Struct nom::lib::std::alloc::System

pub struct System;

The default memory allocator provided by the operating system.

This is based on malloc on Unix platforms and HeapAlloc on Windows, plus related functions.

This type implements the GlobalAlloc trait and Rust programs by default work as if they had this definition:

use std::alloc::System;

#[global_allocator]
static A: System = System;

fn main() {
    let a = Box::new(4); // Allocates from the system allocator.
    println!("{}", a);
}

You can also define your own wrapper around System if you'd like, such as keeping track of the number of all bytes allocated:

use std::alloc::{System, GlobalAlloc, Layout};
use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};

struct Counter;

static ALLOCATED: AtomicUsize = AtomicUsize::new(0);

unsafe impl GlobalAlloc for Counter {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        let ret = System.alloc(layout);
        if !ret.is_null() {
            ALLOCATED.fetch_add(layout.size(), SeqCst);
        }
        return ret
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout);
        ALLOCATED.fetch_sub(layout.size(), SeqCst);
    }
}

#[global_allocator]
static A: Counter = Counter;

fn main() {
    println!("allocated bytes before main: {}", ALLOCATED.load(SeqCst));
}

It can also be used directly to allocate memory independently of whatever global allocator has been selected for a Rust program. For example if a Rust program opts in to using jemalloc as the global allocator, System will still allocate memory using malloc and HeapAlloc.

Trait Implementations

impl Allocator for System

pub fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>

🔬 This is a nightly-only experimental API. (allocator_api)

Attempts to allocate a block of memory.

pub fn allocate_zeroed(
    &self,
    layout: Layout
) -> Result<NonNull<[u8]>, AllocError>

🔬 This is a nightly-only experimental API. (allocator_api)

Behaves like allocate, but also ensures that the returned memory is zero-initialized.

pub unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout)

🔬 This is a nightly-only experimental API. (allocator_api)

Deallocates the memory referenced by ptr.

pub unsafe fn grow(
    &self,
    ptr: NonNull<u8>,
    old_layout: Layout,
    new_layout: Layout
) -> Result<NonNull<[u8]>, AllocError>

🔬 This is a nightly-only experimental API. (allocator_api)

Attempts to extend the memory block.

pub unsafe fn grow_zeroed(
    &self,
    ptr: NonNull<u8>,
    old_layout: Layout,
    new_layout: Layout
) -> Result<NonNull<[u8]>, AllocError>

🔬 This is a nightly-only experimental API. (allocator_api)

Behaves like grow, but also ensures that the new contents are set to zero before being returned.

pub unsafe fn shrink(
    &self,
    ptr: NonNull<u8>,
    old_layout: Layout,
    new_layout: Layout
) -> Result<NonNull<[u8]>, AllocError>

🔬 This is a nightly-only experimental API. (allocator_api)

Attempts to shrink the memory block.

pub fn by_ref(&self) -> &Self

🔬 This is a nightly-only experimental API. (allocator_api)

Creates a "by reference" adaptor for this instance of Allocator.

impl Clone for System

pub fn clone(&self) -> System

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for System

impl Debug for System

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

Formats the value using the given formatter.

impl Default for System

pub fn default() -> System

Returns the "default value" for a type.

impl GlobalAlloc for System

pub unsafe fn alloc(&self, layout: Layout) -> *mut u8

Allocate memory as described by the given layout.

pub unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8

Behaves like alloc, but also ensures that the contents are set to zero before being returned.

pub unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout)

Deallocate the block of memory at the given ptr pointer with the given layout.

pub unsafe fn realloc(
    &self,
    ptr: *mut u8,
    layout: Layout,
    new_size: usize
) -> *mut u8

Shrink or grow a block of memory to the given new_size. The block is described by the given ptr pointer and layout.