FrameTracker.h revision 4b0eba949cc026ffb2c75313042d8a7bcb3fcf86 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
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 */
16
17#ifndef ANDROID_FRAMETRACKER_H
18#define ANDROID_FRAMETRACKER_H
19
20#include <stddef.h>
21
22#include <utils/Mutex.h>
23#include <utils/Timers.h>
24#include <utils/RefBase.h>
25
26namespace android {
27
28class String8;
29class Fence;
30
31// FrameTracker tracks information about the most recently rendered frames. It
32// uses a circular buffer of frame records, and is *NOT* thread-safe -
33// mutexing must be done at a higher level if multi-threaded access is
34// possible.
35//
36// Some of the time values tracked may be set either as a specific timestamp
37// or a fence.  When a non-NULL fence is set for a given time value, the
38// signal time of that fence is used instead of the timestamp.
39class FrameTracker {
40
41public:
42    // NUM_FRAME_RECORDS is the size of the circular buffer used to track the
43    // frame time history.
44    enum { NUM_FRAME_RECORDS = 128 };
45
46    FrameTracker();
47
48    // setDesiredPresentTime sets the time at which the current frame
49    // should be presented to the user under ideal (i.e. zero latency)
50    // conditions.
51    void setDesiredPresentTime(nsecs_t desiredPresentTime);
52
53    // setFrameReadyTime sets the time at which the current frame became ready
54    // to be presented to the user.  For example, if the frame contents is
55    // being written to memory by some asynchronous hardware, this would be
56    // the time at which those writes completed.
57    void setFrameReadyTime(nsecs_t readyTime);
58
59    // setFrameReadyFence sets the fence that is used to get the time at which
60    // the current frame became ready to be presented to the user.
61    void setFrameReadyFence(const sp<Fence>& readyFence);
62
63    // setActualPresentTime sets the timestamp at which the current frame became
64    // visible to the user.
65    void setActualPresentTime(nsecs_t displayTime);
66
67    // setActualPresentFence sets the fence that is used to get the time
68    // at which the current frame became visible to the user.
69    void setActualPresentFence(const sp<Fence>& fence);
70
71    // advanceFrame advances the frame tracker to the next frame.
72    void advanceFrame();
73
74    // clear resets all the tracked frame data to zero.
75    void clear();
76
77    // dump appends the current frame display time history to the result string.
78    void dump(String8& result) const;
79
80private:
81    struct FrameRecord {
82        FrameRecord() :
83            desiredPresentTime(0),
84            frameReadyTime(0),
85            actualPresentTime(0) {}
86        nsecs_t desiredPresentTime;
87        nsecs_t frameReadyTime;
88        nsecs_t actualPresentTime;
89        sp<Fence> frameReadyFence;
90        sp<Fence> actualPresentFence;
91    };
92
93    // processFences iterates over all the frame records that have a fence set
94    // and replaces that fence with a timestamp if the fence has signaled.  If
95    // the fence is not signaled the record's displayTime is set to INT64_MAX.
96    //
97    // This method is const because although it modifies the frame records it
98    // does so in such a way that the information represented should not
99    // change.  This allows it to be called from the dump method.
100    void processFencesLocked() const;
101
102    // mFrameRecords is the circular buffer storing the tracked data for each
103    // frame.
104    FrameRecord mFrameRecords[NUM_FRAME_RECORDS];
105
106    // mOffset is the offset into mFrameRecords of the current frame.
107    size_t mOffset;
108
109    // mNumFences is the total number of fences set in the frame records.  It
110    // is incremented each time a fence is added and decremented each time a
111    // signaled fence is removed in processFences or if advanceFrame clobbers
112    // a fence.
113    //
114    // The number of fences is tracked so that the run time of processFences
115    // doesn't grow with NUM_FRAME_RECORDS.
116    int mNumFences;
117
118    // mMutex is used to protect access to all member variables.
119    mutable Mutex mMutex;
120};
121
122}
123
124#endif // ANDROID_FRAMETRACKER_H
125