Add Java API for rocksdb::CancelAllBackgroundWork() (#6657)

Summary:
Adding a Java API for rocksdb::CancelAllBackgroundWork() so that the user can call this (when required) before closing the DB. This is to **prevent the crashes when manual compaction is running and the user decides to close the DB**.

Calling CancelAllBackgroundWork() seems to be the recommended way to make sure that it's safe to close the DB (according to RocksDB FAQ: https://github.com/facebook/rocksdb/wiki/RocksDB-FAQ#basic-readwrite).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6657

Reviewed By: cheng-chang

Differential Revision: D20896395

Pulled By: pdillinger

fbshipit-source-id: 8a8208c10093db09bd35db9af362211897870d96

java/rocksjni/rocksjni.cc

@@ -2610,6 +2610,17 @@ jobjectArray Java_org_rocksdb_RocksDB_compactFiles(
   return ROCKSDB_NAMESPACE::JniUtil::toJavaStrings(env, &output_file_names);
 }
 
+/*
+ * Class:     org_rocksdb_RocksDB
+ * Method:    cancelAllBackgroundWork
+ * Signature: (JZ)V
+ */
+void Java_org_rocksdb_RocksDB_cancelAllBackgroundWork(
+        JNIEnv*, jobject, jlong jdb_handle, jboolean jwait) {
+    auto* db = reinterpret_cast<ROCKSDB_NAMESPACE::DB*>(jdb_handle);
+    rocksdb::CancelAllBackgroundWork(db, jwait);
+}
+
 /*
  * Class:     org_rocksdb_RocksDB
  * Method:    pauseBackgroundWork

java/src/main/java/org/rocksdb/RocksDB.java

@@ -3479,6 +3479,17 @@ public class RocksDB extends RocksObject {
         compactionJobInfo == null ? 0 : compactionJobInfo.nativeHandle_));
   }
 
+  /**
+   * This function will cancel all currently running background processes.
+   *
+   * @param wait if true, wait for all background work to be cancelled before
+   *   returning.
+   *
+   */
+  public void cancelAllBackgroundWork(boolean wait) {
+    cancelAllBackgroundWork(nativeHandle_, wait);
+  }
+
   /**
    * This function will wait until all currently running background processes
    * finish. After it returns, no background process will be run until
@@ -4457,6 +4468,8 @@ public class RocksDB extends RocksObject {
       final int outputLevel,
       final int outputPathId,
       final long compactionJobInfoHandle) throws RocksDBException;
+  private native void cancelAllBackgroundWork(final long handle,
+      final boolean wait);
   private native void pauseBackgroundWork(final long handle)
       throws RocksDBException;
   private native void continueBackgroundWork(final long handle)

java/src/test/java/org/rocksdb/RocksDBTest.java

@@ -1084,6 +1084,57 @@ public class RocksDBTest {
     }
   }
 
+  @Test
+  public void continueBackgroundWorkAfterCancelAllBackgroundWork() throws RocksDBException {
+    final int KEY_SIZE = 20;
+    final int VALUE_SIZE = 300;
+    try (final DBOptions opt = new DBOptions().
+        setCreateIfMissing(true).
+        setCreateMissingColumnFamilies(true);
+         final ColumnFamilyOptions new_cf_opts = new ColumnFamilyOptions()
+    ) {
+      final List<ColumnFamilyDescriptor> columnFamilyDescriptors =
+          Arrays.asList(
+              new ColumnFamilyDescriptor(RocksDB.DEFAULT_COLUMN_FAMILY),
+              new ColumnFamilyDescriptor("new_cf".getBytes(), new_cf_opts)
+          );
+
+      final List<ColumnFamilyHandle> columnFamilyHandles = new ArrayList<>();
+      // open the database
+      try (final RocksDB db = RocksDB.open(opt,
+          dbFolder.getRoot().getAbsolutePath(),
+          columnFamilyDescriptors,
+          columnFamilyHandles)) {
+        try {
+          db.cancelAllBackgroundWork(true);
+          try {
+            db.put(new byte[KEY_SIZE], new byte[VALUE_SIZE]);
+            db.flush(new FlushOptions().setWaitForFlush(true));
+            fail("Expected RocksDBException to be thrown if we attempt to trigger a flush after" +
+                " all background work is cancelled.");
+          } catch (RocksDBException ignored) { }
+        } finally {
+          for (final ColumnFamilyHandle handle : columnFamilyHandles) {
+            handle.close();
+          }
+        }
+      }
+    }
+  }
+
+  @Test
+  public void cancelAllBackgroundWorkTwice() throws RocksDBException {
+    try (final Options options = new Options().setCreateIfMissing(true);
+         final RocksDB db = RocksDB.open(options,
+             dbFolder.getRoot().getAbsolutePath())
+    ) {
+      // Cancel all background work synchronously
+      db.cancelAllBackgroundWork(true);
+      // Cancel all background work asynchronously
+      db.cancelAllBackgroundWork(false);
+    }
+  }
+
   @Test
   public void pauseContinueBackgroundWork() throws RocksDBException {
     try (final Options options = new Options().setCreateIfMissing(true);