001// Copyright 2006, 2008, 2010 The Apache Software Foundation 002// 003// Licensed under the Apache License, Version 2.0 (the "License"); 004// you may not use this file except in compliance with the License. 005// You may obtain a copy of the License at 006// 007// http://www.apache.org/licenses/LICENSE-2.0 008// 009// Unless required by applicable law or agreed to in writing, software 010// distributed under the License is distributed on an "AS IS" BASIS, 011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 012// See the License for the specific language governing permissions and 013// limitations under the License. 014 015package org.apache.tapestry5.services; 016 017import org.apache.tapestry5.annotations.HeartbeatDeferred; 018 019/** 020 * Allows for deferred execution of logic, useful when trying to get multiple components to coordinate behavior. A 021 * component may add a command to be executed "{@linkplain #end() at the end of the heartbeat}". The classic example of 022 * this is a Label and the field it labels; since we don't know which order the two will render, we can't tell if the 023 * field's id is correct until after both have rendered. 024 * <p/> 025 * The Heartbeat is injected into components via the {@link org.apache.tapestry5.annotations.Environmental} annotation. 026 */ 027public interface Heartbeat 028{ 029 /** 030 * Begins a new Heartbeat. Heartbeats nest. Every call to begin() should be matched by a call to {@link #end()}. 031 */ 032 void begin(); 033 034 /** 035 * Executes all commands since the most recent {@link #begin()}. 036 */ 037 void end(); 038 039 /** 040 * Adds a new command to the current Heartbeat. The command will be executed by {@link #end()}. 041 * 042 * @param command 043 * command to be executed at the end of the heartbeat 044 * @see HeartbeatDeferred 045 */ 046 void defer(Runnable command); 047}