Binder传输数据大小限制，你真的get到了吗?

2024年4月13日 互联网

 

                                      Binder传输数据大小限制，你真的get到了吗?

      Binder通信，我想对于Android开发的读者来说，一定并不陌生。可是你知道Binder传输的数据有大小限制吗，下面让我们从源码和实例角度带领读者来分析一把。

 

Binder传输数据大小的限制

     对于通过Intent跨进程传递数据大家都应该很清楚，但是Intent携带的数据大小限制是多少，这个可能大家都没有思考了，那么下面以一个实际的案例来说明，具体代码见如下：

 

        Intent intent = new Intent();Bitmap  mBmp = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);Bitmap b1 = Bitmap.createScaledBitmap(mBmp, 1024, 1024, false);intent.putExtra("byte data", b1);sendBroadcast(intent);

 执行如下代码片段会出现如下的错误信息，FAILED BINDER TRANSACTION ，很明显和Binder传输有关系，那么下面来分析一下

10-18 16:04:39.113  3514  3514 E JavaBinder: !!! FAILED BINDER TRANSACTION !!!  (parcel size = 4194612)
10-18 16:04:39.115  3514  3514 D AndroidRuntime: Shutting down VM
10-18 16:04:39.118  3514  3514 E AndroidRuntime: FATAL EXCEPTION: main
10-18 16:04:39.118  3514  3514 E AndroidRuntime: Process: com.xxx.printtest, PID: 3514
10-18 16:04:39.118  3514  3514 E AndroidRuntime: java.lang.RuntimeException: android.os.TransactionTooLargeException: data parcel size 4194612 bytes
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.app.ContextImpl.sendBroadcast(ContextImpl.java:961)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.content.ContextWrapper.sendBroadcast(ContextWrapper.java:428)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at com.xxx.api.test.MyJobServiceActivity.FUN3(MyJobServiceActivity.java:71)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at com.xxx.api.test.MyJobServiceActivity$1.onClick(MyJobServiceActivity.java:51)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.view.View.performClick(View.java:5637)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.view.View$PerformClick.run(View.java:22433)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.os.Handler.handleCallback(Handler.java:751)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:95)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:154)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:6121)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)
10-18 16:04:39.118  3514  3514 E AndroidRuntime: Caused by: android.os.TransactionTooLargeException: data parcel size 4194612 bytes
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.os.BinderProxy.transactNative(Native Method)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.os.BinderProxy.transact(Binder.java:623)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.app.ActivityManagerProxy.broadcastIntent(ActivityManagerNative.java:3536)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        at android.app.ContextImpl.sendBroadcast(ContextImpl.java:956)
10-18 16:04:39.118  3514  3514 E AndroidRuntime:        ... 12 more

Intent携带信息的大小受Binder限制

      普通的应用是由Zygote孵化而来的用户进程，所映射的Binder内存大小是不到1M的，准确说是 110241024) - (4096 *2) ：这个限制定义在frameworks/native/libs/binder/processState.cpp类中，如果传输说句超过这个大小，系统就会报错，因为Binder本身就是为了进程间频繁而灵活的通信所设计的，并不是为了拷贝大数据而使用的，所以当传递大的数据时会出现上述的错误

#define BINDER_VM_SIZE ((1*1024*1024) - (4096 *2))
ProcessState::ProcessState(): mDriverFD(open_driver())//打开Binder设备驱动, mVMStart(MAP_FAILED), mManagesContexts(false), mBinderContextCheckFunc(NULL), mBinderContextUserData(NULL), mThreadPoolStarted(false), mThreadPoolSeq(1)
{if (mDriverFD >= 0) {// XXX Ideally, there should be a specific define for whether we// have mmap (or whether we could possibly have the kernel module// availabla).
#if !defined(HAVE_WIN32_IPC)// mmap the binder, providing a chunk of virtual address space to receive transactions.//采用内存映射函数mmap，给binder分配一块虚拟地址空间，用来接收事务mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);if (mVMStart == MAP_FAILED) {// *sigh*ALOGE("Using /dev/binder failed: unable to mmap transaction memory.\n");close(mDriverFD);//没有足够空间飞培给/dev/binder，则关闭驱动mDriverFD = -1;}
#elsemDriverFD = -1;
#endif}LOG_ALWAYS_FATAL_IF(mDriverFD < 0, "Binder driver could not be opened.  Terminating.");
}

 

可以看到内存映射的时候已经限制了最大的数据，所以超过了内存映射的限制就会出现上述的错误。

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