
         }

         drop(read_guard);
     }

     #[test]
     fn test_into_inner() {
         let m = RwLock::new(NonCopy(10));
         assert_eq!(m.into_inner().unwrap(), NonCopy(10));
     }

     #[test]
     fn test_into_inner_drop() {
         struct Foo(Arc<AtomicUsize>);
         impl Drop for Foo {
             fn drop(&mut self) {
                 self.0.fetch_add(1, Ordering::SeqCst);
             }
         }
         let num_drops = Arc::new(AtomicUsize::new(0));
         let m = RwLock::new(Foo(num_drops.clone()));
         assert_eq!(num_drops.load(Ordering::SeqCst), 0);
         {
             let _inner = m.into_inner().unwrap();
             assert_eq!(num_drops.load(Ordering::SeqCst), 0);
         }
         assert_eq!(num_drops.load(Ordering::SeqCst), 1);
     }

     #[test]
     fn test_into_inner_poison() {
         let m = Arc::new(RwLock::new(NonCopy(10)));
         let m2 = m.clone();
         let _ = thread::spawn(move || {
             let _lock = m2.write().unwrap();
             panic!("test panic in inner thread to poison RwLock");
         }).join();

         assert!(m.is_poisoned());
         match Arc::try_unwrap(m).unwrap().into_inner() {
             Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
             Ok(x) => panic!("into_inner of poisoned RwLock is Ok: {:?}", x),
         }
     }

     #[test]
     fn test_get_mut() {
         let mut m = RwLock::new(NonCopy(10));
         *m.get_mut().unwrap() = NonCopy(20);
         assert_eq!(m.into_inner().unwrap(), NonCopy(20));
     }

     #[test]
     fn test_get_mut_poison() {
         let m = Arc::new(RwLock::new(NonCopy(10)));
         let m2 = m.clone();
         let _ = thread::spawn(move || {
             let _lock = m2.write().unwrap();
             panic!("test panic in inner thread to poison RwLock");
         }).join();

         assert!(m.is_poisoned());
         match Arc::try_unwrap(m).unwrap().get_mut() {
             Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
             Ok(x) => panic!("get_mut of poisoned RwLock is Ok: {:?}", x),
         }
     }
 }
	// 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 fmt;
	use marker;
	use mem;
	use ops::{Deref, DerefMut};
	use ptr;
	use sys_common::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 priority policy of the lock is dependent on the underlying operating
	/// system's implementation, and this type does not guarantee that any
	/// particular policy will be used.
	///
	/// The type parameter `T` represents the data that this lock protects. It is
	/// required that `T` satisfies `Send` to be shared across threads 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
	///
	/// An `RwLock`, like `Mutex`, will become poisoned on a panic. 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(5);
	///
	/// // 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(feature = "rust1", since = "1.0.0")]
	pub struct RwLock<T: ?Sized> {
	inner: Box<sys::RWLock>,
	poison: poison::Flag,
	data: UnsafeCell<T>,
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	unsafe impl<T: ?Sized + Send + Sync> Send for RwLock<T> {}
	#[stable(feature = "rust1", since = "1.0.0")]
	unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}

	/// RAII structure used to release the shared read access of a lock when
	/// dropped.
	#[must_use]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub struct RwLockReadGuard<'a, T: ?Sized + 'a> {
	__lock: &'a RwLock<T>,
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'a, T: ?Sized> !marker::Send for RwLockReadGuard<'a, T> {}

	/// RAII structure used to release the exclusive write access of a lock when
	/// dropped.
	#[must_use]
	#[stable(feature = "rust1", since = "1.0.0")]
	pub struct RwLockWriteGuard<'a, T: ?Sized + 'a> {
	__lock: &'a RwLock<T>,
	__poison: poison::Guard,
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'a, T: ?Sized> !marker::Send for RwLockWriteGuard<'a, T> {}

	impl<T> RwLock<T> {
	/// Creates a new instance of an `RwLock<T>` which is unlocked.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::RwLock;
	///
	/// let lock = RwLock::new(5);
	/// ```
	#[stable(feature = "rust1", since = "1.0.0")]
	pub fn new(t: T) -> RwLock<T> {
	RwLock {
	inner: box sys::RWLock::new(),
	poison: poison::Flag::new(),
	data: UnsafeCell::new(t),
	}
	}
	}

	impl<T: ?Sized> RwLock<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.
	///
	/// # Errors
	///
	/// 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(feature = "rust1", since = "1.0.0")]
	pub fn read(&self) -> LockResult<RwLockReadGuard<T>> {
	unsafe {
	self.inner.read();
	RwLockReadGuard::new(self)
	}
	}

	/// Attempts to acquire this rwlock with shared read access.
	///
	/// If the access could not be granted at this time, then `Err` is returned.
	/// Otherwise, an RAII guard is returned which will release the shared access
	/// when it is dropped.
	///
	/// This function does not block.
	///
	/// This function does not provide any guarantees with respect to the ordering
	/// of whether contentious readers or writers will acquire the lock first.
	///
	/// # Errors
	///
	/// 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(feature = "rust1", since = "1.0.0")]
	pub fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>> {
	unsafe {
	if self.inner.try_read() {
	Ok(RwLockReadGuard::new(self)?)
	} else {
	Err(TryLockError::WouldBlock)
	}
	}
	}

	/// Locks 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.
	///
	/// # Errors
	///
	/// 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(feature = "rust1", since = "1.0.0")]
	pub fn write(&self) -> LockResult<RwLockWriteGuard<T>> {
	unsafe {
	self.inner.write();
	RwLockWriteGuard::new(self)
	}
	}

	/// Attempts to lock this rwlock with exclusive write access.
	///
	/// If the lock could not be acquired at this time, then `Err` is returned.
	/// Otherwise, an RAII guard is returned which will release the lock when
	/// it is dropped.
	///
	/// This function does not block.
	///
	/// This function does not provide any guarantees with respect to the ordering
	/// of whether contentious readers or writers will acquire the lock first.
	///
	/// # Errors
	///
	/// 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(feature = "rust1", since = "1.0.0")]
	pub fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>> {
	unsafe {
	if self.inner.try_write() {
	Ok(RwLockWriteGuard::new(self)?)
	} else {
	Err(TryLockError::WouldBlock)
	}
	}
	}

	/// Determines whether the lock is poisoned.
	///
	/// If another thread is active, the lock can still become poisoned at any
	/// time. You should not trust a `false` value for program correctness
	/// without additional synchronization.
	#[inline]
	#[stable(feature = "sync_poison", since = "1.2.0")]
	pub fn is_poisoned(&self) -> bool {
	self.poison.get()
	}

	/// Consumes this `RwLock`, returning the underlying data.
	///
	/// # Errors
	///
	/// 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.
	#[stable(feature = "rwlock_into_inner", since = "1.6.0")]
	pub fn into_inner(self) -> LockResult<T> where T: Sized {
	// We know statically that there are no outstanding references to
	// `self` so there's no need to lock the inner lock.
	//
	// To get the inner value, we'd like to call `data.into_inner()`,
	// but because `RwLock` impl-s `Drop`, we can't move out of it, so
	// we'll have to destructure it manually instead.
	unsafe {
	// Like `let RwLock { inner, poison, data } = self`.
	let (inner, poison, data) = {
	let RwLock { ref inner, ref poison, ref data } = self;
	(ptr::read(inner), ptr::read(poison), ptr::read(data))
	};
	mem::forget(self);
	inner.destroy(); // Keep in sync with the `Drop` impl.
	drop(inner);

	poison::map_result(poison.borrow(), \|_\| data.into_inner())
	}
	}

	/// Returns a mutable reference to the underlying data.
	///
	/// Since this call borrows the `RwLock` mutably, no actual locking needs to
	/// take place---the mutable borrow statically guarantees no locks exist.
	///
	/// # Errors
	///
	/// 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.
	#[stable(feature = "rwlock_get_mut", since = "1.6.0")]
	pub fn get_mut(&mut self) -> LockResult<&mut T> {
	// We know statically that there are no other references to `self`, so
	// there's no need to lock the inner lock.
	let data = unsafe { &mut *self.data.get() };
	poison::map_result(self.poison.borrow(), \|_\| data)
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<T: ?Sized> Drop for RwLock<T> {
	#[unsafe_destructor_blind_to_params]
	fn drop(&mut self) {
	// IMPORTANT: This code needs to be kept in sync with `RwLock::into_inner`.
	unsafe { self.inner.destroy() }
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
	match self.try_read() {
	Ok(guard) => write!(f, "RwLock {{ data: {:?} }}", &*guard),
	Err(TryLockError::Poisoned(err)) => {
	write!(f, "RwLock {{ data: Poisoned({:?}) }}", &**err.get_ref())
	},
	Err(TryLockError::WouldBlock) => write!(f, "RwLock {{ <locked> }}")
	}
	}
	}

	#[stable(feature = "rw_lock_default", since = "1.9.0")]
	impl<T: Default> Default for RwLock<T> {
	fn default() -> RwLock<T> {
	RwLock::new(Default::default())
	}
	}

	impl<'rwlock, T: ?Sized> RwLockReadGuard<'rwlock, T> {
	unsafe fn new(lock: &'rwlock RwLock<T>)
	-> LockResult<RwLockReadGuard<'rwlock, T>> {
	poison::map_result(lock.poison.borrow(), \|_\| {
	RwLockReadGuard {
	__lock: lock,
	}
	})
	}
	}

	impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
	unsafe fn new(lock: &'rwlock RwLock<T>)
	-> LockResult<RwLockWriteGuard<'rwlock, T>> {
	poison::map_result(lock.poison.borrow(), \|guard\| {
	RwLockWriteGuard {
	__lock: lock,
	__poison: guard,
	}
	})
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
	type Target = T;

	fn deref(&self) -> &T {
	unsafe { &*self.__lock.data.get() }
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
	type Target = T;

	fn deref(&self) -> &T {
	unsafe { &*self.__lock.data.get() }
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'rwlock, T: ?Sized> DerefMut for RwLockWriteGuard<'rwlock, T> {
	fn deref_mut(&mut self) -> &mut T {
	unsafe { &mut *self.__lock.data.get() }
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
	fn drop(&mut self) {
	unsafe { self.__lock.inner.read_unlock(); }
	}
	}

	#[stable(feature = "rust1", since = "1.0.0")]
	impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
	fn drop(&mut self) {
	self.__lock.poison.done(&self.__poison);
	unsafe { self.__lock.inner.write_unlock(); }
	}
	}

	#[cfg(test)]
	mod tests {
	#![allow(deprecated)] // rand

	use prelude::v1::*;

	use rand::{self, Rng};
	use sync::mpsc::channel;
	use thread;
	use sync::{Arc, RwLock, TryLockError};
	use sync::atomic::{AtomicUsize, Ordering};

	#[derive(Eq, PartialEq, Debug)]
	struct NonCopy(i32);

	#[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 frob() {
	const N: usize = 10;
	const M: usize = 1000;

	let r = Arc::new(RwLock::new(()));

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

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

	#[test]
	fn test_rw_arc_no_poison_rr() {
	let arc = Arc::new(RwLock::new(1));
	let arc2 = arc.clone();
	let _: Result<(), _> = thread::spawn(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(1));
	let arc2 = arc.clone();
	let _: Result<(), _> = thread::spawn(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(0));
	let arc2 = arc.clone();
	let (tx, rx) = channel();

	thread::spawn(move\|\| {
	let mut lock = arc2.write().unwrap();
	for _ in 0..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 0..5 {
	let arc3 = arc.clone();
	children.push(thread::spawn(move\|\| {
	let lock = arc3.read().unwrap();
	assert!(*lock >= 0);
	}));
	}

	// Wait for children to pass their asserts
	for r in children {
	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(1));
	let arc2 = arc.clone();
	let _ = thread::spawn(move\|\| -> () {
	struct Unwinder {
	i: Arc<RwLock<isize>>,
	}
	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);
	}

	#[test]
	fn test_rwlock_unsized() {
	let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
	{
	let b = &mut *rw.write().unwrap();
	b[0] = 4;
	b[2] = 5;
	}
	let comp: &[i32] = &[4, 2, 5];
	assert_eq!(&*rw.read().unwrap(), comp);
	}

	#[test]
	fn test_rwlock_try_write() {
	use mem::drop;

	let lock = RwLock::new(0isize);
	let read_guard = lock.read().unwrap();

	let write_result = lock.try_write();
	match write_result {
	Err(TryLockError::WouldBlock) => (),
	Ok(_) => assert!(false, "try_write should not succeed while read_guard is in scope"),
	Err(_) => assert!(false, "unexpected error"),
	}

	drop(read_guard);
	}

	#[test]
	fn test_into_inner() {
	let m = RwLock::new(NonCopy(10));
	assert_eq!(m.into_inner().unwrap(), NonCopy(10));
	}

	#[test]
	fn test_into_inner_drop() {
	struct Foo(Arc<AtomicUsize>);
	impl Drop for Foo {
	fn drop(&mut self) {
	self.0.fetch_add(1, Ordering::SeqCst);
	}
	}
	let num_drops = Arc::new(AtomicUsize::new(0));
	let m = RwLock::new(Foo(num_drops.clone()));
	assert_eq!(num_drops.load(Ordering::SeqCst), 0);
	{
	let _inner = m.into_inner().unwrap();
	assert_eq!(num_drops.load(Ordering::SeqCst), 0);
	}
	assert_eq!(num_drops.load(Ordering::SeqCst), 1);
	}

	#[test]
	fn test_into_inner_poison() {
	let m = Arc::new(RwLock::new(NonCopy(10)));
	let m2 = m.clone();
	let _ = thread::spawn(move \|\| {
	let _lock = m2.write().unwrap();
	panic!("test panic in inner thread to poison RwLock");
	}).join();

	assert!(m.is_poisoned());
	match Arc::try_unwrap(m).unwrap().into_inner() {
	Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
	Ok(x) => panic!("into_inner of poisoned RwLock is Ok: {:?}", x),
	}
	}

	#[test]
	fn test_get_mut() {
	let mut m = RwLock::new(NonCopy(10));
	*m.get_mut().unwrap() = NonCopy(20);
	assert_eq!(m.into_inner().unwrap(), NonCopy(20));
	}

	#[test]
	fn test_get_mut_poison() {
	let m = Arc::new(RwLock::new(NonCopy(10)));
	let m2 = m.clone();
	let _ = thread::spawn(move \|\| {
	let _lock = m2.write().unwrap();
	panic!("test panic in inner thread to poison RwLock");
	}).join();

	assert!(m.is_poisoned());
	match Arc::try_unwrap(m).unwrap().get_mut() {
	Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
	Ok(x) => panic!("get_mut of poisoned RwLock is Ok: {:?}", x),
	}
	}
	}