Create Framework 设计巧妙点.md

blogs/Android/Framework/Interview/综合性面试题/Framework 设计巧妙点.md

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+---
+Framework 设计巧妙点
+---
+
+1. 对 Framework 的涉猎有一定的广度和深度
+2. 对系统设计有自己的总结和思考
+
+#### 例子
+
+1. Binder 调用，模糊进程边界
+2. Bitmap 大图传输，高性能
+3. Zygote 创建进程，资源共享
+4. Intent 解耦，模糊进程
+
+Binder 调用：
+
+1. 请求转发
+2. Binder 对象的传递
+
+Bitmap 大图传输：
+
+```c++
+static jboolean Bitmap_writeToParcel(JNIEnv* env, jobject, ...){
+    int fd = androidBitmap->getAshmemFd();
+    if(fd>=0&&!isMutable&&p->allowFds()){
+        p->writeDupImmutableBlobFileDescriptor(fd);
+        return JNI_TRUE;
+    }
+}
+static jobject Bitmap_createFromParcel(JNIEnv* env, jobject parcel){
+    if(blob.fd()>=0 && (blob.isMutable()||!isMutable) && (size>=ASHMEM_BITMAP_MIN_SIZE)){
+        nativeBitmap = GraphicsJNI::mapAshmemPixelRef(env, bitmap.get(), ctable, dupFd, const_cast<void*>(blob.data()), !isMutable);
+    }
+}
+```
+
+Zygote 创建进程：
+
+```c++
+int main(int argc, char* const argv[]){
+	runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
+}
+// ZygoteInit#main
+public static void main(String argv[]){
+    preload();
+    startSystemServer(abList, socketName);
+    runSelectLoop(abiList);
+}
+```
+
+Intent 解耦：
+
+```java
+Intent registerReceiver(..., IIntentReceiver receiver, IntentFilter filter, ...){
+	ReceiverList rl = mRegistedReceivers.get(receiver.asBinder());
+	if(rl == null){
+		rl = new ReceiverList(this, ..., yserId, receiver);
+		rl.app.receivers.add(rl);
+		mRegisteredReceivers.put(receiver.asBinder(), rl);
+	}
+	BroadcastFilter bf = new BroadcastFilter(filter, rl, callerOackage, ...);
+	rl.add(bf);
+	mReceiverResolver.addFilter(bf);
+}
+```
+
+```java
+int broadcastIntentLocked(ProcessRecord callerApp, ...){
+	List receivers = null;
+    List<BroadcastFilter> registeredReceivers = null;
+    registeredReceivers = mReceiverResolver.queryIntent(intent, ...);
+    
+    int NR = registeredReceivers.size();
+    final BroadcastQueue queue = broadcastQueueForIntent(intent);
+    BroadcastRecord r = new BroadcastRecord(queue, intent, ...);
+    queue.enqueueParallelBroadcastLocked(r);
+    queue.scheduleBroadcastLocked();
+    return ActivityManager.BROADCAST_SUCCESS;
+}
+```
+
+```java
+while(mParallelBroadcasts.size()>0){
+	r = mParallelBroadcasts.remove(0);
+    final int N = r.receivers.size();
+    for(int i=0;i<N;i++){
+        Object target = r.receivers.get(i);
+        deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false);
+    }
+}
+```
+