The Tor Browser / file comparison
comparison: mobile/android/base/gfx/DrawTimingQueue.java
mobile/android/base/gfx/DrawTimingQueue.java
- branch
- TOR_BUG_3246
- changeset 4
- fc2d59ddac77
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| -1:000000000000 | 0:b7d2426ea109 |
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| 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/. */ | |
| 5 | |
| 6 package org.mozilla.gecko.gfx; | |
| 7 | |
| 8 import android.os.SystemClock; | |
| 9 | |
| 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; | |
| 29 | |
| 30 private final DisplayPortMetrics[] mMetrics; | |
| 31 private final long[] mTimestamps; | |
| 32 | |
| 33 private int mHead; | |
| 34 private int mTail; | |
| 35 | |
| 36 DrawTimingQueue() { | |
| 37 mMetrics = new DisplayPortMetrics[BUFFER_SIZE]; | |
| 38 mTimestamps = new long[BUFFER_SIZE]; | |
| 39 mHead = BUFFER_SIZE - 1; | |
| 40 mTail = 0; | |
| 41 } | |
| 42 | |
| 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 } | |
| 56 | |
| 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 } | |
| 86 | |
| 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 } |
