r[runtime]

The Rust runtime

This section documents features that define some aspects of the Rust runtime.

r[runtime.global_allocator]

The global_allocator attribute

r[runtime.global_allocator.intro] The global_allocator [attribute][attributes] selects a [memory allocator][std::alloc].

[!EXAMPLE]

use core::alloc::{GlobalAlloc, Layout};
use std::alloc::System;

struct MyAllocator;

unsafe impl GlobalAlloc for MyAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        unsafe { System.alloc(layout) }
    }
    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        unsafe { System.dealloc(ptr, layout) }
    }
}

#[global_allocator]
static GLOBAL: MyAllocator = MyAllocator;

r[runtime.global_allocator.syntax] The global_allocator attribute uses the [MetaWord] syntax.

r[runtime.global_allocator.allowed-positions] The global_allocator attribute may only be applied to a static item whose type implements the GlobalAlloc trait.

r[runtime.global_allocator.duplicates] The global_allocator attribute may only be used once on an item.

r[runtime.global_allocator.single] The global_allocator attribute may only be used once in the crate graph.

r[runtime.global_allocator.stdlib] The global_allocator attribute is exported from the [standard library prelude][core::prelude::v1].

r[runtime.windows_subsystem]

The windows_subsystem attribute

r[runtime.windows_subsystem.intro] The windows_subsystem [attribute][attributes] sets the subsystem when linking on a Windows target.

[!EXAMPLE]

#![windows_subsystem = "windows"]

r[runtime.windows_subsystem.syntax] The windows_subsystem attribute uses the [MetaNameValueStr] syntax. Accepted values are "console" and "windows".

r[runtime.windows_subsystem.allowed-positions] The windows_subsystem attribute may only be applied to the crate root.

r[runtime.windows_subsystem.duplicates] Only the first use of windows_subsystem has effect.

[!NOTE] rustc lints against any use following the first. This may become an error in the future.

r[runtime.windows_subsystem.ignored] The windows_subsystem attribute is ignored on non-Windows targets and non-bin crate types.

r[runtime.windows_subsystem.console] The "console" subsystem is the default. If a console process is run from an existing console then it will be attached to that console; otherwise a new console window will be created.

r[runtime.windows_subsystem.windows] The "windows" subsystem will run detached from any existing console.

[!NOTE] The "windows" subsystem is commonly used by GUI applications that do not want to display a console window on startup.