Android WorkManager浅谈

@Override
  public void run() {
    try {
      if (mWorkContinuation.hasCycles()) {
        throw new IllegalStateException(
            String.format("WorkContinuation has cycles (%s)", mWorkContinuation));
      }
      boolean needsScheduling = addToDatabase();
      if (needsScheduling) {
      
        final Context context =
            mWorkContinuation.getWorkManagerImpl().getApplicationContext();
        PackageManagerHelper.setComponentEnabled(context, RescheduleReceiver.class, true);
        scheduleWorkInBackground();
      }
      mOperation.setState(Operation.SUCCESS);
    } catch (Throwable exception) {
      mOperation.setState(new Operation.State.FAILURE(exception));
    }
  }
  /**
   * Schedules work on the background scheduler.
   */
  @VisibleForTesting
  public void scheduleWorkInBackground() {
    WorkManagerImpl workManager = mWorkContinuation.getWorkManagerImpl();
    Schedulers.schedule(
        workManager.getConfiguration(),
        workManager.getWorkDatabase(),
        workManager.getSchedulers());
  }

/**
   * Schedules {@link WorkSpec}s while honoring the {@link Scheduler#MAX_SCHEDULER_LIMIT}.
   *
   * @param workDatabase The {@link WorkDatabase}.
   * @param schedulers  The {@link List} of {@link Scheduler}s to delegate to.
   */
  public static void schedule(
      @NonNull Configuration configuration,
      @NonNull WorkDatabase workDatabase,
      List<Scheduler  schedulers) {
    if (schedulers == null || schedulers.size() == 0) {
      return;
    }

    ...

    if (eligibleWorkSpecs != null && eligibleWorkSpecs.size()   0) {
      WorkSpec[] eligibleWorkSpecsArray = eligibleWorkSpecs.toArray(new WorkSpec[0]);
      // Delegate to the underlying scheduler.
      for (Scheduler scheduler : schedulers) {
        scheduler.schedule(eligibleWorkSpecsArray);
      }
    }
  }

@WorkerThread
@Override
public void run() {
mTags = mWorkTagDao.getTagsForWorkSpecId(mWorkSpecId);
mWorkDescription = createWorkDescription(mTags);
runWorker();
}
private void runWorker() {
if (tryCheckForInterruptionAndResolve()) {
return;
}
mWorkDatabase.beginTransaction();
try {
mWorkSpec = mWorkSpecDao.getWorkSpec(mWorkSpecId);
if (mWorkSpec == null) {
Logger.get().error(
TAG,
String.format("Didn't find WorkSpec for id %s", mWorkSpecId));
resolve(false);
return;
}
// running, finished, or is blocked.
if (mWorkSpec.state != ENQUEUED) {
resolveIncorrectStatus();
mWorkDatabase.setTransactionSuccessful();
return;
}
// Case 1:
// Ensure that Workers that are backed off are only executed when they are supposed to.
// GreedyScheduler can schedule WorkSpecs that have already been backed off because
// it is holding on to snapshots of WorkSpecs. So WorkerWrapper needs to determine
// if the ListenableWorker is actually eligible to execute at this point in time.
// Case 2:
// On API 23, we double scheduler Workers because JobScheduler prefers batching.
// So is the Work is periodic, we only need to execute it once per interval.
// Also potential bugs in the platform may cause a Job to run more than once.
if (mWorkSpec.isPeriodic() || mWorkSpec.isBackedOff()) {
long now = System.currentTimeMillis();
if (now < mWorkSpec.calculateNextRunTime()) {
resolve(false);
return;
}
}
mWorkDatabase.setTransactionSuccessful();
} finally {
mWorkDatabase.endTransaction();
}
// Merge inputs. This can be potentially expensive code, so this should not be done inside
// a database transaction.
Data input;
if (mWorkSpec.isPeriodic()) {
input = mWorkSpec.input;
} else {
InputMerger inputMerger = InputMerger.fromClassName(mWorkSpec.inputMergerClassName);
if (inputMerger == null) {
Logger.get().error(TAG, String.format("Could not create Input Merger %s",
mWorkSpec.inputMergerClassName));
setFailedAndResolve();
return;
}
List<Data  inputs = new ArrayList< ();
inputs.add(mWorkSpec.input);
inputs.addAll(mWorkSpecDao.getInputsFromPrerequisites(mWorkSpecId));
input = inputMerger.merge(inputs);
}
WorkerParameters params = new WorkerParameters(
UUID.fromString(mWorkSpecId),
input,
mTags,
mRuntimeExtras,
mWorkSpec.runAttemptCount,
mConfiguration.getExecutor(),
mWorkTaskExecutor,
mConfiguration.getWorkerFactory());
// Not always creating a worker here, as the WorkerWrapper.Builder can set a worker override
// in test mode.
if (mWorker == null) {
mWorker = mConfiguration.getWorkerFactory().createWorkerWithDefaultFallback(
mAppContext,
mWorkSpec.workerClassName,
params);
}
if (mWorker == null) {
Logger.get().error(TAG,
String.format("Could not create Worker %s", mWorkSpec.workerClassName));
setFailedAndResolve();
return;
}
if (mWorker.isUsed()) {
Logger.get().error(TAG,
String.format("Received an already-used Worker %s; WorkerFactory should return "
+ "new instances",
mWorkSpec.workerClassName));
setFailedAndResolve();
return;
}
mWorker.setUsed();
// Try to set the work to the running state. Note that this may fail because another thread
// may have modified the DB since we checked last at the top of this function.
if (trySetRunning()) {
if (tryCheckForInterruptionAndResolve()) {
return;
}
final SettableFuture<ListenableWorker.Result  future = SettableFuture.create();
// Call mWorker.startWork() on the main thread.
mWorkTaskExecutor.getMainThreadExecutor()
.execute(new Runnable() {
@Override
public void run() {
try {
mInnerFuture = mWorker.startWork();
future.setFuture(mInnerFuture);
} catch (Throwable e) {
future.setException(e);
}
}
});
// Avoid synthetic accessors.
final String workDescription = mWorkDescription;
future.addListener(new Runnable() {
@Override
@SuppressLint("SyntheticAccessor")
public void run() {
try {
// If the ListenableWorker returns a null result treat it as a failure.
ListenableWorker.Result result = future.get();
if (result == null) {
Logger.get().error(TAG, String.format(
"%s returned a null result. Treating it as a failure.",
mWorkSpec.workerClassName));
} else {
mResult = result;
}
} catch (CancellationException exception) {
// Cancellations need to be treated with care here because innerFuture
// cancellations will bubble up, and we need to gracefully handle that.
Logger.get().info(TAG, String.format("%s was cancelled", workDescription),
exception);
} catch (InterruptedException | ExecutionException exception) {
Logger.get().error(TAG,
String.format("%s failed because it threw an exception/error",
workDescription), exception);
} finally {
onWorkFinished();
}
}
}, mWorkTaskExecutor.getBackgroundExecutor());
} else {
resolveIncorrectStatus();
}
}

future.addListener(new Runnable() {
@Override
@SuppressLint("SyntheticAccessor")
public void run() {
try {
// If the ListenableWorker returns a null result treat it as a failure.
ListenableWorker.Result result = future.get();
if (result == null) {
Logger.get().error(TAG, String.format(
"%s returned a null result. Treating it as a failure.",
mWorkSpec.workerClassName));
} else {
mResult = result;
}
} catch (CancellationException exception) {
// Cancellations need to be treated with care here because innerFuture
// cancellations will bubble up, and we need to gracefully handle that.
Logger.get().info(TAG, String.format("%s was cancelled", workDescription),
exception);
} catch (InterruptedException | ExecutionException exception) {
Logger.get().error(TAG,
String.format("%s failed because it threw an exception/error",
workDescription), exception);
} finally {
onWorkFinished();
}
}
}, mWorkTaskExecutor.getBackgroundExecutor());

@Override
public final @NonNull ListenableFuture<Result  startWork() {
mFuture = SettableFuture.create();
getBackgroundExecutor().execute(new Runnable() {
@Override
public void run() {
Result result = doWork();
mFuture.set(result);
}
});
return mFuture;
}

1. 2019-02-02 15:35:41.682 30526-30542/com.outman.study.workmanagerdemo I/WM-WorkerWrapper: Work [ id=3d775394-e0d7-44e3-a670-c3527a3245ee, tags={ com.outman.study.workmanagerdemo.SimpleWorker } ] was cancelled
2.   java.util.concurrent.CancellationException: Task was cancelled.
3.     at androidx.work.impl.utils.futures.AbstractFuture.cancellationExceptionWithCause(AbstractFuture.java:1184)
4.     at androidx.work.impl.utils.futures.AbstractFuture.getDoneValue(AbstractFuture.java:514)
5.     at androidx.work.impl.utils.futures.AbstractFuture.get(AbstractFuture.java:475)
6.     at androidx.work.impl.WorkerWrapper$2.run(WorkerWrapper.java:264)
7.     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
8.     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
9.     at java.lang.Thread.run(Thread.java:764)