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/*
* Copyright (C) 2017 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 com.android.internal.util;
import static com.android.internal.util.Preconditions.checkArgumentPositive;
import java.lang.reflect.Array;
import java.util.Arrays;
/**
* A simple ring buffer structure with bounded capacity backed by an array.
* Events can always be added at the logical end of the buffer. If the buffer is
* full, oldest events are dropped when new events are added.
* {@hide}
*/
public class RingBuffer<T> {
// Array for storing events.
private final T[] mBuffer;
// Cursor keeping track of the logical end of the array. This cursor never
// wraps and instead keeps track of the total number of append() operations.
private long mCursor = 0;
public RingBuffer(Class<T> c, int capacity) {
checkArgumentPositive(capacity, "A RingBuffer cannot have 0 capacity");
// Java cannot create generic arrays without a runtime hint.
mBuffer = (T[]) Array.newInstance(c, capacity);
}
public int size() {
return (int) Math.min(mBuffer.length, (long) mCursor);
}
public boolean isEmpty() {
return size() == 0;
}
public void clear() {
for (int i = 0; i < size(); ++i) {
mBuffer[i] = null;
}
mCursor = 0;
}
public void append(T t) {
mBuffer[indexOf(mCursor++)] = t;
}
/**
* Returns object of type <T> at the next writable slot, creating one if it is not already
* available. In case of any errors while creating the object, <code>null</code> will
* be returned.
*/
public T getNextSlot() {
final int nextSlotIdx = indexOf(mCursor++);
if (mBuffer[nextSlotIdx] == null) {
mBuffer[nextSlotIdx] = createNewItem();
}
return mBuffer[nextSlotIdx];
}
/**
* @return a new object of type <T> or null if a new object could not be created.
*/
protected T createNewItem() {
try {
return (T) mBuffer.getClass().getComponentType().newInstance();
} catch (IllegalAccessException | InstantiationException e) {
return null;
}
}
public T[] toArray() {
// Only generic way to create a T[] from another T[]
T[] out = Arrays.copyOf(mBuffer, size(), (Class<T[]>) mBuffer.getClass());
// Reverse iteration from youngest event to oldest event.
long inCursor = mCursor - 1;
int outIdx = out.length - 1;
while (outIdx >= 0) {
out[outIdx--] = (T) mBuffer[indexOf(inCursor--)];
}
return out;
}
private int indexOf(long cursor) {
return (int) Math.abs(cursor % mBuffer.length);
}
}
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