Make RocksDB instance responsible for closing associated ColumnFamilyHandle instances (#7428)
Summary: - Takes the burden off developer to close ColumnFamilyHandle instances before closing RocksDB instance - The change is backward-compatible ---- Previously the pattern for working with Column Families was: ```java try (final ColumnFamilyOptions cfOpts = new ColumnFamilyOptions().optimizeUniversalStyleCompaction()) { // list of column family descriptors, first entry must always be default column family final List<ColumnFamilyDescriptor> cfDescriptors = Arrays.asList( new ColumnFamilyDescriptor(RocksDB.DEFAULT_COLUMN_FAMILY, cfOpts), new ColumnFamilyDescriptor("my-first-columnfamily".getBytes(), cfOpts) ); // a list which will hold the handles for the column families once the db is opened final List<ColumnFamilyHandle> columnFamilyHandleList = new ArrayList<>(); try (final DBOptions options = new DBOptions() .setCreateIfMissing(true) .setCreateMissingColumnFamilies(true); final RocksDB db = RocksDB.open(options, "path/to/do", cfDescriptors, columnFamilyHandleList)) { try { // do something } finally { // NOTE user must explicitly frees the column family handles before freeing the db for (final ColumnFamilyHandle columnFamilyHandle : columnFamilyHandleList) { columnFamilyHandle.close(); } } // frees the column family options } } // frees the db and the db options ``` With the changes in this PR, the Java user no longer has to worry about manually closing the Column Families, which allows them to write simpler symmetrical create/free oriented code like this: ```java try (final ColumnFamilyOptions cfOpts = new ColumnFamilyOptions().optimizeUniversalStyleCompaction()) { // list of column family descriptors, first entry must always be default column family final List<ColumnFamilyDescriptor> cfDescriptors = Arrays.asList( new ColumnFamilyDescriptor(RocksDB.DEFAULT_COLUMN_FAMILY, cfOpts), new ColumnFamilyDescriptor("my-first-columnfamily".getBytes(), cfOpts) ); // a list which will hold the handles for the column families once the db is opened final List<ColumnFamilyHandle> columnFamilyHandleList = new ArrayList<>(); try (final DBOptions options = new DBOptions() .setCreateIfMissing(true) .setCreateMissingColumnFamilies(true); final RocksDB db = RocksDB.open(options, "path/to/do", cfDescriptors, columnFamilyHandleList)) { // do something } // frees the column family options, then frees the db and the db options } } ``` **NOTE**: The changes in this PR are backwards API compatible, which means existing code using the original approach will also continue to function correctly. Pull Request resolved: https://github.com/facebook/rocksdb/pull/7428 Reviewed By: cheng-chang Differential Revision: D24063348 Pulled By: jay-zhuang fbshipit-source-id: 648d7526669923128c863ead94516bf4d50ac658
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