// SPDX-License-Identifier: Apache-2.0 OR MIT use std::fmt::{self, Debug};use std::thread::{self, ThreadId}; /// ThreadBound is a Sync-maker and Send-maker that allows accessing a value/// of type T only from the original thread on which the ThreadBound was/// constructed.pub(crate) struct ThreadBound<T> {    value: T,    thread_id: ThreadId,} unsafe impl<T> Sync for ThreadBound<T> {} // Send bound requires Copy, as otherwise Drop could run in the wrong place.//// Today Copy and Drop are mutually exclusive so `T: Copy` implies `T: !Drop`.// This impl needs to be revisited if that restriction is relaxed in the future.unsafe impl<T: Copy> Send for ThreadBound<T> {} impl<T> ThreadBound<T> {    pub(crate) fn new(value: T) -> Self {        ThreadBound {            value,            thread_id: thread::current().id(),        }    }     pub(crate) fn get(&self) -> Option<&T> {        if thread::current().id() == self.thread_id {            Some(&self.value)        } else {            None        }    }} impl<T: Debug> Debug for ThreadBound<T> {    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {        match self.get() {            Some(value) => Debug::fmt(value, formatter),            None => formatter.write_str("unknown"),        }    }} // Copy the bytes of T, even if the currently running thread is the "wrong"// thread. This is fine as long as the original thread is not simultaneously// mutating this value via interior mutability, which would be a data race.//// Currently `T: Copy` is sufficient to guarantee that T contains no interior// mutability, because _all_ interior mutability in Rust is built on// std::cell::UnsafeCell, which has no Copy impl. This impl needs to be// revisited if that restriction is relaxed in the future.impl<T: Copy> Copy for ThreadBound<T> {} impl<T: Copy> Clone for ThreadBound<T> {    fn clone(&self) -> Self {        *self    }}