Java 并发

Concurrency 并发

Synchronized 语句块

package synchronizing;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SheepManager {
	
	private int sheepCount = 0;
	
	// private void incrementAndReport() {
	private void incrementAndReport() {
		synchronized(this) {
        System.out.print((++sheepCount)+" ");
        }
	}

	public static void main(String[] args) {

		ExecutorService service = null;
		try {
			service = Executors.newFixedThreadPool(20);
			
			SheepManager manager = new SheepManager();
			for(int i = 0; i < 10; i++) 
				service.submit(()-> manager.incrementAndReport());
			} finally {
				if (service != null) service.shutdown();
			}
	}
}

使用 Monitor 或称为 Lock，使用 synchronized 的时候，注意🔒的对象是那个。保证同步，就要去要锁同一个对象。

并发集合类

类名称	接口	元素有序？	可排序？	阻塞？
ConcurrentHashMap	ConcurrentMap	No	No	No
ConcurrentLinkedDeque	Deque	Yes	No	No
ConcurrentLinkedQueue	Queue	Yes	No	No
ConcurrentSkipListMap	ConcurrentMap, SortedMap, NavigableMap	Yes	Yes	No
ConcurrentSkipListSet	SortedSet, NavigableSet	Yes	Yes	No
CopyOnWriteArrayList	List	Yes	No	No
CopyOnWriteArraySet	Set	Yes	No	No
LinkedBlockingDeque	BlockingQueue, BlockingDeque	Yes	No	Yes
LinkedBlockingQueue	BlockingQueue	Yes	No	Yes

Understanding CopyOnWrite Collections

List<Integer> list = new CopyOnWriteArrayList<>(Arrays.asList(4,3,52));
for (Integer item: list) {
	System.out.print(item+" ");
	list.add(9);
}
System.out.println();
System.out.println("Size: "+list.size());