1.28.0[][src]Struct 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;

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);

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[src]

impl Clone for System[src]

impl Copy for System[src]

impl Debug for System[src]

impl Default for System[src]

impl GlobalAlloc for System[src]

Auto Trait Implementations

impl RefUnwindSafe for System[src]

impl Send for System[src]

impl Sync for System[src]

impl Unpin for System[src]

impl UnwindSafe for System[src]

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.