默默的点滴

Overview

First of all let's overview the structure of a typical Android app containing native code:

The app code is stored inside an .apk file that is essentially a ZIP archive containing the classes.dex file (with all the Java code) and one or more native libraries in lib\<EABI name> subdirectory. The typical lifecycle of an application with native code is the following:

1. The Android OS loads the Java code and starts executing it
2. The Java code calls System.loadLibrary() to load a native library.
3. The Java code starts calling functions from the native code.

Each native library exists in 2 versions:

•  A "full" version debugging information that associates code addresses inside the library with source files and lines. This version resides in obj\local\armeabi under your project directory.
• A "stripped" version without the debugging information that resides in libs\armeabi and gets packaged into the APK file.

While the Android device runs the smaller "stripped" version of the library, the GDB debugger needs the larger "non-stripped" version to map source files into addresses and vice versa:

Setting breakpoints

When you set a breakpoint on a given line of a source file, the GDB debugger needs to perform certain computations before the breakpoint can be physically created and starts triggering. Assume libNative1 is loaded at address 0x10000 and the user is setting a breakpoint in line 24 of c:\main.cpp. GDB will do the following before it can set a breakpoint:

1. GDB starts searching all loaded libraries for the file called "c:\main.cpp". In this example the Android OS only reports the libNative1.so library.
2. GDB looks inside obj\local\armeabi for a file called libNative1.so which is the "non-stripped" version of the library containing the debug information. GDB reads the symbol table from it and finds c:\main.cpp inside it.
3. Based on the symbol table GDB computes that line 24 corresponds to offset +0x2. It adds 0x2 to the load address of libNative1.so (0x10000) and sets the breakpoint at 0x10002.

If any of the 3 steps fail, the breakpoint will not be created, or will be created wrongly and will never be hit. The next section explains how to diagnose and fix the related problems.

Diagnosing the problems

This section provides detailed instructions how to check for the most common problems with breakpoints caused by non-standard configurations or missing files:

A. Ensure that the library is loaded

First thing to do is to determine if the native library has been actually loaded and if GDB knows about it. It is done by running the "info shared" command in GDB:

The output from the info shared command should include 3 important lines:

1. Loaded symbols for "linker"
2. Loaded symbols for "libc.so"
3. Loaded symbols for all native libraries you want to debug.

Here's an example of those lines:

If some of the libraries are not present, you can force GDB to manually reload the symbols by running the following command in GDB:

The obj/local/armeabi directory of your project should be present among the reported directories and it should contain the .so file with symbols. If not, copy the correct .so file into a directory listed here and rerun the "sharedlibrary" command.

You can alternatively force GDB to search additional directories for the .so file using the set solib-search-path command.

If your .so library is not present in the list, it has not been loaded by the Java code yet. Please ensure that System.loadLibrary() is called from your Java code and that it succeeds without any Java exceptions.

B. Ensure that you are using correct file paths

A common cause of many breakpoint problems is a configuration when the directories using for building and debugging your project are different. E.g. if the library was compiled from c:\projects and then the sources were moved to d:\projects, setting a breakpoint in d:\projects\main.cpp will fail, as GDB will not accept c:\projects\main.cpp as a substitute.

Those problems can be diagnosed by looking into the source file lists and comparing them with the file used to set a breakpoint. First of all, remove your breakpoint, try setting your breakpoint again and watch what GDB command is issued by your IDE:

The -break-insert command used to set a breakpoint will specify a path to your source file.

Run the "info sources" command to see the source files discovered by GDB:

Copy the output of the command to the clipboard (Ctrl-A, Ctrl-C), paste it into a text editor and search for the source file you are trying to debug (e.g. MyAndroidApp.c):

If the file is not present in the list, you have loaded a wrong version of the .so file (see previous section). If the file is present, but the path is different from the one used in -break-insert command, you have found the cause of your problem. Rebuild your app using the new path, or move the file back to an old location so that the path used for creating breakpoints matches the path reported by the "info sources" command.

Note that GDB requires the file path to be EXACTLY the same as reported by "info sources", including double slash before "jni".

C. Recheck file versions and do a clean build

If your breakpoints are set, but never hit, there is probably a mismatch between the .so file version loaded into the Android application and the .so file version used by GDB to compute addresses from source lines. The most common cause for it is the bug in the Android loader that loads the armeabi library instead of the armeabi-v7a version. If you suspect this to happen, change your build configuration to build either armeabi, or armeabi-v7a platform, but not both at the same time and rebuild your application.'

引用自  http://www.codeproject.com/Articles/493043/Why-your-Android-NDK-breakpoints-might-fail-and-ho

Android 2.3起，新增加了一个新的类，叫StrictMode(android.os.StrictMode)。这个类可以用来帮助开发者改进他们编写的应用，并且提供了各种的策略，这些策略能随时检查报告开发者开发应用中存在的问题，比如可以监视那些本不应该在主线程中完成的工作或者其他的一些不规范和不好的代码。

StrictMode的策略和规则

　　目前，有两大类的策略可供使用

一类是关于常用的监控方面的

Disk Reads 磁盘读

Disk Writes 磁盘写

Network access 网络访问

Custom Slow Code 自定义的运行速度慢的代码分析

前面三种的意思读者应该很清楚，就是正如它们的名字所示，分别对磁盘的读和写，网络访问进行监控。而第四种的自定义慢代码分析，是仅当访问调用类的时后才触发的，可以通过这种

方法去监视运行缓慢的代码。当在主线程中调用时，这些验证规则就会起作用去检查你的代码。比如，当你的应用在下载或者解析大量的数据时，你可以触发自定义运行速度慢代码的查询分、

析，作用很大。StrictMode可以用于捕捉发生在应用程序主线程中耗时的磁盘、网络访问或函数调用，可以帮助开发者使其改进程序，使主线程处理UI和动画在磁盘读写和网络操作时变得更平

滑，避免主线程被阻塞的发生。

另一类是关于VM虚拟机等方面的策略

内存泄露的Activity对象

内存泄露的SQLite对象

内存泄露的释放的对象

其中，内存泄露的Activity对象和内存泄露的SQLite对象都比较好理解，而所谓对关闭对象的检查，主要是去监那些本该释放的对象，比如应该调用close()方法的对象

相关的违反情况可以记录在LogCat中或者存储在DropBox中(android.os.DropBox)服务中

　　如何使用：

　　放在activity的周期onCreate方法中