feat: Adding threads1.rs with a focus on JoinHandles and waiting for
spawned threads to finish. Moved the original threads1.rs to threads2.rs with the focus on the Mutex and modifying shared data. #892
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@ -1,32 +1,31 @@
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// threads1.rs
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// Make this compile! Execute `rustlings hint threads1` for hints :)
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// The idea is the thread spawned on line 22 is completing jobs while the main thread is
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// monitoring progress until 10 jobs are completed. Because of the difference between the
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// spawned threads' sleep time, and the waiting threads sleep time, when you see 6 lines
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// of "waiting..." and the program ends without timing out when running,
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// you've got it :)
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// Make this compile and run! Execute 'rustlings hint threads1' for hints :)
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// This program should wait until all the spawned threads have finished before exiting.
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// I AM NOT DONE
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use std::sync::Arc;
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use std::thread;
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use std::time::Duration;
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struct JobStatus {
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jobs_completed: u32,
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}
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fn main() {
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let status = Arc::new(JobStatus { jobs_completed: 0 });
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let status_shared = status.clone();
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thread::spawn(move || {
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for _ in 0..10 {
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let mut handles = vec![];
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for i in 0..10 {
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thread::spawn(move || {
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thread::sleep(Duration::from_millis(250));
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status_shared.jobs_completed += 1;
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}
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});
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while status.jobs_completed < 10 {
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println!("waiting... ");
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thread::sleep(Duration::from_millis(500));
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println!("thread {} is complete", i);
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});
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}
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let mut completed_threads = 0;
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for handle in handles {
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// TODO: a struct is returned from thread::spawn, can you use it?
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completed_threads += 1;
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}
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if completed_threads != 10 {
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panic!("Oh no! All the spawned threads did not finish!");
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}
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}
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34
exercises/threads/threads2.rs
Normal file
34
exercises/threads/threads2.rs
Normal file
@ -0,0 +1,34 @@
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// threads2.rs
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// Make this compile! Execute `rustlings hint threads2` for hints :)
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// Building on the last exercise, we want all of the threads to complete their work but this time
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// the spawned threads need to be in charge of updating a shared value: JobStatus.jobs_completed
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// I AM NOT DONE
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use std::sync::Arc;
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use std::thread;
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use std::time::Duration;
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struct JobStatus {
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jobs_completed: u32,
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}
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fn main() {
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let status = Arc::new(JobStatus { jobs_completed: 0 });
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let mut handles = vec![];
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for _ in 0..10 {
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let status_shared = status.clone();
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let handle = thread::spawn(move || {
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thread::sleep(Duration::from_millis(250));
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// TODO: You must take an action before you update a shared value
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status_shared.jobs_completed += 1;
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});
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handles.push(handle);
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}
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for handle in handles {
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handle.join().unwrap();
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// TODO: Print the value of the JobStatus.jobs_completed. Did you notice anything
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// interesting in the output? Do you have to 'join' on all the handles?
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println!("jobs completed {}", ???);
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}
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}
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24
info.toml
24
info.toml
@ -878,6 +878,22 @@ name = "threads1"
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path = "exercises/threads/threads1.rs"
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mode = "compile"
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hint = """
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`JoinHandle` is a struct that is returned from a spawned thread:
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https://doc.rust-lang.org/std/thread/fn.spawn.html
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A challenge with multi-threaded applications is that the main thread can
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finish before the spawned threads are completed.
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https://doc.rust-lang.org/book/ch16-01-threads.html#waiting-for-all-threads-to-finish-using-join-handle
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Collect the JoinHandles and wait for them to finish.
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https://doc.rust-lang.org/std/thread/struct.JoinHandle.html
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"""
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[[exercises]]
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name = "threads2"
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path = "exercises/threads/threads2.rs"
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mode = "compile"
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hint = """
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`Arc` is an Atomic Reference Counted pointer that allows safe, shared access
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to **immutable** data. But we want to *change* the number of `jobs_completed`
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so we'll need to also use another type that will only allow one thread to
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@ -898,14 +914,6 @@ while they are sleeping, since this will prevent the other thread from
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being allowed to get the lock. Locks are automatically released when
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they go out of scope.
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Ok, so, real talk, this was actually tricky for *me* to do too. And
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I could see a lot of different problems you might run into, so at this
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point I'm not sure which one you've hit :)
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Please open an issue if you're still running into a problem that
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these hints are not helping you with, or if you've looked at the sample
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answers and don't understand why they work and yours doesn't.
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If you've learned from the sample solutions, I encourage you to come
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back to this exercise and try it again in a few days to reinforce
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what you've learned :)"""
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