基于android-4.4源码分析
sensor service init
首先是SystemServer中的初始化入口，位于frameworks/base/services/java/com/android/server/SystemServer.java
在main()函数中调用nativeInit()，它位于
frameworks/base/services/jni/com_android_server_SystemServer.cpp
static JNINativeMethod gMethods[] = {
/* name, signature, funcPtr */
{ "nativeInit", "()V", (void*) android_server_SystemServer_nativeInit },
};
static void android_server_SystemServer_nativeInit(JNIEnv* env, jobject clazz) {
char propBuf[PROPERTY_VALUE_MAX];
property_get("system_init.startsensorservice", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the sensor service
SensorService::instantiate();
}
}
native层SystemServer只做了一件事，调用SensorService::instantiate()
SensorService继承自BinderService，BinderService中定义了instantiate()
frameworks/native/services/sensorservice/SensorService.h
class SensorService :
public BinderService<SensorService>,
public BnSensorServer,
protected Thread
{
friend class BinderService<SensorService>;
static char const* getServiceName() ANDROID_API { return "sensorservice"; }
...
}
frameworks/native/include/binder/BinderService.h
template<typename SERVICE>
class BinderService
{
public:
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(
String16(SERVICE::getServiceName()),
new SERVICE(), allowIsolated);
}
static void instantiate() { publish(); }
...
};
instantiate()调用publish()，publish()会new一个SensorService的实例，并添加到service manager中，对应java层中的IServiceManager，都是app端的binder，通过aidl的方式调用服务端的远程方法
defaultServiceManager位于frameworks/native/libs/binder/IServiceManager.cpp
sp<IServiceManager> defaultServiceManager()
{
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
AutoMutex _l(gDefaultServiceManagerLock);
while (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
if (gDefaultServiceManager == NULL)
sleep(1);
}
}
return gDefaultServiceManager;
}
class BpServiceManager : public BpInterface<IServiceManager>
{
virtual status_t addService(const String16& name, const sp<IBinder>& service,
bool allowIsolated)
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeString16(name);
data.writeStrongBinder(service);
data.writeInt32(allowIsolated ? 1 : 0);
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
}
addService时有sp
onFirstRef()属于父类RefBase，该函数在强引用sp新增引用计数时调用
SensorManager init
回到前面，instantiate()之后SensorService注册完毕
app通过getSystemService(Context.SENSOR_SERVICE)可以获取到sensor服务，它需要先在ContextImpl中初始化
registerService(SENSOR_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
return new SystemSensorManager(ctx.getOuterContext(),
ctx.mMainThread.getHandler().getLooper());
}});
frameworks/base/core/java/android/hardware/SystemSensorManager.java
public SystemSensorManager(Context context, Looper mainLooper) {
mMainLooper = mainLooper;
mTargetSdkLevel = context.getApplicationInfo().targetSdkVersion;
synchronized(sSensorModuleLock) {
if (!sSensorModuleInitialized) {
sSensorModuleInitialized = true;
nativeClassInit();
// initialize the sensor list
final ArrayList<Sensor> fullList = sFullSensorsList;
int i = 0;
do {
Sensor sensor = new Sensor();
i = nativeGetNextSensor(sensor, i);
if (i>=0) {
//Log.d(TAG, "found sensor: " + sensor.getName() +
// ", handle=" + sensor.getHandle());
fullList.add(sensor);
sHandleToSensor.append(sensor.getHandle(), sensor);
}
} while (i>0);
}
}
}
nativeClassInit位于frameworks/base/core/jni/android_hardware_SensorManager.cpp，
static void
nativeClassInit (JNIEnv *_env, jclass _this)
{
jclass sensorClass = _env->FindClass("android/hardware/Sensor");
SensorOffsets& sensorOffsets = gSensorOffsets;
sensorOffsets.name = _env->GetFieldID(sensorClass, "mName", "Ljava/lang/String;");
sensorOffsets.vendor = _env->GetFieldID(sensorClass, "mVendor", "Ljava/lang/String;");
sensorOffsets.version = _env->GetFieldID(sensorClass, "mVersion", "I");
sensorOffsets.handle = _env->GetFieldID(sensorClass, "mHandle", "I");
sensorOffsets.type = _env->GetFieldID(sensorClass, "mType", "I");
sensorOffsets.range = _env->GetFieldID(sensorClass, "mMaxRange", "F");
sensorOffsets.resolution = _env->GetFieldID(sensorClass, "mResolution","F");
sensorOffsets.power = _env->GetFieldID(sensorClass, "mPower", "F");
sensorOffsets.minDelay = _env->GetFieldID(sensorClass, "mMinDelay", "I");
sensorOffsets.fifoReservedEventCount =
_env->GetFieldID(sensorClass, "mFifoReservedEventCount", "I");
sensorOffsets.fifoMaxEventCount = _env->GetFieldID(sensorClass, "mFifoMaxEventCount", "I");
}
static jint
nativeGetNextSensor(JNIEnv *env, jclass clazz, jobject sensor, jint next)
{
SensorManager& mgr(SensorManager::getInstance());
Sensor const* const* sensorList;
size_t count = mgr.getSensorList(&sensorList);
if (size_t(next) >= count)
return -1;
Sensor const* const list = sensorList[next];
const SensorOffsets& sensorOffsets(gSensorOffsets);
jstring name = env->NewStringUTF(list->getName().string());
jstring vendor = env->NewStringUTF(list->getVendor().string());
env->SetObjectField(sensor, sensorOffsets.name, name);
env->SetObjectField(sensor, sensorOffsets.vendor, vendor);
env->SetIntField(sensor, sensorOffsets.version, list->getVersion());
env->SetIntField(sensor, sensorOffsets.handle, list->getHandle());
env->SetIntField(sensor, sensorOffsets.type, list->getType());
env->SetFloatField(sensor, sensorOffsets.range, list->getMaxValue());
env->SetFloatField(sensor, sensorOffsets.resolution, list->getResolution());
env->SetFloatField(sensor, sensorOffsets.power, list->getPowerUsage());
env->SetIntField(sensor, sensorOffsets.minDelay, list->getMinDelay());
env->SetIntField(sensor, sensorOffsets.fifoReservedEventCount,
list->getFifoReservedEventCount());
env->SetIntField(sensor, sensorOffsets.fifoMaxEventCount, list->getFifoMaxEventCount());
next++;
return size_t(next) < count ? next : 0;
}
frameworks/native/libs/gui/SensorManager.cpp
SensorManager是一个Singleton，如果SensorManager对象不存在会先new一个
SensorManager的构造函数会调用assertStateLocked()
SensorManager::SensorManager()
: mSensorList(0)
{
assertStateLocked();
}
status_t SensorManager::assertStateLocked() const {
if (mSensorServer == NULL) {
// try for one second
const String16 name("sensorservice");
for (int i=0 ; i<4 ; i++) {
status_t err = getService(name, &mSensorServer);
if (err == NAME_NOT_FOUND) {
usleep(250000);
continue;
}
if (err != NO_ERROR) {
return err;
}
break;
}
class DeathObserver : public IBinder::DeathRecipient {
SensorManager& mSensorManger;
virtual void binderDied(const wp<IBinder>& who) {
ALOGW("sensorservice died [%p]", who.unsafe_get());
mSensorManger.sensorManagerDied();
}
public:
DeathObserver(SensorManager& mgr) : mSensorManger(mgr) { }
};
mDeathObserver = new DeathObserver(*const_cast<SensorManager *>(this));
mSensorServer->asBinder()->linkToDeath(mDeathObserver);
mSensors = mSensorServer->getSensorList();
size_t count = mSensors.size();
mSensorList = (Sensor const**)malloc(count * sizeof(Sensor*));
for (size_t i=0 ; i<count ; i++) {
mSensorList[i] = mSensors.array() + i;
}
}
return NO_ERROR;
}