# Mutex A synchronization primitive that protects shared mutable state via mutual exclusion. ``` @frozen struct Mutex where Value : ~Copyable ``` ## Overview The `Mutex` type offers non-recursive exclusive access to the state it is protecting by blocking threads attempting to acquire the lock. Only one execution context at a time has access to the value stored within the `Mutex` allowing for exclusive access. An example use of `Mutex` in a class used simultaneously by many threads protecting a `Dictionary` value: ``` class Manager { let cache = Mutex<[Key: Resource]>([:]) func saveResource(_ resource: Resource, as key: Key) { cache.withLock { $0[key] = resource } } } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)