From 15764d7f37160d81c3489c860c868c3e92d6c637 Mon Sep 17 00:00:00 2001
From: lowasser <lowasser@google.com>
Date: Wed, 30 May 2018 14:19:31 -0700
Subject: [PATCH] Fix b/80241237 to correctly *not* change segment weight, nor
 report an eviction, when a compute() call does not change the present value.

RELNOTES=Fix a bug where Cache.asMap.compute* methods could cause nonsensical weights to be stored, breaking cache eviction.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=198618238
---
 .../cache/LocalCacheMapComputeTest.java       | 24 +++++++++++++++++++
 .../com/google/common/cache/LocalCache.java   |  3 ++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java b/guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java
index 94fbf82907e6..c49b80e1e6bb 100644
--- a/guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java
+++ b/guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java
@@ -55,6 +55,30 @@ public void testComputeIfAbsent() {
     assertEquals(1, cache.size());
   }
 
+  public void testComputeIfAbsentEviction() {
+    // b/80241237
+
+    Cache<String, String> c = CacheBuilder.newBuilder().maximumSize(1).build();
+
+    assertThat(c.asMap().computeIfAbsent("hash-1", k -> "")).isEqualTo("");
+    assertThat(c.asMap().computeIfAbsent("hash-1", k -> "")).isEqualTo("");
+    assertThat(c.asMap().computeIfAbsent("hash-1", k -> "")).isEqualTo("");
+    assertThat(c.size()).isEqualTo(1);
+    assertThat(c.asMap().computeIfAbsent("hash-2", k -> "")).isEqualTo("");
+  }
+
+  public void testComputeEviction() {
+    // b/80241237
+
+    Cache<String, String> c = CacheBuilder.newBuilder().maximumSize(1).build();
+
+    assertThat(c.asMap().compute("hash-1", (k, v) -> "a")).isEqualTo("a");
+    assertThat(c.asMap().compute("hash-1", (k, v) -> "b")).isEqualTo("b");
+    assertThat(c.asMap().compute("hash-1", (k, v) -> "c")).isEqualTo("c");
+    assertThat(c.size()).isEqualTo(1);
+    assertThat(c.asMap().computeIfAbsent("hash-2", k -> "")).isEqualTo("");
+  }
+
   public void testComputeIfPresent() {
     cache.put(key, "1");
     // simultaneous update for same key, expect count successful updates
diff --git a/guava/src/com/google/common/cache/LocalCache.java b/guava/src/com/google/common/cache/LocalCache.java
index 6d21f97a6166..87e9d5c755f1 100644
--- a/guava/src/com/google/common/cache/LocalCache.java
+++ b/guava/src/com/google/common/cache/LocalCache.java
@@ -2243,7 +2243,8 @@ V compute(K key, int hash, BiFunction<? super K, ? super V, ? extends V> functio
         if (newValue != null) {
           if (valueReference != null && newValue == valueReference.get()) {
             loadingValueReference.set(newValue);
-            setValue(e, key, newValue, now);
+            e.setValueReference(valueReference);
+            recordWrite(e, 0, now); // no change in weight
             return newValue;
           }
           try {