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/*
 * Copyright 2009 Google Inc.
 * 
 * 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 com.google.gwt.core.client;

import com.google.gwt.core.client.impl.SchedulerImpl;

/**
 * This class provides low-level task scheduling primitives. Any exceptions
 * thrown by the command objects executed by the scheduler will be passed to the
 * {@link GWT.UncaughtExceptionHandler} if one is installed.
 * 
 * 

* NOTE: If you are using a timer to schedule a UI animation, use * {@link com.google.gwt.animation.client.AnimationScheduler} instead. The * browser can optimize your animation for maximum performance. *

* * @see com.google.gwt.core.client.testing.StubScheduler */ public abstract class Scheduler { /** * General-purpose Command interface for tasks that repeat. */ public interface RepeatingCommand { /** * Returns true if the RepeatingCommand should be invoked again. */ boolean execute(); } /** * General-purpose Command interface. */ public interface ScheduledCommand { /** * Invokes the command. */ void execute(); } /** * Returns the default implementation of the Scheduler API. */ public static Scheduler get() { return SchedulerImpl.INSTANCE; } /** * A deferred command is executed after the browser event loop returns. */ public abstract void scheduleDeferred(ScheduledCommand cmd); /** * An "entry" command will be executed before GWT-generated code is invoked by * the browser's event loop. The {@link RepeatingCommand} will be called once * per entry from the event loop until false is returned. This * type of command is appropriate for instrumentation or code that needs to * know when "something happens." *

* If an entry command schedules another entry command, the second command * will be executed before control flow continues to the GWT-generated code. */ public abstract void scheduleEntry(RepeatingCommand cmd); /** * An "entry" command will be executed before GWT-generated code is invoked by * the browser's event loop. This type of command is appropriate for code that * needs to know when "something happens." *

* If an entry command schedules another entry command, the second command * will be executed before control flow continues to the GWT-generated code. */ public abstract void scheduleEntry(ScheduledCommand cmd); /** * A "finally" command will be executed before GWT-generated code returns * control to the browser's event loop. The {@link RepeatingCommand#execute()} * method will be called once per exit to the event loop until * false is returned. This type of command is appropriate for * instrumentation or cleanup code. *

* If a finally command schedules another finally command, the second command * will be executed before control flow returns to the browser. */ public abstract void scheduleFinally(RepeatingCommand cmd); /** * A "finally" command will be executed before GWT-generated code returns * control to the browser's event loop. This type of command is used to * aggregate small amounts of work before performing a non-recurring, * heavyweight operation. *

* If a finally command schedules another finally command, the second command * will be executed before control flow returns to the browser. *

* Consider the following: * *

   * try {
   *   nativeEventCallback(); // Calls scheduleFinally one or more times
   * } finally {
   *   executeFinallyCommands();
   * }
   * 
* * @see com.google.gwt.dom.client.StyleInjector */ public abstract void scheduleFinally(ScheduledCommand cmd); /** * Schedules a repeating command that is scheduled with a constant delay. That * is, the next invocation of the command will be scheduled for * delayMs milliseconds after the last invocation completes. *

* For example, assume that a command takes 30ms to run and a 100ms delay is * provided. The second invocation of the command will occur at 130ms after * the first invocation starts. * * @param cmd the command to execute * @param delayMs the amount of time to wait after one invocation ends before * the next invocation */ public abstract void scheduleFixedDelay(RepeatingCommand cmd, int delayMs); /** * Schedules a repeating command that is scheduled with a constant * periodicity. That is, the command will be invoked every * delayMs milliseconds, regardless of how long the previous * invocation took to complete. * * @param cmd the command to execute * @param delayMs the period with which the command is executed */ public abstract void scheduleFixedPeriod(RepeatingCommand cmd, int delayMs); /** * Schedules a repeating command that performs incremental work. This type of * command is encouraged for long-running processes that perform computation * or that manipulate the DOM. The commands in this queue are invoked many * times in rapid succession and are then deferred to allow the browser to * process its event queue. * * @param cmd the command to execute */ public abstract void scheduleIncremental(RepeatingCommand cmd); }





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