本文參考一個朋友兼同事ShadowN1ght的文章客戶端到驅(qū)動通信流程；用一個簡單的案例闡述了完整的Binder 通信過程；
Binder之于Android，猶如電話之于人類，都是用于傳遞信息；
寫這篇文章前我醞釀了很久，不知道該何從下筆，文章寫了又刪，刪了又寫，因為始終感覺寫的有點(diǎn)雜，一不注意就丟失了主線；現(xiàn)在通過跟蹤一個完整的Binder調(diào)用來說明Binder IPC的過程——PowerManger調(diào)用isScreenOn();
方案設(shè)計：Binder通信涉及APP層，framework層，Kernel層，雖然涉及的東西比較雜，但是都是代碼實現(xiàn)的，既然如此，我們都可以通過增加調(diào)試Log信息來跟蹤這個流程，本文的思路就是如此； 為了更好的理解 Binder 通信過程，你最好有一套完整的 Android 源碼，再配上一個代碼搜索神器 OpenGrok，如果你沒有 android源碼，不想自己搭建 OpenGrok 服務(wù)器，這里推薦一個公開的 Android Code In OpenGrok，只不過由于網(wǎng)速問題你可能得多花點(diǎn)時間等待；
1. APP——> frameworkimport com.example.bindservice.ProcessInfo;
public class MainActivity extends AppCompatActivity {
String TAG = "Bindertest MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.mybtn).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
ProcessInfo processInfo = new ProcessInfo();
processInfo.nativeSelfCall();
PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
Log.e(TAG,"App begin nativeCall");
boolean bool = powerManager.isScreenOn();
Log.e(TAG,"App end nativeCall");
Log.e(TAG,"" + bool);
}
});
}
}Binder過程很簡單，就是調(diào)用了powerManager.isScreenOn();//Binder Call 代碼;
processInfo.nativeSelfCall()是自己添加的JNI，目的是向Binder Kernel中傳遞cmd，然后在Binder Kernel中根據(jù)cmd獲取到應(yīng)用進(jìn)程ID，過濾Log；這里暫時不說；
/frameworks/base/core/java/android/os/PowerManager.java
@Deprecated
public boolean isScreenOn() {
return isInteractive();
}
public boolean isInteractive() {
try {
return mService.isInteractive();
} catch (RemoteException e) {
return false;
}
}PowerManger.java中的isScreenOn最終會調(diào)用 mService.isInteractive()；這里的mService是什么呢？？？
mServicefinal IPowerManager mService;
/**
* {@hide}
*/
public PowerManager(Context context, IPowerManager service, Handler handler) {
mContext = context;
mService = service;//mService初始化是在PowerManager構(gòu)造方法中
mHandler = handler;
}mService 是IPowerManager 對象；這里根據(jù)名字我們就知道IPowerManager是通過AIDL生成的代碼，可以在Android Studio中查找；找到：
out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/os/IPowerManager.java
------> IPowerManager.java——>Proxy
@Override
public boolean isInteractive() throws android.os.RemoteException {
android.os.Parcel _data = android.os.Parcel.obtain();
android.os.Parcel _reply = android.os.Parcel.obtain();
boolean _result;
try {
_data.writeInterfaceToken(DESCRIPTOR);
mRemote.transact(Stub.TRANSACTION_isInteractive, _data, _reply, 0);//核心核心
_reply.readException();
_result = (0 != _reply.readInt());
} finally {
_reply.recycle();
_data.recycle();
}
return _result;
}_data用于包裝客戶端數(shù)據(jù)，_reply用于從服務(wù)端獲取數(shù)據(jù)，mRemote是android.os.IBinder對象，DESCRIPTOR標(biāo)識了IPowerManager ，DESCRIPTOR = "android.os.IPowerManager"；TRANSACTION_isInteractive 是方法號，TRANSACTION_isInteractive = (android.os.IBinder.FIRST_CALL_TRANSACTION + 11)；_result即我們應(yīng)用層得到的值，這里是根據(jù)reply獲取的值來賦值的；
這里我重點(diǎn)看看mRemote； ------> IPowerManager.java——>Proxy
......
private static class Proxy implements android.os.IPowerManager {
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote) {
mRemote = remote;//賦值
}
@Override
public android.os.IBinder asBinder() {
return mRemote;
}
......
}這里mRemote是在Proxy的構(gòu)造方法中被調(diào)用，那Proxy是在什么地方調(diào)用呢？ ------>IPowerManager.java——>Stub
/**
* Cast an IBinder object into an android.os.IPowerManager interface,
* generating a proxy if needed.
*/
public static android.os.IPowerManager asInterface(android.os.IBinder obj) {
if ((obj == null)) {
return null;
}
android.os.IInterface iin = obj.queryLocalInterface(DESCRIPTOR);
if (((iin != null) && (iin instanceof android.os.IPowerManager))) {
return ((android.os.IPowerManager) iin);
}
return new android.os.IPowerManager.Stub.Proxy(obj);//調(diào)用Proxy構(gòu)造函數(shù)
}這里IPowerManger.Stub asInterface在什么地方調(diào)用呢？asInterface返回的對象是IPowerManager對象；在Android Studio 查看該方法在那些地方被調(diào)用，你會發(fā)現(xiàn)有很對，但是我相信你會特別在ContextImpl的；
/frameworks/base/core/java/android/app/ContextImpl.java
------> ContextImpl.java
registerService(POWER_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
IBinder b = ServiceManager.getService(POWER_SERVICE);
IPowerManager service = IPowerManager.Stub.asInterface(b);
//調(diào)用IPowerManger.stub.asInterface，傳入的IBinder對象參數(shù)是從
//ServiceManager.getService(POWER_SERVICE)獲取的
if (service == null) {
Log.wtf(TAG, "Failed to get power manager service.");
}
return new PowerManager(ctx.getOuterContext(),
service, ctx.mMainThread.getHandler());//返回PowerManager對象，
//這里的service就是PowerManger類中的mService，
//我們在應(yīng)用層調(diào)用的 (PowerManager) getSystemService(Context.POWER_SERVICE)
//得到的powerManger對象就是這里返回的new PowerManager，這部分代碼跟著邏輯就能看到；
}});看到registerService方法，我相信很多人都很熟悉，這里的service就是PowerManger類中的mService，
應(yīng)用層調(diào)用的 (PowerManager) getSystemService(Context.POWER_SERVICE)得到的powerManger對象
就是這里返回的new PowerManager，順著Activity的getSystemService方法的邏輯看就會清楚；
PowerManager中的mService就是這里的service，通過 IPowerManager.Stub.asInterface(b)獲得；
IBinder b = ServiceManager.getService(POWER_SERVICE);
IPowerManager service = IPowerManager.Stub.asInterface(b);
這里真正開始接觸IBiner，這里做個標(biāo)記，等會可能會回頭再來看，
這里調(diào)用 IPowerManager.Stub.asInterface(b)的IBinder b參數(shù)是從ServiceManager.getService(POWER_SERVICE)獲取的，那這個IBinder b值是什么呢？？？（我這里先透露一下，IBinder b是一個BinderProxy對象）
/frameworks/base/core/java/android/os/ServiceManager.java
------> ServiceManager.java
/**
* Returns a reference to a service with the given name.
*
* @param name the name of the service to get
* @return a reference to the service, or <code>null</code> if the service doesn't exist
*/
public static IBinder getService(String name) {
try {
IBinder service = sCache.get(name);
if (service != null) {
return service;
} else {
return getIServiceManager().getService(name);//核心核心
}
} catch (RemoteException e) {
Log.e(TAG, "error in getService", e);
}
return null;
}這里先從緩存中獲取IBinder，緩存中沒有則調(diào)用getIServiceManager().getService(name)獲取； ------> ServiceManager.java
private static IServiceManager getIServiceManager() {
if (sServiceManager != null) {
return sServiceManager;
}
// Find the service manager
sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject());//核心核心
return sServiceManager;
}/frameworks/base/core/java/android/os/ServiceManagerNative.java
ServiceManagerNative.asInterface(BinderInternal.getContextObject())的參數(shù)為BinderInternal.getContextObject();
------> ServiceManagerNative.java
static public IServiceManager asInterface(IBinder obj)
{
if (obj == null) {
return null;
}
IServiceManager in =
(IServiceManager)obj.queryLocalInterface(descriptor);//如果沒有真正的跨進(jìn)程通信，則從這里返回
//Binder 類有實現(xiàn)，BinderProxy沒有實現(xiàn)queryLocalInterface方法；
if (in != null) {
return in;//判斷是否是真的跨進(jìn)程，比如應(yīng)用內(nèi)部實現(xiàn)service，就沒真正跨進(jìn)程，從這里返回；
}
return new ServiceManagerProxy(obj);//核心核心核心，跨進(jìn)程
}使用OpenGrok搜索"implements IBinder"，會發(fā)現(xiàn)Binder.java 文件中class Binder和
class BinderProxy兩個類實現(xiàn)了IBinder；此處我先不確定queryLocalInterface是否是調(diào)用的這里；我們先確定
static public IServiceManager asInterface(IBinder obj)的參數(shù)IBinder obj；obj是ServiceManager.java中調(diào)用ServiceManagerNative.asInterface(BinderInternal.getContextObject())傳遞過來的，所以
obj = BinderInternal.getContextObject()；我們看看ServiceManagerProxy的構(gòu)造方法，會發(fā)現(xiàn)ServiceManagerProxy中
public ServiceManagerProxy(IBinder remote) {
mRemote = remote;
}，即BinderInternal.getContextObject()的返回值將賦值給mRemote
/frameworks/base/core/java/com/android/internal/os/BinderInternal.java
------> BinderInternal.java
public static final native IBinder getContextObject();這里使用JNI來獲取IBinder對象；根據(jù)Android JNI命名規(guī)則，我們知道getContextObject方法在android_util_Binder.cpp中實現(xiàn)；
------> android_util_Binder.cpp
static const JNINativeMethod gBinderInternalMethods[] = {
/* name, signature, funcPtr */
{ "getContextObject", "()Landroid/os/IBinder;", (void*)android_os_BinderInternal_getContextObject },
{ "joinThreadPool", "()V", (void*)android_os_BinderInternal_joinThreadPool },
{ "disableBackgroundScheduling", "(Z)V", (void*)android_os_BinderInternal_disableBackgroundScheduling },
{ "handleGc", "()V", (void*)android_os_BinderInternal_handleGc }
};
static jobject android_os_BinderInternal_getContextObject(JNIEnv* env, jobject clazz)
{
sp<IBinder> b = ProcessState::self()->getContextObject(NULL);//ProcessState采用單列，整個應(yīng)用只有一個實例
return javaObjectForIBinder(env, b);//將native binder轉(zhuǎn)換為Java Binder對象，這里返回BinderProxy對象，下面會說明；
}這里通過 ProcessState創(chuàng)建native IBinder對象；再調(diào)用javaObjectForIBinder將native Binder對象轉(zhuǎn)換成Java層的Binder對象；
------> ProcessState.cpp
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)//caller 上面?zhèn)鬟f的值為null
{
return getStrongProxyForHandle(0);//參數(shù)為0
}
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{
sp<IBinder> result;
AutoMutex _l(mLock);
handle_entry* e = lookupHandleLocked(handle);//此時handle=0
if (e != NULL) {
// We need to create a new BpBinder if there isn't currently one, OR we
// are unable to acquire a weak reference on this current one. See comment
// in getWeakProxyForHandle() for more info about this.
IBinder* b = e->binder;
if (b == NULL || !e->refs->attemptIncWeak(this)) {
if (handle == 0) {
// Special case for context manager...
// The context manager is the only object for which we create
// a BpBinder proxy without already holding a reference.
// Perform a dummy transaction to ensure the context manager
// is registered before we create the first local reference
// to it (which will occur when creating the BpBinder).
// If a local reference is created for the BpBinder when the
// context manager is not present, the driver will fail to
// provide a reference to the context manager, but the
// driver API does not return status.
//
// Note that this is not race-free if the context manager
// dies while this code runs.
//
// TODO: add a driver API to wait for context manager, or
// stop special casing handle 0 for context manager and add
// a driver API to get a handle to the context manager with
// proper reference counting.
Parcel data;
status_t status = IPCThreadState::self()->transact(
0, IBinder::PING_TRANSACTION, data, NULL, 0);
if (status == DEAD_OBJECT)
return NULL;
}
b = new BpBinder(handle); //創(chuàng)建BpBinder，即b = new BpBinder(0);
e->binder = b;
if (b) e->refs = b->getWeakRefs();
result = b;//用new BpBinder(0)給result賦值，最后返回result
} else {
// This little bit of nastyness is to allow us to add a primary
// reference to the remote proxy when this team doesn't have one
// but another team is sending the handle to us.
result.force_set(b);
e->refs->decWeak(this);
}
}
return result;//返回new BpBinder(0)
}sp<IBinder> b = ProcessState::self()->getContextObject(NULL)返回的是new BpBinder(0);返回到android_os_BinderInternal_getContextObject方法中，接下來會調(diào)用javaObjectForIBinder方法；
------> javaObjectForIBinder
jobject javaObjectForIBinder(JNIEnv* env, const sp<IBinder>& val)
{
if (val == NULL) return NULL;
if (val->checkSubclass(&gBinderOffsets)) {
// One of our own!
jobject object = static_cast<JavaBBinder*>(val.get())->object();
LOGDEATH("objectForBinder %p: it's our own %p!\n", val.get(), object);
return object;
}
// For the rest of the function we will hold this lock, to serialize
// looking/creation of Java proxies for native Binder proxies.
AutoMutex _l(mProxyLock);
// Someone else's... do we know about it?
jobject object = (jobject)val->findObject(&gBinderProxyOffsets);//gBinderProxyOffsets很重要，
//gBinderProxyOffets在int_register_android_os_BinderProxy中初始化，指向Java層的BinderProxy(核心核心核心)，
//int_register_android_os_BinderProxy在register_android_os_Binder中調(diào)用，register_android_os_Binder
//在開機(jī)過程中AndroidRuntime.startReg方法中被調(diào)用；
if (object != NULL) {
jobject res = jniGetReferent(env, object);
if (res != NULL) {
ALOGV("objectForBinder %p: found existing %p!\n", val.get(), res);
return res;
}
LOGDEATH("Proxy object %p of IBinder %p no longer in working set!!!", object, val.get());
android_atomic_dec(&gNumProxyRefs);
val->detachObject(&gBinderProxyOffsets);
env->DeleteGlobalRef(object);
}
object = env->NewObject(gBinderProxyOffsets.mClass, gBinderProxyOffsets.mConstructor);
//gBinderProxyOffsets.mClass指向BinderProxy class，gBinderProxyOffsets.mConstructor指向BinderProxy構(gòu)造方法；
if (object != NULL) {
LOGDEATH("objectForBinder %p: created new proxy %p !\n", val.get(), object);
// The proxy holds a reference to the native object.
env->SetLongField(object, gBinderProxyOffsets.mObject, (jlong)val.get());//val是BpBinder，
//這里利用JNI 調(diào)用java將讀到的BpBinder 對象val存入BinderProxy的mObject變量中
val->incStrong((void*)javaObjectForIBinder);
// The native object needs to hold a weak reference back to the
// proxy, so we can retrieve the same proxy if it is still active.
jobject refObject = env->NewGlobalRef(
env->GetObjectField(object, gBinderProxyOffsets.mSelf));
val->attachObject(&gBinderProxyOffsets, refObject,
jnienv_to_javavm(env), proxy_cleanup);
// Also remember the death recipients registered on this proxy
sp<DeathRecipientList> drl = new DeathRecipientList;
drl->incStrong((void*)javaObjectForIBinder);
env->SetLongField(object, gBinderProxyOffsets.mOrgue, reinterpret_cast<jlong>(drl.get()));
// Note that a new object reference has been created.
android_atomic_inc(&gNumProxyRefs);
incRefsCreated(env);
}
return object;//返回Java BinderProxy對象
}所以前面BinderInternal.java 中 getContextObject()方法會返回一個BinderProxy對象；并將獲取到的BpBinder對象存入Java層BinderProxy類的mObject變量中；
是不是有點(diǎn)蒙圈了，休息休息休息休息一下下，你還記得我們的這個BinderProxy返回到什么地方嗎？哈哈，反正我是記得；因為我都記下來了，哈哈；BinderProxy是BinderInternal.getContextObject()返回的，即這個BinderProxy將作為ServiceManagerNative.java 中static public IServiceManager asInterface(IBinder obj)方法的參數(shù)IBinder obj；如果Binder通信確實跨進(jìn)程ServiceManagerNative.java的asInterface方法將返回
new ServiceManagerProxy(BinderProxy binderProxy)
到這里我想使用goto 語句了，調(diào)到我想去的地方，還記得我們是從什么時候開始分析這個IBinder對象的嗎？
------> ContextImpl.java
registerService(POWER_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
IBinder b = ServiceManager.getService(POWER_SERVICE);
IPowerManager service = IPowerManager.Stub.asInterface(b);
//調(diào)用IPowerManger.stub.asInterface，傳入的IBinder對象參數(shù)是從
//ServiceManager.getService(POWER_SERVICE)獲取的
if (service == null) {
Log.wtf(TAG, "Failed to get power manager service.");
}
return new PowerManager(ctx.getOuterContext(),
service, ctx.mMainThread.getHandler());//返回PowerManager對象，
//這里的service就是PowerManger類中的mService，
//我們在應(yīng)用層調(diào)用的 (PowerManager) getSystemService(Context.POWER_SERVICE)
//得到的powerManger對象就是這里返回的new PowerManager，這部分代碼跟著邏輯就能看到；
}});我們重新回到ContextImpl.java 中開始分析， IBinder b = ServiceManager.getService(POWER_SERVICE);其實就是ServiceManagerProxy的getService方法，ServiceManagerProxy類中mRemote的值就是BinderProxy，所以 IBinder b = ServiceManager.getService(POWER_SERVICE)最終會調(diào)用ServiceManagerProxy的方法；
------> ServiceMangerNative.java ——>ServiceManagerProxy
public IBinder getService(String name) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IServiceManager.descriptor);
data.writeString(name);
mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
IBinder binder = reply.readStrongBinder();//這里返回IBinder對象
reply.recycle();
data.recycle();
return binder;
}IPowerManager service = IPowerManager.Stub.asInterface(b)，這里asInterface方法的參數(shù)b就是ServiceManagerProxy類中g(shù)etService返回的IBinder，這里是通過reply.readStrongBinder()；reply是一個Parcel；
/frameworks/base/core/java/android/os/Parcel.java
------> Parcel.java
public final IBinder readStrongBinder() {
return nativeReadStrongBinder(mNativePtr);//JNI方法
}我們根據(jù)Android JNI命名規(guī)則，可以到android_os_Parcel.cpp中查看nativeReadStrongBinder方法：
------> android_os_Parcel.cpp
static jobject android_os_Parcel_readStrongBinder(JNIEnv* env, jclass clazz, jlong nativePtr)
{
Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
if (parcel != NULL) {
return javaObjectForIBinder(env, parcel->readStrongBinder());//這個方法前面有說過，
//根據(jù)parcel->readStrongBinder()的值返回，
//提前透露一下，parcel->readStrongBinder()返回的值是BpBinder對象
}
return NULL;
}parcel->readStrongBinder() ------> Parcel.cpp
sp<IBinder> Parcel::readStrongBinder() const
{
sp<IBinder> val;
unflatten_binder(ProcessState::self(), *this, &val);//核心，解析Binder
return val;
}
------> Parcel.cpp
status_t unflatten_binder(const sp<ProcessState>& proc,
const Parcel& in, sp<IBinder>* out)
{
const flat_binder_object* flat = in.readObject(false);
if (flat) {
switch (flat->type) {
case BINDER_TYPE_BINDER://Binder實體
*out = reinterpret_cast<IBinder*>(flat->cookie);
return finish_unflatten_binder(NULL, *flat, in);
case BINDER_TYPE_HANDLE://Binder 引用，我們這里是通過ServiceManager.getService獲取的服務(wù)代理，即Binder引用
*out = proc->getStrongProxyForHandle(flat->handle);//核心核心，是不是很熟悉呢？？？
//該方法返回一個new BpBinder(flat->handle)，這里的new BpBinder將會傳遞給readStringBinder方法的&val然后直接返回；
return finish_unflatten_binder(
static_cast<BpBinder*>(out->get()), *flat, in);//類型轉(zhuǎn)換
}
}
return BAD_TYPE;
}Parcel.cpp中的readStrongBinder方法將返回一個new BpBinder()對象，接著繼續(xù)返回給android_os_Parcel.cpp的android_os_Parcel_readStrongBinder，在android_os_Parcel_readStrongBinder中調(diào)用javaObjectForIBinder方法將這個BpBinder對象轉(zhuǎn)換為Java 層的BinderProxy對象返回，javaObjectForIBinder還會調(diào)用SetLongField將獲取到的BpBinder對象保存到j(luò)ava層BinderProxy類的mObject變量中，所以呢所以呢？？？ServiceManagerProxy的getService方法將返回一個BinderProxy對象
再回到ContextImpl中，你將會明白所有參數(shù)：
IBinder b = ServiceManager.getService(POWER_SERVICE) //IBinder b其實就是一個BinderProxy對象，是不是和前面透露的保持一致，其實我都怕透露出錯，哈哈
IPowerManager service = IPowerManager.Stub.asInterface(b);//這里我們知道asInterface(b)最終會將參數(shù)b傳遞到IPowerManager.Stub.Proxy的構(gòu)造函數(shù)，將BinderProxy對象賦值給IPowerManager.Stub.Proxy的mRemote；IPowerManager.Stub.asInterface(b)調(diào)用最終會返回IPowerManager.Stub.Proxy對象；
有沒有真相大白的感覺，困擾你的mRemote終于驗明正身了；又沒有很興奮激動，反正我還是比較激動的。
小結(jié)：本小結(jié)主要闡述了Binder通信從APP層到framework層的通信過程，即
PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE)
boolean bool = powerManager.isScreenOn()=========>mService.isInteractive（mService是IPowerManager對象）=========>mRemote.transact(Stub.TRANSACTION_isInteractive, _data, _reply, 0)（mRemote是一個BinderProxy對象）=========>BinderProxy.transact；下一篇文章將從BinderProxy開始分析
|
