Android system_server进程的初始化过程(包含jvm的初始化）

喜欢ヅ旅行 2023-10-18 22:35 85阅读 0赞

在Android系统中，如果用ps来查看进程列表的话，会发现有一个进程是zygote，它的父进程是init，而且，它是所有应用的父进程；还有一个进程是system\_server，它的父进程是zygote。

事实上， zygote正是我们所说的JVM。而system\_server进程又该如何理解呢？其实，它是整个Android Framework所在的进程。这样，我们所说的android系统最核心的组成部分就呈现给大家了(当然，这里先将kernel和应用除外），即jvm+framework。本文描述了整个jvm 和 system\_server的初始化过程，这篇文章是在本博另外一篇文章"android初始化流程”的基础上继续探讨的。

一. zygote进程是通过app\_process的方式启动的，而且是在init.rc中指定的，具体如下：  
service zygote /system/bin/app\_process -Xzygote /system/bin --zygote --start-system-server

app\_process是一个用可执行程序，代码位于： frameworks\\base\\cmds\\app\_process\\目录下。

二. system\_server既然是zygote的子进程，理所当然，是由zygote来初始化的。

**1. 通过app\_process启动zygote**：  
（1）app\_main.cpp中的main函数：  
int main(int argc, const char\* const argv\[\])  
\{  
// These are global variables in ProcessState.cpp  
mArgC = argc;  
mArgV = argv;  
  
mArgLen = 0;  
for (int i=0; i<argc; i++) \{  
mArgLen += strlen(argv\[i\]) + 1;  
\}  
mArgLen--;  
  
  
AppRuntime runtime;  
const char \*arg;  
const char \*argv0;  
  
  
argv0 = argv\[0\];  
  
  
// Process command line arguments  
// ignore argv\[0\]  
argc--;  
argv++;  
  
  
// Everything up to '--' or first non '-' arg goes to the vm  
  
int i = runtime.addVmArguments(argc, argv);  
  
  
// Next arg is parent directory  
if (i < argc) \{  
runtime.mParentDir = argv\[i++\];  
\}  
  
  
// Next arg is startup classname or "--zygote"  
if (i < argc) \{  
arg = argv\[i++\];  
if (0 == strcmp("--zygote", arg)) \{  
bool startSystemServer = (i < argc) ?  
strcmp(argv\[i\], "--start-system-server") == 0 : false;  
setArgv0(argv0, "zygote");  
set\_process\_name("zygote");  
**runtime.start("com.android.internal.os.ZygoteInit",  
startSystemServer);**  
\} else \{  
set\_process\_name(argv0);  
  
  
runtime.mClassName = arg;  
  
  
// Remainder of args get passed to startup class main()  
runtime.mArgC = argc-i;  
runtime.mArgV = argv+i;  
  
  
LOGV("App process is starting with pid=%d, class=%s.\\n",  
getpid(), runtime.getClassName());  
runtime.start();  
\}  
\} else \{  
LOG\_ALWAYS\_FATAL("app\_process: no class name or --zygote supplied.");  
fprintf(stderr, "Error: no class name or --zygote supplied.\\n");  
app\_usage();  
return 10;  
\}  
\}  
  
（2）**AndroidRuntime.cpp中的start**（位于frameworks\\base\\core\\jni\\AndroidRuntime.cpp）：  
void AndroidRuntime::start(const char\* className, const bool startSystemServer)  
\{  
LOGD("\\n>>>>>>>**>>>>>>> AndroidRuntime START <<<<<<<**<<<<<<<\\n");  
......

**preloadClasses();  
//cacheRegisterMaps();  
preloadResources();**

......  
/\*  
\* Initialize the VM.  
\*  
\* The JavaVM\* is essentially per-process, and the JNIEnv\* is per-thread.  
\* If this call succeeds, the VM is ready, and we can start issuing  
\* JNI calls.  
\*/  
if (**JNI\_CreateJavaVM**(&mJavaVM, &env, &initArgs) < 0) \{  
LOGE("JNI\_CreateJavaVM failed\\n");  
goto bail;  
\}  
/\*  
\* We want to call main() with a String array with arguments in it.  
\* At present we only have one argument, the class name. Create an  
\* array to hold it.  
\*/  
jclass stringClass;  
jobjectArray strArray;  
jstring classNameStr;  
jstring startSystemServerStr;  
  
  
stringClass = env->FindClass("java/lang/String");  
assert(stringClass != NULL);  
strArray = env->NewObjectArray(2, stringClass, NULL);  
assert(strArray != NULL);  
classNameStr = env->NewStringUTF(className);  
assert(classNameStr != NULL);  
env->SetObjectArrayElement(strArray, 0, classNameStr);  
startSystemServerStr = env->NewStringUTF(startSystemServer ?  
"true" : "false");  
env->SetObjectArrayElement(strArray, 1, startSystemServerStr);  
  
  
/\*  
\* Start VM. This thread becomes the main thread of the VM, and will  
\* not return until the VM exits.  
\*/  
jclass startClass;  
jmethodID startMeth;  
  
  
slashClassName = strdup(className);  
for (cp = slashClassName; \*cp != '\\0'; cp++)  
if (\*cp == '.')  
\*cp = '/';  
  
  
startClass = env->FindClass(slashClassName);  
if (startClass == NULL) \{  
LOGE("JavaVM unable to locate class '%s'\\n", slashClassName);  
/\* keep going \*/  
\} else \{  
startMeth = env->**GetStaticMethodID**(startClass, "main",  
"(\[Ljava/lang/String;)V");  
if (startMeth == NULL) \{  
LOGE("JavaVM unable to find main() in '%s'\\n", className);  
/\* keep going \*/  
\} else \{  
env->**CallStaticVoidMethod**(startClass, startMeth, strArray);  
  
  
\#if 0  
if (env->ExceptionCheck())  
threadExitUncaughtException(env);  
\#endif  
\}  
\}  
  
  
LOGD("Shutting down VM\\n");  
if (mJavaVM->DetachCurrentThread() != JNI\_OK)  
LOGW("Warning: unable to detach main thread\\n");  
if (mJavaVM->DestroyJavaVM() != 0)  
LOGW("Warning: VM did not shut down cleanly\\n");  
  
  
bail:  
free(slashClassName);  
free(stackTraceFile);  
\}  
  
说明：  
（1） LOGD("\\n>>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<\\n");  
这个log信息应该不陌生了吧。

（2） preloadClasses(); 和preloadResources();， 顾名思义，它加载了许多class和resources，libmedia\_jni.so 和libwebcore就是在这里加载的（在本文最后面，会给出相关的log信息，里面显示了加载了哪些库，一定要看喔:））。

（3） JNI\_CreateJavaVM， 用于初始化虚拟机。

（4） GetStaticMethodID和 CallStaticVoidMethod就会调用 传入的class的对应的方法。  
这里，class是ZygoteInit,方法是main, 而ZygoteInit位于ZygoteInit.java中，注意，从这里开始，  
首次以java定义的类来调用，因为在这之前，jvm也初始化好了，需要jniEnv的参数也设置好了。  
**于是，就会执行到下面的ZygoteInit.java的main函数中**。  
**2. ZygoteInit.java**   
代码:  
位于frameworks\\base\\core\\java\\com\\android\\internal\\os目录下。  
在它的main函数中，最主要的就是：  
 **startSystemServer()**; 这个函数也位于ZygoteInit.java中，代码如下：  
/\*\*  
\* Prepare the arguments and fork for the system server process.  
\*/  
private static boolean startSystemServer()  
throws MethodAndArgsCaller, RuntimeException \{  
/\* Hardcoded command line to start the system server \*/  
String args\[\] = \{  
"--setuid=1000",  
"--setgid=1000",  
"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,3001,3002,3003",  
"--capabilities=121715744,121715744",  
"--runtime-init",  
"--nice-name=**system\_server**",  
"**com.android.server.SystemServer**",  
\};  
ZygoteConnection.Arguments parsedArgs = null;  
  
  
int pid;  
  
  
try \{  
parsedArgs = new ZygoteConnection.Arguments(args);  
  
  
/\*  
\* Enable debugging of the system process if \*either\* the command line flags  
\* indicate it should be debuggable or the ro.debuggable system property  
\* is set to "1"  
\*/  
int debugFlags = parsedArgs.debugFlags;  
if ("1".equals(SystemProperties.get("ro.debuggable")))  
debugFlags |= Zygote.DEBUG\_ENABLE\_DEBUGGER;  
  
  
/\* Request to fork the system server process \*/  
pid = **Zygote.forkSystemServer**(  
parsedArgs.uid, parsedArgs.gid,  
parsedArgs.gids, debugFlags, null);  
\} catch (IllegalArgumentException ex) \{  
throw new RuntimeException(ex);  
\}  
  
/\* For child process \*/  
if (pid == 0) \{  
handleSystemServerProcess(parsedArgs);  
\}  
  
  
return true;  
｝  
  
说明：  
（1） 设置进程的参数是system\_server， ；  
对应的类是com.android.server.SystemServer。  
（2） Zygote.forkSystemServer真正地fork一个进程,参数前面已经设置好了，所以，这个fork出来的进程就是system\_server,而这个进程恰恰是zygote的子进程（用ps可以看到）。  
（3） Zygote.**forkSystemServer**相关：  
它调用了forkAndSpecialize(dalvik\\libcore\\dalvik\\src\\main\\java\\dalvik\\system\\zytote.java), 而后者又通过jni的方式调用到  
Dalvik\_dalvik\_system\_Zygote\_forkSystemServer(dalvik\\vm\\native\\dalvik\_system\_Zygote.c),继而调用到forkAndSpecializeCommon,在这个函数中，通过 fork()函数来真正创建一个进程。这里，如果看log的话，有打印语句：LOGE("System server process %d has died. Restarting Zygote!", pid);， 而这个log在本文最后给出的log中也是有体现的。  
所以，最终，还是回到了下层的c或者cpp代码中; 而jvm只不过是对fork（）进行了封装，当然，这只是它的一个必不可少的功能之一而已。  
**3. system\_server**：

system\_server上面也提到了，是一个进程，事实上，它是整个Framework的主进程，在这个进程中，会创建并启动一个thread,而这个线程是整个framework的主线程，在这个线程中，这里声明并初始化了所有的framework组件。代码位于：

**systemserver.java**(位于frameworks\\base\\services\\java\\com\\android\\server）

至此， 整个Android os 可以认为是启动完毕。

**4. log,是在开机过程中抓取的，当然，用的是logcat**:

09-07 06:21:52.288: DEBUG/AndroidRuntime(541): >>>>>>**>>>>>>>> AndroidRuntime START** <<<<<<<<<<<<<<  
09-07 06:21:52.288: DEBUG/AndroidRuntime(541): CheckJNI is ON  
......  
09-07 06:21:52.937: INFO/(542): ServiceManager: 0xac38  
09-07 06:21:52.957: INFO/AudioFlinger(542): AudioFlinger's thread ready to run for output 0  
09-07 06:21:52.957: INFO/CameraService(542): CameraService started: pid=542  
09-07 06:21:52.978: DEBUG/AndroidRuntime(541): --- registering native functions ---  
09-07 06:21:53.308: INFO/Zygote(541): **Preloading classes**...  
09-07 06:21:53.318: DEBUG/dalvikvm(541): GC freed 764 objects / 42216 bytes in 11ms  
09-07 06:21:53.517: DEBUG/dalvikvm(541): GC freed 278 objects / 17160 bytes in 4ms  
09-07 06:21:53.898: DEBUG/dalvikvm(541): GC freed 208 objects / 12696 bytes in 6ms  
09-07 06:21:53.988: DEBUG/dalvikvm(541): Trying to load lib /system/lib/**libmedia\_jni**.so 0x0  
09-07 06:21:54.148: DEBUG/dalvikvm(541): Added shared lib /system/lib/libmedia\_jni.so 0x0  
09-07 06:21:54.148: DEBUG/dalvikvm(541): Trying to load lib /system/lib/libmedia\_jni.so 0x0  
09-07 06:21:54.158: DEBUG/dalvikvm(541): Shared lib '/system/lib/libmedia\_jni.so' already loaded in same CL 0x0  
09-07 06:21:54.158: DEBUG/dalvikvm(541): Trying to load lib /system/lib/libmedia\_jni.so 0x0  
09-07 06:21:54.158: DEBUG/dalvikvm(541): Shared lib '/system/lib/libmedia\_jni.so' already loaded in same CL 0x0  
09-07 06:21:54.158: DEBUG/dalvikvm(541): Trying to load lib /system/lib/libmedia\_jni.so 0x0  
09-07 06:21:54.158: DEBUG/dalvikvm(541): Shared lib '/system/lib/libmedia\_jni.so' already loaded in same CL 0x0  
09-07 06:21:54.168: DEBUG/dalvikvm(541): GC freed 462 objects / 29144 bytes in 8ms  
......  
09-07 06:21:58.748: DEBUG/dalvikvm(541): Trying to load lib /system/lib/**libwebcore**.so 0x0  
09-07 06:21:58.828: DEBUG/dalvikvm(541): Added shared lib /system/lib/libwebcore.so 0x0  
......  
09-07 06:22:02.258: INFO/Zygote(541): ...preloaded 1166 classes in 8951ms.  
09-07 06:22:02.337: DEBUG/dalvikvm(541): GC freed 313 objects / 19952 bytes in 67ms  
09-07 06:22:02.337: INFO/Zygote(541): **Preloading resources..**.  
......  
09-07 06:22:03.509: INFO/dalvikvm(541): Splitting out new zygote heap  
09-07 06:22:03.569: INFO/dalvikvm(541): **System server process 570 has been created**  
09-07 06:22:03.569: INFO/Zygote(541): Accepting command socket connections  
09-07 06:22:03.638: INFO/jdwp(570): received file descriptor 10 from ADB  
09-07 06:22:03.797: DEBUG/dalvikvm(570): Trying to load lib /system/lib/**libandroid\_servers**.so 0x0  
09-07 06:22:04.008: DEBUG/dalvikvm(570): Added shared lib /system/lib/libandroid\_servers.so 0x0  
09-07 06:22:04.027: INFO/sysproc(570): Entered **system\_init**()  
09-07 06:22:04.051: INFO/sysproc(570): ServiceManager: 0x16c900  
09-07 06:22:04.051: INFO/SurfaceFlinger(570): SurfaceFlinger is starting  
09-07 06:22:04.058: INFO/SurfaceFlinger(570): SurfaceFlinger's main thread ready to run. Initializing graphics H/W...  
09-07 06:22:04.079: ERROR/MemoryHeapBase(570): error opening /dev/pmem: No such file or directory  
09-07 06:22:04.087: ERROR/SurfaceFlinger(570): Couldn't open /sys/power/wait\_for\_fb\_sleep or /sys/power/wait\_for\_fb\_wake  
09-07 06:22:04.117: ERROR/GLLogger(570): couldn't load <libhgl.so> library (Cannot find library)  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): EGL informations:  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): \# of configs : 6  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): vendor : Android  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): version : 1.31 Android META-EGL  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): extensions:  
09-07 06:22:04.127: INFO/SurfaceFlinger(570): Client API: OpenGL ES  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): using (fd=22)  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): id =  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): xres = 320 px  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): yres = 480 px  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): xres\_virtual = 320 px  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): yres\_virtual = 960 px  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): bpp = 16  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): r = 11:5  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): g = 5:6  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): b = 0:5  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): width = 49 mm (165.877548 dpi)  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): height = 74 mm (164.756760 dpi)  
09-07 06:22:04.127: INFO/EGLDisplaySurface(570): refresh rate = 60.00 Hz  
09-07 06:22:04.138: WARN/HAL(570): load: module=/system/lib/hw/copybit.goldfish.so error=Cannot find library  
09-07 06:22:04.138: WARN/HAL(570): load: module=/system/lib/hw/copybit.default.so error=Cannot find library  
09-07 06:22:04.138: WARN/SurfaceFlinger(570): ro.sf.lcd\_density not defined, using 160 dpi by default.  
09-07 06:22:04.148: INFO/SurfaceFlinger(570): OpenGL informations:  
09-07 06:22:04.148: INFO/SurfaceFlinger(570): vendor : Android  
09-07 06:22:04.148: INFO/SurfaceFlinger(570): renderer : Android PixelFlinger 1.0  
09-07 06:22:04.148: INFO/SurfaceFlinger(570): version : OpenGL ES-CM 1.0  
09-07 06:22:04.148: INFO/SurfaceFlinger(570): extensions: GL\_OES\_byte\_coordinates GL\_OES\_fixed\_point GL\_OES\_single\_precision GL\_OES\_read\_format GL\_OES\_compressed\_paletted\_texture GL\_OES\_draw\_texture GL\_OES\_matrix\_get GL\_OES\_query\_matrix GL\_ARB\_texture\_compression GL\_ARB\_texture\_non\_power\_of\_two GL\_ANDROID\_direct\_texture GL\_ANDROID\_user\_clip\_plane GL\_ANDROID\_vertex\_buffer\_object GL\_ANDROID\_generate\_mipmap  
09-07 06:22:04.148: WARN/HAL(570): load: module=/system/lib/hw/copybit.goldfish.so error=Cannot find library  
09-07 06:22:04.148: WARN/HAL(570): load: module=/system/lib/hw/copybit.default.so error=Cannot find library  
09-07 06:22:04.148: WARN/HAL(570): load: module=/system/lib/hw/overlay.goldfish.so error=Cannot find library  
09-07 06:22:04.148: WARN/HAL(570): load: module=/system/lib/hw/overlay.default.so error=Cannot find library  
09-07 06:22:04.167: INFO/sysproc(570): System server: starting Android runtime.  
09-07 06:22:04.167: INFO/sysproc(570): System server: starting Android services.  
09-07 06:22:04.179: INFO/SystemServer(570): Entered the Android system server!  
09-07 06:22:04.209: INFO/sysproc(570): System server: entering thread pool.  
09-07 06:22:04.267: ERROR/GLLogger(570): couldn't load <libhgl.so> library (Cannot find library)  
09-07 06:22:04.338: INFO/SystemServer(570): Starting Power Manager.  
09-07 06:22:04.387: INFO/ARMAssembler(570): generated scanline\_\_00000077:03545404\_00000A01\_00000000 \[ 30 ipp\] (51 ins) at \[0x190ed0:0x190f9c\] in 6840752 ns  
09-07 06:22:04.397: INFO/SystemServer(570): Starting Activity Manager.  
09-07 06:22:04.578: INFO/SystemServer(570): Starting telephony registry  
09-07 06:22:04.588: INFO/SystemServer(570): Starting Package Manager.  
09-07 06:22:04.619: INFO/Installer(570): connecting...  
09-07 06:22:04.619: INFO/installd(543): new connection  
......

当然，这里的信息足够多的，有兴趣的朋友不妨用这种方法去理解和研究一下android启动过程。

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