add tool for printing out retry policy choices (#1997)

common/examples/backoff-print.rs

@@ -0,0 +1,31 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//! Show example retry intervals and times for the internal service policy
+
+use omicron_common::backoff;
+use omicron_common::backoff::Backoff;
+
+fn main() {
+    let mut policy = backoff::retry_policy_long();
+    let mut total_duration = std::time::Duration::from_secs(0);
+    loop {
+        let nmin = total_duration.as_secs() / 60;
+        let nsecs = total_duration.as_secs() % 60;
+        let nmillis = total_duration.as_millis() % 1000;
+        print!("at T={:3}m{:02}.{:03}s: ", nmin, nsecs, nmillis);
+
+        if let Some(next) = policy.next_backoff() {
+            let nmin = next.as_secs() / 60;
+            let nsecs = next.as_secs() % 60;
+            let nmillis = next.as_millis() % 1000;
+            println!("wait {:3}m{:02}.{:03}s", nmin, nsecs, nmillis);
+            total_duration = total_duration + next;
+
+            if nmin >= 60 {
+                break;
+            }
+        }
+    }
+}