add a test case for ElasticByteBufferPool

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/ElasticByteBufferPool.java

@@ -126,7 +126,5 @@ public synchronized void putBuffer(ByteBuffer buffer) {
    */
   @InterfaceAudience.Private
   @InterfaceStability.Unstable
-  public int size(boolean direct) {
-    return getBufferTree(direct).size();
-  }
+  public abstract int getCurrentBuffersCount(boolean direct);
 }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/TestElasticByteBufferPool.java

@@ -0,0 +1,35 @@
+package org.apache.hadoop.io;
+
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+import java.nio.ByteBuffer;
+
+public class TestElasticByteBufferPool {
+  @Test
+  public void testGarbageCollection() throws Exception {
+    final ElasticByteBufferPool ebbp = new WeakReferencedElasticByteBufferPool();
+    ByteBuffer buffer1 = ebbp.getBuffer(true, 5);
+    ByteBuffer buffer2 = ebbp.getBuffer(true, 10);
+    ByteBuffer buffer3 = ebbp.getBuffer(true, 15);
+
+    // the pool is empty yet
+    Assertions.assertThat(ebbp.getCurrentBuffersCount(true)).isEqualTo(0);
+
+    // put the buffers back to the pool
+    ebbp.putBuffer(buffer2);
+    ebbp.putBuffer(buffer3);
+    Assertions.assertThat(ebbp.getCurrentBuffersCount(true)).isEqualTo(2);
+
+    // release the references to be garbage-collected
+    buffer2 = null;
+    buffer3 = null;
+    System.gc();
+
+    // call getBuffer() to trigger the cleanup
+    ByteBuffer buffer4 = ebbp.getBuffer(true, 10);
+
+    // the pool should be empty. buffer2, buffer3 should be garbage-collected
+    Assertions.assertThat(ebbp.getCurrentBuffersCount(true)).isEqualTo(0);
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSStripedInputStream.java

@@ -555,16 +555,16 @@ public void testCloseDoesNotAllocateNewBuffer() throws Exception {
       final ElasticByteBufferPool ebbp =
           (ElasticByteBufferPool) stream.getBufferPool();
       // first clear existing pool
-      LOG.info("Current pool size: direct: " + ebbp.size(true) + ", indirect: "
-          + ebbp.size(false));
+      LOG.info("Current pool size: direct: " + ebbp.getCurrentBuffersCount(true) + ", indirect: "
+          + ebbp.getCurrentBuffersCount(false));
       emptyBufferPoolForCurrentPolicy(ebbp, true);
       emptyBufferPoolForCurrentPolicy(ebbp, false);
-      final int startSizeDirect = ebbp.size(true);
-      final int startSizeIndirect = ebbp.size(false);
+      final int startSizeDirect = ebbp.getCurrentBuffersCount(true);
+      final int startSizeIndirect = ebbp.getCurrentBuffersCount(false);
       // close should not allocate new buffers in the pool.
       stream.close();
-      assertEquals(startSizeDirect, ebbp.size(true));
-      assertEquals(startSizeIndirect, ebbp.size(false));
+      assertEquals(startSizeDirect, ebbp.getCurrentBuffersCount(true));
+      assertEquals(startSizeIndirect, ebbp.getCurrentBuffersCount(false));
     }
   }
 
@@ -621,10 +621,10 @@ public void testReadWhenLastIncompleteCellComeInToDecodeAlignedStripe()
   private void emptyBufferPoolForCurrentPolicy(ElasticByteBufferPool ebbp,
       boolean direct) {
     int size;
-    while ((size = ebbp.size(direct)) != 0) {
+    while ((size = ebbp.getCurrentBuffersCount(direct)) != 0) {
       ebbp.getBuffer(direct,
           ecPolicy.getCellSize() * ecPolicy.getNumDataUnits());
-      if (size == ebbp.size(direct)) {
+      if (size == ebbp.getCurrentBuffersCount(direct)) {
         // if getBuffer didn't decrease size, it means the pool for the buffer
         // corresponding to current ecPolicy is empty
         break;

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestReconstructStripedFile.java

@@ -828,7 +828,7 @@ public void interceptFreeBlockReaderBuffer() {
 
   private void assertBufferPoolIsEmpty(ElasticByteBufferPool bufferPool,
       boolean direct) {
-    while (bufferPool.size(direct) != 0) {
+    while (bufferPool.getCurrentBuffersCount(direct) != 0) {
       // iterate all ByteBuffers in ElasticByteBufferPool
       ByteBuffer byteBuffer =  bufferPool.getBuffer(direct, 0);
       Assert.assertEquals(0, byteBuffer.position());
@@ -837,7 +837,7 @@ private void assertBufferPoolIsEmpty(ElasticByteBufferPool bufferPool,
 
   private void emptyBufferPool(ElasticByteBufferPool bufferPool,
       boolean direct) {
-    while (bufferPool.size(direct) != 0) {
+    while (bufferPool.getCurrentBuffersCount(direct) != 0) {
       bufferPool.getBuffer(direct, 0);
     }
   }