📑 How to run two threads in java one after another
How to achieve this
- Thread A should first acquire lock on the object of ResourceLock
- instantiate synchronised lock
- Thread A should check whether flag==1
- if no , then wait
- if yes, then print A , and set flag=2 so that next turn is for thread 2 and then Notify all the waiting threads by using notifyAll method.
- once notified all the waiting threads will wake up that is in our case thread B and thread C but as the value of flag is 2 then only thread B is going to run and other threads will go to waiting state
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Code to run three threads one after the another one
/**
* threadTest
*/
public class threadTest {
public static void main(String[] args) {
ResourceLock lock=new ResourceLock();
Thread A = new ThreadA(lock);
Thread B=new ThreadB(lock);
Thread C=new ThreadC(lock);
A.start();
B.start();
C.start();
}
}
class ThreadA extends Thread {
ResourceLock lock;
ThreadA(ResourceLock lock) {
this.lock=lock;
}
@Override
public void run() {
synchronized(lock) {
if (lock.flag==1) {
System.out.println("A");
lock.flag=2;
lock.notifyAll();
}
else{
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
class ThreadB extends Thread {
ResourceLock lock;
ThreadB(ResourceLock lock2) {
this.lock=lock2;
}
@Override
public void run() {
synchronized(lock) {
if (lock.flag==2) {
System.out.println("B");
lock.flag=3;
lock.notifyAll();
}
else{
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
class ThreadC extends Thread {
ResourceLock lock;
ThreadC(ResourceLock lock) {
this.lock=lock;
}
@Override
public void run() {
synchronized(lock) {
if (lock.flag==3) {
System.out.println("C");
lock.flag=1;
lock.notifyAll();
}
else{
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
class ResourceLock {
public volatile int flag=1; //since we wants to start from flag 1
}
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