Fix compatibility between the cache compute methods and a load.

Fixes #5348
Fixes #5342
Fixes #2827
Resolves underlying cause of #2108

RELNOTES=Fix compatibility between the cache compute methods and a load.
PiperOrigin-RevId: 357192480

Author: ben-manes

guava-tests/test/com/google/common/cache/LocalCacheMapComputeTest.java

@@ -18,6 +18,12 @@
 
 import static com.google.common.truth.Truth.assertThat;
 
+import com.google.common.util.concurrent.UncheckedExecutionException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Queue;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 import java.util.function.IntConsumer;
 import java.util.stream.IntStream;
@@ -91,6 +97,31 @@ public void testComputeIfPresent() {
     assertThat(cache.getIfPresent(key).split(delimiter)).hasLength(count + 1);
   }
 
+  public void testComputeIfPresentRemove() {
+    List<RemovalNotification<Integer, Integer>> notifications = new ArrayList<>();
+    Cache<Integer, Integer> cache =
+        CacheBuilder.newBuilder()
+            .removalListener(
+                new RemovalListener<Integer, Integer>() {
+                  @Override
+                  public void onRemoval(RemovalNotification<Integer, Integer> notification) {
+                    notifications.add(notification);
+                  }
+                })
+            .build();
+    cache.put(1, 2);
+
+    // explicitly remove the existing value
+    cache.asMap().computeIfPresent(1, (key, value) -> null);
+    assertThat(notifications).hasSize(1);
+    CacheTesting.checkEmpty(cache);
+
+    // ensure no zombie entry remains
+    cache.asMap().computeIfPresent(1, (key, value) -> null);
+    assertThat(notifications).hasSize(1);
+    CacheTesting.checkEmpty(cache);
+  }
+
   public void testUpdates() {
     cache.put(key, "1");
     // simultaneous update for same key, some null, some non-null
@@ -113,6 +144,41 @@ public void testCompute() {
     assertEquals(0, cache.size());
   }
 
+  public void testComputeWithLoad() {
+    Queue<RemovalNotification<String, String>> notifications = new ConcurrentLinkedQueue<>();
+    cache =
+        CacheBuilder.newBuilder()
+            .removalListener(
+                new RemovalListener<String, String>() {
+                  @Override
+                  public void onRemoval(RemovalNotification<String, String> notification) {
+                    notifications.add(notification);
+                  }
+                })
+            .expireAfterAccess(500000, TimeUnit.MILLISECONDS)
+            .maximumSize(count)
+            .build();
+
+    cache.put(key, "1");
+    // simultaneous load and deletion
+    doParallelCacheOp(
+        count,
+        n -> {
+          try {
+            cache.get(key, () -> key);
+            cache.asMap().compute(key, (k, v) -> null);
+          } catch (ExecutionException e) {
+            throw new UncheckedExecutionException(e);
+          }
+        });
+
+    CacheTesting.checkEmpty(cache);
+    for (RemovalNotification<String, String> entry : notifications) {
+      assertThat(entry.getKey()).isNotNull();
+      assertThat(entry.getValue()).isNotNull();
+    }
+  }
+
   public void testComputeExceptionally() {
     try {
       doParallelCacheOp(

guava/src/com/google/common/cache/LocalCache.java

@@ -2188,7 +2188,7 @@ V waitForLoadingValue(ReferenceEntry<K, V> e, K key, ValueReference<K, V> valueR
     V compute(K key, int hash, BiFunction<? super K, ? super V, ? extends V> function) {
       ReferenceEntry<K, V> e;
       ValueReference<K, V> valueReference = null;
-      LoadingValueReference<K, V> loadingValueReference = null;
+      ComputingValueReference<K, V> computingValueReference = null;
       boolean createNewEntry = true;
       V newValue;
 
@@ -2229,33 +2229,33 @@ V compute(K key, int hash, BiFunction<? super K, ? super V, ? extends V> functio
 
         // note valueReference can be an existing value or even itself another loading value if
         // the value for the key is already being computed.
-        loadingValueReference = new LoadingValueReference<>(valueReference);
+        computingValueReference = new ComputingValueReference<>(valueReference);
 
         if (e == null) {
           createNewEntry = true;
           e = newEntry(key, hash, first);
-          e.setValueReference(loadingValueReference);
+          e.setValueReference(computingValueReference);
           table.set(index, e);
         } else {
-          e.setValueReference(loadingValueReference);
+          e.setValueReference(computingValueReference);
         }
 
-        newValue = loadingValueReference.compute(key, function);
+        newValue = computingValueReference.compute(key, function);
         if (newValue != null) {
           if (valueReference != null && newValue == valueReference.get()) {
-            loadingValueReference.set(newValue);
+            computingValueReference.set(newValue);
             e.setValueReference(valueReference);
             recordWrite(e, 0, now); // no change in weight
             return newValue;
           }
           try {
             return getAndRecordStats(
-                key, hash, loadingValueReference, Futures.immediateFuture(newValue));
+                key, hash, computingValueReference, Futures.immediateFuture(newValue));
           } catch (ExecutionException exception) {
             throw new AssertionError("impossible; Futures.immediateFuture can't throw");
           }
-        } else if (createNewEntry) {
-          removeLoadingValue(key, hash, loadingValueReference);
+        } else if (createNewEntry || valueReference.isLoading()) {
+          removeLoadingValue(key, hash, computingValueReference);
           return null;
         } else {
           removeEntry(e, hash, RemovalCause.EXPLICIT);
@@ -3603,6 +3603,17 @@ public ValueReference<K, V> copyFor(
     }
   }
 
+  static class ComputingValueReference<K, V> extends LoadingValueReference<K, V> {
+    ComputingValueReference(ValueReference<K, V> oldValue) {
+      super(oldValue);
+    }
+
+    @Override
+    public boolean isLoading() {
+      return false;
+    }
+  }
+
   // Queues
 
   /**
@@ -3927,7 +3938,7 @@ long longSize() {
     Segment<K, V>[] segments = this.segments;
     long sum = 0;
     for (int i = 0; i < segments.length; ++i) {
-      sum += Math.max(0, segments[i].count); // see https://github.com/google/guava/issues/2108
+      sum += segments[i].count;
     }
     return sum;
   }