PoisonErrorRwLockReadGuardT

PoisonError is a type in the Rust standard library that represents the situation where a synchronization primitive has been poisoned after a thread panicked. In the context of an RwLock (read-write lock), poisoning occurs when a thread panics while holding either the read lock or the write lock. If the lock is poisoned, other threads attempting to acquire the lock receive an error of the form Err(PoisonError<Guard>), where Guard is either a RwLockReadGuard or a RwLockWriteGuard.

A PoisonError conveys that the guarded data may have been left in an inconsistent state due to the panic. The guard inside the PoisonError is the exact type of access that was poisoned, enabling recovery attempts. To reclaim the inner guard, you can call into_inner on the PoisonError, returning the guarded value and allowing the program to continue using the data, typically after performing any necessary invariants checks or reinitialization.

Handling strategies vary. Some code propagates the poisoning error to callers, signaling that recovery is needed at a higher level. Other code chooses to recover locally by extracting the inner guard with into_inner and proceeding, but only after ensuring the data’s invariants are upheld. In all cases, poisoning is a signal that a panic occurred while holding the lock, and it should influence how the protected data is accessed subsequently.

Notes for practice: poisoning is per lock, and a lock can become poisoned if a thread panics while holding it. The behavior applies to both read and write guards of an RwLock, reflecting the exact access that was poisoned.