基于Android 9.0
1.概述
Android音频系统中，有两大服务AudioFlinger和AudioPolicy，这两个服务都运行在audioserver进程中。这里来整理以下audioserver启动流程。
2.加载audioserver.rc
Android是基于Linux内核的，而在Linux中，启动的第一个进程就是init进程，其他进程都是init进程的子进程。在init进程的启动过程中，会解析Linux的配置脚本init.rc文件。根据init.rc文件的内容，init进程会装载Android的文件系统，创建系统目录，启动Android系统重要的守护进程，这些进程包括USB守护进程，adb守护进程，vold守护进程等。
同时，init进程还会启动AudioServer（音频服务），ServiceManager（Binder服务管家）等重要服务。init进程还会孵化出Zygote进程，Zygote进程是Android系统的首个Java进程，Zygote是所有Java进程的父进程，如图所示：
（1）init进程执行main()方法
对应main.cpp中main方法，然后会调用到SecondStageMain()方法。
// system/core/init/init.cpp
int SecondStageMain(int argc, char** argv) {
//......
LoadBootScripts(am, sm);
//......
}
接着看LoadBootScripts代码：
static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
Parser parser = CreateParser(action_manager, service_list);
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
parser.ParseConfig("/init.rc");
// audioserver.rc的位置
if (!parser.ParseConfig("/system/etc/init")) {
late_import_paths.emplace_back("/system/etc/init");
}
if (!parser.ParseConfig("/product/etc/init")) {
late_import_paths.emplace_back("/product/etc/init");
}
if (!parser.ParseConfig("/product_services/etc/init")) {
late_import_paths.emplace_back("/product_services/etc/init");
}
if (!parser.ParseConfig("/odm/etc/init")) {
late_import_paths.emplace_back("/odm/etc/init");
}
if (!parser.ParseConfig("/vendor/etc/init")) {
late_import_paths.emplace_back("/vendor/etc/init");
}
} else {
parser.ParseConfig(bootscript);
}
}
LoadBootScrips会首先加载init.rc文件，然后会加载/system/etc/init/、/product/etc/init/、/odm/etc/init/、/vendor/etc/init目录下的rc文件。而audioserver.rc位于/system/etc/init目录下。
3.启动audioserver进程
看一下audioserver.rc文件，init进程中加载audioserver.rc文件，并启动audioserver进程。
# frameworks/av/media/audioserver/audioserver.rc
service audioserver /system/bin/audioserver
class core
user audioserver #设置所有者
# media gid needed for /dev/fm (radio) and for /data/misc/media (tee)
#设置所属组
group audio camera drmrpc inet media mediadrm net_bt net_bt_admin net_bw_acct wakelock
capabilities BLOCK_SUSPEND
ioprio rt 4 #io优先级
writepid /dev/cpuset/foreground/tasks /dev/stune/foreground/tasks
onrestart restart vendor.audio-hal-2-0
onrestart restart vendor.audio-hal-4-0-msd
# Keep the original service name for backward compatibility when upgrading
# O-MR1 devices with framework-only.
onrestart restart audio-hal-2-0 #重启该进程时，执行restart audio-hal-2-0命令
# 使用setprop命令可以杀进程和拉起来
on property:vts.native_server.on=1
stop audioserver
on property:vts.native_server.on=0
start audioserver
on init
mkdir /dev/socket/audioserver 0775 audioserver audioserver
4.audioserver main
// frameworks/av/media/audioserver/main_audioserver.cpp
int main(int argc __unused, char **argv)
{
// TODO: update with refined parameters
limitProcessMemory(
"audio.maxmem", /* "ro.audio.maxmem", property that defines limit */
(size_t)512 * (1 << 20), /* SIZE_MAX, upper limit in bytes */
20 /* upper limit as percentage of physical RAM */);
signal(SIGPIPE, SIG_IGN);
bool doLog = (bool) property_get_bool("ro.test_harness", 0);
pid_t childPid;
// FIXME The advantage of making the process containing media.log service the parent process of
// the process that contains the other audio services, is that it allows us to collect more
// detailed information such as signal numbers, stop and continue, resource usage, etc.
// But it is also more complex. Consider replacing this by independent processes, and using
// binder on death notification instead.
if (doLog && (childPid = fork()) != 0) {
//如果doLog为true,fork子进程。
// media.log service
//prctl(PR_SET_NAME, (unsigned long) "media.log", 0, 0, 0);
// unfortunately ps ignores PR_SET_NAME for the main thread, so use this ugly hack
strcpy(argv[0], "media.log");
sp<ProcessState> proc(ProcessState::self());
MediaLogService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
// ......
} else {
// all other services
if (doLog) {
prctl(PR_SET_PDEATHSIG, SIGKILL); // if parent media.log dies before me, kill me also
setpgid(0, 0); // but if I die first, don't kill my parent
}
android::hardware::configureRpcThreadpool(4, false /*callerWillJoin*/);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate(); // 启动AudioFlinger
AudioPolicyService::instantiate(); // 启动AudioPolicyService
// AAudioService should only be used in OC-MR1 and later.
// And only enable the AAudioService if the system MMAP policy explicitly allows it.
// This prevents a client from misusing AAudioService when it is not supported.
aaudio_policy_t mmapPolicy = property_get_int32(AAUDIO_PROP_MMAP_POLICY,
AAUDIO_POLICY_NEVER);
if (mmapPolicy == AAUDIO_POLICY_AUTO || mmapPolicy == AAUDIO_POLICY_ALWAYS) {
AAudioService::instantiate();
}
SoundTriggerHwService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
}
主要工作：
- 启动AudioFlinger；
- 启动AudioPolicyService；
- 如果支持AAudioService，启动它;
- 启动语音识别模块SoundTriggerHwService;
- 创建线程池，并将当前线程加入线程池。
4.1 AudioFlinger初始化
接着看AudioFlinger::instantiate()，AudioFlinger并没有实现instantiate函数，直接在其父类找到对应函数。
// frameworks/native/libs/binder/include/binder/BinderService.h
template<typename SERVICE>
class BinderService
{
public:
static status_t publish(bool allowIsolated = false,
int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated,
dumpFlags);
}
static void publishAndJoinThreadPool(
bool allowIsolated = false,
int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
publish(allowIsolated, dumpFlags);
joinThreadPool();
}
static void instantiate() { publish(); }
// ......
};
-
获取IServiceManager；
-
new SERVICE()，对应new AudioFlinger();
-
将AudioFlinger注册到ServiceManager，方便后续别的进程使用该服务。
接着看AudioFlinger初始化方法，主要默认参数赋值。智能指针首次初始化会调用onFirstRef函数。创建PatchPanel，mMode设为AUDIO_MODE_NORMAL。
AudioFlinger::AudioFlinger()
: BnAudioFlinger(),
mMediaLogNotifier(new AudioFlinger::MediaLogNotifier()),
mPrimaryHardwareDev(NULL),
mAudioHwDevs(NULL),
mHardwareStatus(AUDIO_HW_IDLE),
mMasterVolume(1.0f),
mMasterMute(false),
// mNextUniqueId(AUDIO_UNIQUE_ID_USE_MAX),
mMode(AUDIO_MODE_INVALID),
mBtNrecIsOff(false),
mIsLowRamDevice(true),
mIsDeviceTypeKnown(false),
mTotalMemory(0),
mClientSharedHeapSize(kMinimumClientSharedHeapSizeBytes),
mGlobalEffectEnableTime(0),
mPatchPanel(this),
mSystemReady(false)
{
// unsigned instead of audio_unique_id_use_t, because ++ operator is unavailable for enum
for (unsigned use = AUDIO_UNIQUE_ID_USE_UNSPECIFIED; use < AUDIO_UNIQUE_ID_USE_MAX; use++) {
// zero ID has a special meaning, so unavailable
mNextUniqueIds[use] = AUDIO_UNIQUE_ID_USE_MAX;
}
const bool doLog = property_get_bool("ro.test_harness", false);
if (doLog) {
mLogMemoryDealer = new MemoryDealer(kLogMemorySize, "LogWriters",
MemoryHeapBase::READ_ONLY);
(void) pthread_once(&sMediaLogOnce, sMediaLogInit);
}
// reset battery stats.
// if the audio service has crashed, battery stats could be left
// in bad state, reset the state upon service start.
BatteryNotifier::getInstance().noteResetAudio();
mDevicesFactoryHal = DevicesFactoryHalInterface::create();
mEffectsFactoryHal = EffectsFactoryHalInterface::create();
mMediaLogNotifier->run("MediaLogNotifier");
}
void AudioFlinger::onFirstRef()
{
Mutex::Autolock _l(mLock);
/* TODO: move all this work into an Init() function */
char val_str[PROPERTY_VALUE_MAX] = { 0 };
if (property_get("ro.audio.flinger_standbytime_ms", val_str, NULL) >= 0) {
uint32_t int_val;
if (1 == sscanf(val_str, "%u", &int_val)) {
mStandbyTimeInNsecs = milliseconds(int_val);
ALOGI("Using %u mSec as standby time.", int_val);
} else {
mStandbyTimeInNsecs = kDefaultStandbyTimeInNsecs;
ALOGI("Using default %u mSec as standby time.",
(uint32_t)(mStandbyTimeInNsecs / 1000000));
}
}
mMode = AUDIO_MODE_NORMAL;
gAudioFlinger = this;
}
4.2 AudioPolicyService初始化
AudioPolicyService和AudioFlinger都是BinderService子类，其instantiate是类似的，创建AudioPolicyService，注册到ServiceManager中。
（1）接着看AudioPolicyService初始化。
AudioPolicyService::AudioPolicyService()
: BnAudioPolicyService(), mpAudioPolicyDev(NULL), mpAudioPolicy(NULL),
mAudioPolicyManager(NULL), mAudioPolicyClient(NULL), mPhoneState(AUDIO_MODE_INVALID)
{
}
void AudioPolicyService::onFirstRef()
{
{
Mutex::Autolock _l(mLock);
// start audio commands thread
mAudioCommandThread = new AudioCommandThread(String8("ApmAudio"), this);
// start output activity command thread
mOutputCommandThread = new AudioCommandThread(String8("ApmOutput"), this);
mAudioPolicyClient = new AudioPolicyClient(this);
mAudioPolicyManager = createAudioPolicyManager(mAudioPolicyClient);、、创建AudioPolicyManage对象
}
// load audio processing modules
sp<AudioPolicyEffects>audioPolicyEffects = new AudioPolicyEffects();
{
Mutex::Autolock _l(mLock);
mAudioPolicyEffects = audioPolicyEffects;
}
mUidPolicy = new UidPolicy(this);
mUidPolicy->registerSelf();
mSensorPrivacyPolicy = new SensorPrivacyPolicy(this);
mSensorPrivacyPolicy->registerSelf();
}
-
创建tone播放线程并启动；
-
创建audio command线程并启动；
-
创建audio输出命令线程并启动；
-
创建AudioPolicyClient对象，AudioFlinger和AudioPolicyService通信的中间；
-
创建AudioPolicyManage对象。
（2）接着看一下AudioPolicyManager初始化：
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
: AudioPolicyManager(clientInterface, false /*forTesting*/)
{
loadConfig();
initialize();
}
void AudioPolicyManager::loadConfig() {
if (deserializeAudioPolicyXmlConfig(getConfig()) != NO_ERROR) {
ALOGE("could not load audio policy configuration file, setting defaults");
getConfig().setDefault();
}
}
loadConfig加载音频配置文件audio_policy_configuration.xml，对其中的配置项进行解析。
（3）接着看initialize
status_t AudioPolicyManager::initialize() {
// Once policy config has been parsed, retrieve an instance of the engine and initialize it.
audio_policy::EngineInstance *engineInstance = audio_policy::EngineInstance::getInstance();
if (!engineInstance) {
ALOGE("%s: Could not get an instance of policy engine", __FUNCTION__);
return NO_INIT;
}
// Retrieve the Policy Manager Interface
mEngine = engineInstance->queryInterface<AudioPolicyManagerInterface>();
if (mEngine == NULL) {
ALOGE("%s: Failed to get Policy Engine Interface", __FUNCTION__);
return NO_INIT;
}
mEngine->setObserver(this);
status_t status = mEngine->initCheck();
if (status != NO_ERROR) {
LOG_FATAL("Policy engine not initialized(err=%d)", status);
return status;
}
// mAvailableOutputDevices and mAvailableInputDevices now contain all attached devices
// open all output streams needed to access attached devices
for (const auto& hwModule : mHwModulesAll) {
hwModule->setHandle(mpClientInterface->loadHwModule(hwModule->getName()));
if (hwModule->getHandle() == AUDIO_MODULE_HANDLE_NONE) {
ALOGW("could not open HW module %s", hwModule->getName());
continue;
}
mHwModules.push_back(hwModule);
// open all output streams needed to access attached devices
// except for direct output streams that are only opened when they are actually
// required by an app.
// This also validates mAvailableOutputDevices list
for (const auto& outProfile : hwModule->getOutputProfiles()) {
if (!outProfile->canOpenNewIo()) {
ALOGE("Invalid Output profile max open count %u for profile %s",
outProfile->maxOpenCount, outProfile->getTagName().c_str());
continue;
}
if (!outProfile->hasSupportedDevices()) {
ALOGW("Output profile contains no device on module %s", hwModule->getName());
continue;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_TTS) != 0) {
mTtsOutputAvailable = true;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_DIRECT) != 0) {
continue;
}
const DeviceVector &supportedDevices = outProfile->getSupportedDevices();
DeviceVector availProfileDevices = supportedDevices.filter(mAvailableOutputDevices);
sp<DeviceDescriptor> supportedDevice = 0;
if (supportedDevices.contains(mDefaultOutputDevice)) {
supportedDevice = mDefaultOutputDevice;
} else {
// choose first device present in profile's SupportedDevices also part of
// mAvailableOutputDevices.
if (availProfileDevices.isEmpty()) {
continue;
}
supportedDevice = availProfileDevices.itemAt(0);
}
if (!mAvailableOutputDevices.contains(supportedDevice)) {
continue;
}
sp<SwAudioOutputDescriptor> outputDesc = new SwAudioOutputDescriptor(outProfile,
mpClientInterface);
audio_io_handle_t output = AUDIO_IO_HANDLE_NONE;
status_t status = outputDesc->open(nullptr, DeviceVector(supportedDevice),
AUDIO_STREAM_DEFAULT,
AUDIO_OUTPUT_FLAG_NONE, &output);
if (status != NO_ERROR) {
ALOGW("Cannot open output stream for devices %s on hw module %s",
supportedDevice->toString().c_str(), hwModule->getName());
continue;
}
for (const auto &device : availProfileDevices) {
// give a valid ID to an attached device once confirmed it is reachable
if (!device->isAttached()) {
device->attach(hwModule);
}
}
if (mPrimaryOutput == 0 &&
outProfile->getFlags() & AUDIO_OUTPUT_FLAG_PRIMARY) {
mPrimaryOutput = outputDesc;
}
addOutput(output, outputDesc);
setOutputDevices(outputDesc,
DeviceVector(supportedDevice),
true,
0,
NULL);
}
// open input streams needed to access attached devices to validate
// mAvailableInputDevices list
for (const auto& inProfile : hwModule->getInputProfiles()) {
if (!inProfile->canOpenNewIo()) {
ALOGE("Invalid Input profile max open count %u for profile %s",
inProfile->maxOpenCount, inProfile->getTagName().c_str());
continue;
}
if (!inProfile->hasSupportedDevices()) {
ALOGW("Input profile contains no device on module %s", hwModule->getName());
continue;
}
// chose first device present in profile's SupportedDevices also part of
// available input devices
const DeviceVector &supportedDevices = inProfile->getSupportedDevices();
DeviceVector availProfileDevices = supportedDevices.filter(mAvailableInputDevices);
if (availProfileDevices.isEmpty()) {
ALOGE("%s: Input device list is empty!", __FUNCTION__);
continue;
}
sp<AudioInputDescriptor> inputDesc =
new AudioInputDescriptor(inProfile, mpClientInterface);
audio_io_handle_t input = AUDIO_IO_HANDLE_NONE;
status_t status = inputDesc->open(nullptr,
availProfileDevices.itemAt(0),
AUDIO_SOURCE_MIC,
AUDIO_INPUT_FLAG_NONE,
&input);
if (status != NO_ERROR) {
ALOGW("Cannot open input stream for device %s on hw module %s",
availProfileDevices.toString().c_str(),
hwModule->getName());
continue;
}
for (const auto &device : availProfileDevices) {
// give a valid ID to an attached device once confirmed it is reachable
if (!device->isAttached()) {
device->attach(hwModule);
device->importAudioPort(inProfile, true);
}
}
inputDesc->close();
}
}
// make sure all attached devices have been allocated a unique ID
auto checkAndSetAvailable = [this](auto& devices) {
for (size_t i = 0; i < devices.size();) {
const auto &device = devices[i];
if (!device->isAttached()) {
ALOGW("device %s is unreachable", device->toString().c_str());
devices.remove(device);
continue;
}
// Device is now validated and can be appended to the available devices of the engine
setEngineDeviceConnectionState(device, AUDIO_POLICY_DEVICE_STATE_AVAILABLE);
i++;
}
};
checkAndSetAvailable(mAvailableOutputDevices);
checkAndSetAvailable(mAvailableInputDevices);
// make sure default device is reachable
if (mDefaultOutputDevice == 0 || !mAvailableOutputDevices.contains(mDefaultOutputDevice)) {
ALOGE_IF(mDefaultOutputDevice != 0, "Default device %s is unreachable",
mDefaultOutputDevice->toString().c_str());
status = NO_INIT;
}
// If microphones address is empty, set it according to device type
for (size_t i = 0; i < mAvailableInputDevices.size(); i++) {
if (mAvailableInputDevices[i]->address().isEmpty()) {
if (mAvailableInputDevices[i]->type() == AUDIO_DEVICE_IN_BUILTIN_MIC) {
mAvailableInputDevices[i]->setAddress(String8(AUDIO_BOTTOM_MICROPHONE_ADDRESS));
} else if (mAvailableInputDevices[i]->type() == AUDIO_DEVICE_IN_BACK_MIC) {
mAvailableInputDevices[i]->setAddress(String8(AUDIO_BACK_MICROPHONE_ADDRESS));
}
}
}
if (mPrimaryOutput == 0) {
ALOGE("Failed to open primary output");
status = NO_INIT;
}
// Silence ALOGV statements
property_set("log.tag." LOG_TAG, "D");
updateDevicesAndOutputs();
return status;
}
依次加载 HwModule并打开其所含 profile 的 outputStream 及 inputStream。audio module模块包括：primary、A2DP、USB、remote_submix、hearing_aid。
5.总结
audioserver启动会开启AudioFlinger和AudioPolicyService两个服务，这两个服务会加载配置文件，解析音频输入输出硬件信息，并且加载HIDL，建立与hadware通信的连接。至此音频模块就加载完成了。
