KAFKA-14500; [4/N] Add Timer interface (#13708)

Reviewers: David Jacot <djacot@confluent.io>

group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/Timer.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.coordinator.group.runtime;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * An interface to schedule and cancel operations.
+ */
+public interface Timer {
+
+    /**
+     * Add an operation to the timer. If an operation with the same key
+     * already exists, replace it with the new operation.
+     *
+     * @param key         The key to identify this operation.
+     * @param delay       The delay to wait before expiring.
+     * @param unit        The delay unit.
+     * @param operation   The operation to perform upon expiration.
+     */
+    void schedule(String key, long delay, TimeUnit unit, Runnable operation);
+
+    /**
+     * Remove an operation corresponding to a given key.
+     *
+     * @param key The key.
+     */
+    void cancel(String key);
+}