| // 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 alloc_crate::sync::Arc; |
| use core::cell::Cell; |
| use core::cell::UnsafeCell; |
| use core::ptr; |
| use crate::sync::SgxThreadMutex as Mutex; |
| use crate::sys_common; |
| |
| pub struct Lazy<T> { |
| // We never call `lock.init()`, so it is UB to attempt to acquire this mutex reentrantly! |
| lock: Mutex, |
| ptr: Cell<*mut Arc<T>>, |
| } |
| |
| #[inline] |
| const fn done<T>() -> *mut Arc<T> { |
| 1_usize as *mut _ |
| } |
| |
| unsafe impl<T> Sync for Lazy<T> {} |
| |
| impl<T> Lazy<T> { |
| pub const fn new() -> Lazy<T> { |
| Lazy { lock: Mutex::new(), ptr: Cell::new(ptr::null_mut()) } |
| } |
| } |
| |
| impl<T: Send + Sync + 'static> Lazy<T> { |
| /// Safety: `init` must not call `get` on the variable that is being |
| /// initialized. |
| pub unsafe fn get(&'static self, init: fn() -> Arc<T>) -> Option<Arc<T>> { |
| let r = self.lock.lock(); |
| if r.is_err() { |
| return None; |
| } |
| let ptr = self.ptr.get(); |
| let ret = if ptr.is_null() { |
| Some(self.init(init)) |
| } else if ptr == done() { |
| None |
| } else { |
| Some((*ptr).clone()) |
| }; |
| self.lock.unlock(); |
| ret |
| } |
| |
| // Must only be called with `lock` held |
| unsafe fn init(&'static self, init: fn() -> Arc<T>) -> Arc<T> { |
| // If we successfully register an at exit handler, then we cache the |
| // `Arc` allocation in our own internal box (it will get deallocated by |
| // the at exit handler). Otherwise we just return the freshly allocated |
| // `Arc`. |
| let registered = sys_common::at_exit(move || { |
| self.lock.lock(); |
| let ptr = self.ptr.replace(done()); |
| self.lock.unlock(); |
| drop(Box::from_raw(ptr)) |
| }); |
| // This could reentrantly call `init` again, which is a problem |
| // because our `lock` allows reentrancy! |
| // That's why `get` is unsafe and requires the caller to ensure no reentrancy happens. |
| let ret = init(); |
| if registered.is_ok() { |
| self.ptr.set(Box::into_raw(Box::new(ret.clone()))); |
| } |
| ret |
| } |
| } |
| |
| #[allow(dead_code)] |
| pub struct LazyStatic<T> { |
| lock: Mutex, |
| opt: UnsafeCell<Option<Arc<T>>>, |
| } |
| |
| unsafe impl<T> Sync for LazyStatic<T> {} |
| |
| #[allow(dead_code)] |
| impl<T> LazyStatic<T> { |
| pub const fn new() -> LazyStatic<T> { |
| LazyStatic { lock: Mutex::new(), opt: UnsafeCell::new(None) } |
| } |
| } |
| |
| #[allow(dead_code)] |
| impl<T: Send + Sync + 'static> LazyStatic<T> { |
| pub unsafe fn get(&'static self, init: fn() -> Arc<T>) -> Option<Arc<T>> { |
| let r = self.lock.lock(); |
| if r.is_err() { |
| return None; |
| } |
| let ret = match *self.opt.get() { |
| Some(ref arc) => Some(arc.clone()), |
| None => Some(self.init(init)), |
| }; |
| self.lock.unlock(); |
| ret |
| } |
| |
| unsafe fn init(&'static self, init: fn() -> Arc<T>) -> Arc<T> { |
| let ret = init(); |
| *self.opt.get() = Some(ret.clone()); |
| ret |
| } |
| } |