壮心未与年俱老,死去犹能作鬼雄。这篇文章主要讲述Android系统启动流程分析相关的知识,希望能为你提供帮助。
随着android版本的升级,aosp项目中的代码也有了些变化,本文基于Android 7.0分析Android系统启动流程.当我们按下电源键后,整个Android设备大体经过了一下过程:
文章图片
今天我们只想来分析init进程及其后的过程,也就是下图所示部分:
文章图片
init进程 init进程会解析init.rc文件(关于init.rc中的语法,可以参见之前写的深入分析AIL语言及init.rc文件),加载相关分区,并启动相关服务.
init进程在/system/core/init/init.cpp在init.rc中,Zygote进程被启动.Zygote进程是其他所有进程的孵化器.init.rc通过include引入init.zygote.rc,这里以init.zygote64.rc为例:
init.rc文件在/system/core/rootdir下
init.rc文件由parser.cpp解析,在/system/core/init/init_parser.cpp
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
class main
priority -20
user root
group root readproc
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart audioserver
onrestart restart cameraserver
onrestart restart media
onrestart restart netd
writepid /dev/cpuset/foreground/tasks
对个脚本简单分析:
service zygote /system/bin/app_process64
:service命令告诉init进程要创建一个名字为zygote的进程,这个zygote进程执行的程序是/system/bin/app_process64,后面是传给app_process64程序的参数.socket zygote stream 660 root system
:表示zygote进程需要一个名为”zygote”的socket,该socket用来实现进程间的通信.当新启动一个应用时,ActivityManagerService想向该Socket发起请求,请求zygote进程fork出一个新的进程.- 后面的onrestart表示zygote重启时需要执行的动作.
位于/frameworks/base/cmds/app_process/app_main.cpp,其入口函数是main():
int main(int argc, char* const argv[])
{
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) <
0) {
LOG_ALWAYS_FATAL("
PR_SET_NO_NEW_PRIVS failed: %s"
, strerror(errno));
}if (!LOG_NDEBUG) {
String8 argv_String;
for (int i =
0;
i <
argc;
+
+
i) {
argv_String.append("
\\"
"
);
argv_String.append(argv[i]);
argv_String.append("
\\"
"
);
}
ALOGV("
app_process main with argv: %s"
, argv_String.string());
}AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0]
argc--;
argv+
+
;
const char* spaced_commands[] =
{ "
-cp"
, "
-classpath"
};
bool known_command =
false;
int i;
for (i =
0;
i <
argc;
i+
+
) {
if (known_command =
=
true) {
runtime.addOption(strdup(argv[i]));
ALOGV("
app_process main add known option '
%s'
"
, argv[i]);
known_command =
false;
continue;
}for (int j =
0;
j <
static_cast<
int>
(sizeof(spaced_commands) / sizeof(spaced_commands[0]));
+
+
j) {
if (strcmp(argv[i], spaced_commands[j]) =
=
0) {
known_command =
true;
ALOGV("
app_process main found known command '
%s'
"
, argv[i]);
}
}if (argv[i][0] !=
'
-'
) {
break;
}
if (argv[i][1] =
=
'
-'
&
&
argv[i][2] =
=
0) {
+
+
i;
// Skip --.
break;
}runtime.addOption(strdup(argv[i]));
ALOGV("
app_process main add option '
%s'
"
, argv[i]);
}// Parse runtime arguments.Stop at first unrecognized option.
bool zygote =
false;
bool startSystemServer =
false;
bool application =
false;
String8 niceName;
String8 className;
+
+
i;
// Skip unused "
parent dir"
argument.
while (i <
argc) {
const char* arg =
argv[i+
+
];
if (strcmp(arg, "
--zygote"
) =
=
0) {
zygote =
true;
niceName =
ZYGOTE_NICE_NAME;
} else if (strcmp(arg, "
--start-system-server"
) =
=
0) {
//init.zygote64.rc中接受的参数,表示启动SystemServer组件
startSystemServer =
true;
} else if (strcmp(arg, "
--application"
) =
=
0) {
application =
true;
} else if (strncmp(arg, "
--nice-name=
"
, 12) =
=
0) {
niceName.setTo(arg +
12);
} else if (strncmp(arg, "
--"
, 2) !=
0) {
className.setTo(arg);
break;
} else {
--i;
break;
}
}Vector<
String8>
args;
if (!className.isEmpty()) {args.add(application ? String8("
application"
) : String8("
tool"
));
runtime.setClassNameAndArgs(className, argc - i, argv +
i);
if (!LOG_NDEBUG) {
String8 restOfArgs;
char* const* argv_new =
argv +
i;
int argc_new =
argc - i;
for (int k =
0;
k <
argc_new;
+
+
k) {
restOfArgs.append("
\\"
"
);
restOfArgs.append(argv_new[k]);
restOfArgs.append("
\\"
"
);
}
ALOGV("
Class name =
%s, args =
%s"
, className.string(), restOfArgs.string());
}
} else {
// We'
re in zygote mode.
maybeCreateDalvikCache();
if (startSystemServer) {
args.add(String8("
start-system-server"
));
}char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) =
=
0) {
LOG_ALWAYS_FATAL("
app_process: Unable to determine ABI list from property %s."
,
ABI_LIST_PROPERTY);
return 11;
}String8 abiFlag("
--abi-list=
"
);
abiFlag.append(prop);
args.add(abiFlag);
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (;
i <
argc;
+
+
i) {
args.add(String8(argv[i]));
}
}if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string(), true /* setProcName */);
}if (zygote) {
//此处见到了我们熟悉的ZygoteInit,但该方法的具体实现在//AndroidRuntime.start()
runtime.start("
com.android.internal.os.ZygoteInit"
, args, zygote);
} else if (className) {
runtime.start("
com.android.internal.os.RuntimeInit"
, args, zygote);
} else {
fprintf(stderr, "
Error: no class name or --zygote supplied.\\n"
);
app_usage();
LOG_ALWAYS_FATAL("
app_process: no class name or --zygote supplied."
);
}
}
上述代码总体比较简单,主要是处理相关参数,并创建AppRuntime,由于在init.rc文件中,app_process启动参数被设置为
--zygote --start-system-server
,因此会执行runtime.start("
com.android.internal.os.ZygoteInit"
, args, zygote)
,现在我们来看看AppRuntime的具体实现,它同样在 在/frameworks/base/cmds/app_process/app_main.cpp:
class AppRuntime : public AndroidRuntime
{
public:
AppRuntime(char* argBlockStart, const size_t argBlockLength)
: AndroidRuntime(argBlockStart, argBlockLength)
, mClass(NULL)
{
}void setClassNameAndArgs(const String8&
className, int argc, char * const *argv) {
mClassName =
className;
for (int i =
0;
i <
argc;
+
+
i) {
mArgs.add(String8(argv[i]));
}
}virtual void onVmCreated(JNIEnv* env)
{
if (mClassName.isEmpty()) {
return;
// Zygote. Nothing to do here.
}char* slashClassName =
toSlashClassName(mClassName.string());
mClass =
env->
FindClass(slashClassName);
if (mClass =
=
NULL) {
ALOGE("
ERROR: could not find class '
%s'
\\n"
, mClassName.string());
}
free(slashClassName);
mClass =
reinterpret_cast<
jclass>
(env->
NewGlobalRef(mClass));
}virtual void onStarted()
{
sp<
ProcessState>
proc =
ProcessState::self();
ALOGV("
App process: starting thread pool.\\n"
);
proc->
startThreadPool();
AndroidRuntime* ar =
AndroidRuntime::getRuntime();
ar->
callMain(mClassName, mClass, mArgs);
IPCThreadState::self()->
stopProcess();
}virtual void onZygoteInit()
{
sp<
ProcessState>
proc =
ProcessState::self();
ALOGV("
App process: starting thread pool.\\n"
);
proc->
startThreadPool();
}virtual void onExit(int code)
{
if (mClassName.isEmpty()) {
// if zygote
IPCThreadState::self()->
stopProcess();
}AndroidRuntime::onExit(code);
}String8 mClassName;
Vector<
String8>
mArgs;
jclass mClass;
};
AppRuntime继承AndroidRuntime,而AndroidRuntime位于
/frameworks/base/core/jni/AndroidRuntime.cpp.
而start()方法便是定义在AndroidRuntime的虚方法:
//这里的className的值就是com.android.intrnal.os.ZygoteInit
void AndroidRuntime::start(const char* className, const Vector<
String8>
&
options, bool zygote)
{
//...省略多行代码static const String8 startSystemServer("
start-system-server"
);
for (size_t i =
0;
i <
options.size();
+
+
i) {
if (options[i] =
=
startSystemServer) {
/* track our progress through the boot sequence */
const int LOG_BOOT_PROGRESS_START =
3000;
LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START,ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
}
}const char* rootDir =
getenv("
ANDROID_ROOT"
);
if (rootDir =
=
NULL) {
rootDir =
"
/system"
;
if (!hasDir("
/system"
)) {
LOG_FATAL("
No root directory specified, and /android does not exist."
);
return;
}
setenv("
ANDROID_ROOT"
, rootDir, 1);
}//1. 启动虚拟机
if (startVm(&
mjavaVM, &
env, zygote) !=
0) {
return;
}
onVmCreated(env);
//2. 调用startReg()注册JNI方法
if (startReg(env) <
0) {
ALOGE("
Unable to register all android natives\\n"
);
return;
}jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
stringClass =
env->
FindClass("
java/lang/String"
);
assert(stringClass !=
NULL);
strArray =
env->
NewObjectArray(options.size() +
1, stringClass, NULL);
assert(strArray !=
NULL);
classNameStr =
env->
NewStringUTF(className);
assert(classNameStr !=
NULL);
env->
SetObjectArrayElement(strArray, 0, classNameStr);
for (size_t i =
0;
i <
options.size();
+
+
i) {
jstring optionsStr =
env->
NewStringUTF(options.itemAt(i).string());
assert(optionsStr !=
NULL);
env->
SetObjectArrayElement(strArray, i +
1, optionsStr);
}char* slashClassName =
toSlashClassName(className);
jclass startClass =
env->
FindClass(slashClassName);
if (startClass =
=
NULL) {
ALOGE("
JavaVM unable to locate class '
%s'
\\n"
, slashClassName);
} else {
//3. 本质就是调用com.android.intrnal.os.ZygoteInit类的main函数
jmethodID startMeth =
env->
GetStaticMethodID(startClass, "
main"
,
"
([Ljava/lang/String;
)V"
);
if (startMeth =
=
NULL) {
ALOGE("
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
}
}
free(slashClassName);
// 省略多行代码
}
在start()方法中主要做三件事情:
1. 调用startVM()函数启动虚拟机
2. 调用startReg()注册JNI方法
3. 调用com.android.internal.os.ZygoteInit.java类的main函数.
走进ZygoteInit 关于前两者就不细说了,重点来关注我们熟悉的ZygoteInit.java.它在
rameworks/base/core/Java/com/android/internal/os/ZygoteInit.java,我们直接来看他的main方法:
public static void main(String argv[]) {
ZygoteServer zygoteServer =
new ZygoteServer();
ZygoteHooks.startZygoteNoThreadCreation();
try {
Os.setpgid(0, 0);
} catch (ErrnoException ex) {
throw new RuntimeException("
Failed to setpgid(0,0)"
, ex);
}try {
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "
ZygoteInit"
);
RuntimeInit.enableDdms();
// Start profiling the zygote initialization.
SamplingProfilerIntegration.start();
boolean startSystemServer =
false;
String socketName =
"
zygote"
;
String abiList =
null;
for (int i =
1;
i <
argv.length;
i+
+
) {
if ("
start-system-server"
.equals(argv[i])) {
startSystemServer =
true;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList =
argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName =
argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("
Unknown command line argument: "
+
argv[i]);
}
}if (abiList =
=
null) {
throw new RuntimeException("
No ABI list supplied."
);
}
//创建名为zygote的socket
zygoteServer.registerServerSocket(socketName);
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "
ZygotePreload"
);
//省略多行参数
SamplingProfilerIntegration.writeZygoteSnapshot();
// Do an initial gc to clean up after startup
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "
PostZygoteInitGC"
);
gcAndFinalize();
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
Trace.setTracingEnabled(false);
Zygote.nativeUnmountStorageOnInit();
ZygoteHooks.stopZygoteNoThreadCreation();
//由于在init.rc中设置了start-system-server参数,因此
//这里将启动SystemServer,可见SystemServer由Zygote创//建的第一个进程
if (startSystemServer) {
//启动SystemServer组件
startSystemServer(abiList, socketName, zygoteServer);
}Log.i(TAG, "
Accepting command socket connections"
);
//等待ActivityManagerService请求
zygoteServer.runSelectLoop(abiList);
zygoteServer.closeServerSocket();
} catch (Zygote.MethodAndArgsCaller caller) {
caller.run();
} catch (Throwable ex) {
Log.e(TAG, "
System zygote died with exception"
, ex);
zygoteServer.closeServerSocket();
throw ex;
}
}
这里的main()方法中主要做了三件事情
1. 通过
registerServerSocket()
来创建Socket,它将作为服务端用来和作为客户端的ActivityManagerService进行通信 2. 通过
startSystemServer()
方法来启动SystemServer 3. 最后通过通过
runSelectLoop
方法使得刚才创建的Socket进入无限循环,以等待来自ActivityManagerService请求Zygote中Socket创建 首先来看
resiterServerSocket()
它在:void registerServerSocket(String socketName) {
if (mServerSocket =
=
null) {
int fileDesc;
final String fullSocketName =
ANDROID_SOCKET_PREFIX +
socketName;
try {
String env =
System.getenv(fullSocketName);
//从环境变量env中获取文件描述符,
fileDesc =
Integer.parseInt(env);
} catch (RuntimeException ex) {
throw new RuntimeException(fullSocketName +
"
unset or invalid"
, ex);
}try {
//通过文件描述符创建socket,该描述符代表/dev/socket/zygote文件.
FileDescriptor fd =
new FileDescriptor();
fd.setInt$(fileDesc);
mServerSocket =
new LocalServerSocket(fd);
} catch (IOException ex) {
throw new RuntimeException(
"
Error binding to local socket '
"
+
fileDesc +
"
'
"
, ex);
}
}
}
方法主要通过文件描述符创建socket,该文件描述代表/dev/socket/zygote文件,现在看看开头init.rc中的配置:
socket zygote stream 660 root system
Zygote启动SystemServer 现在来看startSystemServer()方法:
private static boolean startSystemServer(String abiList, String socketName, ZygoteServer zygoteServer)
throws Zygote.MethodAndArgsCaller, RuntimeException {
long capabilities =
posixCapabilitiesAsBits(
OsConstants.CAP_IPC_LOCK,
OsConstants.CAP_KILL,
OsConstants.CAP_NET_ADMIN,
OsConstants.CAP_NET_BIND_SERVICE,
OsConstants.CAP_NET_BROADCAST,
OsConstants.CAP_NET_RAW,
OsConstants.CAP_SYS_MODULE,
OsConstants.CAP_SYS_NICE,
OsConstants.CAP_SYS_RESOURCE,
OsConstants.CAP_SYS_TIME,
OsConstants.CAP_SYS_TTY_CONFIG,
OsConstants.CAP_WAKE_ALARM
);
if (!SystemProperties.getBoolean(PROPERTY_RUNNING_IN_CONTAINER, false)) {
capabilities |=
posixCapabilitiesAsBits(OsConstants.CAP_BLOCK_SUSPEND);
}
/* Hardcoded command line to start the system server */
String args[] =
{
"
--setuid=
1000"
,
"
--setgid=
1000"
,
"
--setgroups=
1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1032,3001,3002,3003,3006,3007,3009,3010"
,
"
--capabilities=
"
+
capabilities +
"
,"
+
capabilities,
"
--nice-name=
system_server"
,
"
--runtime-args"
,
"
com.android.server.SystemServer"
,
};
ZygoteConnection.Arguments parsedArgs =
null;
int pid;
try {
parsedArgs =
new ZygoteConnection.Arguments(args);
ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
//创建子进程
pid =
Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}//pid=
0表示子进程,此处就是SystemServer进程
if (pid =
=
0) {
//用于处理系统中有两个Zygote进程的情况,由于通常我们不会配置两个Zygote,因此暂时不关注
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
//Zygote创建的子进程(此处就是SystemServer)不需要使用Zygote中创建的Socket文件描述符,因此通过closeServerSocket()关闭它.
zygoteServer.closeServerSocket();
handleSystemServerProcess(parsedArgs);
}return true;
}
这里首先通过Zygote.forkSystemServer()创建一个系统服务进程.与该方法相似还有forkAndSpecialize(),用于创建一个普通应用进程.进程创建成功后返回pid为0.由于此处生成的新进程和Zygote进程一模一样,也就是说这个新进程中同样包含了刚才创建的Socket,但是该Socket在此处无效,因此要将其关闭.接下来调用handleSystemServerProcess()处理刚才新建的进程即SystemServer进程,需要注意此时已经工作在SystemServer进程中了:
private static void handleSystemServerProcess(
ZygoteConnection.Arguments parsedArgs)
throws Zygote.MethodAndArgsCaller {
//省略多行代码,此处invokeWith为null
if (parsedArgs.invokeWith !=
null) {
String[] args =
parsedArgs.remainingArgs;
if (systemServerClasspath !=
null) {
//省略多行代码
} else {ClassLoader cl =
null;
if (systemServerClasspath !=
null) {
//为SysteServer进程创建PathClassLoader类加载器
cl =
createSystemServerClassLoader(systemServerClasspath,
parsedArgs.targetSdkVersion);
Thread.currentThread().setContextClassLoader(cl);
}RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
}}
该函数继续调用RuntimeInit.zygoteInit()进一步执行启动SystemServer组件的操作.继续来看 RuntimeInit.zygoteInit()的具体实现,它在
/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java文件中:
public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws Zygote.MethodAndArgsCaller {
//...省略多行代码commonInit();
nativeZygoteInit();
applicationInit(targetSdkVersion, argv, classLoader);
}
在该方法中主要调用了三个方法:
- commonInit():为当前进程的VM设置未捕获异常处理器
- nativeZygoteInit():Binder驱动初始化,该方法完成后,就可以通过该Binder进行进程通信
- applicationInit():主要用调用com.android.server.SystemServer类的main()方法
nativeZygoteInit()是一个本地方法,其对应实现在frameworks/base/core/jni/AndroidRuntime.cpp中:
static void com_android_internal_os_RuntimeInit_nativeZygoteInit(JNIEnv* env, jobject clazz)
{
gCurRuntime->
onZygoteInit();
}
这里的gCurRuntime是AppRuntime的指针,在frameworks/base/core/jni/AndroidRuntime.cpp中定义,并在AndroidRuntime的够赞函数中初始化:
//定义
static AndroidRuntime* gCurRuntime =
NULL;
...//在frameworks/base/cmds/app_process/app_main.cpp的main()方法中被调用
AndroidRuntime::AndroidRuntime(char* argBlockStart, const size_t argBlockLength) :
mExitWithoutCleanup(false),
mArgBlockStart(argBlockStart),
mArgBlockLength(argBlockLength)
{
SkGraphics::Init();
mOptions.setCapacity(20);
assert(gCurRuntime =
=
NULL);
gCurRuntime =
this;
}
继续来看onZygoteInit():
virtual void onZygoteInit()
{
sp<
ProcessState>
proc =
ProcessState::self();
ALOGV("
App process: starting thread pool.\\n"
);
proc->
startThreadPool();
}
这里调用ProcessState::startThreadPool()方法启动线程池,这个线程池就是用来和Binder驱动程序进程交互的.(Binder驱动本质就是一个文件,位于/dev/binder),关于线程池具体创建的过程暂不做说明.
现在来看applicationInit():
private static void applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
//省略多行代码
invokeStaticMain(args.startClass, args.startArgs, classLoader);
}
这里继续调用了invokeStaticMain()进行后续工作:
private static void invokeStaticMain(String className, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
Class<
?>
cl;
try {
cl =
Class.forName(className, true, classLoader);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"
Missing class when invoking static main "
+
className,
ex);
}Method m;
try {
m =
cl.getMethod("
main"
, new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
//...
} catch (SecurityException ex) {
//...
}// 省略多行代码/*
* This throw gets caught in ZygoteInit.main(), which responds
* by invoking the exception'
s run() method. This arrangement
* clears up all the stack frames that were required in setting
* up the process.
*/
throw new ZygoteInit.MethodAndArgsCaller(m, argv);
}
此时要执行的是com.android.server.SystemServer的中mian()方法.此外真正执行的过程是在Zygote.MethodAndArgsCaller的run()方法中:
public static class MethodAndArgsCaller extends Exception
implements Runnable {
/** method to call */
private final Method mMethod;
/** argument array */
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod =
method;
mArgs =
args;
}public void run() {
try {
mMethod.invoke(null, new Object[] { mArgs });
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
//省略多行代码
}
}
}
MethodAndArgsCaller继承Exception并实现Runnable接口,作为一个异常他被ZygoteInit.main()捕获并处理:
public static void main(String argv[]) {
// ...
try {
//...省略多行代码
startSystemServer(abiList, socketName);
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (Throwable ex) {
//...
}
}
现在SystemServer的
main()
已经被调用,我们顺着来看一下实现:public class SystemServer{public static void main(String[] args) {
new SystemServer().run();
}private void run() {
try {
//...省略一些初始化操作android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
//初始化主线程Looper
Looper.prepareMainLooper();
//创建SystemServiceManager对象
mSystemServiceManager =
new SystemServiceManager(mSystemContext);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}// 启动关键服务
startBootstrapServices();
//启动核心服务
startCoreServices();
//启动其他服务
startOtherServices();
//...省略多行代码//启动消息循环
Looper.loop();
}}
在main()方法中调用了run()方法继续启动操作.在run方法中这三个方法非常重要:
- startBootstrapServices():启动引导服务,比如AMS,PMS等
- startCoreServices():启动核心服务,比如BatteryService等
- startOtherServices():启动其他服务,比如NetworkStatsService等.
Socket循环监听 到目前为止,关于
ZygoteServer.registerServerSocket()
和startSystemServer()
的大体流程我们已经弄清除,接下来就是ZygoteServer.runSelectLoop()
方法:void runSelectLoop(String abiList) throws Zygote.MethodAndArgsCaller {
ArrayList<
FileDescriptor>
fds =
new ArrayList<
FileDescriptor>
();
ArrayList<
ZygoteConnection>
peers =
new ArrayList<
ZygoteConnection>
();
fds.add(mServerSocket.getFileDescriptor());
peers.add(null);
while (true) {
StructPollfd[] pollFds =
new StructPollfd[fds.size()];
for (int i =
0;
i <
pollFds.length;
+
+
i) {
pollFds[i] =
new StructPollfd();
pollFds[i].fd =
fds.get(i);
pollFds[i].events =
(short) POLLIN;
}
try {
Os.poll(pollFds, -1);
} catch (ErrnoException ex) {
throw new RuntimeException("
poll failed"
, ex);
}
for (int i =
pollFds.length - 1;
i >
=
0;
--i) {
if ((pollFds[i].revents &
POLLIN) =
=
0) {
continue;
}
if (i =
=
0) {
//监听Socket链接,如果你做过Socket编程就发现此处充当了服务端Socket
ZygoteConnection newPeer =
acceptCommandPeer(abiList);
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
//重点关注runOnce()方法
boolean done =
peers.get(i).runOnce(this);
if (done) {
peers.remove(i);
fds.remove(i);
}
}
}
}
}
该方法非常简单:不断的处理来自客户端AMS的请求,然后交给runOnce().此处可见Android 7.0应用启动流程分析
【Android系统启动流程分析】到现在为止,整个SystemServer进程的启动流程已经明确看,用一张顺序图大体的表示上述的整个流程:
文章图片
总结
- 系统启动时init进程会创建Zygote进程,Zygote进程负责后续Android应用框架层的其他进程的创建和启动.
- Zygote进程会首先创建一个SystemSever进程,然后由SystemServer负责启动系统关键服务,如ActivityManagerService或者PackageManagerService等.
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