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Context.java
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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.promise.Promise;
import java.util.concurrent.TimeUnit;
/**
* A context provides an API to {@link Task}s for the purpose of scheduling
* other tasks. Each task gets its own context, but contexts are hierarchical
* such that any state changes made from this context are visible to other
* contexts in the hierarchy.
* <p/>
* If a task finished while it still has pending timers or tasks, those
* timers and tasks will be cancelled - they are guaranteed not to execute.
*
* @author Chris Pettitt (cpettitt@linkedin.com)
*/
public interface Context
{
/**
* Creates a timer that will invoke the given task if the calling task has
* not yet finished.
*
* @param time the time for the timeout
* @param unit the unit of the time
* @param task the task to run if the timeout expires
* @return a handle that can be used to explicitly cancel the timer
*/
Cancellable createTimer(long time, TimeUnit unit, Task<?> task);
/**
* Runs one or more tasks in parallel.
*
* @param tasks the tasks to run
*/
void run(Task<?>... tasks);
/**
* Provides a mechanism of ordering the execution of some child tasks after
* the resolution of the given promises (which may also be tasks).
*
* @param promises the promises that must be resolved before executing
* tasks from {@link After}
* @return a handle that can be used to schedule tasks that will be executed
* after the given promises are resolved.
*/
After after(Promise<?>... promises);
/**
* Provides a mechanism for "plugins" to generate data which should be passed in via the context.
* The intent is that the "plugin" registers engine specific data it needed via the engine builder.
* Then the run method can access this data via the getEngineProperty() method.
*
* @param key The key to the engine related property which the Task will access.
* @return The engine related property which has been stored with this key.
*/
Object getEngineProperty(String key);
}