Avoid overflow for 146 years of JVM time for common timers

2 files changed, 12 insertions, 15 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/concurrent/SystemTimer.java b/vespajlib/src/main/java/com/yahoo/concurrent/SystemTimer.java
index 8111d52a10f..9bb320ad0a9 100644
--- a/vespajlib/src/main/java/com/yahoo/concurrent/SystemTimer.java
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/SystemTimer.java
@@ -42,21 +42,18 @@ public enum SystemTimer implements Timer {
 
     SystemTimer() {
         long napTime = adjustTimeoutByDetectedHz(Duration.ofMillis(1)).toMillis();
-        millis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime());
-        Thread thread = new Thread() {
-
-            @Override
-            public void run() {
-                while (true) {
-                    millis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime());
-                    try {
-                        Thread.sleep(napTime);
-                    } catch (InterruptedException e) {
-                        break;
-                    }
+        long creationNanos = System.nanoTime();
+        millis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - creationNanos);
+        Thread thread = new Thread(() -> {
+            while (true) {
+                millis = TimeUnit.NANOSECONDS.toMillis(System.nanoTime()) - creationNanos;
+                try {
+                    Thread.sleep(napTime);
+                } catch (InterruptedException e) {
+                    break;
                 }
             }
-        };
+        });
         thread.setDaemon(true);
         thread.setName("vespa-system-timer");
         thread.start();
diff --git a/vespajlib/src/main/java/com/yahoo/concurrent/Timer.java b/vespajlib/src/main/java/com/yahoo/concurrent/Timer.java
index c41c762c989..46d72f6d5ad 100644
--- a/vespajlib/src/main/java/com/yahoo/concurrent/Timer.java
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/Timer.java
@@ -20,7 +20,8 @@ public interface Timer {
      * @return The current value of the timer, in milliseconds.
      */
     long milliTime();
-    Timer monotonic = () -> TimeUnit.NANOSECONDS.toMillis(System.nanoTime());
+    long creationNanos = System.nanoTime(); // Avoid monotonic timer overflow for the first 146 years of JVM uptime.
+    Timer monotonic = () -> TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - creationNanos);
     static Timer wrap(Clock original) {
         return new Timer() {
             private final Clock clock = original;
@@ -30,6 +31,5 @@ public interface Timer {
                 return clock.millis();
             }
         }; }
-
     default Instant instant() { return Instant.ofEpochMilli(milliTime()); }
 }