_ Git - rust-lightning/blob - lightning/src/debug_sync.rs

   1 pub use ::alloc::sync::Arc;
   2 use core::ops::{Deref, DerefMut};
   3 use core::time::Duration;
   4
   5 use std::collections::HashSet;
   6 use std::cell::RefCell;
   7
   8 use std::sync::atomic::{AtomicUsize, Ordering};
   9 use std::sync::Mutex as StdMutex;
  10 use std::sync::MutexGuard as StdMutexGuard;
  11 use std::sync::RwLock as StdRwLock;
  12 use std::sync::RwLockReadGuard as StdRwLockReadGuard;
  13 use std::sync::RwLockWriteGuard as StdRwLockWriteGuard;
  14 use std::sync::Condvar as StdCondvar;
  15
  16 #[cfg(feature = "backtrace")]
  17 use {prelude::{HashMap, hash_map}, backtrace::Backtrace, std::sync::Once};
  18
  19 #[cfg(not(feature = "backtrace"))]
  20 struct Backtrace{}
  21 #[cfg(not(feature = "backtrace"))]
  22 impl Backtrace { fn new() -> Backtrace { Backtrace {} } }
  23
  24 pub type LockResult<Guard> = Result<Guard, ()>;
  25
  26 pub struct Condvar {
  27         inner: StdCondvar,
  28 }
  29
  30 impl Condvar {
  31         pub fn new() -> Condvar {
  32                 Condvar { inner: StdCondvar::new() }
  33         }
  34
  35         pub fn wait<'a, T>(&'a self, guard: MutexGuard<'a, T>) -> LockResult<MutexGuard<'a, T>> {
  36                 let mutex: &'a Mutex<T> = guard.mutex;
  37                 self.inner.wait(guard.into_inner()).map(|lock| MutexGuard { mutex, lock }).map_err(|_| ())
  38         }
  39
  40         #[allow(unused)]
  41         pub fn wait_timeout<'a, T>(&'a self, guard: MutexGuard<'a, T>, dur: Duration) -> LockResult<(MutexGuard<'a, T>, ())> {
  42                 let mutex = guard.mutex;
  43                 self.inner.wait_timeout(guard.into_inner(), dur).map(|(lock, _)| (MutexGuard { mutex, lock }, ())).map_err(|_| ())
  44         }
  45
  46         pub fn notify_all(&self) { self.inner.notify_all(); }
  47 }
  48
  49 thread_local! {
  50         /// We track the set of locks currently held by a reference to their `LockMetadata`
  51         static LOCKS_HELD: RefCell<HashSet<Arc<LockMetadata>>> = RefCell::new(HashSet::new());
  52 }
  53 static LOCK_IDX: AtomicUsize = AtomicUsize::new(0);
  54
  55 #[cfg(feature = "backtrace")]
  56 static mut LOCKS: Option<StdMutex<HashMap<String, Arc<LockMetadata>>>> = None;
  57 #[cfg(feature = "backtrace")]
  58 static LOCKS_INIT: Once = Once::new();
  59
  60 /// Metadata about a single lock, by id, the set of things locked-before it, and the backtrace of
  61 /// when the Mutex itself was constructed.
  62 struct LockMetadata {
  63         lock_idx: u64,
  64         locked_before: StdMutex<HashSet<LockDep>>,
  65         _lock_construction_bt: Backtrace,
  66 }
  67 impl PartialEq for LockMetadata {
  68         fn eq(&self, o: &LockMetadata) -> bool { self.lock_idx == o.lock_idx }
  69 }
  70 impl Eq for LockMetadata {}
  71 impl std::hash::Hash for LockMetadata {
  72         fn hash<H: std::hash::Hasher>(&self, hasher: &mut H) { hasher.write_u64(self.lock_idx); }
  73 }
  74
  75 struct LockDep {
  76         lock: Arc<LockMetadata>,
  77         lockdep_trace: Option<Backtrace>,
  78 }
  79 impl LockDep {
  80         /// Note that `Backtrace::new()` is rather expensive so we rely on the caller to fill in the
  81         /// `lockdep_backtrace` field after ensuring we need it.
  82         fn new_without_bt(lock: &Arc<LockMetadata>) -> Self {
  83                 Self { lock: Arc::clone(lock), lockdep_trace: None }
  84         }
  85 }
  86 impl PartialEq for LockDep {
  87         fn eq(&self, o: &LockDep) -> bool { self.lock.lock_idx == o.lock.lock_idx }
  88 }
  89 impl Eq for LockDep {}
  90 impl std::hash::Hash for LockDep {
  91         fn hash<H: std::hash::Hasher>(&self, hasher: &mut H) { hasher.write_u64(self.lock.lock_idx); }
  92 }
  93
  94 #[cfg(feature = "backtrace")]
  95 fn get_construction_location(backtrace: &Backtrace) -> String {
  96         // Find the first frame that is after `debug_sync` (or that is in our tests) and use
  97         // that as the mutex construction site. Note that the first few frames may be in
  98         // the `backtrace` crate, so we have to ignore those.
  99         let sync_mutex_constr_regex = regex::Regex::new(r"lightning.*debug_sync.*new").unwrap();
 100         let mut found_debug_sync = false;
 101         for frame in backtrace.frames() {
 102                 for symbol in frame.symbols() {
 103                         let symbol_name = symbol.name().unwrap().as_str().unwrap();
 104                         if !sync_mutex_constr_regex.is_match(symbol_name) {
 105                                 if found_debug_sync {
 106                                         if let Some(col) = symbol.colno() {
 107                                                 return format!("{}:{}:{}", symbol.filename().unwrap().display(), symbol.lineno().unwrap(), col);
 108                                         } else {
 109                                                 // Windows debug symbols don't support column numbers, so fall back to
 110                                                 // line numbers only if no `colno` is available
 111                                                 return format!("{}:{}", symbol.filename().unwrap().display(), symbol.lineno().unwrap());
 112                                         }
 113                                 }
 114                         } else { found_debug_sync = true; }
 115                 }
 116         }
 117         panic!("Couldn't find mutex construction callsite");
 118 }
 119
 120 impl LockMetadata {
 121         fn new() -> Arc<LockMetadata> {
 122                 let backtrace = Backtrace::new();
 123                 let lock_idx = LOCK_IDX.fetch_add(1, Ordering::Relaxed) as u64;
 124
 125                 let res = Arc::new(LockMetadata {
 126                         locked_before: StdMutex::new(HashSet::new()),
 127                         lock_idx,
 128                         _lock_construction_bt: backtrace,
 129                 });
 130
 131                 #[cfg(feature = "backtrace")]
 132                 {
 133                         let lock_constr_location = get_construction_location(&res._lock_construction_bt);
 134                         LOCKS_INIT.call_once(|| { unsafe { LOCKS = Some(StdMutex::new(HashMap::new())); } });
 135                         let mut locks = unsafe { LOCKS.as_ref() }.unwrap().lock().unwrap();
 136                         match locks.entry(lock_constr_location) {
 137                                 hash_map::Entry::Occupied(e) => return Arc::clone(e.get()),
 138                                 hash_map::Entry::Vacant(e) => { e.insert(Arc::clone(&res)); },
 139                         }
 140                 }
 141                 res
 142         }
 143
 144         // Returns whether we were a recursive lock (only relevant for read)
 145         fn _pre_lock(this: &Arc<LockMetadata>, read: bool) -> bool {
 146                 let mut inserted = false;
 147                 LOCKS_HELD.with(|held| {
 148                         // For each lock which is currently locked, check that no lock's locked-before
 149                         // set includes the lock we're about to lock, which would imply a lockorder
 150                         // inversion.
 151                         for locked in held.borrow().iter() {
 152                                 if read && *locked == *this {
 153                                         // Recursive read locks are explicitly allowed
 154                                         return;
 155                                 }
 156                         }
 157                         for locked in held.borrow().iter() {
 158                                 if !read && *locked == *this {
 159                                         // With `feature = "backtrace"` set, we may be looking at different instances
 160                                         // of the same lock.
 161                                         debug_assert!(cfg!(feature = "backtrace"), "Tried to acquire a lock while it was held!");
 162                                 }
 163                                 for locked_dep in locked.locked_before.lock().unwrap().iter() {
 164                                         if locked_dep.lock == *this && locked_dep.lock != *locked {
 165                                                 #[cfg(feature = "backtrace")]
 166                                                 panic!("Tried to violate existing lockorder.\nMutex that should be locked after the current lock was created at the following backtrace.\nNote that to get a backtrace for the lockorder violation, you should set RUST_BACKTRACE=1\nLock being taken constructed at: {} ({}):\n{:?}\nLock constructed at: {} ({})\n{:?}\n\nLock dep created at:\n{:?}\n\n",
 167                                                         get_construction_location(&this._lock_construction_bt), this.lock_idx, this._lock_construction_bt,
 168                                                         get_construction_location(&locked._lock_construction_bt), locked.lock_idx, locked._lock_construction_bt,
 169                                                         locked_dep.lockdep_trace);
 170                                                 #[cfg(not(feature = "backtrace"))]
 171                                                 panic!("Tried to violate existing lockorder. Build with the backtrace feature for more info.");
 172                                         }
 173                                 }
 174                                 // Insert any already-held locks in our locked-before set.
 175                                 let mut locked_before = this.locked_before.lock().unwrap();
 176                                 let mut lockdep = LockDep::new_without_bt(locked);
 177                                 if !locked_before.contains(&lockdep) {
 178                                         lockdep.lockdep_trace = Some(Backtrace::new());
 179                                         locked_before.insert(lockdep);
 180                                 }
 181                         }
 182                         held.borrow_mut().insert(Arc::clone(this));
 183                         inserted = true;
 184                 });
 185                 inserted
 186         }
 187
 188         fn pre_lock(this: &Arc<LockMetadata>) { Self::_pre_lock(this, false); }
 189         fn pre_read_lock(this: &Arc<LockMetadata>) -> bool { Self::_pre_lock(this, true) }
 190
 191         fn try_locked(this: &Arc<LockMetadata>) {
 192                 LOCKS_HELD.with(|held| {
 193                         // Since a try-lock will simply fail if the lock is held already, we do not
 194                         // consider try-locks to ever generate lockorder inversions. However, if a try-lock
 195                         // succeeds, we do consider it to have created lockorder dependencies.
 196                         let mut locked_before = this.locked_before.lock().unwrap();
 197                         for locked in held.borrow().iter() {
 198                                 let mut lockdep = LockDep::new_without_bt(locked);
 199                                 if !locked_before.contains(&lockdep) {
 200                                         lockdep.lockdep_trace = Some(Backtrace::new());
 201                                         locked_before.insert(lockdep);
 202                                 }
 203                         }
 204                         held.borrow_mut().insert(Arc::clone(this));
 205                 });
 206         }
 207 }
 208
 209 pub struct Mutex<T: Sized> {
 210         inner: StdMutex<T>,
 211         deps: Arc<LockMetadata>,
 212 }
 213
 214 #[must_use = "if unused the Mutex will immediately unlock"]
 215 pub struct MutexGuard<'a, T: Sized + 'a> {
 216         mutex: &'a Mutex<T>,
 217         lock: StdMutexGuard<'a, T>,
 218 }
 219
 220 impl<'a, T: Sized> MutexGuard<'a, T> {
 221         fn into_inner(self) -> StdMutexGuard<'a, T> {
 222                 // Somewhat unclear why we cannot move out of self.lock, but doing so gets E0509.
 223                 unsafe {
 224                         let v: StdMutexGuard<'a, T> = std::ptr::read(&self.lock);
 225                         std::mem::forget(self);
 226                         v
 227                 }
 228         }
 229 }
 230
 231 impl<T: Sized> Drop for MutexGuard<'_, T> {
 232         fn drop(&mut self) {
 233                 LOCKS_HELD.with(|held| {
 234                         held.borrow_mut().remove(&self.mutex.deps);
 235                 });
 236         }
 237 }
 238
 239 impl<T: Sized> Deref for MutexGuard<'_, T> {
 240         type Target = T;
 241
 242         fn deref(&self) -> &T {
 243                 &self.lock.deref()
 244         }
 245 }
 246
 247 impl<T: Sized> DerefMut for MutexGuard<'_, T> {
 248         fn deref_mut(&mut self) -> &mut T {
 249                 self.lock.deref_mut()
 250         }
 251 }
 252
 253 impl<T> Mutex<T> {
 254         pub fn new(inner: T) -> Mutex<T> {
 255                 Mutex { inner: StdMutex::new(inner), deps: LockMetadata::new() }
 256         }
 257
 258         pub fn lock<'a>(&'a self) -> LockResult<MutexGuard<'a, T>> {
 259                 LockMetadata::pre_lock(&self.deps);
 260                 self.inner.lock().map(|lock| MutexGuard { mutex: self, lock }).map_err(|_| ())
 261         }
 262
 263         pub fn try_lock<'a>(&'a self) -> LockResult<MutexGuard<'a, T>> {
 264                 let res = self.inner.try_lock().map(|lock| MutexGuard { mutex: self, lock }).map_err(|_| ());
 265                 if res.is_ok() {
 266                         LockMetadata::try_locked(&self.deps);
 267                 }
 268                 res
 269         }
 270 }
 271
 272 pub struct RwLock<T: Sized> {
 273         inner: StdRwLock<T>,
 274         deps: Arc<LockMetadata>,
 275 }
 276
 277 pub struct RwLockReadGuard<'a, T: Sized + 'a> {
 278         lock: &'a RwLock<T>,
 279         first_lock: bool,
 280         guard: StdRwLockReadGuard<'a, T>,
 281 }
 282
 283 pub struct RwLockWriteGuard<'a, T: Sized + 'a> {
 284         lock: &'a RwLock<T>,
 285         guard: StdRwLockWriteGuard<'a, T>,
 286 }
 287
 288 impl<T: Sized> Deref for RwLockReadGuard<'_, T> {
 289         type Target = T;
 290
 291         fn deref(&self) -> &T {
 292                 &self.guard.deref()
 293         }
 294 }
 295
 296 impl<T: Sized> Drop for RwLockReadGuard<'_, T> {
 297         fn drop(&mut self) {
 298                 if !self.first_lock {
 299                         // Note that its not strictly true that the first taken read lock will get unlocked
 300                         // last, but in practice our locks are always taken as RAII, so it should basically
 301                         // always be true.
 302                         return;
 303                 }
 304                 LOCKS_HELD.with(|held| {
 305                         held.borrow_mut().remove(&self.lock.deps);
 306                 });
 307         }
 308 }
 309
 310 impl<T: Sized> Deref for RwLockWriteGuard<'_, T> {
 311         type Target = T;
 312
 313         fn deref(&self) -> &T {
 314                 &self.guard.deref()
 315         }
 316 }
 317
 318 impl<T: Sized> Drop for RwLockWriteGuard<'_, T> {
 319         fn drop(&mut self) {
 320                 LOCKS_HELD.with(|held| {
 321                         held.borrow_mut().remove(&self.lock.deps);
 322                 });
 323         }
 324 }
 325
 326 impl<T: Sized> DerefMut for RwLockWriteGuard<'_, T> {
 327         fn deref_mut(&mut self) -> &mut T {
 328                 self.guard.deref_mut()
 329         }
 330 }
 331
 332 impl<T> RwLock<T> {
 333         pub fn new(inner: T) -> RwLock<T> {
 334                 RwLock { inner: StdRwLock::new(inner), deps: LockMetadata::new() }
 335         }
 336
 337         pub fn read<'a>(&'a self) -> LockResult<RwLockReadGuard<'a, T>> {
 338                 let first_lock = LockMetadata::pre_read_lock(&self.deps);
 339                 self.inner.read().map(|guard| RwLockReadGuard { lock: self, guard, first_lock }).map_err(|_| ())
 340         }
 341
 342         pub fn write<'a>(&'a self) -> LockResult<RwLockWriteGuard<'a, T>> {
 343                 LockMetadata::pre_lock(&self.deps);
 344                 self.inner.write().map(|guard| RwLockWriteGuard { lock: self, guard }).map_err(|_| ())
 345         }
 346
 347         pub fn try_write<'a>(&'a self) -> LockResult<RwLockWriteGuard<'a, T>> {
 348                 let res = self.inner.try_write().map(|guard| RwLockWriteGuard { lock: self, guard }).map_err(|_| ());
 349                 if res.is_ok() {
 350                         LockMetadata::try_locked(&self.deps);
 351                 }
 352                 res
 353         }
 354 }
 355
 356 pub type FairRwLock<T> = RwLock<T>;
 357
 358 mod tests {
 359         use super::{RwLock, Mutex};
 360
 361         #[test]
 362         #[should_panic]
 363         #[cfg(not(feature = "backtrace"))]
 364         fn recursive_lock_fail() {
 365                 let mutex = Mutex::new(());
 366                 let _a = mutex.lock().unwrap();
 367                 let _b = mutex.lock().unwrap();
 368         }
 369
 370         #[test]
 371         fn recursive_read() {
 372                 let lock = RwLock::new(());
 373                 let _a = lock.read().unwrap();
 374                 let _b = lock.read().unwrap();
 375         }
 376
 377         #[test]
 378         #[should_panic]
 379         fn lockorder_fail() {
 380                 let a = Mutex::new(());
 381                 let b = Mutex::new(());
 382                 {
 383                         let _a = a.lock().unwrap();
 384                         let _b = b.lock().unwrap();
 385                 }
 386                 {
 387                         let _b = b.lock().unwrap();
 388                         let _a = a.lock().unwrap();
 389                 }
 390         }
 391
 392         #[test]
 393         #[should_panic]
 394         fn write_lockorder_fail() {
 395                 let a = RwLock::new(());
 396                 let b = RwLock::new(());
 397                 {
 398                         let _a = a.write().unwrap();
 399                         let _b = b.write().unwrap();
 400                 }
 401                 {
 402                         let _b = b.write().unwrap();
 403                         let _a = a.write().unwrap();
 404                 }
 405         }
 406
 407         #[test]
 408         #[should_panic]
 409         fn read_lockorder_fail() {
 410                 let a = RwLock::new(());
 411                 let b = RwLock::new(());
 412                 {
 413                         let _a = a.read().unwrap();
 414                         let _b = b.read().unwrap();
 415                 }
 416                 {
 417                         let _b = b.read().unwrap();
 418                         let _a = a.read().unwrap();
 419                 }
 420         }
 421
 422         #[test]
 423         fn read_recursive_no_lockorder() {
 424                 // Like the above, but note that no lockorder is implied when we recursively read-lock a
 425                 // RwLock, causing this to pass just fine.
 426                 let a = RwLock::new(());
 427                 let b = RwLock::new(());
 428                 let _outer = a.read().unwrap();
 429                 {
 430                         let _a = a.read().unwrap();
 431                         let _b = b.read().unwrap();
 432                 }
 433                 {
 434                         let _b = b.read().unwrap();
 435                         let _a = a.read().unwrap();
 436                 }
 437         }
 438
 439         #[test]
 440         #[should_panic]
 441         fn read_write_lockorder_fail() {
 442                 let a = RwLock::new(());
 443                 let b = RwLock::new(());
 444                 {
 445                         let _a = a.write().unwrap();
 446                         let _b = b.read().unwrap();
 447                 }
 448                 {
 449                         let _b = b.read().unwrap();
 450                         let _a = a.write().unwrap();
 451                 }
 452         }
 453 }