Concurrency

Which of the following options correctly create an ExecutorService instance?. Please select 2 options.

• var es = ExecutorService.getInstance();

• var es = new ExecutorService();

• var es = Executors.newFixedThreadPool(2);

• var es = Executor.getSingleThreadExecutor();

• var es = Executors.newVirtualThreadPerTaskExecutor();

Which of the following code fragments will you use to create an ExecutorService?. Please select 3 options.

• ExecutorService

• Executor

• Executors

• .newSingleThreadExecutor();

• .newVirtualThreadPerTaskExecutor();

Which of the following statements correctly create a virtual thread? (Assume that r refers to a Runnable instance.). Please select 1 option.

• Thread t = new VirtualThread(r);

• Thread t = new VirtualThread(r);

• VirtualThread t = Thread.ofVirtual();

• Thread t = Thread.ofVirtual();

• Thread t = Thread.ofVirtual().unstarted(r);

Given:

ReadWriteLock rl = new ReentrantReadWriteLock();

Lock rlock = rl.readLock();

Lock wlock = rl.writeLock();

Identify correct statements regarding code that appears after the above code. (Consider each option individually.). Please select 3 options.

• rlock.lock();
  System.out.println("read lock acquired");
  wlock.lock();
  System.out.println("write lock acquired");
  
  This code will print both the statements.

• wlock.lock();
  System.out.println("write lock acquired");
  rlock.lock();
  System.out.println("read lock acquired");
  
  This code will print both the statements.

• rlock.lock();
  System.out.println("read lock acquired");
  rlock.lock();
  System.out.println("read lock acquired again");
  
  This code will print both the statements.

• rlock.lock();
  rlock.lock();
  rlock.unlock();
  wlock.lock();
  System.out.println("write lock acquired");
  
  This code will print the statement.

• rlock.lock();
  try{
      wlock.tryLock();
      wlock.unlock();
      System.out.println("write lock acquired ");
  }catch(Exception e) {
      e.printStackTrace();
  }
  
  This code will print an exception stack trace.

You have a collection (say, an ArrayList) which is read by multiple reader threads and which is modified by a single writer thread. The collection allows multiple concurrent reads but does not tolerate concurrent read and write. Which of the following strategies will you use to obtain best performance?. Please select 1 option.

• synchronize all access to the collection.

• make the collection variable final.

• make the collection variable final and volatile.

• Wrap the collection into its synchronized version using Collections.synchronizedCollection().

• Encapsulate the collection into another class and use ReadWriteLock to manage read and write access

What will the following code print?

AtomicInteger ai = new AtomicInteger();

Stream<Integer> stream = Stream.of(11, 11, 22, 33).parallel();

stream.filter(

e->{ ai.incrementAndGet();

return e%2==0;

});

System.out.println(ai); Please select 1 option.

• 0

• Any number between 1 to 4.

• 4

• Any number between 0 to 3

If a synchronized method ends up throwing an exception to the caller, the lock acquired by the thread associated with this method due to the usage of the synchronized keyword is released automatically. Please select 1 option.

• true

• false

Please select 1 option.

• It may print any combination of the keys except an empty list.

• It may print any combination except: c,

• It may print any combination except: a, or b, or a, b, or b, a or an empty list.

• It may print any combination except: b, c,

• It may print any combination except: a, b,

What can be inserted at //2 so that 6 will be printed by the following code?

AtomicInteger ai = new AtomicInteger(5);

//2 INSERT CODE HERE

System.out.println(x);

Please select 2 options.

• int x = ai.increment();

• int x = ai.getAndIncrement();

• int x = ai + 1;

• int x = ai.incrementAndGet();

• int x = ai.addAndGet(1);