feat: add object pool for cdylib

wfassoc-cdylib/src/object_pool.rs

@@ -0,0 +1,65 @@
+//! When exporting resources for C interface, resource management and ownership are important things.
+//! In this dynamic library, we hold all resources' ownership in Rust world,
+//! and only expose a token for C code manipulation.
+//! 
+//! We need to create a container for holding all resources and providing corresponding operations.
+//! So we introduce [ObjectPool] in this module for this purpose.
+use slotmap::{DefaultKey, Key, KeyData, SlotMap};
+use thiserror::Error as TeError;
+
+/// Error occurs when operating with [ObjectPool].
+#[derive(Debug, TeError)]
+pub enum Error {
+    #[error("given token is not presented in object pool")]
+    NoSuchToken,
+}
+
+/// The token for fetching obejct in [ObjectPool].
+pub type Token = u64;
+
+/// A pool for managing objects with unique tokens.
+/// 
+/// It is highly suggested to use this pool with [std::sync::RwLock] guard.
+pub struct ObjectPool<T> {
+    objs: SlotMap<DefaultKey, T>,
+}
+
+impl<T> ObjectPool<T> {
+    pub fn new() -> Self {
+        Self {
+            objs: SlotMap::new(),
+        }
+    }
+
+    fn key_to_token(key: &DefaultKey) -> Token {
+        key.data().as_ffi()
+    }
+
+    fn token_to_key(token: Token) -> DefaultKey {
+        DefaultKey::from(KeyData::from_ffi(token))
+    }
+
+    pub fn allocate(&mut self, value: T) -> Result<Token, Error> {
+        let key = self.objs.insert(value);
+        Ok(Self::key_to_token(&key))
+    }
+
+    pub fn delete(&mut self, token: Token) -> Result<(), Error> {
+        match self.objs.remove(Self::token_to_key(token)) {
+            Some(_) => Ok(()),
+            None => Err(Error::NoSuchToken),
+        }
+    }
+
+    pub fn get(&self, token: Token) -> Result<&T, Error> {
+        self.objs
+            .get(Self::token_to_key(token))
+            .ok_or(Error::NoSuchToken)
+    }
+
+    pub fn get_mut(&mut self, token: Token) -> Result<&mut T, Error> {
+        self.objs
+            .get_mut(Self::token_to_key(token))
+            .ok_or(Error::NoSuchToken)
+    }
+}