SynchronizedList

如何正确使用SynchronizedList?

操作List，已经做了同步synchronized，还会有ConcurrentModificationException，知道为什么吗?


1.

static class SynchronizedList<E>
        extends SynchronizedCollection<E>
        implements List<E> {
        private static final long serialVersionUID = -7754090372962971524L;

        final List<E> list;

        SynchronizedList(List<E> list) {
            super(list);
            this.list = list;
        }
        SynchronizedList(List<E> list, Object mutex) {
            super(list, mutex);
            this.list = list;
        }

        public boolean equals(Object o) {
            if (this == o)
                return true;
            synchronized (mutex) {return list.equals(o);}
        }
        public int hashCode() {
            synchronized (mutex) {return list.hashCode();}
        }

        public E get(int index) {
            synchronized (mutex) {return list.get(index);}
        }
        public E set(int index, E element) {
            synchronized (mutex) {return list.set(index, element);}
        }
        public void add(int index, E element) {
            synchronized (mutex) {list.add(index, element);}
        }
        public E remove(int index) {
            synchronized (mutex) {return list.remove(index);}
        }

        public int indexOf(Object o) {
            synchronized (mutex) {return list.indexOf(o);}
        }
        public int lastIndexOf(Object o) {
            synchronized (mutex) {return list.lastIndexOf(o);}
        }

        public boolean addAll(int index, Collection<? extends E> c) {
            synchronized (mutex) {return list.addAll(index, c);}
        }

        [b]public ListIterator<E> listIterator() {
            return list.listIterator(); // Must be manually synched by user
        }

        public ListIterator<E> listIterator(int index) {
            return list.listIterator(index); // Must be manually synched by user
        }[/b]

    }

static class SynchronizedCollection<E> implements Collection<E>, Serializable {
        private static final long serialVersionUID = 3053995032091335093L;

        final Collection<E> c;  // Backing Collection
        final Object mutex;     // Object on which to synchronize

        [b]SynchronizedCollection(Collection<E> c) {
            this.c = Objects.requireNonNull(c);
            mutex = this;
        }[/b]

2. 可以看出这个类的大多数方法通过同步块实现,
List<User> list = Collections.synchronizedList();
锁为synchronizedList.

3. iterator. stream, parallelStream 多线程操作必须用户自己实现同步
同步方法

package perf;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class Test {

	public static void main(String[] args) throws InterruptedException {

		
		List<User> list = Collections.synchronizedList(new ArrayList<User>());
		// lock
		final List<User> mutex = list;

		for (int i = 0; i < 100000; i++) {
			User user = new User();
			user.setName("" + i);
			list.add(user);
		}

		System.out.println("list = " + list.size());

		new Thread(new Runnable() {

			@Override
			public void run() {
				// use lock
				synchronized (mutex) {
					for (Iterator<User> it = list.iterator(); it.hasNext();) {
						User user = it.next();
						if (user.getName().indexOf("9") != -1) {
							it.remove();
						}
					}
				}
			}
		}).start();

		new Thread(new Runnable() {

			@Override
			public void run() {
				// use lock
				synchronized (mutex) {
					for (Iterator<User> it = list.iterator(); it.hasNext();) {
						User user = it.next();
						if (user.getName().indexOf("8") != -1) {
							it.remove();
						}
					}
				}
			}
		}).start();

		Thread.currentThread().sleep(1000L);

		System.out.println("list = " + list.size());
		System.out.println("list = " + list.isEmpty());
	}
}

class User {
	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}