apache-kafka_0_9-lib/src/main/java/org/apache/kafka/common/security/kerberos/LoginManager.java
public void release() {
        synchronized (LoginManager.class) {
            if (refCount == 0)
                throw new IllegalStateException("release called on LoginManager with refCount == 0");
            else if (refCount == 1) {
                CACHED_INSTANCES.remove(loginType);
                login.shutdown();
            }
            --refCount;
        }
    }
public void release() {
        synchronized (LoginManager.class) {
            if (refCount == 0)
                throw new IllegalStateException("release called on LoginManager with refCount == 0");
            else if (refCount == 1) {
                CACHED_INSTANCES.remove(loginType);
                login.shutdown();
            }
            --refCount;
        }
    }
Decrease the reference count for this instance and release resources if it reaches 0.