vendor/rustc-rayon/examples/cpu_monitor.rs

   1 use docopt::Docopt;
   2 use std::io;
   3 use std::process;
   4
   5 const USAGE: &str = "
   6 Usage: cpu_monitor [options] <scenario>
   7        cpu_monitor --help
   8
   9 A test for monitoring how much CPU usage Rayon consumes under various
  10 scenarios. This test is intended to be executed interactively, like so:
  11
  12     cargo run --example cpu_monitor -- tasks_ended
  13
  14 The list of scenarios you can try are as follows:
  15
  16 - tasks_ended: after all tasks have finished, go to sleep
  17 - task_stall_root: a root task stalls for a very long time
  18 - task_stall_scope: a task in a scope stalls for a very long time
  19
  20 Options:
  21     -h, --help                   Show this message.
  22     -d N, --depth N              Control how hard the dummy task works [default: 27]
  23 ";
  24
  25 #[derive(serde::Deserialize)]
  26 pub struct Args {
  27     arg_scenario: String,
  28     flag_depth: usize,
  29 }
  30
  31 fn main() {
  32     let args: &Args = &Docopt::new(USAGE)
  33         .and_then(|d| d.deserialize())
  34         .unwrap_or_else(|e| e.exit());
  35
  36     match &args.arg_scenario[..] {
  37         "tasks_ended" => tasks_ended(args),
  38         "task_stall_root" => task_stall_root(args),
  39         "task_stall_scope" => task_stall_scope(args),
  40         _ => {
  41             println!("unknown scenario: `{}`", args.arg_scenario);
  42             println!("try --help");
  43             process::exit(1);
  44         }
  45     }
  46 }
  47
  48 fn wait_for_user() {
  49     let mut input = String::new();
  50     io::stdin().read_line(&mut input).unwrap();
  51 }
  52
  53 fn task(args: &Args) {
  54     fn join_recursively(n: usize) {
  55         if n == 0 {
  56             return;
  57         }
  58         rayon::join(|| join_recursively(n - 1), || join_recursively(n - 1));
  59     }
  60
  61     println!("Starting heavy work at depth {}...wait.", args.flag_depth);
  62     join_recursively(args.flag_depth);
  63     println!("Heavy work done; check top. You should see CPU usage drop to zero soon.");
  64     println!("Press <enter> to quit...");
  65 }
  66
  67 fn tasks_ended(args: &Args) {
  68     task(args);
  69     wait_for_user();
  70 }
  71
  72 fn task_stall_root(args: &Args) {
  73     rayon::join(|| task(args), wait_for_user);
  74 }
  75
  76 fn task_stall_scope(args: &Args) {
  77     rayon::scope(|scope| {
  78         scope.spawn(move |_| task(args));
  79         scope.spawn(move |_| wait_for_user());
  80     });
  81 }