Android 消息处理源码分析（1）

Android 消息处理源码分析（1）在Android中，通常被使用的消息队列的代码在目录\sources\android-22\android\os下，，涉及到以下几个类文件Handler.java

Looper.java

Message.java

MessageQueue.java

Message.javapublic final class Message implements Parcelable {public int what; //消息种类public int arg1; //低开销的整型参数public int arg2;public Object obj; //Object型数据public Messenger replyTo; //消息处理完后通知给发送者/*package*/ int flags; //消息标记：正在使用和异步等/*package*/ long when; //消息创建时的时间/*package*/ Bundle data; //消息附带的额外数据/*package*/ Handler target; //消息接受者，处理者/*package*/ Runnable callback; //优先使用回调处理来处理消息/*package*/ Message next; //下一个消息，形成链表private static Message sPool; //消息池中的头消息上面中的target,通常由重新实现的Handler子类的handleMessage函数来处理消息 public static Message obtain() {//获取消息的函数，如果有消息的话则获取出来m，链表指针移动一位，否则则返回一条空消息synchronized (sPoolSync) {if (sPool != null) {Message m = sPool;sPool = m.next;m.next = null;m.flags = 0; // clear in-use flagsPoolSize–;return m;}}return new Message();} public void sendToTarget() { //发送消息给处理者target.sendMessage(this); //调用Handler.java中的函数}}MessageQueue.javapublic final class MessageQueue {Message mMessages; //当前要处理的消息//当需要从链表中获取一个消息时，就会调用next函数，若消息队列中没有消息，则会阻塞等待，通过调用nativePollOnce函数来完成Message next() {…}boolean enqueueMessage(Message msg, long when) {//按时间顺序添加消息if (msg.target == null) {throw new IllegalArgumentException("Message must have a target.");}if (msg.isInUse()) {throw new IllegalStateException(msg + " This message is already in use.");}synchronized (this) {if (mQuitting) {IllegalStateException e = new IllegalStateException(msg.target + " sending message to a Handler on a dead thread");Log.w("MessageQueue", e.getMessage(), e);msg.recycle();return false;}msg.markInUse();msg.when = when;Message p = mMessages;boolean needWake;if (p == null || when == 0 || when < p.when) {// New head, wake up the event queue if blocked.msg.next = p;mMessages = msg;needWake = mBlocked;} else {// Inserted within the middle of the queue. Usually we don't have to wake// up the event queue unless there is a barrier at the head of the queue// and the message is the earliest asynchronous message in the queue.needWake = mBlocked && p.target == null && msg.isAsynchronous();Message prev;for (;;) {prev = p;p = p.next;if (p == null || when < p.when) {break;}if (needWake && p.isAsynchronous()) {needWake = false;}}msg.next = p; // invariant: p == prev.nextprev.next = msg;}// We can assume mPtr != 0 because mQuitting is false.if (needWake) {nativeWake(mPtr); //调用底层唤醒函数，管道唤醒}}return true;}

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