1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
/*
* Copyright (C) 2012 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.volley.toolbox;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* ByteArrayPool is a source and repository of <code>byte[]</code> objects. Its purpose is to supply
* those buffers to consumers who need to use them for a short period of time and then dispose of
* them. Simply creating and disposing such buffers in the conventional manner can considerable heap
* churn and garbage collection delays on Android, which lacks good management of short-lived heap
* objects. It may be advantageous to trade off some memory in the form of a permanently allocated
* pool of buffers in order to gain heap performance improvements; that is what this class does.
*
* <p>A good candidate user for this class is something like an I/O system that uses large temporary
* <code>byte[]</code> buffers to copy data around. In these use cases, often the consumer wants the
* buffer to be a certain minimum size to ensure good performance (e.g. when copying data chunks off
* of a stream), but doesn't mind if the buffer is larger than the minimum. Taking this into account
* and also to maximize the odds of being able to reuse a recycled buffer, this class is free to
* return buffers larger than the requested size. The caller needs to be able to gracefully deal
* with getting buffers any size over the minimum.
*
* <p>If there is not a suitably-sized buffer in its recycling pool when a buffer is requested, this
* class will allocate a new buffer and return it.
*
* <p>This class has no special ownership of buffers it creates; the caller is free to take a buffer
* it receives from this pool, use it permanently, and never return it to the pool; additionally, it
* is not harmful to return to this pool a buffer that was allocated elsewhere, provided there are
* no other lingering references to it.
*
* <p>This class ensures that the total size of the buffers in its recycling pool never exceeds a
* certain byte limit. When a buffer is returned that would cause the pool to exceed the limit,
* least-recently-used buffers are disposed.
*/
public class ByteArrayPool {
/** The buffer pool, arranged both by last use and by buffer size */
private final List<byte[]> mBuffersByLastUse = new ArrayList<>();
private final List<byte[]> mBuffersBySize = new ArrayList<>(64);
/** The total size of the buffers in the pool */
private int mCurrentSize = 0;
/**
* The maximum aggregate size of the buffers in the pool. Old buffers are discarded to stay
* under this limit.
*/
private final int mSizeLimit;
/** Compares buffers by size */
protected static final Comparator<byte[]> BUF_COMPARATOR =
new Comparator<byte[]>() {
@Override
public int compare(byte[] lhs, byte[] rhs) {
return lhs.length - rhs.length;
}
};
/** @param sizeLimit the maximum size of the pool, in bytes */
public ByteArrayPool(int sizeLimit) {
mSizeLimit = sizeLimit;
}
/**
* Returns a buffer from the pool if one is available in the requested size, or allocates a new
* one if a pooled one is not available.
*
* @param len the minimum size, in bytes, of the requested buffer. The returned buffer may be
* larger.
* @return a byte[] buffer is always returned.
*/
public synchronized byte[] getBuf(int len) {
for (int i = 0; i < mBuffersBySize.size(); i++) {
byte[] buf = mBuffersBySize.get(i);
if (buf.length >= len) {
mCurrentSize -= buf.length;
mBuffersBySize.remove(i);
mBuffersByLastUse.remove(buf);
return buf;
}
}
return new byte[len];
}
/**
* Returns a buffer to the pool, throwing away old buffers if the pool would exceed its allotted
* size.
*
* @param buf the buffer to return to the pool.
*/
public synchronized void returnBuf(byte[] buf) {
if (buf == null || buf.length > mSizeLimit) {
return;
}
mBuffersByLastUse.add(buf);
int pos = Collections.binarySearch(mBuffersBySize, buf, BUF_COMPARATOR);
if (pos < 0) {
pos = -pos - 1;
}
mBuffersBySize.add(pos, buf);
mCurrentSize += buf.length;
trim();
}
/** Removes buffers from the pool until it is under its size limit. */
private synchronized void trim() {
while (mCurrentSize > mSizeLimit) {
byte[] buf = mBuffersByLastUse.remove(0);
mBuffersBySize.remove(buf);
mCurrentSize -= buf.length;
}
}
}
|
