Synchronization of run() method

Question

public class Process extends Thread {

   private static int count=0;

   @Override
   public void run()
   {
       for (int i=0; i< 1000000000; i++)
              count++;
   } }

Consider the above snippet. If more threads of type Process are running, this code is not thread-safe due to the cuncurrent access to the static variable.

How to make this code "thread safe"?

Is it an option to enclose count++ within a static synchronized method and invoking this instead?

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/atomic/AtomicInteger.html — Blorgbeard, May 12 '16 at 22:15
`1 000 000 000` is not a valid integer literal. Use `1000000000` or `1_000_000_000`. — Andreas, May 12 '16 at 22:49

Sleiman Jneidi · Accepted Answer · 2016-05-12T22:47:06.583

You better use a builtin synchronized accumulator like AtomicInteger

 AtomicInteger count = new AtomicInteger(0);

 for (int i=0; i< 1000000000; i++)
      count.incrementAndGet();

Another accumulator that comes with Java 8 is the LongAdder which gives a higher throughput under high contention at the expense of more space

 LongAdder longAdder = new LongAdder();

 for (int i=0; i< 1000000000; i++)
    longAdder.increment();

 System.out.println(longAdder.sum());

AtomicInteger and locks are great for concurrent access but if parallelism is what you trying to achieve then give LongAccumulator and LongAdders a look, they should scale better on multi-core

score 2 · Answer 2 · answered May 12 '16 at 22:16

2

Use AtomicInteger instead of int, or perform the critical work under synchronization:

private static final Object lock = new Object();

...

synchronized(lock) {
  count++;
}

answered May 12 '16 at 22:16

erickson

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Synchronization of run() method

2 Answers2