android28 系统源码
参考文档：ibinderForJavaObject 与 javaObjectForIBinder
主要类介绍
1 Binder代理：
BinderProxy(Java)：java层对象，具有跨进程能力（通过BpBinder）
BinderProxyNativeData（C++结构体）：持有BpBinder对象，BinderProxy.mNativeData中保存BinderProxyNativeData对象地址
BpBinder(C++)：BinderProxy对象对应的C++对象，具有跨进程能力
2 Binder本地：
Binder(Java)：java层对象，服务端实现类
JavaBBinderHolder(C++)：持有JavaBBinder对象
JavaBBinder(C++)：Binder对象的C++对象，继承BBinder
JavaObjectForIBinder和ibinderForJavaObject负责native层Binder对象和java层Binder对象相互转换。
JavaObjectForIBinder()主要作用
1 JavaBBinder对象 => Binder对象
2 BpBinder对象 => BinderProxy对象
ibinderForJavaObject()主要作用
1 Binder对象 => JavaBBinder对象
2 BinderProxy对象 => BpBinder对象
具体注释看源码
/frameworks/base/core/jni/android_util_Binder.cpp
class JavaBBinder : public BBinder{
......
jobject object() const {
return mObject; // 保存Binder对象。
}
......
}
struct BinderProxyNativeData {
// BpBinder对象指针
sp<IBinder> mObject;
.......
};
class JavaBBinderHolder {
......
private:
Mutex mLock;
wp<JavaBBinder> mBinder; // JavaBBinder对象指针
};
// val 可以JavaBBinder对象，或者BpBinder对象
jobject javaObjectForIBinder(JNIEnv* env, const sp& val) {
if (val == NULL) return NULL;
// 1 如果是JavaBBinder对象，直接返回对应的Binder对象。
if (val->checkSubclass(&gBinderOffsets)) {
// It's a JavaBBinder created by ibinderForJavaObject. Already has Java object.
jobject object = static_cast(val.get())->object();
LOGDEATH("objectForBinder %p: it's our own %p!\n", val.get(), object);
return object;
}
// 2 如果是BpBinder对象
AutoMutex _l(gProxyLock);
// 使用缓存的BinderProxyNativeData对象，避免重新分配
BinderProxyNativeData* nativeData = gNativeDataCache;
if (nativeData == nullptr) {
nativeData = new BinderProxyNativeData();
}
// 3 通过BinderProxy.getInstance(long nativeData, long iBinder)获得BinderProxy对象
// BinderProxy对象可能是新创建的，也可能是已存在的。
// 保证一个BpBinder对象对应一个BinderProxy对象。
jobject object = env->CallStaticObjectMethod(gBinderProxyOffsets.mClass, gBinderProxyOffsets.mGetInstance, (jlong) nativeData, (jlong) val.get());
if (env->ExceptionCheck()) {
// In the exception case, getInstance still took ownership of nativeData.
gNativeDataCache = nullptr;
return NULL;
}
// 通过BindProxy.mNativeData，获取对应的BinderProxyNativeData对象
BinderProxyNativeData* actualNativeData = getBPNativeData(env, object);
if (actualNativeData == nativeData) {
// New BinderProxy; we still have exclusive access.
// 4 新创建BinderProxy，actualNativeData == nativeData为true。
nativeData->mOrgue = new DeathRecipientList;
nativeData->mObject = val;
gNativeDataCache = nullptr;
++gNumProxies;
if (gNumProxies >= gProxiesWarned + PROXY_WARN_INTERVAL) {
ALOGW("Unexpectedly many live BinderProxies: %d\n", gNumProxies);
gProxiesWarned = gNumProxies;
}
} else {
// 5 使用已存在的BinderProxy，则nativeData在缓存起来，以后使用
// nativeData wasn't used. Reuse it the next time.
gNativeDataCache = nativeData;
}
// 返回BinderProxy对象
return object;
}
BinderProxyNativeData* getBPNativeData(JNIEnv* env, jobject obj) {
// 通过BinderProxy.mNativeData获得BinderProxyNativeData对象
return (BinderProxyNativeData *) env->GetLongField(obj, gBinderProxyOffsets.mNativeData);
}
sp<IBinder> ibinderForJavaObject(JNIEnv* env, jobject obj){
if (obj == NULL) return NULL;
// Instance of Binder?
// 1 如果是Binder对象，直接去Binder.mObject(这是JavaBBinderHolder对象)
if (env->IsInstanceOf(obj, gBinderOffsets.mClass)) {
JavaBBinderHolder* jbh = (JavaBBinderHolder*) env->GetLongField(obj, gBinderOffsets.mObject);
//JavaBBinderHolder.get() 获得JavaBBinder对象
return jbh->get(env, obj);
}
// Instance of BinderProxy?
// 2 如果是BinderProxy对象，通过BinderProxy.mNativeData获得BinderProxyNativeData对象
if (env->IsInstanceOf(obj, gBinderProxyOffsets.mClass)) {
// BinderProxyNativeData.mObject就是BpBinder对象
return getBPNativeData(env, obj)->mObject;
}
ALOGW("ibinderForJavaObject: %p is not a Binder object", obj); return NULL;
}
static int int_register_android_os_BinderProxy(JNIEnv* env){
jclass clazz = FindClassOrDie(env, "java/lang/Error");
gErrorOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
clazz = FindClassOrDie(env, kBinderProxyPathName);
gBinderProxyOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
// BinderProxy.getInstance() 根据BpBinder地址，获得BinderProxy
gBinderProxyOffsets.mGetInstance = GetStaticMethodIDOrDie(env, clazz, "getInstance", "(JJ)Landroid/os/BinderProxy;");
gBinderProxyOffsets.mSendDeathNotice = GetStaticMethodIDOrDie(env, clazz, "sendDeathNotice", "(Landroid/os/IBinder$DeathRecipient;)V");
gBinderProxyOffsets.mDumpProxyDebugInfo = GetStaticMethodIDOrDie(env, clazz, "dumpProxyDebugInfo", "()V");
// BinderProxy.mNativeData，保存C++的BinderProxyNativeData对象
gBinderProxyOffsets.mNativeData = GetFieldIDOrDie(env, clazz, "mNativeData", "J");
clazz = FindClassOrDie(env, "java/lang/Class");
gClassOffsets.mGetName = GetMethodIDOrDie(env, clazz, "getName", "()Ljava/lang/String;");
return RegisterMethodsOrDie( env, kBinderProxyPathName, gBinderProxyMethods, NELEM(gBinderProxyMethods));
}
static int int_register_android_os_Binder(JNIEnv* env) {
jclass clazz = FindClassOrDie(env, kBinderPathName);
gBinderOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
gBinderOffsets.mExecTransact = GetMethodIDOrDie(env, clazz, "execTransact", "(IJJI)Z");
// Binder.mObject保存JavaBBinderHolder对象地址，JavaBBinderHolder对象保存这BBinder对象
gBinderOffsets.mObject = GetFieldIDOrDie(env, clazz, "mObject", "J");
return RegisterMethodsOrDie( env, kBinderPathName, gBinderMethods, NELEM(gBinderMethods));
}
final class BinderProxy implements IBinder
private static BinderProxy getInstance(long nativeData, long iBinder) {
BinderProxy result;
try {
// 以Bpbinder地址为key
result = sProxyMap.get(iBinder);
if (result != null) {
return result;
}
// 创建BinderProxy，传入BinderProxyNativeData地址
result = new BinderProxy(nativeData);
} catch (Throwable e) {
// We're throwing an exception (probably OOME); don't drop nativeData.
NativeAllocationRegistry.applyFreeFunction(NoImagePreloadHolder.sNativeFinalizer, nativeData);
throw e;
}
NoImagePreloadHolder.sRegistry.registerNativeAllocation(result, nativeData);
// The registry now owns nativeData, even if registration threw an exception.
// 设置map，map的value是弱引用
sProxyMap.set(iBinder, result);
return result;
}
