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//! //! The main `Desync` struct //! use super::scheduler::*; use std::sync::Arc; use futures::sync::oneshot; use futures::future::Future; /// /// A data storage structure used to govern synchronous and asynchronous access to an underlying object. /// pub struct Desync<T: Send> { /// Queue used for scheduling runtime for this object queue: Arc<JobQueue>, /// Data for this object. Boxed so the pointer remains the same through the lifetime of the object. data: Box<T> } // Rust actually derives this anyway at the moment unsafe impl<T: Send> Send for Desync<T> {} // True iff queue: Sync unsafe impl<T: Send> Sync for Desync<T> {} /// /// Used for passing the data pointer through to the queue /// /// 'Safe' because the queue is synchronised during drop, so we can never use the pointer /// if the object does not exist. /// struct DataRef<T: Send>(*const T); unsafe impl<T: Send> Send for DataRef<T> {} // TODO: we can change DataRef to Shared (https://doc.rust-lang.org/std/ptr/struct.Shared.html in the future) // TODO: T does not need to be static as we know that its lifetime is at least the lifetime of Desync<T> and hence the queue impl<T: 'static+Send> Desync<T> { /// /// Creates a new Desync object /// pub fn new(data: T) -> Desync<T> { let queue = queue(); Desync { queue: queue, data: Box::new(data) } } /// /// Performs an operation asynchronously on this item. This function will return /// immediately and the job will happen on a separate thread at some time in the /// future (generally fairly soon). /// /// Jobs are always performed in the order that they are queued and are always /// performed synchronously with respect to this object. /// #[inline] #[deprecated(since="0.3.0", note="please use `desync` instead")] pub fn r#async<TFn>(&self, job: TFn) where TFn: 'static+Send+FnOnce(&mut T) -> () { self.desync(job) } /// /// Performs an operation asynchronously on this item. This function will return /// immediately and the job will happen on a separate thread at some time in the /// future (generally fairly soon). /// /// Jobs are always performed in the order that they are queued and are always /// performed synchronously with respect to this object. /// pub fn desync<TFn>(&self, job: TFn) where TFn: 'static+Send+FnOnce(&mut T) -> () { unsafe { // As drop() is the last thing called, we know that this object will still exist at the point where the queue makes the asynchronous callback let data = DataRef(&*self.data); desync(&self.queue, move || { let data = data.0 as *mut T; job(&mut *data); }) } } /// /// Performs an operation synchronously on this item. This will be queued with any other /// jobs that this item may be performing, and this function will not return until the /// job is complete and the result is available. /// pub fn sync<TFn, Result>(&self, job: TFn) -> Result where TFn: Send+FnOnce(&mut T) -> Result, Result: Send { let result = unsafe { // As drop() is the last thing called, we know that this object will still exist at the point where the callback occurs let data = DataRef(&*self.data); sync(&self.queue, move || { let data = data.0 as *mut T; job(&mut *data) }) }; result } /// /// Performs an operation asynchronously on the contents of this item, returning the /// result via a future. /// pub fn future<TFn, Item: 'static+Send>(&self, job: TFn) -> impl Future<Item=Item, Error=oneshot::Canceled>+Send where TFn: 'static+Send+FnOnce(&mut T) -> Item { let (send, receive) = oneshot::channel(); self.desync(|data| { let result = job(data); if let Err(_result) = send.send(result) { // The listening side disconnected: we'll throw away the result and act like a normal desync instead } }); receive } /// /// After the pending operations for this item are performed, waits for the /// supplied future to complete and then calls the specified function /// pub fn after<'a, TFn, Item: 'static+Send, Error: 'static+Send, Res: 'static+Send, Fut: 'a+Future<Item=Item, Error=Error>+Send>(&self, after: Fut, job: TFn) -> impl 'a+Future<Item=Res, Error=Error>+Send where TFn: 'static+Send+FnOnce(&mut T, Result<Item, Error>) -> Result<Res, Error> { unsafe { // As drop() is the last thing called, we know that this object will still exist at the point where // Also, we'll have exclusive access to this object when the callback occurs let data = DataRef(&*self.data); scheduler().after(&self.queue, after, move |future_result| { let data = data.0 as *mut T; job(&mut *data, future_result) }) } } } impl<T: Send> Drop for Desync<T> { fn drop(&mut self) { // Ensure that everything on the queue has committed by queueing a last synchronous event // (Not synchronising the queue would make this unsafe as we would hold on to a pointer to // the internal data structure) sync(&self.queue, || {}); } }