Synchronization is used in multithreaded programming to prevent race conditions when multiple threads access shared resources. It is implemented using monitors in Java - only one thread can own a monitor at a time. The synchronized keyword is used to synchronize methods and blocks of code so only one thread can execute that code at a time. Daemon threads are low priority background threads that do not prevent the JVM from terminating when only daemon threads are running. Thread groups allow grouping of threads to manipulate them collectively.

1. OBJECT ORIENTEDPROGRAMMING
UNIT-IV
MULTITHREADING AND GENERIC
PROGRAMMING
Inter Thread Communication
Thread Synchronization
Thread Deamon

2. THREAD SYNCHRONIZATION
 Multi threaded Programming
 Pbm:
 When multiple threads try to access the same
resource
produce erroneous and unforeseen results.
 Soln:
 Synchronized keyword or method
 is used to provide mutually exclusive access to a
shared resource with multiple threads

4. GENERAL FORM OF SYNCHRONIZATION
// Only one thread can execute at a time.
// sync_object is a reference to an object whose lock
associates with the monitor.
// The code is said to be synchronized on the monitor object
synchronized(sync_object)
{
// Access shared variables and other shared resources
}

5.  synchronization is implemented in Java with a
concept called monitors.
 Only one thread can own a monitor at a given time.
 When a thread acquires a lock, it is said to have
entered the monitor.
 All other threads (need the resource) will be
suspended until the first thread exits the monitor.

6. // A Java program to demonstrate working of synchronized.
import java.io.*;
import java.util.*;
// A Class used to send a message
class Sender
{
public void send(String msg)
{
System.out.println("Sendingt" + msg );
try
{
Thread.sleep(1000);
}
catch (Exception e)
{
System.out.println("Thread interrupted.");
}
System.out.println("n" + msg + "Sent");
}
}

7. // Class for send a message using Threads
class ThreadedSend extends Thread
{
private String msg;
private Thread t;
Sender sender;
// Recieves a message object and a string message to be sent
ThreadedSend(String m, Sender obj)
{
msg = m;
sender = obj;
}
public void run()
{
// Only one thread can send a message at a time.
synchronized(sender)
{
sender.send(msg);
}
}
}

8. // Driver class
class SyncDemo
{
public static void main(String args[])
{
Sender snd = new Sender();
ThreadedSend S1 = new ThreadedSend( " Hi " , snd );
ThreadedSend S2 = new ThreadedSend( " Bye " , snd );
S1.start();
S2.start();
try
{
// wait for threads to end
S1.join(); S2.join();
}
catch(Exception e)
{ System.out.println("Interrupted"); }
}
}

9. OUTPUT
Sending Hi
Hi Sent
Sending Bye
Bye Sent

10. // A Java program to demonstrate working of synchronized.
import java.io.*;
import java.util.*;
// A Class used to send a message
class Sender
{
public synchronized void send(String msg)
{
System.out.println("Sendingt" + msg );
try
{
Thread.sleep(1000);
}
catch (Exception e)
{
System.out.println("Thread interrupted.");
}
System.out.println("n" + msg + "Sent");
}
}

11. JAVA MONITOR

12. INTER THREAD COMMUNICATION
 When multiple threads are running inside an
application, most of them will need to communicate
with each other in some form.
 Threads can communicate each other using
wait() :Causes current thread to release the
lock and wait until either another thread
invokes the notify()
notify():Wakes up a single thread that is
waiting on this object's monitor
notifyAll() :Wakes up all threads that are
waiting on this object's monitor

14. DAEMON THREAD
 Daemon thread is a low priority thread
 runs in background to perform tasks such as
garbage collection.
 Properties:
 JVM does not care whether Daemon
thread is running or not.
 It is an utmost low priority thread.
 JVM terminates itself when all user
threads finish their execution

15. METHODS
 void setDaemon(boolean status)
 used to mark the current thread as
daemon thread or user thread
 Example:
 tD.setDaemon(false) : tD is a user thread
 tD.setDaemon(True) : tD becomes a
Deamon Thread
 boolean isDaemon():
 used to check that current is daemon.
 It returns true if the thread is Daemon
else it returns false.

16. // Java program to demonstrate the usage of
// setDaemon() and isDaemon() method.
public class Daemon1 extends Thread
{
public Daemon1(String name){
super(name);
}
public void run()
{
// Checking whether the thread is Daemon or not
if(Thread.currentThread().isDaemon())
{
System.out.println(getName() + " is Daemon
thread");
}
else
{
System.out.println(getName() + " is User thread");
}
}

17. public static void main(String[] args)
{
Daemon1 t1 = new Daemon1("t1");
Daemon1 t2 = new Daemon1("t2");
Daemon1 t3 = new Daemon1("t3");
// Setting user thread t1 to Daemon
t1.setDaemon(true);
// starting first 2 threads
t1.start();
t2.start();
// Setting user thread t3 to Daemon
t3.setDaemon(true);
t3.start();
}
}

19. THREAD GROUP
 Thread groups provide a mechanism for collecting
multiple threads into a single object and
manipulating those threads all at once

20. CONSTRUCTOR
No. Constructor Description
1) ThreadGroup(String name) creates a thread group
with given name.
2) ThreadGroup(ThreadGroup
parent, String name)
creates a thread group
with given parent group
and name.
ThreadGroup tg1 = new ThreadGroup("Group A");
Thread t1 = new Thread(tg1,new MyRunnable(),"one");
Thread t2 = new Thread(tg1,new MyRunnable(),"two");
Thread t3 = new Thread(tg1,new MyRunnable(),"three");