I implemented a code that maintains Serial communications to different ports.
However, the same code is working perfectly with USB port /dev/ttyUSB0, but not working on port /dev/ttyAMA0 (This port is operating if I use PI4J library)
Baud rates :
/dev/ttyAMA0 - 115200
/dev/ttyUSB0 - 9600
I'm running on a raspberry pi 3B with Java 9
What I am missing here?
This is my code:
public class JSerialComm extends BaseSerial
{
private SerialPort serial = null;
private Object recLock = new Object();
public JSerialComm()
{
super();
}
#Override
protected boolean checkIsClosed()
{
return this.serial == null || !this.serial.isOpen();
}
#Override
protected void registerToSerialEventListener()
{
this.serial.addDataListener(new SerialPortPacketListener()
{
#Override
public void serialEvent(SerialPortEvent event)
{
try
{
synchronized (recLock)
{
if(event.getSerialPort().bytesAvailable()>=getPacketSize())
{
final byte[] newData = new byte[getPacketSize()];
event.getSerialPort().readBytes(newData, getPacketSize());
notifyHandlers(newData);
}
}
}
catch(Exception e)
{
}
}
#Override
public int getListeningEvents()
{
return SerialPort.LISTENING_EVENT_DATA_AVAILABLE;
}
#Override
public int getPacketSize()
{
return MindoLifeJSerialComm.this.getPacketSize();
}
});
}
#Override
protected int sendByteToSerial(byte[] input) throws Exception
{
return sendByteToSerial(input,input.length);
}
#Override
protected void openPort(String portName, int baudRate) throws Exception
{
for (SerialPort port : SerialPort.getCommPorts())
{
if (portName.toLowerCase().endsWith(port.getSystemPortName().toLowerCase()))
{
serial = port;
}
}
if(serial == null)
{
throw new Exception("Couldn't find port " + portName );
}
serial.setBaudRate(baudRate);
serial.setComPortTimeouts(SerialPort.TIMEOUT_NONBLOCKING, 0, 0);
serial.setFlowControl(SerialPort.FLOW_CONTROL_DISABLED);
serial.setParity(SerialPort.NO_PARITY);
serial.setNumStopBits(SerialPort.ONE_STOP_BIT);
if (!serial.openPort())
{
throw new Exception("Couldn't open port " + portName + " opened with baud " + baudRate);
}
}
#Override
protected int sendByteToSerial(byte[] input, int length) throws Exception {
int res = serial.writeBytes(input, length);
// TODO:flush
return res;
}
#Override
protected void closePort() {
this.serial.closePort();
}
}
Base class:
public abstract class BaseSerial
{
HasSerialMessageHandler handler;
private Object recLock = new Object();
private int packetSize = 1;
private String portName;
protected final void notifyHandlers(byte[] newData)
{
if (handler != null)
{
handler.incoming(newData);
}
}
private Object writeLock = new Object();
public int write(byte[] input) throws Exception
{
return write(input, -1);
}
public int write(byte[] input, int length) throws Exception
{
int res = sendByteToSerial(input,length);
return res;
}
public void addListener(final HasSerialMessageHandler handler) throws TooManyListenersException
{
this.handler = handler;
registerToSerialEventListener();
}
public boolean isClosed()
{
return checkIsClosed();
}
public void open(String portName, int baudRate) throws Exception
{
this.portName = portName;
openPort(portName, baudRate);
Thread.sleep(1000);
}
public int getPacketSize()
{
return packetSize;
}
public void setPacketSize(int packetSize)
{
this.packetSize = packetSize;
}
public void close()
{
closePort();
}
public String getPortName()
{
return portName;
}
protected abstract boolean checkIsClosed();
protected abstract void registerToSerialEventListener();
protected abstract void openPort(String portName, int baudRate) throws Exception;
protected abstract int sendByteToSerial(byte[] input) throws Exception;
protected abstract int sendByteToSerial(byte[] input, int length) throws Exception;
protected abstract void closePort();
}
Init and Usage (For both ports):
public class Main
{
public static void main(String[] args)
{
BaseSerial serial = new JSerialComm ();
serial.setPacketSize(14);
serial.addListener(new HasSerialMessageHandler() {
#Override
public void incoming(final byte[] message)
{
if (message.length > 0)
{
sysout(message);
}
}
serial.open("/dev/ttyAMA0", 115200);
});
}
}
My /etc/inittab is set as the following:
1:2345:respawn:/sbin/getty --noclear 38400 tty1
2:23:respawn:/sbin/getty 38400 tty2
3:23:respawn:/sbin/getty 38400 tty3
4:23:respawn:/sbin/getty 38400 tty4
5:23:respawn:/sbin/getty 38400 tty5
6:23:respawn:/sbin/getty 38400 tty6
# Example how to put a getty on a serial line (for a terminal)
#
#T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100
#T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100
# Example how to put a getty on a modem line.
#
#T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3
#Spawn a getty on Raspberry Pi serial line
#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100
I'm trying to solve single consumer/producer problem using monitor in Java, and the code is as follows. When I run this code, it will finally get stucked. The most typical case is that the consumer calls wait(), and then the producer keeps producing but cannot notify the consumer (although it will call notify()). I don't know why it's happening. Java code:
import java.util.*;
class Monitor {
int length;
int size;
int begin, end;
int queue[];
private static Random randGenerator;
public Monitor() {}
public Monitor(int length) {
this.length = length;
this.size = 0;
begin = end = 0;
queue = new int[length];
randGenerator = new Random(10);
}
public synchronized void produce() throws InterruptedException {
while(size == length) {
System.out.println("Producer waiting");
wait();
}
int produced = randGenerator.nextInt();
size++;
queue[end] = produced;
end = (end + 1) % length;
System.out.println("Produce element " + produced + " size "+size);
// When size is not 1, no thread is blocked and therefore don't need to notify
if(size == 1) {
System.out.println("Notify consumer");
notify();
}
}
public synchronized void consume() throws InterruptedException {
while(size == 0) {
System.out.println("Consumer waiting, size " + size);
wait();
}
size--;
System.out.println("Consume element " + queue[begin] + " size " + size);
begin = (begin + 1) % length;
if(size == length - 1) {
System.out.println("Notify producer");
notify();
}
}
}
class Producer implements Runnable {
Monitor producer;
public Producer(Monitor m) {
producer = m;
}
#Override
public void run() {
producer = new Monitor();
System.out.println("Producer created");
try {
while(true) {
producer.produce();
}
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class Consumer implements Runnable {
Monitor consumer;
public Consumer(Monitor m) {
consumer = m;
}
#Override
public void run() {
System.out.println("Consumer created");
consumer = new Monitor();
try {
while(true) {
consumer.consume();
}
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public class monitorTest {
public static void main(String args[]) {
Monitor monitor = new Monitor(10);
Thread t1 = new Thread(new Producer(monitor));
Thread t2 = new Thread(new Consumer(monitor));
t1.start();
t2.start();
}
}
When the control of each thread enters the produce() or consume() methods, the size and length are both zero and hence both threads are waiting for the other to notify. Break this and your code will come out of the deadlock.
public synchronized void produce() throws InterruptedException {
while(size == length) { // size is 0 and length is 0; so wait
System.out.println("Producer waiting");
wait();
}
public synchronized void consume() throws InterruptedException {
while(size == 0) { // size is 0 so wait
System.out.println("Consumer waiting, size " + size);
wait();
}
This is happening because you have a default constructor which you are calling inside the run() method of your Producer and Consumer objects.
class Producer implements Runnable {
Monitor producer;
public Producer(Monitor m) {
producer = m;
}
#Override
public void run() {
producer = new Monitor(); // REMOVE THIS
class Consumer implements Runnable {
Monitor consumer;
public Consumer(Monitor m) {
consumer = m;
}
#Override
public void run() {
System.out.println("Consumer created");
consumer = new Monitor(); // AND REMOVE THIS
Hope this helps!
I am reading this page about coroutines in Python and this Wikipedia page. I saw that there are a few libraries in Java implementing coroutines.
My question is: is there any known reason why the Java designers decided not to implement coroutines so far and is there any plan to include it in a future version of Java?
Thanks.
Actually the concept of a co-routine was the first design of the Java threading system. The wait/notify mechanism is a simplistic form of co-routine where notify is equivalent to yield etc.
Since then much has been done, particularly to make structures thread-safe rather than algorithms. This derives from the realization that it is not the code that must synchronize/yield but the data structure used to communicate between the threads that must be thread-safe.
Project Loom
Continuations and Coroutines will come to Java in the nearer future and they’ll be called virtual threads (also referred to as fibers). There’s a project called Loom:
Project Loom is intended to explore, incubate and deliver Java VM features and APIs built on top of them for the purpose of supporting easy-to-use, high-throughput lightweight concurrency and new programming models on the Java platform. This is accomplished by the addition of the following constructs:
Virtual threads
Delimited continuations
Tail-call elimination
Further reading: https://cr.openjdk.java.net/~rpressler/loom/Loom-Proposal.html
To quote that document:
It is the goal of this project to add a public delimited continuation (or coroutine) construct to the Java platform. However, this goal is secondary to fibers …
Preliminary builds of Project Loom are available now, based on early-access Java 16.
On the "are there any plans ..." part of the question, the answer is:
Not at this stage
The JEP list (http://openjdk.java.net/jeps/0) does not make any mention of coroutines. The list covers features added in Java 8, added or targeted for Java 9, or proposed for future releases.
Interestingly, there was an RFE submitted in March 2013 (https://bugs.openjdk.java.net/browse/JDK-8029988). The RFE only got one vote, and it was closed 9 months with the suggestion to submit a JEP. Nobody has bothered to take the idea any further, which to me is telling.
It's synced with Java 15 build 7.
Link
There's an another choice is here for Java6+
A pythonic coroutine implementation:
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
class CorRunRAII {
private final List<WeakReference<? extends CorRun>> resources = new ArrayList<>();
public CorRunRAII add(CorRun resource) {
if (resource == null) {
return this;
}
resources.add(new WeakReference<>(resource));
return this;
}
public CorRunRAII addAll(List<? extends CorRun> arrayList) {
if (arrayList == null) {
return this;
}
for (CorRun corRun : arrayList) {
add(corRun);
}
return this;
}
#Override
protected void finalize() throws Throwable {
super.finalize();
for (WeakReference<? extends CorRun> corRunWeakReference : resources) {
CorRun corRun = corRunWeakReference.get();
if (corRun != null) {
corRun.stop();
}
}
}
}
class CorRunYieldReturn<ReceiveType, YieldReturnType> {
public final AtomicReference<ReceiveType> receiveValue;
public final LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue;
CorRunYieldReturn(AtomicReference<ReceiveType> receiveValue, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
this.receiveValue = receiveValue;
this.yieldReturnValue = yieldReturnValue;
}
}
interface CorRun<ReceiveType, YieldReturnType> extends Runnable, Callable<YieldReturnType> {
boolean start();
void stop();
void stop(final Throwable throwable);
boolean isStarted();
boolean isEnded();
Throwable getError();
ReceiveType getReceiveValue();
void setResultForOuter(YieldReturnType resultForOuter);
YieldReturnType getResultForOuter();
YieldReturnType receive(ReceiveType value);
ReceiveType yield();
ReceiveType yield(YieldReturnType value);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another);
<TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value);
}
abstract class CorRunSync<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private ReceiveType receiveValue;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList = new ArrayList<>();
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Throwable error;
private YieldReturnType resultForOuter;
#Override
public boolean start() {
boolean isStarted = this.isStarted.getAndSet(true);
if ((! isStarted)
&& (! isEnded())) {
receive(null);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(Throwable throwable) {
isEnded.set(true);
if (throwable != null) {
error = throwable;
}
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
child.stop();
}
}
}
#Override
public boolean isStarted() {
return isStarted.get();
}
#Override
public boolean isEnded() {
return isEnded.get();
}
#Override
public Throwable getError() {
return error;
}
#Override
public ReceiveType getReceiveValue() {
return receiveValue;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter = resultForOuter;
}
#Override
public YieldReturnType getResultForOuter() {
return resultForOuter;
}
#Override
public synchronized YieldReturnType receive(ReceiveType value) {
receiveValue = value;
run();
return getResultForOuter();
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(YieldReturnType value) {
resultForOuter = value;
return receiveValue;
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(CorRun<TargetReceiveType, TargetYieldReturnType> another, TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
boolean isStarted = another.start();
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
return another.receive(value);
}
}
#Override
public void run() {
try {
this.call();
}
catch (Exception e) {
e.printStackTrace();
stop(e);
return;
}
}
}
abstract class CorRunThread<ReceiveType, YieldReturnType> implements CorRun<ReceiveType, YieldReturnType> {
private final ExecutorService childExecutorService = newExecutorService();
private ExecutorService executingOnExecutorService;
private static final CorRunYieldReturn DUMMY_COR_RUN_YIELD_RETURN = new CorRunYieldReturn(new AtomicReference<>(null), new LinkedBlockingDeque<AtomicReference>());
private final CorRun<ReceiveType, YieldReturnType> self;
public final List<WeakReference<CorRun>> potentialChildrenCoroutineList;
private CorRunYieldReturn<ReceiveType, YieldReturnType> lastCorRunYieldReturn;
private final LinkedBlockingDeque<CorRunYieldReturn<ReceiveType, YieldReturnType>> receiveQueue;
// Outside
private AtomicBoolean isStarted = new AtomicBoolean(false);
private AtomicBoolean isEnded = new AtomicBoolean(false);
private Future<YieldReturnType> future;
private Throwable error;
private final AtomicReference<YieldReturnType> resultForOuter = new AtomicReference<>();
CorRunThread() {
executingOnExecutorService = childExecutorService;
receiveQueue = new LinkedBlockingDeque<>();
potentialChildrenCoroutineList = new ArrayList<>();
self = this;
}
#Override
public void run() {
try {
self.call();
}
catch (Exception e) {
stop(e);
return;
}
stop();
}
#Override
public abstract YieldReturnType call();
#Override
public boolean start() {
return start(childExecutorService);
}
protected boolean start(ExecutorService executorService) {
boolean isStarted = this.isStarted.getAndSet(true);
if (!isStarted) {
executingOnExecutorService = executorService;
future = (Future<YieldReturnType>) executingOnExecutorService.submit((Runnable) self);
}
return isStarted;
}
#Override
public void stop() {
stop(null);
}
#Override
public void stop(final Throwable throwable) {
if (throwable != null) {
error = throwable;
}
isEnded.set(true);
returnYieldValue(null);
// Do this for making sure the coroutine has checked isEnd() after getting a dummy value
receiveQueue.offer(DUMMY_COR_RUN_YIELD_RETURN);
for (WeakReference<CorRun> weakReference : potentialChildrenCoroutineList) {
CorRun child = weakReference.get();
if (child != null) {
if (child instanceof CorRunThread) {
((CorRunThread)child).tryStop(childExecutorService);
}
}
}
childExecutorService.shutdownNow();
}
protected void tryStop(ExecutorService executorService) {
if (this.executingOnExecutorService == executorService) {
stop();
}
}
#Override
public boolean isEnded() {
return isEnded.get() || (
future != null && (future.isCancelled() || future.isDone())
);
}
#Override
public boolean isStarted() {
return isStarted.get();
}
public Future<YieldReturnType> getFuture() {
return future;
}
#Override
public Throwable getError() {
return error;
}
#Override
public void setResultForOuter(YieldReturnType resultForOuter) {
this.resultForOuter.set(resultForOuter);
}
#Override
public YieldReturnType getResultForOuter() {
return this.resultForOuter.get();
}
#Override
public YieldReturnType receive(ReceiveType value) {
LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue = new LinkedBlockingDeque<>();
offerReceiveValue(value, yieldReturnValue);
try {
AtomicReference<YieldReturnType> takeValue = yieldReturnValue.take();
return takeValue == null ? null : takeValue.get();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
#Override
public ReceiveType yield() {
return yield(null);
}
#Override
public ReceiveType yield(final YieldReturnType value) {
returnYieldValue(value);
return getReceiveValue();
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another) {
return yieldFrom(another, null);
}
#Override
public <TargetReceiveType, TargetYieldReturnType> TargetYieldReturnType yieldFrom(final CorRun<TargetReceiveType, TargetYieldReturnType> another, final TargetReceiveType value) {
if (another == null || another.isEnded()) {
throw new RuntimeException("Call null or isEnded coroutine");
}
boolean isStarted = false;
potentialChildrenCoroutineList.add(new WeakReference<CorRun>(another));
synchronized (another) {
if (another instanceof CorRunThread) {
isStarted = ((CorRunThread)another).start(childExecutorService);
}
else {
isStarted = another.start();
}
boolean isJustStarting = ! isStarted;
if (isJustStarting && another instanceof CorRunSync) {
return another.getResultForOuter();
}
TargetYieldReturnType send = another.receive(value);
return send;
}
}
#Override
public ReceiveType getReceiveValue() {
setLastCorRunYieldReturn(takeLastCorRunYieldReturn());
return lastCorRunYieldReturn.receiveValue.get();
}
protected void returnYieldValue(final YieldReturnType value) {
CorRunYieldReturn<ReceiveType, YieldReturnType> corRunYieldReturn = lastCorRunYieldReturn;
if (corRunYieldReturn != null) {
corRunYieldReturn.yieldReturnValue.offer(new AtomicReference<>(value));
}
}
protected void offerReceiveValue(final ReceiveType value, LinkedBlockingDeque<AtomicReference<YieldReturnType>> yieldReturnValue) {
receiveQueue.offer(new CorRunYieldReturn(new AtomicReference<>(value), yieldReturnValue));
}
protected CorRunYieldReturn<ReceiveType, YieldReturnType> takeLastCorRunYieldReturn() {
try {
return receiveQueue.take();
} catch (InterruptedException e) {
e.printStackTrace();
}
return null;
}
protected void setLastCorRunYieldReturn(CorRunYieldReturn<ReceiveType,YieldReturnType> lastCorRunYieldReturn) {
this.lastCorRunYieldReturn = lastCorRunYieldReturn;
}
protected ExecutorService newExecutorService() {
return Executors.newCachedThreadPool(getThreadFactory());
}
protected ThreadFactory getThreadFactory() {
return new ThreadFactory() {
#Override
public Thread newThread(final Runnable runnable) {
Thread thread = new Thread(runnable);
thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
#Override
public void uncaughtException(Thread thread, Throwable throwable) {
throwable.printStackTrace();
if (runnable instanceof CorRun) {
CorRun self = (CorRun) runnable;
self.stop(throwable);
thread.interrupt();
}
}
});
return thread;
}
};
}
}
Now you can use pythonic coroutines in this way
(e.g. fibonacci numbers)
Thread Version:
class Fib extends CorRunThread<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
do {
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
// A pythonic "yield", i.e., it returns `a` to the caller and waits `times` value from the next caller
times = yield(a);
} while (! isEnded());
setResultForOuter(Integer.MAX_VALUE);
return getResultForOuter();
}
}
class MainRun extends CorRunThread<String, String> {
#Override
public String call() {
// The fib coroutine would be recycled by its parent
// (no requirement to call its start() and stop() manually)
// Otherwise, if you want to share its instance and start/stop it manually,
// please start it before being called by yieldFrom() and stop it in the end.
Fib fib = new Fib();
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
// A pythonic "yield from", i.e., it calls fib with `i` parameter and waits for returned value as `current`
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
setResultForOuter(result);
return result;
}
}
Sync(non-thread) version:
class Fib extends CorRunSync<Integer, Integer> {
#Override
public Integer call() {
Integer times = getReceiveValue();
int a = 1, b = 1;
for (int i = 0; times != null && i < times; i++) {
int temp = a + b;
a = b;
b = temp;
}
yield(a);
return getResultForOuter();
}
}
class MainRun extends CorRunSync<String, String> {
#Override
public String call() {
CorRun<Integer, Integer> fib = null;
try {
fib = new Fib();
} catch (Exception e) {
e.printStackTrace();
}
String result = "";
Integer current;
int times = 10;
for (int i = 0; i < times; i++) {
current = yieldFrom(fib, i);
if (fib.getError() != null) {
throw new RuntimeException(fib.getError());
}
if (current == null) {
continue;
}
if (i > 0) {
result += ",";
}
result += current;
}
stop();
setResultForOuter(result);
if (Utils.isEmpty(result)) {
throw new RuntimeException("Error");
}
return result;
}
}
Execution(Both versions will work):
// Run the entry coroutine
MainRun mainRun = new MainRun();
mainRun.start();
// Wait for mainRun ending for 5 seconds
long startTimestamp = System.currentTimeMillis();
while(!mainRun.isEnded()) {
if (System.currentTimeMillis() - startTimestamp > TimeUnit.SECONDS.toMillis(5)) {
throw new RuntimeException("Wait too much time");
}
}
// The result should be "1,1,2,3,5,8,13,21,34,55"
System.out.println(mainRun.getResultForOuter());
I have a problem with possible deadlock in "producer - consumer task".
Everything should be working in following way:
Producer should generate and add int[] arrays to collection
Consumer should take those arrays, put them to second collection and print in output
In debbug mode I have noticed that after a while both taks are suspended on this.wait(); method.
Could you help me and explain what is wrong with this code? :)
Thanks!
Producer task class
public class ProducerTask extends Thread{
private static final Object bufforLock = new Object();
private static LinkedList<Integer[]> buffor;
public ProducerTask(){
if(buffor == null)
buffor = new LinkedList<>();
this.setName("#ProducerTask");
}
#Override
public void run() {
synchronized (this) {
try {
for (int i = 0; i < 100; i++) {
while (isBufforFull()) {
System.err.println("ProducerTask is waiting");
this.wait();
}
Integer[] randomIntArray = getRandomIntArray();
addToBuffor(randomIntArray);
}
}
catch (InterruptedException ex) {
}
}
}
public static void removeLast(){
synchronized(bufforLock){
buffor.removeLast();
bufforLock.notifyAll();
}
}
public static Integer[] getLast(){
synchronized(bufforLock){
return buffor.getLast();
}
}
public static boolean isBufforFull(){
synchronized(bufforLock){
return buffor.size() == 10;
}
}
public static boolean isBufforEmpty(){
synchronized(bufforLock){
return buffor.isEmpty();
}
}
public static void addToBuffor(Integer[] array){
synchronized(bufforLock){
buffor.addFirst(array);
bufforLock.notifyAll();
}
}
public static LinkedList<Integer[]> getBuffor(){
synchronized(bufforLock){
return buffor;
}
}
private Integer[] getRandomIntArray(){
int maxSize = 10;
Integer[] array = new Integer[maxSize];
for(int i = 0 ; i < maxSize ; i++){
int value = (int) (Math.random() * 100);
array[i] = Integer.valueOf(value);
}
return array;
}
}
Consumer task class
public class ConsumerTask extends Thread {
private static LinkedList<Integer[]> buffor;
public ConsumerTask() {
if (buffor == null) {
buffor = new LinkedList<>();
}
this.setName("#ConsumerTask");
}
#Override
public void run() {
synchronized (this) {
try {
while (true) {
while (ProducerTask.isBufforEmpty()) {
System.err.println("ConsumerTask is waiting");
this.wait();
}
Integer[] array = ProducerTask.getLast();
this.arraySortByInserting(array);
this.buffor.addFirst(array);
ProducerTask.removeLast();
}
}
catch (InterruptedException ex) {}
}
}
private Integer[] arraySortByInserting(Integer[] aArrayToSort) {
if(aArrayToSort == null || aArrayToSort.length == 0)
return null;
this.printArray(aArrayToSort, "Array before sorting");
for (int i = 1; i < aArrayToSort.length; i++) {
int intValue = aArrayToSort[i];
int j = i;
while ((j > 0) && (aArrayToSort[j - 1] > intValue)) {
aArrayToSort[j] = aArrayToSort[j - 1];
j--;
}
aArrayToSort[j] = intValue;
}
this.printArray(aArrayToSort, "Array after sorting");
return aArrayToSort;
}
private void printArray(Integer[] aArray, String aMessage) {
System.out.print(aMessage + " [");
for (int intElement : aArray) {
System.out.print(intElement + " ");
}
System.out.print("]");
System.out.println();
}
}
You need a common object which would be used for inter thread communication.
Right now you are using this as object on which you get lock on and you notify on bufferLock in producer thread and same applies for consumer thread.
Remember both are two different instances and both successfully obtain lock on individual objects and then both enters wait state.
I am trying to implement Bully Algorithm in Java using threads.
Here is the code which I have written.
package newbully;
public class NewBully {
public static void main(String[] args) {
int total_processes = 4;
Thread1[] t = new Thread1[total_processes];
for (int i = 0; i < total_processes; i++) {
t[i] = new Thread1(new Process(i+1, i+1), total_processes);
}
try {
Election.initialElection(t);
} catch (Exception e) {
System.out.println("Possibly you are using null references in array");
}
for (int i = 0; i < total_processes; i++) {
new Thread(t[i]).start();
}
}
}
package newbully;
public class Election {
private static boolean pingFlag = false;
private static boolean electionFlag = false;
private static boolean messageFlag = false;
public static boolean isMessageFlag() {
return messageFlag;
}
public static void setMessageFlag(boolean messageFlag) {
Election.messageFlag = messageFlag;
}
public static boolean isPingFlag() {
return pingFlag;
}
public static void setPingFlag(boolean pingFlag) {
Election.pingFlag = pingFlag;
}
public static boolean isElectionFlag() {
return electionFlag;
}
public static void setElectionFlag(boolean electionFlag) {
Election.electionFlag = electionFlag;
}
public static void initialElection(Thread1[] t) {
Process temp = new Process(-1, -1);
for (int i = 0; i < t.length; i++) {
if (temp.getPriority() < t[i].getProcess().getPriority()) {
temp = t[i].getProcess();
}
}
t[temp.pid - 1].getProcess().CoOrdinatorFlag = true;
}
}
package newbully;
public class Process {
int pid;
boolean downflag,CoOrdinatorFlag;
public boolean isCoOrdinatorFlag() {
return CoOrdinatorFlag;
}
public void setCoOrdinatorFlag(boolean isCoOrdinator) {
this.CoOrdinatorFlag = isCoOrdinator;
}
int priority;
public boolean isDownflag() {
return downflag;
}
public void setDownflag(boolean downflag) {
this.downflag = downflag;
}
public int getPid() {
return pid;
}
public void setPid(int pid) {
this.pid = pid;
}
public int getPriority() {
return priority;
}
public void setPriority(int priority) {
this.priority = priority;
}
public Process() {
}
public Process(int pid, int priority) {
this.pid = pid;
this.downflag = false;
this.priority = priority;
this.CoOrdinatorFlag = false;
}
}
package newbully;
import java.util.*;
import java.io.*;
import java.net.*;
public class Thread1 implements Runnable {
private Process process;
private int total_processes;
ServerSocket[] sock;
Random r;
public Process getProcess() {
return process;
}
public void setProcess(Process process) {
this.process = process;
}
public Thread1(Process process, int total_processes) {
this.process = process;
this.total_processes = total_processes;
this.r = new Random();
this.sock = new ServerSocket[total_processes];
}
private void recovery() {
}
synchronized private void pingCoOrdinator() {
try {
if (Election.isPingFlag()) {
wait();
}
if (!Election.isElectionFlag()) {
Election.setPingFlag(true);
System.out.println("Process[" + this.process.getPid() + "]: Are you alive?");
Socket outgoing = new Socket(InetAddress.getLocalHost(), 12345);
outgoing.close();
Election.setPingFlag(false);
notifyAll();
}
} catch (Exception ex) {
//Initiate Election
System.out.println("process[" + this.process.getPid() + "]: -> Co-Ordinator is down\nInitiating Election");
Election.setElectionFlag(true);
Election.setPingFlag(false);
notifyAll();
}
}
synchronized private void executeJob() {
int temp = r.nextInt(20);
for (int i = 0; i <= temp; i++) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
System.out.println("Error Executing Thread:" + process.getPid());
System.out.println(e.getMessage());
}
}
}
synchronized private boolean sendMessage() {
boolean response = false;
int i = 0;
try {
if (Election.isMessageFlag()) {
wait();
}
Election.setMessageFlag(true);
for (i = this.process.getPid() + 1; i <= this.total_processes; i++) {
try {
Socket electionMessage = new Socket(InetAddress.getLocalHost(), 10000 + i);
System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "] responded to election message successfully");
electionMessage.close();
response = true;
} catch (Exception ex) {
System.out.println("Process[" + this.process.getPid() + "] -> Process[" + i + "] did not respond to election message");
}
}
Election.setMessageFlag(false);
notifyAll();
} catch (Exception ex1) {
System.out.println(ex1.getMessage());
}
return response;
}
synchronized private void serve() {
try {
//service counter
ServerSocket s = new ServerSocket(12345);
for (int counter = 0; counter <= 10; counter++) {
Socket incoming = s.accept();
System.out.println("Process[" + this.process.getPid() + "]:Yes");
Scanner scan = new Scanner(incoming.getInputStream());
PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
if (scan.hasNextLine()) {
if (scan.nextLine().equals("Who is the co-ordinator?")) {
System.out.print("Process[" + this.process.getPid() + "]:");
out.println(this.process);
}
}
if (counter == 10) {//after serving 10 requests go down
this.process.setCoOrdinatorFlag(false);
this.process.setDownflag(true);
try {
incoming.close();
s.close();
sock[this.process.getPid() - 1].close();
Thread.sleep((this.r.nextInt(10) + 1) * 50000);//going down
recovery();
} catch (InterruptedException e) {
System.out.println(e.getMessage());
}
}
}
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
}
#Override
public void run() {
try {
sock[this.process.getPid() - 1] = new ServerSocket(10000 + this.process.getPid());
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
while (true) {
if (process.isCoOrdinatorFlag()) {
//serve other processes
serve();
} else {
while (true) {
//Execute some task
executeJob();
//Ping the co-ordinator
pingCoOrdinator();
if (Election.isElectionFlag()) {
if (!sendMessage()) {//elect self as co-ordinator
System.out.println("New Co-Ordinator: Process[" + this.process.getPid() + "]");
this.process.setCoOrdinatorFlag(true);
Election.setElectionFlag(false);
break;
}
}
}
}
}
}
}
When I am trying to execute the code out of the 4 threads which I have created some threads are waiting premanently using wait() call. They are not being notified by notifyAll(). Can anyone suggest why this is happening?
Each thread is calling wait() on itself (on its own Thread1 instance). That means that when you call notifyAll() on that same Thread1 instance, only the single Thread1 that is waiting it will be notified, and not all the other threads.
What you have to do is make all your Thread1 objects call wait() on a single, common object, and also call notifyAll() on that same object.
Ofcourse you have to synchronize on the common object when you call wait() or notifyAll() on it; if you don't do that, you'll get an IllegalMonitorStateException.
// Object to be used as a lock; pass this to all Thread1 instances
Object lock = new Object();
// Somewhere else in your code
synchronized (lock) {
lock.wait();
}
// Where you want to notify
synchronized (lock) {
lock.notifyAll();
}
Both notify() (or notifyAll()) and wait() must be written into synchronized block on the same monitor.
For example:
synchronized(myLock) {
wait();
}
..................
synchronized(myLock) {
notifyAll();
}