MediaServer中包括了系統中的許多重要的Server：

• AudioFlinger：音頻系統中的核心服務
• AudioPolicyService：音頻系統中關于音頻策略的重要服務
• MediaPlayerService：多媒體系統中的重要服務
• CameraService：有關照相和攝像的重要服務

同時，分析MediaServer對于理解Android中的IPC機制能夠提供較好的幫助。Android系統基本上可以看做是一個基于Binder機制的C/S架構，對于Binder機制的理解相對比較復雜，如果能夠通過具體的例子入手會比較容易理解。

Android的通信體制架構

Android的通信機制基本上可以看做是Client、Server和ServiceManager三者之間的交互：

Server首先要注冊一些Service到ServiceManager，在這里Server是ServiceManager的客戶端；

如果某個Client要使用Service，則首先到ServiceManager中獲得該Service的相關信息，所有Client是ServiceManager的客戶端；

Client得到Service信息，然后和該Service所在的Server進程建立通信之后使用Service，在這里Client是Server的客戶端。?
在這些交互的過程中，Android系統都是使用的Binder來進行通信。

MediaServer入口函數

MS是一個可執行程序，它的入口函數是main函數，所在文件位置：frameworks\base\media\mediaserver\main_mediaserver.cpp?
代碼如下：

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">int main(int argc, char<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">**</span> argv) {sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>ProcessState<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> proc(ProcessState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::self</span>());sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IServiceManager<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> sm <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> defaultServiceManager();ALOGI(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ServiceManager: %p"</span>, sm<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>get());AudioFlinger<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::instantiate</span>();MediaPlayerService<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::instantiate</span>();CameraService<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::instantiate</span>();AudioPolicyService<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::instantiate</span>();ProcessState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::self</span>()<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>startThreadPool();IPCThreadState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::self</span>()<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>joinThreadPool(); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

可以看到，在main函數中，

我們首先獲得了一個ProcessState的實例，由self方法我們可以猜得到該類使用了單例模式；

接下來我們調用了defaultServiceManager方法獲得IServiceManager實例；

接下來進行了幾個重要服務的初始化工作；

調用startThreadPool方法和joinThreadPool方法。

ProcessState類的分析

文件位置：frameworks\base\libs\binder\ProcessState.cpp?
self方法：在main函數中，我們調用了self方法得到了一個ProcessState實例，下面我們來看看這個方法

<code class="hljs php has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">sp<ProcessState> ProcessState::<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>() {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gProcess != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">NULL</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> gProcess;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//提供原子操作</span>AutoMutex _l(gProcessMutex);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gProcess == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">NULL</span>) gProcess = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ProcessState;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> gProcess; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

可以看到，不出所料，ProcessState使用的就是單例模式。?
接下來我們來看一看ProcessState的構造函數：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">ProcessState::ProcessState(): mDriverFD(open_driver()), mVMStart(MAP_FAILED), mManagesContexts(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>), mBinderContextCheckFunc(NULL), mBinderContextUserData(NULL), mThreadPoolStarted(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>), mThreadPoolSeq(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mDriverFD >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// XXX Ideally, there should be a specific define for whether we</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// have mmap (or whether we could possibly have the kernel module</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// availabla).</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">if</span> !defined(HAVE_WIN32_IPC)</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// mmap the binder, 提供一個虛擬放入地址內存空間塊去接收事務</span>mVMStart = mmap(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (mVMStart == MAP_FAILED) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// *sigh*</span>ALOGE(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Using /dev/binder failed: unable to mmap transaction memory.\n"</span>);close(mDriverFD);mDriverFD = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;} <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">else</span></span>mDriverFD = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>; <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="box-sizing: border-box;">endif</span></span>}LOG_ALWAYS_FATAL_IF(mDriverFD < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Binder driver could not be opened. Terminating."</span>); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>

可以看到，在構造函數中首先調用了open_driver函數并將返回值賦給了mDriverFD，讓我們來看看這個函數：

<code class="hljs perl has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">static <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> open_driver() {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> fd = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">open</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"/dev/binder"</span>, O_RDWR);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (fd >= <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">fcntl</span>(fd, F_SETFD, FD_CLOEXEC);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> vers;status_t result = ioctl(fd, BINDER_VERSION, &vers);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (result == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {ALOGE(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Binder ioctl to obtain version failed: <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%s</span>"</span>, strerror(errno));<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">close</span>(fd);fd = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (result != <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> || vers != BINDER_CURRENT_PROTOCOL_VERSION) {ALOGE(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Binder driver protocol does not match user space protocol!"</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">close</span>(fd);fd = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;}size_t maxThreads = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>;result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (result == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) {ALOGE(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Binder ioctl to set max threads failed: <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%s</span>"</span>, strerror(errno));}} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {ALOGW(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Opening '/dev/binder' failed: <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%s</span>\n"</span>, strerror(errno));}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> fd; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>

可以看到open_driver函數主要是打開了/dev/binder這個設備并返回了這個設備的fd。

接下來我繼續回到構造函數中，在mDriverFD中保存了這個設備的fd，接著我們又對其他的成員變量做了一些初始化，然后調用mmap函數為Binder設備開辟一塊內存由于接收數據。

總結一下，我們的ProcessState類的任務：

打開了Binder設備，并保存了設備的fd；

利用保存的fd為Binder設備開辟一塊內存用于接收數據；

因為ProcessState采用了單例模式，因此每個進程只能打開一次Binder設備。

defaultServiceManager函數分析

文件位置：frameworks\base\libs\binder\IServiceManager.cpp

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IServiceManager<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> defaultServiceManager() {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gDefaultServiceManager <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">!=</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> gDefaultServiceManager;{AutoMutex _l(gDefaultServiceManagerLock);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (gDefaultServiceManager <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>) {gDefaultServiceManager <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> interface_cast<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IServiceManager<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>(ProcessState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::self</span>()<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>getContextObject(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>));}}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> gDefaultServiceManager; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li></ul>

可以看到gDefaultServiceManager函數主要是對gDefaultServiceManager 進行賦值，首先我們來看看這個函數的傳入參數： ProcessState::self()->getContextObject(NULL)

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IBinder<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> ProcessState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::getContextObject</span>(const sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IBinder<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">>&</span> caller) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> getStrongProxyForHandle(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>); }sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IBinder<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> ProcessState<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;">::getStrongProxyForHandle</span>(int32_t <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">handle</span>) {sp<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span>IBinder<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span> result;AutoMutex _l(mLock);handle_entry<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span> e <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> lookupHandleLocked(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">handle</span>);<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (e <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">!=</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span>) {<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果現在不存在或者我們不能得到它的引用時，我們需要創建一個新的BpBinder, </span>IBinder<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">*</span> b <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> e<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>binder;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (b <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">==</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NULL</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">||</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">!</span>e<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>refs<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>attemptIncWeak(this)) {b <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">new</span> BpBinder(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">handle</span>); e<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>binder <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> b;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (b) e<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>refs <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> b<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>getWeakRefs();result <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> b;} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {result<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>force_set(b);e<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>refs<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-></span>decWeak(this);}}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> result; }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>

可以看到其實我們返回了一個BpBinder(handle)；handle的值為0。

interface_cast看起來像一個強制類型轉換，其實是一個模板函數，下面我們來看看它的廬山真面目：

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">template</span><<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typename</span> INTERFACE> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">inline</span> sp<INTERFACE> interface_cast(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> sp<IBinder>& obj) {<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> INTERFACE::asInterface(obj); }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

我們傳入的模板是IServiceManager，則實際上調用的就是IServiceManager的asInterface方法。?
asInterface方法的聲明和實現實際上是通過兩個宏定義實現的，位于IInterface.h文件中：

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#define DECLARE_META_INTERFACE(INTERFACE) \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::String16 descriptor; \<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> android::sp<I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE> asInterface( \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::sp<android::IBinder>& obj); \<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">virtual</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::String16& getInterfaceDescriptor() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>; \I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE(); \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">virtual</span> ~I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE(); \</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME) \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::String16 I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::descriptor(NAME); \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::String16& \I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::getInterfaceDescriptor() const { \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::descriptor; \</span>} \android::sp<I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE> I##INTERFACE::asInterface( \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> android::sp<android::IBinder>& obj) \{ \android::sp<I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE> intr; \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (obj != NULL) { \intr = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static_cast</span><I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE*>( \</span>obj->queryLocalInterface( \I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::descriptor).get()); \</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (intr == NULL) { \intr = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Bp<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE(obj); \</span>} \} \<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> intr; \} \I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::I##INTERFACE() { } \</span>I<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">##INTERFACE::~I##INTERFACE() { } \</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li></ul>

將INTERFACE替換為IServiceManager后可以得到：

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">static const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:String16</span> descriptor; static <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:sp<IServiceManager></span> asInterface( const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:sp<android</span><span class="hljs-constant" style="box-sizing: border-box;">::IBinder</span>>& obj); virtual const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:String16&</span> getInterfaceDescriptor() const; <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager</span>(); virtual ~<span class="hljs-constant" style="box-sizing: border-box;">IServiceManager</span>(); const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:String16</span> <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>descriptor(<span class="hljs-constant" style="box-sizing: border-box;">NAME</span>); const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:String16&</span> <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>getInterfaceDescriptor() const { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>descriptor; } <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:sp<IServiceManager></span> <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>asInterface( const <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:sp<android</span><span class="hljs-constant" style="box-sizing: border-box;">::IBinder</span>>& obj) { <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">android:</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:sp<IServiceManager></span> intr; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (obj != <span class="hljs-constant" style="box-sizing: border-box;">NULL</span>) { intr = static_cast<<span class="hljs-constant" style="box-sizing: border-box;">IServiceManager</span>*>( obj->queryLocalInterface( <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>descriptor).get()); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (intr == <span class="hljs-constant" style="box-sizing: border-box;">NULL</span>) { intr = new <span class="hljs-constant" style="box-sizing: border-box;">BpServiceManager</span>(obj); } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> intr; } <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::IServiceManager</span>() { } <span class="hljs-constant" style="box-sizing: border-box;">IServiceManager::</span>~<span class="hljs-constant" style="box-sizing: border-box;">IServiceManager</span>() { } </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>

可以看到asInterface方法最終實際上返回了一個BpServiceManager對象。?
總結一下defaultServiceManager方法的工作：

創建了一個BpBinder對象，用來負責客戶端Binder通信（之后會講到），因為對于ServiceManager來說我們是客戶端，所以在這里我們創建了Binder的客戶端；

創建了一個BpServiceManager對象，主要負責IServiceManager的業務函數，在他的內部持有一個BpBinder對象mRemote。

類關系總結

看到這里，已經有點眼花繚亂了，又是IBinder，又是IServiceManager，又是BpBinder，又是BpServiceManager，是時候來總結一下這些類的關系了，翻了一下這些類，下面用一個不標準的UML圖來說明一下：?

需要注意的是：

RefBase是Android中所有類的祖先，相當于Java中Object；

BpBinder和BBinder都是Android中Binder通信的代表類，其中BpBinder是客戶端用來與Server交互的代理類，p代表的就是proxy，而BBinder則是交互的目的端；

BpBinder和BBinder是相互對應的，Binder系統會通過handle來標識對應的BBinder；I

Interface為server端提供接口，它的子類聲明了service能夠實現的所有的方法；

client端在查詢SM獲得所需的的BpBinder后，BpRefBase負責管理當前獲得的BpBinder實例；

BnInterface和BpInterface是兩個接口類：BnInterface類型定義了一個onTransact函數，這個函數負責解包收到的數據l并執行client端的請求的方法；使用 BpInterface，client的應用能夠想本地調用一樣直接調用server端的方法，而不用去關心具體的binder IPC實現；

BnServiceManager中n代表的是native，與Bn相對應的應該是BpServiceManager，表示ServiceManager的業務代理類。

原文地址：?http://blog.csdn.net/smbroe/article/details/44685651

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