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rust-rocksdb/src/column_family.rs

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5.0 KiB

// Copyright 2020 Tyler Neely
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use crate::{db::MultiThreaded, ffi, Options};
use std::sync::Arc;
/// The name of the default column family.
///
/// The column family with this name is created implicitly whenever column
/// families are used.
pub const DEFAULT_COLUMN_FAMILY_NAME: &str = "default";
/// A descriptor for a RocksDB column family.
///
/// A description of the column family, containing the name and `Options`.
pub struct ColumnFamilyDescriptor {
pub(crate) name: String,
pub(crate) options: Options,
}
impl ColumnFamilyDescriptor {
// Create a new column family descriptor with the specified name and options.
pub fn new<S>(name: S, options: Options) -> Self
where
S: Into<String>,
{
Self {
name: name.into(),
options,
}
}
}
/// An opaque type used to represent a column family. Returned from some functions, and used
/// in others
pub struct ColumnFamily {
pub(crate) inner: *mut ffi::rocksdb_column_family_handle_t,
}
/// A specialized opaque type used to represent a column family by the [`MultiThreaded`]
/// mode. Clone (and Copy) is derived to behave like `&ColumnFamily` (this is used for
/// single-threaded mode). `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.
pub struct BoundColumnFamily<'a> {
pub(crate) inner: *mut ffi::rocksdb_column_family_handle_t,
pub(crate) multi_threaded_cfs: std::marker::PhantomData<&'a MultiThreaded>,
}
// internal struct which isn't exposed to public api.
// but its memory will be exposed after transmute()-ing to BoundColumnFamily.
// ColumnFamily's lifetime should be bound to DB. But, db holds cfs and cfs can't easily
// self-reference DB as its lifetime due to rust's type system
pub(crate) struct UnboundColumnFamily {
pub(crate) inner: *mut ffi::rocksdb_column_family_handle_t,
}
impl UnboundColumnFamily {
pub(crate) fn bound_column_family<'a>(self: Arc<Self>) -> Arc<BoundColumnFamily<'a>> {
// SAFETY: the new BoundColumnFamily here just adding lifetime,
// so that column family handle won't outlive db.
unsafe { Arc::from_raw(Arc::into_raw(self).cast()) }
}
}
fn destroy_handle(handle: *mut ffi::rocksdb_column_family_handle_t) {
// SAFETY: This should be called only from various Drop::drop(), strictly keeping a 1-to-1
// ownership to avoid double invocation to the rocksdb function with same handle.
unsafe {
ffi::rocksdb_column_family_handle_destroy(handle);
}
}
impl Drop for ColumnFamily {
fn drop(&mut self) {
destroy_handle(self.inner);
}
}
// these behaviors must be identical between BoundColumnFamily and UnboundColumnFamily
// due to the unsafe transmute() in bound_column_family()!
impl<'a> Drop for BoundColumnFamily<'a> {
fn drop(&mut self) {
destroy_handle(self.inner);
}
}
impl Drop for UnboundColumnFamily {
fn drop(&mut self) {
destroy_handle(self.inner);
}
}
/// Handy type alias to hide actual type difference to reference [`ColumnFamily`]
/// depending on the `multi-threaded-cf` crate feature.
#[cfg(not(feature = "multi-threaded-cf"))]
pub type ColumnFamilyRef<'a> = &'a ColumnFamily;
#[cfg(feature = "multi-threaded-cf")]
pub type ColumnFamilyRef<'a> = Arc<BoundColumnFamily<'a>>;
/// Utility trait to accept both supported references to `ColumnFamily`
/// (`&ColumnFamily` and `BoundColumnFamily`)
pub trait AsColumnFamilyRef {
fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t;
}
impl AsColumnFamilyRef for ColumnFamily {
fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t {
self.inner
}
}
impl<'a> AsColumnFamilyRef for &'a ColumnFamily {
fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t {
self.inner
}
}
// Only implement for Arc-ed BoundColumnFamily as this tightly coupled and
// implementation detail, considering use of std::mem::transmute. BoundColumnFamily
// isn't expected to be used as naked.
// Also, ColumnFamilyRef might not be Arc<BoundColumnFamily<'a>> depending crate
// feature flags so, we can't use the type alias here.
impl<'a> AsColumnFamilyRef for Arc<BoundColumnFamily<'a>> {
fn inner(&self) -> *mut ffi::rocksdb_column_family_handle_t {
self.inner
}
}
unsafe impl Send for ColumnFamily {}
unsafe impl Send for UnboundColumnFamily {}
unsafe impl Sync for UnboundColumnFamily {}
unsafe impl<'a> Send for BoundColumnFamily<'a> {}