通过AtomicBoolean 和队列实现一个线程FIFO的Lock工具,
一步步接近AQS!!!
package com.horizon.thread.aqs; import java.util.Queue; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.atomic.AtomicBoolean; import java.util.concurrent.locks.LockSupport; public class FIFOMutex { private final AtomicBoolean locked = new AtomicBoolean(false); /** * 线程先进先出队列 */ private final Queue<Thread> waiters = new ConcurrentLinkedQueue<Thread>(); public void lock() { boolean wasInterrupted = false; Thread current = Thread.currentThread(); //把当前线程加入队列 waiters.add(current); // Block while not first in queue or cannot acquire lock //如果当前线程不是第一个:不是第一个肯定,肯定有其他线程在持有资源(保证公平性) //即使是第一个:加锁失败,即使是第一个线程,如果上一个线程没有释放锁 ,那么也应该进入等待 while (waiters.peek() != current || !locked.compareAndSet(false, true)) { LockSupport.park(this); if (Thread.interrupted()) // ignore interrupts while waiting wasInterrupted = true; } //可以把第一个线程移除了,因为已经占用了资源 waiters.remove(); if (wasInterrupted) // reassert interrupt status on exit current.interrupt(); } public void unlock() { //释放锁,其他的线程 此时也不能占用资源 locked.set(false); //此时线程才可以真正执行 LockSupport.unpark(waiters.peek()); } }
package com.horizon.thread.aqs; import java.util.Queue; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.atomic.AtomicBoolean; import java.util.concurrent.locks.LockSupport; public class FIFOMutex { private final AtomicBoolean locked = new AtomicBoolean(false); /** * 线程先进先出队列 */ private final Queue<Thread> waiters = new ConcurrentLinkedQueue<Thread>(); public void lock() { boolean wasInterrupted = false; Thread current = Thread.currentThread(); //把当前线程加入队列 waiters.add(current); // Block while not first in queue or cannot acquire lock //如果当前线程不是第一个:不是第一个肯定,肯定有其他线程在持有资源(保证公平性) //即使是第一个:加锁失败,即使是第一个线程,如果上一个线程没有释放锁 ,那么也应该进入等待 while (waiters.peek() != current || !locked.compareAndSet(false, true)) { LockSupport.park(this); if (Thread.interrupted()) // ignore interrupts while waiting wasInterrupted = true; } //可以把第一个线程移除了,因为已经占用了资源 waiters.remove(); if (wasInterrupted) // reassert interrupt status on exit current.interrupt(); } public void unlock() { //释放锁,其他的线程 此时也不能占用资源 locked.set(false); //此时线程才可以真正执行 LockSupport.unpark(waiters.peek()); } }