ConditionSynchronizedBlock.java

/**
 * Proves that we can put a condition in the parameter of a synchronized block.
 * 
 * <p>Ex. 
 * <br>{@code synchronized (first ? mLock1 : mLock2)}
 */
public class ConditionSynchronizedBlock {
	
	public static void main(String [ ] a) {
		ConditionSynchronizedBlock tested = new ConditionSynchronizedBlock();
		new Thread(new Runnable() {
			public void run() {
				tested.lock1();
			}
		}).start();
		new Thread(new Runnable() {
			public void run() {
				tested.acquire(false);
				tested.acquire(true);
			}
		}).start();
	}
	
	private final Object mLock1 = new Object();
	private final Object mLock2 = new Object();
	
	private void lock1() {
		printThreadMsg("locking first");
		synchronized (mLock1) {
			printThreadMsg("locked first");
			try {
				printThreadMsg("pausing");
				Thread.sleep(2_000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		printThreadMsg("released first");
	}
	
	private void acquire(boolean first) {
		printThreadMsg("acquiring " + (first ? "first" : "second"));
		synchronized (first ? mLock1 : mLock2) {
			printThreadMsg("acquired " + (first ? "first" : "second"));
		}
		printThreadMsg("released " + (first ? "first" : "second"));
	}
	
	private void printThreadMsg(String msg) {
		String fullMsg = String.format("%d %s: %s", System.nanoTime(), Thread.currentThread().getName(), msg);
		System.out.println(fullMsg);
	}

}