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SnappyData store based off Pivotal GemFireXD
/** Notice of modification as required by the LGPL
* This file was modified by Gemstone Systems Inc. on
* $Date$
**/
// $Id: ReusableThread.java,v 1.7 2005/01/16 01:04:52 belaban Exp $
package com.gemstone.org.jgroups.util;
import com.gemstone.org.jgroups.util.GemFireTracer;
/**
* Reusable thread class. Instead of creating a new thread per task, this instance can be reused
* to run different tasks in turn. This is done by looping and assigning the Runnable task objects
* whose run method is then called.
* Tasks are Runnable objects and should be prepared to terminate when they receive an
* InterruptedException. This is thrown by the stop() method.
*
* The following situations have to be tested:
*
* - ReusableThread is started. Then, brefore assigning a task, it is stopped again
*
- ReusableThread is started, assigned a long running task. Then, before task is done,
* stop() is called
*
- ReusableThread is started, assigned a task. Then waitUntilDone() is called, then stop()
*
- ReusableThread is started, assigned a number of tasks (waitUntilDone() called between tasks),
* then stopped
*
- ReusableThread is started, assigned a task
*
*
* @author Bela Ban
*/
public class ReusableThread implements Runnable {
volatile Thread thread=null; // thread that works on the task
Runnable task=null; // task assigned to thread
String thread_name="ReusableThread";
volatile boolean suspended=false;
protected static final GemFireTracer log=GemFireTracer.getLog(ReusableThread.class);
final long TASK_JOIN_TIME=3000; // wait 3 secs for an interrupted thread to terminate
public ReusableThread() {
}
public ReusableThread(String thread_name) {
this.thread_name=thread_name;
}
public boolean done() {
return task == null;
}
public boolean available() {
return done();
}
public boolean isAlive() {
synchronized(this) {
return thread != null && thread.isAlive();
}
}
/**
* Will always be called from synchronized method, no need to do our own synchronization
*/
public void start() {
if(thread == null || (thread != null && !thread.isAlive())) {
thread=new Thread(this, thread_name);
thread.setDaemon(true);
thread.start();
}
}
/**
* Stops the thread by setting thread=null and interrupting it. The run() method catches the
* InterruptedException and checks whether thread==null. If this is the case, it will terminate
*/
public void stop() {
Thread tmp=null;
if(log.isTraceEnabled()) log.trace("entering THIS");
synchronized(this) {
if(log.isTraceEnabled())
log.trace("entered THIS (thread=" + printObj(thread) +
", task=" + printObj(task) + ", suspended=" + suspended + ')');
if(thread != null && thread.isAlive()) {
tmp=thread;
thread=null; // signals the thread to stop
task=null;
if(log.isTraceEnabled()) log.trace("notifying thread");
notifyAll();
if(log.isTraceEnabled()) log.trace("notifying thread completed");
}
thread=null;
task=null;
}
if(tmp != null && tmp.isAlive()) {
long s1=System.currentTimeMillis(), s2=0;
if(log.isTraceEnabled()) log.trace("join(" + TASK_JOIN_TIME + ')');
tmp.interrupt();
try {
tmp.join(TASK_JOIN_TIME);
}
catch(InterruptedException e) {
Thread.currentThread().interrupt(); // GemStoneAddition -- propagate to caller
}
s2=System.currentTimeMillis();
if(log.isTraceEnabled()) log.trace("join(" + TASK_JOIN_TIME + ") completed in " + (s2 - s1));
if(tmp.isAlive())
if(log.isErrorEnabled()) log.error(ExternalStrings.ReusableThread_THREAD_IS_STILL_ALIVE);
tmp=null;
}
}
/**
* Suspends the thread. Does nothing if already suspended. If a thread is waiting to be assigned a task, or
* is currently running a (possibly long-running) task, then it will be suspended the next time it
* waits for suspended==false (second wait-loop in run())
*/
public void suspend() {
synchronized(this) {
if(log.isTraceEnabled()) log.trace("suspended=" + suspended + ", task=" + printObj(task));
if(suspended)
return; // already suspended
else
suspended=true;
}
}
/**
* Resumes the thread. Noop if not suspended
*/
public void resume() {
synchronized(this) {
suspended=false;
notifyAll(); // notifies run(): the wait on suspend() is released
}
}
/**
* Assigns a task to the thread. If the thread is not running, it will be started. It it is
* already working on a task, it will reject the new task. Returns true if task could be
* assigned auccessfully
*/
public boolean assignTask(Runnable t) {
synchronized(this) {
start(); // creates and starts the thread if not yet running
if(task == null) {
task=t;
notifyAll(); // signals run() to start working (first wait-loop)
return true;
}
else {
if(log.isErrorEnabled())
log.error("already working on a thread: current_task=" + task + ", new task=" + t +
", thread=" + thread + ", is alive=" + (thread != null ? "" + thread.isAlive() : "null"));
return false;
}
}
}
/**
* Delicate piece of code (means very important :-)). Works as follows: loops until stop is true.
* Waits in a loop until task is assigned. Then runs the task and notifies waiters that it's done
* when task is completed. Then returns to the first loop to wait for more work. Does so until
* stop() is called, which sets stop=true and interrupts the thread. If waiting for a task, the
* thread terminates. If running a task, the task is interrupted, and the thread terminates. If the
* task is not interrupible, the stop() method will wait for 3 secs (join on the thread), then return.
* This means that the run() method of the task will complete and only then will the thread be
* garbage-collected.
*/
public void run() {
while(thread != null) { // Stop sets thread=null
try {
if(log.isTraceEnabled()) log.trace("entering ASSIGN");
synchronized(this) {
if(log.isTraceEnabled())
log.trace("entered ASSIGN (task=" + printObj(task) + ", thread=" + printObj(thread) + ')');
while(task == null && thread != null) { // first wait-loop: wait for task to be assigned (assignTask())
if(log.isTraceEnabled()) log.trace("wait ASSIGN");
wait();
if(log.isTraceEnabled()) log.trace("wait ASSIGN completed");
}
}
}
catch(InterruptedException ex) { // on assignTask()
if(log.isTraceEnabled()) log.trace("interrupt on ASSIGN");
break; // GemStoneAddition exit loop and thread
}
if(thread == null) return; // we need to terminate
try {
if(log.isTraceEnabled()) log.trace("entering SUSPEND");
synchronized(this) {
if(log.isTraceEnabled())
log.trace("entered SUSPEND (suspended=" + suspended + ", task=" + printObj(task) + ')');
while(suspended && thread != null) { // second wait-loop: wait for thread to resume (resume())
if(log.isTraceEnabled()) log.trace("wait SUSPEND");
wait();
if(log.isTraceEnabled()) log.trace("wait SUSPEND completed");
}
}
}
catch(InterruptedException ex) { // on resume()
if(log.isTraceEnabled()) log.trace("interrupt on RESUME");
break; // GemStoneAddition exit loop and thread
}
if(thread == null) return; // we need to terminate
if(task != null) {
if(log.isTraceEnabled()) log.trace("running task");
try {
task.run(); //here we are actually running the task
}
catch(RuntimeException ex) {
if(log.isErrorEnabled()) log.error(ExternalStrings.ReusableThread_FAILED_RUNNING_TASK, ex);
}
if(log.isTraceEnabled()) log.trace("task completed");
}
if(log.isTraceEnabled()) log.trace("entering THIS");
synchronized(this) {
if(log.isTraceEnabled()) log.trace("entered THIS");
task=null;
if(log.isTraceEnabled()) log.trace("notify THIS");
notifyAll();
if(log.isTraceEnabled()) log.trace("notify THIS completed");
}
}
if(log.isTraceEnabled()) log.trace("terminated");
}
String printObj(Object obj) {
if(obj == null)
return "null";
else
return "non-null";
}
public void waitUntilDone() {
if(log.isTraceEnabled()) log.trace("entering THIS");
synchronized(this) {
if(log.isTraceEnabled()) log.trace("entered THIS (task=" + printObj(task) + ')');
while(task != null) {
boolean interrupted = Thread.interrupted(); // GemStoneAddition
try {
if(log.isTraceEnabled()) log.trace("wait THIS");
wait();
if(log.isTraceEnabled()) log.trace("wait THIS completed");
}
catch(InterruptedException e) {
interrupted = true; // GemStoneAddition
break; // GemStoneAddition
}
finally { // GemStoneAddition
if (interrupted) {
Thread.currentThread().interrupt();
}
}
}
}
}
@Override // GemStoneAddition
public String toString() {
return "suspended=" + suspended;
}
}