Struct bumpalo::Bump

pub struct Bump { /* private fields */ }

An arena to bump allocate into.

Example

use bumpalo::Bump;

// Create a new bump arena.
let bump = Bump::new();

// Allocate values into the arena.
let forty_two = bump.alloc(42);
assert_eq!(*forty_two, 42);

// Mutable references are returned from allocation.
let mut s = bump.alloc("bumpalo");
*s = "the bump allocator; and also is a buffalo";

Implementations

impl Bump

pub fn new() -> Bump

Construct a new arena to bump allocate into.

Example

let bump = bumpalo::Bump::new();

pub fn reset(&mut self)

Reset this bump allocator.

Performs mass deallocation on everything allocated in this arena by resetting the pointer into the underlying chunk of memory to the start of the chunk. Does not run any Drop implementations on deallocated objects; see the BumpAllocSafe marker trait for details.

If this arena has allocated multiple chunks to bump allocate into, then the excess chunks are returned to the global allocator.

Example

let mut bump = bumpalo::Bump::new();

// Allocate a bunch of things.
{
    for i in 0..100 {
        bump.alloc(i);
    }
}

// Reset the arena.
bump.reset();

// Allocate some new things in the space previously occupied by the
// original things.
for j in 200..400 {
    bump.alloc(j);
}

pub fn alloc<T: BumpAllocSafe>(&self, val: T) -> &mut T

Allocate an object.

Example

let bump = bumpalo::Bump::new();
let x = bump.alloc("hello");
assert_eq!(*x, "hello");

Panics

Panics if size_of::<T>() > 65520 or if align_of::<T>() > 8.

pub unsafe fn each_allocated_chunk<F>(&mut self, f: F)where
    F: for<'a> FnMut(&'a [u8]),

Call f on each chunk of allocated memory that this arena has bump allocated into.

f is invoked in order of allocation: oldest chunks first, newest chunks last.

Safety

Because this method takes &mut self, we know that the bump arena reference is unique and therefore there aren’t any active references to any of the objects we’ve allocated in it either. This potential aliasing of exclusive references is one common footgun for unsafe code that we don’t need to worry about here.

However, there could be regions of uninitilized memory used as padding between allocations. Reading uninitialized memory is big time undefined behavior!

The only way to guarantee that there is no padding between allocations is if both of these properties hold:

1. Every object allocated in this arena has the same alignment.
2. Every object’s size is a multiple of its alignment.

A simple way to fulfill these requirements is by allocating only objects of the same type.

If you want to use this each_allocated_chunk method, it is your responsibility to ensure that these properties hold!

Example

let mut bump = bumpalo::Bump::new();

// Allocate a bunch of things in this bump arena, potentially causing
// additional memory chunks to be reserved.
for i in 0..10000 {
    bump.alloc(i);
}

// Iterate over each chunk we've bump allocated into. This is safe
// because we have only allocated `usize` objects in this arena.
unsafe {
    bump.each_allocated_chunk(|ch| {
        println!("Used a chunk that is {} bytes long", ch.len());
    });
}

Trait Implementations

impl Debug for Bump

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

Formats the value using the given formatter.

impl Drop for Bump

fn drop(&mut self)

Executes the destructor for this type.