If I understand correctly, this corresponds to `lock` in C#:

    lock (_gate) {
        x[i] --;
    }

At least in C# it is considered preferable to lock on a private field, as opposed to locking on `this`, so nobody else also locks on your instance, potentially causing a deadlock.

I suppose this applies to `@synchronized` in Objective C as well.

I like that .NET Framework also provides some useful atomic methods, including this one:

    Interlocked.Decrement (ref x[i]);

They come in handy.