Remove need for &mut self in create_cf and drop_cf (v2)

.github/workflows/rust.yml

@@ -88,7 +88,14 @@ jobs:
         with:
           command: test
           args: --manifest-path=librocksdb-sys/Cargo.toml
-      - name: Run rocksdb tests
+      - name: Run rocksdb tests (single-threaded cf alterations)
         uses: actions-rs/cargo@v1
         with:
           command: test
+      - name: Run rocksdb tests (multi-threaded cf alterations)
+        uses: actions-rs/cargo@v1
+        env:
+          RUSTFLAGS=-Awarnings # Suppress "variable does not need to be mutable" warnings
+        with:
+          command: test
+          args: --features multi-threaded-as-default

Cargo.toml

@@ -24,6 +24,7 @@ lz4 = ["librocksdb-sys/lz4"]
 zstd = ["librocksdb-sys/zstd"]
 zlib = ["librocksdb-sys/zlib"]
 bzip2 = ["librocksdb-sys/bzip2"]
+multi-threaded-as-default = []
 
 [dependencies]
 libc = "0.2"

src/backup.rs

@@ -235,7 +235,7 @@ impl Default for BackupEngineOptions {
         unsafe {
             let opts = ffi::rocksdb_options_create();
             if opts.is_null() {
-                panic!("Could not create RocksDB backup options".to_owned());
+                panic!("Could not create RocksDB backup options");
             }
             BackupEngineOptions { inner: opts }
         }
@@ -247,7 +247,7 @@ impl Default for RestoreOptions {
         unsafe {
             let opts = ffi::rocksdb_restore_options_create();
             if opts.is_null() {
-                panic!("Could not create RocksDB restore options".to_owned());
+                panic!("Could not create RocksDB restore options");
             }
             RestoreOptions { inner: opts }
         }

src/column_family.rs

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use crate::{ffi, Options};
+use crate::{db::MultiThreaded, ffi, Options};
 
 /// The name of the default column family.
 ///
@@ -48,3 +48,30 @@ pub struct ColumnFamily {
 }
 
 unsafe impl Send for ColumnFamily {}
+
+/// A specialized opaque type used to represent a column family. Used for multi-threaded
+/// mode. Clone (and Copy) is derived to behave like &ColumnFamily (used for
+/// single-threaded). Clone/Copy is safe because this lifetime is bound to DB like
+/// iterators/snapshots. On top of it, this is as cheap and small as &ColumnFamily because
+/// this only has a single pointer-wide field.
+#[derive(Clone, Copy)]
+pub struct BoundColumnFamily<'a> {
+    pub(crate) inner: *mut ffi::rocksdb_column_family_handle_t,
+    pub(crate) multi_threaded_cfs: std::marker::PhantomData<&'a MultiThreaded>,
+}
+
+pub trait ColumnFamilyRef {
+    fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t;
+}
+
+impl<'a> ColumnFamilyRef for &'a ColumnFamily {
+    fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t {
+        self.inner
+    }
+}
+
+impl<'a> ColumnFamilyRef for BoundColumnFamily<'a> {
+    fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t {
+        self.inner
+    }
+}