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/*
* Copyright (C) 2014 The Android Open Source Project
*
* 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 android.hardware.camera2.utils;
import android.hardware.camera2.utils.TaskDrainer.DrainListener;
import android.os.Handler;
/**
* Keep track of a single concurrent task starting and finishing;
* allow draining the existing task and figuring out when the task has finished
* (and won't restart).
*
* <p>The initial state is to allow all tasks to be started and finished. A task may only be started
* once, after which it must be finished before starting again. Likewise, finishing a task
* that hasn't been started is also not allowed.</p>
*
* <p>When draining begins, the task cannot be started again. This guarantees that at some
* point the task will be finished forever, at which point the {@link DrainListener#onDrained}
* callback will be invoked.</p>
*/
public class TaskSingleDrainer {
private final TaskDrainer<Object> mTaskDrainer;
private final Object mSingleTask = new Object();
/**
* Create a new task drainer; {@code onDrained} callbacks will be posted to the listener
* via the {@code handler}.
*
* @param handler a non-{@code null} handler to use to post runnables to
* @param listener a non-{@code null} listener where {@code onDrained} will be called
*/
public TaskSingleDrainer(Handler handler, DrainListener listener) {
mTaskDrainer = new TaskDrainer<>(handler, listener);
}
/**
* Create a new task drainer; {@code onDrained} callbacks will be posted to the listener
* via the {@code handler}.
*
* @param handler a non-{@code null} handler to use to post runnables to
* @param listener a non-{@code null} listener where {@code onDrained} will be called
* @param name an optional name used for debug logging
*/
public TaskSingleDrainer(Handler handler, DrainListener listener, String name) {
mTaskDrainer = new TaskDrainer<>(handler, listener, name);
}
/**
* Mark this asynchronous task as having started.
*
* <p>The task cannot be started more than once without first having finished. Once
* draining begins with {@link #beginDrain}, no new tasks can be started.</p>
*
* @see #taskFinished
* @see #beginDrain
*
* @throws IllegalStateException
* If attempting to start a task which is already started (and not finished),
* or if attempting to start a task after draining has begun.
*/
public void taskStarted() {
mTaskDrainer.taskStarted(mSingleTask);
}
/**
* Do not allow any more task re-starts; once the existing task is finished,
* fire the {@link DrainListener#onDrained} callback asynchronously.
*
* <p>This operation is idempotent; calling it more than once has no effect.</p>
*/
public void beginDrain() {
mTaskDrainer.beginDrain();
}
/**
* Mark this asynchronous task as having finished.
*
* <p>The task cannot be finished if it hasn't started. Once finished, a task
* cannot be finished again (unless it's started again).</p>
*
* @see #taskStarted
* @see #beginDrain
*
* @throws IllegalStateException
* If attempting to start a task which is already finished (and not re-started),
*/
public void taskFinished() {
mTaskDrainer.taskFinished(mSingleTask);
}
}
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