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Synchronized provides a simple Swift-y implementation of a lock and a recursive lock. Lock wraps os_unfair_lock. RecursiveLock wraps pthread_mutex_t. Synchronized's API is designed for convenience and simplicity.

The two lock's APIs are identical and limited to two public methods: func locked<T>(_ block: () throws -> T) rethrows -> T and func tryLocked(_ block: () throws -> Void) rethrows. locked() blocks on contention and then executes the supplied closure, returning or throwing the closure's return value or thrown error. tryLocked() attemps to acquire the lock. If the lock can be acquired, the supplied closure is executed and true is returned. If the lock cannot be acquired, the closure is not executed and false is returned.

Synchronized also provides Locked which wraps an entity and only allows access to it via the secure method access(_:). Locked makes it easy to ensure your class only accesses its mutable state in a safe manner.

@synchonized replacement

Synchronized started life as a simple (and simplified) re-implmentation of Objective-C's @synchronized for Swift. If you're interested in that version, you should look at v1.2.1.


let lock = Lock()
let lockInput: Int = 0
let lockOutput = lock.locked { lockInput + 1 }
XCTAssertEqual(1, lockOutput)

let recursiveLock = RecursiveLock()
let recursiveLockInput: Int = 0
let recursiveLockOutput = recursiveLock.locked { recursiveLockInput + 1 }
XCTAssertEqual(1, recursiveLockOutput)

let lockedInput = Locked(0)
lockedInput.access { $0 += 1 }
XCTAssertEqual(1, lockedInput.access { $0 })


Swift Package Manager

To use Synchronized with the Swift Package Manager, add a dependency to your Package.swift file:

let package = Package(
  dependencies: [
    .package(url: "", .upToNextMajor(from: "4.0.0"))

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  • Swift Tools 5.7.0
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Last updated: Thu May 16 2024 22:50:13 GMT-0900 (Hawaii-Aleutian Daylight Time)