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Android NDK学习 <六> 复杂结构动态库处理和第三方库的移植

 
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0. 动态库加载方式：
方法1：在运行时动态链接库，动态地将程序和共享库链接并让 Linux 在执行时加载库(动态链接，系统加载)
方法2：动态加载库并在程序控制之下使用它们。(动态加载)

Android<wbr>NDK学习<wbr><六><wbr>复杂结构动态库处理和第三方库的移植

动态链接(系统加载)：是指在编译应用程序时，使用 -lxxx 来指定需要链接哪个库。此时，应用程序(ELF)中会指明哪些符号未被填充，且放在哪些动态库中。LD_LIBRARY_PATH则指明动态库在哪里存放。系统会将此动态库加载到内存中使用。

动态加载：使用dlopen打开指定的动态库。并使用dlsym<wbr>获取符号地址。这是插件式程序的必备方式。<br><span style="word-wrap:normal; word-break:normal"><br><br><br><br><span style="word-wrap:normal; word-break:normal">1. C++大型程序常见的模块组织方式</span><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">：</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">不少C++大型程序以如下方式设计：</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">1. 有一个主程序块，此程序块通常作用是读取配置文件，并根据配置文件动态加载以插件形式提供的功能模块。(即dlopen(插件)) 并维护主循环，每次循环中依次调用每个插件中的某功能（dlsym（符号）并运行）。</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">在退出时，使用dlclose() 将各插件移出内存并退出主循环。</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">2. 不同插件同样利用配置文件维护他们所用到的自有模块。(dlopen, dlsym)</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">3. 如有必要，各插件以动态库的形式共同使用某模块(尤其是第三方模块)。 (使用动态链接，系统加载的方式)</span></span><br><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">例如：</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">某程序以如下方式构建：</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">1. 核心程序为一个应用程序，此应用程序主要通过分析配置文件，决定加载哪些插件。同时，它维护一个循环，每个循环中调用插件的特定符号(update)。</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">2. 插件包括：音频库，文件系统，动作分析系统等。同时，各个游戏逻辑也作为插件存在。即从大厅进入游戏，其实就是替换一些插件。</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">3. 游戏模块依赖于引擎A。(以动态链接，系统加载方式使用)</span></span><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">这样，在Linux下，可以将引擎以及底层库放置于LD_LIBRARY_PATH制定位置。整个软件可正常运行。</span></span><br><br><br><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">2. Android 下对NDK动态库的使用</span>：</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">Android下，对于动态加载的库(dlopen(lib)),使用绝对路径就可以解决问题。</span></span><br><span style="word-wrap:normal; word-break:normal"><span style="word-wrap:normal; word-break:normal">对于动态链接(系统加载)的动态库，因为没有LD_LIBRARY_PATH方式，则可以采用在Activity的静态模块中使用System.LoadLibrary()方式提前加载于内存空间。</span></span><br></span></wbr>

<wbr>static<br> {</wbr>
<wbr><wbr>System.loadLibrary("gnustl_shared");<wbr></wbr></wbr></wbr>
<wbr><wbr>System.loadLibrary("testcplus");<wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr>System.loadLibrary("hello-jni");</wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
}


3. 复杂情况下NDK动态库的组织：
使用上面所说的方法，可以解决非常简单的动态加载的动态库。但对于比较复杂的动态库。则有很多问题。
例如：某些动态库有很多全局变量，且包含一些状态信息。
而Activity在onDestory()后，进程并未完全退出。此时，动态库依然存在于内存之中。此时，再次运行应用程序。全局变量和状态还是使用之前的值。这会对逻辑造成很大困难。


于是采用如下方式：

首先：Java程序使用System.LoadLibrary()仅调用C++库(libgnustl_shared.so)以及一个非常干净简单的动态库A。

此动态库A，提供2个主要功能。Init(), UnInit().
在Init（）中，它作两件事：
1. 采用dlopen()方式将所有动态链接(系统加载)的库(如上面所说引擎)加入内存(关键点)
2. 采用dlopen()方式将需要dlopen() 的模块(如游戏逻辑)加入。

在UnInit()中。依次dlclose（）；






其次，动态库A所dlopen（）的游戏逻辑动态库，直接使用函数名而非dlopen，dlsym的方式使用符号。这样，Linux下的代码，就不需要做任何修改即可。

在NDK 编译游戏逻辑时，指明LOCAL_SHARED_LIBRARIES := 引擎。


也就是说：System.LoadLibrary（A），将最简单的壳子动态库加入内存。

此壳子动态库A在onCreate（）时调用dlopen将所有所需动态库加入内存(引擎，游戏)。
在onDestory（）时，则dlclose（）,将动态库移出内存。

而在循环中，游戏动态库被dlopen,dlsym取出相应几个有限的符号并调用。

而在这些符号内，他们直接使用引擎提供的函数。因为此时引擎已经被加载入内存。所以可以使用。


dlclose时，游戏和引擎都被移出内存。


(注：有很多游戏，但引擎只有一个，游戏使用此共同的引擎提供的函数)





第三方C++库的移植:
在开发Android大型程序时,不可避免要用到很多第三方OpenSouce.而大多数第三方库采用AutoConfig，或者CMake等特定编译工具编译。现在就说说如何利用NDK将其编译成咱们能够使用的静态库或者动态库。

现在以xiph-ogg为例，演示如何使用ＮＤＫ编译这些第三方库。

0. 准备工作：
下载xiph source code.
要编译的内容是：
xiph/ogg：生成libogg.so或者libogg.a
xiph/vorbis: 生成libvorbisfile.so <wbr>libvorbis.so 或者对应.a .<br><br> 1. 确定库所包含的源文件：<br> 编译libogg.so,需要编译的源文件包括：<br> bitwise.c framing.c<br><br><br> 2.组织文件和写Android.mk+Application.mk<br> Sam作如下目录结构：<br> xiph/ogg/jni/<br></wbr>
这里包含4个文件：<wbr>bitwise.c framing.c， Android.mk, Application.mk<br><br> 作Android.mk如下：注意需要填写的资源文件(两个.c)以及指定-I目录。<br></wbr>
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_ARM_MODE := arm
LOCAL_MODULE := ogg
LOCAL_SRC_FILES := bitwise.c framing.c
LOCAL_CXXFLAGS :=
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/ogg/include
#LOCAL_SHARED_LIBRARIES := <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
LOCAL_LDLIBS := -llog
#include $(BUILD_EXECUTABLE) <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
include $(BUILD_SHARED_LIBRARY)
#include $(BUILD_STATIC_LIBRARY)<wbr><br><br></wbr>
编译之：
../../../../../ndk-build -B V=1
在xiph/ogg/libs/armeabi-v7a/下生成libogg.so



libvorbisfile.so <wbr>libvorbis.so的建立也一样，Android.mk如下：<br></wbr>
LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_ARM_MODE := arm
LOCAL_MODULE := vorbis
LOCAL_SRC_FILES := mdct.c smallft.c block.c envelope.c window.c lsp.c lpc.c <wbr>analysis.c synthesis.c psy.c info.c floor1.c floor0.c \</wbr>
<wbr>res0.c mapping0.c registry.c codebook.c sharedbook.c lookup.c bitrate.c</wbr>
LOCAL_CXXFLAGS :=
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/ogg/include
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/vorbis/include
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/vorbis/lib

LOCAL_LDLIBS := -lm
LOCAL_LDLIBS += -logg

#LOCAL_SHARED_LIBRARIES := <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
LOCAL_LDLIBS += -llog
LOCAL_LDLIBS += -L/opt/Android-NDK/android-ndk-r8b/samples/xiph/NDK_Build/ogg/libs/armeabi-v7a
#include $(BUILD_EXECUTABLE) <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
include $(BUILD_SHARED_LIBRARY)
#include $(BUILD_STATIC_LIBRARY) <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>




include $(CLEAR_VARS)
LOCAL_ARM_MODE := arm
LOCAL_MODULE := vorbisfile
LOCAL_SRC_FILES := vorbisfile.c
LOCAL_CXXFLAGS :=
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/ogg/include
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/vorbis/include
LOCAL_CFLAGS += -I/opt/Android-NDK/android-ndk-r8b/samples/xiph/xiph/vorbis/lib

LOCAL_LDLIBS := -lm
LOCAL_LDLIBS += -logg
LOCAL_LDLIBS += -lvorbis

#LOCAL_SHARED_LIBRARIES := <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>\</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
LOCAL_LDLIBS += -llog
LOCAL_LDLIBS += -L/opt/Android-NDK/android-ndk-r8b/samples/xiph/NDK_Build/ogg/libs/armeabi-v7a
LOCAL_LDLIBS += -L/opt/Android-NDK/android-ndk-r8b/samples/xiph/NDK_Build/vorbis/libs/armeabi-v7a
#include $(BUILD_EXECUTABLE) <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>\</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
include $(BUILD_SHARED_LIBRARY)
#include $(BUILD_STATIC_LIBRARY) <wbr></wbr>

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