Support custom trailer

.github/workflows/ci.yml

@@ -85,18 +85,25 @@ jobs:
         # --no-self-update is necessary because the windows environment cannot self-update rustup.exe.
         run: rustup update stable --no-self-update && rustup default stable
       - name: Test
-        run: . ci/test-stable.sh test
+        run: . ci/test-stable.sh test 
 
-  # Nightly
-  nightly:
-    name: nightly
-    runs-on: ubuntu-latest
+  # no std
+  no_std:
+    name: no_std
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
+    runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
       - name: Install Rust
-        run: rustup update $nightly && rustup default $nightly
+        # --no-self-update is necessary because the windows environment cannot self-update rustup.exe.
+        run: rustup update stable --no-self-update && rustup default stable
       - name: Test
-        run: . ci/test-stable.sh test
+        run: cargo test --no-default-features --features alloc
 
   # Run tests on some extra platforms
   cross:
@@ -212,7 +219,7 @@ jobs:
       - rustfmt
       - clippy
       - stable
-      - nightly
+      - no_std
       - sanitizer
       - valgrind 
       - minrust

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "skl"
-version = "0.4.0"
+version = "0.5.0"
 edition = "2021"
 repository = "https://github.com/al8n/skl-rs"
 description = "A lock-free thread-safe concurrent ARENA based (heap backend or memory map backend) skiplist implementation which helps develop MVCC memtable for LSM-Tree."
@@ -40,13 +40,10 @@ loom = "0.7"
 
 [target.'cfg(target_family = "wasm")'.dependencies]
 getrandom = { version = "0.2", features = ["js"] }
-rand = { version = "0.8", default-features = false, features = ["getrandom"] }
-
-[target.'cfg(not(target_family = "wasm"))'.dependencies]
-rand = { version = "0.8", default-features = false }
 
 [dependencies]
 crossbeam-utils = { version = "0.8", default-features = false }
+rand = { version = "0.8", default-features = false, features = ["getrandom"] }
 
 fs4 = { version = "0.8", optional = true }
 memmap2 = { version = "0.9", optional = true }

README.md

@@ -24,18 +24,19 @@
 
     ```toml
     [dependencies]
-    skl = "0.4"
+    skl = "0.5"
     ```
 
 - Enable memory map backend
 
     ```toml
     [dependencies]
-    skl = { version = "0.4", features = ["memmap"] }
+    skl = { version = "0.5", features = ["memmap"] }
     ```
 
 ## Features
 
+- **MVCC and 3D access**: Builtin MVCC (multiple versioning concurrency control) and key-value-version access support.
 - **Lock-free and Concurrent-Safe:** SkipMap and SkipSet provide lock-free operations, ensuring efficient concurrent access without the need for explicit locking mechanisms.
 - **Extensible for Key-Value Database Developers:** Designed as a low-level crate, SkipMap and SkipSet offer a flexible foundation for key-value database developers. You can easily build your own memtable or write-ahead-log (WAL) using these structures.
 - **Memory Efficiency:** These data structures are optimized for minimal memory overhead. They operate around references, avoiding unnecessary allocations and deep copies, which can be crucial for efficient memory usage.
@@ -85,10 +86,12 @@ Please see [examples](https://github.com/al8n/skl-rs/tree/main/examples) folder
 
 ## Pedigree
 
-This code is inspired and modified based on Cockroachdb's pebble arenaskl code:
+This code is inspired and modified based on Cockroachdb's pebble arenaskl and Dgraph's badger skl code:
 
 https://github.com/cockroachdb/pebble/tree/master/internal/arenaskl
 
+https://github.com/dgraph-io/badger/tree/master/skl
+
 The pebble's arenaskl code is based on Andy Kimball's arenaskl code:
 
 https://github.com/andy-kimball/arenaskl

src/arena.rs

@@ -69,32 +69,28 @@ impl Arena {
 
 impl Arena {
   #[inline]
-  const fn min_cap<const N: u64>() -> usize {
-    (N * 2) as usize
-  }
-
-  #[inline]
-  pub(super) fn new_vec<const N: u64>(n: usize) -> Self {
+  pub(super) fn new_vec(n: usize, min_cap: usize) -> Self {
     Self::new(Shared::new_vec(
-      n.max(Self::min_cap::<N>()),
+      n.max(min_cap),
       mem::align_of::<u64>().max(NODE_ALIGNMENT_FACTOR),
     ))
   }
 
   #[cfg(all(feature = "memmap", not(target_family = "wasm")))]
   #[inline]
-  pub(super) fn new_mmap<const N: u64>(
+  pub(super) fn new_mmap(
     n: usize,
+    min_cap: usize,
     file: std::fs::File,
     lock: bool,
   ) -> std::io::Result<Self> {
-    Shared::new_mmaped(n.max(Self::min_cap::<N>()), file, lock).map(Self::new)
+    Shared::new_mmaped(n.max(min_cap), file, lock).map(Self::new)
   }
 
   #[cfg(all(feature = "memmap", not(target_family = "wasm")))]
   #[inline]
-  pub(super) fn new_anonymous_mmap<const N: u64>(n: usize) -> std::io::Result<Self> {
-    Shared::new_mmaped_anon(n.max(Self::min_cap::<N>())).map(Self::new)
+  pub(super) fn new_anonymous_mmap(n: usize, min_cap: usize) -> std::io::Result<Self> {
+    Shared::new_mmaped_anon(n.max(min_cap)).map(Self::new)
   }
 
   #[inline]
@@ -191,29 +187,6 @@ impl Arena {
   }
 }
 
-impl Clone for Arena {
-  fn clone(&self) -> Self {
-    unsafe {
-      let shared: *mut Shared = self.inner.load(Ordering::Relaxed).cast();
-
-      let old_size = (*shared).refs.fetch_add(1, Ordering::Release);
-      if old_size > usize::MAX >> 1 {
-        abort();
-      }
-
-      // Safety:
-      // The ptr is always non-null, we just initialized it.
-      // And this ptr is only deallocated when the arena is dropped.
-      Self {
-        cap: (*shared).cap(),
-        inner: AtomicPtr::new(shared as _),
-        data_ptr: self.data_ptr,
-        n: self.n.clone(),
-      }
-    }
-  }
-}
-
 impl Drop for Arena {
   fn drop(&mut self) {
     unsafe {
@@ -255,24 +228,3 @@ impl Drop for Arena {
     }
   }
 }
-
-#[inline(never)]
-#[cold]
-fn abort() -> ! {
-  #[cfg(feature = "std")]
-  {
-    std::process::abort();
-  }
-
-  #[cfg(not(feature = "std"))]
-  {
-    struct Abort;
-    impl Drop for Abort {
-      fn drop(&mut self) {
-        panic!();
-      }
-    }
-    let _a = Abort;
-    panic!("abort");
-  }
-}

src/lib.rs

@@ -3,7 +3,7 @@
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(docsrs, allow(unused_attributes))]
 #![deny(missing_docs)]
-#![allow(clippy::type_complexity, clippy::mut_from_ref)]
+#![allow(unexpected_cfgs, clippy::type_complexity, clippy::mut_from_ref)]
 
 #[cfg(not(feature = "std"))]
 extern crate alloc as std;
@@ -99,6 +99,20 @@ impl Comparator for Descend {
   }
 }
 
+/// A trait for extra information that can be stored with entry in the skiplist.
+pub trait Trailer: Copy {
+  /// Returns the version of the trailer.
+  fn version(&self) -> u64;
+}
+
+impl Trailer for u64 {
+  /// Returns the version of the trailer.
+  #[inline]
+  fn version(&self) -> u64 {
+    *self
+  }
+}
+
 mod sync {
   #[cfg(not(loom))]
   pub(crate) use core::sync::atomic::*;