本文摘自写给应用开发的 Android Framework 教程 ，完整教程请查阅 yuandaimaahao.gitee.io/androidfram... 更为详细的视频教程与答疑服务，请联系微信 zzh0838
本文基于 aosp android-12.0.0_r26 分支讲解
一个简单的 main 函数执行完毕后，整个进程也就结束了，为了让一个进程长时间的运行下去，就需要无限循环加事件通知的机制，这类机制的伪代码描述如下：
cpp
int main()
{
while(true)
{
1. 线程进入休眠状态，等待通知；
2. 其它地方给当前线程发送通知，线程从休眠中唤醒，读取通知，处理通知
3. 进入下一个循环
}
return 0;
}在上一节，我们已经了解了 Android Native 层的 Looper 机制，接下来我们接着学习 Android Java 层的 Looper 机制。
这里先给出 Android Java Looper 的整体框架图，接着我们再根据源码逐步分析：
Java Looper 的使用
首先我们从一个典型的 Looper 线程来看看 Looper 具体是怎么使用的：
java
// 典型的关于Handler/Looper的线程
class LooperThread extends Thread {
public Handler mHandler;
public void run() {
Looper.prepare();
mHandler = new Handler() {
public void handleMessage(Message msg) {
//定义消息处理逻辑.
Message msg = Message.obtain();
}
};
Looper.loop();
}
}
// 其他线程
Message msg = Message.obtain();
msg.what = 2;
msg.obj = "B";
// 向 looper 发送一个消息
looperThread.mHandler.sendMessage(msg);使用上来说：
Looper 线程：
- 调用
Looper.prepare()初始化 Looper - 初始化一个 Handler 对象
- Looper.loop() 进入循环休眠状态
其他线程：
- 获取到 Looper 线程中的 Handler 对象
- 构建一个 Message 对象
- 调用 Handler 对象的 sendMessage 发送消息给 Looper
Looper.prepare() 实现分析
java
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));
} prepare 中首先从线程本地数据区取 Looper，如果没有，就 new 一个 Looper，并存到线程本地数据区中。
接下来看看 new 一个 Looper 的过程：
java
private Looper(boolean quitAllowed) {
mQueue = new MessageQueue(quitAllowed); //创建MessageQueue对象
mThread = Thread.currentThread();
}构造函数中，new 了一个 MessageQueue，获取到了当前线程 Thread 对象。
接着看 MessageQueue 的初始化过程：
java
MessageQueue(boolean quitAllowed) {
mQuitAllowed = quitAllowed;
mPtr = nativeInit();
}
private native static long nativeInit();这里调用了 native 方法 nativeInit，对应的 JNI 函数是
android_os_MessageQueue_nativeInit：
cpp
static jlong android_os_MessageQueue_nativeInit(JNIEnv* env, jclass clazz) {
NativeMessageQueue* nativeMessageQueue = new NativeMessageQueue();
if (!nativeMessageQueue) {
jniThrowRuntimeException(env, "Unable to allocate native queue");
return 0;
}
nativeMessageQueue->incStrong(env);
return reinterpret_cast<jlong>(nativeMessageQueue);
}这里，核心内容就是初始化一个 NativeMessageQueue 对象，并将其地址返回给 Java 层。我们接着看 NativeMessageQueue 对象的初始化过程：
cpp
// NativeMessageQueue 构造函数
NativeMessageQueue::NativeMessageQueue() :
mPollEnv(NULL), mPollObj(NULL), mExceptionObj(NULL) {
// 初始化 Native 层的 looper
mLooper = Looper::getForThread();
if (mLooper == NULL) {
mLooper = new Looper(false);
Looper::setForThread(mLooper);
}
}NativeMessageQueue 的构造函数中，从本地线程区获取当前线程的 Looper 对象，没有的话，就初始化一个，并存在线程本地数据区中。
Native 层 Looper 对象的初始化，核心内容就三点：
- 初始化一个 eventfd
- 初始化一个 epoll
- 把 eventfd 放到 epoll 池中
具体代码请参考Android Native Looper 机制的 Native Looper 源码分析 章节，这里不再重复。
Looper.loop()
初始化工作完成后，我们接着再来看看 loop 方法都执行了哪些操作：
java
public static void loop() {
// 获取 TLS 存储的 Looper 对象
final Looper me = myLooper();
if (me == null) {
throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
}
if (me.mInLoop) {
Slog.w(TAG, "Loop again would have the queued messages be executed"
+ " before this one completed.");
}
me.mInLoop = true;
// Make sure the identity of this thread is that of the local process,
// and keep track of what that identity token actually is.
Binder.clearCallingIdentity();
final long ident = Binder.clearCallingIdentity();
// Allow overriding a threshold with a system prop. e.g.
// adb shell 'setprop log.looper.1000.main.slow 1 && stop && start'
final int thresholdOverride =
SystemProperties.getInt("log.looper."
+ Process.myUid() + "."
+ Thread.currentThread().getName()
+ ".slow", 0);
me.mSlowDeliveryDetected = false;
// 进入无限循环，调用 loopOnce 进入休眠状态
for (;;) {
if (!loopOnce(me, ident, thresholdOverride)) {
return;
}
}
}
public static @Nullable Looper myLooper() {
return sThreadLocal.get();
}代码很长，但是核心功能就两点：
- 获取 TLS 存储的 Looper 对象
- 进入无限循环，调用 loopOnce 进入休眠状态
接下来就来看看 loopOnce 到底是怎么工作的
java
private static boolean loopOnce(final Looper me,
final long ident, final int thresholdOverride) {
// 获取 Message，可能阻塞
Message msg = me.mQueue.next();
if (msg == null) {
// No message indicates that the message queue is quitting.
return false;
}
// This must be in a local variable, in case a UI event sets the logger
final Printer logging = me.mLogging;
if (logging != null) {
logging.println(">>>>> Dispatching to " + msg.target + " "
+ msg.callback + ": " + msg.what);
}
// Make sure the observer won't change while processing a transaction.
final Observer observer = sObserver;
final long traceTag = me.mTraceTag;
long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;
long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;
if (thresholdOverride > 0) {
slowDispatchThresholdMs = thresholdOverride;
slowDeliveryThresholdMs = thresholdOverride;
}
final boolean logSlowDelivery = (slowDeliveryThresholdMs > 0) && (msg.when > 0);
final boolean logSlowDispatch = (slowDispatchThresholdMs > 0);
final boolean needStartTime = logSlowDelivery || logSlowDispatch;
final boolean needEndTime = logSlowDispatch;
if (traceTag != 0 && Trace.isTagEnabled(traceTag)) {
Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
}
final long dispatchStart = needStartTime ? SystemClock.uptimeMillis() : 0;
final long dispatchEnd;
Object token = null;
if (observer != null) {
token = observer.messageDispatchStarting();
}
long origWorkSource = ThreadLocalWorkSource.setUid(msg.workSourceUid);
try {
//分发消息，调用 handler 中的回调函数
msg.target.dispatchMessage(msg);
if (observer != null) {
observer.messageDispatched(token, msg);
}
dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
} catch (Exception exception) {
if (observer != null) {
observer.dispatchingThrewException(token, msg, exception);
}
throw exception;
} finally {
ThreadLocalWorkSource.restore(origWorkSource);
if (traceTag != 0) {
Trace.traceEnd(traceTag);
}
}
if (logSlowDelivery) {
if (me.mSlowDeliveryDetected) {
if ((dispatchStart - msg.when) <= 10) {
Slog.w(TAG, "Drained");
me.mSlowDeliveryDetected = false;
}
} else {
if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
msg)) {
// Once we write a slow delivery log, suppress until the queue drains.
me.mSlowDeliveryDetected = true;
}
}
}
if (logSlowDispatch) {
showSlowLog(slowDispatchThresholdMs, dispatchStart, dispatchEnd, "dispatch", msg);
}
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}
// Make sure that during the course of dispatching the
// identity of the thread wasn't corrupted.
final long newIdent = Binder.clearCallingIdentity();
if (ident != newIdent) {
Log.wtf(TAG, "Thread identity changed from 0x"
+ Long.toHexString(ident) + " to 0x"
+ Long.toHexString(newIdent) + " while dispatching to "
+ msg.target.getClass().getName() + " "
+ msg.callback + " what=" + msg.what);
}
msg.recycleUnchecked();
return true;
} 代码很长，核心流程不多：
- 通过 MessageQueue 的 next 方法拿到一个 Message，这里可能会阻塞休眠，具体为什么，后面马上说
- 通过 dispatchMessage 调用 Handler 中的回调方法
接着就来看 mQueue.next() 的实现：
java
Message next() {
// Return here if the message loop has already quit and been disposed.
// This can happen if the application tries to restart a looper after quit
// which is not supported.
final long ptr = mPtr;
if (ptr == 0) {
return null;
}
int pendingIdleHandlerCount = -1; // -1 only during first iteration
int nextPollTimeoutMillis = 0;
for (;;) {
if (nextPollTimeoutMillis != 0) {
Binder.flushPendingCommands();
}
// 陷入 Native 层，进入休眠状态
nativePollOnce(ptr, nextPollTimeoutMillis);
//......
}
}
private native void nativePollOnce(long ptr, int timeoutMillis);这里调用 nativePollOnce 陷入 Native 层，进入休眠状态，nativePollOnce 是一个 Native 方法，对应的 JNI 函数如下：
cpp
static void android_os_MessageQueue_nativePollOnce(JNIEnv* env, jobject obj,
jlong ptr, jint timeoutMillis) {
NativeMessageQueue* nativeMessageQueue = reinterpret_cast<NativeMessageQueue*>(ptr);
nativeMessageQueue->pollOnce(env, obj, timeoutMillis);
}通过传入的指针，获取到 Native 层的 NativeMessageQueue 对象，接着调用 NativeMessageQueue 对象的 pollOnce 方法：
cpp
void NativeMessageQueue::pollOnce(JNIEnv* env, jobject pollObj, int timeoutMillis) {
mPollEnv = env;
mPollObj = pollObj;
// 内部调用 epoll_wait 阻塞
mLooper->pollOnce(timeoutMillis);
mPollObj = NULL;
mPollEnv = NULL;
if (mExceptionObj) {
env->Throw(mExceptionObj);
env->DeleteLocalRef(mExceptionObj);
mExceptionObj = NULL;
}
}这里会调用 Native 层 Looper 的 pollOnce 函数，pollOnce 内部主要是调用 epoll_wait 来进入休眠状态。pollOnce 的具体代码分析可以参考Android Native Looper 机制，这里不再重复。
至此，我们的线程就下 cpu，进入休眠状态。
接下里我们就来看看怎么把休眠中的线程唤醒。
发送消息
发送消息大致两步：
- 初始化一个 Handler 对象，覆写 Handler 的 handleMessage 方法
- 构建一个 Message 对象，通过 Handler 的 sendMessage 方法发送消息
Handler 初始化过程
在使用 Looper 的线程中通常会初始化一个 Handler 对象：
java
// new 一个 Handler，覆写 handleMessage 方法
mHandler = new Handler() {
public void handleMessage(Message msg) {
//定义消息处理逻辑.
}
};Handler 的构造函数：
java
public Handler() {
this(null, false);
}
public Handler(@Nullable Callback callback, boolean async) {
//......
//拿到当前线程的 Looper 对象
mLooper = Looper.myLooper();
if (mLooper == null) {
throw new RuntimeException(
"Can't create handler inside thread " + Thread.currentThread()
+ " that has not called Looper.prepare()");
}
mQueue = mLooper.mQueue;
mCallback = callback;
mAsynchronous = async;
}初始化过程中，要对 Handler 中有两个重要变量进行赋值：
- mLooper：当前线程中的 Looper 对象
- mQueue：当前线程中的 Looper 对象的 MessageQueue 成员
做好以上的准备工作后，就可以向 Looper 发送消息了：
java
// 构建一个 Message
Message msg = Message.obtain();
msg.what = 2;
msg.obj = "B";
// 通过 Handler 的 sendMessage 方法发送消息
mHandler.sendMessage(msg);我们先看看 Message 的初始化过程：
java
// frameworks/base/core/java/android/os/Message.java
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();
}从缓存 sPool 里面取 Message，如果没有的话就 new 一个 Message。
接着我们来看 sendMessage 的过程：
java
// frameworks/base/core/java/android/os/Handler.java
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) {
// 注意这里，把 handler 赋值给了 msg 的 target 成员
msg.target = this;
msg.workSourceUid = ThreadLocalWorkSource.getUid();
if (mAsynchronous) {
msg.setAsynchronous(true);
}
return queue.enqueueMessage(msg, uptimeMillis);
}sendMessage 内部把 handler 赋值给了 msg 的 target 成员，最终调用到 MessageQueue 的 enqueueMessage 方法：
java
boolean enqueueMessage(Message msg, long when) {
if (msg.target == null) {
throw new IllegalArgumentException("Message must have a target.");
}
synchronized (this) {
if (msg.isInUse()) {
throw new IllegalStateException(msg + " This message is already in use.");
}
if (mQuitting) {
IllegalStateException e = new IllegalStateException(
msg.target + " sending message to a Handler on a dead thread");
Log.w(TAG, e.getMessage(), e);
msg.recycle();
return false;
}
msg.markInUse();
msg.when = when;
Message p = mMessages;
boolean needWake;
// 把传入的 Message 插入 mMessages 链表
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.next
prev.next = msg;
}
// 唤醒 native 层的 epoll
// We can assume mPtr != 0 because mQuitting is false.
if (needWake) {
nativeWake(mPtr);
}
}
return true;
}enqueueMessage 代码有点长，核心逻辑就两点：
- 把传入的 Message 插入 mMessages 链表
- 调用 native 方法 nativeWake 唤醒 native 层的 epoll
接下来我们看看 nativeWake 的具体实现：
java
private native static void nativeWake(long ptr);
// nativeWake 对应的 JNI 函数
static void android_os_MessageQueue_nativeWake(JNIEnv* env, jclass clazz, jlong ptr) {
NativeMessageQueue* nativeMessageQueue = reinterpret_cast<NativeMessageQueue*>(ptr);
nativeMessageQueue->wake();
}
void NativeMessageQueue::wake() {
mLooper->wake();
}
// eventfd 写数据，唤醒 epoll
void Looper::wake() {
uint64_t inc = 1;
ssize_t nWrite = TEMP_FAILURE_RETRY(write(mWakeEventFd.get(), &inc, sizeof(uint64_t)));
if (nWrite != sizeof(uint64_t)) {
if (errno != EAGAIN) {
LOG_ALWAYS_FATAL("Could not write wake signal to fd %d (returned %zd): %s",
mWakeEventFd.get(), nWrite, strerror(errno));
}
}
}nativeWake 最终就是调用 native 层 mLooper 的 wake 函数，在 wake 函数中向 eventfd 写入数据，唤醒与 eventfd 绑定的 epoll。接下来我们就来看看 epoll 唤醒以后得流程。
唤醒后的流程
cpp
void NativeMessageQueue::pollOnce(JNIEnv* env, jobject pollObj, int timeoutMillis) {
mPollEnv = env;
mPollObj = pollObj;
// Looper 线程阻塞在 Native 层的这里
mLooper->pollOnce(timeoutMillis);
mPollObj = NULL;
mPollEnv = NULL;
if (mExceptionObj) {
env->Throw(mExceptionObj);
env->DeleteLocalRef(mExceptionObj);
mExceptionObj = NULL;
}
}唤醒后，回到上层函数 android_os_MessageQueue_nativePollOnce：
cpp
static void android_os_MessageQueue_nativePollOnce(JNIEnv* env, jobject obj,
jlong ptr, jint timeoutMillis) {
NativeMessageQueue* nativeMessageQueue = reinterpret_cast<NativeMessageQueue*>(ptr);
nativeMessageQueue->pollOnce(env, obj, timeoutMillis);
}接着，再回到更上一层 Java 层的 next 方法中：
Java
Message next() {
// Return here if the message loop has already quit and been disposed.
// This can happen if the application tries to restart a looper after quit
// which is not supported.
final long ptr = mPtr;
if (ptr == 0) {
return null;
}
int pendingIdleHandlerCount = -1; // -1 only during first iteration
int nextPollTimeoutMillis = 0;
for (;;) {
if (nextPollTimeoutMillis != 0) {
Binder.flushPendingCommands();
}
//从这个位置唤醒
nativePollOnce(ptr, nextPollTimeoutMillis);
// 从 mMessages 链表中选取一个合适的 message 返回
synchronized (this) {
// Try to retrieve the next message. Return if found.
final long now = SystemClock.uptimeMillis();
Message prevMsg = null;
Message msg = mMessages;
if (msg != null && msg.target == null) {
// Stalled by a barrier. Find the next asynchronous message in the queue.
do {
prevMsg = msg;
msg = msg.next;
} while (msg != null && !msg.isAsynchronous());
}
if (msg != null) {
if (now < msg.when) {
// Next message is not ready. Set a timeout to wake up when it is ready.
nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
} else {
// Got a message.
mBlocked = false;
if (prevMsg != null) {
prevMsg.next = msg.next;
} else {
mMessages = msg.next;
}
msg.next = null;
if (DEBUG) Log.v(TAG, "Returning message: " + msg);
msg.markInUse();
return msg;
}
} else {
// No more messages.
nextPollTimeoutMillis = -1;
}
// Process the quit message now that all pending messages have been handled.
if (mQuitting) {
dispose();
return null;
}
// If first time idle, then get the number of idlers to run.
// Idle handles only run if the queue is empty or if the first message
// in the queue (possibly a barrier) is due to be handled in the future.
if (pendingIdleHandlerCount < 0
&& (mMessages == null || now < mMessages.when)) {
pendingIdleHandlerCount = mIdleHandlers.size();
}
if (pendingIdleHandlerCount <= 0) {
// No idle handlers to run. Loop and wait some more.
mBlocked = true;
continue;
}
if (mPendingIdleHandlers == null) {
mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
}
mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
}
// Run the idle handlers.
// We only ever reach this code block during the first iteration.
for (int i = 0; i < pendingIdleHandlerCount; i++) {
final IdleHandler idler = mPendingIdleHandlers[i];
mPendingIdleHandlers[i] = null; // release the reference to the handler
boolean keep = false;
try {
keep = idler.queueIdle();
} catch (Throwable t) {
Log.wtf(TAG, "IdleHandler threw exception", t);
}
if (!keep) {
synchronized (this) {
mIdleHandlers.remove(idler);
}
}
}
// Reset the idle handler count to 0 so we do not run them again.
pendingIdleHandlerCount = 0;
// While calling an idle handler, a new message could have been delivered
// so go back and look again for a pending message without waiting.
nextPollTimeoutMillis = 0;
}
}唤醒后，一般的流程就是从 mMessages 中找个合适的 message 返回，返回后进入上一层：
java
private static boolean loopOnce(final Looper me,
final long ident, final int thresholdOverride) {
// 从这里返回
Message msg = me.mQueue.next();
if (msg == null) {
// No message indicates that the message queue is quitting.
return false;
}
// This must be in a local variable, in case a UI event sets the logger
final Printer logging = me.mLogging;
if (logging != null) {
logging.println(">>>>> Dispatching to " + msg.target + " "
+ msg.callback + ": " + msg.what);
}
// Make sure the observer won't change while processing a transaction.
final Observer observer = sObserver;
final long traceTag = me.mTraceTag;
long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;
long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;
if (thresholdOverride > 0) {
slowDispatchThresholdMs = thresholdOverride;
slowDeliveryThresholdMs = thresholdOverride;
}
final boolean logSlowDelivery = (slowDeliveryThresholdMs > 0) && (msg.when > 0);
final boolean logSlowDispatch = (slowDispatchThresholdMs > 0);
final boolean needStartTime = logSlowDelivery || logSlowDispatch;
final boolean needEndTime = logSlowDispatch;
if (traceTag != 0 && Trace.isTagEnabled(traceTag)) {
Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
}
final long dispatchStart = needStartTime ? SystemClock.uptimeMillis() : 0;
final long dispatchEnd;
Object token = null;
if (observer != null) {
token = observer.messageDispatchStarting();
}
long origWorkSource = ThreadLocalWorkSource.setUid(msg.workSourceUid);
try {
//分发消息，调用 handler 中的回调函数
msg.target.dispatchMessage(msg);
if (observer != null) {
observer.messageDispatched(token, msg);
}
dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
} catch (Exception exception) {
if (observer != null) {
observer.dispatchingThrewException(token, msg, exception);
}
throw exception;
} finally {
ThreadLocalWorkSource.restore(origWorkSource);
if (traceTag != 0) {
Trace.traceEnd(traceTag);
}
}
if (logSlowDelivery) {
if (me.mSlowDeliveryDetected) {
if ((dispatchStart - msg.when) <= 10) {
Slog.w(TAG, "Drained");
me.mSlowDeliveryDetected = false;
}
} else {
if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
msg)) {
// Once we write a slow delivery log, suppress until the queue drains.
me.mSlowDeliveryDetected = true;
}
}
}
if (logSlowDispatch) {
showSlowLog(slowDispatchThresholdMs, dispatchStart, dispatchEnd, "dispatch", msg);
}
if (logging != null) {
logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
}
// Make sure that during the course of dispatching the
// identity of the thread wasn't corrupted.
final long newIdent = Binder.clearCallingIdentity();
if (ident != newIdent) {
Log.wtf(TAG, "Thread identity changed from 0x"
+ Long.toHexString(ident) + " to 0x"
+ Long.toHexString(newIdent) + " while dispatching to "
+ msg.target.getClass().getName() + " "
+ msg.callback + " what=" + msg.what);
}
msg.recycleUnchecked();
return true;
} 代码很多，核心的流程只有两点：
- next() 处返回一个合适的 message
- 通过 msg.target.dispatchMessage(msg) 调用 handler 中的回调
至此，整个 Looper 流程就走完了。
参考资料
- Android消息机制1-Handler(Java层)
- Android消息机制2-Handler(Native层)
- Android Handler之同步屏障机制(sync barrier)
- Android Sync Barrier机制
关于
我叫阿豪，2015 年本科毕业于国防科学技术大学指挥信息系统专业，毕业后从事信息化装备的研发工作，主要研究方向是 Android Framework 与 Linux Kernel。
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