add noop demo

Author: nikomatsakis

rayon-demo/src/main.rs

@@ -9,6 +9,7 @@ mod life;
 mod matmul;
 mod mergesort;
 mod nbody;
+mod noop;
 mod quicksort;
 mod sieve;
 mod tsp;
@@ -81,6 +82,7 @@ Benchmarks:
   - sieve: Finding primes using a Sieve of Eratosthenes.
   - matmul: Parallel matrix multiplication.
   - mergesort: Parallel mergesort.
+  - noop: Launch empty tasks to measure CPU usage.
   - quicksort: Parallel quicksort.
   - tsp: Traveling salesman problem solver (sample data sets in `data/tsp`).
 ";
@@ -106,6 +108,7 @@ fn main() {
         "sieve" => sieve::main(&args[1..]),
         "tsp" => tsp::main(&args[1..]),
         "life" => life::main(&args[1..]),
+        "noop" => noop::main(&args[1..]),
         _ => usage(),
     }
 }

rayon-demo/src/noop/mod.rs

@@ -0,0 +1,28 @@
+const USAGE: &str = "
+Usage: noop [--sleep N] [--iters N]
+
+Noop loop to measure CPU usage. See rayon-rs/rayon#642.
+
+Options:
+    --sleep N       How long to sleep (in millis) between doing a spawn. [default: 10]
+    --iters N        Total time to execution (in millis). [default: 100]
+";
+
+use docopt::Docopt;
+
+#[derive(Deserialize)]
+pub struct Args {
+    flag_sleep: u64,
+    flag_iters: u64,
+}
+
+pub fn main(args: &[String]) {
+    let args: Args = Docopt::new(USAGE)
+        .and_then(|d| d.argv(args).deserialize())
+        .unwrap_or_else(|e| e.exit());
+
+    for _ in 1..args.flag_iters {
+        std::thread::sleep(std::time::Duration::from_millis(args.flag_sleep));
+        rayon::spawn(move || {  } );
+    }
+}