3e6a8cfbdb
I've seen from a cursory glance on the repo that a lot of people struggle with this problem set because of the ambiguity in the instructions (See issues #287, #743, #567). I'd like to recommend perhaps putting a TODO on the lines that need changing to stop people from falling down rabbit holes and pursuing completely different solution to the exercise that avoids the core pedagogical content of the problem, which is an understanding of how Arc is an atomic reference counting primitive that relies on .lock() and .unwrap() to solve shared state concurrency problems with the Mutex primitive. I've also added comments in the instructions to highlight why it is that the solution is solved when the program prints the counter to the screen 6 times, as this was unclear and was distracting students from the core takeaway of the exercise.
44 lines
1.8 KiB
Rust
44 lines
1.8 KiB
Rust
// 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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// Why 6 lines, you ask? because the program will spawn one new thread that will increment
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// the Jobstatus on 250ms intervals. At the same time, our original thread will check
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// the Jobstatus at 500ms intervals. So, this count should be ~0 on the first iteration of
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// the `while` loop; ~2 on the second iteration; ~4 on the third iteration; finally,
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// ~10 on the sixth. Why? Because by the time our main thread peeks at the JobStatus counter,
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// our second spawned thread will have already run two incremental operations on it.
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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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// TODO: Change the line below
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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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// The code below spawns a single new thread that will run a for-loop code block 10 times.
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thread::spawn(move || {
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for _ in 0..10 {
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thread::sleep(Duration::from_millis(250));
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// TODO: change the line below
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status_shared.jobs_completed += 1;
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}
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});
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// The code below will check the count on JobStatus on 500ms intervals.
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// TODO: Change the line below
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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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}
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}
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