use std::sync::Arc;
//@ Our next stop are the concurrency features of Rust. We are going to write our own small version of "grep",
-//@ called *rgrep*, and it is going to make use of concurrency: One thread reads the input files, one thread does
+//@ called *rgrep*, and it is going to perform three jobs concurrently: One thread reads the input files, one thread does
//@ the actual matching, and one thread writes the output. I already mentioned in the beginning of the course that
//@ Rust's type system (more precisely, the discipline of ownership and borrowing) will help us to avoid a common
-//@ pitfall of concurrent programming: data races.
+//@ pitfall of concurrent programming: data races. We will see how that works concretely.
// 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/>
+// to complete the job: Which files to work on, which pattern to look for, and how to output.
//@ Besides just printing all the matching lines, we will also offer to count them, or alternatively to sort them.
#[derive(Clone,Copy)]
pub enum OutputMode {
run(options);
}
-// **Exercise 12.1**: Change rgrep such that it prints not only the matching lines, but also the name of the file
+// **Exercise 13.1**: 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.
//@ programs memory safe, and that prevents us from invalidating iterators, also helps secure our multi-threaded code against
//@ data races. For example, notice how `read_files` sends a `String` to `filter_lines`. At run-time, only the pointer to
//@ the character data will actually be moved around (just like when a `String` is passed to a function with full ownership). However,
-//@ `read_files` has to *give up* ownership of the string to perform `send`, to it is impossible for an outstanding borrow to
-//@ still be around. After it sent the string to the other side, `read_files` has no pointer into the string content
+//@ `read_files` has to *give up* ownership of the string to perform `send`, to it is impossible for the string to still be borrowed.
+//@ After it sent the string to the other side, `read_files` has no pointer into the string content
//@ anymore, and hence no way to race on the data with someone else.
//@
-//@ There is a little more to this. Remember the `'static` bound we had to add to `register` in the previous part, to make
+//@ There is a little more to this. Remember the `'static` bound we had to add to `register` in the previous parts, to make
//@ sure that the callbacks do not reference any pointers that might become invalid? This is just as crucial for spawning
//@ a thread: In general, that thread could last for much longer than the current stack frame. Thus, it must not use
//@ any pointers to data in that stack frame. This is achieved by requiring the `FnOnce` closure passed to `thread::spawn`
-//@ to be valid for lifetime `'static`, as you can see in [its documentation](http://doc.rust-lang.org/stable/std/thread/fn.spawn.html).
+//@ to be valid for lifetime `'static`, as you can see in [its documentation](https://doc.rust-lang.org/stable/std/thread/fn.spawn.html).
//@ This avoids another kind of data race, where the thread's access races with the callee deallocating its stack frame.
//@ It is only thanks to the concept of lifetimes that this can be expressed as part of the type of `spawn`.
//@
//@ The answer is already hinted at in the error: It will say something about `Send`. You may have noticed that the closure in
//@ `thread::spawn` does not just have a `'static` bound, but also has to satisfy `Send`. `Send` is a trait, and just like `Copy`,
-//@ it's just a marker - there are no functions provided by `Send`. What the trait says is that types which are `Send`, can be
+//@ it's just a marker - there are no functions provided by `Send`. What the trait says is that types which are `Send` can be
//@ safely sent to another thread without causing trouble. Of course, all the primitive data-types are `Send`. So is `Arc`,
-//@ which is why Rust accepted our code. But `Rc` is not `Send`, and for a good reason!
+//@ which is why Rust accepted our code. But `Rc` is not `Send`, and for a good reason! If had two `Rc` to the same data, and
+//@ sent one of them to another thread, things could go havoc due to the lack of synchronization.
//@
//@ Now, `Send` as a trait is fairly special. It has a so-called *default implementation*. This means that *every type* implements
//@ `Send`, unless it opts out. Opting out is viral: If your type contains a type that opted out, then you don't have `Send`, either.
//@ So if the environment of your closure contains an `Rc`, it won't be `Send`, preventing it from causing trouble. If however every
//@ captured variable *is* `Send`, then so is the entire environment, and you are good.
-//@ [index](main.html) | [previous](part12.html) | [next](part14.html)
+//@ [index](main.html) | [previous](part12.html) | [raw source](workspace/src/part13.rs) | [next](part14.html)
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