沧州手机网站开发,北京快三是官方的吗,公司徽标设计图片,河南制作网站公司消息机制 概念ThreadLocalMessageQueueLooperHandlerrunOnUiThread() 概念
MessageQueue#xff1a;采用单链表的方法存储消息列表Looper#xff1a;查询MessageQueue是否有新消息#xff0c;有则处理#xff0c;无则等待ThreadLocal#xff1a;用于Handler获取当前线程的… 消息机制 概念ThreadLocalMessageQueueLooperHandlerrunOnUiThread() 概念
MessageQueue采用单链表的方法存储消息列表Looper查询MessageQueue是否有新消息有则处理无则等待ThreadLocal用于Handler获取当前线程的Looper线程默认没有Looper当使用Handler时需要手动创建ActivityThread被创建时会初始化主线程的Looper故主线程中默认可以使用Handler
ThreadLocal
ThreadLocal是线程内部数据存储类通过它可以在指定线程中存储数据且只能在该线程中访问如在调用栈比较深时用于存储监听器不需要全局变量即可实现监听线程的全部执行过程且避免了监听器通过参数去传递
public class MainActivity extends AppCompatActivity {private static final String TAG MainActivity;private ThreadLocalBoolean mBooleanThreadLocal new ThreadLocal();protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mBooleanThreadLocal.set(true);Log.d(TAG, onCreate: Thread#main mBooleanThreadLocal mBooleanThreadLocal.get());new Thread(Thread#1){Overridepublic void run() {mBooleanThreadLocal.set(false);Log.d(TAG, onCreate: Thread#1 mBooleanThreadLocal mBooleanThreadLocal.get());}}.start();new Thread(Thread#2){Overridepublic void run() {Log.d(TAG, onCreate: Thread#2 mBooleanThreadLocal mBooleanThreadLocal.get());}}.start();}
}打印如下虽然不同线程使用同一个ThreadLocal对象但值却不一样
Thread#main mBooleanThreadLocal true
Thread#1 mBooleanThreadLocal false
Thread#2 mBooleanThreadLocal null其set()方法如下内部通过所传入线程threadLocalsThreadLocalMap.Entry存储数据
public void set(T value) {Thread t Thread.currentThread();ThreadLocalMap map getMap(t);if (map ! null)map.set(this, value);elsecreateMap(t, value);
}ThreadLocalMap getMap(Thread t) {return t.threadLocals;
}void createMap(Thread t, T firstValue) {t.threadLocals new ThreadLocalMap(this, firstValue);
}ThreadLocalMap(ThreadLocal? firstKey, Object firstValue) {table new Entry[INITIAL_CAPACITY];int i firstKey.threadLocalHashCode (INITIAL_CAPACITY - 1);table[i] new Entry(firstKey, firstValue);size 1;setThreshold(INITIAL_CAPACITY);
}static class Entry extends WeakReferenceThreadLocal? {Object value;Entry(ThreadLocal? k, Object v) {super(k);value v;}
}再看下set()的实际实现
private void set(ThreadLocal? key, Object value) {Entry[] tab table;int len tab.length;int i key.threadLocalHashCode (len-1);for (Entry e tab[i];e ! null;e tab[i nextIndex(i, len)]) {ThreadLocal? k e.get();if (k key) {e.value value;return;}if (k null) {replaceStaleEntry(key, value, i);return;}}tab[i] new Entry(key, value);int sz size;if (!cleanSomeSlots(i, sz) sz threshold)rehash();
}其get()方法如下若存在则返回数据不存在则创建ThreadLocalMap存储默认值null并返回
public T get() {Thread t Thread.currentThread();ThreadLocalMap map getMap(t);if (map ! null) {ThreadLocalMap.Entry e map.getEntry(this);if (e ! null) {T result (T)e.value;return result;}}return setInitialValue();
}private T setInitialValue() {T value initialValue();Thread t Thread.currentThread();ThreadLocalMap map getMap(t);if (map ! null)map.set(this, value);elsecreateMap(t, value);return value;
}protected T initialValue() {return null;
}MessageQueue
如下为插入操作enqueueMessage()主要为链表的插入
boolean enqueueMessage(Message msg, long when) {......synchronized (this) {......msg.markInUse();msg.when when;Message p mMessages;boolean needWake;if (p null || when 0 || when p.when) {msg.next p;mMessages msg;needWake mBlocked;} else {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; prev.next msg;}if (needWake) {nativeWake(mPtr);}}return true;
}如下为读取操作死循环遍历链表在规定时间后将Message返回并从链表删除
Message next() {......for (; ; ) {......synchronized (this) {final long now SystemClock.uptimeMillis();Message prevMsg null;Message msg mMessages;if (msg ! null msg.target null) {do {prevMsg msg;msg msg.next;} while (msg ! null !msg.isAsynchronous());}if (msg ! null) {if (now msg.when) {nextPollTimeoutMillis (int) Math.min(msg.when - now, Integer.MAX_VALUE);} else {mBlocked false;if (prevMsg ! null) {prevMsg.next msg.next;} else {mMessages msg.next;}msg.next null;msg.markInUse();return msg;}} ......}......}
}Looper
使用Handler需要Looper否则会报错 可修改为如下
public class MainActivity extends AppCompatActivity {private static final String TAG MainActivity;protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);new Thread(Thread#1) {Overridepublic void run() {Looper.prepare();Looper looper Looper.myLooper();Handler handler new Handler();Looper.loop();}}.start();}
}prepare()创建Looper内部创建MessageQueue并存储到ThreadLocal
public static void prepare() {prepare(true);
}private static void prepare(boolean quitAllowed) {if (sThreadLocal.get() ! null) {throw new RuntimeException(Only one Looper may be created per thread);}sThreadLocal.set(new Looper(quitAllowed));
}private Looper(boolean quitAllowed) {mQueue new MessageQueue(quitAllowed);mThread Thread.currentThread();
}loop()开启消息循环
死循环一直从MessageQueue的next()方法获取Messagequit()、quitSafely()可让next()返回null退出Looper前者直接退出后者处理完MessageQueue中的已有消息后退出退出后handler的send()返回false调用Handler的dispatchMessage()回到创建Handler所在的Looper中执行
public static void loop() {final Looper me myLooper();......final MessageQueue queue me.mQueue;for (;;) {Message msg queue.next();if (msg null) {return;}......try {msg.target.dispatchMessage(msg);......}......}
}Handler
sendMessage()将Message插入到MessageQueue
public final boolean sendMessage(NonNull Message msg) {return sendMessageDelayed(msg, 0);
}public final boolean sendMessageDelayed(NonNull Message msg, long delayMillis) {if (delayMillis 0) {delayMillis 0;}return sendMessageAtTime(msg, SystemClock.uptimeMillis() delayMillis);
}public boolean sendMessageAtTime(NonNull Message msg, long uptimeMillis) {MessageQueue queue mQueue;if (queue null) {RuntimeException e new RuntimeException(this sendMessageAtTime() called with no mQueue);Log.w(Looper, e.getMessage(), e);return false;}return enqueueMessage(queue, msg, uptimeMillis);
}private boolean enqueueMessage(NonNull MessageQueue queue, NonNull Message msg,long uptimeMillis) {msg.target this;msg.workSourceUid ThreadLocalWorkSource.getUid();if (mAsynchronous) {msg.setAsynchronous(true);}return queue.enqueueMessage(msg, uptimeMillis);
}dispatchMessage()方法
msg.callback即是传进来的Runnable若不为空则调用其run()判断mCallback是否为空不为空调用其handleMessage()当不想继承Handler创建子类时其用于创建匿名内部类否则调用子类的handleMessage() public void dispatchMessage(NonNull Message msg) {if (msg.callback ! null) {handleCallback(msg);} else {if (mCallback ! null) {if (mCallback.handleMessage(msg)) {return;}}handleMessage(msg);}}private static void handleCallback(Message message) {message.callback.run();}runOnUiThread()
Activity中的runOnUiThread()若当前线程是主线程则直接执行否则调用主线程创建的Handler中的post()
public final void runOnUiThread(Runnable action) {if (Thread.currentThread() ! mUiThread) {mHandler.post(action);} else {action.run();}
}
