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// 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 prelude::v1::*;
use boxed;
use cell::UnsafeCell;
use rt;
use sync::{StaticMutex, Arc};
pub struct Lazy<T> {
pub lock: StaticMutex,
pub ptr: UnsafeCell<*mut Arc<T>>,
pub init: fn() -> Arc<T>,
}
unsafe impl<T> Sync for Lazy<T> {}
macro_rules! lazy_init {
($init:expr) => (::io::lazy::Lazy {
lock: ::sync::MUTEX_INIT,
ptr: ::cell::UnsafeCell { value: 0 as *mut _ },
init: $init,
})
}
impl<T: Send + Sync + 'static> Lazy<T> {
pub fn get(&'static self) -> Option<Arc<T>> {
let _g = self.lock.lock();
unsafe {
let ptr = *self.ptr.get();
if ptr.is_null() {
Some(self.init())
} else if ptr as usize == 1 {
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 = rt::at_exit(move || {
let g = self.lock.lock();
let ptr = *self.ptr.get();
*self.ptr.get() = 1 as *mut _;
drop(g);
drop(Box::from_raw(ptr))
});
let ret = (self.init)();
if registered.is_ok() {
*self.ptr.get() = boxed::into_raw(Box::new(ret.clone()));
}
return ret
}
}
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