Java/Threads/Lock Synchronize
Содержание
- 1 A reader-writer lock from "Java Threads" by Scott Oak and Henry Wong.
- 2 Boolean lock
- 3 Byte FIFO
- 4 Coordinates threads for multi-threaded operations
- 5 Daemon Lock
- 6 Determining If the Current Thread Is Holding a Synchronized Lock
- 7 Handle concurrent read/write: use synchronized to lock the data
- 8 Interruptible Synchronized Block
- 9 Invoke a series of runnables as closely to synchronously as possible
- 10 Lock for read and write
- 11 No synchronize
- 12 Object FIFO
- 13 Operations that may seem safe are not, when threads are present
- 14 Read Write Lock
- 15 Signaling
- 16 Simple Object FIFO
- 17 Static synchronize
- 18 Static synchronized block
- 19 Synchronized Block demo
- 20 Synchronize method
- 21 Synchronizing blocks instead of entire methods
- 22 Synchronizing on another object
- 23 Thread deadlock
- 24 Thread: Dining Philosophers
- 25 Thread notify
- 26 Threads join
- 27 Thread synchronization
A reader-writer lock from "Java Threads" by Scott Oak and Henry Wong.
<source lang="java">
/*
* JCommon : a free general purpose class library for the Java(tm) platform * * * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors. * * Project Info: http://www.jfree.org/jcommon/index.html * * This library is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 2.1 of the License, or * (at your option) any later version. * * This library is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public * License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, * USA. * * [Java is a trademark or registered trademark of Sun Microsystems, Inc. * in the United States and other countries.] * * --------------------- * ReaderWriterLock.java * --------------------- * * $Id: ReaderWriterLock.java,v 1.3 2005/10/18 13:18:34 mungady Exp $ * * Changes * ------- * 29-Jan-2003 : Added standard header (DG); * */
import java.util.ArrayList; import java.util.Iterator; /**
* A reader-writer lock from "Java Threads" by Scott Oak and Henry Wong. * * @author Scott Oak and Henry Wong */
public class ReaderWriterLock {
/**
* A node for the waiting list.
*
* @author Scott Oak and Henry Wong
*/
private static class ReaderWriterNode {
/** A reader. */
protected static final int READER = 0;
/** A writer. */
protected static final int WRITER = 1;
/** The thread. */
protected Thread t;
/** The state. */
protected int state;
/** The number of acquires. */
protected int nAcquires;
/**
* Creates a new node.
*
* @param t
* the thread.
* @param state
* the state.
*/
private ReaderWriterNode(final Thread t, final int state) {
this.t = t;
this.state = state;
this.nAcquires = 0;
}
}
/** The waiting threads. */
private ArrayList waiters;
/**
* Default constructor.
*/
public ReaderWriterLock() {
this.waiters = new ArrayList();
}
/**
* Grab the read lock.
*/
public synchronized void lockRead() {
final ReaderWriterNode node;
final Thread me = Thread.currentThread();
final int index = getIndex(me);
if (index == -1) {
node = new ReaderWriterNode(me, ReaderWriterNode.READER);
this.waiters.add(node);
} else {
node = (ReaderWriterNode) this.waiters.get(index);
}
while (getIndex(me) > firstWriter()) {
try {
wait();
} catch (Exception e) {
System.err.println("ReaderWriterLock.lockRead(): exception.");
System.err.print(e.getMessage());
}
}
node.nAcquires++;
}
/**
* Grab the write lock.
*/
public synchronized void lockWrite() {
final ReaderWriterNode node;
final Thread me = Thread.currentThread();
final int index = getIndex(me);
if (index == -1) {
node = new ReaderWriterNode(me, ReaderWriterNode.WRITER);
this.waiters.add(node);
} else {
node = (ReaderWriterNode) this.waiters.get(index);
if (node.state == ReaderWriterNode.READER) {
throw new IllegalArgumentException("Upgrade lock");
}
node.state = ReaderWriterNode.WRITER;
}
while (getIndex(me) != 0) {
try {
wait();
} catch (Exception e) {
System.err.println("ReaderWriterLock.lockWrite(): exception.");
System.err.print(e.getMessage());
}
}
node.nAcquires++;
}
/**
* Unlock.
*/
public synchronized void unlock() {
final ReaderWriterNode node;
final Thread me = Thread.currentThread();
final int index = getIndex(me);
if (index > firstWriter()) {
throw new IllegalArgumentException("Lock not held");
}
node = (ReaderWriterNode) this.waiters.get(index);
node.nAcquires--;
if (node.nAcquires == 0) {
this.waiters.remove(index);
}
notifyAll();
}
/**
* Returns the index of the first waiting writer.
*
* @return The index.
*/
private int firstWriter() {
final Iterator e = this.waiters.iterator();
int index = 0;
while (e.hasNext()) {
final ReaderWriterNode node = (ReaderWriterNode) e.next();
if (node.state == ReaderWriterNode.WRITER) {
return index;
}
index += 1;
}
return Integer.MAX_VALUE;
}
/**
* Returns the index of a thread.
*
* @param t
* the thread.
*
* @return The index.
*/
private int getIndex(final Thread t) {
final Iterator e = this.waiters.iterator();
int index = 0;
while (e.hasNext()) {
final ReaderWriterNode node = (ReaderWriterNode) e.next();
if (node.t == t) {
return index;
}
index += 1;
}
return -1;
}
}
</source>
Boolean lock
<source lang="java">
public class BestReplacement extends Object {
private Thread internalThread;
private volatile boolean stopRequested;
private BooleanLock suspendRequested;
private BooleanLock internalThreadSuspended;
public BestReplacement() {
stopRequested = false;
suspendRequested = new BooleanLock(false);
internalThreadSuspended = new BooleanLock(false);
Runnable r = new Runnable() {
public void run() {
try {
runWork();
} catch (Exception x) {
x.printStackTrace();
}
}
};
internalThread = new Thread(r);
internalThread.start();
}
private void runWork() {
int count = 0;
while (!stopRequested) {
try {
waitWhileSuspended();
} catch (InterruptedException x) {
Thread.currentThread().interrupt();
continue;
}
System.out.println("Part I - count=" + count);
try {
Thread.sleep(1000);
} catch (InterruptedException x) {
Thread.currentThread().interrupt();
}
System.out.println("Part II - count=" + count);
try {
Thread.sleep(1000);
} catch (InterruptedException x) {
Thread.currentThread().interrupt();
}
System.out.println("Part III - count=" + count);
count++;
}
}
private void waitWhileSuspended() throws InterruptedException {
synchronized (suspendRequested) {
if (suspendRequested.isTrue()) {
try {
internalThreadSuspended.setValue(true);
suspendRequested.waitUntilFalse(0);
} finally {
internalThreadSuspended.setValue(false);
}
}
}
}
public void suspendRequest() {
suspendRequested.setValue(true);
}
public void resumeRequest() {
suspendRequested.setValue(false);
}
public boolean waitForActualSuspension(long msTimeout)
throws InterruptedException {
return internalThreadSuspended.waitUntilTrue(msTimeout);
}
public void stopRequest() {
stopRequested = true;
internalThread.interrupt();
}
public boolean isAlive() {
return internalThread.isAlive();
}
public static void main(String[] args) {
try {
BestReplacement br = new BestReplacement();
System.out
.println(" just created, br.isAlive()=" + br.isAlive());
Thread.sleep(4200);
long startTime = System.currentTimeMillis();
br.suspendRequest();
System.out.println(" just submitted a suspendRequest");
boolean suspensionTookEffect = br.waitForActualSuspension(10000);
long stopTime = System.currentTimeMillis();
if (suspensionTookEffect) {
System.out.println(" the internal thread took "
+ (stopTime - startTime) + " ms to notice "
+ "\n the suspend request and is now "
+ "suspended.");
} else {
System.out.println(" the internal thread did not notice "
+ "the suspend request " + "\n within 10 seconds.");
}
Thread.sleep(5000);
br.resumeRequest();
System.out.println("Submitted a resumeRequest");
Thread.sleep(2200);
br.stopRequest();
System.out.println("Submitted a stopRequest");
} catch (InterruptedException x) {
// ignore
}
}
} class BooleanLock extends Object {
private boolean value;
public BooleanLock(boolean initialValue) {
value = initialValue;
}
public BooleanLock() {
this(false);
}
public synchronized void setValue(boolean newValue) {
if ( newValue != value ) {
value = newValue;
notifyAll();
}
}
public synchronized boolean waitToSetTrue(long msTimeout)
throws InterruptedException {
boolean success = waitUntilFalse(msTimeout);
if ( success ) {
setValue(true);
}
return success;
}
public synchronized boolean waitToSetFalse(long msTimeout)
throws InterruptedException {
boolean success = waitUntilTrue(msTimeout);
if ( success ) {
setValue(false);
}
return success;
}
public synchronized boolean isTrue() {
return value;
}
public synchronized boolean isFalse() {
return !value;
}
public synchronized boolean waitUntilTrue(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(true, msTimeout);
}
public synchronized boolean waitUntilFalse(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(false, msTimeout);
}
public synchronized boolean waitUntilStateIs(
boolean state,
long msTimeout
) throws InterruptedException {
if ( msTimeout == 0L ) {
while ( value != state ) {
wait();
}
return true;
}
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ( ( value != state ) && ( msRemaining > 0L ) ) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
return ( value == state );
}
}
</source>
Byte FIFO
<source lang="java">
import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; public class ByteFIFOTest extends Object {
private ByteFIFO fifo;
private byte[] srcData;
public ByteFIFOTest() throws IOException {
fifo = new ByteFIFO(20);
makeSrcData();
System.out.println("srcData.length=" + srcData.length);
Runnable srcRunnable = new Runnable() {
public void run() {
src();
}
};
Thread srcThread = new Thread(srcRunnable);
srcThread.start();
Runnable dstRunnable = new Runnable() {
public void run() {
dst();
}
};
Thread dstThread = new Thread(dstRunnable);
dstThread.start();
}
private void makeSrcData() throws IOException {
String[] list = {
"The first string is right here",
"The second string is a bit longer and also right here",
"The third string",
"ABCDEFGHIJKLMNOPQRSTUVWXYZ",
"0123456789",
"The last string in the list"
};
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(list);
oos.flush();
oos.close();
srcData = baos.toByteArray();
}
private void src() {
try {
boolean justAddOne = true;
int count = 0;
while ( count < srcData.length ) {
if ( !justAddOne ) {
int writeSize = (int) ( 40.0 * Math.random() );
writeSize = Math.min(writeSize, srcData.length - count);
byte[] buf = new byte[writeSize];
System.arraycopy(srcData, count, buf, 0, writeSize);
fifo.add(buf);
count += writeSize;
System.out.println("just added " + writeSize + " bytes");
} else {
fifo.add(srcData[count]);
count++;
System.out.println("just added exactly 1 byte");
}
justAddOne = !justAddOne;
}
} catch ( InterruptedException x ) {
x.printStackTrace();
}
}
private void dst() {
try {
boolean justAddOne = true;
int count = 0;
byte[] dstData = new byte[srcData.length];
while ( count < dstData.length ) {
if ( !justAddOne ) {
byte[] buf = fifo.removeAll();
if ( buf.length > 0 ) {
System.arraycopy(buf, 0, dstData, count, buf.length);
count += buf.length;
}
System.out.println(
"just removed " + buf.length + " bytes");
} else {
byte b = fifo.remove();
dstData[count] = b;
count++;
System.out.println(
"just removed exactly 1 byte");
}
justAddOne = !justAddOne;
}
System.out.println("received all data, count=" + count);
ObjectInputStream ois = new ObjectInputStream(
new ByteArrayInputStream(dstData));
String[] line = (String[]) ois.readObject();
for ( int i = 0; i < line.length; i++ ) {
System.out.println("line[" + i + "]=" + line[i]);
}
} catch ( ClassNotFoundException x1 ) {
x1.printStackTrace();
} catch ( IOException iox ) {
iox.printStackTrace();
} catch ( InterruptedException x ) {
x.printStackTrace();
}
}
public static void main(String[] args) {
try {
new ByteFIFOTest();
} catch ( IOException iox ) {
iox.printStackTrace();
}
}
} class ByteFIFO extends Object {
private byte[] queue;
private int capacity;
private int size;
private int head;
private int tail;
public ByteFIFO(int cap) {
capacity = ( cap > 0 ) ? cap : 1; // at least 1
queue = new byte[capacity];
head = 0;
tail = 0;
size = 0;
}
public int getCapacity() {
return capacity;
}
public synchronized int getSize() {
return size;
}
public synchronized boolean isEmpty() {
return ( size == 0 );
}
public synchronized boolean isFull() {
return ( size == capacity );
}
public synchronized void add(byte b)
throws InterruptedException {
waitWhileFull();
queue[head] = b;
head = ( head + 1 ) % capacity;
size++;
notifyAll(); // let any waiting threads know about change
}
public synchronized void add(byte[] list)
throws InterruptedException {
// For efficiency, the bytes are copied in blocks
// instead of one at a time. As space becomes available,
// more bytes are copied until all of them have been
// added.
int ptr = 0;
while ( ptr < list.length ) {
// If full, the lock will be released to allow
// another thread to come in and remove bytes.
waitWhileFull();
int space = capacity - size;
int distToEnd = capacity - head;
int blockLen = Math.min(space, distToEnd);
int bytesRemaining = list.length - ptr;
int copyLen = Math.min(blockLen, bytesRemaining);
System.arraycopy(list, ptr, queue, head, copyLen);
head = ( head + copyLen ) % capacity;
size += copyLen;
ptr += copyLen;
// Keep the lock, but let any waiting threads
// know that something has changed.
notifyAll();
}
}
public synchronized byte remove()
throws InterruptedException {
waitWhileEmpty();
byte b = queue[tail];
tail = ( tail + 1 ) % capacity;
size--;
notifyAll(); // let any waiting threads know about change
return b;
}
public synchronized byte[] removeAll() {
// For efficiency, the bytes are copied in blocks
// instead of one at a time.
if ( isEmpty() ) {
// Nothing to remove, return a zero-length
// array and do not bother with notification
// since nothing was removed.
return new byte[0];
}
// based on the current size
byte[] list = new byte[size];
// copy in the block from tail to the end
int distToEnd = capacity - tail;
int copyLen = Math.min(size, distToEnd);
System.arraycopy(queue, tail, list, 0, copyLen);
// If data wraps around, copy the remaining data
// from the front of the array.
if ( size > copyLen ) {
System.arraycopy(
queue, 0, list, copyLen, size - copyLen);
}
tail = ( tail + size ) % capacity;
size = 0; // everything has been removed
// Signal any and all waiting threads that
// something has changed.
notifyAll();
return list;
}
public synchronized byte[] removeAtLeastOne()
throws InterruptedException {
waitWhileEmpty(); // wait for a least one to be in FIFO
return removeAll();
}
public synchronized boolean waitUntilEmpty(long msTimeout)
throws InterruptedException {
if ( msTimeout == 0L ) {
waitUntilEmpty(); // use other method
return true;
}
// wait only for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ( !isEmpty() && ( msRemaining > 0L ) ) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or may have met condition,
// calc return value.
return isEmpty();
}
public synchronized void waitUntilEmpty()
throws InterruptedException {
while ( !isEmpty() ) {
wait();
}
}
public synchronized void waitWhileEmpty()
throws InterruptedException {
while ( isEmpty() ) {
wait();
}
}
public synchronized void waitUntilFull()
throws InterruptedException {
while ( !isFull() ) {
wait();
}
}
public synchronized void waitWhileFull()
throws InterruptedException {
while ( isFull() ) {
wait();
}
}
}
</source>
Coordinates threads for multi-threaded operations
<source lang="java">
/* Copyright (C) 2005-2008 by Peter Eastman
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. */
import java.util.concurrent.atomic.*; import java.util.*; /**
* This class coordinates threads for multi-threaded operations. The execution model * provided by this class is a single "task" (e.g. tracing a ray through a single pixel) * which must be executed many times. The task is parameterized by a single index * (e.g. the column containing the pixel).*
* To use this class, pass it an object which implements the Task interface. It * automatically creates an appropriate number of threads based on the number of * available processors. When you call run(), the task is repeatedly executed by * the worker threads, with the index running * over the desired range. You may invoke run() any number of times (e.g. once * for each row of the image). Finally, call finish() to clean up the worker threads. */ public class ThreadManager { private int numIndices; private AtomicInteger nextIndex; private Thread thread[]; private HashSet<Thread> waitingThreads; private Task task; private Object controller; private boolean controllerWaiting; /** * Create a new uninitialized ThreadManager. You must invoke setNumIndices() and setTask() * to initialize it before calling run(). */ public ThreadManager() { this(0, null); } /** * Create a new ThreadManager. * * @param numIndices the number of values the index should take on (from 0 to numIndices-1) * @param task the task to perform */ public ThreadManager(int numIndices, Task task) { this.numIndices = numIndices; this.task = task; nextIndex = new AtomicInteger(numIndices); controller = new Object(); controllerWaiting = false; waitingThreads = new HashSet<Thread>(); } /** * Create and start the worker threads. This is invoked the first time run() is called. */ private void createThreads() { // Create a worker thread for each processor. thread = new Thread [Runtime.getRuntime().availableProcessors()]; for (int i = 0; i < thread.length; i++) { thread[i] = new Thread("Worker thread "+(i+1)) { public void run() { // Repeatedly perform the task until we are finished. while (true) { try { int index = nextIndex(); task.execute(index); } catch (InterruptedException ex) { task.cleanup(); return; } catch (Exception ex) { cancel(); ex.printStackTrace(); } } } }; thread[i].start(); } } /** * Set the number of values the index should take on. This must be invoked from the same * thread that instantiated the ThreadManager and that calls run(). */ public void setNumIndices(int numIndices) { this.numIndices = numIndices; nextIndex.set(numIndices); } /** * Set the Task to be executed by the worker threads. If another Task has already been set, * that one is discarded immediately and cleanup() will never be invoked on in. This method * must be invoked from the same thread that instantiated the ThreadManager and that calls run(). */ public void setTask(Task task) { this.task = task; } /** * Perform the task the specified number of times. This method blocks until all * occurrences of the task are completed. If the current thread is interrupted * while this method is in progress, all of the worker threads will be interrupted * and disposed of. */ public void run() { controllerWaiting = false; nextIndex.set(0); waitingThreads.clear(); if (thread == null) createThreads(); // Notify all the worker threads, then wait for them to finish. synchronized (this) { notifyAll(); } synchronized (controller) { try { controllerWaiting = true; controller.wait(); } catch (InterruptedException ex) { finish(); } } } /** * Cancel a run which is in progress. Calling this method does not interrupt any tasks that * are currently executing, but it prevents any more from being started until the next time * run() is called. */ public void cancel() { nextIndex.set(numIndices); } /** * Dispose of all the worker threads. Once this has been called, do not call run() again. */ public void finish() { if (thread != null) for (int i = 0; i < thread.length; i++) thread[i].interrupt(); } private int nextIndex() throws InterruptedException { int index; while ((index = nextIndex.getAndIncrement()) >= numIndices) { // Wait until run() is called again. synchronized (this) { waitingThreads.add(Thread.currentThread()); if (waitingThreads.size() == thread.length) { while (!controllerWaiting) wait(1); synchronized (controller) { controller.notify(); } } wait(); } } return index; } /** * This interface defines a task to be performed by the worker threads. */ public static interface Task { /** * Execute the task for the specified index. */ public void execute(int index); /** * This is called once from each worker thread when finish() is called. It gives a chance * to do any necessary cleanup. */ public void cleanup(); } } </source>
Daemon Lock
<source lang="java">
/*
*
* Copyright (c) 1997-1999 Scott Oaks and Henry Wong. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and
* without fee is hereby granted.
*
* This sample source code is provided for example only,
* on an unsupported, as-is basis.
*
* AUTHOR MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. AUTHOR SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*
* THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
* CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
* PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
* NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
* SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
* SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
* PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES"). AUTHOR
* SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
* HIGH RISK ACTIVITIES.
*/
public class DaemonLock implements Runnable {
private int lockCount = 0;
public synchronized void acquire() {
if (lockCount++ == 0) {
Thread t = new Thread(this);
t.setDaemon(false);
t.start();
}
}
public synchronized void release() {
if (--lockCount == 0) {
notify();
}
}
public synchronized void run() {
while (lockCount != 0) {
try {
wait();
} catch (InterruptedException ex) {};
}
}
}
</source>
Determining If the Current Thread Is Holding a Synchronized Lock
<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
}
public synchronized void myMethod() {
Object o = new Object();
System.out.println(Thread.holdsLock(o));
synchronized (o) {
System.out.println(Thread.holdsLock(o));
}
System.out.println(Thread.holdsLock(this));
}
}
</source>
Handle concurrent read/write: use synchronized to lock the data
<source lang="java">
import java.util.Iterator; import java.util.Vector; public class Main {
Vector data = new Vector();
public Main() {
new Producer().start();
new Consumer().start();
}
public static void main(String[] args) throws Exception {
new Main();
}
class Consumer extends Thread {
Consumer() {
super("Consumer");
}
public void run() {
while (true) {
synchronized (data) {
Iterator it = data.iterator();
while (it.hasNext())
it.next();
}
}
}
}
class Producer extends Thread {
Producer() {
super("Producer");
}
public void run() {
while (true) {
data.addElement(new Object());
if (data.size() > 1000)
data.removeAllElements();
}
}
}
}
</source>
Interruptible Synchronized Block
<source lang="java">
public class InterruptibleSyncBlock extends Object {
private Object longLock;
private BooleanLock busyLock;
public InterruptibleSyncBlock() {
longLock = new Object();
busyLock = new BooleanLock(false);
}
public void doStuff() throws InterruptedException {
print("about to try to get exclusive access " + "to busyLock");
busyLock.waitToSetTrue(0);
try {
print("about to try to get exclusive access " + "to longLock");
synchronized (longLock) {
print("got exclusive access to longLock");
try {
Thread.sleep(10000);
} catch (InterruptedException x) {
// ignore
}
print("about to relinquish exclusive access " + "to longLock");
}
} finally {
print("about to free up busyLock");
busyLock.setValue(false);
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.err.println(name + ": " + msg);
}
private static Thread launch(final InterruptibleSyncBlock sb, String name) {
Runnable r = new Runnable() {
public void run() {
print("in run()");
try {
sb.doStuff();
} catch (InterruptedException x) {
print("InterruptedException thrown " + "from doStuff()");
}
}
};
Thread t = new Thread(r, name);
t.start();
return t;
}
public static void main(String[] args) {
try {
InterruptibleSyncBlock sb = new InterruptibleSyncBlock();
Thread t1 = launch(sb, "T1");
Thread.sleep(500);
Thread t2 = launch(sb, "T2");
Thread t3 = launch(sb, "T3");
Thread.sleep(1000);
print("about to interrupt T2");
t2.interrupt();
print("just interrupted T2");
} catch (InterruptedException x) {
x.printStackTrace();
}
}
} class BooleanLock extends Object {
private boolean value;
public BooleanLock(boolean initialValue) {
value = initialValue;
}
public BooleanLock() {
this(false);
}
public synchronized void setValue(boolean newValue) {
if ( newValue != value ) {
value = newValue;
notifyAll();
}
}
public synchronized boolean waitToSetTrue(long msTimeout)
throws InterruptedException {
boolean success = waitUntilFalse(msTimeout);
if ( success ) {
setValue(true);
}
return success;
}
public synchronized boolean waitToSetFalse(long msTimeout)
throws InterruptedException {
boolean success = waitUntilTrue(msTimeout);
if ( success ) {
setValue(false);
}
return success;
}
public synchronized boolean isTrue() {
return value;
}
public synchronized boolean isFalse() {
return !value;
}
public synchronized boolean waitUntilTrue(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(true, msTimeout);
}
public synchronized boolean waitUntilFalse(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(false, msTimeout);
}
public synchronized boolean waitUntilStateIs(
boolean state,
long msTimeout
) throws InterruptedException {
if ( msTimeout == 0L ) {
while ( value != state ) {
wait(); // wait indefinitely until notified
}
// condition has finally been met
return true;
}
// only wait for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ( ( value != state ) && ( msRemaining > 0L ) ) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or may have met value,
// calculate return value.
return ( value == state );
}
}
</source>
Invoke a series of runnables as closely to synchronously as possible
<source lang="java">
/*
* 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. */
import java.util.ArrayList; import java.util.List; import java.util.Iterator; import java.util.Collections; import java.util.Random; /**
* The purpose of this class is to invoke a series of runnables as * closely to synchronously as possible. It does this by starting * a thread for each one, getting the threads into there run method, * then quickly running through (in random order) and notifying each * thread. */
public class ThreadPounder {
List runnables;
Object [] threads;
Object lock = new Object();
public ThreadPounder(List runnables)
throws InterruptedException {
this(runnables, new Random(1234));
}
public ThreadPounder(List runnables, Random rand)
throws InterruptedException {
this.runnables = new ArrayList(runnables);
Collections.shuffle(this.runnables, rand);
threads = new Object[this.runnables.size()];
int i=0;
Iterator iter= this.runnables.iterator();
synchronized (lock) {
while (iter.hasNext()) {
Thread t = new SyncThread((Runnable)iter.next());
t.start();
lock.wait();
threads[i] = t;
i++;
}
}
}
public void start() {
synchronized(this) {
this.notifyAll();
}
}
class SyncThread extends Thread {
Runnable toRun;
public long runTime;
public SyncThread(Runnable toRun) {
this.toRun = toRun;
}
public void run() {
try {
synchronized (ThreadPounder.this) {
synchronized (lock) {
// Let pounder know I"m ready to go
lock.notify();
}
// Wait for pounder to wake me up.
ThreadPounder.this.wait();
}
toRun.run();
} catch (InterruptedException ie) {
}
}
}
public static void main(String [] str) {
List l = new ArrayList(20);
for (int i=0; i<20; i++) {
final int x = i;
l.add(new Runnable() {
public void run() {
System.out.println("Thread " + x);
}
});
}
try {
ThreadPounder tp = new ThreadPounder(l);
System.out.println("Starting:" );
tp.start();
System.out.println("All Started:" );
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
</source>
Lock for read and write
<source lang="java">
/*
*
* Copyright (c) 1997-1999 Scott Oaks and Henry Wong. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and
* without fee is hereby granted.
*
* This sample source code is provided for example only,
* on an unsupported, as-is basis.
*
* AUTHOR MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. AUTHOR SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*
* THIS SOFTWARE IS NOT DESIGNED OR INTENDED FOR USE OR RESALE AS ON-LINE
* CONTROL EQUIPMENT IN HAZARDOUS ENVIRONMENTS REQUIRING FAIL-SAFE
* PERFORMANCE, SUCH AS IN THE OPERATION OF NUCLEAR FACILITIES, AIRCRAFT
* NAVIGATION OR COMMUNICATION SYSTEMS, AIR TRAFFIC CONTROL, DIRECT LIFE
* SUPPORT MACHINES, OR WEAPONS SYSTEMS, IN WHICH THE FAILURE OF THE
* SOFTWARE COULD LEAD DIRECTLY TO DEATH, PERSONAL INJURY, OR SEVERE
* PHYSICAL OR ENVIRONMENTAL DAMAGE ("HIGH RISK ACTIVITIES"). AUTHOR
* SPECIFICALLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR
* HIGH RISK ACTIVITIES.
*/
import java.util.*; class RWNode {
static final int READER = 0;
static final int WRITER = 1;
Thread t;
int state;
int nAcquires;
RWNode(Thread t, int state) {
this.t = t;
this.state = state;
nAcquires = 0;
}
} public class RWLock {
private Vector waiters;
private int firstWriter() {
Enumeration e;
int index;
for (index = 0, e = waiters.elements();
e.hasMoreElements(); index++) {
RWNode node = (RWNode) e.nextElement();
if (node.state == RWNode.WRITER)
return index;
}
return Integer.MAX_VALUE;
}
private int getIndex(Thread t) {
Enumeration e;
int index;
for (index = 0, e = waiters.elements();
e.hasMoreElements(); index++) {
RWNode node = (RWNode) e.nextElement();
if (node.t == t)
return index;
}
return -1;
}
public RWLock() {
waiters = new Vector();
}
public synchronized void lockRead() {
RWNode node;
Thread me = Thread.currentThread();
int index = getIndex(me);
if (index == -1) {
node = new RWNode(me, RWNode.READER);
waiters.addElement(node);
}
else node = (RWNode) waiters.elementAt(index);
while (getIndex(me) > firstWriter()) {
try {
wait();
} catch (Exception e) {}
}
node.nAcquires++;
}
public synchronized void lockWrite() {
RWNode node;
Thread me = Thread.currentThread();
int index = getIndex(me);
if (index == -1) {
node = new RWNode(me, RWNode.WRITER);
waiters.addElement(node);
}
else {
node = (RWNode) waiters.elementAt(index);
if (node.state == RWNode.READER)
throw new IllegalArgumentException("Upgrade lock");
node.state = RWNode.WRITER;
}
while (getIndex(me) != 0) {
try {
wait();
} catch (Exception e) {}
}
node.nAcquires++;
}
public synchronized void unlock() {
RWNode node;
Thread me = Thread.currentThread();
int index;
index = getIndex(me);
if (index > firstWriter())
throw new IllegalArgumentException("Lock not held");
node = (RWNode) waiters.elementAt(index);
node.nAcquires--;
if (node.nAcquires == 0) {
waiters.removeElementAt(index);
notifyAll();
}
}
}
</source>
No synchronize
<source lang="java">
public class WithoutSync extends Object {
private static int nextSerialNum = 10001;
public static int getNextSerialNum() {
int sn = nextSerialNum;
try { Thread.sleep(1000); }
catch ( InterruptedException x ) { }
nextSerialNum++;
return sn;
}
private static void print(String msg) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + ": " + msg);
}
public static void main(String[] args) {
try {
Runnable r = new Runnable() {
public void run() {
print("getNextSerialNum()=" +
getNextSerialNum());
}
};
Thread threadA = new Thread(r, "threadA");
threadA.start();
Thread.sleep(1500);
Thread threadB = new Thread(r, "threadB");
threadB.start();
Thread.sleep(500);
Thread threadC = new Thread(r, "threadC");
threadC.start();
Thread.sleep(2500);
Thread threadD = new Thread(r, "threadD");
threadD.start();
} catch ( InterruptedException x ) {
// ignore
}
}
}
</source>
Object FIFO
<source lang="java">
public class ObjectFIFOTest extends Object {
private static void fullCheck(ObjectFIFO fifo) {
try {
// Sync"d to allow messages to print while
// condition is still true.
synchronized (fifo) {
while (true) {
fifo.waitUntilFull();
print("FULL");
fifo.waitWhileFull();
print("NO LONGER FULL");
}
}
} catch (InterruptedException ix) {
return;
}
}
private static void emptyCheck(ObjectFIFO fifo) {
try {
// Sync"d to allow messages to print while
// condition is still true.
synchronized (fifo) {
while (true) {
fifo.waitUntilEmpty();
print("EMPTY");
fifo.waitWhileEmpty();
print("NO LONGER EMPTY");
}
}
} catch (InterruptedException ix) {
return;
}
}
private static void consumer(ObjectFIFO fifo) {
try {
print("just entered consumer()");
for (int i = 0; i < 3; i++) {
synchronized (fifo) {
Object obj = fifo.remove();
print("DATA-OUT - did remove(), obj=" + obj);
}
Thread.sleep(3000);
}
synchronized (fifo) {
boolean resultOfWait = fifo.waitUntilEmpty(500);
print("did waitUntilEmpty(500), resultOfWait=" + resultOfWait
+ ", getSize()=" + fifo.getSize());
}
for (int i = 0; i < 3; i++) {
synchronized (fifo) {
Object[] list = fifo.removeAll();
print("did removeAll(), list.length=" + list.length);
for (int j = 0; j < list.length; j++) {
print("DATA-OUT - list[" + j + "]=" + list[j]);
}
}
Thread.sleep(100);
}
for (int i = 0; i < 3; i++) {
synchronized (fifo) {
Object[] list = fifo.removeAtLeastOne();
print("did removeAtLeastOne(), list.length=" + list.length);
for (int j = 0; j < list.length; j++) {
print("DATA-OUT - list[" + j + "]=" + list[j]);
}
}
Thread.sleep(1000);
}
while (!fifo.isEmpty()) {
synchronized (fifo) {
Object obj = fifo.remove();
print("DATA-OUT - did remove(), obj=" + obj);
}
Thread.sleep(1000);
}
print("leaving consumer()");
} catch (InterruptedException ix) {
return;
}
}
private static void producer(ObjectFIFO fifo) {
try {
print("just entered producer()");
int count = 0;
Object obj0 = new Integer(count);
count++;
synchronized (fifo) {
fifo.add(obj0);
print("DATA-IN - did add(), obj0=" + obj0);
boolean resultOfWait = fifo.waitUntilEmpty(500);
print("did waitUntilEmpty(500), resultOfWait=" + resultOfWait
+ ", getSize()=" + fifo.getSize());
}
for (int i = 0; i < 10; i++) {
Object obj = new Integer(count);
count++;
synchronized (fifo) {
fifo.add(obj);
print("DATA-IN - did add(), obj=" + obj);
}
Thread.sleep(1000);
}
Thread.sleep(2000);
Object obj = new Integer(count);
count++;
synchronized (fifo) {
fifo.add(obj);
print("DATA-IN - did add(), obj=" + obj);
}
Thread.sleep(500);
Integer[] list1 = new Integer[3];
for (int i = 0; i < list1.length; i++) {
list1[i] = new Integer(count);
count++;
}
synchronized (fifo) {
fifo.addEach(list1);
print("did addEach(), list1.length=" + list1.length);
}
Integer[] list2 = new Integer[8];
for (int i = 0; i < list2.length; i++) {
list2[i] = new Integer(count);
count++;
}
synchronized (fifo) {
fifo.addEach(list2);
print("did addEach(), list2.length=" + list2.length);
}
synchronized (fifo) {
fifo.waitUntilEmpty();
print("fifo.isEmpty()=" + fifo.isEmpty());
}
print("leaving producer()");
} catch (InterruptedException ix) {
return;
}
}
private static synchronized void print(String msg) {
System.out.println(Thread.currentThread().getName() + ": " + msg);
}
public static void main(String[] args) {
final ObjectFIFO fifo = new ObjectFIFO(5);
Runnable fullCheckRunnable = new Runnable() {
public void run() {
fullCheck(fifo);
}
};
Thread fullCheckThread = new Thread(fullCheckRunnable, "fchk");
fullCheckThread.setPriority(9);
fullCheckThread.setDaemon(true); // die automatically
fullCheckThread.start();
Runnable emptyCheckRunnable = new Runnable() {
public void run() {
emptyCheck(fifo);
}
};
Thread emptyCheckThread = new Thread(emptyCheckRunnable, "echk");
emptyCheckThread.setPriority(8);
emptyCheckThread.setDaemon(true); // die automatically
emptyCheckThread.start();
Runnable consumerRunnable = new Runnable() {
public void run() {
consumer(fifo);
}
};
Thread consumerThread = new Thread(consumerRunnable, "cons");
consumerThread.setPriority(7);
consumerThread.start();
Runnable producerRunnable = new Runnable() {
public void run() {
producer(fifo);
}
};
Thread producerThread = new Thread(producerRunnable, "prod");
producerThread.setPriority(6);
producerThread.start();
}
} class ObjectFIFO extends Object {
private Object[] queue;
private int capacity;
private int size;
private int head;
private int tail;
public ObjectFIFO(int cap) {
capacity = (cap > 0) ? cap : 1; // at least 1
queue = new Object[capacity];
head = 0;
tail = 0;
size = 0;
}
public int getCapacity() {
return capacity;
}
public synchronized int getSize() {
return size;
}
public synchronized boolean isEmpty() {
return (size == 0);
}
public synchronized boolean isFull() {
return (size == capacity);
}
public synchronized void add(Object obj) throws InterruptedException {
waitWhileFull();
queue[head] = obj;
head = (head + 1) % capacity;
size++;
notifyAll(); // let any waiting threads know about change
}
public synchronized void addEach(Object[] list) throws InterruptedException {
//
// You might want to code a more efficient
// implementation here ... (see ByteFIFO.java)
//
for (int i = 0; i < list.length; i++) {
add(list[i]);
}
}
public synchronized Object remove() throws InterruptedException {
waitWhileEmpty();
Object obj = queue[tail];
// don"t block GC by keeping unnecessary reference
queue[tail] = null;
tail = (tail + 1) % capacity;
size--;
notifyAll(); // let any waiting threads know about change
return obj;
}
public synchronized Object[] removeAll() throws InterruptedException {
//
// You might want to code a more efficient
// implementation here ... (see ByteFIFO.java)
//
Object[] list = new Object[size]; // use the current size
for (int i = 0; i < list.length; i++) {
list[i] = remove();
}
// if FIFO was empty, a zero-length array is returned
return list;
}
public synchronized Object[] removeAtLeastOne() throws InterruptedException {
waitWhileEmpty(); // wait for a least one to be in FIFO
return removeAll();
}
public synchronized boolean waitUntilEmpty(long msTimeout)
throws InterruptedException {
if (msTimeout == 0L) {
waitUntilEmpty(); // use other method
return true;
}
// wait only for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while (!isEmpty() && (msRemaining > 0L)) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or may have met condition,
// calc return value.
return isEmpty();
}
public synchronized void waitUntilEmpty() throws InterruptedException {
while (!isEmpty()) {
wait();
}
}
public synchronized void waitWhileEmpty() throws InterruptedException {
while (isEmpty()) {
wait();
}
}
public synchronized void waitUntilFull() throws InterruptedException {
while (!isFull()) {
wait();
}
}
public synchronized void waitWhileFull() throws InterruptedException {
while (isFull()) {
wait();
}
}
}
</source>
Operations that may seem safe are not, when threads are present
<source lang="java">
// : c13:SerialNumberChecker.java // Operations that may seem safe are not, // when threads are present. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. // Reuses storage so we don"t run out of memory:
class CircularSet {
private int[] array;
private int len;
private int index = 0;
public CircularSet(int size) {
array = new int[size];
len = size;
// Initialize to a value not produced
// by the SerialNumberGenerator:
for (int i = 0; i < size; i++)
array[i] = -1;
}
public synchronized void add(int i) {
array[index] = i;
// Wrap index and write over old elements:
index = ++index % len;
}
public synchronized boolean contains(int val) {
for (int i = 0; i < len; i++)
if (array[i] == val)
return true;
return false;
}
} public class SerialNumberChecker {
private static CircularSet serials = new CircularSet(1000);
static class SerialChecker extends Thread {
SerialChecker() {
start();
}
public void run() {
while (true) {
int serial = SerialNumberGenerator.nextSerialNumber();
if (serials.contains(serial)) {
System.out.println("Duplicate: " + serial);
System.exit(0);
}
serials.add(serial);
}
}
}
public static void main(String[] args) {
for (int i = 0; i < 10; i++)
new SerialChecker();
// Stop after 4 seconds:
new Timeout(4000, "No duplicates detected");
}
} ///:~
class SerialNumberGenerator {
private static volatile int serialNumber = 0;
public static int nextSerialNumber() {
return serialNumber++;
}
} ///:~ class Timeout extends java.util.Timer {
public Timeout(int delay, final String msg) {
super(true); // Daemon thread
schedule(new TimerTask() {
public void run() {
System.out.println(msg);
System.exit(0);
}
}, delay);
}
} ///:~
</source>
Read Write Lock
<source lang="java">
/*
* Copyright 2002 (C) TJDO. * All rights reserved. * * This software is distributed under the terms of the TJDO License version 1.0. * See the terms of the TJDO License in the documentation provided with this software. * * $Id: ReadWriteLock.java,v 1.5 2006/08/02 22:41:25 jackknifebarber Exp $ */
/**
* A simple read-write lock implementation. Multiple threads may lock using * readLock(), only one can lock using writeLock(). The caller is responsible * for coding a try-finally that ensures unlock() is called for every readLock() * and writeLock() call. * * <p>A ReadWriteLock is recursive; with one exception, a thread can re-lock an * object it already has locked. Multiple read locks can be acquired by the * same thread, as can multiple write locks. The exception however is that a * write lock cannot be acquired when a read lock is already held (to allow * this would cause deadlocks). * * <p>Successive lock calls from the same thread must be matched by an * equal number of unlock() calls. * * @author * @version $Revision: 1.5 $ */
public class ReadWriteLock {
private static final int WAIT_LOG_INTERVAL = 5000; /** A count for each thread indicating the number of read locks it holds. */ private ThreadLocal readLocksByThread; /** The number of read locks held across all threads. */ private int readLocks; /** The number of write locks held (by writeLockedBy). */ private int writeLocks; /** The thread holding the write lock(s), if any. */ private Thread writeLockedBy;
/**
* An object holding a per-thread read-lock count.
*/
private static class Count
{
public int value = 0;
}
/**
* Constructs read-write lock.
*/
public ReadWriteLock()
{
readLocksByThread = new ThreadLocal()
{
public Object initialValue()
{
return new Count();
}
};
readLocks = 0;
writeLocks = 0;
writeLockedBy = null;
}
/**
* Acquire a read lock. The calling thread will be suspended until no other
* thread holds a write lock.
*
* <p>If the calling thread already owns a write lock for the object a read
* lock is immediately acquired.
*
* @exception InterruptedException
* If the thread is interrupted while attempting to acquire the lock.
*/
public synchronized void readLock() throws InterruptedException
{
Thread me = Thread.currentThread();
Count myReadLocks = (Count)readLocksByThread.get();
if (writeLockedBy != me)
{
while (writeLocks > 0)
{
wait(WAIT_LOG_INTERVAL);
if (writeLocks > 0)
System.out.println("Still waiting for read lock on ");
}
}
++readLocks;
++myReadLocks.value;
}
/**
* Acquire a write lock. The calling thread will be suspended until no
* other thread holds a read or write lock.
*
* <p>This method cannot be called if the thread already owns a read lock on
* the same ReadWriteLock object, otherwise an
* IllegalStateException is thrown.
*
* @exception IllegalStateException
* If the thread already holds a read lock on the same object.
* @exception InterruptedException
* If the thread is interrupted while attempting to acquire the lock.
*/
public synchronized void writeLock() throws InterruptedException
{
Thread me = Thread.currentThread();
Count myReadLocks = (Count)readLocksByThread.get();
if (myReadLocks.value > 0)
throw new IllegalStateException("Thread already holds a read lock");
if (writeLockedBy != me)
{
while (writeLocks > 0 || readLocks > 0)
{
wait(WAIT_LOG_INTERVAL);
if (writeLocks > 0 || readLocks > 0)
System.out.println("Still waiting for write lock on ");
}
writeLockedBy = me;
}
++writeLocks;
}
/**
* Release a read or write lock. Must be called in a finally block after
* acquiring a lock.
*/
public synchronized void unlock()
{
Thread me = Thread.currentThread();
Count myReadLocks = (Count)readLocksByThread.get();
if (myReadLocks.value > 0)
{
--myReadLocks.value;
--readLocks;
}
else if (writeLockedBy == me)
{
if (writeLocks > 0)
{
if (--writeLocks == 0)
writeLockedBy = null;
}
}
notifyAll();
}
public String toString()
{
StringBuffer s = new StringBuffer(super.toString());
s.append(": readLocks = ").append(readLocks)
.append(", writeLocks = ").append(writeLocks)
.append(", writeLockedBy = ").append(writeLockedBy);
return s.toString();
}
}
</source>
Signaling
<source lang="java">
public class Signaling extends Object {
private BooleanLock readyLock;
public Signaling(BooleanLock readyLock) {
this.readyLock = readyLock;
Runnable r = new Runnable() {
public void run() {
try {
runWork();
} catch (Exception x) {
// in case ANY exception slips through
x.printStackTrace();
}
}
};
Thread internalThread = new Thread(r, "internal");
internalThread.start();
}
private void runWork() {
try {
print("about to wait for readyLock to be true");
readyLock.waitUntilTrue(0); // 0 - wait forever
print("readyLock is now true");
} catch (InterruptedException x) {
print("interrupted while waiting for readyLock " + "to become true");
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.err.println(name + ": " + msg);
}
public static void main(String[] args) {
try {
print("creating BooleanLock instance");
BooleanLock ready = new BooleanLock(false);
print("creating Signaling instance");
new Signaling(ready);
print("about to sleep for 3 seconds");
Thread.sleep(3000);
print("about to setValue to true");
ready.setValue(true);
print("ready.isTrue()=" + ready.isTrue());
} catch (InterruptedException x) {
x.printStackTrace();
}
}
} class BooleanLock extends Object {
private boolean value;
public BooleanLock(boolean initialValue) {
value = initialValue;
}
public BooleanLock() {
this(false);
}
public synchronized void setValue(boolean newValue) {
if (newValue != value) {
value = newValue;
notifyAll();
}
}
public synchronized boolean waitToSetTrue(long msTimeout)
throws InterruptedException {
boolean success = waitUntilFalse(msTimeout);
if (success) {
setValue(true);
}
return success;
}
public synchronized boolean waitToSetFalse(long msTimeout)
throws InterruptedException {
boolean success = waitUntilTrue(msTimeout);
if (success) {
setValue(false);
}
return success;
}
public synchronized boolean isTrue() {
return value;
}
public synchronized boolean isFalse() {
return !value;
}
public synchronized boolean waitUntilTrue(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(true, msTimeout);
}
public synchronized boolean waitUntilFalse(long msTimeout)
throws InterruptedException {
return waitUntilStateIs(false, msTimeout);
}
public synchronized boolean waitUntilStateIs(boolean state, long msTimeout)
throws InterruptedException {
if (msTimeout == 0L) {
while (value != state) {
wait(); // wait indefinitely until notified
}
// condition has finally been met
return true;
}
// only wait for the specified amount of time
long endTime = System.currentTimeMillis() + msTimeout;
long msRemaining = msTimeout;
while ((value != state) && (msRemaining > 0L)) {
wait(msRemaining);
msRemaining = endTime - System.currentTimeMillis();
}
// May have timed out, or may have met value,
// calculate return value.
return (value == state);
}
}
</source>
Simple Object FIFO
<source lang="java">
public class SimpleObjectFIFO extends Object {
private Object[] queue;
private int capacity;
private int size;
private int head;
private int tail;
public SimpleObjectFIFO(int cap) {
capacity = (cap > 0) ? cap : 1; // at least 1
queue = new Object[capacity];
head = 0;
tail = 0;
size = 0;
}
public synchronized int getSize() {
return size;
}
public synchronized boolean isFull() {
return (size == capacity);
}
public synchronized void add(Object obj) throws InterruptedException {
while (isFull()) {
wait();
}
queue[head] = obj;
head = (head + 1) % capacity;
size++;
notifyAll(); // let any waiting threads know about change
}
public synchronized Object remove() throws InterruptedException {
while (size == 0) {
wait();
}
Object obj = queue[tail];
queue[tail] = null; // don"t block GC by keeping unnecessary reference
tail = (tail + 1) % capacity;
size--;
notifyAll(); // let any waiting threads know about change
return obj;
}
public synchronized void printState() {
StringBuffer sb = new StringBuffer();
sb.append("SimpleObjectFIFO:\n");
sb.append(" capacity=" + capacity + "\n");
sb.append(" size=" + size);
if (isFull()) {
sb.append(" - FULL");
} else if (size == 0) {
sb.append(" - EMPTY");
}
sb.append("\n");
sb.append(" head=" + head + "\n");
sb.append(" tail=" + tail + "\n");
for (int i = 0; i < queue.length; i++) {
sb.append(" queue[" + i + "]=" + queue[i] + "\n");
}
System.out.print(sb);
}
public static void main(String[] args) {
try {
SimpleObjectFIFO fifo = new SimpleObjectFIFO(5);
fifo.printState();
fifo.add("S01");
fifo.printState();
fifo.add("S02");
fifo.printState();
fifo.add("S03");
fifo.printState();
Object obj = fifo.remove();
System.out.println("just removed obj=" + obj);
fifo.printState();
fifo.add("S04");
fifo.printState();
fifo.add("S05");
fifo.printState();
fifo.add("S06");
fifo.printState();
} catch (InterruptedException x) {
x.printStackTrace();
}
}
}
</source>
Static synchronize
<source lang="java">
public class StaticSync extends Object {
private static int nextSerialNum = 10001;
public static synchronized int getNextSerialNum() {
int sn = nextSerialNum;
try { Thread.sleep(1000); }
catch ( InterruptedException x ) { }
nextSerialNum++;
return sn;
}
private static void print(String msg) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + ": " + msg);
}
public static void main(String[] args) {
try {
Runnable r = new Runnable() {
public void run() {
print("getNextSerialNum()=" +
getNextSerialNum());
}
};
Thread threadA = new Thread(r, "threadA");
threadA.start();
Thread.sleep(1500);
Thread threadB = new Thread(r, "threadB");
threadB.start();
Thread.sleep(500);
Thread threadC = new Thread(r, "threadC");
threadC.start();
Thread.sleep(2500);
Thread threadD = new Thread(r, "threadD");
threadD.start();
} catch ( InterruptedException x ) {
// ignore
}
}
}
</source>
Static synchronized block
<source lang="java">
public class StaticBlock extends Object {
public static synchronized void staticA() {
System.out.println("entering staticA()");
try {
Thread.sleep(5000);
} catch (InterruptedException x) {
}
System.out.println("leaving staticA()");
}
public static void staticB() {
synchronized (StaticBlock.class) {
System.out.println("in staticB() : inside sync block");
try {
Thread.sleep(2000);
} catch (InterruptedException x) {
}
}
}
public static void main(String[] args) {
Runnable runA = new Runnable() {
public void run() {
StaticBlock.staticA();
}
};
Thread threadA = new Thread(runA, "A");
threadA.start();
try {
Thread.sleep(200);
} catch (InterruptedException x) {
}
Runnable runB = new Runnable() {
public void run() {
StaticBlock.staticB();
}
};
Thread threadB = new Thread(runB, "B");
threadB.start();
}
}
</source>
Synchronized Block demo
<source lang="java">
public class SyncBlock extends Object {
private Object longLock;
public SyncBlock() {
longLock = new Object();
}
public void doStuff() {
print("about to try to get exclusive access " + "to longLock");
synchronized (longLock) {
print("got exclusive access to longLock");
try {
Thread.sleep(10000);
} catch (InterruptedException x) {
}
print("about to relinquish exclusive access to " + "longLock");
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.err.println(name + ": " + msg);
}
private static Thread launch(final SyncBlock sb, String name) {
Runnable r = new Runnable() {
public void run() {
print("in run()");
sb.doStuff();
}
};
Thread t = new Thread(r, name);
t.start();
return t;
}
public static void main(String[] args) {
try {
SyncBlock sb = new SyncBlock();
Thread t1 = launch(sb, "T1");
Thread.sleep(500);
Thread t2 = launch(sb, "T2");
Thread t3 = launch(sb, "T3");
Thread.sleep(1000);
print("about to interrupt T2");
t2.interrupt();
print("just interrupted T2");
} catch (InterruptedException x) {
x.printStackTrace();
}
}
}
</source>
Synchronize method
<source lang="java">
public class OnlyOneInMethod extends Object {
private String objID;
public OnlyOneInMethod(String objID) {
this.objID = objID;
}
public synchronized void doStuff(int val) {
print("entering doStuff()");
int num = val * 2 + objID.length();
print("local variable num=" + num);
try {
Thread.sleep(2000);
} catch (InterruptedException x) {
}
print("leaving doStuff()");
}
public void print(String msg) {
threadPrint("objID=" + objID + " - " + msg);
}
public static void threadPrint(String msg) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + ": " + msg);
}
public static void main(String[] args) {
final OnlyOneInMethod ooim = new OnlyOneInMethod("obj1");
Runnable runA = new Runnable() {
public void run() {
ooim.doStuff(3);
}
};
Thread threadA = new Thread(runA, "threadA");
threadA.start();
try {
Thread.sleep(200);
} catch (InterruptedException x) {
}
Runnable runB = new Runnable() {
public void run() {
ooim.doStuff(7);
}
};
Thread threadB = new Thread(runB, "threadB");
threadB.start();
}
}
</source>
Synchronizing blocks instead of entire methods
<source lang="java">
// : c13:CriticalSection.java // Synchronizing blocks instead of entire methods. Also // demonstrates protection of a non-thread-safe class // with a thread-safe one. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. import java.util.ArrayList; import java.util.List; import java.util.Timer; import java.util.TimerTask; public class CriticalSection {
public static void main(String[] args) {
// Test the two different approaches:
final PairManipulator pm1 = new PairManipulator(new PairManager1()), pm2 = new PairManipulator(
new PairManager2());
new Timer(true).schedule(new TimerTask() {
public void run() {
System.out.println("pm1: " + pm1);
System.out.println("pm2: " + pm2);
System.exit(0);
}
}, 500); // run() after 500 milliseconds
}
} ///:~
class Pair { // Not thread-safe
private int x, y;
public Pair(int x, int y) {
this.x = x;
this.y = y;
}
public Pair() {
this(0, 0);
}
public int getX() {
return x;
}
public int getY() {
return y;
}
public void incrementX() {
x++;
}
public void incrementY() {
y++;
}
public String toString() {
return "x: " + x + ", y: " + y;
}
public class PairValuesNotEqualException extends RuntimeException {
public PairValuesNotEqualException() {
super("Pair values not equal: " + Pair.this);
}
}
// Arbitrary invariant -- both variables must be equal:
public void checkState() {
if (x != y)
throw new PairValuesNotEqualException();
}
} // Protect a Pair inside a thread-safe class: abstract class PairManager {
protected Pair p = new Pair();
private List storage = new ArrayList();
public synchronized Pair getPair() {
// Make a copy to keep the original safe:
return new Pair(p.getX(), p.getY());
}
protected void store() {
storage.add(getPair());
}
// A "template method":
public abstract void doTask();
} // Synchronize the entire method: class PairManager1 extends PairManager {
public synchronized void doTask() {
p.incrementX();
p.incrementY();
store();
}
} // Use a critical section: class PairManager2 extends PairManager {
public void doTask() {
synchronized (this) {
p.incrementX();
p.incrementY();
}
store();
}
} class PairManipulator extends Thread {
private PairManager pm;
private int checkCounter = 0;
private class PairChecker extends Thread {
PairChecker() {
start();
}
public void run() {
while (true) {
checkCounter++;
pm.getPair().checkState();
}
}
}
public PairManipulator(PairManager pm) {
this.pm = pm;
start();
new PairChecker();
}
public void run() {
while (true) {
pm.doTask();
}
}
public String toString() {
return "Pair: " + pm.getPair() + " checkCounter = " + checkCounter;
}
}
</source>
Synchronizing on another object
<source lang="java">
// : c13:SyncObject.java // Synchronizing on another object // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. class DualSynch {
private Object syncObject = new Object();
public synchronized void f() {
System.out.println("Inside f()");
// Doesn"t release lock:
try {
Thread.sleep(500);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println("Leaving f()");
}
public void g() {
synchronized (syncObject) {
System.out.println("Inside g()");
try {
Thread.sleep(500);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println("Leaving g()");
}
}
} public class SyncObject {
public static void main(String[] args) {
final DualSynch ds = new DualSynch();
new Thread() {
public void run() {
ds.f();
}
}.start();
ds.g();
}
} ///:~
</source>
Thread deadlock
<source lang="java">
public class Deadlock extends Object {
private String objID;
public Deadlock(String id) {
objID = id;
}
public synchronized void checkOther(Deadlock other) {
print("entering checkOther()");
try {
Thread.sleep(2000);
} catch (InterruptedException x) {
}
print("invoke "other.action()"");
other.action();
print("leaving checkOther()");
}
public synchronized void action() {
print("entering action()");
// simulate some work here
try {
Thread.sleep(500);
} catch (InterruptedException x) {
}
print("leaving action()");
}
public void print(String msg) {
threadPrint("objID=" + objID + " - " + msg);
}
public static void threadPrint(String msg) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + ": " + msg);
}
public static void main(String[] args) {
final Deadlock obj1 = new Deadlock("Thread 1");
final Deadlock obj2 = new Deadlock("Thread 2");
Runnable runA = new Runnable() {
public void run() {
obj1.checkOther(obj2);
}
};
Thread thread = new Thread(runA, "A");
thread.start();
try {
Thread.sleep(200);
} catch (InterruptedException x) {
}
Runnable runB = new Runnable() {
public void run() {
obj2.checkOther(obj1);
}
};
Thread threadB = new Thread(runB, "B");
threadB.start();
try {
Thread.sleep(5000);
} catch (InterruptedException x) {
}
threadPrint("finished sleeping");
threadPrint("about to interrupt() threadA");
thread.interrupt();
try {
Thread.sleep(1000);
} catch (InterruptedException x) {
}
threadPrint("about to interrupt() threadB");
threadB.interrupt();
try {
Thread.sleep(1000);
} catch (InterruptedException x) {
}
threadPrint("did that break the deadlock?");
}
}
</source>
Thread: Dining Philosophers
<source lang="java">
/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*
* Copyright (c) 2006 Sun Microsystems, Inc. All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* -Redistribution of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* -Redistribution in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* Neither the name of Sun Microsystems, Inc. or the names of contributors may
* be used to endorse or promote products derived from this software without
* specific prior written permission.
*
* This software is provided "AS IS," without a warranty of any kind. ALL
* EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
* ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
* OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MIDROSYSTEMS, INC. ("SUN")
* AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
* AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
* REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
* INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
* OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
* EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
*
* You acknowledge that this software is not designed, licensed or intended
* for use in the design, construction, operation or maintenance of any
* nuclear facility.
*/
import java.awt.Color; import java.awt.Dimension; import java.awt.GridBagConstraints; import java.awt.GridBagLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.net.URL; import javax.swing.BorderFactory; import javax.swing.ImageIcon; import javax.swing.JButton; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.JSlider; import javax.swing.event.ChangeEvent; import javax.swing.event.ChangeListener; public class DiningPhilosophers extends javax.swing.JApplet implements
ActionListener, ChangeListener {
private JButton stopStartButton = new JButton("start");
// delays can go from 0 to 10,000 milliseconds, initial value is 500
int grabDelay = 500;
private JSlider grabDelaySlider = new JSlider(JSlider.HORIZONTAL, 0, 100, 5);
private JLabel label = new JLabel(" 500 milliseconds");
private JPanel philosopherArea;
public ImageIcon[] imgs = new ImageIcon[3];
Chopstick[] chopsticks = new Chopstick[NUMPHILS];
String[] names = { "Arisduktle", "Dukrates", "Pythagoduke", "Duko",
"Dukimedes" };
static final int NUMPHILS = 5;
static final int HUNGRYDUKE = 0;
static final int RIGHTSPOONDUKE = 1;
static final int BOTHSPOONSDUKE = 2;
private int width = 0;
private int height = 0;
private double spacing;
private static final double MARGIN = 10.0f;
private Philosopher[] philosophers = new Philosopher[NUMPHILS];
public void init() {
imgs[HUNGRYDUKE] = new ImageIcon(getURL("images/hungryduke.gif"));
imgs[RIGHTSPOONDUKE] = new ImageIcon(
getURL("images/rightspoonduke.gif"));
imgs[BOTHSPOONSDUKE] = new ImageIcon(
getURL("images/bothspoonsduke.gif"));
width = imgs[HUNGRYDUKE].getIconWidth() + (int) (MARGIN * 2.0);
height = imgs[HUNGRYDUKE].getIconHeight() + (int) (MARGIN * 2.0);
spacing = width + MARGIN;
GridBagLayout gridBag = new GridBagLayout();
GridBagConstraints c = new GridBagConstraints();
JPanel contentPane = new JPanel();
contentPane.setLayout(gridBag);
philosopherArea = new JPanel(null);
philosopherArea.setBackground(Color.white);
Dimension preferredSize = createPhilosophersAndChopsticks();
philosopherArea.setBorder(BorderFactory.createCompoundBorder(
BorderFactory.createLoweredBevelBorder(), BorderFactory
.createEmptyBorder(5, 5, 5, 5)));
philosopherArea.setPreferredSize(preferredSize);
c.fill = GridBagConstraints.BOTH;
c.weighty = 1.0;
c.gridwidth = GridBagConstraints.REMAINDER; //end row
gridBag.setConstraints(philosopherArea, c);
contentPane.add(philosopherArea);
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1.0;
c.weighty = 0.0;
gridBag.setConstraints(stopStartButton, c);
contentPane.add(stopStartButton);
c.gridwidth = GridBagConstraints.RELATIVE; //don"t end row
c.weightx = 1.0;
c.weighty = 0.0;
gridBag.setConstraints(grabDelaySlider, c);
contentPane.add(grabDelaySlider);
c.weightx = 0.0;
c.gridwidth = GridBagConstraints.REMAINDER; //end row
gridBag.setConstraints(label, c);
contentPane.add(label);
contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
stopStartButton.addActionListener(this);
grabDelaySlider.addChangeListener(this);
}
public void actionPerformed(ActionEvent e) {
if (stopStartButton.getText().equals("stop/reset")) {
stopPhilosophers();
stopStartButton.setText("start");
} else if (stopStartButton.getText().equals("start")) {
startPhilosophers();
stopStartButton.setText("stop/reset");
}
}
public void stateChanged(ChangeEvent e) {
JSlider source = (JSlider) e.getSource();
grabDelay = source.getValue() * 100;
label.setText(String.valueOf(grabDelay + " milliseconds"));
}
public void startPhilosophers() {
for (int i = 0; i < NUMPHILS; i++)
philosophers[i].philThread.start();
}
public void stopPhilosophers() {
for (int i = 0; i < NUMPHILS; i++)
philosophers[i].philThread.interrupt();
}
public Dimension createPhilosophersAndChopsticks() {
double x, y;
double radius = 80.0;
double centerAdj = 85.0;
double radians;
Dimension preferredSize = new Dimension(0, 0);
/*
* for a straight line y = MARGIN;
*/
for (int i = 0; i < NUMPHILS; i++)
chopsticks[i] = new Chopstick();
for (int i = 0; i < NUMPHILS; i++) {
/*
* for a straight line x = i * spacing;
*/
radians = i * (2.0 * Math.PI / (double) NUMPHILS);
x = Math.sin(radians) * radius + centerAdj;
y = Math.cos(radians) * radius + centerAdj;
philosophers[i] = new Philosopher(this, i, imgs[HUNGRYDUKE]);
philosophers[i].setBounds((int) x, (int) y, width, height);
philosopherArea.add(philosophers[i]);
if ((int) x > preferredSize.width)
preferredSize.width = (int) x;
if ((int) y > preferredSize.height)
preferredSize.height = (int) y;
}
preferredSize.width += width;
preferredSize.height += height;
return preferredSize;
}
protected URL getURL(String filename) {
URL codeBase = getCodeBase();
URL url = null;
try {
url = new URL(codeBase, filename);
} catch (java.net.MalformedURLException e) {
System.out.println("Couldn"t create image: "
+ "badly specified URL");
return null;
}
return url;
}
} /*
* This class requires no changes from the 1.0 version. It"s kept here so the * rest of the example can compile. */
class Philosopher extends JLabel implements Runnable {
private Chopstick leftStick, rightStick;
private boolean sated;
private DiningPhilosophers parent;
private int position;
Thread philThread = null;
public Philosopher(DiningPhilosophers parent, int position, ImageIcon img) {
super(parent.names[position], img, JLabel.CENTER);
this.parent = parent;
this.position = position;
setVerticalTextPosition(JLabel.BOTTOM);
setHorizontalTextPosition(JLabel.CENTER);
// identify the chopsticks to my right and left
this.rightStick = parent.chopsticks[position];
if (position == 0) {
this.leftStick = parent.chopsticks[parent.NUMPHILS - 1];
} else {
this.leftStick = parent.chopsticks[position - 1];
}
// I"m hungry
this.sated = false;
philThread = new Thread(this);
}
public void run() {
try {
while (true) {
Thread.sleep((int) (Math.random() * parent.grabDelay));
setText(" ");
rightStick.grab();
setIcon(parent.imgs[parent.RIGHTSPOONDUKE]);
Thread.sleep((int) (Math.random() * parent.grabDelay));
leftStick.grab();
setIcon(parent.imgs[parent.BOTHSPOONSDUKE]);
Thread.sleep((int) (Math.random() * parent.grabDelay));
rightStick.release();
leftStick.release();
setIcon(parent.imgs[parent.HUNGRYDUKE]);
setText("Mmmm!");
sated = true;
Thread.sleep((int) (Math.random() * parent.grabDelay * 4));
sated = false;
}
} catch (java.lang.InterruptedException e) {
}
leftStick.releaseIfMine();
rightStick.releaseIfMine();
setIcon(parent.imgs[parent.HUNGRYDUKE]);
setText(parent.names[position]);
sated = false;
philThread = new Thread(this);
}
} class Chopstick {
Thread holder = null;
public synchronized void grab() throws InterruptedException {
while (holder != null)
wait();
holder = Thread.currentThread();
}
public synchronized void release() {
holder = null;
notify();
}
public synchronized void releaseIfMine() {
if (holder == Thread.currentThread())
holder = null;
notify();
}
}
</source>
Thread notify
<source lang="java">
import java.util.Collections; import java.util.LinkedList; import java.util.List; public class EarlyNotify extends Object {
private List list;
public EarlyNotify() {
list = Collections.synchronizedList(new LinkedList());
}
public String removeItem() throws InterruptedException {
synchronized (list) {
while (list.isEmpty()) {
print("wait()");
list.wait();
print("done with wait()");
}
String item = (String) list.remove(0);
return item;
}
}
public void addItem(String item) {
print("entering");
synchronized (list) {
list.add(item);
print("added: "" + item + """);
list.notifyAll();
print("notified");
}
print("leaving");
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
public static void main(String[] args) {
final EarlyNotify enf = new EarlyNotify();
Runnable runA = new Runnable() {
public void run() {
try {
String item = enf.removeItem();
print("returned: "" + item + """);
} catch (InterruptedException ix) {
print("interrupted!");
} catch (Exception x) {
print("threw an Exception!!!\n" + x);
}
}
};
Runnable runB = new Runnable() {
public void run() {
enf.addItem("Hello!");
}
};
try {
Thread threadA1 = new Thread(runA, "A");
threadA1.start();
Thread.sleep(500);
Thread threadA2 = new Thread(runA, "B");
threadA2.start();
Thread.sleep(500);
Thread threadB = new Thread(runB, "C");
threadB.start();
Thread.sleep(1000);
threadA1.interrupt();
threadA2.interrupt();
} catch (InterruptedException x) {
}
}
}
</source>
Threads join
<source lang="java">
public class JoinDemo extends Object {
public static Thread createThread(String name, long napTime) {
final long sleepTime = napTime;
Runnable r = new Runnable() {
public void run() {
try {
print("in run() - entering");
Thread.sleep(sleepTime);
} catch ( InterruptedException x ) {
print("interrupted!");
} finally {
print("in run() - leaving");
}
}
};
Thread t = new Thread(r, name);
t.start();
return t;
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
public static void main(String[] args) {
Thread[] t = new Thread[3];
t[0] = createThread("thread A", 2000);
t[1] = createThread("thread B", 1000);
t[2] = createThread("thread C", 3000);
for ( int i = 0; i < t.length; i++ ) {
try {
String idxStr = "thread[" + i + "]";
String name = "[" + t[i].getName() + "]";
print(idxStr + ".isAlive()=" +
t[i].isAlive() + " " + name);
print("about to do: " + idxStr +
".join() " + name);
long start = System.currentTimeMillis();
t[i].join(); // wait for the thread to die
long stop = System.currentTimeMillis();
print(idxStr + ".join() - took " +
( stop - start ) + " ms " + name);
} catch ( InterruptedException x ) {
print("interrupted waiting on #" + i);
}
}
}
}
</source>
Thread synchronization
<source lang="java">
public class TwoObjects extends Object {
private String objID;
public TwoObjects(String objID) {
this.objID = objID;
}
public synchronized void synchronizedMethod(int val) {
print("entering synchronized method()");
int num = val * 2 + objID.length();
print("in doStuff() - local variable num=" + num);
try {
Thread.sleep(2000);
} catch (InterruptedException x) {
}
print("leaving synchronized method");
}
public void print(String msg) {
threadPrint("objID=" + objID + " - " + msg);
}
public static void threadPrint(String msg) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + ": " + msg);
}
public static void main(String[] args) {
final TwoObjects obj1 = new TwoObjects("obj1");
final TwoObjects obj2 = new TwoObjects("obj2");
Runnable runA = new Runnable() {
public void run() {
obj1.synchronizedMethod(3);
}
};
Thread threadA = new Thread(runA, "threadA");
threadA.start();
try {
Thread.sleep(200);
} catch (InterruptedException x) {
}
Runnable runB = new Runnable() {
public void run() {
obj2.synchronizedMethod(7);
}
};
Thread threadB = new Thread(runB, "threadB");
threadB.start();
}
}
</source>
