sgx_tstd/src/sync/rwlock.rs - incubator-teaclave-sgx-sdk - Git at Google

 // Licensed to the Apache Software Foundation (ASF) under one
 // or more contributor license agreements.  See the NOTICE file
 // distributed with this work for additional information
 // regarding copyright ownership.  The ASF licenses this file
 // to you under the Apache License, Version 2.0 (the
 // "License"); you may not use this file except in compliance
 // with the License.  You may obtain a copy of the License at
 //
 //   http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing,
 // software distributed under the License is distributed on an
 // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 // KIND, either express or implied.  See the License for the
 // specific language governing permissions and limitations
 // under the License..

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

 use sgx_libc as libc;

 pub use crate::sys_common::rwlock::SgxThreadRwLock;


 /// 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).
 ///
 /// In comparison, a [`Mutex`] does not distinguish between readers or writers
 /// that acquire the lock, therefore blocking any threads waiting for the lock to
 /// become available. An `RwLock` will allow any number of readers to acquire the
 /// lock as long as a writer is not holding the lock.
 ///
 /// 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. In particular, a writer which is waiting to
 /// acquire the lock in `write` might or might not block concurrent calls to
 /// `read`, e.g.:
 ///
 /// <details><summary>Potential deadlock example</summary>
 ///
 /// ```text
 /// // Thread 1             |  // Thread 2
 /// let _rg = lock.read();  |
 ///                         |  // will block
 ///                         |  let _wg = lock.write();
 /// // may deadlock         |
 /// let _rg = lock.read();  |
 /// ```
 /// </details>
 ///
 /// 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 content of the lock.
 ///
 /// # Poisoning
 ///
 /// An `RwLock`, like [`SgxMutex`], 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::SgxRwLock as 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
 /// ```
 ///
 /// [`SgxMutex`]: super::SgxMutex
 pub struct SgxRwLock<T: ?Sized> {
     inner: sys::SgxMovableThreadRwLock,
     poison: poison::Flag,
     data: UnsafeCell<T>,
 }

 unsafe impl<T: ?Sized + Send> Send for SgxRwLock<T> {}
 unsafe impl<T: ?Sized + Send + Sync> Sync for SgxRwLock<T> {}

 /// RAII structure used to release the shared read access of a lock when
 /// dropped.
 ///
 /// This structure is created by the [`read`] and [`try_read`] methods on
 /// [`RwLock`].
 ///
 /// [`read`]: RwLock::read
 /// [`try_read`]: RwLock::try_read
 pub struct SgxRwLockReadGuard<'a, T: ?Sized + 'a> {
     lock: &'a SgxRwLock<T>,
 }

 impl<T: ?Sized> !Send for SgxRwLockReadGuard<'_, T> {}
 unsafe impl<T: ?Sized + Sync> Sync for SgxRwLockReadGuard<'_, T> {}

 /// RAII structure used to release the exclusive write access of a lock when
 /// dropped.
 ///
 /// This structure is created by the [`write`] and [`try_write`] methods
 /// on [`RwLock`].
 ///
 /// [`write`]: RwLock::write
 /// [`try_write`]: RwLock::try_write
 pub struct SgxRwLockWriteGuard<'a, T: ?Sized + 'a> {
     lock: &'a SgxRwLock<T>,
     poison: poison::Guard,
 }

 impl<T: ?Sized> !Send for SgxRwLockWriteGuard<'_, T> {}
 unsafe impl<T: ?Sized + Sync> Sync for SgxRwLockWriteGuard<'_, T> {}

 impl<T> SgxRwLock<T> {
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let lock = RwLock::new(5);
     /// ```
     pub fn new(t: T) -> SgxRwLock<T> {
         SgxRwLock {
             inner: sys::SgxMovableThreadRwLock::new(),
             poison: poison::Flag::new(),
             data: UnsafeCell::new(t),
         }
     }
 }

 impl<T: ?Sized> SgxRwLock<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.
     ///
     /// # Panics
     ///
     /// This function might panic when called if the lock is already held by the current thread.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::{Arc, SgxRwLock as RwLock};
     /// use std::thread;
     ///
     /// let lock = Arc::new(RwLock::new(1));
     /// let c_lock = Arc::clone(&lock);
     ///
     /// let n = lock.read().unwrap();
     /// assert_eq!(*n, 1);
     ///
     /// thread::spawn(move || {
     ///     let r = c_lock.read();
     ///     assert!(r.is_ok());
     /// }).join().unwrap();
     /// ```
     #[inline]
     pub fn read(&self) -> LockResult<SgxRwLockReadGuard<'_, T>> {
         unsafe {
             let ret = self.inner.read();
             match ret {
                 Err(libc::EAGAIN) => panic!("rwlock maximum reader count exceeded"),
                 Err(libc::EDEADLK) => panic!("rwlock read lock would result in deadlock"),
                 _ => SgxRwLockReadGuard::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 the [`Poisoned`] error if the RwLock is poisoned.
     /// An RwLock is poisoned whenever a writer panics while holding an exclusive
     /// lock. `Poisoned` will only be returned if the lock would have otherwise been
     /// acquired.
     ///
     /// This function will return the [`WouldBlock`] error if the RwLock could not
     /// be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let lock = RwLock::new(1);
     ///
     /// match lock.try_read() {
     ///     Ok(n) => assert_eq!(*n, 1),
     ///     Err(_) => unreachable!(),
     /// };
     /// ```
     #[inline]
     pub fn try_read(&self) -> TryLockResult<SgxRwLockReadGuard<'_, T>> {
         unsafe {
             match self.inner.try_read() {
                 Ok(_) => Ok(SgxRwLockReadGuard::new(self)?),
                 Err(_) => 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.
     ///
     /// # Panics
     ///
     /// This function might panic when called if the lock is already held by the current thread.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let lock = RwLock::new(1);
     ///
     /// let mut n = lock.write().unwrap();
     /// *n = 2;
     ///
     /// assert!(lock.try_read().is_err());
     /// ```
     #[inline]
     pub fn write(&self) -> LockResult<SgxRwLockWriteGuard<'_, T>> {
         unsafe {
             match self.inner.write() {
                 Err(libc::EAGAIN) => panic!("rwlock maximum writer count exceeded"),
                 Err(libc::EDEADLK) => panic!("rwlock write lock would result in deadlock"),
                 _ => SgxRwLockWriteGuard::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 the [`Poisoned`] error if the RwLock is
     /// poisoned. An RwLock is poisoned whenever a writer panics while holding
     /// an exclusive lock. `Poisoned` will only be returned if the lock would have
     /// otherwise been acquired.
     ///
     /// This function will return the [`WouldBlock`] error if the RwLock could not
     /// be acquired because it was already locked exclusively.
     ///
     /// [`Poisoned`]: TryLockError::Poisoned
     /// [`WouldBlock`]: TryLockError::WouldBlock
     ///
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let lock = RwLock::new(1);
     ///
     /// let n = lock.read().unwrap();
     /// assert_eq!(*n, 1);
     ///
     /// assert!(lock.try_write().is_err());
     /// ```
     #[inline]
     pub fn try_write(&self) -> TryLockResult<SgxRwLockWriteGuard<'_, T>> {
         unsafe {
             match self.inner.try_write() {
                 Ok(_) => Ok(SgxRwLockWriteGuard::new(self)?),
                 Err(_) => 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.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::{Arc, SgxRwLock as RwLock};
     /// use std::thread;
     ///
     /// let lock = Arc::new(RwLock::new(0));
     /// let c_lock = Arc::clone(&lock);
     ///
     /// let _ = thread::spawn(move || {
     ///     let _lock = c_lock.write().unwrap();
     ///     panic!(); // the lock gets poisoned
     /// }).join();
     /// assert_eq!(lock.is_poisoned(), true);
     /// ```
     #[inline]
     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.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let lock = RwLock::new(String::new());
     /// {
     ///     let mut s = lock.write().unwrap();
     ///     *s = "modified".to_owned();
     /// }
     /// assert_eq!(lock.into_inner().unwrap(), "modified");
     /// ```
     pub fn into_inner(self) -> LockResult<T>
     where
         T: Sized,
     {
         let data = self.data.into_inner();
         poison::map_result(self.poison.borrow(), |_| data)
     }

     /// 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.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::sync::SgxRwLock as RwLock;
     ///
     /// let mut lock = RwLock::new(0);
     /// *lock.get_mut().unwrap() = 10;
     /// assert_eq!(*lock.read().unwrap(), 10);
     /// ```
     pub fn get_mut(&mut self) -> LockResult<&mut T> {
         let data = self.data.get_mut();
         poison::map_result(self.poison.borrow(), |_| data)
     }
 }

 impl<T: ?Sized + fmt::Debug> fmt::Debug for SgxRwLock<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let mut d = f.debug_struct("SgxRwLock");
         match self.try_read() {
             Ok(guard) => {
                 d.field("data", &&*guard);
             }
             Err(TryLockError::Poisoned(err)) => {
                 d.field("data", &&**err.get_ref());
             }
             Err(TryLockError::WouldBlock) => {
                 struct LockedPlaceholder;
                 impl fmt::Debug for LockedPlaceholder {
                     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                         f.write_str("<locked>")
                     }
                 }
                 d.field("data", &LockedPlaceholder);
             }
         }
         d.field("poisoned", &self.poison.get());
         d.finish_non_exhaustive()
     }
 }

 impl<T: Default> Default for SgxRwLock<T> {
     /// Creates a new `SgxRwLock<T>`, with the `Default` value for T.
     fn default() -> SgxRwLock<T> {
         SgxRwLock::new(Default::default())
     }
 }

 impl<T> From<T> for SgxRwLock<T> {
     /// Creates a new instance of an `SgxRwLock<T>` which is unlocked.
     /// This is equivalent to [`SgxRwLock::new`].
     fn from(t: T) -> Self {
         SgxRwLock::new(t)
     }
 }

 impl<'rwlock, T: ?Sized> SgxRwLockReadGuard<'rwlock, T> {

     unsafe fn new(lock: &'rwlock SgxRwLock<T>) -> LockResult<SgxRwLockReadGuard<'rwlock, T>> {
         poison::map_result(lock.poison.borrow(), |_| SgxRwLockReadGuard { lock })
     }
 }

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

 impl<T: fmt::Debug> fmt::Debug for SgxRwLockReadGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         (**self).fmt(f)
     }
 }

 impl<T: ?Sized + fmt::Display> fmt::Display for SgxRwLockReadGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         (**self).fmt(f)
     }
 }

 impl<T: fmt::Debug> fmt::Debug for SgxRwLockWriteGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         (**self).fmt(f)
     }
 }

 impl<T: ?Sized + fmt::Display> fmt::Display for SgxRwLockWriteGuard<'_, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         (**self).fmt(f)
     }
 }

 impl<T: ?Sized> Deref for SgxRwLockReadGuard<'_, T> {
     type Target = T;

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

 impl<T: ?Sized> Deref for SgxRwLockWriteGuard<'_, T> {
     type Target = T;

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

 impl<T: ?Sized> DerefMut for SgxRwLockWriteGuard<'_, T> {
     fn deref_mut(&mut self) -> &mut T {
         unsafe { &mut *self.lock.data.get() }
     }
 }

 impl<T: ?Sized> Drop for SgxRwLockReadGuard<'_, T> {
     fn drop(&mut self) {
         let result = unsafe {
             self.lock.inner.read_unlock()
         };
         debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxRwLock: {}", result.unwrap_err());
     }
 }

 impl<T: ?Sized> Drop for SgxRwLockWriteGuard<'_, T> {
     fn drop(&mut self) {
         self.lock.poison.done(&self.poison);
         let result = unsafe {
             self.lock.inner.write_unlock()
         };
         debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxRwLock: {}", result.unwrap_err());
     }
 }
	// Licensed to the Apache Software Foundation (ASF) under one
	// or more contributor license agreements. See the NOTICE file
	// distributed with this work for additional information
	// regarding copyright ownership. The ASF licenses this file
	// to you under the Apache License, Version 2.0 (the
	// "License"); you may not use this file except in compliance
	// with the License. You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing,
	// software distributed under the License is distributed on an
	// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
	// KIND, either express or implied. See the License for the
	// specific language governing permissions and limitations
	// under the License..

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

	use sgx_libc as libc;

	pub use crate::sys_common::rwlock::SgxThreadRwLock;


	/// 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).
	///
	/// In comparison, a [`Mutex`] does not distinguish between readers or writers
	/// that acquire the lock, therefore blocking any threads waiting for the lock to
	/// become available. An `RwLock` will allow any number of readers to acquire the
	/// lock as long as a writer is not holding the lock.
	///
	/// 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. In particular, a writer which is waiting to
	/// acquire the lock in `write` might or might not block concurrent calls to
	/// `read`, e.g.:
	///
	/// <details><summary>Potential deadlock example</summary>
	///
	/// ```text
	/// // Thread 1 \| // Thread 2
	/// let _rg = lock.read(); \|
	/// \| // will block
	/// \| let _wg = lock.write();
	/// // may deadlock \|
	/// let _rg = lock.read(); \|
	/// ```
	/// </details>
	///
	/// 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 content of the lock.
	///
	/// # Poisoning
	///
	/// An `RwLock`, like [`SgxMutex`], 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::SgxRwLock as 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
	/// ```
	///
	/// [`SgxMutex`]: super::SgxMutex
	pub struct SgxRwLock<T: ?Sized> {
	inner: sys::SgxMovableThreadRwLock,
	poison: poison::Flag,
	data: UnsafeCell<T>,
	}

	unsafe impl<T: ?Sized + Send> Send for SgxRwLock<T> {}
	unsafe impl<T: ?Sized + Send + Sync> Sync for SgxRwLock<T> {}

	/// RAII structure used to release the shared read access of a lock when
	/// dropped.
	///
	/// This structure is created by the [`read`] and [`try_read`] methods on
	/// [`RwLock`].
	///
	/// [`read`]: RwLock::read
	/// [`try_read`]: RwLock::try_read
	pub struct SgxRwLockReadGuard<'a, T: ?Sized + 'a> {
	lock: &'a SgxRwLock<T>,
	}

	impl<T: ?Sized> !Send for SgxRwLockReadGuard<'_, T> {}
	unsafe impl<T: ?Sized + Sync> Sync for SgxRwLockReadGuard<'_, T> {}

	/// RAII structure used to release the exclusive write access of a lock when
	/// dropped.
	///
	/// This structure is created by the [`write`] and [`try_write`] methods
	/// on [`RwLock`].
	///
	/// [`write`]: RwLock::write
	/// [`try_write`]: RwLock::try_write
	pub struct SgxRwLockWriteGuard<'a, T: ?Sized + 'a> {
	lock: &'a SgxRwLock<T>,
	poison: poison::Guard,
	}

	impl<T: ?Sized> !Send for SgxRwLockWriteGuard<'_, T> {}
	unsafe impl<T: ?Sized + Sync> Sync for SgxRwLockWriteGuard<'_, T> {}

	impl<T> SgxRwLock<T> {
	/// Creates a new instance of an `RwLock<T>` which is unlocked.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let lock = RwLock::new(5);
	/// ```
	pub fn new(t: T) -> SgxRwLock<T> {
	SgxRwLock {
	inner: sys::SgxMovableThreadRwLock::new(),
	poison: poison::Flag::new(),
	data: UnsafeCell::new(t),
	}
	}
	}

	impl<T: ?Sized> SgxRwLock<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.
	///
	/// # Panics
	///
	/// This function might panic when called if the lock is already held by the current thread.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::{Arc, SgxRwLock as RwLock};
	/// use std::thread;
	///
	/// let lock = Arc::new(RwLock::new(1));
	/// let c_lock = Arc::clone(&lock);
	///
	/// let n = lock.read().unwrap();
	/// assert_eq!(*n, 1);
	///
	/// thread::spawn(move \|\| {
	/// let r = c_lock.read();
	/// assert!(r.is_ok());
	/// }).join().unwrap();
	/// ```
	#[inline]
	pub fn read(&self) -> LockResult<SgxRwLockReadGuard<'_, T>> {
	unsafe {
	let ret = self.inner.read();
	match ret {
	Err(libc::EAGAIN) => panic!("rwlock maximum reader count exceeded"),
	Err(libc::EDEADLK) => panic!("rwlock read lock would result in deadlock"),
	_ => SgxRwLockReadGuard::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 the [`Poisoned`] error if the RwLock is poisoned.
	/// An RwLock is poisoned whenever a writer panics while holding an exclusive
	/// lock. `Poisoned` will only be returned if the lock would have otherwise been
	/// acquired.
	///
	/// This function will return the [`WouldBlock`] error if the RwLock could not
	/// be acquired because it was already locked exclusively.
	///
	/// [`Poisoned`]: TryLockError::Poisoned
	/// [`WouldBlock`]: TryLockError::WouldBlock
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let lock = RwLock::new(1);
	///
	/// match lock.try_read() {
	/// Ok(n) => assert_eq!(*n, 1),
	/// Err(_) => unreachable!(),
	/// };
	/// ```
	#[inline]
	pub fn try_read(&self) -> TryLockResult<SgxRwLockReadGuard<'_, T>> {
	unsafe {
	match self.inner.try_read() {
	Ok(_) => Ok(SgxRwLockReadGuard::new(self)?),
	Err(_) => 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.
	///
	/// # Panics
	///
	/// This function might panic when called if the lock is already held by the current thread.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let lock = RwLock::new(1);
	///
	/// let mut n = lock.write().unwrap();
	/// *n = 2;
	///
	/// assert!(lock.try_read().is_err());
	/// ```
	#[inline]
	pub fn write(&self) -> LockResult<SgxRwLockWriteGuard<'_, T>> {
	unsafe {
	match self.inner.write() {
	Err(libc::EAGAIN) => panic!("rwlock maximum writer count exceeded"),
	Err(libc::EDEADLK) => panic!("rwlock write lock would result in deadlock"),
	_ => SgxRwLockWriteGuard::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 the [`Poisoned`] error if the RwLock is
	/// poisoned. An RwLock is poisoned whenever a writer panics while holding
	/// an exclusive lock. `Poisoned` will only be returned if the lock would have
	/// otherwise been acquired.
	///
	/// This function will return the [`WouldBlock`] error if the RwLock could not
	/// be acquired because it was already locked exclusively.
	///
	/// [`Poisoned`]: TryLockError::Poisoned
	/// [`WouldBlock`]: TryLockError::WouldBlock
	///
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let lock = RwLock::new(1);
	///
	/// let n = lock.read().unwrap();
	/// assert_eq!(*n, 1);
	///
	/// assert!(lock.try_write().is_err());
	/// ```
	#[inline]
	pub fn try_write(&self) -> TryLockResult<SgxRwLockWriteGuard<'_, T>> {
	unsafe {
	match self.inner.try_write() {
	Ok(_) => Ok(SgxRwLockWriteGuard::new(self)?),
	Err(_) => 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.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::{Arc, SgxRwLock as RwLock};
	/// use std::thread;
	///
	/// let lock = Arc::new(RwLock::new(0));
	/// let c_lock = Arc::clone(&lock);
	///
	/// let _ = thread::spawn(move \|\| {
	/// let _lock = c_lock.write().unwrap();
	/// panic!(); // the lock gets poisoned
	/// }).join();
	/// assert_eq!(lock.is_poisoned(), true);
	/// ```
	#[inline]
	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.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let lock = RwLock::new(String::new());
	/// {
	/// let mut s = lock.write().unwrap();
	/// *s = "modified".to_owned();
	/// }
	/// assert_eq!(lock.into_inner().unwrap(), "modified");
	/// ```
	pub fn into_inner(self) -> LockResult<T>
	where
	T: Sized,
	{
	let data = self.data.into_inner();
	poison::map_result(self.poison.borrow(), \|_\| data)
	}

	/// 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.
	///
	/// # Examples
	///
	/// ```
	/// use std::sync::SgxRwLock as RwLock;
	///
	/// let mut lock = RwLock::new(0);
	/// *lock.get_mut().unwrap() = 10;
	/// assert_eq!(*lock.read().unwrap(), 10);
	/// ```
	pub fn get_mut(&mut self) -> LockResult<&mut T> {
	let data = self.data.get_mut();
	poison::map_result(self.poison.borrow(), \|_\| data)
	}
	}

	impl<T: ?Sized + fmt::Debug> fmt::Debug for SgxRwLock<T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	let mut d = f.debug_struct("SgxRwLock");
	match self.try_read() {
	Ok(guard) => {
	d.field("data", &&*guard);
	}
	Err(TryLockError::Poisoned(err)) => {
	d.field("data", &&**err.get_ref());
	}
	Err(TryLockError::WouldBlock) => {
	struct LockedPlaceholder;
	impl fmt::Debug for LockedPlaceholder {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	f.write_str("<locked>")
	}
	}
	d.field("data", &LockedPlaceholder);
	}
	}
	d.field("poisoned", &self.poison.get());
	d.finish_non_exhaustive()
	}
	}

	impl<T: Default> Default for SgxRwLock<T> {
	/// Creates a new `SgxRwLock<T>`, with the `Default` value for T.
	fn default() -> SgxRwLock<T> {
	SgxRwLock::new(Default::default())
	}
	}

	impl<T> From<T> for SgxRwLock<T> {
	/// Creates a new instance of an `SgxRwLock<T>` which is unlocked.
	/// This is equivalent to [`SgxRwLock::new`].
	fn from(t: T) -> Self {
	SgxRwLock::new(t)
	}
	}

	impl<'rwlock, T: ?Sized> SgxRwLockReadGuard<'rwlock, T> {

	unsafe fn new(lock: &'rwlock SgxRwLock<T>) -> LockResult<SgxRwLockReadGuard<'rwlock, T>> {
	poison::map_result(lock.poison.borrow(), \|_\| SgxRwLockReadGuard { lock })
	}
	}

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

	impl<T: fmt::Debug> fmt::Debug for SgxRwLockReadGuard<'_, T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	(**self).fmt(f)
	}
	}

	impl<T: ?Sized + fmt::Display> fmt::Display for SgxRwLockReadGuard<'_, T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	(**self).fmt(f)
	}
	}

	impl<T: fmt::Debug> fmt::Debug for SgxRwLockWriteGuard<'_, T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	(**self).fmt(f)
	}
	}

	impl<T: ?Sized + fmt::Display> fmt::Display for SgxRwLockWriteGuard<'_, T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	(**self).fmt(f)
	}
	}

	impl<T: ?Sized> Deref for SgxRwLockReadGuard<'_, T> {
	type Target = T;

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

	impl<T: ?Sized> Deref for SgxRwLockWriteGuard<'_, T> {
	type Target = T;

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

	impl<T: ?Sized> DerefMut for SgxRwLockWriteGuard<'_, T> {
	fn deref_mut(&mut self) -> &mut T {
	unsafe { &mut *self.lock.data.get() }
	}
	}

	impl<T: ?Sized> Drop for SgxRwLockReadGuard<'_, T> {
	fn drop(&mut self) {
	let result = unsafe {
	self.lock.inner.read_unlock()
	};
	debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxRwLock: {}", result.unwrap_err());
	}
	}

	impl<T: ?Sized> Drop for SgxRwLockWriteGuard<'_, T> {
	fn drop(&mut self) {
	self.lock.poison.done(&self.poison);
	let result = unsafe {
	self.lock.inner.write_unlock()
	};
	debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxRwLock: {}", result.unwrap_err());
	}
	}