/*
* 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.
*
* <p>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.
*
* <p>One-shot tasks are scheduled to run at an absolute time or after a relative
* delay.
*
* <p>Recurring tasks are scheduled with either a fixed period or a fixed rate:
* <ul>
* <li>With the default <strong>fixed-period execution</strong>, 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}.
* <li>With <strong>fixed-rate execution</strong>, 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.
* </ul>
*
* <p>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.
*
* <p>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.
*
* @throws NullPointerException if {@code name == 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.
*
* @throws NullPointerException if {@code name == 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);
}
}
}