[HOTFIX] Add workaround for SPARK-7660 to fix JavaAPISuite failures.

core/src/test/java/org/apache/spark/shuffle/unsafe/UnsafeShuffleWriterSuite.java

@@ -35,6 +35,7 @@ import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 import org.mockito.invocation.InvocationOnMock;
 import org.mockito.stubbing.Answer;
+import org.xerial.snappy.buffer.CachedBufferAllocator;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.lessThan;
@@ -96,6 +97,13 @@ public class UnsafeShuffleWriterSuite {
   @After
   public void tearDown() {
     Utils.deleteRecursively(tempDir);
+    // This call is a workaround for SPARK-7660, a snappy-java bug which is exposed by this test
+    // suite. Clearing the cached buffer allocator's pool of reusable buffers masks this bug,
+    // preventing a test failure in JavaAPISuite that would otherwise occur. The underlying bug
+    // needs to be fixed, but in the meantime this workaround avoids spurious Jenkins failures.
+    synchronized (CachedBufferAllocator.class) {
+      CachedBufferAllocator.queueTable.clear();
+    }
     final long leakedMemory = taskMemoryManager.cleanUpAllAllocatedMemory();
     if (leakedMemory != 0) {
       fail("Test leaked " + leakedMemory + " bytes of managed memory");