/*
* Copyright (C) 2011 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.layoutlib.bridge.util;
import com.android.internal.util.ArrayUtils;
import com.android.internal.util.GrowingArrayUtils;
import android.util.SparseArray;
import java.lang.ref.WeakReference;
/**
* This is a custom {@link SparseArray} that uses {@link WeakReference} around the objects added
* to it. When the array is compacted, not only deleted indices but also empty references
* are removed, making the array efficient at removing references that were reclaimed.
*
* The code is taken from {@link SparseArray} directly and adapted to use weak references.
*
* Because our usage means that we never actually call {@link #remove(long)} or
* {@link #delete(long)}, we must manually check if there are reclaimed references to
* trigger an internal compact step (which is normally only triggered when an item is manually
* removed).
*
* SparseArrays map integral values to Objects. Unlike a normal array of Objects,
* there can be gaps in the indices. It is intended to be more efficient
* than using a HashMap to map Integers (or Longs) to Objects.
*/
@SuppressWarnings("unchecked")
public class SparseWeakArray<E> {
private static final Object DELETED_REF = new Object();
private static final WeakReference<?> DELETED = new WeakReference(DELETED_REF);
private boolean mGarbage = false;
/**
* Creates a new SparseArray containing no mappings.
*/
public SparseWeakArray() {
this(10);
}
/**
* Creates a new SparseArray containing no mappings that will not
* require any additional memory allocation to store the specified
* number of mappings.
*/
public SparseWeakArray(int initialCapacity) {
mKeys = ArrayUtils.newUnpaddedLongArray(initialCapacity);
mValues = new WeakReference[mKeys.length];
mSize = 0;
}
/**
* Gets the Object mapped from the specified key, or <code>null</code>
* if no such mapping has been made.
*/
public E get(long key) {
return get(key, null);
}
/**
* Gets the Object mapped from the specified key, or the specified Object
* if no such mapping has been made.
*/
public E get(long key, E valueIfKeyNotFound) {
int i = binarySearch(mKeys, 0, mSize, key);
if (i < 0 || mValues[i] == DELETED || mValues[i].get() == null) {
return valueIfKeyNotFound;
} else {
return (E) mValues[i].get();
}
}
/**
* Removes the mapping from the specified key, if there was any.
*/
public void delete(long key) {
int i = binarySearch(mKeys, 0, mSize, key);
if (i >= 0) {
if (mValues[i] != DELETED) {
mValues[i] = DELETED;
mGarbage = true;
}
}
}
/**
* Alias for {@link #delete(long)}.
*/
public void remove(long key) {
delete(key);
}
/**
* Removes the mapping at the specified index.
*/
public void removeAt(int index) {
if (mValues[index] != DELETED) {
mValues[index] = DELETED;
mGarbage = true;
}
}
private void gc() {
int n = mSize;
int o = 0;
long[] keys = mKeys;
WeakReference<?>[] values = mValues;
for (int i = 0; i < n; i++) {
WeakReference<?> val = values[i];
// Don't keep any non DELETED values, but only the one that still have a valid
// reference.
if (val != DELETED && val.get() != null) {
if (i != o) {
keys[o] = keys[i];
values[o] = val;
}
o++;
}
}
mGarbage = false;
mSize = o;
}
/**
* Adds a mapping from the specified key to the specified value,
* replacing the previous mapping from the specified key if there
* was one.
*/
public void put(long key, E value) {
int i = binarySearch(mKeys, 0, mSize, key);
if (i >= 0) {
mValues[i] = new WeakReference(value);
} else {
i = ~i;
if (i < mSize && (mValues[i] == DELETED || mValues[i].get() == null)) {
mKeys[i] = key;
mValues[i] = new WeakReference(value);
return;
}
if (mSize >= mKeys.length && (mGarbage || hasReclaimedRefs())) {
gc();
// Search again because indices may have changed.
i = ~binarySearch(mKeys, 0, mSize, key);
}
mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
mValues = GrowingArrayUtils.insert(mValues, mSize, i, new WeakReference(value));
mSize++;
}
}
/**
* Returns the number of key-value mappings that this SparseArray
* currently stores.
*/
public int size() {
if (mGarbage) {
gc();
}
return mSize;
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the key from the <code>index</code>th key-value mapping that this
* SparseArray stores.
*/
public long keyAt(int index) {
if (mGarbage) {
gc();
}
return mKeys[index];
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the value from the <code>index</code>th key-value mapping that this
* SparseArray stores.
*/
public E valueAt(int index) {
if (mGarbage) {
gc();
}
return (E) mValues[index].get();
}
/**
* Given an index in the range <code>0...size()-1</code>, sets a new
* value for the <code>index</code>th key-value mapping that this
* SparseArray stores.
*/
public void setValueAt(int index, E value) {
if (mGarbage) {
gc();
}
mValues[index] = new WeakReference(value);
}
/**
* Returns the index for which {@link #keyAt} would return the
* specified key, or a negative number if the specified
* key is not mapped.
*/
public int indexOfKey(long key) {
if (mGarbage) {
gc();
}
return binarySearch(mKeys, 0, mSize, key);
}
/**
* Returns an index for which {@link #valueAt} would return the
* specified key, or a negative number if no keys map to the
* specified value.
* Beware that this is a linear search, unlike lookups by key,
* and that multiple keys can map to the same value and this will
* find only one of them.
*/
public int indexOfValue(E value) {
if (mGarbage) {
gc();
}
for (int i = 0; i < mSize; i++)
if (mValues[i].get() == value)
return i;
return -1;
}
/**
* Removes all key-value mappings from this SparseArray.
*/
public void clear() {
int n = mSize;
WeakReference<?>[] values = mValues;
for (int i = 0; i < n; i++) {
values[i] = null;
}
mSize = 0;
mGarbage = false;
}
/**
* Puts a key/value pair into the array, optimizing for the case where
* the key is greater than all existing keys in the array.
*/
public void append(long key, E value) {
if (mSize != 0 && key <= mKeys[mSize - 1]) {
put(key, value);
return;
}
if (mSize >= mKeys.length && (mGarbage || hasReclaimedRefs())) {
gc();
}
mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
mValues = GrowingArrayUtils.append(mValues, mSize, new WeakReference(value));
mSize++;
}
private boolean hasReclaimedRefs() {
for (int i = 0 ; i < mSize ; i++) {
if (mValues[i].get() == null) { // DELETED.get() never returns null.
return true;
}
}
return false;
}
private static int binarySearch(long[] a, int start, int len, long key) {
int high = start + len, low = start - 1, guess;
while (high - low > 1) {
guess = (high + low) / 2;
if (a[guess] < key)
low = guess;
else
high = guess;
}
if (high == start + len)
return ~(start + len);
else if (a[high] == key)
return high;
else
return ~high;
}
private long[] mKeys;
private WeakReference<?>[] mValues;
private int mSize;
}
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