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//! # Diplomatic Bag
//! A mechanism for dealing with [`!Send`][`Send`] types when you really need
//! them to be [`Send`].
//!
//! This library provides the [`DiplomaticBag<T>`] type that is [`Send`] and
//! [`Sync`] even if the type it wraps is not. It does this by preventing direct
//! access to the wrapped type but instead provides methods for interacting with
//! it on a thread that it never leaves.
//!
//! This is useful for when you have a [`!Send`][`Send`] type (usually an FFI
//! type) that you need store for a long period of time, and needs to be
//! accessible from multiple threads, for example, in async code.
//!
//! # Examples
//! ```
//! # use diplomatic_bag::DiplomaticBag;
//! # use std::{cell::RefCell, rc::Rc};
//! // `Rc` is neither `Send` nor `Sync`
//! let foo = DiplomaticBag::new(|_| Rc::new(RefCell::new(0)));
//!
//! std::thread::spawn({
//! let foo = foo.clone();
//! move || {
//! foo.as_ref().map(|_, rc| {
//! *rc.borrow_mut() = 1;
//! });
//! }
//! });
//! ```
//! Now, being able to send an `Rc` around isn't very useful, but this comes in
//! handy when dealing with FFI types that must remain on the same thread for
//! their existence.
#![doc(html_root_url = "https://docs.rs/diplomatic-bag/0.3.1")]
#![warn(
keyword_idents,
rustdoc::missing_crate_level_docs,
missing_debug_implementations,
missing_docs,
non_ascii_idents
)]
#![forbid(unsafe_op_in_unsafe_fn)]
use crossbeam_channel::{bounded, unbounded, Sender};
use once_cell::sync::Lazy;
use std::{
fmt,
marker::PhantomData,
mem::{self, ManuallyDrop},
ptr,
thread::ThreadId,
};
/// The (sender for) the thread that all the values live on. This is lazily
/// created when the first `DiplomaticBag` is created, but will never shut down.
static THREAD_SENDER: Lazy<(Sender<Message>, ThreadId)> = Lazy::new(|| {
let (sender, receiver) = unbounded::<Message>();
let thread = std::thread::spawn({
move || {
while let Ok(closure) = receiver.recv() {
closure();
}
}
});
(sender, thread.thread().id())
});
/// A wrapper around a `T` that always implements [`Send`] and [`Sync`], but
/// doesn't allow direct access to it's internals.
///
/// For example, this doesn't compile:
/// ```compile_fail
/// let mut foo = 0;
/// // `*mut T` doesn't implement `Send` or `Sync`
/// let bar = (&mut foo) as *mut ();
/// std::thread::spawn(|| bar);
/// ```
/// but this will:
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let mut foo = ();
/// // `*mut T` doesn't implement `Send` or `Sync`,
/// // but `DiplomaticBag<*mut T>` does.
/// let bar = DiplomaticBag::new(|_| (&mut foo) as *mut ());
/// std::thread::spawn(|| bar);
/// ```
///
/// # Panics
/// All `DiplomaticBag`s share the same underlying thread, so if any panic, then
/// every bag immediately becomes unusable, and no new bags are able to be
/// created. This also means that the destructors of every value alive at that
/// point will never be run, potentially leaking some resources. Most of the
/// functions on a bag will panic if the underlying thread has stopped for any
/// reason.
///
/// # Blocking
/// Another consequence of every bag using the same thread is that no two values
/// can be modified concurrently, essentially sharing a lock on the thread. In
/// general, you should be protected from this; [`run`] and all the methods on
/// this type will detect if they are being run on the worker thread and will
/// avoid "taking the lock", alternatively you can use the [`BaggageHandler`] to
/// wrap and unwrap diplomatic bags safely.
/// You should aim to do as little computation as possible inside the closures
/// you provide to the functions on this type to prevent your code from blocking
/// the progress of others. All functions block until they have completed
/// executing the closure on the worker thread.
pub struct DiplomaticBag<T> {
/// The actual value we are storing, wrapped in an [`Untouchable<T>`] so
/// that we don't accidentally run code on it, for example drop code.
value: Untouchable<T>,
}
// SAFETY: This is the whole point of the library, Send and Sync are safe to
// implement because accessing the variable held by the DiplomaticBag is unsafe.
unsafe impl<T> Send for DiplomaticBag<T> {}
unsafe impl<T> Sync for DiplomaticBag<T> {}
impl<T> DiplomaticBag<T> {
/// Create a new `DiplomaticBag` by invoking the provided closure and
/// wrapping up the value that it produces. For why you would want to do
/// this look at the type-level or crate-level docs.
pub fn new<F>(f: F) -> Self
where
F: FnOnce(BaggageHandler) -> T,
F: Send,
{
run(|handler| DiplomaticBag {
value: Untouchable::new(f(handler)),
})
}
/// Maps a `DiplomaticBag<T>` to a `DiplomaticBag<U>`, by running a closure
/// on the wrapped value.
///
/// This closure must be [`Send`] as it will run on a worker thread. It
/// should also not panic, if it does all other active bags will leak, see
/// the type-level docs for more information.
///
/// If you need to access the contents of multiple bags simultaneously, you can
/// use the provided [`BaggageHandler`], alternatively see the
/// [`zip()`][Self::zip()] method.
///
/// # Panics
/// This function will panic if there is an issue with the underlying worker
/// thread, which is usually caused by this or another bag panicking.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// # use std::{cell::RefCell, rc::Rc};
/// let foo = DiplomaticBag::new(|_| Rc::new(RefCell::new(5)));
/// let five = foo.map(|_, foo| {
/// Rc::try_unwrap(foo).unwrap().into_inner()
/// });
/// # assert_eq!(5, five.into_inner());
/// ```
pub fn map<U, F>(self, f: F) -> DiplomaticBag<U>
where
F: FnOnce(BaggageHandler, T) -> U,
F: Send,
{
run(move |handler| {
// Safety:
// `into_inner` can only be called on the worker thread, as it gives
// access to a value of type `T` and `T` isn't necessarily `Send`,
// however that's where this will run.
let value = unsafe { self.into_inner_unchecked() };
DiplomaticBag {
value: Untouchable::new(f(handler, value)),
}
})
}
/// Maps a `DiplomaticBag<T>` to a `U`, by running a closure on the wrapped
/// value.
///
/// This closure must be [`Send`] as it will run on a worker thread. It
/// should also not panic, if it does all other active bags will leak, see
/// the type-level docs for more information.
///
/// This function is especially useful for mapping over wrapper types like
/// `Vec`, `Result`, `Option` (although see [`transpose()`][Self::transpose()]
/// for those last two). It allows this by giving a [`BaggageHandler`] to
/// the closure, which provides methods to wrap and unwrap `DiplomaticBag`s.
///
/// # Panics
/// This function will panic if there is an issue with the underlying worker
/// thread, which is usually caused by this or another bag panicking.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let foo = DiplomaticBag::new(|_| vec!["ho"; 3]);
/// let foo: Vec<_> = foo.and_then(|handler, foo| {
/// foo.into_iter().map(|item| handler.wrap(item)).collect()
/// });
/// # assert_eq!(&"ho", foo[0].as_ref().into_inner());
/// ```
pub fn and_then<U, F>(self, f: F) -> U
where
U: Send,
F: FnOnce(BaggageHandler, T) -> U,
F: Send,
{
run(move |handler| {
// Safety:
// `into_inner` can only be called on the worker thread, as it gives
// access to a value of type `T` and `T` isn't necessarily `Send`,
// however that's where this will run.
let value = unsafe { self.into_inner_unchecked() };
f(handler, value)
})
}
/// Combine a `DiplomaticBag<T>` and a `DiplomaticBag<U>` into a
/// `DiplomaticBag<(T, U)>`.
///
/// This is useful when combined with [`map()`][Self::map()] to allow
/// interacting with the internals of multiple bags simultaneously.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let one = DiplomaticBag::new(|_| 1);
/// let two = DiplomaticBag::new(|_| 2);
/// let three = one.zip(two).map(|_, (one, two)| one + two);
/// # assert_eq!(3, three.into_inner());
/// ```
pub fn zip<U>(self, other: DiplomaticBag<U>) -> DiplomaticBag<(T, U)> {
// Safety:
// We immediately wrap up the values returned by `into_inner_unchecked`
// so they spend the minimum amount of time on this thread. The only
// danger here is them accidentally getting dropped on this thread, but
// none of these functions can panic.
let value = unsafe {
Untouchable::new((self.into_inner_unchecked(), other.into_inner_unchecked()))
};
DiplomaticBag { value }
}
/// Converts a `&DiplomaticBag<T>` into a `DiplomaticBag<&T>`.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let a = DiplomaticBag::new(|_| 0);
/// let b = a.as_ref().map(|_, a| a.clone());
/// # assert_eq!(a, b);
/// ```
pub fn as_ref(&self) -> DiplomaticBag<&T> {
// Safety:
// `as_ref` produces a `&T`, which is not necessarily `Send` as `T` may
// not be `Sync`. However it is immediately wrapped in an `Untouchable`
// again and `&T`s are only read explicitly.
let value = unsafe { Untouchable::new(self.value.as_ref()) };
DiplomaticBag { value }
}
/// Converts a `&mut DiplomaticBag<T>` into a `DiplomaticBag<&mut T>`.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let mut a = DiplomaticBag::new(|_| 1);
/// let mut b = DiplomaticBag::new(|_| 2);
/// a.as_mut().zip(b.as_mut()).map(|_, (a, b)| {
/// std::mem::swap(a, b);
/// });
/// # assert_eq!(2, a.into_inner());
/// # assert_eq!(1, b.into_inner());
/// ```
pub fn as_mut(&mut self) -> DiplomaticBag<&mut T> {
// Safety:
// `as_mut` produces a `&mut T`, which is not necessarily `Send` as `T`
// may not be `Send`. However it is immediately wrapped in an
// `Untouchable` again and `&mut T`s are only read explicitly.
let value = unsafe { Untouchable::new(self.value.as_mut()) };
DiplomaticBag { value }
}
/// Unwrap the `DiplomaticBag` and retrieve the inner value.
///
/// # Safety
/// This must only be called from the worker thread if `T` is not
/// `Send` as it was created on that thread.
unsafe fn into_inner_unchecked(self) -> T {
// Unfortunately you can't destructure `Drop` types at the moment, this
// is the current workaround: pull all the fields out and then forget
// the outer struct so the drop code isn't run. Note that the memory is
// still freed as the bag was moved into this function, but every field
// should be read out so that all of their destructors are run.
let value = unsafe { ptr::read(&self.value) };
mem::forget(self);
// Safety: We forward these safety requirements to our caller.
unsafe { value.into_inner() }
}
}
impl<T: Send> DiplomaticBag<T> {
/// Unwrap a value in a [`DiplomaticBag<T>`], allowing it to be used on this
/// thread.
///
/// This is only possible if `T` is [`Send`], as otherwise accessing the
/// value on an arbitrary thread is UB. However, if `T` is [`Sync`] then you
/// can run the following to obtain a `&T`.
/// ```
/// # fn foo<T: Sync>(bag: &diplomatic_bag::DiplomaticBag<T>) -> &T {
/// bag.as_ref().into_inner()
/// # }
/// ```
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let one = DiplomaticBag::new(|_| 1);
/// let two = DiplomaticBag::new(|_| 2);
/// let eq = one.zip(two).map(|_, (one, two)| one == two).into_inner();
/// # assert!(!eq);
/// ```
pub fn into_inner(self) -> T {
unsafe { self.into_inner_unchecked() }
}
}
impl<T, E> DiplomaticBag<Result<T, E>> {
/// Convert a `DiplomaticBag<Result<T, E>>` into a
/// `Result<DiplomaticBag<T>, DiplomaticBag<E>>`.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// fn foo() -> Result<DiplomaticBag<()>, String> {
/// let bag = DiplomaticBag::new(|_| {
/// Ok(())
/// });
/// bag.transpose().map_err(|err| err.into_inner())
/// }
/// ```
pub fn transpose(self) -> Result<DiplomaticBag<T>, DiplomaticBag<E>> {
// Safety:
// Unclear, this isn't safe by the letter of the law as we read the
// bytes of inner to determine if it's `Ok` or `Err`. However, although
// not yet defined, `Send` and `Sync` are probably safety invariants,
// not validity invariants. This means we can violate the contracts in
// unsafe code soundly, as long as the T is never exposed on a different
// thread to (uncontrolled) safe code.
//
// This only reads whether this is `Ok` or `Err` and this method cannot
// panic, so no code that uses the thread invariant can observe T or E.
let inner = unsafe { self.into_inner_unchecked() };
match inner {
Ok(val) => Ok(DiplomaticBag {
value: Untouchable::new(val),
}),
Err(err) => Err(DiplomaticBag {
value: Untouchable::new(err),
}),
}
}
}
impl<T> DiplomaticBag<Option<T>> {
/// Convert a `DiplomaticBag<Option<T>>` into a
/// `Option<DiplomaticBag<T>>`.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// DiplomaticBag::new(|_| Some(())).transpose().unwrap_or_default();
/// ```
pub fn transpose(self) -> Option<DiplomaticBag<T>> {
// Safety:
// Same as above `transpose` for `DiplomaticBag<Result<T, E>>`.
let inner = unsafe { self.into_inner_unchecked() };
inner.map(|val| DiplomaticBag {
value: Untouchable::new(val),
})
}
}
/// `Drop` the inner type when the `DiplomaticBag` is dropped.
///
/// Ideally, this would only be implemented when `T` is `Drop` but `Drop` must
/// be implemented for all specializations of a generic type or none. However,
/// it does use [`std::mem::needs_drop`] to identify if the drop code needs to
/// be run.
impl<T> Drop for DiplomaticBag<T> {
fn drop(&mut self) {
if !std::mem::needs_drop::<T>() {
// If no drop code needs to be run for `T` we are fine to simply
// deallocate it.
return;
}
let _ = try_run(|_| {
// Safety:
// The inner value must only be accessed from the worker thread, and
// that is where this closure will run.
unsafe {
Untouchable::drop(&mut self.value);
}
});
}
}
/// This `Debug` impl currently won't forward any formatting specifiers except
/// for the `alternate` specifier (`#`).
impl<T: fmt::Debug> fmt::Debug for DiplomaticBag<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
struct AsIs(String);
impl fmt::Debug for AsIs {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.write_str(&self.0)
}
}
let alt = f.alternate();
// Basically, run Debug on the worker thread, then send the resulting String back
let res = self
.as_ref()
.map(move |_, this| {
if alt {
format!("{:#?}", this)
} else {
format!("{:?}", this)
}
})
.into_inner();
let res = AsIs(res); // So that we don't format it with quotes, etc.
f.debug_struct("DiplomaticBag")
.field("inner", &res)
.finish()
}
}
// We can, however, implement a bunch of other useful standard traits, as below.
// Annoyingly, `serde::Serialize`, and `serde::Deserialize` both suffer from a worse
// problem than `Debug` does. They have over 30 methods that would each need to
// syncronise with the worker thread, rather than just a single result that comes
// out the end. `Display` also has the same problem, and since it is more intended
// for non-technical users, an implementation that doesn't forward all the formatting
// parameters would be worse. `From`, and `TryFrom` fail due to the orphan rules.
// `AsRef` and `AsMut` can be implemented but conflict with the existing `as_ref`
// and `as_mut` methods, and I'm not sure the confusion is worth it.
impl<T: Default> Default for DiplomaticBag<T> {
fn default() -> Self {
DiplomaticBag::new(|_| T::default())
}
}
impl<T: Clone> Clone for DiplomaticBag<T> {
fn clone(&self) -> Self {
self.as_ref().map(|_, val| T::clone(val))
}
}
impl<T: PartialEq> PartialEq for DiplomaticBag<T> {
fn eq(&self, other: &Self) -> bool {
self.as_ref()
.zip(other.as_ref())
.map(|_, (this, other)| T::eq(this, other))
.into_inner()
}
}
impl<T: Eq> Eq for DiplomaticBag<T> {}
impl<T: PartialOrd> PartialOrd for DiplomaticBag<T> {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
self.as_ref()
.zip(other.as_ref())
.map(|_, (this, other)| T::partial_cmp(this, other))
.into_inner()
}
}
impl<T: Ord> Ord for DiplomaticBag<T> {
fn cmp(&self, other: &Self) -> std::cmp::Ordering {
self.as_ref()
.zip(other.as_ref())
.map(|_, (this, other)| T::cmp(this, other))
.into_inner()
}
}
/// A type that allows wrapping and unwrapping [`DiplomaticBag`]s inside the
/// execution context of another bag.
///
/// This allows computations on the wrapped values of multiple bags, and
/// provides a mechanism for returning `!Send` and `!Sync` types from
/// computations done on values inside bags.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let one = DiplomaticBag::new(|_handler| 1);
/// let two = DiplomaticBag::new(|_handler| 2);
/// let three = one.and_then(|handler, one| {
/// let three = one + handler.unwrap(two.as_ref());
/// handler.wrap(three)
/// });
/// # assert_eq!(3, three.into_inner());
#[derive(Debug, Clone, Copy)]
pub struct BaggageHandler(PhantomData<*mut ()>);
impl BaggageHandler {
/// Create a new `BaggageHandler`.
///
/// # Safety
/// This must only be called from the worker thread, as it allows safe
/// wrapping and unwrapping of `DiplomaticBag`s.
unsafe fn new() -> Self {
Self(PhantomData)
}
/// Wrap a value in a [`DiplomaticBag`], allowing it to be sent to other
/// threads even if it is not `Send`.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let foo: DiplomaticBag<u8> = DiplomaticBag::new(|_handler| 2);
/// let bar: DiplomaticBag<u8> =
/// foo.and_then(|handler, value| handler.wrap(value.clone()));
/// ```
pub fn wrap<T>(&self, value: T) -> DiplomaticBag<T> {
DiplomaticBag {
value: Untouchable::new(value),
}
}
/// Unwrap a value in a [`DiplomaticBag`], allowing it to be used inside
/// the execution context of another bag.
///
/// # Examples
/// ```
/// # use diplomatic_bag::DiplomaticBag;
/// let one = DiplomaticBag::new(|_handler| 1);
/// let two = DiplomaticBag::new(|_handler| 2);
/// let three = one.and_then(|handler, one| one + handler.unwrap(two));
/// # assert_eq!(3, three);
/// ```
pub fn unwrap<T>(&self, proxy: DiplomaticBag<T>) -> T {
unsafe { proxy.into_inner_unchecked() }
}
}
/// Run an arbitrary closure on the shared worker thread.
///
/// # Panics
/// This panics if the provided closure fails or the worker thread is not
/// running, which will happen if a previous operation panicked.
pub fn run<R, F>(f: F) -> R
where
R: Send,
F: FnOnce(BaggageHandler) -> R,
F: Send,
{
try_run(f).unwrap()
}
/// Run an arbitrary closure on the shared worker thread, similar to the
/// [`run()`][Self::run()] method. However, this does _not_ panic if the
/// worker thread has stopped unlike [`run`].
///
/// # Errors
/// This will throw an error if the operation fails, usually due to an issue
/// with the worker thread. See the [`Error`] type for more details.
fn try_run<R, F>(f: F) -> Result<R, Error>
where
R: Send,
F: FnOnce(BaggageHandler) -> R,
F: Send,
{
let (task_sender, worker) = &*THREAD_SENDER;
if std::thread::current().id() == *worker {
// If the current thread is the worker thread then run the closure.
// This (mostly) prevents a deadlock where a closure on the worker
// thread is waiting for another operation in the worker threads queue.
// Safety: we are on the worker thread.
let baggage_handler = unsafe { BaggageHandler::new() };
return Ok(f(baggage_handler));
}
// Set up a rendezvous channel so that the closure can return the value.
let (sender, receiver) = bounded(0);
// This is the closure that will get run on the worker thread, it gets
// boxed up as we're passing ownership to that thread and we can't pass
// it directly due to every invocation of this function potentially
// having a different closure type.
let closure = Box::new(move || {
let baggage_handler = unsafe { BaggageHandler::new() };
let value = f(baggage_handler);
let _ = sender.send(value);
// Note that after calling `send` we have dropped or returned all values
// that could possibly be holding references to data on the calling
// thread, which makes it safe for `try_run` to return.
}) as Box<dyn FnOnce() + Send>;
// Extend the closure's lifetime as rust doesn't know that we won't return
// until the closure has given all possible references back to us.
// Safety:
// We have to be careful with this closure from now on but we know that
// anything borrowed by the closure must live at least as long as this
// function call. So we must be careful that this closure is dropped before
// this function returns and `result` is dropped.
let closure: Box<dyn FnOnce() + Send + 'static> = unsafe { mem::transmute(closure) };
// Send the closure to the worker thread!
// `task_sender` is an unbounded channel so this shouldn't block but
// it may fail if the worker thread has stopped. In that case the
// message gets given back to us and immediately dropped, satisfying the
// closure safety conditions.
task_sender.send(closure).map_err(|_| Error::Send)?;
// The closure is now running/pending on the worker thread. It will notify
// us when it's done and in the meantime we must keep everything alive.
// Note that `recv` can fail, but only in the case where the channel gets
// disconnected and the only way that can happen is if the worker thread
// drops the message, so we're safe to exit.
receiver.recv().map_err(|_| Error::Recv)
}
/// The error type used by [`DiplomaticBag<T>::try_run()`].
///
/// This indicates that the underlying worker thread is not running, this is
/// probably because a user provided closure panicked and crashed the thread.
///
/// [`DiplomaticBag<T>::try_run()`]: DiplomaticBag::try_run()
#[derive(Debug)]
enum Error {
/// An issue occurred with sending the closure to the worker thread.
/// This would usually indicate that the worker thread has stopped for some
/// reason (presumably a user provided closure panicked).
Send,
/// An issue occurred while waiting for the worker thread to send the
/// notification back, either the closure panicked or something in the
/// queue before us panicked.
Recv,
}
impl std::error::Error for Error {}
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("diplomatic bag worker thread not running")
}
}
/// The code to run on the worker thread.
type Message = Box<dyn FnOnce() + Send + 'static>;
/// A wrapper type that makes it completely unsafe to access the type that it
/// wraps. This is what makes the [`DiplomaticBag`] type `Send` and `Sync` even
/// when `T` is not. It has similar semantics to [`ManuallyDrop`] as it just
/// wraps one.
#[repr(transparent)]
struct Untouchable<T>(ManuallyDrop<T>);
impl<T> Untouchable<T> {
/// Create a new `Untouchable`.
fn new(value: T) -> Self {
Self(ManuallyDrop::new(value))
}
/// Consume the `Untouchable` and get the wrapped type out.
///
/// # Safety
/// This must be called on the same thread that the type was created on if
/// `T` is not `Send`.
unsafe fn into_inner(self) -> T {
ManuallyDrop::into_inner(self.0)
}
/// Get a shared reference to the wrapped type.
///
/// # Safety
/// This must be called on the same thread that the type was created on if
/// `T` is not `Sync`.
unsafe fn as_ref(&self) -> &T {
&self.0
}
/// Get a shared reference to the wrapped type.
///
/// # Safety
/// This must be called on the same thread that the type was created on if
/// `T` is not `Send`.
unsafe fn as_mut(&mut self) -> &mut T {
&mut self.0
}
/// Runs the drop code on the wrapped value.
///
/// # Safety
/// This must be called on the same thread that the type was created on if
/// `T` is not `Send`. It must also only ever be called once, and the value
/// inside the `Untouchable` never accessed again. Preferably, the
/// `Untouchable` should be immediately dropped after calling this method.
unsafe fn drop(&mut self) {
unsafe { ManuallyDrop::drop(&mut self.0) };
}
}
// Safety:
// It is unsafe to access the value inside an `Untouchable`, so it's ok for the
// wrapper to be `Send` and `Sync`.
unsafe impl<T> Send for Untouchable<T> {}
unsafe impl<T> Sync for Untouchable<T> {}
#[cfg(test)]
mod tests {
use slotmap::{DefaultKey, SlotMap};
use static_assertions::{assert_impl_all, assert_not_impl_any};
use std::{
cell::{Cell, RefCell},
marker::PhantomData,
sync::{
atomic::{AtomicBool, Ordering},
Arc,
},
};
use super::*;
thread_local! {
static TEST: RefCell<SlotMap<DefaultKey, u32>> = RefCell::new(SlotMap::new());
}
struct NotSend {
key: DefaultKey,
value: Cell<u32>,
marker: PhantomData<*mut ()>,
}
impl NotSend {
fn new() -> Self {
let value = rand::random();
let key = TEST.with(|map| map.borrow_mut().insert(value));
Self {
key,
value: Cell::new(value),
marker: PhantomData,
}
}
fn change(&self) {
self.value.set(rand::random());
TEST.with(|map| map.borrow_mut()[self.key] = self.value.get())
}
fn verify(&self) {
assert_eq!(
Some(self.value.get()),
TEST.with(|map| map.borrow().get(self.key).copied())
);
}
}
impl Drop for NotSend {
fn drop(&mut self) {
self.verify()
}
}
assert_impl_all!(DiplomaticBag<*mut ()>: Send, Sync);
assert_not_impl_any!(BaggageHandler: Send, Sync);
assert_impl_all!(Error: std::error::Error, Send, Sync);
#[test]
fn create_and_drop() {
let _value = DiplomaticBag::new(|_| NotSend::new());
}
#[test]
fn execute() {
let value = DiplomaticBag::new(|_| NotSend::new());
value.map(|_, value| value.verify());
}
#[test]
fn execute_ref() {
let value = DiplomaticBag::new(|_| NotSend::new());
value.as_ref().map(|_, value| {
value.verify();
value.change();
});
}
#[test]
fn execute_mut() {
let mut value = DiplomaticBag::new(|_| NotSend::new());
value.as_mut().map(|_, value| {
value.verify();
value.change();
});
}
#[test]
fn drop_inner() {
let atomic = Arc::new(AtomicBool::new(false));
struct SetOnDrop(Arc<AtomicBool>);
impl Drop for SetOnDrop {
fn drop(&mut self) {
self.0.store(true, Ordering::SeqCst);
}
}
let bag = DiplomaticBag::new(|_| SetOnDrop(atomic.clone()));
assert!(!atomic.load(Ordering::SeqCst));
drop(bag);
assert!(atomic.load(Ordering::SeqCst));
}
#[test]
fn readme_version() {
version_sync::assert_markdown_deps_updated!("README.md");
}
#[test]
fn html_root_url_version() {
version_sync::assert_html_root_url_updated!("src/lib.rs");
}
}