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;

#[global_allocator]
static A: System = System;

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

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));
}Run

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 Debug for System[src]

impl Copy for System[src]

impl Clone for System[src]

fn clone_from(&mut self, source: &Self)1.0.0[src]

Performs copy-assignment from source. Read more

impl Default for System[src]

impl GlobalAlloc for System[src]

impl Alloc for System[src]

fn usable_size(&self, layout: &Layout) -> (usize, usize)[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Returns bounds on the guaranteed usable size of a successful allocation created with the specified layout. Read more

unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr>[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Behaves like alloc, but also returns the whole size of the returned block. For some layout inputs, like arrays, this may include extra storage usable for additional data. Read more

unsafe fn realloc_excess(
    &mut self,
    ptr: NonNull<u8>,
    layout: Layout,
    new_size: usize
) -> Result<Excess, AllocErr>
[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Behaves like realloc, but also returns the whole size of the returned block. For some layout inputs, like arrays, this may include extra storage usable for additional data. Read more

unsafe fn grow_in_place(
    &mut self,
    ptr: NonNull<u8>,
    layout: Layout,
    new_size: usize
) -> Result<(), CannotReallocInPlace>
[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Attempts to extend the allocation referenced by ptr to fit new_size. Read more

unsafe fn shrink_in_place(
    &mut self,
    ptr: NonNull<u8>,
    layout: Layout,
    new_size: usize
) -> Result<(), CannotReallocInPlace>
[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Attempts to shrink the allocation referenced by ptr to fit new_size. Read more

fn alloc_one<T>(&mut self) -> Result<NonNull<T>, AllocErr>[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Allocates a block suitable for holding an instance of T. Read more

unsafe fn dealloc_one<T>(&mut self, ptr: NonNull<T>)[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Deallocates a block suitable for holding an instance of T. Read more

fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Allocates a block suitable for holding n instances of T. Read more

unsafe fn realloc_array<T>(
    &mut self,
    ptr: NonNull<T>,
    n_old: usize,
    n_new: usize
) -> Result<NonNull<T>, AllocErr>
[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Reallocates a block previously suitable for holding n_old instances of T, returning a block suitable for holding n_new instances of T. Read more

unsafe fn dealloc_array<T>(
    &mut self,
    ptr: NonNull<T>,
    n: usize
) -> Result<(), AllocErr>
[src]

🔬 This is a nightly-only experimental API. (allocator_api #32838)

Deallocates a block suitable for holding n instances of T. Read more

Auto Trait Implementations

impl Send for System

impl Sync for System

Blanket Implementations

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

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

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

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

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

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

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.