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//! Std locks without poisoning. A panic while one is held leaves its data as it was, and
//! every lock of this kind here guards counters, tables or caches that stay usable: so
//! the next user takes the data as it is instead of panicking too. (The tokio locks
//! around the document and the peers don't poison.)
use std::sync::{Mutex, MutexGuard, RwLock, RwLockReadGuard, RwLockWriteGuard};
pub(crate) trait MutexExt<T> {
/// Locks, recovering from a poisoned mutex.
fn lock_or_recover(&self) -> MutexGuard<'_, T>;
}
impl<T> MutexExt<T> for Mutex<T> {
fn lock_or_recover(&self) -> MutexGuard<'_, T> {
self.lock().unwrap_or_else(|poisoned| poisoned.into_inner())
}
}
pub(crate) trait RwLockExt<T> {
/// Locks for reading, recovering from a poisoned lock.
fn read_or_recover(&self) -> RwLockReadGuard<'_, T>;
/// Locks for writing, recovering from a poisoned lock.
fn write_or_recover(&self) -> RwLockWriteGuard<'_, T>;
}
impl<T> RwLockExt<T> for RwLock<T> {
fn read_or_recover(&self) -> RwLockReadGuard<'_, T> {
self.read().unwrap_or_else(|poisoned| poisoned.into_inner())
}
fn write_or_recover(&self) -> RwLockWriteGuard<'_, T> {
self.write()
.unwrap_or_else(|poisoned| poisoned.into_inner())
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn a_panic_while_locked_doesnt_spread() {
let mutex = std::sync::Arc::new(Mutex::new(1));
let poisoner = std::sync::Arc::clone(&mutex);
let _ = std::thread::spawn(move || {
let _guard = poisoner.lock().unwrap();
panic!("while holding the lock");
})
.join();
assert!(mutex.is_poisoned());
assert_eq!(*mutex.lock_or_recover(), 1);
}
}
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