binder oneway 机制

blogs/Android/Framework/Interview/进程间通信相关/说一说 binder 的 oneway 机制.md

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+---
+说一说 binder 的 oneway 机制
+---
+
+1. binder 的 oneway 是什么意思？
+2. oneway 有哪些特性？
+3. 它的实现原理是怎样的？
+
+```java
+interface IRemoteCaller{
+	void publishBinder(ICallback callback);
+}
+public void publishBinder(ICallback callback){
+    mRemote.transact(Stub.TRANSACTION_publishBinder, _data, _reply, 0);
+}
+
+oneway interface IRemoteCaller{
+    void publishBinder(ICallback callback);
+}
+public void publishBinder(ICallback callback){
+    mRemote.transact(Stub.TRANSACTION_publishBinder, _data, null, IBinder.FLAG_ONEWAY);
+}
+```
+
+```c++
+// 带 oneway
+status_t transact(int32_t handle, uint32_t code, Parcel& data, Parcel* reply, uint32_t flags){
+	writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
+    waitForResponse(NULL, NULL);
+}
+// 不带 oneway
+status_t transact(int32_t handle, uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){
+    writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
+    waitForResponse(reply);
+}
+```
+
+![](https://i.loli.net/2020/03/28/8ENCcGDdYVlUKQm.png)
+
+例子：
+
+```java
+final void scheduleLauncherActivity(Intent intent, IBinder token, ...){
+    mRemote.transact(SCHEDULT_LAUNCH_ACTIVITY_TRANSACTION, data, null, IBinder.FLAG_ONEWAY);
+}
+oneway interface IWindow{}
+oneway interface IServiceConnection{}
+oneway interface IIntentReceiver{}
+```
+
+#### 总结
+
+1. oneway 是异步 binder 调用
+2. server 端串行化处理
+3. oneway 的实现机制
+