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// Copyright 2022 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//! Synchronization primitives for Netstack3.
#![deny(missing_docs, unreachable_patterns, unused)]
extern crate alloc;
#[cfg(loom)]
extern crate loom as std;
pub mod rc;
/// A [`std::sync::Mutex`] assuming lock poisoning will never occur.
#[derive(Debug, Default)]
pub struct Mutex<T>(std::sync::Mutex<T>);
/// Lock guard for access to a [`Mutex`].
pub type LockGuard<'a, T> = lock_guard::LockGuard<'a, Mutex<T>, std::sync::MutexGuard<'a, T>>;
impl<T> Mutex<T> {
/// Creates a new mutex in an unlocked state ready for use.
pub fn new(t: T) -> Mutex<T> {
Mutex(std::sync::Mutex::new(t))
}
/// Acquires a mutex, blocking the current thread until it is able to do so.
///
/// See [`std::sync::Mutex::lock`] for more details.
///
/// # Panics
///
/// This method may panic if the calling thread is already holding the
/// lock.
#[inline]
#[cfg_attr(feature = "recursive-lock-panic", track_caller)]
pub fn lock(&self) -> LockGuard<'_, T> {
lock_guard::LockGuard::new(self, |Self(m)| m.lock().expect("unexpectedly poisoned"))
}
/// Consumes this mutex, returning the underlying data.
#[inline]
pub fn into_inner(self) -> T {
let Self(mutex) = self;
mutex.into_inner().expect("unexpectedly poisoned")
}
/// Returns a mutable reference to the underlying data.
///
/// Since this call borrows the [`Mutex`] mutably, no actual locking needs
/// to take place. See [`std::sync::Mutex::get_mut`] for more details.
#[inline]
// TODO(https://github.com/tokio-rs/loom/pull/322): remove the disable for
// loom once loom's lock type supports the method.
#[cfg(not(loom))]
pub fn get_mut(&mut self) -> &mut T {
self.0.get_mut().expect("unexpectedly poisoned")
}
}
/// A [`std::sync::RwLock`] assuming lock poisoning will never occur.
#[derive(Debug, Default)]
pub struct RwLock<T>(std::sync::RwLock<T>);
/// Lock guard for read access to a [`RwLock`].
pub type RwLockReadGuard<'a, T> =
lock_guard::LockGuard<'a, RwLock<T>, std::sync::RwLockReadGuard<'a, T>>;
/// Lock guard for write access to a [`RwLock`].
pub type RwLockWriteGuard<'a, T> =
lock_guard::LockGuard<'a, RwLock<T>, std::sync::RwLockWriteGuard<'a, T>>;
impl<T> RwLock<T> {
/// Creates a new instance of an `RwLock<T>` which is unlocked.
pub fn new(t: T) -> RwLock<T> {
RwLock(std::sync::RwLock::new(t))
}
/// Locks this rwlock with shared read access, blocking the current thread
/// until it can be acquired.
///
/// See [`std::sync::RwLock::read`] for more details.
///
/// # Panics
///
/// This method may panic if the calling thread already holds the read or
/// write lock.
#[inline]
#[cfg_attr(feature = "recursive-lock-panic", track_caller)]
pub fn read(&self) -> RwLockReadGuard<'_, T> {
lock_guard::LockGuard::new(self, |Self(rw)| rw.read().expect("unexpectedly poisoned"))
}
/// Locks this rwlock with exclusive write access, blocking the current
/// thread until it can be acquired.
///
/// See [`std::sync::RwLock::write`] for more details.
///
/// # Panics
///
/// This method may panic if the calling thread already holds the read or
/// write lock.
#[inline]
#[cfg_attr(feature = "recursive-lock-panic", track_caller)]
pub fn write(&self) -> RwLockWriteGuard<'_, T> {
lock_guard::LockGuard::new(self, |Self(rw)| rw.write().expect("unexpectedly poisoned"))
}
/// Consumes this rwlock, returning the underlying data.
#[inline]
pub fn into_inner(self) -> T {
let Self(rwlock) = self;
rwlock.into_inner().expect("unexpectedly poisoned")
}
/// Returns a mutable reference to the underlying data.
///
/// Since this call borrows the [`RwLock`] mutably, no actual locking needs
/// to take place. See [`std::sync::RwLock::get_mut`] for more details.
#[inline]
// TODO(https://github.com/tokio-rs/loom/pull/322): remove the disable for
// loom once loom's lock type supports the method.
#[cfg(not(loom))]
pub fn get_mut(&mut self) -> &mut T {
self.0.get_mut().expect("unexpectedly poisoned")
}
}
mod lock_guard {
#[cfg(not(feature = "recursive-lock-panic"))]
use core::marker::PhantomData;
use core::ops::{Deref, DerefMut};
#[cfg(feature = "recursive-lock-panic")]
use crate::lock_tracker::LockTracker;
/// An RAII implementation used to release a lock when dropped.
///
/// Wraps inner guard to provide lock instrumentation (when the appropriate
/// feature is enabled).
pub struct LockGuard<'a, L, G> {
guard: G,
// Placed after `guard` so that the tracker's destructor is run (and the
// unlock is tracked) after the lock is actually unlocked.
#[cfg(feature = "recursive-lock-panic")]
_lock_tracker: LockTracker<'a, L>,
#[cfg(not(feature = "recursive-lock-panic"))]
_marker: PhantomData<&'a L>,
}
impl<'a, L, G> LockGuard<'a, L, G> {
/// Returns a new lock guard.
#[cfg_attr(feature = "recursive-lock-panic", track_caller)]
pub fn new<F: FnOnce(&'a L) -> G>(lock: &'a L, lock_fn: F) -> Self {
#[cfg(feature = "recursive-lock-panic")]
let lock_tracker = LockTracker::new(lock);
Self {
guard: lock_fn(lock),
#[cfg(feature = "recursive-lock-panic")]
_lock_tracker: lock_tracker,
#[cfg(not(feature = "recursive-lock-panic"))]
_marker: PhantomData,
}
}
}
impl<L, G: Deref> Deref for LockGuard<'_, L, G> {
type Target = G::Target;
fn deref(&self) -> &G::Target {
self.guard.deref()
}
}
impl<L, G: DerefMut> DerefMut for LockGuard<'_, L, G> {
fn deref_mut(&mut self) -> &mut G::Target {
self.guard.deref_mut()
}
}
}
#[cfg(feature = "recursive-lock-panic")]
mod lock_tracker {
use core::{cell::RefCell, panic::Location};
use std::collections::HashMap;
std::thread_local! {
static HELD_LOCKS: RefCell<HashMap<*const usize, &'static Location<'static>>> =
RefCell::new(HashMap::new());
}
/// An RAII object to keep track of a lock that is (or soon to be) held.
///
/// The `Drop` implementation of this struct removes the lock from the
/// thread-local table of held locks.
pub(crate) struct LockTracker<'a, L>(&'a L);
impl<'a, L> LockTracker<'a, L> {
/// Tracks that the lock is to be held.
///
/// This method adds the lock to the thread-local table of held locks.
///
/// # Panics
///
/// Panics if the lock is already held by the calling thread.
#[track_caller]
pub(crate) fn new(lock: &'a L) -> Self {
{
let ptr = lock as *const _ as *const _;
match HELD_LOCKS.with(|l| l.borrow_mut().insert(ptr, Location::caller())) {
None => {}
Some(prev_lock_caller) => {
panic!("lock already held; ptr = {:p}\n{}", ptr, prev_lock_caller)
}
}
}
Self(lock)
}
}
impl<L> Drop for LockTracker<'_, L> {
fn drop(&mut self) {
let Self(lock) = self;
let ptr = *lock as *const _ as *const _;
assert_ne!(
HELD_LOCKS.with(|l| l.borrow_mut().remove(&ptr)),
None,
"must have previously been locked; ptr = {:p}",
ptr
);
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::thread;
#[test]
fn mutex_lock_and_write() {
let m = Mutex::<u32>::new(0);
{
let mut guard = m.lock();
assert_eq!(*guard, 0);
*guard = 5;
}
{
let guard = m.lock();
assert_eq!(*guard, 5);
}
}
#[test]
fn mutex_lock_from_different_threads() {
const NUM_THREADS: u32 = 4;
let m = Mutex::<u32>::new(u32::MAX);
let m = &m;
thread::scope(|s| {
for i in 0..NUM_THREADS {
let _: thread::ScopedJoinHandle<'_, _> = s.spawn(move || {
let prev = {
let mut guard = m.lock();
let prev = *guard;
*guard = i;
prev
};
assert!(prev == u32::MAX || prev < NUM_THREADS);
});
}
});
let guard = m.lock();
assert!(*guard < NUM_THREADS);
}
#[test]
#[should_panic(expected = "lock already held")]
#[cfg(feature = "recursive-lock-panic")]
fn mutex_double_lock_panic() {
let m = Mutex::<u32>::new(0);
let _ok_guard = m.lock();
let _panic_guard = m.lock();
}
#[test]
fn rwlock_read_lock() {
let rw = RwLock::<u32>::new(0);
{
let guard = rw.read();
assert_eq!(*guard, 0);
}
{
let guard = rw.read();
assert_eq!(*guard, 0);
}
}
#[test]
fn rwlock_write_lock() {
let rw = RwLock::<u32>::new(0);
{
let mut guard = rw.write();
assert_eq!(*guard, 0);
*guard = 5;
}
{
let guard = rw.write();
assert_eq!(*guard, 5);
}
}
#[test]
fn rwlock_read_and_write_from_different_threads() {
const NUM_THREADS: u32 = 4;
let rw = RwLock::<u32>::new(u32::MAX);
let rw = &rw;
thread::scope(|s| {
for i in 0..NUM_THREADS {
let _: thread::ScopedJoinHandle<'_, _> = s.spawn(move || {
let prev = if i % 2 == 0 {
// Only threads with even numbered `i` performs a write.
let mut guard = rw.write();
let prev = *guard;
*guard = i;
prev
} else {
let guard = rw.read();
*guard
};
assert!(prev == u32::MAX || (prev < NUM_THREADS && prev % 2 == 0));
});
}
});
let val = *rw.read();
assert!(val < NUM_THREADS && val % 2 == 0);
}
#[test]
#[cfg_attr(feature = "recursive-lock-panic", should_panic(expected = "lock already held"))]
fn mutex_double_read() {
let rw = RwLock::<u32>::new(0);
let ok_guard = rw.read();
assert_eq!(*ok_guard, 0);
let maybe_panic_guard = rw.read();
assert_eq!(*maybe_panic_guard, 0);
}
#[test]
#[should_panic(expected = "lock already held")]
#[cfg(feature = "recursive-lock-panic")]
fn mutex_double_write_panic() {
let rw = RwLock::<u32>::new(0);
let _ok_guard = rw.write();
let _panic_guard = rw.write();
}
#[test]
#[should_panic(expected = "lock already held")]
#[cfg(feature = "recursive-lock-panic")]
fn mutex_double_read_then_write_panic() {
let rw = RwLock::<u32>::new(0);
let _ok_guard = rw.read();
let _panic_guard = rw.write();
}
#[test]
#[should_panic(expected = "lock already held")]
#[cfg(feature = "recursive-lock-panic")]
fn mutex_double_write_then_read_panic() {
let rw = RwLock::<u32>::new(0);
let _ok_guard = rw.read();
let _panic_guard = rw.write();
}
}