Struct Arena 

pub struct Arena { /* private fields */ }

A bump allocator for transaction-scoped memory.

Provides fast allocation by simply incrementing a pointer. Memory is organized in chunks that grow as needed. The arena can be reset for reuse without deallocating the underlying memory.

Security

The arena zeros all memory on reset to prevent data leakage between transactions. This is critical when the arena may hold sensitive data like encryption keys or user credentials.

Example

use thunderdb::arena::Arena;

let mut arena = Arena::new(1024);

// Fast bump allocation
let slice1 = arena.alloc(32);
slice1.fill(0xAA);

// Copy data into arena
let data = b"hello world";
let copied = arena.copy_slice(data);
assert_eq!(copied, data);

// Reset for reuse (memory is zeroed)
arena.reset();
assert_eq!(arena.bytes_used(), 0);

Implementations

impl Arena

pub fn new(chunk_size: usize) -> Self

Creates a new arena with the specified chunk size.

Arguments

• chunk_size - Size of each memory chunk in bytes.

Panics

Panics if chunk_size is 0.

pub fn with_default_size() -> Self

Creates a new arena with default chunk size (64KB).

pub fn with_capacity(initial_capacity: usize) -> Self

Creates a new arena with specified initial capacity.

Pre-allocates a single chunk of the given size.

pub fn alloc(&mut self, size: usize) -> &mut [u8]

Allocates size bytes from the arena.

Returns a mutable slice of zeroed memory. The allocation is bump-pointer style and very fast (O(1) typical).

If the current chunk doesn’t have enough space, a new chunk is allocated.

Arguments

• size - Number of bytes to allocate.

Returns

A mutable slice of size bytes, initialized to zero.

pub fn alloc_aligned(&mut self, size: usize, align: usize) -> &mut [u8]

Allocates size bytes with specified alignment.

Useful for cache-line alignment (64 bytes) or page alignment to avoid false sharing and improve memory access patterns.

Arguments

• size - Number of bytes to allocate.
• align - Required alignment (must be power of 2).

Returns

A mutable slice of size bytes, with the starting address aligned to align bytes.

Panics

Panics if align is not a power of 2.

Performance

Common alignments:

• 64: Cache line (avoids false sharing)
• 4096: Page alignment (for mmap-friendly buffers)
• 32768: HPC page size (matches PAGE_SIZE)

pub fn copy_slice(&mut self, data: &[u8]) -> &[u8]

Allocates and copies data into the arena.

This is a convenience method that allocates space and copies the provided slice in one operation.

Arguments

• data - The data to copy into the arena.

Returns

A slice pointing to the copied data within the arena.

pub fn reset(&mut self)

Resets the arena for reuse.

This clears all allocations but keeps the underlying memory for reuse. All memory is zeroed to prevent data leakage.

Security

Memory is explicitly zeroed to ensure no sensitive data from previous transactions leaks to new allocations.

pub fn bytes_used(&self) -> usize

Returns the total bytes currently allocated.

pub fn capacity(&self) -> usize

Returns the total capacity across all chunks.

pub fn chunk_count(&self) -> usize

Returns the number of chunks allocated.

Trait Implementations

impl Debug for Arena

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Arena

fn default() -> Self

Returns the “default value” for a type.