| // Copyright 2015 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 cell::Cell; |
| use ptr; |
| use sync::Arc; |
| use sys_common; |
| use sys_common::mutex::Mutex; |
| |
| pub struct Lazy<T> { |
| lock: Mutex, |
| ptr: Cell<*mut Arc<T>>, |
| init: fn() -> Arc<T>, |
| } |
| |
| #[inline] |
| const fn done<T>() -> *mut Arc<T> { 1_usize as *mut _ } |
| |
| unsafe impl<T> Sync for Lazy<T> {} |
| |
| impl<T: Send + Sync + 'static> Lazy<T> { |
| pub const fn new(init: fn() -> Arc<T>) -> Lazy<T> { |
| Lazy { |
| lock: Mutex::new(), |
| ptr: Cell::new(ptr::null_mut()), |
| init, |
| } |
| } |
| |
| pub fn get(&'static self) -> Option<Arc<T>> { |
| unsafe { |
| let _guard = self.lock.lock(); |
| let ptr = self.ptr.get(); |
| if ptr.is_null() { |
| Some(self.init()) |
| } else if ptr == done() { |
| None |
| } else { |
| Some((*ptr).clone()) |
| } |
| } |
| } |
| |
| unsafe fn init(&'static self) -> 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 || { |
| let ptr = { |
| let _guard = self.lock.lock(); |
| self.ptr.replace(done()) |
| }; |
| drop(Box::from_raw(ptr)) |
| }); |
| let ret = (self.init)(); |
| if registered.is_ok() { |
| self.ptr.set(Box::into_raw(Box::new(ret.clone()))); |
| } |
| ret |
| } |
| } |