From de364e2bf71f6dccf37aa25b316d6bf82d257bae Mon Sep 17 00:00:00 2001
From: Omooo <869759698@qq.com>
Date: Mon, 30 Mar 2020 20:10:26 +0800
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diff --git a/blogs/Android/Framework/Interview/技巧心得相关/跨进程传递大图片.md b/blogs/Android/Framework/Interview/技巧心得相关/跨进程传递大图片.md
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+---
+跨进程传递大图片
+---
+
+1. 了解各种跨进程传输数据的方式及各自优缺点
+2. 了解 TransactionTooLargeException 的触发原因和底层机制
+3. 了解 Bitmap 传输底层原理
+
+#### 方案
+
+1. 给图片保存到固定的地方，传 key 给对方
+2. 通过 IPC 的方式转发图片数据
+   1. Binder
+   2. Socket、管道
+   3. 共享内存
+
+#### TransactionTooLargeException
+
+1. 发出去的或者返回的数据量太大
+2. Binder 缓存用于该进程所有正在进行中的 Binder 事务
+3. 大数据量打碎分批发，或按需发
+
+```c++
+jboolean BinderProxy_transact(JNIEnv* env, ...){
+    status_t err = target->transact(code, *data, reply, flags);
+    signalExceptionForError(env, obj, err, true, data->dataSize());
+    return JNI_FALSE;
+}
+void signalExceptionForError(JNIEnv* env, jobject obj, status_t err, ...){
+    switch(err){
+        case FAILED_TRANSACTION:{
+            if(canThrowRemoteException && parcelSize > 200*1024){
+                exceptionToThrow = "android/os/TransactionTooLargeException";
+            }
+            jniThrowException(env, exceptionToThrow, msg);
+        }break;
+    }
+}
+```
+
+```c++
+status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult){
+	while(1){
+		if((err=talkWithDriver())<NO_ERROR)break;
+        switch(cmd){
+            case BR_FAILED_REPLY:
+                err = FAILED_TRANSACTION;
+                goto finish;
+        }
+	}
+    return err;
+}
+void binder_transaction(struct binder_proc *proc, struct binder_thread *thread, struct binder_transaction_data *tr, int reply){
+    t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags&TF_ONE_WAY));
+    if(t>buffer == NULL){
+        return_error = BR_FAILED_REPLY;
+        goto err_binder_alloc_buf_failed;
+    }
+}
+```
+
+```java
+Bundle b = new Bundle();
+b.putParcelable("bitmap", mBitmap);
+intent.putExtra(b);
+
+Bundle b = new Bundle();
+b.putBinder("binder", new IRemoteCaller.Stub(){
+    @Override
+    public Bitmap getBitmap() throws RemoteException{
+        return mBitmap;
+    }
+});
+intent.putExtras(b);
+```
+
+```java
+int startActivity(IApplicationThread caller, String callingPackage, Intent intent, ...){
+    Parcel data = Parcel.obtain();
+    intent.writeToParcel(data, 0);
+    mRemote.transct(START_ACTIVITY_TRANSACTION, data, reply, 0);
+}
+```
+
+#### 总结：怎么跨进程传递大图片？
+
+1. 图片写到文件，路径传到另一个进程，再读出来
+2. intent 传图，但是容易抛异常，原因是什么？
+3. binder 调用传图，底层 ashmem 机制
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