Hander消息機制源碼分析
一、Hander消息簡單使用
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 這個是不會執行的");
}
};
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主要是消息的發送和消息的接受
常用發送消息方法：
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消息處理
msg.target.dispatchMessage(msg);/***這裏直接將消息發送到handler中處理**/
/** 消息的處理
* Handle system messages here.
*/
public void dispatchMessage(Message msg) {
if (msg.callback != null) {/**消息有回調情況則直接回調**/
handleCallback(msg);
} else {
if (mCallback != null) {/**handler有回調情況則直接回調**/
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);/**沒有回調情況直接調用Handler子類中複寫了handleMessage**/
}
}
三、消息進入隊列
private boolean enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) {
msg.target = this;
if (mAsynchronous) {
msg.setAsynchronous(true);
}
return queue.enqueueMessage(msg, uptimeMillis);
}
消息隊列MessageQueue是鏈表式的隊列。
進入隊列的方法
/****
* 消息進入隊列 MessageQueue
* @param msg 消息
* @param when 執行時間 when= SystemClock.uptimeMillis() + delayMillis
* @return
*/
boolean enqueueMessage(Message msg, long when) {
if (msg.target == null) { /***mmessage最終是要在Handler執行的，**/
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) { /***隊列已經停止工作**/
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，進入隊列失敗**/
return false;
}
msg.markInUse();/**消息標記爲已被使用了**/
msg.when = when;/**消息記錄要在什麼時候執行**/
Message p = mMessages;/***當前Messages隊列，隊列首元素指針**/
boolean needWake; /**當前隊列首元素爲空 或者 該消息是要立即執行 或者 改消息的執行時間比隊列首元素要早 **/
if (p == null || when == 0 || when < p.when) {
// New head, wake up the event queue if blocked.
msg.next = p; /**要插入的消息作爲隊列首元素**/
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();/**一般是不需要喚醒**/
Message prev; /***前一個消息**/
for (;;) {
prev = p;
p = p.next; /**下一個消息**/
if (p == null || when < p.when) {/***下一個消息爲空 或者 插入的消息執行時間要比下一個消息要早，插入的消息要在p的前面**/
break;
}
if (needWake && p.isAsynchronous()) {/**異步則改成不需要喚醒**/
needWake = false;
}
}
msg.next = p; // invariant: p == prev.next
prev.next = msg;/**在prew和msg間插入新消息**/
}
// We can assume mPtr != 0 because mQuitting is false.
if (needWake) {/**需要喚醒的情況***/
nativeWake(mPtr);
}
}
return true;
}
從隊列出的方法。當然是根據消息具體的處理時刻來出隊列的
/**從隊列中取出一個要執行的消息**/
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循環已經終止，直接返回**/
return null;
}
/***掛起空閒要處理的消息的數量**/
int pendingIdleHandlerCount = -1; // -1 only during first iteration
int nextPollTimeoutMillis = 0;/**下一個執行消息的超時時間，單位毫秒ms**/
for (;;) {/**死循環**/
if (nextPollTimeoutMillis != 0) {/**下次要執行超時時間不爲0，則調用Binder的flushPendingCommands對當前任務掛起**/
Binder.flushPendingCommands();
}
nativePollOnce(ptr, nextPollTimeoutMillis);/***線程掛起的時間爲nextPollTimeoutMillis 毫秒**/
synchronized (this) {
// Try to retrieve the next message. Return if found.
final long now = SystemClock.uptimeMillis();/***當前手機系統時間（指定是手機系統啓動時算起）**/
Message prevMsg = null;/**前一個消息***/
Message msg = mMessages;/**隊列首個元素**/
if (msg != null && msg.target == null) {/**這個msg沒有要處理被處理的場所，則取下一個**/
// Stalled by a barrier. Find the next asynchronous message in the queue.
do {
prevMsg = msg;
msg = msg.next;
} while (msg != null && !msg.isAsynchronous());/**msg是要同步的則繼續取下一個**/
}
if (msg != null) {
if (now < msg.when) {/**當前系統時間比消息要執行的時間要早***/
// 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);/**計算出msg下次要執行的時間**/
} else {
// Got a message.
mBlocked = false;/**標記爲不需要阻塞**/
if (prevMsg != null) {
prevMsg.next = msg.next;/**前一個元素直接指向下一個元素的next**/
} else {
mMessages = msg.next;/**前一個元素直接指向下一個元素的next**/
}
msg.next = null; /**取出msg元素***/
if (DEBUG) Log.v(TAG, "Returning message: " + msg);
msg.markInUse();
return msg;/**返回這個元素就完事了**/
}
} else {
// No more messages.
nextPollTimeoutMillis = -1;/**沒有消息的情況***/
}
// Process the quit message now that all pending messages have been handled.
if (mQuitting) {/**處理停止的消息 所有消息被處理掉了**/
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 /**被掛起的消息個數小於0,消息隊列爲空，系統時間早於隊列首個元素的執行時間***/
&& (mMessages == null || now < mMessages.when)) {
pendingIdleHandlerCount = mIdleHandlers.size();/**記錄當前被空閒的回調**/
}
if (pendingIdleHandlerCount <= 0) {/**回調爲<=0**/
// No idle handlers to run. Loop and wait some more.
mBlocked = true;/***進行阻塞**/
continue;
}
if (mPendingIdleHandlers == null) { /**創建最少四個掛起回調數組***/
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];/**掛起回調**/
mPendingIdleHandlers[i] = null; // release the reference to the handler
boolean keep = false;
try {
keep = idler.queueIdle();/**隊列空閒？？？**/
} catch (Throwable t) {
Log.wtf(TAG, "IdleHandler threw exception", t);
}
if (!keep) {/**不保留則直接移除**/
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在消息機制中作用是：消息循環，會不停對從MessageQueue中查看是否有新的消息。如果有新消息則會立即處理。否則一直阻塞在那裏。
/**
* 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();/**拿到當前線程的中的Looper**/
if (me == null) {/**當前looper爲空的情況拋出異常**/
throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
}
final MessageQueue queue = me.mQueue;/**拿到Looper中的消息隊列**/
// 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();/**清空遠程調用端的uid和pid,用當前本地進程的uid和pid替換**/
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;/**減慢傳輸探測**/
for (;;) {/**死循環**/
Message msg = queue.next(); // might block 從隊列中去一個消息處理 可能被阻塞哦
if (msg == null) {/**消息爲空直接返回**/
// 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;/**減慢時間分發**/
long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;/**減慢傳送**/
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);/***這裏直接將消息發送到handler中處理**/
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主線程**/
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);
/**創建主線程Looper**/
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
/**獲取主線的Handler**/
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
Looper.loop();/**啓動loop循環**/
}
主線程的Handler
/**主線程的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) {/**處理消息**/
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<IBinder, ActivityOptions> pair = (Pair<IBinder, ActivityOptions>) 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();
}
}
}