前言：
【Android開發】線程間通訊機制（基礎篇）——Handler、Runnable、HandlerThread、AsyncTask的使用
有時候，如果你能帶著問題或者目標去探索新知識的話，這樣的學習效率就高很多。 所以我們先從最基礎的實現方式（Handler+Message+Runnable）說起。
一、Handler+Message+Runnable內部解析
我們在使用Handler類的時候，都知道有sendMessage（Message）等發送消息的功能和
[java] view plain
copy ? ? ? ? ? ? ?? ????public ?Handler()?{?? ????????this (null ,?false );?? ????}??
[java] view plain
copy public ?Handler(Callback?callback,?boolean ?async)?{??????????if ?(FIND_POTENTIAL_LEAKS)?{?? ????????????final ?Class<??extends ?Handler>?klass?=?getClass();?? ????????????if ?((klass.isAnonymousClass()?||?klass.isMemberClass()?||?klass.isLocalClass())?&&?? ????????????????????(klass.getModifiers()?&?Modifier.STATIC)?==?0 )?{?? ????????????????Log.w(TAG,?"The?following?Handler?class?should?be?static?or?leaks?might?occur:?" ?+?? ????????????????????klass.getCanonicalName());?? ????????????}?? ????????}?? ?? ????????mLooper?=?Looper.myLooper();?? ????????if ?(mLooper?==?null )?{?? ????????????throw ?new ?RuntimeException(?? ????????????????"Can't?create?handler?inside?thread?that?has?not?called?Looper.prepare()" );?? ????????}?? ????????mQueue?=?mLooper.mQueue;?? ????????mCallback?=?callback;?? ????????mAsynchronous?=?async;?? ????}??
? 可以從mLooper = Looper.myLooper()
[java] view plain
copy ?? ???static ?final ?ThreadLocal<Looper>?sThreadLocal?=?new ?ThreadLocal<Looper>();??
[java] view plain
copy ? ? ? ?? ????public ?static ?Looper?myLooper()?{?? ????????return ?sThreadLocal.get();?? ????}??
[java] view plain
copy public ?final ?boolean ?post(Runnable?r)??????{?? ???????return ??sendMessageDelayed(getPostMessage(r),?0 );?? ????}??
[java] view plain
copy private ?static ?Message?getPostMessage(Runnable?r)?{??????????Message?m?=?Message.obtain();?? ????????m.callback?=?r;?? ????????return ?m;?? ????}??
[java] view plain
copy public ?final ?class ?Message?implements ?Parcelable?{????????public ?int ?what;???? ????public ?int ?arg1;???? ????public ?int ?arg2;???? ????public ?Object?obj;???? ????public ?Messenger?replyTo;???? ????long ?when;???? ????Bundle?data;???? ????Handler?target;????????? ????Runnable?callback;????? ????Message?next;???? ????private ?static ?Object?mPoolSync?=?new ?Object();???? ????private ?static ?Message?mPool;???? ????private ?static ?int ?mPoolSize?=?0 ;???? ????private ?static ?final ?int ?MAX_POOL_SIZE?=?10 ;???
? ? ? ?對于源碼的解讀，可以明確兩點：
? ? ? ? 1）Message.obtain()是通過從全局Message pool中讀取一個Message，回收的時候也是將該Message 放入到
? ? ? ? 2）Message中實現了Parcelable接口
[java] view plain
copy ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? ???public ?boolean ?sendMessageAtTime(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);?? ???}??
[java] view plain
copy private ?boolean ?enqueueMessage(MessageQueue?queue,?Message?msg,?long ?uptimeMillis)?{?????????msg.target?=?this ;?? ???????if ?(mAsynchronous)?{?? ???????????msg.setAsynchronous(true );?? ???????}?? ???????return ?queue.enqueueMessage(msg,?uptimeMillis);?? ???}??
[java] view plain
copy ? ? ? ?? ????public ?static ?void ?loop()?{?? ????????final ?Looper?me?=?myLooper();?? ????????if ?(me?==?null )?{?? ????????????throw ?new ?RuntimeException("No?Looper;?Looper.prepare()?wasn't?called?on?this?thread." );?? ????????}?? ????????final ?MessageQueue?queue?=?me.mQueue;?? ?? ?????????? ?????????? ????????Binder.clearCallingIdentity();?? ????????final ?long ?ident?=?Binder.clearCallingIdentity();?? ?? ????????for ?(;;)?{?? ????????????Message?msg?=?queue.next();??? ????????????if ?(msg?==?null )?{?? ?????????????????? ????????????????return ;?? ????????????}?? ?? ?????????????? ????????????Printer?logging?=?me.mLogging;?? ????????????if ?(logging?!=?null )?{?? ????????????????logging.println(">>>>>?Dispatching?to?" ?+?msg.target?+?"?" ?+?? ????????????????????????msg.callback?+?":?" ?+?msg.what);?? ????????????}?? ?? ????????????msg.target.<span?style="color:#ff0000;" ><strong>dispatchMessage</strong></span>(msg);?? ?? ????????????if ?(logging?!=?null )?{?? ????????????????logging.println("<<<<<?Finished?to?" ?+?msg.target?+?"?" ?+?msg.callback);?? ????????????}?? ?? ?????????????? ?????????????? ????????????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.recycle();?? ????????}?? ????}??
里面loop方法找到調用Handler的dispatchMessage的方法，我們再看看Handler的dispatchMessage：
[java] view plain
copy public ?void ?dispatchMessage(Message?msg)?{?????????if ?(msg.callback?!=?null )?{?? ???????????handleCallback(msg);?? ???????}?else ?{?? ???????????if ?(mCallback?!=?null )?{?? ???????????????if ?(mCallback.handleMessage(msg))?{?? ???????????????????return ;?? ???????????????}?? ???????????}?? ???????????handleMessage(msg);?? ???????}?? ???}??
[java] view plain
copy public ?static ?void ?main(String[]?args)?{??????????SamplingProfilerIntegration.start();?? ?? ?????????? ?????????? ?????????? ????????CloseGuard.setEnabled(false );?? ?? ????????Process.setArgV0("<pre-initialized>" );?? ?? ????????Looper.prepareMainLooper();?? ????????if ?(sMainThreadHandler?==?null )?{?? ????????????sMainThreadHandler?=?new ?Handler();?? ????????}?? ?? ????????ActivityThread?thread?=?new ?ActivityThread();?? ????????thread.attach(false );?? ?? ????????if ?(false )?{?? ????????????Looper.myLooper().setMessageLogging(new ?? ????????????????????LogPrinter(Log.DEBUG,?"ActivityThread" ));?? ????????}?? ?? ????????<span?style="color:#ff0000;" >Looper.loop();</span>?? ?? ????????throw ?new ?RuntimeException("Main?thread?loop?unexpectedly?exited" );?? ????}??
二、HandlerThread
[java] view plain
copy public ?class ?HandlerThread?extends ?Thread?{??????int ?mPriority;?? ????int ?mTid?=?-1 ;?? ????Looper?mLooper;?? ?? ????public ?HandlerThread(String?name)?{?? ????????super (name);?? ????????mPriority?=?Process.THREAD_PRIORITY_DEFAULT;?? ????}?? ?????? ????? ? ? ? ? ?? ????public ?HandlerThread(String?name,?int ?priority)?{?? ????????super (name);?? ????????mPriority?=?priority;?? ????}?? ?????? ????? ? ? ?? ????protected ?void ?onLooperPrepared()?{?? ????}?? ?? ????public ?void ?run()?{?? ????????mTid?=?Process.myTid();?? ????????<span?style="color:#ff0000;" >Looper.prepare();</span>?? ????????synchronized ?(this )?{?? ????????????mLooper?=?Looper.myLooper();?? ????????????notifyAll();?? ????????}?? ????????Process.setThreadPriority(mPriority);?? ????????onLooperPrepared();?? ????????<span?style="color:#ff0000;" >Looper.loop();</span>?? ????????mTid?=?-1 ;?? ????}?? ?????? ????? ? ? ? ? ?? ????public ?Looper?getLooper()?{?? ????????if ?(!isAlive())?{?? ????????????return ?null ;?? ????????}?? ?????????? ?????????? ????????synchronized ?(this )?{?? ????????????while ?(isAlive()?&&?mLooper?==?null )?{?? ????????????????try ?{?? ????????????????????wait();?? ????????????????}?catch ?(InterruptedException?e)?{?? ????????????????}?? ????????????}?? ????????}?? ????????return ?mLooper;?? ????}?? ?????? ????? ? ? ? ? ?? ????public ?boolean ?quit()?{?? ????????Looper?looper?=?getLooper();?? ????????if ?(looper?!=?null )?{?? ????????????looper.quit();?? ????????????return ?true ;?? ????????}?? ????????return ?false ;?? ????}?? ?????? ????? ? ?? ????public ?int ?getThreadId()?{?? ????????return ?mTid;?? ????}?? }??
三、AsyncTask
[java] view plain
copy public ?abstract ?class ?AsyncTask<Params,?Progress,?Result>?{??????private ?static ?final ?String?LOG_TAG?=?"AsyncTask" ;?? ?? ????private ?static ?final ?int ?CORE_POOL_SIZE?=?5 ;?? ????private ?static ?final ?int ?MAXIMUM_POOL_SIZE?=?128 ;?? ????private ?static ?final ?int ?KEEP_ALIVE?=?1 ;?? ?? ????private ?static ?final ?ThreadFactory?sThreadFactory?=?new ?ThreadFactory()?{?? ????????private ?final ?AtomicInteger?mCount?=?new ?AtomicInteger(1 );?? ?? ????????public ?Thread?newThread(Runnable?r)?{?? ????????????return ?new ?Thread(r,?"AsyncTask?#" ?+?mCount.getAndIncrement());?? ????????}?? ????};?? ?? ????private ?static ?final ?BlockingQueue<Runnable>?sPoolWorkQueue?=?? ????????????new ?LinkedBlockingQueue<Runnable>(10 );?? ?? ????? ? ?? ????public ?static ?final ?Executor?THREAD_POOL_EXECUTOR?? ????????????=?new ?ThreadPoolExecutor(CORE_POOL_SIZE,?MAXIMUM_POOL_SIZE,?KEEP_ALIVE,?? ????????????????????TimeUnit.SECONDS,?sPoolWorkQueue,?sThreadFactory);?? ?? ????? ? ? ?? ????public ?static ?final ?Executor?SERIAL_EXECUTOR?=?new ?SerialExecutor();?? ?? ????private ?static ?final ?int ?MESSAGE_POST_RESULT?=?0x1 ;?? ????private ?static ?final ?int ?MESSAGE_POST_PROGRESS?=?0x2 ;?? ?? ????private ?static ?final ?InternalHandler?sHandler?=?new ?InternalHandler();?? ?? ????private ?static ?volatile ?Executor?sDefaultExecutor?=?SERIAL_EXECUTOR;?? ????private ?final ?WorkerRunnable<Params,?Result>?mWorker;?? ????private ?final ?FutureTask<Result>?mFuture;?? ?? ????private ?volatile ?Status?mStatus?=?Status.PENDING;?? ?????? ????private ?final ?AtomicBoolean?mCancelled?=?new ?AtomicBoolean();?? ????private ?final ?AtomicBoolean?mTaskInvoked?=?new ?AtomicBoolean();?? ?? ????private ?static ?class ?SerialExecutor?implements ?Executor?{?? ????????final ?ArrayDeque<Runnable>?mTasks?=?new ?ArrayDeque<Runnable>();?? ????????Runnable?mActive;?? ?? ????????public ?synchronized ?void ?execute(final ?Runnable?r)?{?? ????????????mTasks.offer(new ?Runnable()?{?? ????????????????public ?void ?run()?{?? ????????????????????try ?{?? ????????????????????????r.run();?? ????????????????????}?finally ?{?? ????????????????????????scheduleNext();?? ????????????????????}?? ????????????????}?? ????????????});?? ????????????if ?(mActive?==?null )?{?? ????????????????scheduleNext();?? ????????????}?? ????????}?? ?? ????????protected ?synchronized ?void ?scheduleNext()?{?? ????????????if ?((mActive?=?mTasks.poll())?!=?null )?{?? ????????????????THREAD_POOL_EXECUTOR.execute(mActive);?? ????????????}?? ????????}?? ????}?? ?? ????? ? ? ?? ????public ?enum ?Status?{?? ????????? ? ?? ????????PENDING,?? ????????? ? ?? ????????RUNNING,?? ????????? ? ?? ????????FINISHED,?? ????}?? ?? ?????? ????public ?static ?void ?init()?{?? ????????sHandler.getLooper();?? ????}?? ?? ?????? ????public ?static ?void ?setDefaultExecutor(Executor?exec)?{?? ????????sDefaultExecutor?=?exec;?? ????}?? ?? ????? ? ?? ????public ?AsyncTask()?{?? ????????mWorker?=?new ?WorkerRunnable<Params,?Result>()?{?? ????????????public ?Result?call()?throws ?Exception?{?? ????????????????mTaskInvoked.set(true );?? ?? ????????????????Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);?? ?????????????????? ????????????????return ?postResult(doInBackground(mParams));?? ????????????}?? ????????};?? ?? ????????mFuture?=?new ?FutureTask<Result>(mWorker)?{?? ????????????@Override ?? ????????????protected ?void ?done()?{?? ????????????????try ?{?? ????????????????????postResultIfNotInvoked(get());?? ????????????????}?catch ?(InterruptedException?e)?{?? ????????????????????android.util.Log.w(LOG_TAG,?e);?? ????????????????}?catch ?(ExecutionException?e)?{?? ????????????????????throw ?new ?RuntimeException("An?error?occured?while?executing?doInBackground()" ,?? ????????????????????????????e.getCause());?? ????????????????}?catch ?(CancellationException?e)?{?? ????????????????????postResultIfNotInvoked(null );?? ????????????????}?? ????????????}?? ????????};?? ????}?? ?? ????private ?void ?postResultIfNotInvoked(Result?result)?{?? ????????final ?boolean ?wasTaskInvoked?=?mTaskInvoked.get();?? ????????if ?(!wasTaskInvoked)?{?? ????????????postResult(result);?? ????????}?? ????}?? ?? ????private ?Result?postResult(Result?result)?{?? ????????@SuppressWarnings ("unchecked" )?? ????????Message?message?=?sHandler.obtainMessage(MESSAGE_POST_RESULT,?? ????????????????new ?AsyncTaskResult<Result>(this ,?result));?? ????????message.sendToTarget();?? ????????return ?result;?? ????}?? ?? ?????? ????public ?final ?Status?getStatus()?{?? ????????return ?mStatus;?? ????}?? ?? ?????? ????protected ?abstract ?Result?doInBackground(Params...?params);?? ?? ????? ????protected ?void ?onPreExecute()?{?? ????}?? ?? ?????? ????@SuppressWarnings ({"UnusedDeclaration" })?? ????protected ?void ?onPostExecute(Result?result)?{?? ????}?? ?? ?????? ????@SuppressWarnings ({"UnusedDeclaration" })?? ????protected ?void ?onProgressUpdate(Progress...?values)?{?? ????}?? ?? ????? ????@SuppressWarnings ({"UnusedParameters" })?? ????protected ?void ?onCancelled(Result?result)?{?? ????????onCancelled();?? ????}?????? ?????? ?????? ????protected ?void ?onCancelled()?{?? ????}?? ?? ?????? ????public ?final ?boolean ?isCancelled()?{?? ????????return ?mCancelled.get();?? ????}?? ?? ?????? ????public ?final ?boolean ?cancel(boolean ?mayInterruptIfRunning)?{?? ????????mCancelled.set(true );?? ????????return ?mFuture.cancel(mayInterruptIfRunning);?? ????}?? ?? ?????? ????public ?final ?Result?get()?throws ?InterruptedException,?ExecutionException?{?? ????????return ?mFuture.get();?? ????}?? ?? ?????? ????public ?final ?Result?get(long ?timeout,?TimeUnit?unit)?throws ?InterruptedException,?? ????????????ExecutionException,?TimeoutException?{?? ????????return ?mFuture.get(timeout,?unit);?? ????}?? ?? ?????? ????public ?final ?AsyncTask<Params,?Progress,?Result>?execute(Params...?params)?{?? ????????return ?executeOnExecutor(sDefaultExecutor,?params);?? ????}?? ?? ????? ????public ?final ?AsyncTask<Params,?Progress,?Result>?executeOnExecutor(Executor?exec,?? ????????????Params...?params)?{?? ????????if ?(mStatus?!=?Status.PENDING)?{?? ????????????switch ?(mStatus)?{?? ????????????????case ?RUNNING:?? ????????????????????throw ?new ?IllegalStateException("Cannot?execute?task:" ?? ????????????????????????????+?"?the?task?is?already?running." );?? ????????????????case ?FINISHED:?? ????????????????????throw ?new ?IllegalStateException("Cannot?execute?task:" ?? ????????????????????????????+?"?the?task?has?already?been?executed?" ?? ????????????????????????????+?"(a?task?can?be?executed?only?once)" );?? ????????????}?? ????????}?? ?? ????????mStatus?=?Status.RUNNING;?? ?? ????????onPreExecute();?? ?? ????????mWorker.mParams?=?params;?? ????????exec.execute(mFuture);?? ?? ????????return ?this ;?? ????}?? ?? ?????? ????public ?static ?void ?execute(Runnable?runnable)?{?? ????????sDefaultExecutor.execute(runnable);?? ????}?? ?? ?????? ????protected ?final ?void ?publishProgress(Progress...?values)?{?? ????????if ?(!isCancelled())?{?? ????????????sHandler.obtainMessage(MESSAGE_POST_PROGRESS,?? ????????????????????new ?AsyncTaskResult<Progress>(this ,?values)).sendToTarget();?? ????????}?? ????}?? ?? ????private ?void ?finish(Result?result)?{?? ????????if ?(isCancelled())?{?? ????????????onCancelled(result);?? ????????}?else ?{?? ????????????onPostExecute(result);?? ????????}?? ????????mStatus?=?Status.FINISHED;?? ????}?? ?? ????private ?static ?class ?InternalHandler?extends ?Handler?{?? ????????@SuppressWarnings ({"unchecked" ,?"RawUseOfParameterizedType" })?? ????????@Override ?? ????????public ?void ?handleMessage(Message?msg)?{?? ????????????AsyncTaskResult?result?=?(AsyncTaskResult)?msg.obj;?? ????????????switch ?(msg.what)?{?? ????????????????case ?MESSAGE_POST_RESULT:?? ?????????????????????? ????????????????????result.mTask.finish(result.mData[0 ]);?? ????????????????????break ;?? ????????????????case ?MESSAGE_POST_PROGRESS:?? ????????????????????result.mTask.onProgressUpdate(result.mData);?? ????????????????????break ;?? ????????????}?? ????????}?? ????}?? ?? ????private ?static ?abstract ?class ?WorkerRunnable<Params,?Result>?implements ?Callable<Result>?{?? ????????Params[]?mParams;?? ????}?? ?? ????@SuppressWarnings ({"RawUseOfParameterizedType" })?? ????private ?static ?class ?AsyncTaskResult<Data>?{?? ????????final ?AsyncTask?mTask;?? ????????final ?Data[]?mData;?? ?? ????????AsyncTaskResult(AsyncTask?task,?Data...?data)?{?? ????????????mTask?=?task;?? ????????????mData?=?data;?? ????????}?? ????}?? }??
sHandler
Callable 接口,就是有返回值的線程任務。
mFuture
[java] view plain
copy ? ? ? ?? ?private ?void ?finishCompletion()?{?? ??????? ?????for ?(WaitNode?q;?(q?=?waiters)?!=?null ;)?{?? ?????????if ?(UNSAFE.compareAndSwapObject(this ,?waitersOffset,?q,?null ))?{?? ?????????????for ?(;;)?{?? ?????????????????Thread?t?=?q.thread;?? ?????????????????if ?(t?!=?null )?{?? ?????????????????????q.thread?=?null ;?? ?????????????????????LockSupport.unpark(t);?? ?????????????????}?? ?????????????????WaitNode?next?=?q.next;?? ?????????????????if ?(next?==?null )?? ?????????????????????break ;?? ?????????????????q.next?=?null ;??? ?????????????????q?=?next;?? ?????????????}?? ?????????????break ;?? ?????????}?? ?????}?? ?? ????<span?style="color:#cc0000;" >?done();</span>?? ?? ?????callable?=?null ;?????????? ?}??
mWorker和mFuture是實例變量
四、總結
原文地址： http://blog.csdn.net/q376420785/article/details/8883008
總結
以上是生活随笔 為你收集整理的线程间通讯机制（提高篇）——深入浅出实现原理 的全部內容，希望文章能夠幫你解決所遇到的問題。
如果覺得生活随笔 網站內容還不錯，歡迎將生活随笔 推薦給好友。
