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// 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 core::fmt; use core::ops::Deref; use alloc_crate::boxed::Box; use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult}; use crate::sys::mutex as sys; /// The structure of sgx mutex. pub struct SgxReentrantThreadMutex(sys::SgxThreadMutex); unsafe impl Send for SgxReentrantThreadMutex {} unsafe impl Sync for SgxReentrantThreadMutex {} impl SgxReentrantThreadMutex { /// /// The function initializes a trusted mutex object within the enclave. /// /// # Description /// /// When a thread creates a mutex within an enclave, sgx_thread_mutex_ /// init simply initializes the various fields of the mutex object to indicate that /// the mutex is available. rsgx_thread_mutex_init creates a non-recursive /// mutex. The results of using a mutex in a lock or unlock operation before it has /// been fully initialized (for example, the function call to rsgx_thread_mutex_ /// init returns) are undefined. To avoid race conditions in the initialization of a /// trusted mutex, it is recommended statically initializing the mutex with the /// macro SGX_THREAD_MUTEX_INITIALIZER, SGX_THREAD_NON_RECURSIVE_MUTEX_INITIALIZER , /// of, or SGX_THREAD_RECURSIVE_MUTEX_INITIALIZER instead. /// /// # Requirements /// /// Library: libsgx_tstdc.a /// /// # Return value /// /// The trusted mutex object to be initialized. /// pub const fn new() -> SgxReentrantThreadMutex { SgxReentrantThreadMutex(sys::SgxThreadMutex::new(sys::SgxThreadMutexControl::SGX_THREAD_MUTEX_RECURSIVE)) } /// /// The function locks a trusted mutex object within an enclave. /// /// # Description /// /// To acquire a mutex, a thread first needs to acquire the corresponding spin /// lock. After the spin lock is acquired, the thread checks whether the mutex is /// available. If the queue is empty or the thread is at the head of the queue the /// thread will now become the owner of the mutex. To confirm its ownership, the /// thread updates the refcount and owner fields. If the mutex is not available, the /// thread searches the queue. If the thread is already in the queue, but not at the /// head, it means that the thread has previously tried to lock the mutex, but it /// did not succeed and had to wait outside the enclave and it has been /// awakened unexpectedly. When this happens, the thread makes an OCALL and /// simply goes back to sleep. If the thread is trying to lock the mutex for the first /// time, it will update the waiting queue and make an OCALL to get suspended. /// Note that threads release the spin lock after acquiring the mutex or before /// leaving the enclave. /// /// **Note** /// /// A thread should not exit an enclave returning from a root ECALL after acquiring /// the ownership of a mutex. Do not split the critical section protected by a /// mutex across root ECALLs. /// /// # Requirements /// /// Library: libsgx_tstdc.a /// /// # Errors /// /// **EINVAL** /// /// The trusted mutex object is invalid. /// #[inline] pub unsafe fn lock(&self) -> SysError { self.0.lock() } /// /// The function tries to lock a trusted mutex object within an enclave. /// /// # Description /// /// A thread may check the status of the mutex, which implies acquiring the spin /// lock and verifying that the mutex is available and that the queue is empty or /// the thread is at the head of the queue. When this happens, the thread /// acquires the mutex, releases the spin lock and returns 0. Otherwise, the /// thread releases the spin lock and returns EINVAL/EBUSY. The thread is not suspended /// in this case. /// /// **Note** /// /// A thread should not exit an enclave returning from a root ECALL after acquiring /// the ownership of a mutex. Do not split the critical section protected by a /// mutex across root ECALLs. /// /// # Requirements /// /// Library: libsgx_tstdc.a /// /// # Errors /// /// **EINVAL** /// /// The trusted mutex object is invalid. /// /// **EBUSY** /// /// The mutex is locked by another thread or has pending threads to acquire the mutex /// #[inline] pub unsafe fn try_lock(&self) -> SysError { self.0.try_lock() } /// /// The function unlocks a trusted mutex object within an enclave. /// /// # Description /// /// Before a thread releases a mutex, it has to verify it is the owner of the mutex. If /// that is the case, the thread decreases the refcount by 1 and then may either /// continue normal execution or wakeup the first thread in the queue. Note that /// to ensure the state of the mutex remains consistent, the thread that is /// awakened by the thread releasing the mutex will then try to acquire the /// mutex almost as in the initial call to the rsgx_thread_mutex_lock routine. /// /// # Requirements /// /// Library: libsgx_tstdc.a /// /// # Errors /// /// **EINVAL** /// /// The trusted mutex object is invalid or it is not locked by any thread. /// /// **EPERM** /// /// The mutex is locked by another thread. /// #[inline] pub unsafe fn unlock(&self) -> SysError { self.0.unlock() } /// /// The function destroys a trusted mutex object within an enclave. /// /// # Description /// /// rsgx_thread_mutex_destroy resets the mutex, which brings it to its initial /// status. In this process, certain fields are checked to prevent releasing a mutex /// that is still owned by a thread or on which threads are still waiting. /// /// **Note** /// /// Locking or unlocking a mutex after it has been destroyed results in undefined /// behavior. After a mutex is destroyed, it must be re-created before it can be /// used again. /// /// # Requirements /// /// Library: libsgx_tstdc.a /// /// # Errors /// /// **EINVAL** /// /// The trusted mutex object is invalid. /// /// **EBUSY** /// /// The mutex is locked by another thread or has pending threads to acquire the mutex. /// #[inline] pub unsafe fn destroy(&self) -> SysError { self.0.destroy() } } /// A re-entrant mutual exclusion /// /// This mutex will block *other* threads waiting for the lock to become /// available. The thread which has already locked the mutex can lock it /// multiple times without blocking, preventing a common source of deadlocks. pub struct SgxReentrantMutex<T> { inner: Box<SgxReentrantThreadMutex>, poison: poison::Flag, data: T, } unsafe impl<T: Send> Send for SgxReentrantMutex<T> {} unsafe impl<T: Send> Sync for SgxReentrantMutex<T> {} impl<T> SgxReentrantMutex<T> { /// Creates a new reentrant mutex in an unlocked state. pub fn new(t: T) -> SgxReentrantMutex<T> { SgxReentrantMutex{ inner: Box::new(SgxReentrantThreadMutex::new()), poison: poison::Flag::new(), data: t, } } /// Acquires a mutex, blocking the current thread until it is able to do so. /// /// This function will block the caller until it is available to acquire the mutex. /// Upon returning, the thread is the only thread with the mutex held. When the thread /// calling this method already holds the lock, the call shall succeed without /// blocking. /// /// # Errors /// /// If another user of this mutex panicked while holding the mutex, then /// this call will return failure if the mutex would otherwise be /// acquired. pub fn lock(&self) -> LockResult<SgxReentrantMutexGuard<'_, T>> { unsafe { self.inner.lock(); } SgxReentrantMutexGuard::new(&self) } /// Attempts to acquire this lock. /// /// If the lock could not be acquired at this time, then `Err` is returned. /// Otherwise, an RAII guard is returned. /// /// This function does not block. /// /// # Errors /// /// If another user of this mutex panicked while holding the mutex, then /// this call will return failure if the mutex would otherwise be /// acquired. pub fn try_lock(&self) -> TryLockResult<SgxReentrantMutexGuard<'_, T>> { match unsafe { self.inner.try_lock() } { Ok(_) => Ok(SgxReentrantMutexGuard::new(&self)?), Err(_) => Err(TryLockError::WouldBlock), } } } impl<T> Drop for SgxReentrantMutex<T> { fn drop(&mut self) { // This is actually safe b/c we know that there is no further usage of // this mutex (it's up to the user to arrange for a mutex to get // dropped, that's not our job) let result = unsafe { self.inner.destroy() }; debug_assert_eq!(result, Ok(()), "Error when destroy an SgxReentrantMutex: {}", result.unwrap_err()); } } impl<T: fmt::Debug + 'static> fmt::Debug for SgxReentrantMutex<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { match self.try_lock() { Ok(guard) => f.debug_struct("SgxReentrantMutex").field("data", &*guard).finish(), Err(TryLockError::Poisoned(err)) => { f.debug_struct("SgxReentrantMutex").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("SgxReentrantMutex").field("data", &LockedPlaceholder).finish() } } } } /// An RAII implementation of a "scoped lock" of a mutex. When this structure is /// dropped (falls out of scope), the lock will be unlocked. /// /// The data protected by the mutex can be accessed through this guard via its /// Deref implementation. /// /// # Mutability /// /// Unlike `MutexGuard`, `ReentrantMutexGuard` does not implement `DerefMut`, /// because implementation of the trait would violate Rust’s reference aliasing /// rules. Use interior mutability (usually `RefCell`) in order to mutate the /// guarded data. #[must_use] pub struct SgxReentrantMutexGuard<'a, T: 'a> { // funny underscores due to how Deref currently works (it disregards field // privacy). lock: &'a SgxReentrantMutex<T>, poison: poison::Guard, } impl<T> !Send for SgxReentrantMutexGuard<'_, T> {} impl<'mutex, T> SgxReentrantMutexGuard<'mutex, T> { fn new(lock: &'mutex SgxReentrantMutex<T>) -> LockResult<SgxReentrantMutexGuard<'mutex, T>> { poison::map_result(lock.poison.borrow(), |guard| { SgxReentrantMutexGuard { lock: lock, poison: guard, } }) } } impl<T> Deref for SgxReentrantMutexGuard<'_, T> { type Target = T; fn deref(&self) -> &T { &self.lock.data } } impl<T> Drop for SgxReentrantMutexGuard<'_, T> { #[inline] fn drop(&mut self) { let result = unsafe { self.lock.poison.done(&self.poison); self.lock.inner.unlock() }; debug_assert_eq!(result, Ok(()), "Error when unlocking an SgxReentrantMutex: {}", result.unwrap_err()); } } impl<T: fmt::Debug> fmt::Debug for SgxReentrantMutexGuard<'_, T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Debug::fmt(&**self, f) } } impl<T: fmt::Display> fmt::Display for SgxReentrantMutexGuard<'_, T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { (**self).fmt(f) } }