1/*
2 * Copyright (C) 2014 Square, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16package okio;
17
18/**
19 * A collection of unused segments, necessary to avoid GC churn and zero-fill.
20 * This pool is a thread-safe static singleton.
21 */
22final class SegmentPool {
23  static final SegmentPool INSTANCE = new SegmentPool();
24
25  /** The maximum number of bytes to pool. */
26  // TODO: Is 64 KiB a good maximum size? Do we ever have that many idle segments?
27  static final long MAX_SIZE = 64 * 1024; // 64 KiB.
28
29  /** Singly-linked list of segments. */
30  private Segment next;
31
32  /** Total bytes in this pool. */
33  long byteCount;
34
35  private SegmentPool() {
36  }
37
38  Segment take() {
39    synchronized (this) {
40      if (next != null) {
41        Segment result = next;
42        next = result.next;
43        result.next = null;
44        byteCount -= Segment.SIZE;
45        return result;
46      }
47    }
48    return new Segment(); // Pool is empty. Don't zero-fill while holding a lock.
49  }
50
51  void recycle(Segment segment) {
52    if (segment.next != null || segment.prev != null) throw new IllegalArgumentException();
53    synchronized (this) {
54      if (byteCount + Segment.SIZE > MAX_SIZE) return; // Pool is full.
55      byteCount += Segment.SIZE;
56      segment.next = next;
57      segment.pos = segment.limit = 0;
58      next = segment;
59    }
60  }
61}
62