import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Locale;
import java.util.concurrent.TimeUnit;
import javax.annotation.CheckForNull;

/**
 * A rate limiter. Conceptually, a rate limiter distributes permits at a configurable rate. Each
 * {@link #acquire()} blocks if necessary until a permit is available, and then takes it. Once
 * acquired, permits need not be released.
 *