Android Audio代码分析6 - AudioEffect

 

在看AudioSessionId相关代码的时候了解到，共用一个AudioSessionId的AudioTrack和MediaPlayer会共用一个AudioEffect。
今天就来看看AudioEffect是个什么东东。

看这个类的目的，主要是为了搞清楚AudioEffect是个什么东东。
打算重点看看类的介绍及其构造函数上。

*****************************************源码*************************************************

public class AudioEffect {    static {        System.loadLibrary("audioeffect_jni");        native_init();    }...    public AudioEffect(UUID type, UUID uuid, int priority, int audioSession)            throws IllegalArgumentException, UnsupportedOperationException,            RuntimeException {        int[] id = new int[1];        Descriptor[] desc = new Descriptor[1];        // native initialization        int initResult = native_setup(new WeakReference<AudioEffect>(this),                type.toString(), uuid.toString(), priority, audioSession, id,                desc);        if (initResult != SUCCESS && initResult != ALREADY_EXISTS) {            Log.e(TAG, "Error code " + initResult                    + " when initializing AudioEffect.");            switch (initResult) {            case ERROR_BAD_VALUE:                throw (new IllegalArgumentException("Effect type: " + type                        + " not supported."));            case ERROR_INVALID_OPERATION:                throw (new UnsupportedOperationException(                        "Effect library not loaded"));            default:                throw (new RuntimeException(                        "Cannot initialize effect engine for type: " + type                                + "Error: " + initResult));            }        }        mId = id[0];        mDescriptor = desc[0];        synchronized (mStateLock) {            mState = STATE_INITIALIZED;        }    }...}

**********************************************************************************************
源码路径：
frameworks\base\media\java\android\media\audiofx\AudioEffect.java

###########################################说明################################################
先看看整个类的注释：

/** * AudioEffect is the base class for controlling audio effects provided by the android audio * framework. * <p>Applications should not use the AudioEffect class directly but one of its derived classes to * control specific effects: * <ul> *   <li> {@link android.media.audiofx.Equalizer}</li> *   <li> {@link android.media.audiofx.Virtualizer}</li> *   <li> {@link android.media.audiofx.BassBoost}</li> *   <li> {@link android.media.audiofx.PresetReverb}</li> *   <li> {@link android.media.audiofx.EnvironmentalReverb}</li> * </ul> * <p>If the audio effect is to be applied to a specific AudioTrack or MediaPlayer instance, * the application must specify the audio session ID of that instance when creating the AudioEffect. * (see {@link android.media.MediaPlayer#getAudioSessionId()} for details on audio sessions). * To apply an effect to the global audio output mix, session 0 must be specified when creating the * AudioEffect. * <p>Creating an effect on the output mix (audio session 0) requires permission * {@link android.Manifest.permission#MODIFY_AUDIO_SETTINGS} * <p>Creating an AudioEffect object will create the corresponding effect engine in the audio * framework if no instance of the same effect type exists in the specified audio session. * If one exists, this instance will be used. * <p>The application creating the AudioEffect object (or a derived class) will either receive * control of the effect engine or not depending on the priority parameter. If priority is higher * than the priority used by the current effect engine owner, the control will be transfered to the * new object. Otherwise control will remain with the previous object. In this case, the new * application will be notified of changes in effect engine state or control ownership by the * appropiate listener. */

 大致意思如下：
 AudioEffect是由android audio framework提供的控制audio effect的基类。
 应用程序不应该直接创建AudioEffect的对象，而应该创建由其派生的，控制特定effect的类的对象。
 可创建对象的派生类如下：
  *   <li> {@link android.media.audiofx.Equalizer}</li>
 *   <li> {@link android.media.audiofx.Virtualizer}</li>
 *   <li> {@link android.media.audiofx.BassBoost}</li>
 *   <li> {@link android.media.audiofx.PresetReverb}</li>
 *   <li> {@link android.media.audiofx.EnvironmentalReverb}</li>
 * </ul>
 如果一个audio effect被指定给一个特定的AudioTrack或者MediaPlayer，创建AudioEffect对象的时候必须指定一个AudioSessionId。
 如果想创建一个对global audio output mix都起作用的audio effect，需要将AudioSessionId指定为0.
 想创建一个对global audio output mix都起作用的audio effect需要特定的许可：
  * {@link android.Manifest.permission#MODIFY_AUDIO_SETTINGS}
 创建AudioEffect对象时，如果指定的AudioSession中不存在该类型的AudioEffect，则会在audio framework中创建一个effect engine。
 否则，将使用已存在的AudioEffect对象。
 应用程序创建了一个AudioEffect对象后，能否取得effect enging的控制权，取决于优先级。
 如果优先级比正控制effect enging的应用程序的优先级高，则会把控制权抢过来。
 否则只能眼睁睁的看着人家继续控制。
 不过，如果effect enging的状态或者所有权改变时，监听器将会通知应用程序。
 
 再看看其构造函数及注释

     // Constructor, Finalize    // --------------------    /**     * Class constructor.     *     * @param type type of effect engine created. See {@link #EFFECT_TYPE_ENV_REVERB},     *            {@link #EFFECT_TYPE_EQUALIZER} ... Types corresponding to     *            built-in effects are defined by AudioEffect class. Other types     *            can be specified provided they correspond an existing OpenSL     *            ES interface ID and the corresponsing effect is available on     *            the platform. If an unspecified effect type is requested, the     *            constructor with throw the IllegalArgumentException. This     *            parameter can be set to {@link #EFFECT_TYPE_NULL} in which     *            case only the uuid will be used to select the effect.     * @param uuid unique identifier of a particular effect implementation.     *            Must be specified if the caller wants to use a particular     *            implementation of an effect type. This parameter can be set to     *            {@link #EFFECT_TYPE_NULL} in which case only the type will     *            be used to select the effect.     * @param priority the priority level requested by the application for     *            controlling the effect engine. As the same effect engine can     *            be shared by several applications, this parameter indicates     *            how much the requesting application needs control of effect     *            parameters. The normal priority is 0, above normal is a     *            positive number, below normal a negative number.     * @param audioSession system wide unique audio session identifier. If audioSession     *            is not 0, the effect will be attached to the MediaPlayer or     *            AudioTrack in the same audio session. Otherwise, the effect     *            will apply to the output mix.     *     * @throws java.lang.IllegalArgumentException     * @throws java.lang.UnsupportedOperationException     * @throws java.lang.RuntimeException     * @hide     */

  注释中详细介绍了各个参数。
 
  参数type是要创建的effect的类型。标准的类型已经在AudioEffect类中定义了，可以直接使用。
  若要使用其他的类型，需要提供OpenSLES interface ID，并且在平台中存在该类型。
  若指定的类型不存在，则会抛出IllegalArgumentException异常。
  若type为EFFECT_TYPE_NULL，则只会根据uuid来选择effect。
  标准的类型如下：

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++    /**     * The following UUIDs define effect types corresponding to standard audio     * effects whose implementation and interface conform to the OpenSL ES     * specification. The definitions match the corresponding interface IDs in     * OpenSLES_IID.h     */    /**     * UUID for environmental reverb effect     * @hide     */    public static final UUID EFFECT_TYPE_ENV_REVERB = UUID            .fromString("c2e5d5f0-94bd-4763-9cac-4e234d06839e");    /**     * UUID for preset reverb effect     * @hide     */    public static final UUID EFFECT_TYPE_PRESET_REVERB = UUID            .fromString("47382d60-ddd8-11db-bf3a-0002a5d5c51b");    /**     * UUID for equalizer effect     * @hide     */    public static final UUID EFFECT_TYPE_EQUALIZER = UUID            .fromString("0bed4300-ddd6-11db-8f34-0002a5d5c51b");    /**     * UUID for bass boost effect     * @hide     */    public static final UUID EFFECT_TYPE_BASS_BOOST = UUID            .fromString("0634f220-ddd4-11db-a0fc-0002a5d5c51b");    /**     * UUID for virtualizer effect     * @hide     */    public static final UUID EFFECT_TYPE_VIRTUALIZER = UUID            .fromString("37cc2c00-dddd-11db-8577-0002a5d5c51b");    /**     * Null effect UUID. Used when the UUID for effect type of     * @hide     */    public static final UUID EFFECT_TYPE_NULL = UUID            .fromString("ec7178ec-e5e1-4432-a3f4-4657e6795210");//----------------------------------------------------------------

  参数uuid用于指定一个特定effect的实现。
  若uuid为EFFECT_TYPE_NULL，则只会根据type来选择effect。
  关于uuid的取值，搜了下代码，发现，如果type不为EFFECT_TYPE_NULL，uuid多被指定为EFFECT_TYPE_NULL。
  uuid不为EFFECT_TYPE_NULL的地方，type多被指定为EFFECT_TYPE_NULL。
  基本上是靠两个中的一个来选择类型的，为何要两个参数？
  难道type用来指定标准的？uuid用来指定其他的？
  发现有如下的代码：

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++            // creating a volume controller on output mix ensures that ro.audio.silent mutes            // audio after the effects and not before            vc = new AudioEffect(                    AudioEffect.EFFECT_TYPE_NULL,                    UUID.fromString("119341a0-8469-11df-81f9-0002a5d5c51b"),                      0,                      0);//----------------------------------------------------------------

 
  priority是优先级，前文有说过，会根据优先级来判断effect engine的控制权。
 
  audioSession我们已经多次提到过。
  相同audioSession ID的AudioTrack和MediaPlayer共享Audio Effect。
  

    public AudioEffect(UUID type, UUID uuid, int priority, int audioSession)            throws IllegalArgumentException, UnsupportedOperationException,            RuntimeException {        int[] id = new int[1];// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 类Descriptor的注释：    /**     * The effect descriptor contains information on a particular effect implemented in the     * audio framework:<br>     * <ul>     *  <li>type: UUID corresponding to the OpenSL ES interface implemented by this effect</li>     *  <li>uuid: UUID for this particular implementation</li>     *  <li>connectMode: {@link #EFFECT_INSERT} or {@link #EFFECT_AUXILIARY}</li>     *  <li>name: human readable effect name</li>     *  <li>implementor: human readable effect implementor name</li>     * </ul>     * The method {@link #queryEffects()} returns an array of Descriptors to facilitate effects     * enumeration.     */// ----------------------------------------------------------------        Descriptor[] desc = new Descriptor[1];        // native initialization  // native_setup在以前有说过。  // 该函数肯定会调到native中的XXX_native_setup之类的函数中，  // 并最终创建一个native侧的AudioEffect对象，并通过函数函数SetIntField保存到java侧。// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 果然，在文件frameworks\base\media\audioeffect\android_media_AudioEffect.cpp中找到了JNI函数对照表：// Dalvik VM type signaturesstatic JNINativeMethod gMethods[] = {    {"native_init",          "()V",      (void *)android_media_AudioEffect_native_init},    {"native_setup",         "(Ljava/lang/Object;Ljava/lang/String;Ljava/lang/String;II[I[Ljava/lang/Object;)I",                                         (void *)android_media_AudioEffect_native_setup},    {"native_finalize",      "()V",      (void *)android_media_AudioEffect_native_finalize},    {"native_release",       "()V",      (void *)android_media_AudioEffect_native_release},    {"native_setEnabled",    "(Z)I",      (void *)android_media_AudioEffect_native_setEnabled},    {"native_getEnabled",    "()Z",      (void *)android_media_AudioEffect_native_getEnabled},    {"native_hasControl",    "()Z",      (void *)android_media_AudioEffect_native_hasControl},    {"native_setParameter",  "(I[BI[B)I",  (void *)android_media_AudioEffect_native_setParameter},    {"native_getParameter",  "(I[B[I[B)I",  (void *)android_media_AudioEffect_native_getParameter},    {"native_command",       "(II[B[I[B)I", (void *)android_media_AudioEffect_native_command},    {"native_query_effects", "()[Ljava/lang/Object;", (void *)android_media_AudioEffect_native_queryEffects},};// ----------------------------------------------------------------// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 函数android_media_AudioEffect_native_setup的实现也在文件frameworks\base\media\audioeffect\android_media_AudioEffect.cpp中。static jintandroid_media_AudioEffect_native_setup(JNIEnv *env, jobject thiz, jobject weak_this,        jstring type, jstring uuid, jint priority, jint sessionId, jintArray jId, jobjectArray javadesc){    LOGV("android_media_AudioEffect_native_setup");    AudioEffectJniStorage* lpJniStorage = NULL;    int lStatus = AUDIOEFFECT_ERROR_NO_MEMORY;    AudioEffect* lpAudioEffect = NULL;    jint* nId = NULL;    const char *typeStr = NULL;    const char *uuidStr = NULL;    effect_descriptor_t desc;    jobject jdesc;    char str[EFFECT_STRING_LEN_MAX];    jstring jdescType;    jstring jdescUuid;    jstring jdescConnect;    jstring jdescName;    jstring jdescImplementor; // 下面的几步都是参数的获取与判断    if (type != NULL) {        typeStr = env->GetStringUTFChars(type, NULL);        if (typeStr == NULL) {  // Out of memory            jniThrowException(env, "java/lang/RuntimeException", "Out of memory");            goto setup_failure;        }    }    if (uuid != NULL) {        uuidStr = env->GetStringUTFChars(uuid, NULL);        if (uuidStr == NULL) {  // Out of memory            jniThrowException(env, "java/lang/RuntimeException", "Out of memory");            goto setup_failure;        }    }    if (typeStr == NULL && uuidStr == NULL) {        lStatus = AUDIOEFFECT_ERROR_BAD_VALUE;        goto setup_failure;    } // 此处创建了一个AudioEffectJniStorage对象。 // 在看AudioTrack代码的时候，见到过相似的类。 // 是Android进程间共享内存用的。    lpJniStorage = new AudioEffectJniStorage();    if (lpJniStorage == NULL) {        LOGE("setup: Error creating JNI Storage");        goto setup_failure;    }    lpJniStorage->mCallbackData.audioEffect_class = (jclass)env->NewGlobalRef(fields.clazzEffect);    // we use a weak reference so the AudioEffect object can be garbage collected.    lpJniStorage->mCallbackData.audioEffect_ref = env->NewGlobalRef(weak_this);    LOGV("setup: lpJniStorage: %p audioEffect_ref %p audioEffect_class %p, &mCallbackData %p",            lpJniStorage,            lpJniStorage->mCallbackData.audioEffect_ref,            lpJniStorage->mCallbackData.audioEffect_class,            &lpJniStorage->mCallbackData);    if (jId == NULL) {        LOGE("setup: NULL java array for id pointer");        lStatus = AUDIOEFFECT_ERROR_BAD_VALUE;        goto setup_failure;    } // 如我们所料，此处创建了一个native侧的AudioEffect（class AudioEffect : public RefBase）对象。// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 关于类AudioEffect的说明。与java侧类的说明意思相同。    /* Constructor.     * AudioEffect is the base class for creating and controlling an effect engine from     * the application process. Creating an AudioEffect object will create the effect engine     * in the AudioFlinger if no engine of the specified type exists. If one exists, this engine     * will be used. The application creating the AudioEffect object (or a derived class like     * Reverb for instance) will either receive control of the effect engine or not, depending     * on the priority parameter. If priority is higher than the priority used by the current     * effect engine owner, the control will be transfered to the new application. Otherwise     * control will remain to the previous application. In this case, the new application will be     * notified of changes in effect engine state or control ownership by the effect callback.     * After creating the AudioEffect, the application must call the initCheck() method and     * check the creation status before trying to control the effect engine (see initCheck()).     * If the effect is to be applied to an AudioTrack or MediaPlayer only the application     * must specify the audio session ID corresponding to this player.     */// ----------------------------------------------------------------// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 构造函数中，各参数的说明。    /* Constructor.     *     * Parameters:     *     * type:  type of effect created: can be null if uuid is specified. This corresponds to     *        the OpenSL ES interface implemented by this effect.     * uuid:  Uuid of effect created: can be null if type is specified. This uuid corresponds to     *        a particular implementation of an effect type.     * priority:    requested priority for effect control: the priority level corresponds to the     *      value of priority parameter: negative values indicate lower priorities, positive values     *      higher priorities, 0 being the normal priority.     * cbf:         optional callback function (see effect_callback_t)     * user:        pointer to context for use by the callback receiver.     * sessionID:   audio session this effect is associated to. If 0, the effect will be global to     *      the output mix. If not 0, the effect will be applied to all players     *      (AudioTrack or MediaPLayer) within the same audio session.     * output:  HAL audio output stream to which this effect must be attached. Leave at 0 for     *      automatic output selection by AudioFlinger.     */// 这些参数以前都有遇到过。----------------------------------------------------------------++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 类AudioEffect的构造函数代码：//（可见其中没做太多工作。// 主要工作应该是在set函数中完成的。）AudioEffect::AudioEffect(const char *typeStr,                const char *uuidStr,                int32_t priority,                effect_callback_t cbf,                void* user,                int sessionId,                audio_io_handle_t output                )    : mStatus(NO_INIT){    effect_uuid_t type;    effect_uuid_t *pType = NULL;    effect_uuid_t uuid;    effect_uuid_t *pUuid = NULL;    LOGV("Constructor string\n - type: %s\n - uuid: %s", typeStr, uuidStr);    if (typeStr != NULL) {        if (stringToGuid(typeStr, &type) == NO_ERROR) {            pType = &type;        }    }    if (uuidStr != NULL) {        if (stringToGuid(uuidStr, &uuid) == NO_ERROR) {            pUuid = &uuid;        }    }// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// set函数注释：    /* Initialize an uninitialized AudioEffect.    * Returned status (from utils/Errors.h) can be:    *  - NO_ERROR or ALREADY_EXISTS: successful initialization    *  - INVALID_OPERATION: AudioEffect is already initialized    *  - BAD_VALUE: invalid parameter    *  - NO_INIT: audio flinger or audio hardware not initialized    * */ // 代码：status_t AudioEffect::set(const effect_uuid_t *type,                const effect_uuid_t *uuid,                int32_t priority,                effect_callback_t cbf,                void* user,                int sessionId,                audio_io_handle_t output){    sp<IEffect> iEffect;    sp<IMemory> cblk;    int enabled;    LOGV("set %p mUserData: %p", this, user);    if (mIEffect != 0) {        LOGW("Effect already in use");        return INVALID_OPERATION;    }    const sp<IAudioFlinger>& audioFlinger = AudioSystem::get_audio_flinger();    if (audioFlinger == 0) {        LOGE("set(): Could not get audioflinger");        return NO_INIT;    }    if (type == NULL && uuid == NULL) {        LOGW("Must specify at least type or uuid");        return BAD_VALUE;    }    mPriority = priority;    mCbf = cbf;    mUserData = user;    mSessionId = sessionId;    memset(&mDescriptor, 0, sizeof(effect_descriptor_t));    memcpy(&mDescriptor.type, EFFECT_UUID_NULL, sizeof(effect_uuid_t));    memcpy(&mDescriptor.uuid, EFFECT_UUID_NULL, sizeof(effect_uuid_t));    if (type != NULL) {        memcpy(&mDescriptor.type, type, sizeof(effect_uuid_t));    }    if (uuid != NULL) {        memcpy(&mDescriptor.uuid, uuid, sizeof(effect_uuid_t));    } // 这边只是相当于客户端，服务端在audioflinger侧 // Implements the IEffectClient interface // class EffectClient : public android::BnEffectClient,  public android::IBinder::DeathRecipient    mIEffectClient = new EffectClient(this);// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++sp<IEffect> AudioFlinger::createEffect(pid_t pid,        effect_descriptor_t *pDesc,        const sp<IEffectClient>& effectClient,        int32_t priority,        int output,        int sessionId,        status_t *status,        int *id,        int *enabled){    status_t lStatus = NO_ERROR;    sp<EffectHandle> handle;    effect_interface_t itfe;    effect_descriptor_t desc;    sp<Client> client;    wp<Client> wclient;    LOGV("createEffect pid %d, client %p, priority %d, sessionId %d, output %d",            pid, effectClient.get(), priority, sessionId, output); // 参数检查    if (pDesc == NULL) {        lStatus = BAD_VALUE;        goto Exit;    } // AudioSystem::SESSION_OUTPUT_MIX其实就是0. // 介绍AudioSessionId的时候，说过如果AudioSessionid为0，则AudioEffect对整个output mix都起作用。 // 不过需要有特殊的许可。该许可通过函数settingsAllowed来判断// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// 函数settingsAllowed的实现：static bool settingsAllowed() {#ifndef HAVE_ANDROID_OS    return true;#endif#if AUDIOFLINGER_SECURITY_ENABLED    if (getpid() == IPCThreadState::self()->getCallingPid()) return true;    bool ok = checkCallingPermission(String16("android.permission.MODIFY_AUDIO_SETTINGS"));    if (!ok) LOGE("Request requires android.permission.MODIFY_AUDIO_SETTINGS");    return ok;#else    if (!checkCallingPermission(String16("android.permission.MODIFY_AUDIO_SETTINGS")))        LOGW("WARNING: Need to add android.permission.MODIFY_AUDIO_SETTINGS to manifest");    return true;#endif}// ----------------------------------------------------------------    // check audio settings permission for global effects    if (sessionId == AudioSystem::SESSION_OUTPUT_MIX && !settingsAllowed()) {        lStatus = PERMISSION_DENIED;        goto Exit;    }// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++        SESSION_OUTPUT_STAGE = -1, // session for effects attached to a particular output stream                                   // (value must be less than 0)// ----------------------------------------------------------------    // Session AudioSystem::SESSION_OUTPUT_STAGE is reserved for output stage effects    // that can only be created by audio policy manager (running in same process)    if (sessionId == AudioSystem::SESSION_OUTPUT_STAGE && getpid() != pid) {        lStatus = PERMISSION_DENIED;        goto Exit;    }    // check recording permission for visualizer    if ((memcmp(&pDesc->type, SL_IID_VISUALIZATION, sizeof(effect_uuid_t)) == 0 ||         memcmp(&pDesc->uuid, &VISUALIZATION_UUID_, sizeof(effect_uuid_t)) == 0) &&        !recordingAllowed()) {        lStatus = PERMISSION_DENIED;        goto Exit;    }    if (output == 0) {        if (sessionId == AudioSystem::SESSION_OUTPUT_STAGE) {  // 这种情况下，output应该由AudioPolicyManager来指定            // output must be specified by AudioPolicyManager when using session            // AudioSystem::SESSION_OUTPUT_STAGE            lStatus = BAD_VALUE;            goto Exit;        } else if (sessionId == AudioSystem::SESSION_OUTPUT_MIX) {            // if the output returned by getOutputForEffect() is removed before we lock the            // mutex below, the call to checkPlaybackThread_l(output) below will detect it            // and we will exit safely// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++audio_io_handle_t AudioSystem::getOutputForEffect(effect_descriptor_t *desc){    const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();    if (aps == 0) return PERMISSION_DENIED;// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++    virtual audio_io_handle_t getOutputForEffect(effect_descriptor_t *desc)    {        Parcel data, reply;        data.writeInterfaceToken(IAudioPolicyService::getInterfaceDescriptor());        data.write(desc, sizeof(effect_descriptor_t));// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++status_t BnAudioPolicyService::onTransact(    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){...        case GET_OUTPUT_FOR_EFFECT: {            CHECK_INTERFACE(IAudioPolicyService, data, reply);            effect_descriptor_t desc;            data.read(&desc, sizeof(effect_descriptor_t));// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++audio_io_handle_t AudioPolicyService::getOutputForEffect(effect_descriptor_t *desc){    if (mpPolicyManager == NULL) {        return NO_INIT;    }    Mutex::Autolock _l(mLock);// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++audio_io_handle_t AudioPolicyManagerBase::getOutputForEffect(effect_descriptor_t *desc){    LOGV("getOutputForEffect()"); // 函数getOutput以前有看过，不过当时由于篇幅问题，未列出代码，今天列出来看看// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++audio_io_handle_t AudioPolicyManagerBase::getOutput(AudioSystem::stream_type stream,                                    uint32_t samplingRate,                                    uint32_t format,                                    uint32_t channels,                                    AudioSystem::output_flags flags){    audio_io_handle_t output = 0;    uint32_t latency = 0; // 获取策略// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++AudioPolicyManagerBase::routing_strategy AudioPolicyManagerBase::getStrategy(        AudioSystem::stream_type stream) {    // stream to strategy mapping    switch (stream) {    case AudioSystem::VOICE_CALL:    case AudioSystem::BLUETOOTH_SCO:        return STRATEGY_PHONE;    case AudioSystem::RING:    case AudioSystem::NOTIFICATION:    case AudioSystem::ALARM:    case AudioSystem::ENFORCED_AUDIBLE:        return STRATEGY_SONIFICATION;    case AudioSystem::DTMF:        return STRATEGY_DTMF;    default:        LOGE("unknown stream type");    case AudioSystem::SYSTEM:        // NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs        // while key clicks are played produces a poor result    case AudioSystem::TTS:    case AudioSystem::MUSIC:        return STRATEGY_MEDIA;    }}// ----------------------------------------------------------------    routing_strategy strategy = getStrategy((AudioSystem::stream_type)stream); // 获取device// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++uint32_t AudioPolicyManagerBase::getDeviceForStrategy(routing_strategy strategy, bool fromCache){    uint32_t device = 0;    if (fromCache) {        LOGV("getDeviceForStrategy() from cache strategy %d, device %x", strategy, mDeviceForStrategy[strategy]);  // mDeviceForStrategy在以下函数中赋值// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++void AudioPolicyManagerBase::updateDeviceForStrategy(){    for (int i = 0; i < NUM_STRATEGIES; i++) {        mDeviceForStrategy[i] = getDeviceForStrategy((routing_strategy)i, false);    }}// ----------------------------------------------------------------        return mDeviceForStrategy[strategy];    }    switch (strategy) {    case STRATEGY_DTMF:        if (!isInCall()) {            // when off call, DTMF strategy follows the same rules as MEDIA strategy            device = getDeviceForStrategy(STRATEGY_MEDIA, false);            break;        }        // when in call, DTMF and PHONE strategies follow the same rules        // FALL THROUGH    case STRATEGY_PHONE:        // for phone strategy, we first consider the forced use and then the available devices by order        // of priority        switch (mForceUse[AudioSystem::FOR_COMMUNICATION]) {        case AudioSystem::FORCE_BT_SCO:            if (!isInCall() || strategy != STRATEGY_DTMF) {   // 所以device的类型// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++    // output devices    public static final int DEVICE_OUT_EARPIECE = 0x1;    public static final int DEVICE_OUT_SPEAKER = 0x2;    public static final int DEVICE_OUT_WIRED_HEADSET = 0x4;    public static final int DEVICE_OUT_WIRED_HEADPHONE = 0x8;    public static final int DEVICE_OUT_BLUETOOTH_SCO = 0x10;    public static final int DEVICE_OUT_BLUETOOTH_SCO_HEADSET = 0x20;    public static final int DEVICE_OUT_BLUETOOTH_SCO_CARKIT = 0x40;    public static final int DEVICE_OUT_BLUETOOTH_A2DP = 0x80;    public static final int DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100;    public static final int DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER = 0x200;    public static final int DEVICE_OUT_AUX_DIGITAL = 0x400;    public static final int DEVICE_OUT_WIRED_HDMI = 0x4000;    public static final int DEVICE_OUT_DEFAULT = 0x8000;    // input devices    public static final int DEVICE_IN_COMMUNICATION = 0x10000;    public static final int DEVICE_IN_AMBIENT = 0x20000;    public static final int DEVICE_IN_BUILTIN_MIC1 = 0x40000;    public static final int DEVICE_IN_BUILTIN_MIC2 = 0x80000;    public static final int DEVICE_IN_MIC_ARRAY = 0x100000;    public static final int DEVICE_IN_BLUETOOTH_SCO_HEADSET = 0x200000;    public static final int DEVICE_IN_WIRED_HEADSET = 0x400000;    public static final int DEVICE_IN_AUX_DIGITAL = 0x800000;    public static final int DEVICE_IN_DEFAULT = 0x80000000;// ----------------------------------------------------------------                device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_CARKIT;                if (device) break;            }            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_HEADSET;            if (device) break;            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO;            if (device) break;            // if SCO device is requested but no SCO device is available, fall back to default case            // FALL THROUGH        default:    // FORCE_NONE            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADPHONE;            if (device) break;            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADSET;            if (device) break;#ifdef WITH_A2DP            // when not in a phone call, phone strategy should route STREAM_VOICE_CALL to A2DP            if (!isInCall()) {                device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP;                if (device) break;                device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES;                if (device) break;            }#endif            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_EARPIECE;            if (device == 0) {                LOGE("getDeviceForStrategy() earpiece device not found");            }            break;        case AudioSystem::FORCE_SPEAKER:            if (!isInCall() || strategy != STRATEGY_DTMF) {                device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_SCO_CARKIT;                if (device) break;            }#ifdef WITH_A2DP            // when not in a phone call, phone strategy should route STREAM_VOICE_CALL to            // A2DP speaker when forcing to speaker output            if (!isInCall()) {                device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER;                if (device) break;            }#endif            device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER;            if (device == 0) {                LOGE("getDeviceForStrategy() speaker device not found");            }            break;        }    break;    case STRATEGY_SONIFICATION:        // If incall, just select the STRATEGY_PHONE device: The rest of the behavior is handled by        // handleIncallSonification().        if (isInCall()) {            device = getDeviceForStrategy(STRATEGY_PHONE, false);            break;        }        device = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER;        if (device == 0) {            LOGE("getDeviceForStrategy() speaker device not found");        }        // The second device used for sonification is the same as the device used by media strategy        // FALL THROUGH    case STRATEGY_MEDIA: {        uint32_t device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_AUX_DIGITAL;         if (device2 == 0) {            device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HDMI;        }        if (device2 == 0) {            device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADPHONE;        }        if (device2 == 0) {            device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_WIRED_HEADSET;        }#ifdef WITH_A2DP        if (mA2dpOutput != 0) {            if (strategy == STRATEGY_SONIFICATION && !a2dpUsedForSonification()) {                break;            }            if (device2 == 0) {                device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP;            }            if (device2 == 0) {                device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES;            }            if (device2 == 0) {                device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER;            }        }#endif        if (device2 == 0) {            device2 = mAvailableOutputDevices & AudioSystem::DEVICE_OUT_SPEAKER;        }        // device is DEVICE_OUT_SPEAKER if we come from case STRATEGY_SONIFICATION, 0 otherwise        device |= device2;        if (device == 0) {            LOGE("getDeviceForStrategy() speaker device not found");        }        } break;    default:        LOGW("getDeviceForStrategy() unknown strategy: %d", strategy);        break;    }    LOGV("getDeviceForStrategy() strategy %d, device %x", strategy, device);    return device;}// ----------------------------------------------------------------    uint32_t device = getDeviceForStrategy(strategy);    LOGV("getOutput() stream %d, samplingRate %d, format %d, channels %x, flags %x", stream, samplingRate, format, channels, flags);#ifdef AUDIO_POLICY_TEST    if (mCurOutput != 0) {        LOGV("getOutput() test output mCurOutput %d, samplingRate %d, format %d, channels %x, mDirectOutput %d",                mCurOutput, mTestSamplingRate, mTestFormat, mTestChannels, mDirectOutput);        if (mTestOutputs[mCurOutput] == 0) {            LOGV("getOutput() opening test output");            AudioOutputDescriptor *outputDesc = new AudioOutputDescriptor();            outputDesc->mDevice = mTestDevice;            outputDesc->mSamplingRate = mTestSamplingRate;            outputDesc->mFormat = mTestFormat;            outputDesc->mChannels = mTestChannels;            outputDesc->mLatency = mTestLatencyMs;            outputDesc->mFlags = (AudioSystem::output_flags)(mDirectOutput ? AudioSystem::OUTPUT_FLAG_DIRECT : 0);            outputDesc->mRefCount[stream] = 0;   // mpClientInterface在构造函数中被赋值。// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++AudioPolicyManagerBase::AudioPolicyManagerBase(AudioPolicyClientInterface *clientInterface)    :#ifdef AUDIO_POLICY_TEST    Thread(false),#endif //AUDIO_POLICY_TEST    mPhoneState(AudioSystem::MODE_NORMAL), mRingerMode(0),    mMusicStopTime(0), mLimitRingtoneVolume(false), mLastVoiceVolume(-1.0f),    mTotalEffectsCpuLoad(0), mTotalEffectsMemory(0),    mA2dpSuspended(false){    mpClientInterface = clientInterface;    for (int i = 0; i < AudioSystem::NUM_FORCE_USE; i++) {        mForceUse[i] = AudioSystem::FORCE_NONE;    }    // devices available by default are speaker, ear piece and microphone    mAvailableOutputDevices = AudioSystem::DEVICE_OUT_EARPIECE |                        AudioSystem::DEVICE_OUT_SPEAKER;    mAvailableInputDevices = AudioSystem::DEVICE_IN_BUILTIN_MIC;#ifdef WITH_A2DP    mA2dpOutput = 0;    mDuplicatedOutput = 0;    mA2dpDeviceAddress = String8("");#endif    mScoDeviceAddress = String8("");    // open hardware output    AudioOutputDescriptor *outputDesc = new AudioOutputDescriptor();    outputDesc->mDevice = (uint32_t)AudioSystem::DEVICE_OUT_SPEAKER;    mHardwareOutput = mpClientInterface->openOutput(&outputDesc->mDevice,                                    &outputDesc->mSamplingRate,                                    &outputDesc->mFormat,                                    &outputDesc->mChannels,                                    &outputDesc->mLatency,                                    outputDesc->mFlags);    if (mHardwareOutput == 0) {        LOGE("Failed to initialize hardware output stream, samplingRate: %d, format %d, channels %d",                outputDesc->mSamplingRate, outputDesc->mFormat, outputDesc->mChannels);    } else {        addOutput(mHardwareOutput, outputDesc);        setOutputDevice(mHardwareOutput, (uint32_t)AudioSystem::DEVICE_OUT_SPEAKER, true);        //TODO: configure audio effect output stage here    }    updateDeviceForStrategy();#ifdef AUDIO_POLICY_TEST    AudioParameter outputCmd = AudioParameter();    outputCmd.addInt(String8("set_id"), 0);    mpClientInterface->setParameters(mHardwareOutput, outputCmd.toString());    mTestDevice = AudioSystem::DEVICE_OUT_SPEAKER;    mTestSamplingRate = 44100;    mTestFormat = AudioSystem::PCM_16_BIT;    mTestChannels =  AudioSystem::CHANNEL_OUT_STEREO;    mTestLatencyMs = 0;    mCurOutput = 0;    mDirectOutput = false;    for (int i = 0; i < NUM_TEST_OUTPUTS; i++) {        mTestOutputs[i] = 0;    }    const size_t SIZE = 256;    char buffer[SIZE];    snprintf(buffer, SIZE, "AudioPolicyManagerTest");    run(buffer, ANDROID_PRIORITY_AUDIO);#endif //AUDIO_POLICY_TEST}// ----------------------------------------------------------------// AudioPolicyManagerBase对象在AudioPolicyService的构造函数中被创建// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++AudioPolicyService::AudioPolicyService()    : BnAudioPolicyService() , mpPolicyManager(NULL){    char value[PROPERTY_VALUE_MAX];    // start tone playback thread    mTonePlaybackThread = new AudioCommandThread(String8(""));    // start audio commands thread    mAudioCommandThread = new AudioCommandThread(String8("ApmCommandThread"));#if (defined GENERIC_AUDIO) || (defined AUDIO_POLICY_TEST)    mpPolicyManager = new AudioPolicyManagerBase(this);    LOGV("build for GENERIC_AUDIO - using generic audio policy");#else    // if running in emulation - use the emulator driver    if (property_get("ro.kernel.qemu", value, 0)) {        LOGV("Running in emulation - using generic audio policy");        mpPolicyManager = new AudioPolicyManagerBase(this);    }    else {        LOGV("Using hardware specific audio policy");  // 我们用到的肯定是这儿的  // 函数createAudioPolicyManager的实现都在hardware中  // 我们使用到的是alsa中的// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++extern "C" AudioPolicyInterface* createAudioPolicyManager(AudioPolicyClientInterface *clientInterface){// AudioPolicyManagerALSA的构造函数中没作什么特殊处理// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// Nothing currently different between the Base implementation.// 注释说它和base没什么差别// getOutput函数中调用的openOutput接口，应该是在AudioPolicyService中实现的了AudioPolicyManagerALSA::AudioPolicyManagerALSA(AudioPolicyClientInterface *clientInterface)    : AudioPolicyManagerBase(clientInterface){}// ----------------------------------------------------------------    return new AudioPolicyManagerALSA(clientInterface);}// ----------------------------------------------------------------        mpPolicyManager = createAudioPolicyManager(this);    }#endif    // load properties    property_get("ro.camera.sound.forced", value, "0");    mpPolicyManager->setSystemProperty("ro.camera.sound.forced", value);}// ----------------------------------------------------------------// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++audio_io_handle_t AudioPolicyService::openOutput(uint32_t *pDevices,                                uint32_t *pSamplingRate,                                uint32_t *pFormat,                                uint32_t *pChannels,                                uint32_t *pLatencyMs,                                AudioSystem::output_flags flags){    sp<IAudioFlinger> af = AudioSystem::get_audio_flinger();    if (af == 0) {        LOGW("openOutput() could not get AudioFlinger");        return 0;    } // 又调到了audioflinger中// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++int AudioFlinger::openOutput(uint32_t *pDevices,                                uint32_t *pSamplingRate,                                uint32_t *pFormat,                                uint32_t *pChannels,                                uint32_t *pLatencyMs,                                uint32_t flags){    status_t status;    PlaybackThread *thread = NULL;    mHardwareStatus = AUDIO_HW_OUTPUT_OPEN;    uint32_t samplingRate = pSamplingRate ? *pSamplingRate : 0;    uint32_t format = pFormat ? *pFormat : 0;    uint32_t channels = pChannels ? *pChannels : 0;    uint32_t latency = pLatencyMs ? *pLatencyMs : 0;    LOGV("openOutput(), Device %x, SamplingRate %d, Format %d, Channels %x, flags %x",            pDevices ? *pDevices : 0,            samplingRate,            format,            channels,            flags);    if (pDevices == NULL || *pDevices == 0) {        return 0;    }    Mutex::Autolock _l(mLock);// 又调到了HAL层的openOutputStream函数    AudioStreamOut *output = mAudioHardware->openOutputStream(*pDevices,                                                             (int *)&format,                                                             &channels,                                                             &samplingRate,                                                             &status);    LOGV("openOutput() openOutputStream returned output %p, SamplingRate %d, Format %d, Channels %x, status %d",            output,            samplingRate,            format,            channels,            status);    mHardwareStatus = AUDIO_HW_IDLE;    if (output != 0) {        int id = nextUniqueId();        if ((flags & AudioSystem::OUTPUT_FLAG_DIRECT) ||            (format != AudioSystem::PCM_16_BIT) ||            (channels != AudioSystem::CHANNEL_OUT_STEREO)) {            thread = new DirectOutputThread(this, output, id, *pDevices);            LOGV("openOutput() created direct output: ID %d thread %p", id, thread);        } else {            thread = new MixerThread(this, output, id, *pDevices);            LOGV("openOutput() created mixer output: ID %d thread %p", id, thread);#ifdef LVMX            unsigned bitsPerSample =                (format == AudioSystem::PCM_16_BIT) ? 16 :                    ((format == AudioSystem::PCM_8_BIT) ? 8 : 0);            unsigned channelCount = (channels == AudioSystem::CHANNEL_OUT_STEREO) ? 2 : 1;            int audioOutputType = LifeVibes::threadIdToAudioOutputType(thread->id());            LifeVibes::init_aot(audioOutputType, samplingRate, bitsPerSample, channelCount);            LifeVibes::setDevice(audioOutputType, *pDevices);#endif        }        mPlaybackThreads.add(id, thread);        if (pSamplingRate) *pSamplingRate = samplingRate;        if (pFormat) *pFormat = format;        if (pChannels) *pChannels = channels;        if (pLatencyMs) *pLatencyMs = thread->latency();        // notify client processes of the new output creation        thread->audioConfigChanged_l(AudioSystem::OUTPUT_OPENED);        return id;    }    return 0;}// ----------------------------------------------------------------    return af->openOutput(pDevices,                          pSamplingRate,                          (uint32_t *)pFormat,                          pChannels,                          pLatencyMs,                          flags);}// ----------------------------------------------------------------            mTestOutputs[mCurOutput] = mpClientInterface->openOutput(&outputDesc->mDevice,                                            &outputDesc->mSamplingRate,                                            &outputDesc->mFormat,                                            &outputDesc->mChannels,                                            &outputDesc->mLatency,                                            outputDesc->mFlags);            if (mTestOutputs[mCurOutput]) {                AudioParameter outputCmd = AudioParameter();                outputCmd.addInt(String8("set_id"),mCurOutput);                mpClientInterface->setParameters(mTestOutputs[mCurOutput],outputCmd.toString());                addOutput(mTestOutputs[mCurOutput], outputDesc);            }        }        return mTestOutputs[mCurOutput];    }#endif //AUDIO_POLICY_TEST    // open a direct output if required by specified parameters    if (needsDirectOuput(stream, samplingRate, format, channels, flags, device)) {        LOGV("getOutput() opening direct output device %x", device);        AudioOutputDescriptor *outputDesc = new AudioOutputDescriptor();        outputDesc->mDevice = device;        outputDesc->mSamplingRate = samplingRate;        outputDesc->mFormat = format;        outputDesc->mChannels = channels;        outputDesc->mLatency = 0;        outputDesc->mFlags = (AudioSystem::output_flags)(flags | AudioSystem::OUTPUT_FLAG_DIRECT);        outputDesc->mRefCount[stream] = 0;        output = mpClientInterface->openOutput(&outputDesc->mDevice,                                        &outputDesc->mSamplingRate,                                        &outputDesc->mFormat,                                        &outputDesc->mChannels,                                        &outputDesc->mLatency,                                        outputDesc->mFlags);        // only accept an output with the requeted parameters        if (output == 0 ||            (samplingRate != 0 && samplingRate != outputDesc->mSamplingRate) ||            (format != 0 && format != outputDesc->mFormat) ||            (channels != 0 && channels != outputDesc->mChannels)) {            LOGV("getOutput() failed opening direct output: samplingRate %d, format %d, channels %d",                    samplingRate, format, channels);            if (output != 0) {                mpClientInterface->closeOutput(output);            }            delete outputDesc;            return 0;        }        addOutput(output, outputDesc);        return output;    }    if (channels != 0 && channels != AudioSystem::CHANNEL_OUT_MONO &&        channels != AudioSystem::CHANNEL_OUT_STEREO) {        return 0;    }    // open a non direct output    // get which output is suitable for the specified stream. The actual routing change will happen    // when startOutput() will be called    uint32_t a2dpDevice = device & AudioSystem::DEVICE_OUT_ALL_A2DP;    if (AudioSystem::popCount((AudioSystem::audio_devices)device) == 2) {#ifdef WITH_A2DP        if (a2dpUsedForSonification() && a2dpDevice != 0) {            // if playing on 2 devices among which one is A2DP, use duplicated output            LOGV("getOutput() using duplicated output");            LOGW_IF((mA2dpOutput == 0), "getOutput() A2DP device in multiple %x selected but A2DP output not opened", device);            output = mDuplicatedOutput;        } else#endif        {            // if playing on 2 devices among which none is A2DP, use hardware output            output = mHardwareOutput;        }        LOGV("getOutput() using output %d for 2 devices %x", output, device);    } else {#ifdef WITH_A2DP        if (a2dpDevice != 0) {            // if playing on A2DP device, use a2dp output            LOGW_IF((mA2dpOutput == 0), "getOutput() A2DP device %x selected but A2DP output not opened", device);            output = mA2dpOutput;        } else#endif        {            // if playing on not A2DP device, use hardware output            output = mHardwareOutput;        }    }    LOGW_IF((output ==0), "getOutput() could not find output for stream %d, samplingRate %d, format %d, channels %x, flags %x",                stream, samplingRate, format, channels, flags);    return output;}// ----------------------------------------------------------------    // apply simple rule where global effects are attached to the same output as MUSIC streams    return getOutput(AudioSystem::MUSIC);}原来到最后只是获取了MUSIC的output。// ----------------------------------------------------------------    return mpPolicyManager->getOutputForEffect(desc);}// ----------------------------------------------------------------            audio_io_handle_t output = getOutputForEffect(&desc);            reply->writeInt32(static_cast <int>(output));            return NO_ERROR;        } break;...}// ----------------------------------------------------------------        remote()->transact(GET_OUTPUT_FOR_EFFECT, data, &reply);        return static_cast <audio_io_handle_t> (reply.readInt32());    }// ----------------------------------------------------------------    return aps->getOutputForEffect(desc);}// ----------------------------------------------------------------            output = AudioSystem::getOutputForEffect(&desc);        }    }    {        Mutex::Autolock _l(mLock);        if (!EffectIsNullUuid(&pDesc->uuid)) {            // if uuid is specified, request effect descriptor            lStatus = EffectGetDescriptor(&pDesc->uuid, &desc);            if (lStatus < 0) {                LOGW("createEffect() error %d from EffectGetDescriptor", lStatus);                goto Exit;            }        } else {            // if uuid is not specified, look for an available implementation            // of the required type in effect factory            if (EffectIsNullUuid(&pDesc->type)) {                LOGW("createEffect() no effect type");                lStatus = BAD_VALUE;                goto Exit;            }            uint32_t numEffects = 0;            effect_descriptor_t d;            bool found = false;   // 得到Effect的个数            lStatus = EffectQueryNumberEffects(&numEffects);            if (lStatus < 0) {                LOGW("createEffect() error %d from EffectQueryNumberEffects", lStatus);                goto Exit;            }   // 寻找匹配的effect            for (uint32_t i = 0; i < numEffects; i++) {                lStatus = EffectQueryEffect(i, &desc);                if (lStatus < 0) {                    LOGW("createEffect() error %d from EffectQueryEffect", lStatus);                    continue;                }                if (memcmp(&desc.type, &pDesc->type, sizeof(effect_uuid_t)) == 0) {                    // If matching type found save effect descriptor. If the session is                    // 0 and the effect is not auxiliary, continue enumeration in case                    // an auxiliary version of this effect type is available                    found = true;                    memcpy(&d, &desc, sizeof(effect_descriptor_t));                    if (sessionId != AudioSystem::SESSION_OUTPUT_MIX ||                            (desc.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {                        break;                    }                }            }            if (!found) {                lStatus = BAD_VALUE;                LOGW("createEffect() effect not found");                goto Exit;            }            // For same effect type, chose auxiliary version over insert version if            // connect to output mix (Compliance to OpenSL ES)            if (sessionId == AudioSystem::SESSION_OUTPUT_MIX &&                    (d.flags & EFFECT_FLAG_TYPE_MASK) != EFFECT_FLAG_TYPE_AUXILIARY) {                memcpy(&desc, &d, sizeof(effect_descriptor_t));            }        }        // Do not allow auxiliary effects on a session different from 0 (output mix)        if (sessionId != AudioSystem::SESSION_OUTPUT_MIX &&             (desc.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {            lStatus = INVALID_OPERATION;            goto Exit;        }        // return effect descriptor        memcpy(pDesc, &desc, sizeof(effect_descriptor_t));        // If output is not specified try to find a matching audio session ID in one of the        // output threads.        // If output is 0 here, sessionId is neither SESSION_OUTPUT_STAGE nor SESSION_OUTPUT_MIX        // because of code checking output when entering the function.        if (output == 0) {             // look for the thread where the specified audio session is present            for (size_t i = 0; i < mPlaybackThreads.size(); i++) {                if (mPlaybackThreads.valueAt(i)->hasAudioSession(sessionId) != 0) {                    output = mPlaybackThreads.keyAt(i);                    break;                }            }            // If no output thread contains the requested session ID, default to            // first output. The effect chain will be moved to the correct output            // thread when a track with the same session ID is created            if (output == 0 && mPlaybackThreads.size()) {                output = mPlaybackThreads.keyAt(0);            }        }        LOGV("createEffect() got output %d for effect %s", output, desc.name);        PlaybackThread *thread = checkPlaybackThread_l(output);        if (thread == NULL) {            LOGE("createEffect() unknown output thread");            lStatus = BAD_VALUE;            goto Exit;        }        // TODO: allow attachment of effect to inputs        wclient = mClients.valueFor(pid);        if (wclient != NULL) {            client = wclient.promote();        } else {            client = new Client(this, pid);            mClients.add(pid, client);        }  // 在函数AudioEffect::Set函数中创建的EffectClient对象(effectClient)，在此处并未作太多处理，而是直接传给了函数thread->createEffect_l// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++// PlaybackThread::createEffect_l() must be called with AudioFlinger::mLock heldsp<AudioFlinger::EffectHandle> AudioFlinger::PlaybackThread::createEffect_l(        const sp<AudioFlinger::Client>& client,        const sp<IEffectClient>& effectClient,        int32_t priority,        int sessionId,        effect_descriptor_t *desc,        int *enabled,        status_t *status        ){    sp<EffectModule> effect;    sp<EffectHandle> handle;    status_t lStatus;    sp<Track> track;    sp<EffectChain> chain;    bool chainCreated = false;    bool effectCreated = false;    bool effectRegistered = false;    if (mOutput == 0) {        LOGW("createEffect_l() Audio driver not initialized.");        lStatus = NO_INIT;        goto Exit;    }    // Do not allow auxiliary effect on session other than 0    if ((desc->flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY &&        sessionId != AudioSystem::SESSION_OUTPUT_MIX) {        LOGW("createEffect_l() Cannot add auxiliary effect %s to session %d",                desc->name, sessionId);        lStatus = BAD_VALUE;        goto Exit;    }    // Do not allow effects with session ID 0 on direct output or duplicating threads    // TODO: add rule for hw accelerated effects on direct outputs with non PCM format    if (sessionId == AudioSystem::SESSION_OUTPUT_MIX && mType != MIXER) {        LOGW("createEffect_l() Cannot add auxiliary effect %s to session %d",                desc->name, sessionId);        lStatus = BAD_VALUE;        goto Exit;    }    LOGV("createEffect_l() thread %p effect %s on session %d", this, desc->name, sessionId);    { // scope for mLock        Mutex::Autolock _l(mLock);  // 先看是否存在指定session的effect链，如果不存在，创建一个        // check for existing effect chain with the requested audio session        chain = getEffectChain_l(sessionId);        if (chain == 0) {            // create a new chain for this session            LOGV("createEffect_l() new effect chain for session %d", sessionId);            chain = new EffectChain(this, sessionId);            addEffectChain_l(chain);            chain->setStrategy(getStrategyForSession_l(sessionId));            chainCreated = true;        } else {            effect = chain->getEffectFromDesc_l(desc);        }        LOGV("createEffect_l() got effect %p on chain %p", effect == 0 ? 0 : effect.get(), chain.get());  // 是否存在相同描述的effect，不存在的话，创建一个        if (effect == 0) {            int id = mAudioFlinger->nextUniqueId();            // Check CPU and memory usage            lStatus = AudioSystem::registerEffect(desc, mId, chain->strategy(), sessionId, id);            if (lStatus != NO_ERROR) {                goto Exit;            }            effectRegistered = true;            // create a new effect module if none present in the chain            effect = new EffectModule(this, chain, desc, id, sessionId);            lStatus = effect->status();            if (lStatus != NO_ERROR) {                goto Exit;            }            lStatus = chain->addEffect_l(effect);            if (lStatus != NO_ERROR) {                goto Exit;            }            effectCreated = true;            effect->setDevice(mDevice);            effect->setMode(mAudioFlinger->getMode());        }  // 看看下面EffectHandle的注释，便于理解// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++    // The EffectHandle class implements the IEffect interface. It provides resources    // to receive parameter updates, keeps track of effect control    // ownership and state and has a pointer to the EffectModule object it is controlling.    // There is one EffectHandle object for each application controlling (or using)    // an effect module.    // The EffectHandle is obtained by calling AudioFlinger::createEffect().// ----------------------------------------------------------------        // create effect handle and connect it to effect module        handle = new EffectHandle(effect, client, effectClient, priority);        lStatus = effect->addHandle(handle);        if (enabled) {            *enabled = (int)effect->isEnabled();        }    }Exit:    if (lStatus != NO_ERROR && lStatus != ALREADY_EXISTS) {        Mutex::Autolock _l(mLock);        if (effectCreated) {            chain->removeEffect_l(effect);        }        if (effectRegistered) {            AudioSystem::unregisterEffect(effect->id());        }        if (chainCreated) {            removeEffectChain_l(chain);        }        handle.clear();    }    if(status) {        *status = lStatus;    }    return handle;}// ----------------------------------------------------------------        // create effect on selected output trhead        handle = thread->createEffect_l(client, effectClient, priority, sessionId,                &desc, enabled, &lStatus);        if (handle != 0 && id != NULL) {            *id = handle->id();        }    }Exit:    if(status) {        *status = lStatus;    }    return handle;}// ----------------------------------------------------------------    iEffect = audioFlinger->createEffect(getpid(), (effect_descriptor_t *)&mDescriptor,            mIEffectClient, priority, output, mSessionId, &mStatus, &mId, &enabled);    if (iEffect == 0 || (mStatus != NO_ERROR && mStatus != ALREADY_EXISTS)) {        LOGE("set(): AudioFlinger could not create effect, status: %d", mStatus);        return mStatus;    }    mEnabled = (volatile int32_t)enabled;    mIEffect = iEffect;    cblk = iEffect->getCblk();    if (cblk == 0) {        mStatus = NO_INIT;        LOGE("Could not get control block");        return mStatus;    }    mIEffect = iEffect;    mCblkMemory = cblk;    mCblk = static_cast<effect_param_cblk_t*>(cblk->pointer());    int bufOffset = ((sizeof(effect_param_cblk_t) - 1) / sizeof(int) + 1) * sizeof(int);    mCblk->buffer = (uint8_t *)mCblk + bufOffset;    iEffect->asBinder()->linkToDeath(mIEffectClient);    LOGV("set() %p OK effect: %s id: %d status %d enabled %d, ", this, mDescriptor.name, mId, mStatus, mEnabled);    return mStatus;}// ----------------------------------------------------------------    mStatus = set(pType, pUuid, priority, cbf, user, sessionId, output);}// ----------------------------------------------------------------    // create the native AudioEffect object    lpAudioEffect = new AudioEffect(typeStr,                                    uuidStr,                                    priority,                                    effectCallback,                                    &lpJniStorage->mCallbackData,                                    sessionId,                                    0);    if (lpAudioEffect == NULL) {        LOGE("Error creating AudioEffect");        goto setup_failure;    }    lStatus = translateError(lpAudioEffect->initCheck());    if (lStatus != AUDIOEFFECT_SUCCESS && lStatus != AUDIOEFFECT_ERROR_ALREADY_EXISTS) {        LOGE("AudioEffect initCheck failed %d", lStatus);        goto setup_failure;    }    nId = (jint *) env->GetPrimitiveArrayCritical(jId, NULL);    if (nId == NULL) {        LOGE("setup: Error retrieving id pointer");        lStatus = AUDIOEFFECT_ERROR_BAD_VALUE;        goto setup_failure;    }    nId[0] = lpAudioEffect->id();    env->ReleasePrimitiveArrayCritical(jId, nId, 0);    nId = NULL;    if (typeStr) {        env->ReleaseStringUTFChars(type, typeStr);        typeStr = NULL;    }    if (uuidStr) {        env->ReleaseStringUTFChars(uuid, uuidStr);        uuidStr = NULL;    }    // get the effect descriptor    desc = lpAudioEffect->descriptor();    AudioEffect::guidToString(&desc.type, str, EFFECT_STRING_LEN_MAX);    jdescType = env->NewStringUTF(str);    AudioEffect::guidToString(&desc.uuid, str, EFFECT_STRING_LEN_MAX);    jdescUuid = env->NewStringUTF(str);    if ((desc.flags & EFFECT_FLAG_TYPE_MASK) == EFFECT_FLAG_TYPE_AUXILIARY) {        jdescConnect = env->NewStringUTF("Auxiliary");    } else {        jdescConnect = env->NewStringUTF("Insert");    }    jdescName = env->NewStringUTF(desc.name);    jdescImplementor = env->NewStringUTF(desc.implementor);    jdesc = env->NewObject(fields.clazzDesc,                           fields.midDescCstor,                           jdescType,                           jdescUuid,                           jdescConnect,                           jdescName,                           jdescImplementor);    env->DeleteLocalRef(jdescType);    env->DeleteLocalRef(jdescUuid);    env->DeleteLocalRef(jdescConnect);    env->DeleteLocalRef(jdescName);    env->DeleteLocalRef(jdescImplementor);    if (jdesc == NULL) {        LOGE("env->NewObject(fields.clazzDesc, fields.midDescCstor)");        goto setup_failure;    }    env->SetObjectArrayElement(javadesc, 0, jdesc);    env->SetIntField(thiz, fields.fidNativeAudioEffect, (int)lpAudioEffect);    env->SetIntField(thiz, fields.fidJniData, (int)lpJniStorage);    return AUDIOEFFECT_SUCCESS;    // failures:setup_failure:    if (nId != NULL) {        env->ReleasePrimitiveArrayCritical(jId, nId, 0);    }    if (lpAudioEffect) {        delete lpAudioEffect;    }    env->SetIntField(thiz, fields.fidNativeAudioEffect, 0);    if (lpJniStorage) {        delete lpJniStorage;    }    env->SetIntField(thiz, fields.fidJniData, 0);    if (uuidStr != NULL) {        env->ReleaseStringUTFChars(uuid, uuidStr);    }    if (typeStr != NULL) {        env->ReleaseStringUTFChars(type, typeStr);    }    return lStatus;}// ----------------------------------------------------------------        int initResult = native_setup(new WeakReference<AudioEffect>(this),                type.toString(), uuid.toString(), priority, audioSession, id,                desc);        if (initResult != SUCCESS && initResult != ALREADY_EXISTS) {            Log.e(TAG, "Error code " + initResult                    + " when initializing AudioEffect.");            switch (initResult) {            case ERROR_BAD_VALUE:                throw (new IllegalArgumentException("Effect type: " + type                        + " not supported."));            case ERROR_INVALID_OPERATION:                throw (new UnsupportedOperationException(                        "Effect library not loaded"));            default:                throw (new RuntimeException(                        "Cannot initialize effect engine for type: " + type                                + "Error: " + initResult));            }        }        mId = id[0];        mDescriptor = desc[0];        synchronized (mStateLock) {            mState = STATE_INITIALIZED;        }    }

###############################################################################################

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&总结&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
每一个session id都对应一个effect链表。
创建effect时，会首先检查指定session id的effect链表是否存在，不存在的话创建一个。
然后看链表中相同描述的effect是否存在，不存在的话，创建一个。
但没个应用程序都拥有一个自己的EffectHandle。
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&