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# lock()

Attempts to acquire a lock, blocking a thread’s execution until the lock can be acquired.

```
func lock()
```

## Discussion

An application protects a critical section of code by requiring a thread to acquire a lock before executing the code. Once the critical section is completed, the thread relinquishes the lock by invoking [`unlock()`](/documentation/Foundation/NSLocking/unlock()).

## See Also

  [Threading Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Multithreading/Introduction/Introduction.html#//apple_ref/doc/uid/10000057i)


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