JAVA高级面试进阶训练营视频教程

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1、从main日志中找到异常点，例如以下：

08-20 11:05:19.754  5023  5023 E AndroidRuntime: FATAL EXCEPTION: main
08-20 11:05:19.754  5023  5023 E AndroidRuntime: Process: com.android.bluetooth, PID: 5023
08-20 11:05:19.754  5023  5023 E AndroidRuntime: java.lang.RuntimeException: Unable to start receiver com.android.bluetooth.opp.BluetoothOppHandoverReceiver: java.lang.RuntimeException: Adding window failed
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.ActivityThread.handleReceiver(ActivityThread.java:2913)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.ActivityThread.access$1700(ActivityThread.java:177)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1611)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:111)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.os.Looper.loop(Looper.java:194)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5733)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:372)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: Caused by: java.lang.RuntimeException: Adding window failed
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.view.ViewRootImpl.setView(ViewRootImpl.java:668)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:289)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.Dialog.show(Dialog.java:311)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.AlertDialog.show(AlertDialog.java:1127)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at com.android.bluetooth.opp.MzBluetoothTurnOffPromptDialog.showDialog(MzBluetoothTurnOffPromptDialog.java:64)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at com.android.bluetooth.opp.BluetoothOppHandoverReceiver.onReceive(BluetoothOppHandoverReceiver.java:251)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.app.ActivityThread.handleReceiver(ActivityThread.java:2906)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: ... 9 more
08-20 11:05:19.754  5023  5023 E AndroidRuntime: Caused by: android.os.TransactionTooLargeException
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.os.BinderProxy.transactNative(Native Method)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.os.BinderProxy.transact(Binder.java:504)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.view.IWindowSession$Stub$Proxy.addToDisplay(IWindowSession.java:768)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: at android.view.ViewRootImpl.setView(ViewRootImpl.java:657)
08-20 11:05:19.754  5023  5023 E AndroidRuntime: ... 16 more

能够看出是由于binder通信是抛了一个 TransactionTooLargeException异常导致，这时我们须要借助Kernel日志进一步定位问题。

2、从Kernel日志中搜索keyword“5023”和"binder"，例如以下：

 Line 5: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?), -24
 Line 5: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?), -24
 Line 6: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?), -24
 Line 6: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?
), -24
 Line 7: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?), -24
 Line 7: Line 18110: <6>[72111.734216]<0> (2)[1546:Binder_9]binder: 812:1546 to 5023 failed due to 5023 no unused fd available(5023:droid.bluetooth fd leak?
), -24
 Line 8: Line 18112: <6>[72111.734239]<0> (2)[1546:Binder_9]binder: send failed reply for transaction 5183251 to 5023:5023
 Line 8: Line 18112: <6>[72111.734239]<0> (2)[1546:Binder_9]binder: send failed reply for transaction 5183251 to 5023:5023
 Line 9: Line 18112: <6>[72111.734239]<0> (2)[1546:Binder_9]binder: send failed reply for transaction 5183251 to 5023:5023
 Line 9: Line 18112: <6>[72111.734239]<0> (2)[1546:Binder_9]binder: send failed reply for transaction 5183251 to 5023:5023
 Line 10: Line 18114: <3>[72111.734447]<0> (1)[5023:droid.bluetooth]binder: read put err 29201 to user 00000000f4f2f708, thread error 29201:29185
 Line 21: Line 26440: <7>[72131.351513]<1>-(2)[1634:Binder_C][1634:Binder_C] sig 9 to [5023:droid.bluetooth] stat=x
 Line 21: Line 26440: <7>[72131.351513]<1>-(2)[1634:Binder_C][1634:Binder_C] sig 9 to [5023:droid.bluetooth] stat=x

能够看出是binder通信reply时报了异常。无法安装句柄。

相应代码：

驱动Binder.c文件里

			target_fd = task_get_unused_fd_flags(target_proc, O_CLOEXEC);
			if (target_fd < 0) {
				fput(file);
#ifdef MTK_BINDER_DEBUG
				binder_user_error("%d:%d to %d failed due to %d no unused fd available(%d:%s fd leak?), %d\n",
					proc->pid, thread->pid,
					target_proc->pid, target_proc->pid, target_proc->pid,
					target_proc->tsk ?
 target_proc->tsk->comm : "",
					target_fd);
#endif
				return_error = BR_FAILED_REPLY;
				goto err_get_unused_fd_failed;
			}
			task_fd_install(target_proc, target_fd, file);

3、从上面的日志我们能够看出是因为Binder驱动为蓝牙进程安装文件句柄时报了一个error=24。这个类型错误表示caller进程打开的文件句柄过多。无法再创建句柄。这一次Binder通信中传递的句柄无法安装到caller进程中， 进而Binder通信失败。但上层对binder驱动返回的错误类型没有做特别的细分处理，直接抛了一个 TransactionTooLargeException异常 。所以普通情况下报 TransactionTooLargeException类型错误时是须要借助Kernel日志进一步定位。非常多人以为报TransactionTooLargeException就表示在这一次Binder传输中数据过大，事实上并非这样。

4、为什 么 addToDisplay 时 会传递句柄呢？我们知 道上层 应用加入窗体到WindowManagerServic e中是调 addToDisplay接口来完毕的，WindowManagerService为会为每一个新加入的窗体创建一个socket，产生两个句柄。各自是socket读端和写端，socket写端会传递给InputDispatcher，soc ket读端会在 这次Binder传输reply时返回给应用进程。

5、接下来的事情就是查句柄泄露了，可用以下两个命令。做压力測试。然后隔一段时间就“ls -l”一下，看哪个句柄在不停地涨。

cd /proc/pid/fd/
ls -l

6、 最后发现是蓝牙传输小于3M的文件会产生socket泄露。