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//! Customizable user-data wrappers. //! //! ## `NativeClass` and user-data //! //! In Godot Engine, scripted behavior is attached to base objects through "script instances": //! objects that store script state, and allow dynamic dispatch of overridden methods. GDNative //! exposes this to native languages as a `void *` pointer, known as "user-data", that may point //! to anything defined by the native library in question. //! //! Godot is written in C++, and unlike Rust, it doesn't have the same strict reference aliasing //! constraints. This user-data pointer can be aliased mutably, and called freely from different //! threads by the engine or other scripts. Thus, to maintain safety, wrapper types are to be used //! to make sure that the Rust rules for references are always held for the `self` argument, and //! no UB can occur because we freed `owner` or put another script on it. //! //! ## Choosing a wrapper type //! //! The default user data wrapper used by derive macro, when no `user_data` attribute is present, //! is defined as the type alias `DefaultUserData<T>`. Currently, it is `LocalCellData<T>`. This //! may change in the future, and changes to it will not be considered breaking changes. //! //! To choose another wrapper type, put the `#[user_data]` attribute on your `NativeScript` type //! if you are using the derive macro: //! //! ```ignore //! #[derive(NativeClass)] //! #[inherit(gdnative::Node)] //! #[user_data(gdnative::user_data::MutexData<HelloWorld>)] //! struct HelloWorld; //! ``` //! //! ...or, if you are implementing `NativeScript` manually, set the `UserData` associated type //! to the type you choose. //! //! ## Which wrapper to use? //! //! ### Use a `MutexData<T>` when: //! //! - You don't want to handle locks explicitly. //! - Your `NativeClass` type is only `Send`, but not `Sync`. //! //! ### Use a `RwLockData<T>` when: //! //! - You don't want to handle locks explicitly. //! - Some of your exported methods take `&self`, and you don't need them to be exclusive. //! - Your `NativeClass` type is `Send + Sync`. //! //! ### Use a `ArcData<T>` when: //! //! - You want safety for your methods, but can't tolerate lock overhead on each method call. //! - You want fine grained lock control for parallelism. //! - All your exported methods take `&self`. //! - Your `NativeClass` type is `Send + Sync`. //! //! ### Use a `LocalCellData<T>` when: //! //! - Your `NativeClass` type is not `Send`, and you will only ever use it from the thread where //! it's originally created. //! //! ### Use `Aether<T>` when: //! //! - Your `NativeClass` type is a zero-sized type (ZST) that is `Copy + Default`. //! - You don't need to do anything special in `Drop`. use parking_lot::{Mutex, RwLock}; use std::fmt::Debug; use std::marker::PhantomData; use std::mem; use std::sync::Arc; use std::time::Duration; use crate::nativescript::NativeClass; /// Trait for customizable user-data wrappers. /// /// See module-level documentation for detailed explanation on user-data. pub unsafe trait UserData: Sized + Clone { type Target: NativeClass; /// Creates a new owned wrapper from a `NativeClass` instance. /// /// This operation must never fail. fn new(val: Self::Target) -> Self; /// Takes a native instance and returns an opaque pointer that can be used to recover it. /// /// This gives "ownership" to the engine. /// /// This operation must never fail. fn into_user_data(self) -> *const libc::c_void; /// Takes an opaque pointer produced by `into_user_data` and "consumes" it to produce the /// original instance, keeping the reference count. /// /// This should be used when "ownership" is taken from the engine, i.e. destructors. /// Use elsewhere can lead to premature drops of the instance contained inside. /// /// `ptr` is guaranteed to be non-null. /// /// This operation must never fail. /// /// # Safety /// /// `ptr` must be pointing to valid data of the correct type. unsafe fn consume_user_data_unchecked(ptr: *const libc::c_void) -> Self; /// Takes an opaque pointer produced by `into_user_data` and "clones" it to produce the /// original instance, increasing the reference count. /// /// This should be used when user data is "borrowed" from the engine. /// /// `ptr` is guaranteed to be non-null. /// /// This operation must never fail. /// /// # Safety /// /// `ptr` must be pointing to valid data of the correct type. unsafe fn clone_from_user_data_unchecked(ptr: *const libc::c_void) -> Self; } /// Trait for wrappers that can be mapped immutably. pub trait Map: UserData { type Err: Debug; /// Maps a `&T` to `U`. Called for methods that take `&self`. /// /// Implementations of this method must not panic. Failures should be indicated by /// returning `Err`. fn map<F, U>(&self, op: F) -> Result<U, Self::Err> where F: FnOnce(&Self::Target) -> U; } /// Trait for wrappers that can be mapped mutably. pub trait MapMut: UserData { type Err: Debug; /// Maps a `&mut T` to `U`. Called for methods that take `&mut self`. /// /// Implementations of this method must not panic. Failures should be indicated by /// returning `Err`. fn map_mut<F, U>(&self, op: F) -> Result<U, Self::Err> where F: FnOnce(&mut Self::Target) -> U; } /// The default user data wrapper used by derive macro, when no `user_data` attribute is present. /// This may change in the future. pub type DefaultUserData<T> = LocalCellData<T>; /// Error type indicating that an operation can't fail. #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)] pub enum Infallible {} /// Policies to deal with potential deadlocks /// /// As Godot allows mutable pointer aliasing, doing certain things in exported method bodies may /// lead to the engine calling another method on `owner`, leading to another locking attempt /// within the same thread: /// /// - Variant calls on anything may dispatch to a script method. /// - Anything that could emit signals, that are connected to in a non-deferred manner. /// /// As there is no universal way to deal with such situations, behavior of locking wrappers can /// be customized using this enum. #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)] pub enum DeadlockPolicy { /// Block on all locks. Deadlocks are possible. Allow, /// Never block on any locks. Methods will return Nil immediately if the lock isn't /// available. Deadlocks are prevented. Pessimistic, /// Block on locks for at most `Duration`. Methods return Nil on timeout. Deadlocks are /// prevented. Timeout(Duration), } /// Trait defining associated constants for locking wrapper options /// /// This is required because constant generics ([RFC 2000][rfc-2000]) isn't available in stable /// rust yet. /// /// See also `DeadlockPolicy`. /// /// [rfc-2000]: https://github.com/rust-lang/rfcs/blob/master/text/2000-const-generics.md pub trait LockOptions { const DEADLOCK_POLICY: DeadlockPolicy; } /// Default lock policy that may change in future versions. /// /// Currently, it has a deadlock policy of `Allow`. #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)] pub struct DefaultLockPolicy; impl LockOptions for DefaultLockPolicy { const DEADLOCK_POLICY: DeadlockPolicy = DeadlockPolicy::Allow; } /// Error indicating that a lock wasn't obtained. #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Default)] pub struct LockFailed; /// User-data wrapper encapsulating a `Arc<Mutex<T>>`. /// /// The underlying `Mutex` may change in the future. The current implementation is /// `parking_lot`. #[derive(Debug)] pub struct MutexData<T, OPT = DefaultLockPolicy> { lock: Arc<Mutex<T>>, _marker: PhantomData<OPT>, } unsafe impl<T, OPT> UserData for MutexData<T, OPT> where T: NativeClass + Send, OPT: LockOptions, { type Target = T; #[inline] fn new(val: Self::Target) -> Self { MutexData { lock: Arc::new(Mutex::new(val)), _marker: PhantomData, } } #[inline] fn into_user_data(self) -> *const libc::c_void { Arc::into_raw(self.lock) as *const libc::c_void } #[inline] unsafe fn consume_user_data_unchecked(ptr: *const libc::c_void) -> Self { MutexData { lock: Arc::from_raw(ptr as *const Mutex<T>), _marker: PhantomData, } } #[inline] unsafe fn clone_from_user_data_unchecked(ptr: *const libc::c_void) -> Self { let borrowed = Arc::from_raw(ptr as *const Mutex<T>); let lock = borrowed.clone(); mem::forget(borrowed); MutexData { lock, _marker: PhantomData, } } } impl<T, OPT> Map for MutexData<T, OPT> where T: NativeClass + Send, OPT: LockOptions, { type Err = LockFailed; #[inline] fn map<F, U>(&self, op: F) -> Result<U, LockFailed> where F: FnOnce(&T) -> U, { self.map_mut(|val| op(val)) } } impl<T, OPT> MapMut for MutexData<T, OPT> where T: NativeClass + Send, OPT: LockOptions, { type Err = LockFailed; #[inline] fn map_mut<F, U>(&self, op: F) -> Result<U, LockFailed> where F: FnOnce(&mut T) -> U, { let mut guard = match OPT::DEADLOCK_POLICY { DeadlockPolicy::Allow => self.lock.lock(), DeadlockPolicy::Pessimistic => self.lock.try_lock().ok_or(LockFailed)?, DeadlockPolicy::Timeout(dur) => self.lock.try_lock_for(dur).ok_or(LockFailed)?, }; Ok(op(&mut *guard)) } } impl<T, OPT> Clone for MutexData<T, OPT> { #[inline] fn clone(&self) -> Self { MutexData { lock: self.lock.clone(), _marker: PhantomData, } } } /// User-data wrapper encapsulating a `Arc<RwLock<T>>`. /// /// The underlying `RwLock` may change in the future. The current implementation is /// `parking_lot`. #[derive(Debug)] pub struct RwLockData<T, OPT = DefaultLockPolicy> { lock: Arc<RwLock<T>>, _marker: PhantomData<OPT>, } unsafe impl<T, OPT> UserData for RwLockData<T, OPT> where T: NativeClass + Send + Sync, OPT: LockOptions, { type Target = T; #[inline] fn new(val: Self::Target) -> Self { RwLockData { lock: Arc::new(RwLock::new(val)), _marker: PhantomData, } } #[inline] fn into_user_data(self) -> *const libc::c_void { Arc::into_raw(self.lock) as *const libc::c_void } #[inline] unsafe fn consume_user_data_unchecked(ptr: *const libc::c_void) -> Self { RwLockData { lock: Arc::from_raw(ptr as *const RwLock<T>), _marker: PhantomData, } } #[inline] unsafe fn clone_from_user_data_unchecked(ptr: *const libc::c_void) -> Self { let borrowed = Arc::from_raw(ptr as *const RwLock<T>); let lock = borrowed.clone(); mem::forget(borrowed); RwLockData { lock, _marker: PhantomData, } } } impl<T, OPT> Map for RwLockData<T, OPT> where T: NativeClass + Send + Sync, OPT: LockOptions, { type Err = LockFailed; #[inline] fn map<F, U>(&self, op: F) -> Result<U, LockFailed> where F: FnOnce(&T) -> U, { let guard = match OPT::DEADLOCK_POLICY { DeadlockPolicy::Allow => self.lock.read(), DeadlockPolicy::Pessimistic => self.lock.try_read().ok_or(LockFailed)?, DeadlockPolicy::Timeout(dur) => self.lock.try_read_for(dur).ok_or(LockFailed)?, }; Ok(op(&*guard)) } } impl<T, OPT> MapMut for RwLockData<T, OPT> where T: NativeClass + Send + Sync, OPT: LockOptions, { type Err = LockFailed; #[inline] fn map_mut<F, U>(&self, op: F) -> Result<U, LockFailed> where F: FnOnce(&mut T) -> U, { let mut guard = match OPT::DEADLOCK_POLICY { DeadlockPolicy::Allow => self.lock.write(), DeadlockPolicy::Pessimistic => self.lock.try_write().ok_or(LockFailed)?, DeadlockPolicy::Timeout(dur) => self.lock.try_write_for(dur).ok_or(LockFailed)?, }; Ok(op(&mut *guard)) } } impl<T, OPT> Clone for RwLockData<T, OPT> { #[inline] fn clone(&self) -> Self { RwLockData { lock: self.lock.clone(), _marker: PhantomData, } } } /// User-data wrapper encapsulating a `Arc<T>`. Does not implement `MapMut`. #[derive(Debug)] pub struct ArcData<T>(Arc<T>); unsafe impl<T> UserData for ArcData<T> where T: NativeClass + Send + Sync, { type Target = T; #[inline] fn new(val: Self::Target) -> Self { ArcData(Arc::new(val)) } #[inline] fn into_user_data(self) -> *const libc::c_void { Arc::into_raw(self.0) as *const libc::c_void } #[inline] unsafe fn consume_user_data_unchecked(ptr: *const libc::c_void) -> Self { ArcData(Arc::from_raw(ptr as *const T)) } #[inline] unsafe fn clone_from_user_data_unchecked(ptr: *const libc::c_void) -> Self { let borrowed = Arc::from_raw(ptr as *const T); let arc = borrowed.clone(); mem::forget(borrowed); ArcData(arc) } } impl<T> Map for ArcData<T> where T: NativeClass + Send + Sync, { type Err = Infallible; #[inline] fn map<F, U>(&self, op: F) -> Result<U, Infallible> where F: FnOnce(&T) -> U, { Ok(op(&*self.0)) } } impl<T> Clone for ArcData<T> { #[inline] fn clone(&self) -> Self { ArcData(self.0.clone()) } } /// User-data wrapper analogous to a `Arc<RefCell<T>>`, that is restricted to the thread /// where it was originally created. /// /// This works by checking `ThreadId` before touching the underlying reference. If the id /// doesn't match the original thread, `map` and `map_mut` will return an error. #[derive(Debug)] pub struct LocalCellData<T> { inner: Arc<local_cell::LocalCell<T>>, } pub use self::local_cell::LocalCellError; mod local_cell { use std::cell::{Ref, RefCell, RefMut}; use std::thread::{self, ThreadId}; #[derive(Debug)] pub struct LocalCell<T> { thread_id: ThreadId, cell: RefCell<T>, } /// Error indicating that a borrow has failed. #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)] pub enum LocalCellError { DifferentThread { original: ThreadId, current: ThreadId, }, BorrowFailed, } impl<T> LocalCell<T> { #[inline] pub fn new(val: T) -> Self { LocalCell { thread_id: thread::current().id(), cell: RefCell::new(val), } } #[inline] fn inner(&self) -> Result<&RefCell<T>, LocalCellError> { let current = thread::current().id(); if self.thread_id == current { Ok(&self.cell) } else { Err(LocalCellError::DifferentThread { original: self.thread_id, current, }) } } #[inline] pub fn try_borrow(&self) -> Result<Ref<T>, LocalCellError> { let inner = self.inner()?; inner.try_borrow().map_err(|_| LocalCellError::BorrowFailed) } #[inline] pub fn try_borrow_mut(&self) -> Result<RefMut<T>, LocalCellError> { let inner = self.inner()?; inner .try_borrow_mut() .map_err(|_| LocalCellError::BorrowFailed) } } // Implementing Send + Sync is ok because the cell is guarded from access outside the // original thread. unsafe impl<T> Send for LocalCell<T> {} unsafe impl<T> Sync for LocalCell<T> {} } unsafe impl<T> UserData for LocalCellData<T> where T: NativeClass, { type Target = T; #[inline] fn new(val: Self::Target) -> Self { LocalCellData { inner: Arc::new(local_cell::LocalCell::new(val)), } } #[inline] fn into_user_data(self) -> *const libc::c_void { Arc::into_raw(self.inner) as *const libc::c_void } #[inline] unsafe fn consume_user_data_unchecked(ptr: *const libc::c_void) -> Self { LocalCellData { inner: Arc::from_raw(ptr as *const local_cell::LocalCell<T>), } } #[inline] unsafe fn clone_from_user_data_unchecked(ptr: *const libc::c_void) -> Self { let borrowed = Arc::from_raw(ptr as *const local_cell::LocalCell<T>); let arc = borrowed.clone(); mem::forget(borrowed); LocalCellData { inner: arc } } } impl<T> Map for LocalCellData<T> where T: NativeClass, { type Err = LocalCellError; #[inline] fn map<F, U>(&self, op: F) -> Result<U, Self::Err> where F: FnOnce(&Self::Target) -> U, { self.inner.try_borrow().map(|r| op(&*r)) } } impl<T> MapMut for LocalCellData<T> where T: NativeClass, { type Err = LocalCellError; #[inline] fn map_mut<F, U>(&self, op: F) -> Result<U, Self::Err> where F: FnOnce(&mut Self::Target) -> U, { self.inner.try_borrow_mut().map(|mut w| op(&mut *w)) } } impl<T> Clone for LocalCellData<T> { #[inline] fn clone(&self) -> Self { LocalCellData { inner: self.inner.clone(), } } } /// Special user-data wrapper intended for zero-sized types, that does not perform any /// allocation or synchronization at runtime. Does not implement `MapMut`. /// /// `Aether` produces a value using `Default` each time it's mapped. This is most useful when /// used with auto-load scripts to simulate static functions, since actual static functions /// can't be exported in GDNative. #[derive(Copy, Debug)] pub struct Aether<T> { _marker: PhantomData<T>, } unsafe impl<T> Send for Aether<T> {} unsafe impl<T> Sync for Aether<T> {} impl<T> Clone for Aether<T> { #[inline] fn clone(&self) -> Self { Aether::default() } } impl<T> Default for Aether<T> { #[inline] fn default() -> Self { Aether { _marker: PhantomData, } } } unsafe impl<T> UserData for Aether<T> where T: NativeClass + Copy + Default, { type Target = T; #[inline] fn new(_val: Self::Target) -> Self { Aether::default() } #[inline] fn into_user_data(self) -> *const libc::c_void { 1 as *const libc::c_void } #[inline] unsafe fn consume_user_data_unchecked(_ptr: *const libc::c_void) -> Self { Aether::default() } #[inline] unsafe fn clone_from_user_data_unchecked(_ptr: *const libc::c_void) -> Self { Aether::default() } } impl<T> Map for Aether<T> where T: NativeClass + Copy + Default, { type Err = Infallible; #[inline] fn map<F, U>(&self, op: F) -> Result<U, Infallible> where F: FnOnce(&T) -> U, { Ok(op(&Default::default())) } }