import com.firebase.client.Transaction; //导入依赖的package包/类
public void shouldRunCachedTransaction() {
  Firebase child  = ref.child("states/NY");
  Status   status = QuasarUtil.INSTANCE.runInFiber(() -> {
    return new TransactionHandlerCachedAsync() {
      @Override
      protected void requestAsync() {
        child.addValueEventListener(this);
      }

      @Override
      public Transaction.Result doTransaction(MutableData snap) {
        snap.setValue("New York");

        return Transaction.success(snap);
      }
    }.run();
  });

  verify(status, child, "New York");
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
@Override
public void completeTodoList() {
    // Update all child tasks for this key to have done = true.
    Firebase tasksRef = mTasks;
    tasksRef.runTransaction(new Transaction.Handler() {
        @Override
        public Transaction.Result doTransaction(MutableData mutableData) {
            // Note: This is very easy to make conflicts with. It may be better to avoid doing
            // this in a batch or to split up the Task into components.
            for (MutableData taskData : mutableData.getChildren()) {
                TaskSpec spec = taskData.getValue(TaskSpec.class);
                if (!spec.getDone()) {
                    spec.setDone(true);
                }
                taskData.setValue(spec);
            }
            return Transaction.success(mutableData);
        }

        @Override
        public void onComplete(FirebaseError firebaseError, boolean b,
                               DataSnapshot dataSnapshot) {
        }
    });

    // Further, update this todo list to set its last updated time.
    updateListTimestamp();
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
@Override
public Transaction.Result doTransaction(MutableData mutableData) {
    if (mutableData.getValue() == null) {
        mutableData.setValue(increment);
    } else {
        mutableData.setValue((Long) mutableData.getValue() + increment);
    }
    return Transaction.success(mutableData);
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
public void shouldRunUncachedTransaction() {
  AtomicInteger count  = new AtomicInteger(0);

  Firebase      child  = ref.child("states/AL");
  Status        status = QuasarUtil.INSTANCE.runInFiber(() -> {
    return new TransactionHandlerAsync() {
      @Override
      protected void requestAsync() {
        child.runTransaction(this, false);
      }

      @Override
      public Transaction.Result doTransaction(MutableData snap) {
        Object obj = snap.getValue();

        if (count.getAndIncrement() == 0) {
          assertNull(obj);
        } else {
          assertNotNull(obj);

          snap.setValue("Roll Tide");
        }

        return Transaction.success(snap);
      }
    }.run();
  });

  verify(status, child, "Roll Tide");
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
private void reset(@NotNull final Firebase taskRef, @Nullable final String ownerId, @NotNull final String inProgressState, @Nullable final Listener listener, final long retries) {
  taskRef.runTransaction(new Transaction.Handler() {
    @Override
    public Transaction.Result doTransaction(MutableData task) {
      if(task.getValue() == null) {
        return Transaction.success(task);
      }

      Log.log("Resetting task " + taskRef.getKey());

      @SuppressWarnings("unchecked") Map<String, Object> value = task.getValue(Map.class);
      Object taskOwner = value.get(Task.OWNER_KEY);
      // if the ownerId is null it means that we're force resetting this task, so we allow it to go through
      boolean ownersMatch = ownerId == null || ownerId.equals(taskOwner);
      if(inProgressState.equals(value.get(Task.STATE_KEY)) && ownersMatch) {
        value.put(Task.STATE_KEY, taskSpec.getStartState());
        value.put(Task.STATE_CHANGED_KEY, ServerValue.TIMESTAMP);
        value.put(Task.OWNER_KEY, null);
        value.put(Task.ERROR_DETAILS_KEY, null);
        task.setValue(value);
        return Transaction.success(task);
      }
      else {
        if(listener != null) listener.onResetFailed("Couldn't reset this task because it is owned by another worker", false);

        if(!ownersMatch) {
          Log.log("Can't reset task " + taskRef.getKey() + " on " + ownerId + " because it is owned by " + taskOwner);
        }
        else {
          Log.log("Can't reset task " + taskRef.getKey() + " - _state != in_progress_state");
        }
        return Transaction.abort();
      }
    }

    @Override
    public void onComplete(FirebaseError error, boolean committed, DataSnapshot snapshot) {
      String taskKey = snapshot.getKey();
      if(error != null) {
        final long incrementedRetries = retries + 1;
        if(incrementedRetries < Queue.MAX_TRANSACTION_RETRIES) {
          Log.log("Received error while resetting task " + taskKey + "...retrying", error);
          reset(taskRef, ownerId, inProgressState, listener, incrementedRetries);
        }
        else {
          Log.log("Can't reset task " + taskKey + " - transaction errored too many times, no longer retrying", error);
          if(listener != null) listener.onResetFailed("Can't reset task - transaction errored too many times, no longer retrying", true);
        }
      }
      else {
        if(committed && snapshot.exists()) {
          Log.log("reset " + taskKey);
        }
        if(listener != null) listener.onReset();
      }
    }
  }, false);
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
private void resolve(@NotNull final Map<String, Object> newTask, @Nullable final Listener listener, final long retries) {
  Log.debug("Attempting to resolve task " + taskRef.getKey() + " on " + ownerId);

  if(!canActionBeTakenBeforeTransaction(ACTION_RESOLVED, listener)) {
    return;
  }

  taskRef.runTransaction(new Transaction.Handler() {
    private boolean abortedTransactionBecauseOfState;

    @Override
    public Transaction.Result doTransaction(MutableData task) {
      if(!canActionBeTakenInTransaction(listener, ACTION_RESOLVED)) {
        abortedTransactionBecauseOfState = true;
        return Transaction.abort();
      }

      // if this task no longer exists
      if(task.getValue() == null) {
        Log.debug("Tried resolving task " + taskRef.getKey() + " on " + ownerId + " after someone else removed it");
        return Transaction.success(task);
      }

      @SuppressWarnings("unchecked") Map<String, Object> value = task.getValue(Map.class);
      String ourInProgressState = taskSpec.getInProgressState();
      Object taskState = value.get(STATE_KEY);
      Object taskOwner = value.get(OWNER_KEY);
      boolean ownersMatch = ownerId.equals(taskOwner);
      if((ourInProgressState == taskState || (ourInProgressState != null && ourInProgressState.equals(taskState))) && ownersMatch) {
        if(taskSpec.getFinishedState() == null) {
          task.setValue(null);
          return Transaction.success(task);
        }

        newTask.put(STATE_KEY, taskSpec.getFinishedState());
        newTask.put(STATE_CHANGED_KEY, ServerValue.TIMESTAMP);
        newTask.put(OWNER_KEY, null);
        newTask.put(ERROR_DETAILS_KEY, null);
        task.setValue(newTask);
        return Transaction.success(task);
      }
      else {
        if(!ownersMatch) {
          Log.debug("Tried resolving task " + taskRef.getKey() + " on " + ownerId + " but it is owned by " + taskOwner);
        }
        else {
          Log.debug("Tried resolving task " + taskRef.getKey() + " on " + ownerId + " but its _state (" + taskState + ") did not match our _in_progress_state (" + ourInProgressState + ")");
        }

        return Transaction.abort();
      }
    }

    @Override
    public void onComplete(FirebaseError error, boolean committed, DataSnapshot snapshot) {
      final String taskKey = snapshot.getKey();

      if(abortedTransactionBecauseOfState) {
        return;
      }

      if(error != null) {
        final long incrementedRetries = retries + 1;
        if(incrementedRetries < Queue.MAX_TRANSACTION_RETRIES) {
          Log.debug("Received onFailure while resolving task " + taskKey + " on " + ownerId + "...retrying", error);
          resolve(newTask, listener, incrementedRetries);
        }
        else {
          Log.debug("Can't resolve task " + taskKey + " on " + ownerId + " - transaction errored too many times, no longer retrying", error);
          if(listener != null) listener.onFailure("Can't resolve task - transaction errored too many times, no longer retrying", true);
        }
      }
      else {
        onTransactionSuccess(committed, taskKey, ACTION_RESOLVED, listener);
      }
    }
  }, false);
}
 

import com.firebase.client.Transaction; //导入依赖的package包/类
abstract Transaction.Result run(MutableData currentData);