MonoPipe.cpp revision 3b546caeb0a576c4d7d7f1e8d2fdfed2bb8bdeed 
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#define LOG_TAG "MonoPipe"
18//#define LOG_NDEBUG 0
19
20#include <common_time/cc_helper.h>
21#include <cutils/atomic.h>
22#include <cutils/compiler.h>
23#include <utils/LinearTransform.h>
24#include <utils/Log.h>
25#include <utils/Trace.h>
26#include <media/AudioBufferProvider.h>
27#include <media/nbaio/MonoPipe.h>
28#include <media/nbaio/roundup.h>
29
30
31namespace android {
32
33MonoPipe::MonoPipe(size_t reqFrames, NBAIO_Format format, bool writeCanBlock) :
34        NBAIO_Sink(format),
35        mUpdateSeq(0),
36        mReqFrames(reqFrames),
37        mMaxFrames(roundup(reqFrames)),
38        mBuffer(malloc(mMaxFrames * Format_frameSize(format))),
39        mFront(0),
40        mRear(0),
41        mWriteTsValid(false),
42        // mWriteTs
43        mSetpoint((reqFrames * 11) / 16),
44        mWriteCanBlock(writeCanBlock),
45        mIsShutdown(false)
46{
47    CCHelper tmpHelper;
48    status_t res;
49    uint64_t N, D;
50
51    mNextRdPTS = AudioBufferProvider::kInvalidPTS;
52
53    mSamplesToLocalTime.a_zero = 0;
54    mSamplesToLocalTime.b_zero = 0;
55    mSamplesToLocalTime.a_to_b_numer = 0;
56    mSamplesToLocalTime.a_to_b_denom = 0;
57
58    D = Format_sampleRate(format);
59    if (OK != (res = tmpHelper.getLocalFreq(&N))) {
60        ALOGE("Failed to fetch local time frequency when constructing a"
61              " MonoPipe (res = %d).  getNextWriteTimestamp calls will be"
62              " non-functional", res);
63        return;
64    }
65
66    LinearTransform::reduce(&N, &D);
67    static const uint64_t kSignedHiBitsMask   = ~(0x7FFFFFFFull);
68    static const uint64_t kUnsignedHiBitsMask = ~(0xFFFFFFFFull);
69    if ((N & kSignedHiBitsMask) || (D & kUnsignedHiBitsMask)) {
70        ALOGE("Cannot reduce sample rate to local clock frequency ratio to fit"
71              " in a 32/32 bit rational.  (max reduction is 0x%016llx/0x%016llx"
72              ").  getNextWriteTimestamp calls will be non-functional", N, D);
73        return;
74    }
75
76    mSamplesToLocalTime.a_to_b_numer = static_cast<int32_t>(N);
77    mSamplesToLocalTime.a_to_b_denom = static_cast<uint32_t>(D);
78}
79
80MonoPipe::~MonoPipe()
81{
82    free(mBuffer);
83}
84
85ssize_t MonoPipe::availableToWrite() const
86{
87    if (CC_UNLIKELY(!mNegotiated)) {
88        return NEGOTIATE;
89    }
90    // uses mMaxFrames not mReqFrames, so allows "over-filling" the pipe beyond requested limit
91    ssize_t ret = mMaxFrames - (mRear - android_atomic_acquire_load(&mFront));
92    ALOG_ASSERT((0 <= ret) && (ret <= mMaxFrames));
93    return ret;
94}
95
96ssize_t MonoPipe::write(const void *buffer, size_t count)
97{
98    if (CC_UNLIKELY(!mNegotiated)) {
99        return NEGOTIATE;
100    }
101    size_t totalFramesWritten = 0;
102    while (count > 0) {
103        // can't return a negative value, as we already checked for !mNegotiated
104        size_t avail = availableToWrite();
105        size_t written = avail;
106        if (CC_LIKELY(written > count)) {
107            written = count;
108        }
109        size_t rear = mRear & (mMaxFrames - 1);
110        size_t part1 = mMaxFrames - rear;
111        if (part1 > written) {
112            part1 = written;
113        }
114        if (CC_LIKELY(part1 > 0)) {
115            memcpy((char *) mBuffer + (rear << mBitShift), buffer, part1 << mBitShift);
116            if (CC_UNLIKELY(rear + part1 == mMaxFrames)) {
117                size_t part2 = written - part1;
118                if (CC_LIKELY(part2 > 0)) {
119                    memcpy(mBuffer, (char *) buffer + (part1 << mBitShift), part2 << mBitShift);
120                }
121            }
122            android_atomic_release_store(written + mRear, &mRear);
123            totalFramesWritten += written;
124        }
125        if (!mWriteCanBlock || mIsShutdown) {
126            break;
127        }
128        count -= written;
129        buffer = (char *) buffer + (written << mBitShift);
130        // Simulate blocking I/O by sleeping at different rates, depending on a throttle.
131        // The throttle tries to keep the mean pipe depth near the setpoint, with a slight jitter.
132        uint32_t ns;
133        if (written > 0) {
134            size_t filled = (mMaxFrames - avail) + written;
135            // FIXME cache these values to avoid re-computation
136            if (filled <= mSetpoint / 2) {
137                // pipe is (nearly) empty, fill quickly
138                ns = written * ( 500000000 / Format_sampleRate(mFormat));
139            } else if (filled <= (mSetpoint * 3) / 4) {
140                // pipe is below setpoint, fill at slightly faster rate
141                ns = written * ( 750000000 / Format_sampleRate(mFormat));
142            } else if (filled <= (mSetpoint * 5) / 4) {
143                // pipe is at setpoint, fill at nominal rate
144                ns = written * (1000000000 / Format_sampleRate(mFormat));
145            } else if (filled <= (mSetpoint * 3) / 2) {
146                // pipe is above setpoint, fill at slightly slower rate
147                ns = written * (1150000000 / Format_sampleRate(mFormat));
148            } else if (filled <= (mSetpoint * 7) / 4) {
149                // pipe is overflowing, fill slowly
150                ns = written * (1350000000 / Format_sampleRate(mFormat));
151            } else {
152                // pipe is severely overflowing
153                ns = written * (1750000000 / Format_sampleRate(mFormat));
154            }
155        } else {
156            ns = count * (1350000000 / Format_sampleRate(mFormat));
157        }
158        if (ns > 999999999) {
159            ns = 999999999;
160        }
161        struct timespec nowTs;
162        bool nowTsValid = !clock_gettime(CLOCK_MONOTONIC, &nowTs);
163        // deduct the elapsed time since previous write() completed
164        if (nowTsValid && mWriteTsValid) {
165            time_t sec = nowTs.tv_sec - mWriteTs.tv_sec;
166            long nsec = nowTs.tv_nsec - mWriteTs.tv_nsec;
167            ALOGE_IF(sec < 0 || (sec == 0 && nsec < 0),
168                    "clock_gettime(CLOCK_MONOTONIC) failed: was %ld.%09ld but now %ld.%09ld",
169                    mWriteTs.tv_sec, mWriteTs.tv_nsec, nowTs.tv_sec, nowTs.tv_nsec);
170            if (nsec < 0) {
171                --sec;
172                nsec += 1000000000;
173            }
174            if (sec == 0) {
175                if ((long) ns > nsec) {
176                    ns -= nsec;
177                } else {
178                    ns = 0;
179                }
180            }
181        }
182        if (ns > 0) {
183            const struct timespec req = {0, static_cast<long>(ns)};
184            nanosleep(&req, NULL);
185        }
186        // record the time that this write() completed
187        if (nowTsValid) {
188            mWriteTs = nowTs;
189            if ((mWriteTs.tv_nsec += ns) >= 1000000000) {
190                mWriteTs.tv_nsec -= 1000000000;
191                ++mWriteTs.tv_sec;
192            }
193        }
194        mWriteTsValid = nowTsValid;
195    }
196    mFramesWritten += totalFramesWritten;
197    return totalFramesWritten;
198}
199
200void MonoPipe::setAvgFrames(size_t setpoint)
201{
202    mSetpoint = setpoint;
203}
204
205status_t MonoPipe::getNextWriteTimestamp(int64_t *timestamp)
206{
207    int32_t front;
208
209    ALOG_ASSERT(NULL != timestamp);
210
211    if (0 == mSamplesToLocalTime.a_to_b_denom)
212        return UNKNOWN_ERROR;
213
214    observeFrontAndNRPTS(&front, timestamp);
215
216    if (AudioBufferProvider::kInvalidPTS != *timestamp) {
217        // If we have a valid read-pointer and next read timestamp pair, then
218        // use the current value of the write pointer to figure out how many
219        // frames are in the buffer, and offset the timestamp by that amt.  Then
220        // next time we write to the MonoPipe, the data will hit the speakers at
221        // the next read timestamp plus the current amount of data in the
222        // MonoPipe.
223        size_t pendingFrames = (mRear - front) & (mMaxFrames - 1);
224        *timestamp = offsetTimestampByAudioFrames(*timestamp, pendingFrames);
225    }
226
227    return OK;
228}
229
230void MonoPipe::updateFrontAndNRPTS(int32_t newFront, int64_t newNextRdPTS)
231{
232    // Set the MSB of the update sequence number to indicate that there is a
233    // multi-variable update in progress.  Use an atomic store with an "acquire"
234    // barrier to make sure that the next operations cannot be re-ordered and
235    // take place before the change to mUpdateSeq is commited..
236    int32_t tmp = mUpdateSeq | 0x80000000;
237    android_atomic_acquire_store(tmp, &mUpdateSeq);
238
239    // Update mFront and mNextRdPTS
240    mFront = newFront;
241    mNextRdPTS = newNextRdPTS;
242
243    // We are finished with the update.  Compute the next sequnce number (which
244    // should be the old sequence number, plus one, and with the MSB cleared)
245    // and then store it in mUpdateSeq using an atomic store with a "release"
246    // barrier so our update operations cannot be re-ordered past the update of
247    // the sequence number.
248    tmp = (tmp + 1) & 0x7FFFFFFF;
249    android_atomic_release_store(tmp, &mUpdateSeq);
250}
251
252void MonoPipe::observeFrontAndNRPTS(int32_t *outFront, int64_t *outNextRdPTS)
253{
254    // Perform an atomic observation of mFront and mNextRdPTS.  Basically,
255    // atomically observe the sequence number, then observer the variables, then
256    // atomically observe the sequence number again.  If the two observations of
257    // the sequence number match, and the update-in-progress bit was not set,
258    // then we know we have a successful atomic observation.  Otherwise, we loop
259    // around and try again.
260    //
261    // Note, it is very important that the observer be a lower priority thread
262    // than the updater.  If the updater is lower than the observer, or they are
263    // the same priority and running with SCHED_FIFO (implying that quantum
264    // based premption is disabled) then we run the risk of deadlock.
265    int32_t seqOne, seqTwo;
266
267    do {
268        seqOne        = android_atomic_acquire_load(&mUpdateSeq);
269        *outFront     = mFront;
270        *outNextRdPTS = mNextRdPTS;
271        seqTwo        = android_atomic_release_load(&mUpdateSeq);
272    } while ((seqOne != seqTwo) || (seqOne & 0x80000000));
273}
274
275int64_t MonoPipe::offsetTimestampByAudioFrames(int64_t ts, size_t audFrames)
276{
277    if (0 == mSamplesToLocalTime.a_to_b_denom)
278        return AudioBufferProvider::kInvalidPTS;
279
280    if (ts == AudioBufferProvider::kInvalidPTS)
281        return AudioBufferProvider::kInvalidPTS;
282
283    int64_t frame_lt_duration;
284    if (!mSamplesToLocalTime.doForwardTransform(audFrames,
285                                                &frame_lt_duration)) {
286        // This should never fail, but if there is a bug which is causing it
287        // to fail, this message would probably end up flooding the logs
288        // because the conversion would probably fail forever.  Log the
289        // error, but then zero out the ratio in the linear transform so
290        // that we don't try to do any conversions from now on.  This
291        // MonoPipe's getNextWriteTimestamp is now broken for good.
292        ALOGE("Overflow when attempting to convert %d audio frames to"
293              " duration in local time.  getNextWriteTimestamp will fail from"
294              " now on.", audFrames);
295        mSamplesToLocalTime.a_to_b_numer = 0;
296        mSamplesToLocalTime.a_to_b_denom = 0;
297        return AudioBufferProvider::kInvalidPTS;
298    }
299
300    return ts + frame_lt_duration;
301}
302
303void MonoPipe::shutdown(bool newState)
304{
305    mIsShutdown = newState;
306}
307
308bool MonoPipe::isShutdown()
309{
310    return mIsShutdown;
311}
312
313}   // namespace android
314