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