/*
* 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 org.apache.log4j.component.scheduler;
import java.util.List;
import java.util.Vector;
/**
* A simple but still useful implementation of a Scheduler (in memory only).
* <p/>
* This implementation will work very well when the number of scheduled job is
* small, say less than 100 jobs. If a larger number of events need to be
* scheduled, than a better adapted data structure for the jobList can give
* improved performance.
*
* @author Ceki
*/
public class Scheduler extends Thread {
/**
* Job list.
*/
List jobList;
/**
* If set true, scheduler has or should shut down.
*/
boolean shutdown = false;
/**
* Create new instance.
*/
public Scheduler() {
super();
jobList = new Vector();
}
/**
* Find the index of a given job.
* @param job job
* @return -1 if the job could not be found.
*/
int findIndex(final Job job) {
int size = jobList.size();
boolean found = false;
int i = 0;
for (; i < size; i++) {
ScheduledJobEntry se = (ScheduledJobEntry) jobList.get(i);
if (se.job == job) {
found = true;
break;
}
}
if (found) {
return i;
} else {
return -1;
}
}
/**
* Delete the given job.
* @param job job.
* @return true if the job could be deleted, and
* false if the job could not be found or if the Scheduler is about to
* shutdown in which case deletions are not permitted.
*/
public synchronized boolean delete(final Job job) {
// if already shutdown in the process of shutdown, there is no
// need to remove Jobs as they will never be executed.
if (shutdown) {
return false;
}
int i = findIndex(job);
if (i != -1) {
ScheduledJobEntry se = (ScheduledJobEntry) jobList.remove(i);
if (se.job != job) { // this should never happen
new IllegalStateException("Internal programming error");
}
// if the job is the first on the list,
// then notify the scheduler thread to schedule a new job
if (i == 0) {
this.notifyAll();
}
return true;
} else {
return false;
}
}
/**
* Schedule a {@link Job} for execution at system time given by
* the <code>desiredTime</code> parameter.
* @param job job to schedule.
* @param desiredTime desired time of execution.
*/
public synchronized void schedule(final Job job,
final long desiredTime) {
schedule(new ScheduledJobEntry(job, desiredTime));
}
/**
* Schedule a {@link Job} for execution at system time given by
* the <code>desiredTime</code> parameter.
* <p/>
* The job will be rescheduled. It will execute with a frequency determined
* by the period parameter.
* @param job job to schedule.
* @param desiredTime desired time of execution.
* @param period repeat period.
*/
public synchronized void schedule(final Job job,
final long desiredTime,
final long period) {
schedule(new ScheduledJobEntry(job, desiredTime, period));
}
/**
* Change the period of a job. The original job must exist for its period
* to be changed.
* <p/>
* The method returns true if the period could be changed, and false
* otherwise.
* @param job job.
* @param newPeriod new repeat period.
* @return true if period could be changed.
*/
public synchronized boolean changePeriod(final Job job,
final long newPeriod) {
if (newPeriod <= 0) {
throw new IllegalArgumentException(
"Period must be an integer langer than zero");
}
int i = findIndex(job);
if (i == -1) {
return false;
} else {
ScheduledJobEntry se = (ScheduledJobEntry) jobList.get(i);
se.period = newPeriod;
return true;
}
}
/**
* Schedule a job.
* @param newSJE new job entry.
*/
private synchronized void schedule(final ScheduledJobEntry newSJE) {
// disallow new jobs after shutdown
if (shutdown) {
return;
}
int max = jobList.size();
long desiredExecutionTime = newSJE.desiredExecutionTime;
// find the index i such that timeInMillis < jobList[i]
int i = 0;
for (; i < max; i++) {
ScheduledJobEntry sje = (ScheduledJobEntry) jobList.get(i);
if (desiredExecutionTime < sje.desiredExecutionTime) {
break;
}
}
jobList.add(i, newSJE);
// if the jobList was empty, then notify the scheduler thread
if (i == 0) {
this.notifyAll();
}
}
/**
* Shut down scheduler.
*/
public synchronized void shutdown() {
shutdown = true;
}
/**
* Run scheduler.
*/
public synchronized void run() {
while (!shutdown) {
if (jobList.isEmpty()) {
linger();
} else {
ScheduledJobEntry sje = (ScheduledJobEntry) jobList.get(0);
long now = System.currentTimeMillis();
if (now >= sje.desiredExecutionTime) {
executeInABox(sje.job);
jobList.remove(0);
if (sje.period > 0) {
sje.desiredExecutionTime = now + sje.period;
schedule(sje);
}
} else {
linger(sje.desiredExecutionTime - now);
}
}
}
// clear out the job list to facilitate garbage collection
jobList.clear();
jobList = null;
System.out.println("Leaving scheduler run method");
}
/**
* We do not want a single failure to affect the whole scheduler.
* @param job job to execute.
*/
void executeInABox(final Job job) {
try {
job.execute();
} catch (Exception e) {
System.err.println("The execution of the job threw an exception");
e.printStackTrace(System.err);
}
}
/**
* Wait for notification.
*/
void linger() {
try {
while (jobList.isEmpty() && !shutdown) {
this.wait();
}
} catch (InterruptedException ie) {
shutdown = true;
}
}
/**
* Wait for notification or time to elapse.
* @param timeToLinger time to linger.
*/
void linger(final long timeToLinger) {
try {
this.wait(timeToLinger);
} catch (InterruptedException ie) {
shutdown = true;
}
}
/**
* Represents an entry in job scheduler.
*/
static final class ScheduledJobEntry {
/**
* Desired execution time.
*/
long desiredExecutionTime;
/**
* Job to run.
*/
Job job;
/**
* Repeat period.
*/
long period = 0;
/**
* Create new instance.
* @param job job
* @param desiredTime desired time.
*/
ScheduledJobEntry(final Job job, final long desiredTime) {
this(job, desiredTime, 0);
}
/**
* Create new instance.
* @param job job
* @param desiredTime desired time
* @param period repeat period
*/
ScheduledJobEntry(final Job job,
final long desiredTime,
final long period) {
super();
this.desiredExecutionTime = desiredTime;
this.job = job;
this.period = period;
}
}
}