The Rust runtime
This section documents features that define some aspects of the Rust runtime.
The panic_handler
attribute
The panic_handler
attribute can only be applied to a function with signature
fn(&PanicInfo) -> !
. The function marked with this attribute defines the behavior of panics. The
PanicInfo
struct contains information about the location of the panic. There must be a single
panic_handler
function in the dependency graph of a binary, dylib or cdylib crate.
Below is shown a panic_handler
function that logs the panic message and then halts the
thread.
#![no_std]
use core::fmt::{self, Write};
use core::panic::PanicInfo;
struct Sink {
// ..
_0: (),
}
impl Sink {
fn new() -> Sink { Sink { _0: () }}
}
impl fmt::Write for Sink {
fn write_str(&mut self, _: &str) -> fmt::Result { Ok(()) }
}
#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
let mut sink = Sink::new();
// logs "panicked at '$reason', src/main.rs:27:4" to some `sink`
let _ = writeln!(sink, "{}", info);
loop {}
}
Standard behavior
The standard library provides an implementation of panic_handler
that
defaults to unwinding the stack but that can be changed to abort the
process. The standard library's panic behavior can be modified at
runtime with the set_hook function.
The global_allocator
attribute
The global_allocator
attribute is used on a static item implementing the
GlobalAlloc
trait to set the global allocator.
The windows_subsystem
attribute
The windows_subsystem
attribute may be applied at the crate level to set
the subsystem when linking on a Windows target. It uses the
MetaNameValueStr syntax to specify the subsystem with a value of either
console
or windows
. This attribute is ignored on non-Windows targets, and
for non-bin
crate types.
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.
The "windows" subsystem is commonly used by GUI applications that do not want to display a console window on startup. It will run detached from any existing console.
#![allow(unused)] #![windows_subsystem = "windows"] fn main() { }