1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
// 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 sgx_types::SysError;
use sgx_trts::libc;
use core::cell::UnsafeCell;
use core::mem;
use core::ptr;
use core::fmt;
use core::ops::{Deref, DerefMut};
use alloc_crate::boxed::Box;
use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
use crate::sys::rwlock as imp;

/// An OS-based reader-writer lock.
///
/// This structure is entirely unsafe and serves as the lowest layer of a
/// cross-platform binding of system rwlocks. It is recommended to use the
/// safer types at the top level of this crate instead of this type.
pub struct SgxThreadRwLock(imp::SgxThreadRwLock);

unsafe impl Send for SgxThreadRwLock {}
unsafe impl Sync for SgxThreadRwLock {}

impl SgxThreadRwLock {

    /// Creates a new reader-writer lock for use.
    pub const fn new() -> Self {
        SgxThreadRwLock(imp::SgxThreadRwLock::new())
    }

    /// Acquires shared access to the underlying lock, blocking the current
    /// thread to do so.
    #[inline]
    pub unsafe fn read(&self) -> SysError {
        self.0.read()
    }

    /// Attempts to acquire shared access to this lock, returning whether it
    /// succeeded or not.
    ///
    /// This function does not block the current thread.
    #[inline]
    pub unsafe fn try_read(&self) -> SysError {
        self.0.try_read()
    }

    /// Acquires write access to the underlying lock, blocking the current thread
    /// to do so.
    #[inline]
    pub unsafe fn write(&self) -> SysError {
        self.0.write()
    }

    /// Attempts to acquire exclusive access to this lock, returning whether it
    /// succeeded or not.
    ///
    /// This function does not block the current thread.
    #[inline]
    pub unsafe fn try_write(&self) -> SysError {
        self.0.try_write()
    }

    /// Unlocks previously acquired shared access to this lock.
    #[inline]
    pub unsafe fn read_unlock(&self) -> SysError {
        self.0.read_unlock()
    }

    /// Unlocks previously acquired exclusive access to this lock.
    #[inline]
    pub unsafe fn write_unlock(&self) -> SysError {
        self.0.write_unlock()
    }

    /// Destroys OS-related resources with this RWLock.
    #[inline]
    pub unsafe fn destroy(&self) -> SysError {
        self.0.destroy()
    }
}

/// 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.
///
/// 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 [`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.
///
pub struct SgxRwLock<T: ?Sized> {
    inner: Box<SgxThreadRwLock>,
    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`].
pub struct SgxRwLockReadGuard<'a, T: ?Sized + 'a> {
    lock: &'a SgxRwLock<T>,
    poison: poison::Guard,
}

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`].
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.
    pub fn new(t: T) -> SgxRwLock<T> {
        SgxRwLock {
            inner: Box::new(SgxThreadRwLock::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.
    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 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.
    pub fn try_read(&self) -> TryLockResult<SgxRwLockReadGuard<'_, T>> {
        unsafe {
            let ret = self.inner.try_read();
            match ret {
                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.
    pub fn write(&self) -> LockResult<SgxRwLockWriteGuard<'_, T>> {
        unsafe {
            let ret = self.inner.write();
            match ret {
                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 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.
    pub fn try_write(&self) -> TryLockResult<SgxRwLockWriteGuard<'_, T>> {
        unsafe {
            let ret = self.inner.try_write();
            match ret {
                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.
    ///
    #[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.
    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 {
            let (inner, poison, data) = {
                let SgxRwLock { ref inner, ref poison, ref data } = self;
                (ptr::read(inner), ptr::read(poison), ptr::read(data))
            };
            mem::forget(self);
            let _ = inner.destroy();
            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.
    ///
    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)
    }
}

unsafe impl<#[may_dangle] T: ?Sized> Drop for SgxRwLock<T> {
    fn drop(&mut self) {
        // IMPORTANT: This code needs to be kept in sync with `SgxRwLock::into_inner`.
        let result = unsafe { self.inner.destroy() };
        debug_assert_eq!(result, Ok(()), "Error when destroy an SgxMutex: {}", result.unwrap_err());
    }
}

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

                f.debug_struct("SgxRwLock").field("data", &LockedPlaceholder).finish()
            }
        }
    }
}

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`].
    ///
    /// [`SgxRwLock::new`]: #method.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(), |guard| SgxRwLockReadGuard { lock, poison: guard })
    }
}

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 {
        f.debug_struct("SgxRwLockReadGuard").field("lock", &self.lock).finish()
    }
}

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 {
        f.debug_struct("SgxRwLockWriteGuard").field("lock", &self.lock).finish()
    }
}

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.poison.done(&self.poison);
            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) {
        let result = unsafe {
            self.lock.poison.done(&self.poison);
            self.lock.inner.write_unlock()
        };
        debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxRwLock: {}", result.unwrap_err());
    }
}