Add arena

libanalysis/src/arena.rs

@@ -0,0 +1,42 @@
+use parking_lot::RwLock;
+
+const CHUNK_LEN: usize = 16;
+
+pub struct Arena<T> {
+    chunks: RwLock<Vec<Vec<T>>>,
+}
+
+impl<T> Arena<T> {
+    pub fn new(&self) -> Arena<T> {
+        Arena {
+            chunks: RwLock::new(vec![Vec::with_capacity(CHUNK_LEN)]),
+        }
+    }
+
+    pub fn push(&self, value: T) -> usize {
+        let mut guard = self.chunks.write();
+        let mut idx = (guard.len() - 1) * CHUNK_LEN;
+        let chunk = {
+            if guard.last().unwrap().len() == CHUNK_LEN {
+                guard.push(Vec::with_capacity(CHUNK_LEN));
+            }
+            guard.last_mut().unwrap()
+        };
+        assert!(chunk.len() < chunk.capacity());
+        idx += chunk.len();
+        chunk.push(value);
+        idx
+    }
+
+    pub fn get(&self, idx: usize) -> &T {
+        let chunk_idx = idx / CHUNK_LEN;
+        let chunk_off = idx - chunk_idx * CHUNK_LEN;
+        let guard = self.chunks.read();
+        let value = &guard[chunk_idx][chunk_off];
+        unsafe {
+            // We are careful to not move values in chunks,
+            // so this hopefully is safe
+            ::std::mem::transmute::<&T, &T>(value)
+        }
+    }
+}