services/audioflinger/FastMixer.h

/*
 * Copyright (C) 2012 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.
 */

#ifndef ANDROID_AUDIO_FAST_MIXER_H
#define ANDROID_AUDIO_FAST_MIXER_H

#include <linux/futex.h>
#include <sys/syscall.h>
#include <utils/Debug.h>
#include <utils/Thread.h>
#include "StateQueue.h"
#include "FastMixerState.h"

namespace android {

typedef StateQueue<FastMixerState> FastMixerStateQueue;

class FastMixer : public Thread {

public:
            FastMixer() : Thread(false /*canCallJava*/) { }
    virtual ~FastMixer() { }

            FastMixerStateQueue* sq() { return &mSQ; }

private:
    virtual bool                threadLoop();
            FastMixerStateQueue mSQ;

};  // class FastMixer

// Describes the underrun status for a single "pull" attempt
enum FastTrackUnderrunStatus {
    UNDERRUN_FULL,      // framesReady() is full frame count, no underrun
    UNDERRUN_PARTIAL,   // framesReady() is non-zero but < full frame count, partial underrun
    UNDERRUN_EMPTY,     // framesReady() is zero, total underrun
};

// Underrun counters are not reset to zero for new tracks or if track generation changes.
// This packed representation is used to keep the information atomic.
union FastTrackUnderruns {
    FastTrackUnderruns() { mAtomic = 0;
            COMPILE_TIME_ASSERT_FUNCTION_SCOPE(sizeof(FastTrackUnderruns) == sizeof(uint32_t)); }
    FastTrackUnderruns(const FastTrackUnderruns& copyFrom) : mAtomic(copyFrom.mAtomic) { }
    FastTrackUnderruns& operator=(const FastTrackUnderruns& rhs)
            { if (this != &rhs) mAtomic = rhs.mAtomic; return *this; }
    struct {
#define UNDERRUN_BITS 10
#define UNDERRUN_MASK ((1 << UNDERRUN_BITS) - 1)
        uint32_t mFull    : UNDERRUN_BITS; // framesReady() is full frame count
        uint32_t mPartial : UNDERRUN_BITS; // framesReady() is non-zero but < full frame count
        uint32_t mEmpty   : UNDERRUN_BITS; // framesReady() is zero
        FastTrackUnderrunStatus mMostRecent : 2;    // status of most recent framesReady()
    }        mBitFields;
private:
    uint32_t mAtomic;
};

// Represents the dump state of a fast track
struct FastTrackDump {
    FastTrackDump() : mFramesReady(0) { }
    /*virtual*/ ~FastTrackDump() { }
    FastTrackUnderruns mUnderruns;
    size_t mFramesReady;        // most recent value only; no long-term statistics kept
};

// The FastMixerDumpState keeps a cache of FastMixer statistics that can be logged by dumpsys.
// Each individual native word-sized field is accessed atomically.  But the
// overall structure is non-atomic, that is there may be an inconsistency between fields.
// No barriers or locks are used for either writing or reading.
// Only POD types are permitted, and the contents shouldn't be trusted (i.e. do range checks).
// It has a different lifetime than the FastMixer, and so it can't be a member of FastMixer.
struct FastMixerDumpState {
    FastMixerDumpState(
#ifdef FAST_MIXER_STATISTICS
            uint32_t samplingN = kSamplingNforLowRamDevice
#endif
            );
    /*virtual*/ ~FastMixerDumpState();

    void dump(int fd) const;    // should only be called on a stable copy, not the original

    FastMixerState::Command mCommand;   // current command
    uint32_t mWriteSequence;    // incremented before and after each write()
    uint32_t mFramesWritten;    // total number of frames written successfully
    uint32_t mNumTracks;        // total number of active fast tracks
    uint32_t mWriteErrors;      // total number of write() errors
    uint32_t mUnderruns;        // total number of underruns
    uint32_t mOverruns;         // total number of overruns
    uint32_t mSampleRate;
    size_t   mFrameCount;
    struct timespec mMeasuredWarmupTs;  // measured warmup time
    uint32_t mWarmupCycles;     // number of loop cycles required to warmup
    uint32_t mTrackMask;        // mask of active tracks
    FastTrackDump   mTracks[FastMixerState::kMaxFastTracks];

#ifdef FAST_MIXER_STATISTICS
    // Recently collected samples of per-cycle monotonic time, thread CPU time, and CPU frequency.
    // kSamplingN is max size of sampling frame (statistics), and must be a power of 2 <= 0x8000.
    // The sample arrays are virtually allocated based on this compile-time constant,
    // but are only initialized and used based on the runtime parameter mSamplingN.
    static const uint32_t kSamplingN = 0x8000;
    // Compile-time constant for a "low RAM device", must be a power of 2 <= kSamplingN.
    // This value was chosen such that each array uses 1 small page (4 Kbytes).
    static const uint32_t kSamplingNforLowRamDevice = 0x400;
    // Corresponding runtime maximum size of sample arrays, must be a power of 2 <= kSamplingN.
    uint32_t mSamplingN;
    // The bounds define the interval of valid samples, and are represented as follows:
    //      newest open (excluded) endpoint   = lower 16 bits of bounds, modulo N
    //      oldest closed (included) endpoint = upper 16 bits of bounds, modulo N
    // Number of valid samples is newest - oldest.
    uint32_t mBounds;                   // bounds for mMonotonicNs, mThreadCpuNs, and mCpukHz
    // The elements in the *Ns arrays are in units of nanoseconds <= 3999999999.
    uint32_t mMonotonicNs[kSamplingN];  // delta monotonic (wall clock) time
    uint32_t mLoadNs[kSamplingN];       // delta CPU load in time
#ifdef CPU_FREQUENCY_STATISTICS
    uint32_t mCpukHz[kSamplingN];       // absolute CPU clock frequency in kHz, bits 0-3 are CPU#
#endif
    // Increase sampling window after construction, must be a power of 2 <= kSamplingN
    void    increaseSamplingN(uint32_t samplingN);
#endif
};

}   // namespace android

#endif  // ANDROID_AUDIO_FAST_MIXER_H