系统应用在android10以下无法获取到音频设备的更新，普通应用可以获取到

系统应用在android10以下无法获取到音频设备的更新，普通应用可以获取到

**问题现象：**系统应用在android10以下无法获取到音频设备的更新，普通应用可以获取到。

获取所有音频设备的流程分析
AudioDeviceInfo[] devices = audioManager.getDevices(AudioManager.GET_DEVICES_ALL);

AudioManager getDevices最终会调用到updateAudioPortCache
在updateAudioPortCache中根际sAudioPortGeneration标记进行是否主动查询设备列表，代码如下
static int updateAudioPortCache(ArrayList ports, ArrayList patches,
ArrayList previousPorts) {
sAudioPortEventHandler.init();
synchronized (sAudioPortGeneration) {
if (sAudioPortGeneration == AUDIOPORT_GENERATION_INIT) {
//TODO 第一次调用才进行查询
…
}
//TODO 后续直接从sAudioPortsCached缓存中获取
if (ports != null) {
ports.clear();
ports.addAll(sAudioPortsCached);
}
…
}
return SUCCESS;
}

sAudioPortsCached缓存更新流程：
驱动上报最终调用到框架层
android_media_AudioSystem_setDeviceConnectionState ------->
AudioSystem::setDeviceConnectionState ------->
AudioPolicyService::setDeviceConnectionState ------->
AudioPolicyManager::setDeviceConnectionState ------->

AudioPolicyService::AudioPolicyClient::onAudioPortListUpdate() ------>
AudioPolicyService::onAudioPortListUpdate() ------>
AudioPolicyService::AudioCommandThread::updateAudioPortListCommand: 发送 UPDATE_AUDIOPORT_LIST 给
AudioPolicyService::AudioCommandThread ------>
AudioPolicyService::doOnAudioPortListUpdate() ------>
AudioPolicyService::NotificationClient::onAudioPortListUpdate() ------>
AudioSystem::AudioPolicyServiceClient::onAudioPortListUpdate() ------>
mAudioPortCallbacks#onAudioPortListUpdate() .

android_media_AudioSystem.cpp native_setup 注册这个 addAudioPortCallback

当设备列表变化时AudioPolicyService最终会调用到AudioPortEventHandler的postEventFromNative----》handleMessage----》AudioManager.updateAudioPortCache(ports, patches, null);刷新sAudioPortsCached缓存

普通应用可以获取到系统应用获取不到的问题点
void AudioPolicyService::registerClient(const sp& client)
{
…
// TODO 因为系统应用uid都是1000，其他应用已经添加过了，那么我们的系统应用就不会再次添加了导致缓存没有更新
uid_t uid = IPCThreadState::self()->getCallingUid();
if (mNotificationClients.indexOfKey(uid) < 0) {
…
}
}

解决方案1： 更新AudioPolicyService的registerClient函数参考Android10的解决方案
void AudioPolicyService::registerClient(const sp& client)
{
if (client == 0) {
ALOGW(“%s got NULL client”, FUNCTION);
return;
}
Mutex::Autolock _l(mNotificationClientsLock);

uid_t uid = IPCThreadState::self()->getCallingUid();
pid_t pid = IPCThreadState::self()->getCallingPid();
int64_t token = ((int64_t)uid<<32) | pid;

if (mNotificationClients.indexOfKey(token) < 0) {
    sp<NotificationClient> notificationClient = new NotificationClient(this,client,uid,pid);
    ALOGV("registerClient() client %p, uid %d", client.get(), uid);
    mNotificationClients.add(token, notificationClient);

    sp<IBinder> binder = IInterface::asBinder(client);
    binder->linkToDeath(notificationClient);
}

}

**解决方案2：通过反射将 AudioManager 的静态字段 sAudioPortGeneration 设置为 0。AudioManage每次调用getDevices前先重置下状态sAudioPortGeneration （只在Android10以下才需要增加此逻辑）
/
* 将 AudioManager 的静态字段 sAudioPortGeneration 设置为 0
*/
public static void resetAudioPortGeneration() {
try {
Class<?> audioManagerClass = AudioManager.class;
Field sAudioPortGenerationField = audioManagerClass.getDeclaredField(“sAudioPortGeneration”);
sAudioPortGenerationField.setAccessible(true);
sAudioPortGenerationField.set(null, Integer.valueOf(0))
} catch (NoSuchFieldException | IllegalAccessException e) {
e.printStackTrace();
}
}