From ac8e0491a9df75590c315063dbf1800e18a775d3 Mon Sep 17 00:00:00 2001
From: Ben Manes <ben.manes@gmail.com>
Date: Fri, 26 Aug 2022 19:11:31 -0700
Subject: [PATCH] add test for overflow of the ring buffer read/write counters

---
 .../caffeine/cache/BoundedBufferTest.java     | 34 ++++++++++++++-----
 .../caffeine/cache/BoundedLocalCacheTest.java |  4 +--
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedBufferTest.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedBufferTest.java
index a1e790bdb5..d7601684d4 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedBufferTest.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedBufferTest.java
@@ -17,6 +17,7 @@
 
 import static com.google.common.truth.Truth.assertThat;
 
+import java.util.ArrayList;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -31,18 +32,17 @@
  * @author ben.manes@gmail.com (Ben Manes)
  */
 public final class BoundedBufferTest {
-  static final String DUMMY = "test";
 
   @DataProvider
   public Object[][] buffer() {
-    return new Object[][] {{ new BoundedBuffer<String>() }};
+    return new Object[][] {{ new BoundedBuffer<Boolean>() }};
   }
 
   @Test(dataProvider = "buffer")
-  public void offer(BoundedBuffer<String> buffer) {
+  public void offer(BoundedBuffer<Boolean> buffer) {
     ConcurrentTestHarness.timeTasks(10, () -> {
       for (int i = 0; i < 100; i++) {
-        buffer.offer(DUMMY);
+        buffer.offer(Boolean.TRUE);
       }
     });
     assertThat(buffer.writes()).isGreaterThan(0);
@@ -50,9 +50,9 @@ public void offer(BoundedBuffer<String> buffer) {
   }
 
   @Test(dataProvider = "buffer")
-  public void drain(BoundedBuffer<String> buffer) {
+  public void drain(BoundedBuffer<Boolean> buffer) {
     for (int i = 0; i < BoundedBuffer.BUFFER_SIZE; i++) {
-      buffer.offer(DUMMY);
+      buffer.offer(Boolean.TRUE);
     }
     long[] read = new long[1];
     buffer.drainTo(e -> read[0]++);
@@ -62,12 +62,12 @@ public void drain(BoundedBuffer<String> buffer) {
 
   @Test(dataProvider = "buffer")
   @SuppressWarnings("ThreadPriorityCheck")
-  public void offerAndDrain(BoundedBuffer<String> buffer) {
+  public void offerAndDrain(BoundedBuffer<Boolean> buffer) {
     var lock = new ReentrantLock();
     var reads = new AtomicInteger();
     ConcurrentTestHarness.timeTasks(10, () -> {
       for (int i = 0; i < 1000; i++) {
-        boolean shouldDrain = (buffer.offer(DUMMY) == Buffer.FULL);
+        boolean shouldDrain = (buffer.offer(Boolean.TRUE) == Buffer.FULL);
         if (shouldDrain && lock.tryLock()) {
           buffer.drainTo(e -> reads.incrementAndGet());
           lock.unlock();
@@ -79,4 +79,22 @@ public void offerAndDrain(BoundedBuffer<String> buffer) {
     assertThat(reads.longValue()).isEqualTo(buffer.reads());
     assertThat(reads.longValue()).isEqualTo(buffer.writes());
   }
+
+  @Test
+  public void overflow() {
+    var buffer = new BoundedBuffer.RingBuffer<Boolean>(null);
+    buffer.writeCounter = Long.MAX_VALUE;
+    buffer.readCounter = Long.MAX_VALUE;
+
+    buffer.offer(Boolean.TRUE);
+    var data = new ArrayList<>();
+    buffer.drainTo(data::add);
+
+    for (var e : buffer.buffer) {
+      assertThat(e).isNull();
+    }
+    assertThat(data).containsExactly(Boolean.TRUE);
+    assertThat(buffer.readCounter).isEqualTo(Long.MIN_VALUE);
+    assertThat(buffer.writeCounter).isEqualTo(Long.MIN_VALUE);
+  }
 }
diff --git a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedLocalCacheTest.java b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedLocalCacheTest.java
index ada8f5ed14..59353c3125 100644
--- a/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedLocalCacheTest.java
+++ b/caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedLocalCacheTest.java
@@ -687,7 +687,7 @@ public void evict_admit(BoundedLocalCache<Int, Int> cache, CacheContext context)
       assertThat(cache.admit(candidate, victim)).isFalse();
     }
 
-    // Allow
+    // Admit a small, random percentage of warm candidates to protect against hash flooding
     while (cache.frequencySketch().frequency(candidate) < ADMIT_HASHDOS_THRESHOLD) {
       cache.frequencySketch().increment(candidate);
     }
@@ -701,8 +701,8 @@ public void evict_admit(BoundedLocalCache<Int, Int> cache, CacheContext context)
       }
     }
     assertThat(allow).isGreaterThan(0);
-    assertThat(reject).isGreaterThan(0);
     assertThat(reject).isGreaterThan(allow);
+    assertThat(100.0 * allow / (allow + reject)).isIn(Range.open(0.5, 1.5));
   }
 
   @Test(groups = "isolated")