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//! Module for working with channels. Rexport of [`crossbeam_channel`] //! //! //! # Examples //! //! > Several of these examples are copies of the [`chan`] and [`crossbeam_channel`] crates. //! //! [`chan`]: https://github.com/BurntSushi/chan //! [`crossbeam_channel`]: ../../crossbeam_channel/index.html //! //! ## Example: unbounded (async) channel //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! # fn main() { //! let (tx, rx) = ch::unbounded(); //! //! // Can send an arbitrarily large number of messages. //! for i in 0..1000 { //! ch!(tx <- i); //! } //! # } //! ``` //! //! ## Example: bounded (sync) channel //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! # fn main() { //! // Create a channel that can hold at most 5 messages at a time. //! let (tx, rx) = ch::bounded(5); //! //! // Can send only 5 messages. //! for i in 0..5 { //! ch!(tx <- i); //! } //! //! // An attempt to send one more message will fail. //! assert!(tx.try_send(5).is_err()); //! # } //! ``` //! //! ## Example: rendevous channel //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! # fn main() { //! let (send, recv) = ch::bounded(0); //! spawn(move || ch!(send <- 5)); //! assert_eq!(ch!(<- recv), 5); // blocks until the previous send occurs //! # } //! ``` //! //! ## Example: the sentinel channel idiom //! //! When writing concurrent programs with `ergo`, you will often find that you need //! to somehow "wait" until some operation is done. For example, let's say you want //! to run a function in a separate thread, but wait until it completes. Here's //! one way to do it: //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! fn do_work(done: ch::Sender<()>) { //! // do something //! //! // signal that we're done. //! ch!(done <- ()); //! } //! //! fn main() { //! let (sdone, rdone) = ch::bounded(0); //! spawn(move || do_work(sdone)); //! // block until work is done, and then quit the program. //! ch!(<- rdone); //! } //! ``` //! //! In effect, we've created a new channel that sends unit values. When we're //! done doing work, we send a unit value and `main` waits for it to be delivered. //! //! Another way of achieving the same thing is to simply close the channel. Once //! the channel is closed, any previously blocked receive operations become //! immediately unblocked. What's even cooler is that channels are closed //! automatically when all senders are dropped. So the new program looks something //! like this: //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! fn do_work(_done: ch::Sender<()>) { //! // do something //! } //! //! fn main() { //! let (sdone, rdone) = ch::bounded(0); //! spawn(move || do_work(sdone)); //! // Block until the channel is closed. //! // //! // Note: this _expects_ the error that //! // all senders have been dropped and will //! // panic if a value is sent instead. //! ch!(! <- rdone); //! } //! ``` //! //! We no longer need to explicitly do anything with the `_done` channel. We give //! `do_work` ownership of the channel, but as soon as the function stops //! executing, `_done` is dropped, the channel is closed and `rdone.recv()` //! unblocks returning an error, which we expect with `ch!(! <- rdone)`. //! //! ## Example: non-blocking sends/receives //! //! ``` //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! # fn main() { //! let (send, recv) = ch::bounded(1); //! let data = "send data".to_string(); //! match ch!(send <-? data) { //! Some(data) => { //! println!("didn't send data, but got it back: {}", data); //! unreachable!(); // in this case we don't expect it //! } //! None => println!("message sent successfully"), //! } //! //! // attempting to send additional data fails //! let data = "more data".to_string(); //! assert_eq!(Some(data.clone()), ch!(send <-? data)); //! //! match ch!(<-? recv) { //! Some(data) => println!("received data: {}", data), //! None => { //! println!("didn't receive any data yet"); //! unreachable!(); // in this case we don't expect it //! } //! } //! # } //! ``` //! //! ## Example: using `select_loop` //! //! ```rust //! #[macro_use] extern crate ergo_sync; //! use ergo_sync::*; //! //! # fn main() { //! let (tx1, rx1) = ch::unbounded(); //! let (tx2, rx2) = ch::unbounded(); //! //! spawn(move || ch!(tx1 <- "foo")); //! spawn(move || ch!(tx2 <- "bar")); //! //! select_loop! { //! recv(rx1, msg) => { //! println!("Received a message from the first channel: {}", msg); //! } //! recv(rx2, msg) => { //! println!("Received a message from the second channel: {}", msg); //! } //! } //! # } //! ``` //! pub use crossbeam_channel::{bounded, unbounded, IntoIter, Iter, Receiver, RecvError, RecvTimeoutError, Select, SelectRecvError, SelectSendError, SendError, SendTimeoutError, Sender, TryIter, TryRecvError, TrySendError}; /// Use with channels with ergonomic syntax and panic with helpful error messages when /// sending/receiving on a channel is invalid. /// /// - `ch!(send <- 42)` for sending a value. /// - `let v = ch!(<- recv)` for receiving a value. /// - `ch!(! <- recv)` to wait for channels to close. /// - `<-?` for async operation support. /// /// **Blocking syntax:** /// /// - `ch!(send <- value)`: blocks until a value is sent, panics if all receivers are dropped. /// - `ch!(<- recv)`: blocks until a value is received, panics if all senders are dropped. /// - `ch!(! <- recv)`: blocks until all senders are dropped, panics if a value is received. Used /// for signaling. /// /// > This syntax works with both `crossbeam-channel` channels (which are exported by this crate) as /// > well as `std::mspc` channels. /// /// > Note that these operations can deadlock if a channel is leaked. /// /// **Non-Blocking syntax:** /// /// - `ch!(send <-? value)`: returns `None` if the value was sent, `Some(value)` if the value /// was not sent. Panics if all receivers are dropped. /// - `ch!(<-? recv)`: returns `None` if no value is received, `Some(value)` if a value is /// received. Panics if all senders are dropped. /// - `ch!(! <-? recv)`: returns `true` if there are still senders and `false` if the seners have /// been dropped. Panics if a value is received. Use with `while ch!(! <-? recv) { /* ... */ }` /// /// > Non-Blocking syntax does _not_ work with `std::mspc` channels. /// /// # Examples /// /// ## Example: Using `ergo::chan` channels /// /// ```rust /// #[macro_use] extern crate ergo_sync; /// use ergo_sync::*; /// # fn main() { /// let (send, recv) = ch::bounded(3); /// ch!(send <- 4); /// ch!(send <- 7); /// ch!(send <- 42); /// assert_eq!(4, ch!(<- recv)); /// assert_eq!(7, ch!(<- recv)); /// let v = ch!(<- recv); /// assert_eq!(42, v); /// /// drop(send); /// // ch!(<- recv); // panics /// ch!(! <- recv); // succeeds /// # } /// ``` /// /// ## Example: Using `std::mspc` channels /// /// ```rust /// #[macro_use] extern crate ergo_sync; /// use std::sync::mpsc::sync_channel; /// /// # fn main() { /// let (send, recv) = sync_channel(3); /// ch!(send <- 4); /// ch!(send <- 7); /// ch!(send <- 42); /// assert_eq!(4, ch!(<- recv)); /// assert_eq!(7, ch!(<- recv)); /// let v = ch!(<- recv); /// assert_eq!(42, v); /// /// drop(send); /// // ch!(<- recv); // panics /// ch!(! <- recv); // succeeds /// # } /// ``` /// /// ## Example: using non-blocking syntax /// /// ```rust /// #[macro_use] extern crate ergo_sync; /// use ergo_sync::*; /// # fn main() { /// let (send, recv) = ch::bounded(3); /// assert_eq!(None, ch!(<-? recv)); // no values sent yet /// /// assert!(ch!(send <-? 4).is_none()); /// assert_eq!(Some(4), ch!(<-? recv)); /// assert_eq!(None, ch!(<-? recv)); /// /// assert!(ch!(send <-? 7).is_none()); /// assert!(ch!(send <-? 42).is_none()); /// assert!(ch!(send <-? 1).is_none()); /// // further attempts return the value /// assert_eq!(Some(100), ch!(send <-? 100)); /// /// assert_eq!(Some(7), ch!(<-? recv)); /// /// assert_eq!(Some(42), ch!(<-? recv)); /// assert_eq!(Some(1), ch!(<-? recv)); /// assert_eq!(None, ch!(<-? recv)); /// assert!(ch!(! <-? recv)); // senders still exist /// /// drop(send); /// // ch!(<-? recv); // panics /// ch!(! <-? recv); // succeeds /// # } /// ``` #[macro_export] macro_rules! ch { [$send:ident <-? $value:expr] => { match $send.try_send($value) { Ok(()) => None, Err(ch::TrySendError::Full(v)) => Some(v), Err(ch::TrySendError::Disconnected(_)) => { panic!("Attempted to send a value but receivers are disconnected"); } } }; [$send:ident <- $value:expr] => { match $send.send($value) { Ok(_) => {}, Err(err) => panic!("{} for `send`.", err), } }; [<-? $recv:ident] => { match $recv.try_recv() { Ok(v) => Some(v), Err(ch::TryRecvError::Empty) => None, Err(ch::TryRecvError::Disconnected) => { panic!("Attempted to recv a value but senders are disconnected"); } } }; [<- $recv:ident] => { match $recv.recv() { Ok(v) => v, Err(err) => panic!("{} for `recv`.", err), } }; [! <-? $recv:ident] => { match $recv.try_recv() { Ok(v) => panic!("Got {:?} when expecting senders to be closed.", v), Err(ch::TryRecvError::Empty) => true, // senders still exist Err(ch::TryRecvError::Disconnected) => false, // no more senders } }; [! <- $recv:ident] => { match $recv.recv() { Ok(v) => panic!("Got {:?} when expecting senders to be closed.", v), Err(err) => (), } }; } /// Handle an expression that could be `Err` and send it over a channel if it is. /// /// This is the same as the builtin `try!` macro, except if the expression fails than the `Err` is /// sent on the `$send` channel and the requested action is performed. /// /// Suggested possible actions: /// - `continue` /// - `return` /// - `break` /// - some expression that evaluates to a "default value" for that context. /// /// # Examples /// /// ```rust /// #[macro_use] extern crate ergo_sync; /// use ergo_sync::*; /// # fn main() { /// let (send_err, recv_err) = ch::unbounded(); /// let items = &[Ok("this is alright"), Err("not ok"), Err("still not okay")]; /// # let mut okay = 0; /// for item in items.iter() { /// let v = ch_try!(send_err, *item, continue); /// println!("got: {}", v); /// # okay += 1; /// } /// /// drop(send_err); /// let errs: Vec<_> = recv_err.iter().collect(); /// assert_eq!(vec!["not ok", "still not okay"], errs); /// # assert_eq!(1, okay); /// # } /// ``` #[macro_export] macro_rules! ch_try { [$send:ident, $expr:expr, $action:expr] => { match $expr { Ok(v) => v, Err(e) => { ch!($send <- e); $action } } }; }