All Downloads are FREE. Search and download functionalities are using the official Maven repository.

java.util.Timer Maven / Gradle / Ivy

There is a newer version: 1.2.9
Show newest version
/*
 *  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 java.util;

/**
 * Timers schedule one-shot or recurring {@link TimerTask tasks} for execution.
 * Prefer {@link java.util.concurrent.ScheduledThreadPoolExecutor
 * ScheduledThreadPoolExecutor} for new code.
 *
 * 

Each timer has one thread on which tasks are executed sequentially. When * this thread is busy running a task, runnable tasks may be subject to delays. * *

One-shot are scheduled to run at an absolute time or after a relative * delay. * *

Recurring tasks are scheduled with either a fixed period or a fixed rate: *

    *
  • With the default fixed-period execution, each * successive run of a task is scheduled relative to the start time of * the previous run, so two runs are never fired closer together in time * than the specified {@code period}. *
  • With fixed-rate execution, the start time of each * successive run of a task is scheduled without regard for when the * previous run took place. This may result in a series of bunched-up runs * (one launched immediately after another) if delays prevent the timer * from starting tasks on time. *
* *

When a timer is no longer needed, users should call {@link #cancel}, which * releases the timer's thread and other resources. Timers not explicitly * cancelled may hold resources indefinitely. * *

This class does not offer guarantees about the real-time nature of task * scheduling. Multiple threads can share a single timer without * synchronization. */ public class Timer { private static final class TimerImpl extends Thread { private static final class TimerHeap { private int DEFAULT_HEAP_SIZE = 256; private TimerTask[] timers = new TimerTask[DEFAULT_HEAP_SIZE]; private int size = 0; private int deletedCancelledNumber = 0; public TimerTask minimum() { return timers[0]; } public boolean isEmpty() { return size == 0; } public void insert(TimerTask task) { if (timers.length == size) { TimerTask[] appendedTimers = new TimerTask[size * 2]; System.arraycopy(timers, 0, appendedTimers, 0, size); timers = appendedTimers; } timers[size++] = task; upHeap(); } public void delete(int pos) { // posible to delete any position of the heap if (pos >= 0 && pos < size) { timers[pos] = timers[--size]; timers[size] = null; downHeap(pos); } } private void upHeap() { int current = size - 1; int parent = (current - 1) / 2; while (timers[current].when < timers[parent].when) { // swap the two TimerTask tmp = timers[current]; timers[current] = timers[parent]; timers[parent] = tmp; // update pos and current current = parent; parent = (current - 1) / 2; } } private void downHeap(int pos) { int current = pos; int child = 2 * current + 1; while (child < size && size > 0) { // compare the children if they exist if (child + 1 < size && timers[child + 1].when < timers[child].when) { child++; } // compare selected child with parent if (timers[current].when < timers[child].when) { break; } // swap the two TimerTask tmp = timers[current]; timers[current] = timers[child]; timers[child] = tmp; // update pos and current current = child; child = 2 * current + 1; } } public void reset() { timers = new TimerTask[DEFAULT_HEAP_SIZE]; size = 0; } public void adjustMinimum() { downHeap(0); } public void deleteIfCancelled() { for (int i = 0; i < size; i++) { if (timers[i].cancelled) { deletedCancelledNumber++; delete(i); // re-try this point i--; } } } private int getTask(TimerTask task) { for (int i = 0; i < timers.length; i++) { if (timers[i] == task) { return i; } } return -1; } } /** * True if the method cancel() of the Timer was called or the !!!stop() * method was invoked */ private boolean cancelled; /** * True if the Timer has become garbage */ private boolean finished; /** * Contains scheduled events, sorted according to * {@code when} field of TaskScheduled object. */ private TimerHeap tasks = new TimerHeap(); /** * Starts a new timer. * * @param name thread's name * @param isDaemon daemon thread or not */ TimerImpl(String name, boolean isDaemon) { this.setName(name); this.setDaemon(isDaemon); this.start(); } /** * This method will be launched on separate thread for each Timer * object. */ @Override public void run() { while (true) { TimerTask task; synchronized (this) { // need to check cancelled inside the synchronized block if (cancelled) { return; } if (tasks.isEmpty()) { if (finished) { return; } // no tasks scheduled -- sleep until any task appear try { this.wait(); } catch (InterruptedException ignored) { } continue; } long currentTime = System.currentTimeMillis(); task = tasks.minimum(); long timeToSleep; synchronized (task.lock) { if (task.cancelled) { tasks.delete(0); continue; } // check the time to sleep for the first task scheduled timeToSleep = task.when - currentTime; } if (timeToSleep > 0) { // sleep! try { this.wait(timeToSleep); } catch (InterruptedException ignored) { } continue; } // no sleep is necessary before launching the task synchronized (task.lock) { int pos = 0; if (tasks.minimum().when != task.when) { pos = tasks.getTask(task); } if (task.cancelled) { tasks.delete(tasks.getTask(task)); continue; } // set time to schedule task.setScheduledTime(task.when); // remove task from queue tasks.delete(pos); // set when the next task should be launched if (task.period >= 0) { // this is a repeating task, if (task.fixedRate) { // task is scheduled at fixed rate task.when = task.when + task.period; } else { // task is scheduled at fixed delay task.when = System.currentTimeMillis() + task.period; } // insert this task into queue insertTask(task); } else { task.when = 0; } } } boolean taskCompletedNormally = false; try { task.run(); taskCompletedNormally = true; } finally { if (!taskCompletedNormally) { synchronized (this) { cancelled = true; } } } } } private void insertTask(TimerTask newTask) { // callers are synchronized tasks.insert(newTask); this.notify(); } /** * Cancels timer. */ public synchronized void cancel() { cancelled = true; tasks.reset(); this.notify(); } public int purge() { if (tasks.isEmpty()) { return 0; } // callers are synchronized tasks.deletedCancelledNumber = 0; tasks.deleteIfCancelled(); return tasks.deletedCancelledNumber; } } private static final class FinalizerHelper { private final TimerImpl impl; FinalizerHelper(TimerImpl impl) { this.impl = impl; } @Override protected void finalize() throws Throwable { try { synchronized (impl) { impl.finished = true; impl.notify(); } } finally { super.finalize(); } } } private static long timerId; private synchronized static long nextId() { return timerId++; } /* This object will be used in synchronization purposes */ private final TimerImpl impl; // Used to finalize thread @SuppressWarnings("unused") private final FinalizerHelper finalizer; /** * Creates a new named {@code Timer} which may be specified to be run as a * daemon thread. * * @param name the name of the {@code Timer}. * @param isDaemon true if {@code Timer}'s thread should be a daemon thread. * @throws NullPointerException is {@code name} is {@code null} */ public Timer(String name, boolean isDaemon) { if (name == null) { throw new NullPointerException("name == null"); } this.impl = new TimerImpl(name, isDaemon); this.finalizer = new FinalizerHelper(impl); } /** * Creates a new named {@code Timer} which does not run as a daemon thread. * * @param name the name of the Timer. * @throws NullPointerException is {@code name} is {@code null} */ public Timer(String name) { this(name, false); } /** * Creates a new {@code Timer} which may be specified to be run as a daemon thread. * * @param isDaemon {@code true} if the {@code Timer}'s thread should be a daemon thread. */ public Timer(boolean isDaemon) { this("Timer-" + Timer.nextId(), isDaemon); } /** * Creates a new non-daemon {@code Timer}. */ public Timer() { this(false); } /** * Cancels the {@code Timer} and all scheduled tasks. If there is a * currently running task it is not affected. No more tasks may be scheduled * on this {@code Timer}. Subsequent calls do nothing. */ public void cancel() { impl.cancel(); } /** * Removes all canceled tasks from the task queue. If there are no * other references on the tasks, then after this call they are free * to be garbage collected. * * @return the number of canceled tasks that were removed from the task * queue. */ public int purge() { synchronized (impl) { return impl.purge(); } } /** * Schedule a task for single execution. If {@code when} is less than the * current time, it will be scheduled to be executed as soon as possible. * * @param task * the task to schedule. * @param when * time of execution. * @throws IllegalArgumentException * if {@code when.getTime() < 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void schedule(TimerTask task, Date when) { if (when.getTime() < 0) { throw new IllegalArgumentException("when < 0: " + when.getTime()); } long delay = when.getTime() - System.currentTimeMillis(); scheduleImpl(task, delay < 0 ? 0 : delay, -1, false); } /** * Schedule a task for single execution after a specified delay. * * @param task * the task to schedule. * @param delay * amount of time in milliseconds before execution. * @throws IllegalArgumentException * if {@code delay < 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void schedule(TimerTask task, long delay) { if (delay < 0) { throw new IllegalArgumentException("delay < 0: " + delay); } scheduleImpl(task, delay, -1, false); } /** * Schedule a task for repeated fixed-delay execution after a specific delay. * * @param task * the task to schedule. * @param delay * amount of time in milliseconds before first execution. * @param period * amount of time in milliseconds between subsequent executions. * @throws IllegalArgumentException * if {@code delay < 0} or {@code period <= 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void schedule(TimerTask task, long delay, long period) { if (delay < 0 || period <= 0) { throw new IllegalArgumentException(); } scheduleImpl(task, delay, period, false); } /** * Schedule a task for repeated fixed-delay execution after a specific time * has been reached. * * @param task * the task to schedule. * @param when * time of first execution. * @param period * amount of time in milliseconds between subsequent executions. * @throws IllegalArgumentException * if {@code when.getTime() < 0} or {@code period <= 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void schedule(TimerTask task, Date when, long period) { if (period <= 0 || when.getTime() < 0) { throw new IllegalArgumentException(); } long delay = when.getTime() - System.currentTimeMillis(); scheduleImpl(task, delay < 0 ? 0 : delay, period, false); } /** * Schedule a task for repeated fixed-rate execution after a specific delay * has passed. * * @param task * the task to schedule. * @param delay * amount of time in milliseconds before first execution. * @param period * amount of time in milliseconds between subsequent executions. * @throws IllegalArgumentException * if {@code delay < 0} or {@code period <= 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void scheduleAtFixedRate(TimerTask task, long delay, long period) { if (delay < 0 || period <= 0) { throw new IllegalArgumentException(); } scheduleImpl(task, delay, period, true); } /** * Schedule a task for repeated fixed-rate execution after a specific time * has been reached. * * @param task * the task to schedule. * @param when * time of first execution. * @param period * amount of time in milliseconds between subsequent executions. * @throws IllegalArgumentException * if {@code when.getTime() < 0} or {@code period <= 0}. * @throws IllegalStateException * if the {@code Timer} has been canceled, or if the task has been * scheduled or canceled. */ public void scheduleAtFixedRate(TimerTask task, Date when, long period) { if (period <= 0 || when.getTime() < 0) { throw new IllegalArgumentException(); } long delay = when.getTime() - System.currentTimeMillis(); scheduleImpl(task, delay, period, true); } /* * Schedule a task. */ private void scheduleImpl(TimerTask task, long delay, long period, boolean fixed) { synchronized (impl) { if (impl.cancelled) { throw new IllegalStateException("Timer was canceled"); } long when = delay + System.currentTimeMillis(); if (when < 0) { throw new IllegalArgumentException("Illegal delay to start the TimerTask: " + when); } synchronized (task.lock) { if (task.isScheduled()) { throw new IllegalStateException("TimerTask is scheduled already"); } if (task.cancelled) { throw new IllegalStateException("TimerTask is canceled"); } task.when = when; task.period = period; task.fixedRate = fixed; } // insert the newTask into queue impl.insertTask(task); } } }





© 2015 - 2024 Weber Informatics LLC | Privacy Policy