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Android跨進(jìn)程拋異常的原理的實(shí)現(xiàn)

 更新時(shí)間：2018年11月11日 08:47:24   作者：林嘉偉  
這篇文章主要介紹了Android跨進(jìn)程拋異常的原理的實(shí)現(xiàn),小編覺(jué)得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧

今天接到了個(gè)需求,需要用到跨進(jìn)程拋異常。

怎樣將異常從服務(wù)端拋到客戶端

也就是說(shuō)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(shí)現(xiàn)
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(shí)現(xiàn)
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(gè)程序?qū)嶋H上運(yùn)行起來(lái)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(shuō)在service端就已經(jīng)被異常打斷了,并沒(méi)有傳給client端,而且第一個(gè)大大的”Exceptions are not yet supported across processes.”是說(shuō)異常不允許跨進(jìn)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(méi)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(shí)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(shí)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:

  • SecurityException
  • BadParcelableException
  • IllegalArgumentException
  • NullPointerException
  • IllegalStateException
  • NetworkOnMainThreadException
  • UnsupportedOperationException
  • ServiceSpecificException

如果是普通的RuntimeException,這打斷寫入,繼續(xù)拋出。

于是我們將RuntimeException改成它支持的UnsupportedOperationException試試:

// service端改成拋出UnsupportedOperationException
ppublic 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(shí)現(xiàn)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(yùn)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(jìn)程傳遞異常的原理

好,知道了如何去跨進(jìn)程傳遞異常之后,然后我們來(lái)看看異常到底是如何傳遞過(guò)去的。

讓我們?cè)賮?lái)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(guī)行為會(huì)走這里,我們可以不關(guān)注它
    writeInt(EX_HAS_REPLY_HEADER);
    ...
  } else {
   // 一般情況下會(huì)走這里
    writeInt(0);
  }
}

這里給每種支持的異常都編了個(gè)號(hào)碼,它會(huì)往Parcel寫入。而0代表的是沒(méi)有發(fā)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.readException
public final void readException() {
  int code = readExceptionCode();
  if (code != 0) {
    String msg = readString();
    
    //在這個(gè)方法里面創(chuàng)建異常并且拋出
    readException(code, msg);
  }
}

然后這里有個(gè)需要注意的點(diǎn)就是異常必須是寫在Parcel的頭部的,也就是說(shuō)如果沒(méi)有異常,我們先要將0寫到頭部,然后再將返回值繼續(xù)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(shí)候讀取的頭部就能知道到底有沒(méi)有異常,沒(méi)有異常就繼續(xù)讀取返回值,有異常就將異常讀取出來(lái)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(huì)直接拋出
_result = (0 != _reply.readInt()); // 再讀取返回值

也就是Parcel的頭部是一個(gè)標(biāo)志位,標(biāo)志了有異常或者無(wú)異常:

但是我們看到AIDL生成的代碼都是寫入的無(wú)異常,那我們拋出的異常是怎么傳過(guò)去的呢?還記得這個(gè)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?nèi)ndroid.os.Binder.execTransact這里找找看, onTransact方法實(shí)際就是在這里被調(diào)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(shuō)我們服務(wù)端有拋出異常,就會(huì)在catch代碼塊里面先就Parcel的游標(biāo)重置回0,然后往Parcel頭部寫入異常。

好,到了這里其實(shí)整個(gè)流程就差不多了,但是我發(fā)現(xiàn)我沒(méi)有看到那個(gè)”Exceptions are not yet supported across processes.”字符串,這個(gè)不支持的提示又是哪里來(lái)的呢?

讓我們?cè)倩貞浵麓a,在遇到不支持的異常類型的時(shí)候, writeException也會(huì)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(xù)把異常拋出或者創(chuàng)建RuntimeException拋出
  if (code == 0) {
    if (e instanceof RuntimeException) {
      throw (RuntimeException) e;
    }
    throw new RuntimeException(e);
  }
  ...
}

由于這個(gè)writeException,已經(jīng)是在catch代碼塊里面運(yùn)行的了,沒(méi)有人再去catch它,于是就會(huì)打斷這個(gè)流程,直接跳出。形成了一個(gè)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(guò)jni調(diào)到Java的execTransact方法,調(diào)用完之后進(jìn)行ExceptionCheck,如果發(fā)現(xiàn)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?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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