Android O - java.lang.RuntimeException: An error occurred while executing doInBackground()

最近任務列表中多了一個bug，讓在這個sprint中解決掉，bug的堆棧信息如下：

Fatal Exception: java.lang.RuntimeException: An error occurred while executing doInBackground()
       at android.os.AsyncTask$3.done(AsyncTask.java:353)
       at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:383)
       at java.util.concurrent.FutureTask.setException(FutureTask.java:252)
       at java.util.concurrent.FutureTask.run(FutureTask.java:271)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
       at java.lang.Thread.run(Thread.java:764)
Caused by java.lang.SecurityException: Caller no longer running, last stopped +25s437ms because: timed out while starting
       at android.os.Parcel.readException(Parcel.java:1942)
       at android.os.Parcel.readException(Parcel.java:1888)
       at android.app.job.IJobCallback$Stub$Proxy.dequeueWork(IJobCallback.java:191)
       at android.app.job.JobParameters.dequeueWork(JobParameters.java:196)
       at android.support.v4.app.JobIntentService$JobServiceEngineImpl.dequeueWork(JobIntentService.java:309)
       at android.support.v4.app.JobIntentService.dequeueWork(JobIntentService.java:627)
       at android.support.v4.app.JobIntentService$CommandProcessor.doInBackground(JobIntentService.java:384)
       at android.support.v4.app.JobIntentService$CommandProcessor.doInBackground(JobIntentService.java:377)
       at android.os.AsyncTask$2.call(AsyncTask.java:333)
       at java.util.concurrent.FutureTask.run(FutureTask.java:266)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
       at java.lang.Thread.run(Thread.java:764)

由上面的bug信息可知是調用了系統JobIntentService中的AsyncTask中的doInBackground所致, 而doInBackground又調用了dequeueWork，下面是源碼部分（androidx 1.1.0的源碼）：

final class CommandProcessor extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... params) {
        GenericWorkItem work;

        if (DEBUG) Log.d(TAG, "Starting to dequeue work...");

        while ((work = dequeueWork()) != null) {
            if (DEBUG) Log.d(TAG, "Processing next work: " + work);
            onHandleWork(work.getIntent());
            if (DEBUG) Log.d(TAG, "Completing work: " + work);
            work.complete();
        }

        if (DEBUG) Log.d(TAG, "Done processing work!");

        return null;
    }

dequeueWork()的源碼如下, 我們關注mJobImpl != null的部分，又會進入mJobImpl.dequeueWork()的部分：


    GenericWorkItem dequeueWork() {
        if (mJobImpl != null) {
            return mJobImpl.dequeueWork();
        } else {
            synchronized (mCompatQueue) {
                if (mCompatQueue.size() > 0) {
                    return mCompatQueue.remove(0);
                } else {
                    return null;
                }
            }
        }
    }

mJobImpl其實是一個CompatJobEngine類型，源碼以及是實現類JobServiceEngineImpl如下：

	interface CompatJobEngine {
   		 IBinder compatGetBinder();
    	GenericWorkItem dequeueWork();
    }

	@RequiresApi(26)
	 static final class JobServiceEngineImpl extends JobServiceEngine
        implements JobIntentService.CompatJobEngine {
	 @Override
        public JobIntentService.GenericWorkItem dequeueWork() {
            JobWorkItem work;
            synchronized (mLock) {
                if (mParams == null) {
                    return null;
                }
                work = mParams.dequeueWork();
            }
            if (work != null) {
                work.getIntent().setExtrasClassLoader(mService.getClassLoader());
                return new WrapperWorkItem(work);
            } else {
                return null;
            }
        }
    }

從文章開頭的bug信息中看到，接着又進入到了mParams.dequeueWork();中，然後就進入到了Binder機制中，源碼如下，由此可以斷定是在這裏出了問題，拋出了異常，但是因爲這裏屬於源碼部分，不應該屬於我們的職責範圍。

	public @Nullable JobWorkItem dequeueWork() {
    try {
        return getCallback().dequeueWork(getJobId());
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}
		/** @hide */
    @UnsupportedAppUsage
    public IJobCallback getCallback() {
        return IJobCallback.Stub.asInterface(callback);
    }

經過查詢源碼，發現問題出現在framework層，而且網上早已有這個問題的issue:
https://github.com/evernote/android-job/issues/255
https://issuetracker.google.com/issues/63622293
網上遇到這類問題的人很多很多，但是到目前爲止，我查看了最新的google的androidx庫("androidx.core:core-ktx:1.2.0-rc01")，依舊是沒有解決這個問題。

其實查看源碼後發現解決這個問題的方法也比較簡單，就是我們可以新建一個androidx.core.app的包，在其中新建一個類SafeJobIntentService繼承JobIntentService, 之所以這麼做是因爲dequeueWork()方法的權限不是public，我們得寫在同一個包中才能重寫它的方法，進行bug的修復。

@RestrictTo({Scope.LIBRARY})
public abstract class SafeJobIntentService extends JobIntentService {
    public SafeJobIntentService() {
    }

    GenericWorkItem dequeueWork() {
        try {
            return super.dequeueWork();//1 這裏我們對此方法進行了try/catch操作
        } catch (SecurityException var2) {
            var2.printStackTrace();
            return null;
        }
    }

    public void onCreate() {
        super.onCreate();
        if (VERSION.SDK_INT >= 26) {
            this.mJobImpl = new SafeJobServiceEngineImpl(this);
        } else {
            this.mJobImpl = null;
        }
    }
}

@RequiresApi(26)
public class SafeJobServiceEngineImpl extends JobServiceEngine implements CompatJobEngine {
    static final String TAG = "JobServiceEngineImpl";
    static final boolean DEBUG = false;
    final JobIntentService mService;
    final Object mLock = new Object();
    JobParameters mParams;

    SafeJobServiceEngineImpl(JobIntentService service) {
        super(service);
        this.mService = service;
    }

    public IBinder compatGetBinder() {
        return this.getBinder();
    }

    public boolean onStartJob(JobParameters params) {
        this.mParams = params;
        this.mService.ensureProcessorRunningLocked(false);
        return true;
    }

    public boolean onStopJob(JobParameters params) {
        boolean result = this.mService.doStopCurrentWork();
        synchronized(this.mLock) {
            this.mParams = null;
            return result;
        }
    }

    public GenericWorkItem dequeueWork() {
        JobWorkItem work = null;
        synchronized(this.mLock) {
            if (this.mParams == null) {
                return null;
            }

            try {
                work = this.mParams.dequeueWork();
            } catch (SecurityException var5) {
                var5.printStackTrace();
            }
        }

        if (work != null) {
            work.getIntent().setExtrasClassLoader(this.mService.getClassLoader());
            return new SafeJobServiceEngineImpl.WrapperWorkItem(work);
        } else {
            return null;
        }
    }

    final class WrapperWorkItem implements GenericWorkItem {
        final JobWorkItem mJobWork;

        WrapperWorkItem(JobWorkItem jobWork) {
            this.mJobWork = jobWork;
        }

        public Intent getIntent() {
            return this.mJobWork.getIntent();
        }

        public void complete() {
            synchronized(SafeJobServiceEngineImpl.this.mLock) {
                if (SafeJobServiceEngineImpl.this.mParams != null) {
                    try {
                        SafeJobServiceEngineImpl.this.mParams.completeWork(this.mJobWork);
                    } catch (SecurityException  | IllegalArgumentException var4) {
                    // 2 這裏我們也對completeWork進行了try/catch操作
                        var4.printStackTrace();
                    }
                }
            }
        }
    }
}

上面的代碼是在源碼的基礎上僅僅在1和2處做了Exception的處理，其餘的地方沒有變化，可以對比源碼查看比較。
如果你的項目中有的三方庫中已經引入了這個SafeJobIntentService類，但是因爲你使用不了它們的這個類，而你再引用比如implementation 'com.evernote:android-job:1.4.2'庫的話，就會出現duplicate class found in the module, 如果出現這種問題，我們可以通過重新命名類的方式，按照上面的代碼來做處理就好了。
希望Google在未來的庫中加入這個問題的解決辦法。

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