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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
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2.8 kB · 77 lines
Rust
at master
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778// SPDX-License-Identifier: Apache-2.0 OR MIT
use core::sync::atomic::{AtomicUsize, Ordering};use std::sync::Once;
static WORKS: AtomicUsize = AtomicUsize::new(0);static INIT: Once = Once::new();
pub(crate) fn inside_proc_macro() -> bool { match WORKS.load(Ordering::Relaxed) { 1 => return false, 2 => return true, _ => {} }
INIT.call_once(initialize); inside_proc_macro()}
pub(crate) fn force_fallback() { WORKS.store(1, Ordering::Relaxed);}
pub(crate) fn unforce_fallback() { initialize();}
#[cfg(not(no_is_available))]fn initialize() { let available = proc_macro::is_available(); WORKS.store(available as usize + 1, Ordering::Relaxed);}
// Swap in a null panic hook to avoid printing "thread panicked" to stderr,// then use catch_unwind to determine whether the compiler's proc_macro is// working. When proc-macro2 is used from outside of a procedural macro all// of the proc_macro crate's APIs currently panic.//// The Once is to prevent the possibility of this ordering://// thread 1 calls take_hook, gets the user's original hook// thread 1 calls set_hook with the null hook// thread 2 calls take_hook, thinks null hook is the original hook// thread 2 calls set_hook with the null hook// thread 1 calls set_hook with the actual original hook// thread 2 calls set_hook with what it thinks is the original hook//// in which the user's hook has been lost.//// There is still a race condition where a panic in a different thread can// happen during the interval that the user's original panic hook is// unregistered such that their hook is incorrectly not called. This is// sufficiently unlikely and less bad than printing panic messages to stderr// on correct use of this crate. Maybe there is a libstd feature request// here. For now, if a user needs to guarantee that this failure mode does// not occur, they need to call e.g. `proc_macro2::Span::call_site()` from// the main thread before launching any other threads.#[cfg(no_is_available)]fn initialize() { use std::panic::{self, PanicInfo};
type PanicHook = dyn Fn(&PanicInfo) + Sync + Send + 'static;
let null_hook: Box<PanicHook> = Box::new(|_panic_info| { /* ignore */ }); let sanity_check = &*null_hook as *const PanicHook; let original_hook = panic::take_hook(); panic::set_hook(null_hook);
let works = panic::catch_unwind(proc_macro::Span::call_site).is_ok(); WORKS.store(works as usize + 1, Ordering::Relaxed);
let hopefully_null_hook = panic::take_hook(); panic::set_hook(original_hook); if sanity_check != &*hopefully_null_hook { panic!("observed race condition in proc_macro2::inside_proc_macro"); }}