利用AtomicInteger实现一把锁

利用AtomicInteger的cas实现一把自定义的锁,要注意解锁的线程一定是那个加锁的线程,否则会出现别的线程把锁释放掉

先定义一个lock异常类

public class LockException extends Exception{
     
  public LockException(String message) {
     
    super(message);
  }
}

自定义锁

public class CompareAndSetLock {
     
  private final AtomicInteger value = new AtomicInteger(0);
  private Thread currentThread;
  public void tryLock() throws LockException{
     
    final boolean succ = value.compareAndSet(0, 1);
    if (!succ) {
     
      throw new LockException("get the lock failed.");
    }else {
     
      currentThread = Thread.currentThread();
    }
  }
  // unlock方法 可以自己想一下
}

public class CompareAndSetLockTest {
     
  private static final CompareAndSetLock COMPARE_AND_SET_LOCK = new CompareAndSetLock();

  public static void main(String[] args) {
     
    long start = System.currentTimeMillis();
    List<Thread> workers = new ArrayList<>();
    Arrays.asList("M1", "M2", "M3", "M4", "M5", "M6", "M7", "M8").stream()
            .map(CompareAndSetLockTest::createThread)
            .forEach(
                    t -> {
     
                      t.start();
                      workers.add(t);
                    });
    workers.forEach(
            t -> {
     
              try {
     
                t.join();
              } catch (InterruptedException e) {
     
                e.printStackTrace();
              }
            });
    System.out.println("消耗时间为");
    System.out.println(System.currentTimeMillis() - start);
  }

  private static Thread createThread(String name) {
     
    return new Thread(
        () -> {
     
          try {
     
            COMPARE_AND_SET_LOCK.tryLock();
            System.out.println(Thread.currentThread().getName() + " do something....");
            Thread.sleep(10000);
          } catch (LockException | InterruptedException e) {
     
            e.printStackTrace();

          } finally {
     
            COMPARE_AND_SET_LOCK.unLock();
          }
        },
        name);
  }


  private static Thread createThread1(String name) {
     
    return new Thread(
            () -> {
     
              synchronized (CompareAndSetLockTest.class) {
     
                System.out.println(Thread.currentThread().getName() + " do something....");
                try {
     
                  Thread.sleep(10000);
                } catch (InterruptedException e) {
     
                  e.printStackTrace();
                }
              }
            },
            name);
  }

  public static void doSomething1() throws LockException, InterruptedException {
     
    synchronized (CompareAndSetLockTest.class) {
     
      System.out.println(Thread.currentThread().getName() + "do something....");
      Thread.sleep(10000);
    }
  }
}

我们分别调用createThread和createThread1方法看看区别

createThread结果:

M1 do something....
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
com.concurrency.thread.atomic.LockException: get the lock failed.
	at com.concurrency.thread.atomic.CompareAndSetLock.tryLock(CompareAndSetLock.java:17)
	at com.concurrency.thread.atomic.integer.CompareAndSetLockTest.lambda$createThread$2(CompareAndSetLockTest.java:47)
	at java.lang.Thread.run(Thread.java:748)
消耗时间为
10061

Process finished with exit code 0

createThread1结果:

M1 do something....
M8 do something....
M7 do something....
M6 do something....
M5 do something....
M4 do something....
M3 do something....
M2 do something....
消耗时间为
80078

Process finished with exit code 0

自定义的锁如果抢不到就直接释放,synchronized抢不到锁的线程进入阻塞状态,直到抢到锁的线程释放锁后继续争抢锁.