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 // Copyright 2006, 2008, 2010 The Apache Software Foundation
 //
 // Licensed 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.tapestry5.services;
Allows for deferred execution of logic, useful when trying to get multiple components to coordinate behavior. A component may add a command to be executed "at the end of the heartbeat". The classic example of 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 field's id is correct until after both have rendered.

The Heartbeat is injected into components via the org.apache.tapestry5.annotations.Environmental annotation.

public interface Heartbeat
{
    
Begins a new Heartbeat. Heartbeats nest. Every call to begin() should be matched by a call to end().
    void begin();

    
Executes all commands since the most recent begin().
    void end();

    
Adds a new command to the current Heartbeat. The command will be executed by end().

Parameters:
command command to be executed at the end of the heartbeat
See also:
org.apache.tapestry5.annotations.HeartbeatDeferred
    void defer(Runnable command);
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