1 /* 2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. Oracle designates this 7 * particular file as subject to the "Classpath" exception as provided 8 * by Oracle in the LICENSE file that accompanied this code. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 */ 24 25 /* 26 * This file is available under and governed by the GNU General Public 27 * License version 2 only, as published by the Free Software Foundation. 28 * However, the following notice accompanied the original version of this 29 * file: 30 * 31 * Written by Doug Lea with assistance from members of JCP JSR-166 32 * Expert Group and released to the public domain, as explained at 33 * http://creativecommons.org/publicdomain/zero/1.0/ 34 */ 35 36 package java.util.concurrent; 37 38 /** 39 * An {@link ExecutorService} that can schedule commands to run after a given 40 * delay, or to execute periodically. 41 * 42 * <p>The {@code schedule} methods create tasks with various delays 43 * and return a task object that can be used to cancel or check 44 * execution. The {@code scheduleAtFixedRate} and 45 * {@code scheduleWithFixedDelay} methods create and execute tasks 46 * that run periodically until cancelled. 47 * 48 * <p>Commands submitted using the {@link Executor#execute(Runnable)} 49 * and {@link ExecutorService} {@code submit} methods are scheduled 50 * with a requested delay of zero. Zero and negative delays (but not 51 * periods) are also allowed in {@code schedule} methods, and are 52 * treated as requests for immediate execution. 53 * 54 * <p>All {@code schedule} methods accept <em>relative</em> delays and 55 * periods as arguments, not absolute times or dates. It is a simple 56 * matter to transform an absolute time represented as a {@link 57 * java.util.Date} to the required form. For example, to schedule at 58 * a certain future {@code date}, you can use: {@code schedule(task, 59 * date.getTime() - System.currentTimeMillis(), 60 * TimeUnit.MILLISECONDS)}. Beware however that expiration of a 61 * relative delay need not coincide with the current {@code Date} at 62 * which the task is enabled due to network time synchronization 63 * protocols, clock drift, or other factors. 64 * 65 * <p>The {@link Executors} class provides convenient factory methods for 66 * the ScheduledExecutorService implementations provided in this package. 67 * 68 * <h3>Usage Example</h3> 69 * 70 * Here is a class with a method that sets up a ScheduledExecutorService 71 * to beep every ten seconds for an hour: 72 * 73 * <pre> {@code 74 * import static java.util.concurrent.TimeUnit.*; 75 * class BeeperControl { 76 * private final ScheduledExecutorService scheduler = 77 * Executors.newScheduledThreadPool(1); 78 * 79 * public void beepForAnHour() { 80 * final Runnable beeper = new Runnable() { 81 * public void run() { System.out.println("beep"); } 82 * }; 83 * final ScheduledFuture<?> beeperHandle = 84 * scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS); 85 * scheduler.schedule(new Runnable() { 86 * public void run() { beeperHandle.cancel(true); } 87 * }, 60 * 60, SECONDS); 88 * } 89 * }}</pre> 90 * 91 * @since 1.5 92 * @author Doug Lea 93 */ 94 public interface ScheduledExecutorService extends ExecutorService { 95 96 /** 97 * Creates and executes a one-shot action that becomes enabled 98 * after the given delay. 99 * 100 * @param command the task to execute 101 * @param delay the time from now to delay execution 102 * @param unit the time unit of the delay parameter 103 * @return a ScheduledFuture representing pending completion of 104 * the task and whose {@code get()} method will return 105 * {@code null} upon completion 106 * @throws RejectedExecutionException if the task cannot be 107 * scheduled for execution 108 * @throws NullPointerException if command is null 109 */ 110 public ScheduledFuture<?> schedule(Runnable command, 111 long delay, TimeUnit unit); 112 113 /** 114 * Creates and executes a ScheduledFuture that becomes enabled after the 115 * given delay. 116 * 117 * @param callable the function to execute 118 * @param delay the time from now to delay execution 119 * @param unit the time unit of the delay parameter 120 * @param <V> the type of the callable's result 121 * @return a ScheduledFuture that can be used to extract result or cancel 122 * @throws RejectedExecutionException if the task cannot be 123 * scheduled for execution 124 * @throws NullPointerException if callable is null 125 */ 126 public <V> ScheduledFuture<V> schedule(Callable<V> callable, 127 long delay, TimeUnit unit); 128 129 /** 130 * Creates and executes a periodic action that becomes enabled first 131 * after the given initial delay, and subsequently with the given 132 * period; that is, executions will commence after 133 * {@code initialDelay}, then {@code initialDelay + period}, then 134 * {@code initialDelay + 2 * period}, and so on. 135 * 136 * <p>The sequence of task executions continues indefinitely until 137 * one of the following exceptional completions occur: 138 * <ul> 139 * <li>The task is {@linkplain Future#cancel explicitly cancelled} 140 * via the returned future. 141 * <li>The executor terminates, also resulting in task cancellation. 142 * <li>An execution of the task throws an exception. In this case 143 * calling {@link Future#get() get} on the returned future will 144 * throw {@link ExecutionException}. 145 * </ul> 146 * Subsequent executions are suppressed. Subsequent calls to 147 * {@link Future#isDone isDone()} on the returned future will 148 * return {@code true}. 149 * 150 * <p>If any execution of this task takes longer than its period, then 151 * subsequent executions may start late, but will not concurrently 152 * execute. 153 * 154 * @param command the task to execute 155 * @param initialDelay the time to delay first execution 156 * @param period the period between successive executions 157 * @param unit the time unit of the initialDelay and period parameters 158 * @return a ScheduledFuture representing pending completion of 159 * the series of repeated tasks. The future's {@link 160 * Future#get() get()} method will never return normally, 161 * and will throw an exception upon task cancellation or 162 * abnormal termination of a task execution. 163 * @throws RejectedExecutionException if the task cannot be 164 * scheduled for execution 165 * @throws NullPointerException if command is null 166 * @throws IllegalArgumentException if period less than or equal to zero 167 */ 168 public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, 169 long initialDelay, 170 long period, 171 TimeUnit unit); 172 173 /** 174 * Creates and executes a periodic action that becomes enabled first 175 * after the given initial delay, and subsequently with the 176 * given delay between the termination of one execution and the 177 * commencement of the next. 178 * 179 * <p>The sequence of task executions continues indefinitely until 180 * one of the following exceptional completions occur: 181 * <ul> 182 * <li>The task is {@linkplain Future#cancel explicitly cancelled} 183 * via the returned future. 184 * <li>The executor terminates, also resulting in task cancellation. 185 * <li>An execution of the task throws an exception. In this case 186 * calling {@link Future#get() get} on the returned future will 187 * throw {@link ExecutionException}. 188 * </ul> 189 * Subsequent executions are suppressed. Subsequent calls to 190 * {@link Future#isDone isDone()} on the returned future will 191 * return {@code true}. 192 * 193 * @param command the task to execute 194 * @param initialDelay the time to delay first execution 195 * @param delay the delay between the termination of one 196 * execution and the commencement of the next 197 * @param unit the time unit of the initialDelay and delay parameters 198 * @return a ScheduledFuture representing pending completion of 199 * the series of repeated tasks. The future's {@link 200 * Future#get() get()} method will never return normally, 201 * and will throw an exception upon task cancellation or 202 * abnormal termination of a task execution. 203 * @throws RejectedExecutionException if the task cannot be 204 * scheduled for execution 205 * @throws NullPointerException if command is null 206 * @throws IllegalArgumentException if delay less than or equal to zero 207 */ 208 public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, 209 long initialDelay, 210 long delay, 211 TimeUnit unit); 212 213 } 214
