From 041839ceabbc67165512fde0d33c91347b758487 Mon Sep 17 00:00:00 2001
From: Jakub Kotur <qtr@google.com>
Date: Mon, 21 Dec 2020 17:28:15 +0100
Subject: Initial import of rayon-1.5.0.

Bug: 155309706
Change-Id: I6ff7de1cb89d093d7938abf78d586ed76da85b0d
---
 examples/cpu_monitor.rs | 81 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 examples/cpu_monitor.rs

(limited to 'examples/cpu_monitor.rs')

diff --git a/examples/cpu_monitor.rs b/examples/cpu_monitor.rs
new file mode 100644
index 0000000..bbe1316
--- /dev/null
+++ b/examples/cpu_monitor.rs
@@ -0,0 +1,81 @@
+use docopt::Docopt;
+use std::io;
+use std::process;
+
+const USAGE: &str = "
+Usage: cpu_monitor [options] <scenario>
+       cpu_monitor --help
+
+A test for monitoring how much CPU usage Rayon consumes under various
+scenarios. This test is intended to be executed interactively, like so:
+
+    cargo run --example cpu_monitor -- tasks_ended
+
+The list of scenarios you can try are as follows:
+
+- tasks_ended: after all tasks have finished, go to sleep
+- task_stall_root: a root task stalls for a very long time
+- task_stall_scope: a task in a scope stalls for a very long time
+
+Options:
+    -h, --help                   Show this message.
+    -d N, --depth N              Control how hard the dummy task works [default: 27]
+";
+
+#[derive(serde::Deserialize)]
+pub struct Args {
+    arg_scenario: String,
+    flag_depth: usize,
+}
+
+fn main() {
+    let args: &Args = &Docopt::new(USAGE)
+        .and_then(|d| d.deserialize())
+        .unwrap_or_else(|e| e.exit());
+
+    match &args.arg_scenario[..] {
+        "tasks_ended" => tasks_ended(args),
+        "task_stall_root" => task_stall_root(args),
+        "task_stall_scope" => task_stall_scope(args),
+        _ => {
+            println!("unknown scenario: `{}`", args.arg_scenario);
+            println!("try --help");
+            process::exit(1);
+        }
+    }
+}
+
+fn wait_for_user() {
+    let mut input = String::new();
+    io::stdin().read_line(&mut input).unwrap();
+}
+
+fn task(args: &Args) {
+    fn join_recursively(n: usize) {
+        if n == 0 {
+            return;
+        }
+        rayon::join(|| join_recursively(n - 1), || join_recursively(n - 1));
+    }
+
+    println!("Starting heavy work at depth {}...wait.", args.flag_depth);
+    join_recursively(args.flag_depth);
+    println!("Heavy work done; check top. You should see CPU usage drop to zero soon.");
+    println!("Press <enter> to quit...");
+}
+
+fn tasks_ended(args: &Args) {
+    task(args);
+    wait_for_user();
+}
+
+fn task_stall_root(args: &Args) {
+    rayon::join(|| task(args), wait_for_user);
+}
+
+fn task_stall_scope(args: &Args) {
+    rayon::scope(|scope| {
+        scope.spawn(move |_| task(args));
+        scope.spawn(move |_| wait_for_user());
+    });
+}
-- 
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