Schedule on absent lookups if maintenance is required (fixed #420)

Author: ben-manes

caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java

@@ -1878,6 +1878,9 @@ public boolean containsValue(Object value) {
       if (recordStats) {
         statsCounter().recordMisses(1);
       }
+      if (drainStatus() == REQUIRED) {
+        scheduleDrainBuffers();
+      }
       return null;
     }
 

caffeine/src/test/java/com/github/benmanes/caffeine/cache/BoundedLocalCacheTest.java

@@ -543,6 +543,23 @@ public void drain_onRead(Cache<Integer, Integer> cache, CacheContext context) {
     assertThat(buffer.size(), is(0));
   }
 
+  @Test(dataProvider = "caches")
+  @CacheSpec(compute = Compute.SYNC, implementation = Implementation.Caffeine,
+      population = Population.FULL, maximumSize = Maximum.FULL)
+  public void drain_onRead_absent(Cache<Integer, Integer> cache, CacheContext context) {
+    BoundedLocalCache<Integer, Integer> localCache = asBoundedLocalCache(cache);
+    Buffer<Node<Integer, Integer>> buffer = localCache.readBuffer;
+    localCache.get(context.firstKey());
+    assertThat(buffer.size(), is(1));
+
+    assertThat(localCache.get(context.absentKey()), is(nullValue()));
+    assertThat(buffer.size(), is(1));
+
+    localCache.drainStatus = REQUIRED;
+    assertThat(localCache.get(context.absentKey()), is(nullValue()));
+    assertThat(buffer.size(), is(0));
+  }
+
   @Test(dataProvider = "caches")
   @CacheSpec(compute = Compute.SYNC, implementation = Implementation.Caffeine,
       population = Population.EMPTY, maximumSize = Maximum.FULL)