update chapter20

Author: jamesmarva

20 Building a Multithreaded Web Server.md

@@ -74,8 +74,11 @@
 
 ## 3.1 Implementing the Drop Trait on ThreadPool
 
+The error tells us we can’t call join because we only have a mutable borrow of each worker and join takes ownership of its argument.
+We did this in Listing 17-15: if `Worker` holds an `Option<thread::JoinHandle<()>>` instead, we can call the `take` method on the Option to move the value out of the `Some` variant and leave a `None` variant in its place.
 
 
+## 3.2 Signaling to the Threads to Stop Listening for Jobs
 
 
 
@@ -84,12 +87,14 @@
 
 
 
+We could do more here! If you want to continue enhancing this project, here are some ideas:
 
+- Add more documentation to `ThreadPool` and its public methods.
+- Add tests of the library’s functionality.
+- Change calls to `unwrap` to more robust error handling.
+- Use `ThreadPool` to perform some task other than serving web requests.
+- Find a thread pool crate on crates.io and implement a similar web server using the crate instead. Then compare its API and robustness to the thread pool we implemented.
 
 
-
-
-
-
-
+# 4 Summary 
 

code/ch20/c22/src/main.rs

@@ -9,7 +9,7 @@ fn main() {
 type Job = Box<dyn FnOnce() + Send + 'static>;
 struct Worker {
     id: usize,
-    thread: thread::JoinHandle<()>,
+    thread: Option<thread::JoinHandle<()>>,
 }
 
 impl Worker {
@@ -20,7 +20,9 @@ impl Worker {
                job()
            } 
         });
-        Worker{id, thread}
+        Worker{id, 
+            thread:Some(thread)
+        }
     }
 }
 
@@ -52,9 +54,18 @@ impl Drop for ThreadPool {
     fn drop(&mut self) {
         for worker in &mut self.workers {
             println!("Shutting down worker {}", worker.id);
-            worker.thread.join().unwrap();
-        }
-    }
-}
+            // worker.thread.join().unwrap();
 
+            // OK
+            if let Some(thread) = worker.thread.take() {
+                thread.join().unwrap();
+            }
 
+            // OK 
+            // match worker.thread.take() {
+            //     Some(x) => x.join().unwrap(),
+            //     None =>{},
+            // }
+        }
+    }
+}

code/ch20/c23/src/main.rs

@@ -1,3 +1,92 @@
+use std::sync::{Arc, mpsc, Mutex};
+use std::thread;
+use std::time::Duration;
+
 fn main() {
     println!("Hello, world!");
 }
+
+type Job = Box<dyn FnOnce() + Send + 'static>;
+
+enum Message {
+    NewJob(Job),
+    Terminate,
+}
+
+struct Worker{
+    id: usize,
+    thread: Option<thread::JoinHandle<()>>,
+}
+
+impl Worker {
+    fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Message>>>) -> Worker {
+        let thread = thread::spawn(move|| loop {
+            let message = receiver.lock().unwrap().recv().unwrap();
+            match message {
+                Message::NewJob(job) => {
+                    println!("Worker {} got a job; executing.", id);
+                    job();
+                },
+                Message::Terminate => {
+                    println!("Worker {} was told to terminate.", id);
+                    break;
+                },
+            }
+        });
+
+        Worker{
+            id,
+            thread: Some(thread),    
+        }
+    }
+}
+
+struct ThreadPool {
+    workers: Vec<Worker>,
+    sender: mpsc::Sender<Message>,
+}
+
+impl ThreadPool {
+    pub fn new(size: usize) -> ThreadPool {
+        let (sender, receiver) = mpsc::channel();
+        let rece = Arc::new(Mutex::new(receiver));
+        let mut workers = Vec::with_capacity(size);
+
+        for id in 0..size {
+            workers.push(Worker::new(id, Arc::clone(&rece)));
+        }
+        ThreadPool{
+            workers,
+            sender
+        }
+    }
+
+    pub fn execute<T>(&self, t: T) 
+    where 
+        T: FnOnce() + Send + 'static,
+    {
+        let job = Box::new(t);
+        self.sender.send(Message::NewJob(job)).unwrap();
+    }
+}
+
+impl Drop for ThreadPool {
+
+    fn drop(&mut self) {
+        println!("Sending terminate message to all workers.");
+
+        for _ in &self.workers {
+            self.sender.send(Message::Terminate).unwrap();
+        }
+
+        println!("Shutting down all workers.");
+
+        for w in &mut self.workers {
+            println!("Shutting down worker {}", w.id);
+            if let Some(thread) = w.thread.take() {
+                thread.join().unwrap();
+            }
+        }
+
+    }
+}