Handler消息机制源码分析
Hander消息机制源码分析
一、Hander消息简单使用
findViewById(R.id.threadlocal_btn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Thread thread = new Thread("thread#2") {
@Override
public void run() {
Looper.prepare();
handler = new Handler(Looper.myLooper(), new Handler.Callback() {
@Override
public boolean handleMessage(Message msg) {
Log.i(TAG, "handleMessage: currentThreadName=" + Thread.currentThread().getName()) + " msg =" + msg.arg1)
return false;
}
});
Log.i(TAG, "run: 1111");
Looper.loop();
Log.i(TAG, "run: 2222 这个是不会执行的");
}
};
thread.start();
}
});
findViewById(R.id.hander_btn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (handler != null) {
Message message = Message.obtain(handler, -1, 2222, -1);
handler.sendMessageAtTime(message, 2000);
Log.i(TAG, "onClick: 222");
}
}
});二、Handler原理
Handler主要是消息的发送和消息的接受
常用发送消息方法：
handler.postDelayed(new Runnable() {
@Override
public void run() {
}
},300);
public final boolean postDelayed(Runnable r, long delayMillis)
public final boolean sendMessageDelayed(Message msg, long delayMillis)
public boolean sendMessageAtTime(Message msg, long uptimeMillis)
Hander消息处理
msg.target.dispatchMessage(msg);/***这里直接将消息发送到handler中处理**/
/** 消息的处理
* Handle system messages here.
*/
public void dispatchMessage(Message msg) {
if (msg.callback != null) {/**消息有回调情况则直接回调**/
handleCallback(msg);
} else {
if (mCallback != null) {/**handler有回调情况则直接回调**/
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);/**没有回调情况直接调用Handler子类中复写了handleMessage**/
}
}三、消息进入队列
private boolean enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) {
msg.target = this;
if (mAsynchronous) {
msg.setAsynchronous(true);
}
return queue.enqueueMessage(msg, uptimeMillis);
}消息队列MessageQueue是链表式的队列。
进入队列的方法
/****
* 消息进入队列 MessageQueue
* @param msg 消息
* @param when 执行时间 when= SystemClock.uptimeMillis() + delayMillis
* @return
*/
boolean enqueueMessage(Message msg, long when) {
if (msg.target == null) { /***mmessage最终是要在Handler执行的，**/
throw new IllegalArgumentException("Message must have a target.");
}
if (msg.isInUse()) {/**消息已被使用了**/
throw new IllegalStateException(msg + " This message is already in use.");
}
synchronized (this) {
if (mQuitting) { /***队列已经停止工作**/
IllegalStateException e = new IllegalStateException(
msg.target + " sending message to a Handler on a dead thread");
Log.w(TAG, e.getMessage(), e);
msg.recycle();/***回收消息，进入队列失败**/
return false;
}
msg.markInUse();/**消息标记为已被使用了**/
msg.when = when;/**消息记录要在什么时候执行**/
Message p = mMessages;/***当前Messages队列，队列首元素指针**/
boolean needWake; /**当前队列首元素为空 或者 该消息是要立即执行 或者 改消息的执行时间比队列首元素要早 **/
if (p == null || when == 0 || when < p.when) {
// New head, wake up the event queue if blocked.
msg.next = p; /**要插入的消息作为队列首元素**/
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();/**一般是不需要唤醒**/
Message prev; /***前一个消息**/
for (;;) {
prev = p;
p = p.next; /**下一个消息**/
if (p == null || when < p.when) {/***下一个消息为空 或者 插入的消息执行时间要比下一个消息要早，插入的消息要在p的前面**/
break;
}
if (needWake && p.isAsynchronous()) {/**异步则改成不需要唤醒**/
needWake = false;
}
}
msg.next = p; // invariant: p == prev.next
prev.next = msg;/**在prew和msg间插入新消息**/
}
// We can assume mPtr != 0 because mQuitting is false.
if (needWake) {/**需要唤醒的情况***/
nativeWake(mPtr);
}
}
return true;
}从队列出的方法。当然是根据消息具体的处理时刻来出队列的
/**从队列中取出一个要执行的消息**/
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) {/**loop循环已经终止，直接返回**/
return null;
}
/***挂起空闲要处理的消息的数量**/
int pendingIdleHandlerCount = -1; // -1 only during first iteration
int nextPollTimeoutMillis = 0;/**下一个执行消息的超时时间，单位毫秒ms**/
for (;;) {/**死循环**/
if (nextPollTimeoutMillis != 0) {/**下次要执行超时时间不为0，则调用Binder的flushPendingCommands对当前任务挂起**/
Binder.flushPendingCommands();
}
nativePollOnce(ptr, nextPollTimeoutMillis);/***线程挂起的时间为nextPollTimeoutMillis 毫秒**/
synchronized (this) {
// Try to retrieve the next message. Return if found.
final long now = SystemClock.uptimeMillis();/***当前手机系统时间（指定是手机系统启动时算起）**/
Message prevMsg = null;/**前一个消息***/
Message msg = mMessages;/**队列首个元素**/
if (msg != null && msg.target == null) {/**这个msg没有要处理被处理的场所，则取下一个**/
// Stalled by a barrier. Find the next asynchronous message in the queue.
do {
prevMsg = msg;
msg = msg.next;
} while (msg != null && !msg.isAsynchronous());/**msg是要同步的则继续取下一个**/
}
if (msg != null) {
if (now < msg.when) {/**当前系统时间比消息要执行的时间要早***/
// 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);/**计算出msg下次要执行的时间**/
} else {
// Got a message.
mBlocked = false;/**标记为不需要阻塞**/
if (prevMsg != null) {
prevMsg.next = msg.next;/**前一个元素直接指向下一个元素的next**/
} else {
mMessages = msg.next;/**前一个元素直接指向下一个元素的next**/
}
msg.next = null; /**取出msg元素***/
if (DEBUG) Log.v(TAG, "Returning message: " + msg);
msg.markInUse();
return msg;/**返回这个元素就完事了**/
}
} else {
// No more messages.
nextPollTimeoutMillis = -1;/**没有消息的情况***/
}
// Process the quit message now that all pending messages have been handled.
if (mQuitting) {/**处理停止的消息 所有消息被处理掉了**/
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 /**被挂起的消息个数小于0,消息队列为空，系统时间早于队列首个元素的执行时间***/
&& (mMessages == null || now < mMessages.when)) {
pendingIdleHandlerCount = mIdleHandlers.size();/**记录当前被空闲的回调**/
}
if (pendingIdleHandlerCount <= 0) {/**回调为<=0**/
// No idle handlers to run. Loop and wait some more.
mBlocked = true;/***进行阻塞**/
continue;
}
if (mPendingIdleHandlers == null) { /**创建最少四个挂起回调数组***/
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];/**挂起回调**/
mPendingIdleHandlers[i] = null; // release the reference to the handler
boolean keep = false;
try {
keep = idler.queueIdle();/**队列空闲？？？**/
} catch (Throwable t) {
Log.wtf(TAG, "IdleHandler threw exception", t);
}
if (!keep) {/**不保留则直接移除**/
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;
}
}四、Looper的工作原理
Looper在消息机制中作用是：消息循环，会不停对从MessageQueue中查看是否有新的消息。如果有新消息则会立即处理。否则一直阻塞在那里。
/**
* Run the message queue in this thread. Be sure to call
* {@link #quit()} to end the loop.
*/
public static void loop() {
final Looper me = myLooper();/**拿到当前线程的中的Looper**/
if (me == null) {/**当前looper为空的情况抛出异常**/
throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
}
final MessageQueue queue = me.mQueue;/**拿到Looper中的消息队列**/
// 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();/**清空远程调用端的uid和pid,用当前本地进程的uid和pid替换**/
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);
boolean slowDeliveryDetected = false;/**减慢传输探测**/
for (;;) {/**死循环**/
Message msg = queue.next(); // might block 从队列中去一个消息处理 可能被阻塞哦
if (msg == null) {/**消息为空直接返回**/
// No message indicates that the message queue is quitting.
return;
}
// 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);
}
final long traceTag = me.mTraceTag;
long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;/**减慢时间分发**/
long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;/**减慢传送**/
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;
try {
msg.target.dispatchMessage(msg);/***这里直接将消息发送到handler中处理**/
dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
} finally {
if (traceTag != 0) {
Trace.traceEnd(traceTag);
}
}
if (logSlowDelivery) {
if (slowDeliveryDetected) {
if ((dispatchStart - msg.when) <= 10) {
Slog.w(TAG, "Drained");
slowDeliveryDetected = false;
}
} else {
if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
msg)) {
// Once we write a slow delivery log, suppress until the queue drains.
slowDeliveryDetected = 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();/**回收**/
}
} /**UI主线程**/
public static void main(String[] args) {
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
EventLogger.setReporter(new EventLoggingReporter());
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);
/**创建主线程Looper**/
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
/**获取主线的Handler**/
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
Looper.loop();/**启动loop循环**/
}主线程的Handler
/**主线程的Handler**/
class H extends Handler {
public static final int BIND_APPLICATION = 110;
public static final int EXIT_APPLICATION = 111;
public static final int RECEIVER = 113;
public static final int CREATE_SERVICE = 114;
public static final int SERVICE_ARGS = 115;
public static final int STOP_SERVICE = 116;
public static final int CONFIGURATION_CHANGED = 118;
public static final int CLEAN_UP_CONTEXT = 119;
public static final int GC_WHEN_IDLE = 120;
public static final int BIND_SERVICE = 121;
public static final int UNBIND_SERVICE = 122;
public static final int DUMP_SERVICE = 123;
public static final int LOW_MEMORY = 124;
public static final int PROFILER_CONTROL = 127;
public static final int CREATE_BACKUP_AGENT = 128;
public static final int DESTROY_BACKUP_AGENT = 129;
public static final int SUICIDE = 130;
public static final int REMOVE_PROVIDER = 131;
public static final int ENABLE_JIT = 132;
public static final int DISPATCH_PACKAGE_BROADCAST = 133;
public static final int SCHEDULE_CRASH = 134;
public static final int DUMP_HEAP = 135;
public static final int DUMP_ACTIVITY = 136;
public static final int SLEEPING = 137;
public static final int SET_CORE_SETTINGS = 138;
public static final int UPDATE_PACKAGE_COMPATIBILITY_INFO = 139;
public static final int DUMP_PROVIDER = 141;
public static final int UNSTABLE_PROVIDER_DIED = 142;
public static final int REQUEST_ASSIST_CONTEXT_EXTRAS = 143;
public static final int TRANSLUCENT_CONVERSION_COMPLETE = 144;
public static final int INSTALL_PROVIDER = 145;
public static final int ON_NEW_ACTIVITY_OPTIONS = 146;
public static final int ENTER_ANIMATION_COMPLETE = 149;
public static final int START_BINDER_TRACKING = 150;
public static final int STOP_BINDER_TRACKING_AND_DUMP = 151;
public static final int LOCAL_VOICE_INTERACTION_STARTED = 154;
public static final int ATTACH_AGENT = 155;
public static final int APPLICATION_INFO_CHANGED = 156;
public static final int RUN_ISOLATED_ENTRY_POINT = 158;
public static final int EXECUTE_TRANSACTION = 159;
public static final int RELAUNCH_ACTIVITY = 160;
public void handleMessage(Message msg) {/**处理消息**/
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case EXIT_APPLICATION:
if (mInitialApplication != null) {
mInitialApplication.onTerminate();
}
Looper.myLooper().quit();
break;
case RECEIVER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp");
handleReceiver((ReceiverData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceCreate: " + String.valueOf(msg.obj)));
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UNBIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceUnbind");
handleUnbindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SERVICE_ARGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceStart: " + String.valueOf(msg.obj)));
handleServiceArgs((ServiceArgsData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case STOP_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStop");
handleStopService((IBinder)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case CONFIGURATION_CHANGED:
handleConfigurationChanged((Configuration) msg.obj);
break;
case CLEAN_UP_CONTEXT:
ContextCleanupInfo cci = (ContextCleanupInfo)msg.obj;
cci.context.performFinalCleanup(cci.who, cci.what);
break;
case GC_WHEN_IDLE:
scheduleGcIdler();
break;
case DUMP_SERVICE:
handleDumpService((DumpComponentInfo)msg.obj);
break;
case LOW_MEMORY:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "lowMemory");
handleLowMemory();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case PROFILER_CONTROL:
handleProfilerControl(msg.arg1 != 0, (ProfilerInfo)msg.obj, msg.arg2);
break;
case CREATE_BACKUP_AGENT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupCreateAgent");
handleCreateBackupAgent((CreateBackupAgentData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case DESTROY_BACKUP_AGENT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupDestroyAgent");
handleDestroyBackupAgent((CreateBackupAgentData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SUICIDE:
Process.killProcess(Process.myPid());
break;
case REMOVE_PROVIDER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "providerRemove");
completeRemoveProvider((ProviderRefCount)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case ENABLE_JIT:
ensureJitEnabled();
break;
case DISPATCH_PACKAGE_BROADCAST:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastPackage");
handleDispatchPackageBroadcast(msg.arg1, (String[])msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SCHEDULE_CRASH:
throw new RemoteServiceException((String)msg.obj);
case DUMP_HEAP:
handleDumpHeap((DumpHeapData) msg.obj);
break;
case DUMP_ACTIVITY:
handleDumpActivity((DumpComponentInfo)msg.obj);
break;
case DUMP_PROVIDER:
handleDumpProvider((DumpComponentInfo)msg.obj);
break;
case SLEEPING:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "sleeping");
handleSleeping((IBinder)msg.obj, msg.arg1 != 0);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SET_CORE_SETTINGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "setCoreSettings");
handleSetCoreSettings((Bundle) msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UPDATE_PACKAGE_COMPATIBILITY_INFO:
handleUpdatePackageCompatibilityInfo((UpdateCompatibilityData)msg.obj);
break;
case UNSTABLE_PROVIDER_DIED:
handleUnstableProviderDied((IBinder)msg.obj, false);
break;
case REQUEST_ASSIST_CONTEXT_EXTRAS:
handleRequestAssistContextExtras((RequestAssistContextExtras)msg.obj);
break;
case TRANSLUCENT_CONVERSION_COMPLETE:
handleTranslucentConversionComplete((IBinder)msg.obj, msg.arg1 == 1);
break;
case INSTALL_PROVIDER:
handleInstallProvider((ProviderInfo) msg.obj);
break;
case ON_NEW_ACTIVITY_OPTIONS:
Pair pair = (Pair) msg.obj;
onNewActivityOptions(pair.first, pair.second);
break;
case ENTER_ANIMATION_COMPLETE:
handleEnterAnimationComplete((IBinder) msg.obj);
break;
case START_BINDER_TRACKING:
handleStartBinderTracking();
break;
case STOP_BINDER_TRACKING_AND_DUMP:
handleStopBinderTrackingAndDump((ParcelFileDescriptor) msg.obj);
break;
case LOCAL_VOICE_INTERACTION_STARTED:
handleLocalVoiceInteractionStarted((IBinder) ((SomeArgs) msg.obj).arg1,
(IVoiceInteractor) ((SomeArgs) msg.obj).arg2);
break;
case ATTACH_AGENT: {
Application app = getApplication();
handleAttachAgent((String) msg.obj, app != null ? app.mLoadedApk : null);
break;
}
case APPLICATION_INFO_CHANGED:
mUpdatingSystemConfig = true;
try {
handleApplicationInfoChanged((ApplicationInfo) msg.obj);
} finally {
mUpdatingSystemConfig = false;
}
break;
case RUN_ISOLATED_ENTRY_POINT:
handleRunIsolatedEntryPoint((String) ((SomeArgs) msg.obj).arg1,
(String[]) ((SomeArgs) msg.obj).arg2);
break;
case EXECUTE_TRANSACTION:
final ClientTransaction transaction = (ClientTransaction) msg.obj;
mTransactionExecutor.execute(transaction);
break;
case RELAUNCH_ACTIVITY:
handleRelaunchActivityLocally((IBinder) msg.obj);
break;
}
Object obj = msg.obj;
if (obj instanceof SomeArgs) {
((SomeArgs) obj).recycle();
}
}
}