mobile/android/base/gfx/DrawTimingQueue.java@b8a032363ba2
mobile/android/base/gfx/DrawTimingQueue.java
Thu, 22 Jan 2015 13:21:57 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 22 Jan 2015 13:21:57 +0100
- branch
- TOR_BUG_9701
- changeset 15
- b8a032363ba2
- permissions
- -rw-r--r--
Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6
1 /* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
2 * This Source Code Form is subject to the terms of the Mozilla Public
3 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
4 * You can obtain one at http://mozilla.org/MPL/2.0/. */
6 package org.mozilla.gecko.gfx;
8 import android.os.SystemClock;
10 /**
11 * A custom-built data structure to assist with measuring draw times.
12 *
13 * This class maintains a fixed-size circular buffer of DisplayPortMetrics
14 * objects and associated timestamps. It provides only three operations, which
15 * is all we require for our purposes of measuring draw times. Note
16 * in particular that the class is designed so that even though it is
17 * accessed from multiple threads, it does not require synchronization;
18 * any concurrency errors that result from this are handled gracefully.
19 *
20 * Assuming an unrolled buffer so that mTail is greater than mHead, the data
21 * stored in the buffer at entries [mHead, mTail) will never be modified, and
22 * so are "safe" to read. If this reading is done on the same thread that
23 * owns mHead, then reading the range [mHead, mTail) is guaranteed to be safe
24 * since the range itself will not shrink.
25 */
26 final class DrawTimingQueue {
27 private static final String LOGTAG = "GeckoDrawTimingQueue";
28 private static final int BUFFER_SIZE = 16;
30 private final DisplayPortMetrics[] mMetrics;
31 private final long[] mTimestamps;
33 private int mHead;
34 private int mTail;
36 DrawTimingQueue() {
37 mMetrics = new DisplayPortMetrics[BUFFER_SIZE];
38 mTimestamps = new long[BUFFER_SIZE];
39 mHead = BUFFER_SIZE - 1;
40 mTail = 0;
41 }
43 /**
44 * Add a new entry to the tail of the queue. If the buffer is full,
45 * do nothing. This must only be called from the Java UI thread.
46 */
47 boolean add(DisplayPortMetrics metrics) {
48 if (mHead == mTail) {
49 return false;
50 }
51 mMetrics[mTail] = metrics;
52 mTimestamps[mTail] = SystemClock.uptimeMillis();
53 mTail = (mTail + 1) % BUFFER_SIZE;
54 return true;
55 }
57 /**
58 * Find the timestamp associated with the given metrics, AND remove
59 * all metrics objects from the start of the queue up to and including
60 * the one provided. Note that because of draw coalescing, the metrics
61 * object passed in here may not be the one at the head of the queue,
62 * and so we must iterate our way through the list to find it.
63 * This must only be called from the compositor thread.
64 */
65 long findTimeFor(DisplayPortMetrics metrics) {
66 // keep a copy of the tail pointer so that we ignore new items
67 // added to the queue while we are searching. this is fine because
68 // the one we are looking for will either have been added already
69 // or will not be in the queue at all.
70 int tail = mTail;
71 // walk through the "safe" range from mHead to tail; these entries
72 // will not be modified unless we change mHead.
73 int i = (mHead + 1) % BUFFER_SIZE;
74 while (i != tail) {
75 if (mMetrics[i].fuzzyEquals(metrics)) {
76 // found it, copy out the timestamp to a local var BEFORE
77 // changing mHead or add could clobber the timestamp.
78 long timestamp = mTimestamps[i];
79 mHead = i;
80 return timestamp;
81 }
82 i = (i + 1) % BUFFER_SIZE;
83 }
84 return -1;
85 }
87 /**
88 * Reset the buffer to empty.
89 * This must only be called from the compositor thread.
90 */
91 void reset() {
92 // we can only modify mHead on this thread.
93 mHead = (mTail + BUFFER_SIZE - 1) % BUFFER_SIZE;
94 }
95 }
