private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));
    private static final int COUNT_BITS = Integer.SIZE - 3;
    private static final int CAPACITY   = (1 << COUNT_BITS) - 1;

    // runState is stored in the high-order bits
    private static final int RUNNING    = -1 << COUNT_BITS;
    private static final int SHUTDOWN   =  0 << COUNT_BITS;
    private static final int STOP       =  1 << COUNT_BITS;
    private static final int TIDYING    =  2 << COUNT_BITS;
    private static final int TERMINATED =  3 << COUNT_BITS;

    // Packing and unpacking ctl
    private static int runStateOf(int c)     { return c & ~CAPACITY; }
    private static int workerCountOf(int c)  { return c & CAPACITY; }
    private static int ctlOf(int rs, int wc) { return rs | wc; }


ctl包含两个值 

workerCount 线程数
runState 线程池的状态， Running，Shutdown，Stop，Tidying，Terminate 

29位表示workerCount，3位表示当前线程池的状态。
高3位状态值，低28位 线程数
runState is stored in the high-order bits



COUNT_BITS Integer.SIZE-3  明线程数 用29位表示
CAPACITY 左移29位 减一  ，  

ctl&CAPACITY  获取当前线程数



ThreadpoolCtlTest.java


import java.util.concurrent.atomic.AtomicInteger;

public class ThreadpoolCtlTest {

	private static final int COUNT_BITS = Integer.SIZE - 3;
	private static final int CAPACITY = (1 << COUNT_BITS) - 1;

	// runState is stored in the high-order bits
	private static final int RUNNING = -1 << COUNT_BITS;
	private static final int SHUTDOWN = 0 << COUNT_BITS;
	private static final int STOP = 1 << COUNT_BITS;
	private static final int TIDYING = 2 << COUNT_BITS;
	private static final int TERMINATED = 3 << COUNT_BITS;

	// Packing and unpacking ctl
	private static int runStateOf(int c) {
		return c & ~CAPACITY;
	}

	private static int workerCountOf(int c) {
		return c & CAPACITY;
	}

	private static int ctlOf(int rs, int wc) {
		return rs | wc;
	}

	private final static AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));

	private static boolean isRunning(int c) {
		return c < SHUTDOWN;
	}
	
	private static void printCtl(){
		int c = ctl.get();
		System.out.print(c+",");
		System.out.print(isRunning(c)+",");
		System.out.print(runStateOf(c)+",");
		System.out.println(workerCountOf(c));
	}

	public static void main(String[] args) throws Exception {
		System.out.println(0+","+ (~0));
		System.out.println(1+","+ (~1));
	
		System.out.println(CAPACITY);
		System.out.println(~CAPACITY);
		
		printCtl();

		ctl.set(ctlOf(RUNNING, 3));
		printCtl();
	
		ctl.set(ctlOf(SHUTDOWN, 3));
		printCtl();	
	}

}



输出

0,-1
1,-2
536870911
-536870912
-536870912,true,-536870912,0
-536870909,true,-536870912,3
3,false,0,3