Initial commit

src/allocator.rs

@@ -0,0 +1,150 @@
+use std::{
+    mem::size_of,
+    ptr::NonNull,
+    sync::{LazyLock, Mutex},
+};
+
+use crate::bump_allocator::{BUMP_ALLOCATOR, MEMFD_INITIAL_SIZE};
+
+const ALIGNMENT: usize = 8;
+const INITIAL_HEAP_SIZE: usize = MEMFD_INITIAL_SIZE;
+const METADATA_SIZE: usize = size_of::<Metadata>();
+
+pub(crate) static ALLOCATOR: LazyLock<Mutex<Allocator>> =
+    LazyLock::new(|| unsafe { Mutex::new(Allocator::new()) });
+
+struct Metadata {
+    chunk: NonNull<Chunk>,
+}
+
+struct Chunk {
+    buffer: *mut u8,
+    size: usize,
+    in_use: bool,
+    next_chunk: Option<NonNull<Chunk>>,
+    prev_chunk: Option<NonNull<Chunk>>,
+}
+
+pub(crate) struct Allocator {
+    head: NonNull<Chunk>,
+    tail: NonNull<Chunk>,
+}
+
+unsafe impl Send for Chunk {}
+unsafe impl Send for Allocator {}
+
+impl Allocator {
+    unsafe fn new() -> Self {
+        let mut allocator = BUMP_ALLOCATOR.lock().unwrap();
+
+        let mem = allocator.alloc(INITIAL_HEAP_SIZE).unwrap();
+
+        let head = Box::new(Chunk {
+            buffer: mem.byte_add(METADATA_SIZE),
+            size: INITIAL_HEAP_SIZE,
+            in_use: false,
+            next_chunk: None,
+            prev_chunk: None,
+        });
+        let head = NonNull::new(Box::leak(head)).unwrap();
+
+        let mem = mem as *mut Metadata;
+        *mem = Metadata { chunk: head };
+
+        Allocator { head, tail: head }
+    }
+
+    pub(crate) unsafe fn allocate(&mut self, size: usize) -> Option<*mut u8> {
+        let size = (size + ALIGNMENT - 1) / ALIGNMENT * ALIGNMENT;
+
+        let mut head = Some(self.head);
+
+        while head.is_some() {
+            let current_head = head.unwrap().as_mut();
+
+            if !current_head.in_use && current_head.size >= size {
+                if current_head.size == size {
+                    current_head.in_use = true;
+                    return Some(current_head.buffer);
+                }
+
+                let unused_space = Box::new(Chunk {
+                    buffer: current_head.buffer.byte_add(size + METADATA_SIZE),
+                    size: current_head.size - size - METADATA_SIZE,
+                    in_use: false,
+                    next_chunk: current_head.next_chunk,
+                    prev_chunk: head,
+                });
+                let ptr = NonNull::new(Box::leak(unused_space)).unwrap();
+
+                *(ptr.as_ref().buffer.byte_sub(METADATA_SIZE) as *mut Metadata) =
+                    Metadata { chunk: ptr };
+
+                if ptr.as_ref().next_chunk.is_none() {
+                    self.tail = ptr;
+                }
+
+                current_head.in_use = true;
+                current_head.size = size;
+                current_head.next_chunk = Some(ptr);
+
+                return Some(current_head.buffer);
+            }
+
+            head = current_head.next_chunk;
+        }
+
+        // TODO: Try to allocate more space from bump allocator
+
+        None
+    }
+
+    pub(crate) unsafe fn deallocate(&mut self, ptr: *mut u8) {
+        let metadata = ptr.byte_sub(METADATA_SIZE) as *mut Metadata;
+        let metadata = (*metadata).chunk.as_mut();
+
+        debug_assert_eq!(metadata.in_use, true);
+        debug_assert_eq!(metadata.buffer, ptr);
+
+        metadata.in_use = false;
+
+        // TODO: Consolidate chunks
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    extern crate test;
+
+    use core::slice;
+
+    use test::Bencher;
+
+    use super::ALLOCATOR;
+
+    #[test]
+    fn functionality() {
+        let mut allocator = ALLOCATOR.lock().unwrap();
+
+        unsafe {
+            let x = allocator.allocate(10).unwrap();
+            let x = slice::from_raw_parts_mut(x, 10);
+            x[0] = 1;
+            assert_eq!(x[0], 1);
+            allocator.deallocate(x.as_mut_ptr());
+        }
+    }
+
+    #[bench]
+    fn allocator_bench(b: &mut Bencher) {
+        let mut allocator = ALLOCATOR.lock().unwrap();
+
+        b.iter(|| unsafe {
+            let x = allocator.allocate(1).unwrap();
+            let x = slice::from_raw_parts_mut(x, 1);
+            x[0] = 1;
+            assert_eq!(x[0], 1);
+            allocator.deallocate(x.as_mut_ptr());
+        });
+    }
+}