audio_utils/fifo.cpp

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//#define LOG_NDEBUG 0
#define LOG_TAG "audio_utils_fifo"

#include <limits.h>
#include <linux/futex.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>

#include <audio_utils/fifo.h>
#include <audio_utils/roundup.h>
#include <cutils/log.h>
#include <utils/Errors.h>

static int sys_futex(void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
{
    return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
}

audio_utils_fifo_base::audio_utils_fifo_base(uint32_t frameCount)
        __attribute__((no_sanitize("integer"))) :
    mFrameCount(frameCount), mFrameCountP2(roundup(frameCount)),
    mFudgeFactor(mFrameCountP2 - mFrameCount),
    mIsPrivate(true),
    mSharedRear(0), mThrottleFront(NULL)
{
    // actual upper bound on frameCount will depend on the frame size
    LOG_ALWAYS_FATAL_IF(frameCount == 0 || frameCount > ((uint32_t) INT_MAX));
}

audio_utils_fifo_base::~audio_utils_fifo_base()
{
}

uint32_t audio_utils_fifo_base::sum(uint32_t index, uint32_t increment)
        __attribute__((no_sanitize("integer")))
{
    if (mFudgeFactor) {
        uint32_t mask = mFrameCountP2 - 1;
        ALOG_ASSERT((index & mask) < mFrameCount);
        ALOG_ASSERT(increment <= mFrameCountP2);
        if ((index & mask) + increment >= mFrameCount) {
            increment += mFudgeFactor;
        }
        index += increment;
        ALOG_ASSERT((index & mask) < mFrameCount);
        return index;
    } else {
        return index + increment;
    }
}

int32_t audio_utils_fifo_base::diff(uint32_t rear, uint32_t front, size_t *lost)
        __attribute__((no_sanitize("integer")))
{
    uint32_t diff = rear - front;
    if (mFudgeFactor) {
        uint32_t mask = mFrameCountP2 - 1;
        uint32_t rearMasked = rear & mask;
        uint32_t frontMasked = front & mask;
        if (rearMasked >= mFrameCount || frontMasked >= mFrameCount) {
            return -EIO;
        }
        uint32_t genDiff = (rear & ~mask) - (front & ~mask);
        if (genDiff != 0) {
            if (genDiff > mFrameCountP2) {
                if (lost != NULL) {
                    // TODO provide a more accurate estimate
                    *lost = (genDiff / mFrameCountP2) * mFrameCount;
                }
                return -EOVERFLOW;
            }
            diff -= mFudgeFactor;
        }
    }
    // FIFO should not be overfull
    if (diff > mFrameCount) {
        if (lost != NULL) {
            *lost = diff - mFrameCount;
        }
        return -EOVERFLOW;
    }
    return (int32_t) diff;
}

////////////////////////////////////////////////////////////////////////////////

audio_utils_fifo::audio_utils_fifo(uint32_t frameCount, uint32_t frameSize, void *buffer)
        __attribute__((no_sanitize("integer"))) :
    audio_utils_fifo_base(frameCount), mFrameSize(frameSize), mBuffer(buffer)
{
    // maximum value of frameCount * frameSize is INT_MAX (2^31 - 1), not 2^31, because we need to
    // be able to distinguish successful and error return values from read and write.
    LOG_ALWAYS_FATAL_IF(frameCount == 0 || frameSize == 0 || buffer == NULL ||
            frameCount > ((uint32_t) INT_MAX) / frameSize);
}

audio_utils_fifo::~audio_utils_fifo()
{
}

////////////////////////////////////////////////////////////////////////////////

audio_utils_fifo_provider::audio_utils_fifo_provider() :
    mObtained(0)
{
}

audio_utils_fifo_provider::~audio_utils_fifo_provider()
{
}

////////////////////////////////////////////////////////////////////////////////

audio_utils_fifo_writer::audio_utils_fifo_writer(audio_utils_fifo& fifo) :
    audio_utils_fifo_provider(), mFifo(fifo), mLocalRear(0),
    mLowLevelArm(fifo.mFrameCount), mHighLevelTrigger(0), mArmed(false),
    mEffectiveFrames(fifo.mFrameCount)
{
}

audio_utils_fifo_writer::~audio_utils_fifo_writer()
{
}

ssize_t audio_utils_fifo_writer::write(const void *buffer, size_t count, struct timespec *timeout)
        __attribute__((no_sanitize("integer")))
{
    audio_utils_iovec iovec[2];
    ssize_t availToWrite = obtain(iovec, count, timeout);
    if (availToWrite > 0) {
        memcpy((char *) mFifo.mBuffer + iovec[0].mOffset * mFifo.mFrameSize, buffer,
                iovec[0].mLength * mFifo.mFrameSize);
        if (iovec[1].mLength > 0) {
            memcpy((char *) mFifo.mBuffer + iovec[1].mOffset * mFifo.mFrameSize,
                    (char *) buffer + (iovec[0].mLength * mFifo.mFrameSize),
                    iovec[1].mLength * mFifo.mFrameSize);
        }
        release(availToWrite);
    }
    return availToWrite;
}

ssize_t audio_utils_fifo_writer::obtain(audio_utils_iovec iovec[2], size_t count,
        struct timespec *timeout)
        __attribute__((no_sanitize("integer")))
{
    size_t availToWrite;
    if (mFifo.mThrottleFront != NULL) {
        uint32_t front;
        for (;;) {
            front = (uint32_t) atomic_load_explicit(mFifo.mThrottleFront,
                    std::memory_order_acquire);
            int32_t filled = mFifo.diff(mLocalRear, front, NULL /*lost*/);
            if (filled < 0) {
                mObtained = 0;
                return (ssize_t) filled;
            }
            availToWrite = mEffectiveFrames > (uint32_t) filled ?
                    mEffectiveFrames - (uint32_t) filled : 0;
            // TODO pull out "count == 0"
            if (count == 0 || availToWrite > 0 || timeout == NULL ||
                    (timeout->tv_sec == 0 && timeout->tv_nsec == 0)) {
                break;
            }
            int err = sys_futex(mFifo.mThrottleFront,
                    mFifo.mIsPrivate ? FUTEX_WAIT_PRIVATE : FUTEX_WAIT, front, timeout, NULL, 0);
            if (err < 0) {
                switch (errno) {
                case EWOULDBLOCK:
                case EINTR:
                case ETIMEDOUT:
                    break;
                default:
                    LOG_ALWAYS_FATAL("unexpected err=%d errno=%d", err, errno);
                    break;
                }
            }
            timeout = NULL;
        }
    } else {
        availToWrite = mEffectiveFrames;
    }
    if (availToWrite > count) {
        availToWrite = count;
    }
    uint32_t rearMasked = mLocalRear & (mFifo.mFrameCountP2 - 1);
    size_t part1 = mFifo.mFrameCount - rearMasked;
    if (part1 > availToWrite) {
        part1 = availToWrite;
    }
    size_t part2 = part1 > 0 ? availToWrite - part1 : 0;
    iovec[0].mOffset = rearMasked;
    iovec[0].mLength = part1;
    iovec[1].mOffset = 0;
    iovec[1].mLength = part2;
    mObtained = availToWrite;
    return availToWrite;
}

void audio_utils_fifo_writer::release(size_t count)
        __attribute__((no_sanitize("integer")))
{
    if (count > 0) {
        LOG_ALWAYS_FATAL_IF(count > mObtained);
        if (mFifo.mThrottleFront != NULL) {
            uint32_t front = (uint32_t) atomic_load_explicit(mFifo.mThrottleFront,
                    std::memory_order_acquire);
            int32_t filled = mFifo.diff(mLocalRear, front, NULL /*lost*/);
            mLocalRear = mFifo.sum(mLocalRear, count);
            atomic_store_explicit(&mFifo.mSharedRear, (uint_fast32_t) mLocalRear,
                    std::memory_order_release);
            if (filled >= 0) {
                if (filled + count <= mLowLevelArm) {
                    mArmed = true;
                }
                if (mArmed && filled + count >= mHighLevelTrigger) {
                    int err = sys_futex(&mFifo.mSharedRear,
                            mFifo.mIsPrivate ? FUTEX_WAKE_PRIVATE : FUTEX_WAKE,
                            INT_MAX /*waiters*/, NULL, NULL, 0);
                    // err is number of processes woken up
                    if (err < 0) {
                        LOG_ALWAYS_FATAL("%s: unexpected err=%d errno=%d", __func__, err, errno);
                    }
                    mArmed = false;
                }
            }
        } else {
            mLocalRear = mFifo.sum(mLocalRear, count);
            atomic_store_explicit(&mFifo.mSharedRear, (uint_fast32_t) mLocalRear,
                    std::memory_order_release);
        }
        mObtained -= count;
    }
}

////////////////////////////////////////////////////////////////////////////////

audio_utils_fifo_reader::audio_utils_fifo_reader(audio_utils_fifo& fifo, bool throttlesWriter) :
    audio_utils_fifo_provider(), mFifo(fifo), mLocalFront(0), mSharedFront(0),
    mHighLevelArm(0), mLowLevelTrigger(mFifo.mFrameCount), mArmed(false)
{
    if (throttlesWriter) {
        LOG_ALWAYS_FATAL_IF(fifo.mThrottleFront != NULL);
        fifo.mThrottleFront = &mSharedFront;
    }
}

audio_utils_fifo_reader::~audio_utils_fifo_reader()
{
    // TODO Need a way to pass throttle capability to the another reader, should one reader exit.
    if (mFifo.mThrottleFront == &mSharedFront) {
        mFifo.mThrottleFront = NULL;
    }
}

ssize_t audio_utils_fifo_reader::read(void *buffer, size_t count, struct timespec *timeout,
        size_t *lost)
        __attribute__((no_sanitize("integer")))
{
    audio_utils_iovec iovec[2];
    ssize_t availToRead = obtain(iovec, count, timeout, lost);
    if (availToRead > 0) {
        memcpy(buffer, (char *) mFifo.mBuffer + iovec[0].mOffset * mFifo.mFrameSize,
                iovec[0].mLength * mFifo.mFrameSize);
        if (iovec[1].mLength > 0) {
            memcpy((char *) buffer + (iovec[0].mLength * mFifo.mFrameSize),
                    (char *) mFifo.mBuffer + iovec[1].mOffset * mFifo.mFrameSize,
                    iovec[1].mLength * mFifo.mFrameSize);
        }
        release(availToRead);
    }
    return availToRead;
}

ssize_t audio_utils_fifo_reader::obtain(audio_utils_iovec iovec[2], size_t count,
        struct timespec *timeout)
        __attribute__((no_sanitize("integer")))
{
    return obtain(iovec, count, timeout, NULL);
}

void audio_utils_fifo_reader::release(size_t count)
        __attribute__((no_sanitize("integer")))
{
    if (count > 0) {
        LOG_ALWAYS_FATAL_IF(count > mObtained);
        if (mFifo.mThrottleFront == &mSharedFront) {
            uint32_t rear = (uint32_t) atomic_load_explicit(&mFifo.mSharedRear,
                    std::memory_order_acquire);
            int32_t filled = mFifo.diff(rear, mLocalFront, NULL /*lost*/);
            mLocalFront = mFifo.sum(mLocalFront, count);
            atomic_store_explicit(&mSharedFront, (uint_fast32_t) mLocalFront,
                    std::memory_order_release);
            if (filled >= 0) {
                if (filled - count >= mHighLevelArm) {
                    mArmed = true;
                }
                if (mArmed && filled - count <= mLowLevelTrigger) {
                    int err = sys_futex(&mFifo.mSharedRear,
                            mFifo.mIsPrivate ? FUTEX_WAKE_PRIVATE : FUTEX_WAKE,
                            1 /*waiters*/, NULL, NULL, 0);
                    // err is number of processes woken up
                    if (err < 0 || err > 1) {
                        LOG_ALWAYS_FATAL("%s: unexpected err=%d errno=%d", __func__, err, errno);
                    }
                    mArmed = false;
                }
            }
        } else {
            mLocalFront = mFifo.sum(mLocalFront, count);
        }
        mObtained -= count;
    }
}

ssize_t audio_utils_fifo_reader::obtain(audio_utils_iovec iovec[2], size_t count,
        struct timespec *timeout, size_t *lost)
        __attribute__((no_sanitize("integer")))
{
    uint32_t rear;
    for (;;) {
        rear = (uint32_t) atomic_load_explicit(&mFifo.mSharedRear,
                std::memory_order_acquire);
        // TODO pull out "count == 0"
        if (count == 0 || rear != mLocalFront || timeout == NULL ||
                (timeout->tv_sec == 0 && timeout->tv_nsec == 0)) {
            break;
        }
        int err = sys_futex(&mFifo.mSharedRear, mFifo.mIsPrivate ? FUTEX_WAIT_PRIVATE : FUTEX_WAIT,
                rear, timeout, NULL, 0);
        if (err < 0) {
            switch (errno) {
            case EWOULDBLOCK:
            case EINTR:
            case ETIMEDOUT:
                break;
            default:
                LOG_ALWAYS_FATAL("unexpected err=%d errno=%d", err, errno);
                break;
            }
        }
        timeout = NULL;
    }
    int32_t filled = mFifo.diff(rear, mLocalFront, lost);
    if (filled < 0) {
        if (filled == -EOVERFLOW) {
            mLocalFront = rear;
        }
        mObtained = 0;
        return (ssize_t) filled;
    }
    size_t availToRead = (size_t) filled;
    if (availToRead > count) {
        availToRead = count;
    }
    uint32_t frontMasked = mLocalFront & (mFifo.mFrameCountP2 - 1);
    size_t part1 = mFifo.mFrameCount - frontMasked;
    if (part1 > availToRead) {
        part1 = availToRead;
    }
    size_t part2 = part1 > 0 ? availToRead - part1 : 0;
    iovec[0].mOffset = frontMasked;
    iovec[0].mLength = part1;
    iovec[1].mOffset = 0;
    iovec[1].mLength = part2;
    mObtained = availToRead;
    return availToRead;
}