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SeqTask.java
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82 lines (70 loc) · 2.33 KB
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/*
* Copyright 2012 LinkedIn, Inc
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.linkedin.parseq;
import com.linkedin.parseq.internal.SystemHiddenTask;
import com.linkedin.parseq.promise.Promise;
import com.linkedin.parseq.promise.Promises;
import com.linkedin.parseq.promise.SettablePromise;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
* A {@link Task} that will run the constructor-supplied tasks one after the other.
* <p/>
* Use {@link Tasks#seq(Iterable)} or {@link Tasks#seq(java.lang.Iterable)} to create
* instances of this class.
*
* @author Chris Pettitt (cpettitt@linkedin.com)
* @author Chi Chan (ckchan@linkedin.com)
*/
/* package private */ class SeqTask<T> extends SystemHiddenTask<T>
{
private volatile List<Task<?>> _tasks;
public SeqTask(final String name, final Iterable<? extends Task<?>> tasks)
{
super(name);
List<Task<?>> taskList = new ArrayList<Task<?>>();
for(Task<?> task : tasks)
{
taskList.add(task);
}
if (taskList.size() == 0)
{
throw new IllegalArgumentException("No tasks to sequence!");
}
_tasks = Collections.unmodifiableList(taskList);
}
@Override
protected Promise<? extends T> run(final Context context) throws Exception
{
final SettablePromise<T> result = Promises.settable();
Task<?> prevTask = _tasks.get(0);
for (int i = 1; i < _tasks.size(); i++)
{
final Task<?> currTask = _tasks.get(i);
context.after(prevTask).run(currTask);
prevTask = currTask;
}
// This is unsafe, but we don't have the ability to do type checking
// with varargs.
@SuppressWarnings("unchecked")
final Task<T> typedPrevTask = (Task<T>)prevTask;
Promises.propagateResult(typedPrevTask, result);
context.run(_tasks.get(0));
_tasks = null;
return result;
}
}