`acquireFileLock()` and `releaseFileLock()` methods pair is used to protect access to the data file which stores timeout and lock time for certain mutex item. This line unlocks that data file.

I think it's better to clarify on the real example. Let's consider the following steps:

1. Process 1 executes console action.
2. Process 1 calls `acquireLock()` method. Internally this method locks file `mutex.123123.bin` (arbitrary name).
3. Process 2 executes same console action.
4. Process 2 calls `acquireLock()` method and waits while lock on the file `mutex.123123.bin` will be released (i mean line 71).
5. Process 1 writes necessary data to the `mutex.123123.bin` file (e.g. `array(123123123,120)`) and releases lock (by calling `releaseFileLock()`).
6. Process 2 stops waiting for a lock to be released and reads information from `mutex.123123.bin` file. It retrieves `array(123123123,120)` and compares it with the current time. If lock has not expired it just returns false. (It would return true in case lock data file doesn't exist or lock has been expired.)
7. Process 2 exits informing that lock already created.
8. Process 1 performs action's main code, releases lock with `releaseLock()` method and successfully finishes.
9. At this time a new process 3 could be executed and it will successfully run main action code.

This approach gives us ability to create and release locks even in different PHP processes.