native\libs\binder\IServiceManager.cpp
前置了解
//IInterface.h
class BpInterface : public INTERFACE, public BpRefBase
{
public:
explicit BpInterface(const sp<IBinder>& remote); //构造方法传入
protected:
typedef INTERFACE BaseInterface;
virtual IBinder* onAsBinder();
};
template<typename INTERFACE>
inline BpInterface<INTERFACE>::BpInterface(const sp<IBinder>& remote)
: BpRefBase(remote)
{
}
//Binder.h
class BpRefBase : public virtual RefBase
{
protected:
inline IBinder* remote() { return mRemote; }
inline IBinder* remote() const { return mRemote; }
...
}
//Binder.cpp
BpRefBase::BpRefBase(const sp<IBinder>& o)
: mRemote(o.get()), mRefs(nullptr), mState(0)
{
extendObjectLifetime(OBJECT_LIFETIME_WEAK);
if (mRemote) {
mRemote->incStrong(this); // Removed on first IncStrong().
mRefs = mRemote->createWeak(this); // Held for our entire lifetime.
}
}
//Interface.h
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
return INTERFACE::asInterface(obj);
}
template<typename INTERFACE>
inline sp<IInterface> BnInterface<INTERFACE>::queryLocalInterface(
const String16& _descriptor)
{
if (_descriptor == INTERFACE::descriptor) return this;
return nullptr;
}
#define DECLARE_META_INTERFACE(INTERFACE)
const ::android::StaticString16 \
I##INTERFACE##_descriptor_static_str16(__IINTF_CONCAT(u, NAME));\
const ::android::String16 I##INTERFACE::descriptor( \
I##INTERFACE##_descriptor_static_str16); \
const ::android::String16& \
I##INTERFACE::getInterfaceDescriptor() const { \
return I##INTERFACE::descriptor; \
} \
//asInterface 模版方法实现
//1. queryLocalInterface : 有没有设置 descriptor
//2. new Bp##INTERFACE(obj)
::android::sp<I##INTERFACE> I##INTERFACE::asInterface( \
const ::android::sp<::android::IBinder>& obj) \
{ \
::android::sp<I##INTERFACE> intr; \
if (obj != nullptr) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == nullptr) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \
std::unique_ptr<I##INTERFACE> I##INTERFACE::default_impl; \
bool I##INTERFACE::setDefaultImpl(std::unique_ptr<I##INTERFACE> impl)\
{ \
/* Only one user of this interface can use this function */ \
/* at a time. This is a heuristic to detect if two different */ \
/* users in the same process use this function. */ \
assert(!I##INTERFACE::default_impl); \
if (impl) { \
I##INTERFACE::default_impl = std::move(impl); \
return true; \
} \
return false; \
} \
const std::unique_ptr<I##INTERFACE>& I##INTERFACE::getDefaultImpl() \
{ \
return I##INTERFACE::default_impl; \
} \
I##INTERFACE::I##INTERFACE() { } \
I##INTERFACE::~I##INTERFACE() { }
I##INTERFACE 宏展开机制
##是 C++ 预处理器的标记粘贴操作符（Token Pasting Operator），用于将两个标记连接成一个标记。 eg
class IServiceManager : public IInterface {
DECLARE_META_INTERFACE(ServiceManager); // INTERFACE = ServiceManager
// ...
};
// 宏展开
class IServiceManager : public IInterface {
public:
static ::android::sp<IServiceManager> asInterface( // I##ServiceManager = IServiceManager
const ::android::sp<::android::IBinder>& obj);
// ...
};
graph TD
A[DECLARE_META_INTERFACE宏] --> B[生成 asInterface 静态方法]
B --> C[IMPLEMENT_META_INTERFACE宏]
C --> D[实现 asInterface 方法体]
D --> E{obj != nullptr?}
E -->|No| F[返回 nullptr]
E -->|Yes| G[obj->queryLocalInterface]
G --> H{返回值是否为空?}
H -->|不为空| I[本地服务 - 直接返回]
H -->|为空| J[远程服务 - new BpInterface]
I --> K[static_cast转换返回]
J --> L[创建代理对象返回]
定义实现
//IServiceManager.h
namespace android {
// 不是这个
class IServiceManager : public IInterface
{
...
}
//IServiceManager.cpp
namespace android {
//注意: android / os /IServiceManager
using AidlServiceManager = android::os::IServiceManager;
sp<IServiceManager> defaultServiceManager()
{
std::call_once(gSmOnce, []() {
sp<AidlServiceManager> sm = nullptr;
while (sm == nullptr) {
//getContextObject(nullptr) ---> BpBinder::create(0)
sm = interface_cast<AidlServiceManager>(ProcessState::self()->getContextObject(nullptr));
if (sm == nullptr) {
ALOGE("Waiting 1s on context object on %s.", ProcessState::self()->getDriverName().c_str());
sleep(1);
}
}
gDefaultServiceManager = new ServiceManagerShim(sm);
});
return gDefaultServiceManager;
}
...
}
需要注意真正的实现类是 aidl生成的 android/os
具体实现
$ find out/ -name "IServiceManager.h" -o -name "IServiceManager.cpp" [18:46:28]
out/soong/.intermediates/frameworks/native/libs/binder/libbinder/android_arm64_armv8-a_shared/gen/aidl/android/os/IServiceManager.h
out/soong/.intermediates/frameworks/native/libs/binder/libbinder/android_arm64_armv8-a_shared/gen/aidl/frameworks/native/libs/binder/aidl/android/os/IServiceManager.cpp
...
//.../aidl/android/os/IServiceManager.h
namespace android {
namespace os {
class IServiceManager : public ::android::IInterface {
public:
DECLARE_META_INTERFACE(ServiceManager) // INTERFACE = ServiceManager
...
}
...
//.../aidl/android/os/IServiceManager.c
#include <android/os/IServiceManager.h>
#include <android/os/BpServiceManager.h>
namespace android {
namespace os {
DO_NOT_DIRECTLY_USE_ME_IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager")
} // namespace os
} // namespace android
#include <android/os/BpServiceManager.h>
#include <binder/Parcel.h>
#include <android-base/macros.h>
namespace android {
namespace os {
// 客户端实现
BpServiceManager::BpServiceManager(const ::android::sp<::android::IBinder>& _aidl_impl)
: BpInterface<IServiceManager>(_aidl_impl){
}
::android::binder::Status BpServiceManager::getService(const ::std::string& name, ::android::sp<::android::IBinder>* _aidl_return) {
::android::Parcel _aidl_data;
::android::Parcel _aidl_reply;
::android::status_t _aidl_ret_status = ::android::OK;
::android::binder::Status _aidl_status;
...
// remote() : 其实就是_aidl_impl -> BpBinder(0)
_aidl_ret_status = remote()->transact(::android::IBinder::FIRST_CALL_TRANSACTION + 0 /* getService */, _aidl_data, &_aidl_reply);
if (UNLIKELY(_aidl_ret_status == ::android::UNKNOWN_TRANSACTION && IServiceManager::getDefaultImpl())) {
return IServiceManager::getDefaultImpl()->getService(name, _aidl_return);
}
...
return _aidl_status;
}
...
::android::binder::Status BpServiceManager::addService(const ::std::string& name, const ::android::sp<::android::IBinder>& service, bool allowIsolated, int32_t dumpPriority) {
::android::Parcel _aidl_data;
::android::Parcel _aidl_reply;
::android::status_t _aidl_ret_status = ::android::OK;
::android::binder::Status _aidl_status;
_aidl_ret_status = _aidl_data.writeInterfaceToken(getInterfaceDescriptor());
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = _aidl_data.writeUtf8AsUtf16(name);
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = _aidl_data.writeStrongBinder(service);
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = _aidl_data.writeBool(allowIsolated);
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = _aidl_data.writeInt32(dumpPriority);
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = remote()->transact(::android::IBinder::FIRST_CALL_TRANSACTION + 2 /* addService */, _aidl_data, &_aidl_reply);
if (UNLIKELY(_aidl_ret_status == ::android::UNKNOWN_TRANSACTION && IServiceManager::getDefaultImpl())) {
return IServiceManager::getDefaultImpl()->addService(name, service, allowIsolated, dumpPriority);
}
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
_aidl_ret_status = _aidl_status.readFromParcel(_aidl_reply);
if (((_aidl_ret_status) != (::android::OK))) {
goto _aidl_error;
}
if (!_aidl_status.isOk()) {
return _aidl_status;
}
_aidl_error:
_aidl_status.setFromStatusT(_aidl_ret_status);
return _aidl_status;
}
...
} // namespace os
} // namespace android
#include <android/os/BnServiceManager.h>
#include <binder/Parcel.h>
#include <binder/Stability.h>
namespace android {
namespace os {
//服务端实现
BnServiceManager::BnServiceManager()
{
::android::internal::Stability::markCompilationUnit(this);
}
::android::status_t BnServiceManager::onTransact(uint32_t _aidl_code, const ::android::Parcel& _aidl_data, ::android::Parcel* _aidl_reply, uint32_t _aidl_flags) {
::android::status_t _aidl_ret_status = ::android::OK;
switch (_aidl_code) {
case ::android::IBinder::FIRST_CALL_TRANSACTION + 0 /* getService */:
...
default:
{
_aidl_ret_status = ::android::BBinder::onTransact(_aidl_code, _aidl_data, _aidl_reply, _aidl_flags);
}
break;
}
if (_aidl_ret_status == ::android::UNEXPECTED_NULL) {
_aidl_ret_status = ::android::binder::Status::fromExceptionCode(::android::binder::Status::EX_NULL_POINTER).writeToParcel(_aidl_reply);
}
return _aidl_ret_status;
}
} // namespace os
} // namespace android
总结:
defaultServiceManager() -> interface_cast(ProcessState::self()->getContextObject(nullptr)); 相当于: new BpServiceManager(new BpBinder(0))
