今天接到了個需求,需要用到跨進程拋異常。
怎樣將異常從服務端拋到客戶端
也就是說在Service端拋出的異常需要可以在Client端接收。印象中binder是可以傳異常的,所以aidl直接走起:
// aidl文件interface ITestExceptionAidl { boolean testThrowException();}// service端實現public class AidlService extends Service { @Nullable @Override public IBinder onBind(Intent intent) { return new ITestExceptionAidl.Stub() { @Override public boolean testThrowException() throws RemoteException { if (true) { throw new RuntimeException("TestException"); } return true; } }; }}// client端實現bindService(intent, new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { ITestExceptionAidl aidl = ITestExceptionAidl.Stub.asInterface(service); try { aidl.testThrowException(); } catch (Exception e) { Log.e("testtest", "Exception", e); } } @Override public void onServiceDisconnected(ComponentName name) { }}, Context.BIND_AUTO_CREATE);但是這個程序實際上運行起來是這樣的:
01-01 05:31:55.475 4868 4880 E JavaBinder: *** Uncaught remote exception! (Exceptions are not yet supported across processes.)
01-01 05:31:55.475 4868 4880 E JavaBinder: java.lang.RuntimeException: TestException
01-01 05:31:55.475 4868 4880 E JavaBinder: at me.linjw.demo.ipcdemo.AidlService$1.testThrowException(AidlService.java:22)
01-01 05:31:55.475 4868 4880 E JavaBinder: at me.linjw.demo.ipcdemo.ITestExceptionAidl$Stub.onTransact(ITestExceptionAidl.java:48)
01-01 05:31:55.475 4868 4880 E JavaBinder: at android.os.Binder.execTransact(Binder.java:565)
看日志里面的ITestExceptionAidl$Stub.onTransact,也就是說在service端就已經被異常打斷了,并沒有傳給client端,而且第一個大大的”Exceptions are not yet supported across processes.”是說異常不允許跨進程嗎?但是我明明記得AIDL生成的代碼里面就有向Parcel寫入異常啊:
public boolean onTransact(int code, android.os.Parcel data, android.os.Parcel reply, int flags) throws android.os.RemoteException { switch (code) { case INTERFACE_TRANSACTION: { reply.writeString(DESCRIPTOR); return true; } case TRANSACTION_testThrowException: { data.enforceInterface(DESCRIPTOR); boolean _result = this.testThrowException(); reply.writeNoException(); // 這里寫入的是沒有拋出異常 reply.writeInt(((_result) ? (1) : (0))); return true; } } return super.onTransact(code, data, reply, flags);}查找Parcel的源碼,其實是有writeException方法的:
public final void writeException(Exception e) { int code = 0; if (e instanceof Parcelable && (e.getClass().getClassLoader() == Parcelable.class.getClassLoader())) { // We only send Parcelable exceptions that are in the // BootClassLoader to ensure that the receiver can unpack them code = EX_PARCELABLE; } else if (e instanceof SecurityException) { code = EX_SECURITY; } else if (e instanceof BadParcelableException) { code = EX_BAD_PARCELABLE; } else if (e instanceof IllegalArgumentException) { code = EX_ILLEGAL_ARGUMENT; } else if (e instanceof NullPointerException) { code = EX_NULL_POINTER; } else if (e instanceof IllegalStateException) { code = EX_ILLEGAL_STATE; } else if (e instanceof NetworkOnMainThreadException) { code = EX_NETWORK_MAIN_THREAD; } else if (e instanceof UnsupportedOperationException) { code = EX_UNSUPPORTED_OPERATION; } else if (e instanceof ServiceSpecificException) { code = EX_SERVICE_SPECIFIC; } writeInt(code); StrictMode.clearGatheredViolations(); if (code == 0) { if (e instanceof RuntimeException) { throw (RuntimeException) e; } throw new RuntimeException(e); } writeString(e.getMessage()); ...}可以看到其實Parcel是支持寫入異常的,但是只支持Parcelable的異?；蛘呦旅孢@幾種異常:
如果是普通的RuntimeException,這打斷寫入,繼續拋出。
于是我們將RuntimeException改成它支持的UnsupportedOperationException試試:
// service端改成拋出UnsupportedOperationExceptionppublic class AidlService extends Service { @Nullable @Override public IBinder onBind(Intent intent) { return new ITestExceptionAidl.Stub() { @Override public boolean testThrowException() throws RemoteException { if (true) { throw new UnsupportedOperationException("TestException"); } return true; } }; }}// client端實現還是一樣,不變bindService(intent, new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { ITestExceptionAidl aidl = ITestExceptionAidl.Stub.asInterface(service); try { aidl.testThrowException(); } catch (Exception e) { Log.e("testtest", "Exception", e); } } @Override public void onServiceDisconnected(ComponentName name) { }}, Context.BIND_AUTO_CREATE);這樣運行的話客戶端就能捕獲到異常:
01-01 05:49:46.770 19937 19937 E testtest: RemoteException
01-01 05:49:46.770 19937 19937 E testtest: java.lang.UnsupportedOperationException: TestException
01-01 05:49:46.770 19937 19937 E testtest: at android.os.Parcel.readException(Parcel.java:1728)
01-01 05:49:46.770 19937 19937 E testtest: at android.os.Parcel.readException(Parcel.java:1669)
01-01 05:49:46.770 19937 19937 E testtest: at me.linjw.demo.ipcdemo.ITestExceptionAidl$Stub$Proxy.testThrowException(ITestExceptionAidl.java:77)
01-01 05:49:46.770 19937 19937 E testtest: at me.linjw.demo.ipcdemo.MainActivity$3.onServiceConnected(MainActivity.java:132)
01-01 05:49:46.770 19937 19937 E testtest: at android.app.LoadedApk$ServiceDispatcher.doConnected(LoadedApk.java:1465)
01-01 05:49:46.770 19937 19937 E testtest: at android.app.LoadedApk$ServiceDispatcher$RunConnection.run(LoadedApk.java:1482)
01-01 05:49:46.770 19937 19937 E testtest: at android.os.Handler.handleCallback(Handler.java:751)
01-01 05:49:46.770 19937 19937 E testtest: at android.os.Handler.dispatchMessage(Handler.java:95)
01-01 05:49:46.770 19937 19937 E testtest: at android.os.Looper.loop(Looper.java:154)
01-01 05:49:46.770 19937 19937 E testtest: at android.app.ActivityThread.main(ActivityThread.java:6097)
01-01 05:49:46.770 19937 19937 E testtest: at java.lang.reflect.Method.invoke(Native Method)
01-01 05:49:46.770 19937 19937 E testtest: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1052)
01-01 05:49:46.770 19937 19937 E testtest: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:942)
跨進程傳遞異常的原理
好,知道了如何去跨進程傳遞異常之后,然后我們來看看異常到底是如何傳遞過去的。
讓我們再來看看異常寫入的代碼:
// 有異常的情況public final void writeException(Exception e) { int code = 0; if (e instanceof Parcelable && (e.getClass().getClassLoader() == Parcelable.class.getClassLoader())) { // We only send Parcelable exceptions that are in the // BootClassLoader to ensure that the receiver can unpack them code = EX_PARCELABLE; } else if (e instanceof SecurityException) { code = EX_SECURITY; } else if (e instanceof BadParcelableException) { code = EX_BAD_PARCELABLE; } else if (e instanceof IllegalArgumentException) { code = EX_ILLEGAL_ARGUMENT; } else if (e instanceof NullPointerException) { code = EX_NULL_POINTER; } else if (e instanceof IllegalStateException) { code = EX_ILLEGAL_STATE; } else if (e instanceof NetworkOnMainThreadException) { code = EX_NETWORK_MAIN_THREAD; } else if (e instanceof UnsupportedOperationException) { code = EX_UNSUPPORTED_OPERATION; } else if (e instanceof ServiceSpecificException) { code = EX_SERVICE_SPECIFIC; } writeInt(code); StrictMode.clearGatheredViolations(); if (code == 0) { if (e instanceof RuntimeException) { throw (RuntimeException) e; } throw new RuntimeException(e); } writeString(e.getMessage()); // 之后還有一些寫入堆棧的操作,比較多,這里可以不看}public final void writeNoException() { if (StrictMode.hasGatheredViolations()) { // 如果StrictMode收集到了寫違規行為會走這里,我們可以不關注它 writeInt(EX_HAS_REPLY_HEADER); ... } else { // 一般情況下會走這里 writeInt(0); }}這里給每種支持的異常都編了個號碼,它會往Parcel寫入。而0代表的是沒有發生異常。然后再看看讀取異常的代碼:
public boolean testThrowException() throws android.os.RemoteException { android.os.Parcel _data = android.os.Parcel.obtain(); android.os.Parcel _reply = android.os.Parcel.obtain(); boolean _result; try { _data.writeInterfaceToken(DESCRIPTOR); mRemote.transact(Stub.TRANSACTION_testThrowException, _data, _reply, 0); _reply.readException(); _result = (0 != _reply.readInt()); } finally { _reply.recycle(); _data.recycle(); } return _result;}// android.os.Parcel.readExceptionpublic final void readException() { int code = readExceptionCode(); if (code != 0) { String msg = readString(); //在這個方法里面創建異常并且拋出 readException(code, msg); }}然后這里有個需要注意的點就是異常必須是寫在Parcel的頭部的,也就是說如果沒有異常,我們先要將0寫到頭部,然后再將返回值繼續往后面寫入。如果有異常,我們要先將異常編碼寫入頭部,然后就不需要再寫入返回值了。
這樣,在客戶端讀取的時候讀取的頭部就能知道到底有沒有異常,沒有異常就繼續讀取返回值,有異常就將異常讀取出來并且拋出。
// service端代碼boolean _result = this.testThrowException();reply.writeNoException(); // 先寫入異常reply.writeInt(((_result) ? (1) : (0))); // 再寫入返回值// client端代碼mRemote.transact(Stub.TRANSACTION_testThrowException, _data, _reply, 0);_reply.readException(); // 先讀取異常,有異常的話readException方法里面會直接拋出_result = (0 != _reply.readInt()); // 再讀取返回值
也就是Parcel的頭部是一個標志位,標志了有異?；蛘邿o異常:
但是我們看到AIDL生成的代碼都是寫入的無異常,那我們拋出的異常是怎么傳過去的呢?還記得這個打印嗎?
01-01 05:31:55.475 4868 4880 E JavaBinder: *** Uncaught remote exception! (Exceptions are not yet supported across processes.)
01-01 05:31:55.475 4868 4880 E JavaBinder: java.lang.RuntimeException: TestException
01-01 05:31:55.475 4868 4880 E JavaBinder: at me.linjw.demo.ipcdemo.AidlService$1.testThrowException(AidlService.java:22)
01-01 05:31:55.475 4868 4880 E JavaBinder: at me.linjw.demo.ipcdemo.ITestExceptionAidl$Stub.onTransact(ITestExceptionAidl.java:48)
01-01 05:31:55.475 4868 4880 E JavaBinder: at android.os.Binder.execTransact(Binder.java:565)
我們去android.os.Binder.execTransact這里找找看, onTransact方法實際就是在這里被調用的
private boolean execTransact(int code, long dataObj, long replyObj, int flags) { Parcel data = Parcel.obtain(dataObj); Parcel reply = Parcel.obtain(replyObj); boolean res; try { res = onTransact(code, data, reply, flags); } catch (RemoteException|RuntimeException e) { ... reply.setDataPosition(0); reply.writeException(e); res = true; } catch (OutOfMemoryError e) { RuntimeException re = new RuntimeException("Out of memory", e); reply.setDataPosition(0); reply.writeException(re); res = true; } checkParcel(this, code, reply, "Unreasonably large binder reply buffer"); reply.recycle(); data.recycle(); return res;}看,這里如果catch到了方法,也就是說我們服務端有拋出異常,就會在catch代碼塊里面先就Parcel的游標重置回0,然后往Parcel頭部寫入異常。
好,到了這里其實整個流程就差不多了,但是我發現我沒有看到那個”Exceptions are not yet supported across processes.”字符串,這個不支持的提示又是哪里來的呢?
讓我們再回憶下代碼,在遇到不支持的異常類型的時候, writeException也會拋出異常:
public final void writeException(Exception e) { int code = 0; if (e instanceof Parcelable && (e.getClass().getClassLoader() == Parcelable.class.getClassLoader())) { // We only send Parcelable exceptions that are in the // BootClassLoader to ensure that the receiver can unpack them code = EX_PARCELABLE; } else if (e instanceof SecurityException) { code = EX_SECURITY; } else if (e instanceof BadParcelableException) { code = EX_BAD_PARCELABLE; } else if (e instanceof IllegalArgumentException) { code = EX_ILLEGAL_ARGUMENT; } else if (e instanceof NullPointerException) { code = EX_NULL_POINTER; } else if (e instanceof IllegalStateException) { code = EX_ILLEGAL_STATE; } else if (e instanceof NetworkOnMainThreadException) { code = EX_NETWORK_MAIN_THREAD; } else if (e instanceof UnsupportedOperationException) { code = EX_UNSUPPORTED_OPERATION; } else if (e instanceof ServiceSpecificException) { code = EX_SERVICE_SPECIFIC; } writeInt(code); StrictMode.clearGatheredViolations(); // code為0,代表不支持這種異常,繼續把異常拋出或者創建RuntimeException拋出 if (code == 0) { if (e instanceof RuntimeException) { throw (RuntimeException) e; } throw new RuntimeException(e); } ...}由于這個writeException,已經是在catch代碼塊里面運行的了,沒有人再去catch它,于是就會打斷這個流程,直接跳出。形成了一個Uncaught remote exception。
最后我們找到/frameworks/base/core/jni/android_util_Binder.cpp的onTransact方法,這里通過jni調到Java的execTransact方法,調用完之后進行ExceptionCheck,如果發現有異常的話就report_exception:
virtual status_t onTransact(uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags = 0) { JNIEnv* env = javavm_to_jnienv(mVM); IPCThreadState* thread_state = IPCThreadState::self(); const int32_t strict_policy_before = thread_state->getStrictModePolicy(); jboolean res = env->CallBooleanMethod(mObject, gBinderOffsets.mExecTransact, code, reinterpret_cast<jlong>(&data), reinterpret_cast<jlong>(reply), flags); if (env->ExceptionCheck()) { jthrowable excep = env->ExceptionOccurred(); // 就是這里啦 report_exception(env, excep, "*** Uncaught remote exception! " "(Exceptions are not yet supported across processes.)"); res = JNI_FALSE; env->DeleteLocalRef(excep); } ...}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VEVB武林網。
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