Multi thread cross backup with wait / notify

1、 Mission

Create 20 threads, of which 10 threads back up data to database a, the other 10 threads back up data to database B, and the backup of database a and database B run cross.

2、 Realize

1. Implement the task of backing up database a and database B.

2. Create threads separately to perform backup tasks

3. Execute tasks and view results

3、 Conclusion

I think this example is very well written, so I specially recorded it. It summarizes, applies and solves the problems such as the change of wait conditions in the process of thread notify, the "false death" caused by the same kind of wake-up, and so on. The writer's qualifications are still shallow. Please give me some advice if you don't speak well. Thank you!