-// Rust-101, Part 12: Concurrency, Arc, Send
-// =========================================
-
-use std::io::prelude::*;
-use std::{io, fs, thread};
-use std::sync::mpsc::{sync_channel, SyncSender, Receiver};
-use std::sync::Arc;
-
-
-// Before we come to the actual code, we define a data-structure `Options` to store all the information we need
-// to complete the job: Which files to work on, which pattern to look for, and how to output. <br/>
-#[derive(Clone,Copy)]
-pub enum OutputMode {
- Print,
- SortAndPrint,
- Count,
-}
-use self::OutputMode::*;
+// Rust-101, Part 12: Rc, Interior Mutability, Cell, RefCell
+// =========================================================
-pub struct Options {
- pub files: Vec<String>,
- pub pattern: String,
- pub output_mode: OutputMode,
-}
+use std::rc::Rc;
+use std::cell::{Cell, RefCell};
-// The first function reads the files, and sends every line over the `out_channel`.
-fn read_files(options: Arc<Options>, out_channel: SyncSender<String>) {
- for file in options.files.iter() {
- // First, we open the file, ignoring any errors.
- let file = fs::File::open(file).unwrap();
- // Then we obtain a `BufReader` for it, which provides the `lines` function.
- let file = io::BufReader::new(file);
- for line in file.lines() {
- let line = line.unwrap();
- // Now we send the line over the channel, ignoring the possibility of `send` failing.
- out_channel.send(line).unwrap();
- }
- }
- // When we drop the `out_channel`, it will be closed, which the other end can notice.
+
+#[derive(Clone)]
+struct Callbacks {
+ callbacks: Vec<Rc<Fn(i32)>>,
}
-// The second function filters the lines it receives through `in_channel` with the pattern, and sends
-// matches via `out_channel`.
-fn filter_lines(options: Arc<Options>,
- in_channel: Receiver<String>,
- out_channel: SyncSender<String>) {
- // We can simply iterate over the channel, which will stop when the channel is closed.
- for line in in_channel.iter() {
- // `contains` works on lots of types of patterns, but in particular, we can use it to test whether
- // one string is contained in another. This is another example of Rust using traits as substitute for overloading.
- if line.contains(&options.pattern) {
- unimplemented!()
- }
+impl Callbacks {
+ pub fn new() -> Self {
+ Callbacks { callbacks: Vec::new() }
}
-}
-// The third function performs the output operations, receiving the relevant lines on its `in_channel`.
-fn output_lines(options: Arc<Options>, in_channel: Receiver<String>) {
- match options.output_mode {
- Print => {
- // Here, we just print every line we see.
- for line in in_channel.iter() {
- unimplemented!()
- }
- },
- Count => {
- // We are supposed to count the number of matching lines. There's a convenient iterator adapter that
- // we can use for this job.
- unimplemented!()
- },
- SortAndPrint => {
- // We are asked to sort the matching lines before printing. So let's collect them all in a local vector...
- let mut data: Vec<String> = in_channel.iter().collect();
- // ...and implement the actual sorting later.
+ // Registration works just like last time, except that we are creating an `Rc` now.
+ pub fn register<F: Fn(i32)+'static>(&mut self, callback: F) {
+ unimplemented!()
+ }
+
+ pub fn call(&self, val: i32) {
+ // We only need a shared iterator here. Since `Rc` is a smart pointer, we can directly call the callback.
+ for callback in self.callbacks.iter() {
unimplemented!()
}
}
}
-// With the operations of the three threads defined, we can now implement a function that performs grepping according
-// to some given options.
-pub fn run(options: Options) {
- // We move the `options` into an `Arc`, as that's what the thread workers expect.
- let options = Arc::new(options);
-
- // This sets up the channels. We use a `sync_channel` with buffer-size of 16 to avoid needlessly filling RAM.
- let (line_sender, line_receiver) = sync_channel(16);
- let (filtered_sender, filtered_receiver) = sync_channel(16);
-
- // Spawn the read thread: `thread::spawn` takes a closure that is run in a new thread.
- let options1 = options.clone();
- let handle1 = thread::spawn(move || read_files(options1, line_sender));
-
- // Same with the filter thread.
- let options2 = options.clone();
- let handle2 = thread::spawn(move || {
- filter_lines(options2, line_receiver, filtered_sender)
- });
-
- // And the output thread.
- let options3 = options.clone();
- let handle3 = thread::spawn(move || output_lines(options3, filtered_receiver));
-
- // Finally, wait until all three threads did their job.
- handle1.join().unwrap();
- handle2.join().unwrap();
- handle3.join().unwrap();
+// Time for a demo!
+fn demo(c: &mut Callbacks) {
+ c.register(|val| println!("Callback 1: {}", val));
+ c.call(0); c.clone().call(1);
}
-// Now we have all the pieces together for testing our rgrep with some hard-coded options.
pub fn main() {
- let options = Options {
- files: vec!["src/part10.rs".to_string(),
- "src/part11.rs".to_string(),
- "src/part12.rs".to_string()],
- pattern: "let".to_string(),
- output_mode: Print
- };
- run(options);
+ let mut c = Callbacks::new();
+ demo(&mut c);
+}
+
+// ## Interior Mutability
+
+// So, let us put our counter in a `Cell`, and replicate the example from the previous part.
+fn demo_cell(c: &mut Callbacks) {
+ {
+ let count = Cell::new(0);
+ // Again, we have to move ownership if the `count` into the environment closure.
+ c.register(move |val| {
+ // In here, all we have is a shared reference of our environment. But that's good enough for the `get` and `set` of the cell!
+ let new_count = count.get()+1;
+ count.set(new_count);
+ println!("Callback 2: {} ({}. time)", val, new_count);
+ } );
+ }
+
+ c.call(2); c.clone().call(3);
}
-// **Exercise 12.1**: Change rgrep such that it prints not only the matching lines, but also the name of the file
-// and the number of the line in the file. You will have to change the type of the channels from `String` to something
-// that records this extra information.
+// ## `RefCell`
+
+// Our final version of `Callbacks` puts the closure environment into a `RefCell`.
+#[derive(Clone)]
+struct CallbacksMut {
+ callbacks: Vec<Rc<RefCell<FnMut(i32)>>>,
+}
+
+impl CallbacksMut {
+ pub fn new() -> Self {
+ CallbacksMut { callbacks: Vec::new() }
+ }
+
+ pub fn register<F: FnMut(i32)+'static>(&mut self, callback: F) {
+ unimplemented!()
+ }
+
+ pub fn call(&mut self, val: i32) {
+ for callback in self.callbacks.iter() {
+ // We have to *explicitly* borrow the contents of a `RefCell` by calling `borrow` or `borrow_mut`.
+ let mut closure = callback.borrow_mut();
+ // Unfortunately, Rust's auto-dereference of pointers is not clever enough here. We thus have to explicitly
+ // dereference the smart pointer and obtain a mutable reference to the content.
+ (&mut *closure)(val);
+ }
+ }
+}
+
+// Now we can repeat the demo from the previous part - but this time, our `CallbacksMut` type
+// can be cloned.
+fn demo_mut(c: &mut CallbacksMut) {
+ c.register(|val| println!("Callback 1: {}", val));
+ c.call(0);
+
+ {
+ let mut count: usize = 0;
+ c.register(move |val| {
+ count = count+1;
+ println!("Callback 2: {} ({}. time)", val, count);
+ } );
+ }
+ c.call(1); c.clone().call(2);
+}
+// **Exercise 12.1**: Write some piece of code using only the available, public interface of `CallbacksMut` such that a reentrant call to a closure
+// is happening, and the program panics because the `RefCell` refuses to hand out a second mutable borrow of the closure's environment.
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