CODEWITHSUNDEEP
javamultithreading
chiru
chiru

Reputation: 832

2 threads printing numbers in sequence

I have thread t1 printing odd number 1 3 5 7...

I have thread t2 printing even number 0 2 4 6 ...

I want the output to be printed in sequential order from this two threads like

 0 1 2 3 4 5 6 7

I do not want code here please guide me with what framework to use in java?

Upvotes: 3

Views: 2993

Answers (3)

Martin James
Martin James

Reputation: 24847

Two semaphores, one for each thread. Use the semaphores to signal a 'printToken' between the threads. Pseudo:

CreateThread(EvenThread);
CreateThread(OddThread);
Signal(EvenThread);
..
..
EvenThread();
  Wait(EvenSema);
  Print(EvenNumber);
  Signal(OddSema);
..
..
OddThread();
  Wait(OddSema);
  Print(OddNumber);
  Signal(EvenSema);

Upvotes: 1

Bernhard Barker
Bernhard Barker

Reputation: 55609

I'd probably do something like:

public class Counter
{
  private static int c = 0;

  // synchronized means the two threads can't be in here at the same time
  // returns bool because that's a good thing to do, even if currently unused
  public static synchronized boolean incrementAndPrint(boolean even)
  {
    if ((even  && c % 2 == 1) ||
        (!even && c % 2 == 0))
    {
      return false;
    }
    System.out.println(c++);
    return true;
  }
}

Thread 1:

while (true)
{
  if (!Counter.incrementAndPrint(true))
    Thread.sleep(1); // so this thread doesn't lock up processor while waiting
}

Thread 2:

while (true)
{
  if (!Counter.incrementAndPrint(false))
    Thread.sleep(1); // so this thread doesn't lock up processor while waiting
}

Possibly not the most efficient way of doing things.

Upvotes: 1

Affe
Affe

Reputation: 47964

The easiest way to have two threads alternate is for each one to create a java.util.concurrent.CountDownLatch set to a count of 1 after it prints, and then wait for the other thread to release its latch.

Thread A: print 0
Thread A: create a latch
Thread A: call countDown on B's latch
Thread A: await
Thread B: print 1
Thread B: create a latch
Thread B: call countDown on A's latch
Thread B: await

Upvotes: 4

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