20: Add solutions for section "threads1".

Dependencies

• [2] H6XH45OP 0

Change contents

• replacement in exercises/threads/threads1.rs at line 9
  [2.88761]→[2.88761:88799](∅→∅)
  − // I AM NOT DONE

  −

  − use std::sync::Arc;
  [2.88761]

  [2.88799]
  + use std::sync::{Arc, Mutex};
• replacement in exercises/threads/threads1.rs at line 18
  [2.88901]→[2.88901:88961](∅→∅)
  − let status = Arc::new(JobStatus { jobs_completed: 0 });
  [2.88901]

  [2.88961]
  + let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));
• replacement in exercises/threads/threads1.rs at line 23
  [2.89109]→[2.89109:89156](∅→∅)
  − status_shared.jobs_completed += 1;
  [2.89109]

  [2.89156]
  + status_shared.lock().unwrap().jobs_completed += 1;
• replacement in exercises/threads/threads1.rs at line 26
  [2.89174]→[2.89174:89213](∅→∅)
  − while status.jobs_completed < 10 {
  [2.89174]

  [2.89213]
  + while status.lock().unwrap().jobs_completed < 10 {