OnJava8-Examples/lowlevel/SynchronizedComparison.java

// lowlevel/SynchronizedComparison.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Synchronizing blocks instead of entire methods
// speeds up access.
import java.util.*;
import java.util.stream.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import onjava.Nap;

abstract class Guarded {
  AtomicLong callCount = new AtomicLong();
  public abstract void method();
  @Override public String toString() {
    return getClass().getSimpleName() +
      ": " + callCount.get();
  }
}

class SynchronizedMethod extends Guarded {
  @Override public synchronized void method() {
    new Nap(0.01);
    callCount.incrementAndGet();
  }
}

class CriticalSection extends Guarded {
  @Override public void method() {
    new Nap(0.01);
    synchronized(this) {
      callCount.incrementAndGet();
    }
  }
}

class Caller implements Runnable {
  private Guarded g;
  Caller(Guarded g) { this.g = g; }
  private AtomicLong successfulCalls =
    new AtomicLong();
  private AtomicBoolean stop =
    new AtomicBoolean(false);
  @Override public void run() {
    new Timer().schedule(new TimerTask() {
      public void run() { stop.set(true); }
    }, 2500);
    while(!stop.get()) {
      g.method();
      successfulCalls.getAndIncrement();
    }
    System.out.println(
      "-> " + successfulCalls.get());
  }
}

public class SynchronizedComparison {
  static void test(Guarded g) {
    List<CompletableFuture<Void>> callers =
      Stream.of(
        new Caller(g),
        new Caller(g),
        new Caller(g),
        new Caller(g))
        .map(CompletableFuture::runAsync)
        .collect(Collectors.toList());
    callers.forEach(CompletableFuture::join);
    System.out.println(g);
  }
  public static void main(String[] args) {
    test(new CriticalSection());
    test(new SynchronizedMethod());
  }
}
/* Output:
-> 159
-> 159
-> 159
-> 159
CriticalSection: 636
-> 65
-> 21
-> 11
-> 68
SynchronizedMethod: 165
*/