feat(core): Avoid time going backwards for CacheClock (#616)

Ahoo-Wang · Aug 15, 2024 · 89ffd7a · 89ffd7a
1 parent b9729c3
commit 89ffd7a
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Showing 2 changed files with 37 additions and 4 deletions.
diff --git a/cosid-core/src/main/java/me/ahoo/cosid/util/Clock.java b/cosid-core/src/main/java/me/ahoo/cosid/util/Clock.java
@@ -23,10 +23,11 @@
  * @author ahoo wang
  */
 @ThreadSafe
+@FunctionalInterface
 public interface Clock {
 
-    Clock CACHE = new CacheClock();
     Clock SYSTEM = new SystemClock();
+    Clock CACHE = new CacheClock(SYSTEM);
 
     long secondTime();
 
@@ -58,11 +59,13 @@ class CacheClock implements Clock, Runnable {
          * Tolerate a one-second time limit.
          */
         public static final long ONE_SECOND_PERIOD = Duration.ofSeconds(1).toNanos();
+        private final Clock clock;
         private final Thread thread;
         private volatile long lastTime;
 
-        public CacheClock() {
-            this.lastTime = getSystemSecondTime();
+        public CacheClock(Clock clock) {
+            this.clock = clock;
+            this.lastTime = clock.secondTime();
             this.thread = new Thread(this);
             this.thread.setName("CosId-CacheClock");
             this.thread.setDaemon(true);
@@ -77,7 +80,11 @@ public long secondTime() {
         @Override
         public void run() {
             while (!thread.isInterrupted()) {
-                this.lastTime = getSystemSecondTime();
+                long currentTime = clock.secondTime();
+                // Avoid time going backwards
+                if (currentTime > lastTime) {
+                    this.lastTime = currentTime;
+                }
                 LockSupport.parkNanos(this, ONE_SECOND_PERIOD);
             }
         }

diff --git a/cosid-core/src/test/java/me/ahoo/cosid/util/CacheClockTest.java b/cosid-core/src/test/java/me/ahoo/cosid/util/CacheClockTest.java
@@ -13,12 +13,14 @@
 
 package me.ahoo.cosid.util;
 
+import static me.ahoo.cosid.util.Clock.CacheClock.ONE_SECOND_PERIOD;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import lombok.SneakyThrows;
 import org.junit.jupiter.api.Test;
 
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.LockSupport;
 
 
 /**
@@ -45,4 +47,28 @@ void secondTimeWhenSleep() {
         long tolerance = 1L;
         assertTrue(diff <= tolerance);
     }
+
+    @Test
+    void secondTimeIfBackwards() {
+        Clock backwardsClock = new BackwardsClock();
+        Clock cacheClock = new Clock.CacheClock(backwardsClock);
+        long lastTime = cacheClock.secondTime();
+        for (int i = 0; i < 6; i++) {
+            LockSupport.parkNanos(this, ONE_SECOND_PERIOD);
+            long currentTime = cacheClock.secondTime();
+            assertTrue(currentTime >= lastTime);
+            lastTime = currentTime;
+        }
+    }
+
+    static class BackwardsClock implements Clock {
+        private final long[] timeline = new long[]{1, 2, 3, 4, 5};
+        private int index = 0;
+
+        @Override
+        public long secondTime() {
+            int idx = Math.floorMod(index++, timeline.length);
+            return timeline[idx];
+        }
+    }
 }