Cadence Inc Interview Question for Principal Software Engineers


Country: United States
Interview Type: In-Person




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0
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This is how I'd do it,
use counting semaphores for resources
thread will acquire required resources and process for a certain amount of time
release after the sleep
Note : variable time , t and sleep(t) have been used for fine tuning the start time of threads
and would not be required if its too much trouble

public class EgThread {
    private static final Semaphore sem = new Semaphore(10);
    private static final long time = System.currentTimeMillis() + 5000; // not required
    
    public static void main(String[] args) {
        MyThread[] threads = new MyThread[5];
        
        for (int i = 0; i < 5; i++) {
            threads[i] = new MyThread(String.valueOf(i + 1));
        }
        for (int i = 0; i < 5; i++)
            threads[i].start();
        
        try {
            for (int i = 0; i < 5; i++)
                threads[i].join();
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    
    static class MyThread extends Thread {
        String name;
        
        MyThread(String name) {
            this.name = name;
        }
        
        @Override
        public void run() {
            try {
                long t = time - System.currentTimeMillis(); // not required
                sleep(t); //---------------------------------- not required
                for (int i = 0; i < 10; i++) {
                    int req = (int) (6 * Math.random()) + 1;
                    System.out.println("T[" + name + "] run : " + (i + 1) + " asks for " + req + " resources");
                    sem.acquire(req);
                    System.out.println("T[" + name + "] run : " + (i + 1) + " acquires " + req + " resources");
                    sleep((long) (500 * Math.random()) + 200);
                    System.out.println("T[" + name + "] run : " + (i + 1) + " releases " + req + " resources");
                    sem.release(req);
                }
            }
            catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

- PeyarTheriyaa November 11, 2018 | Flag Reply
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This is a good start, but it does not satisfy the "in order" requirement. It's a greedy algorithm that would starve large requests.

- Anonymous March 28, 2019 | Flag
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of 0 vote

Hi, Please share your answers ? will try our level best but could not get.

- Dowlath June 19, 2019 | Flag Reply
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public class Application {

	public static void main(String arg[]) {
		
		ResourceSharing sharedResource = new ResourceSharing(10, 5);
		
		Task tasks [] = new Task[5];
		
		IntStream.range(0, tasks.length).forEach(i -> {
			tasks[i] = new Task(++i, 2+i, sharedResource);
		});
		
		ExecutorService executorService = Executors.newCachedThreadPool();
		Arrays.stream(tasks).forEach(executorService::execute);
		
	}
}


public class Task implements Runnable {

	private int threadNum;
	
	private int requiredResources;
	
	private ResourceSharing sharedResource;
	
	public Task(int threadNum, int requiredResources, ResourceSharing sharedResource) {
		super();
		this.threadNum = threadNum;
		this.requiredResources = requiredResources;
		this.sharedResource = sharedResource;
	}

	@Override
	public void run() {
		try {
			sharedResource.executeUsingResource(threadNum, requiredResources);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}



package phlilospher.sequence;

import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ResourceSharing {

	final private int totalResources;
	
	final private int totalConsumers;
	
	final private Semaphore semaphore;
	
	final private Lock lock;
	
	final private Condition isNotInOrder;
	
	private AtomicInteger currentOrder = new AtomicInteger(1);
	
	public ResourceSharing(int totalResources, int totalConsumers) {
		super();
		this.totalResources = totalResources;
		this.totalConsumers =  totalConsumers;
		this.semaphore = new Semaphore(totalResources);
		this.lock = new ReentrantLock();
		this.isNotInOrder = lock.newCondition();
	}
	
	public void executeUsingResource(int orderNo, int resources) throws InterruptedException {
		if(resources > totalResources || orderNo > totalConsumers)
			throw new IllegalArgumentException();
		lock.lock();
		try {
			while(orderNo != currentOrder.get())
				isNotInOrder.await();
			
			semaphore.acquire(resources);
			System.out.println("Thread : " + orderNo+ " running using resource : "+resources);
			Thread.sleep(10);
			System.out.println("Thread : " + orderNo+ " freeing resource : "+resources);
			semaphore.release(resources);
			
			currentOrder.getAndIncrement();
			isNotInOrder.signalAll();
		} finally {
			lock.unlock();
		}
	}
}

- MatSib July 07, 2019 | Flag Reply
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lock in beginning of the method executeUsingResource will always allow only one thread to execute regardless the available resources
For example : thread t1 using 3 out of 10 resources will hold the lock
thread t2 using 4 out of 7 available resources will wait until t1 releases the lock.

{{
public class ResourceSharing {

final private int totalResources;

final private int totalConsumers;

final private Semaphore semaphore;

private AtomicInteger currentOrder = new AtomicInteger(1);

public ResourceSharing(int totalResources, int totalConsumers) {
super();
this.totalResources = totalResources;
this.totalConsumers = totalConsumers;
this.semaphore = new Semaphore(totalResources);
}

public void executeUsingResource(int orderNo, int resources) throws InterruptedException {
if(resources > totalResources || orderNo > totalConsumers)
throw new IllegalArgumentException();
while(orderNo != currentOrder.get()) {
//busy wait;
Thread.sleep(10);
}
semaphore.acquire(resources);
try {
currentOrder.getAndIncrement();
System.out.println("Thread : " + orderNo+ " running using resource : "+resources);
Thread.sleep(1000);
System.out.println("Thread : " + orderNo+ " freeing resource : "+resources);
} finally {
semaphore.release(resources);
}
}
}
}}
Output :
Thread : 1 running using resource : 3
Thread : 2 running using resource : 4
Thread : 1 freeing resource : 3
Thread : 3 running using resource : 5
Thread : 2 freeing resource : 4
Thread : 3 freeing resource : 5
Thread : 4 running using resource : 6
Thread : 4 freeing resource : 6
Thread : 5 running using resource : 7
Thread : 5 freeing resource : 7

- Anonymous July 09, 2019 | Flag
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of 0 vote

public class ResourceSharing {

	final private int totalResources;
	
	final private int totalConsumers;
	
	final private Semaphore semaphore;
	
	final private Lock lock;
	
	final private Condition isNotInOrder;
	
	private AtomicInteger currentOrder = new AtomicInteger(1);
	
	public ResourceSharing(int totalResources, int totalConsumers) {
		super();
		this.totalResources = totalResources;
		this.totalConsumers =  totalConsumers;
		this.semaphore = new Semaphore(totalResources);
		this.lock = new ReentrantLock();
		this.isNotInOrder = lock.newCondition();
	}
	
	public void executeUsingResource(int orderNo, int resources) throws InterruptedException {
		if(resources > totalResources || orderNo > totalConsumers)
			throw new IllegalArgumentException();
		lock.lock();
		try {
			while(orderNo != currentOrder.get())
				isNotInOrder.await();
			
			semaphore.acquire(resources);
			System.out.println("Thread : " + orderNo+ " running using resource : "+resources);
			Thread.sleep(10);
			System.out.println("Thread : " + orderNo+ " freeing resource : "+resources);
			semaphore.release(resources);
			
			currentOrder.getAndIncrement();
			isNotInOrder.signalAll();
		} finally {
			lock.unlock();
		}
	}
}

- Anonymous July 07, 2019 | Flag Reply


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