Handler 之 Message的获取方法

Message对象三种创建方法:

1.Message message = new message(); 

2.Message message = Message.obtain();

3.Message message = handler.obtainMessage();  内部调用 Message.obtain();

Message.obtain();源码

由源码可知:Message内部有一个 消息池,

obtain是优先从消息池中取:

private static Message sPool;

public static Message obtain() {
        synchronized (sPoolSync) {
            if (sPool != null) {
                Message m = sPool;
                sPool = m.next;
                m.next = null;
                m.flags = 0; // clear in-use flag
                sPoolSize--;
                return m;
            }
        }
        return new Message();
    }

我们再来看看,Message是怎么放入消息池的:

消息回收的时候, 先将Message参数初始化,然后放入sPool

取出和放入代码块用的是相同的锁,所以是同步的

void recycleUnchecked() {
        // Mark the message as in use while it remains in the recycled object pool.
        // Clear out all other details.
        flags = FLAG_IN_USE;
        what = 0;
        arg1 = 0;
        arg2 = 0;
        obj = null;
        replyTo = null;
        sendingUid = UID_NONE;
        workSourceUid = UID_NONE;
        when = 0;
        target = null;
        callback = null;
        data = null;

        synchronized (sPoolSync) {
            if (sPoolSize < MAX_POOL_SIZE) {
                next = sPool;
                sPool = this;
                sPoolSize++;
            }
        }
    }