上一篇讲到Android系统的孵化准备阶段，有了准备阶段的环境，接下来进入孵化阶段。Android系统在孵化完成之后便是启动系统的各项服务，孵化过程中将会创建JVM, 预加载资源，预加载系统类，创建Android运行时等。
Android系统孵化流程图
Android系统启动孵化
frameworks/base/cmds/app_process/app_main.cpp
int main(int argc, char* const argv[])
{
if (!LOG_NDEBUG) { //打印启动参数
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)); //传递参数
// Process command line arguments
// ignore argv[0]
//忽略argv[0] = /system/bin
argc--;
argv++;
// Everything up to '--' or first non '-' arg goes to the vm.
//
// The first argument after the VM args is the "parent dir", which
// is currently unused.
//
// After the parent dir, we expect one or more the following internal
// arguments :
//
// --zygote : Start in zygote mode 启动模式
// --start-system-server : Start the system server. 启动系统服务
// --application : Start in application (stand alone, non zygote) mode. 启动应用
// --nice-name : The nice name for this process. 进程优先级
//
//非孵化启动，参数是类名，所有剩余参数传递到此类的main方法
// For non zygote starts, these arguments will be followed by
// the main class name. All remaining arguments are passed to
// the main method of this class.
//
//孵化启动所有参数将传递到zygote的main函数
// For zygote starts, all remaining arguments are passed to the zygote.
// main function.
//
//我们在重写参数且设置优先级到argv0前必须拷贝参数
// Note that we must copy argument string values since we will rewrite the
// entire argument block when we apply the nice name to argv0.
//
//作为上述规则的例外，“间隔命令”中的任何东西都可以进入VM
// As an exception to the above rule, anything in "spaced commands"
// goes to the vm even though it has a space in it.
const char* spaced_commands[] = { "-cp", "-classpath" };
//允许“间隔命令”完全由1个参数（不含-s）成功
// Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).
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) { // 字符串比较
known_command = true;
ALOGV("app_process main found known command '%s'", argv[i]);
}
}
//跳过 - 或 -- 字符
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; //zygote 或 zygote64
} else if (strcmp(arg, "--start-system-server") == 0) {
startSystemServer = true; //系统服务
} else if (strcmp(arg, "--application") == 0) {
application = true; //应用
} else if (strncmp(arg, "--nice-name=", 12) == 0) {
niceName.setTo(arg + 12); //优先级
} else if (strncmp(arg, "--", 2) != 0) {
className.setTo(arg); //类名
break;
} else {
--i;
break;
}
}
Vector<String8> args;
if (!className.isEmpty()) { //不为空 non zygote
// We're not in zygote mode, the only argument we need to pass
// to RuntimeInit is the application argument.
//
// The Remainder of args get passed to startup class main(). Make
// copies of them before we overwrite them with the process name.
args.add(application ? String8("application") : String8("tool"));
runtime.setClassNameAndArgs(className, argc - i, argv + i);
if (!LOG_NDEBUG) { //打印
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) { //启动系统服务
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) { //取硬件架构属性
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); //加入参数数组
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) { //优先级
runtime.setArgv0(niceName.string(), true /* setProcName */);
}
if (zygote) { //是否启动孵化
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
} else if (className) { //是否启动初始化类
runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
} else {
// supplied 缺失
fprintf(stderr, "Error: no class name or --zygote supplied.\n");
app_usage();
LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
}
}Android运行时启动
frameworks/base/core/jni/AndroidRuntime.cpp
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");
/*
* 'startSystemServer == true' means runtime is obsolete and not run from
* init.rc anymore, so we print out the boot start event here.
*/
for (size_t i = 0; i < options.size(); ++i) {
if (options[i] == startSystemServer) {
/* track our progress through the boot sequence */
//通过启动序列跟踪进度
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);
}
//const char* kernelHack = getenv("LD_ASSUME_KERNEL");
//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);
/* start the virtual machine */
//启动JAVA虚拟机
JniInvocation jni_invocation;
jni_invocation.Init(NULL); //执行初始化 参数为 NULL nothing to do
JNIEnv* env;
if (startVm(&mJavaVM, &env, zygote) != 0) { //2.1启动JAVA虚拟机
return;
}
onVmCreated(env);
/*
* Register android functions.
*/
if (startReg(env) < 0) { //2.2注册JNI函数
ALOGE("Unable to register all android natives\n");
return;
}
/*
* We want to call main() with a String array with arguments in it.
* At present we have two arguments, the class name and an option string.
* Create an array to hold them.
*/
//创建array[] “装载” 类的main()函数参数
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
stringClass = env->FindClass("java/lang/String"); //加载 String 类
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);
}
/*
* Start VM. This thread becomes the main thread of the VM, and will
* not return until the VM exits.
*/
//启动虚拟机,当前线程变为虚拟机的主线程
char* slashClassName = toSlashClassName(className);
jclass startClass = env->FindClass(slashClassName); //jni_internal.cc
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
jmethodID startMeth = env->GetStaticMethodID(startClass, "main", //类的main方法 ps: zygote main()方法
"([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); //2.3调用 main() 方法
#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env); //捕获虚拟机异常
#endif
}
}
free(slashClassName); //释放
ALOGD("Shutting down VM\n");
if (mJavaVM->DetachCurrentThread() != JNI_OK)
ALOGW("Warning: unable to detach main thread\n");
if (mJavaVM->DestroyJavaVM() != 0)
ALOGW("Warning: VM did not shut down cleanly\n");
}启动Android虚拟机
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote) // 启动JAVA虚拟机
{
JavaVMInitArgs initArgs; //虚拟机初始化参数
char propBuf[PROPERTY_VALUE_MAX];
......
/*
* 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(pJavaVM, pEnv, &initArgs) < 0) { //创建虚拟机 java_vm_ext.cc
ALOGE("JNI_CreateJavaVM failed\n");
return -1;
}
return 0;
}注册JNI函数，为虚拟机搭桥
/*
* Register android native functions with the VM.
*/
/*static*/ int AndroidRuntime::startReg(JNIEnv* env) // 注册 JNI 桥函数
{
ATRACE_NAME("RegisterAndroidNatives");
/*
* This hook causes all future threads created in this process to be
* attached to the JavaVM. (This needs to go away in favor of JNI
* Attach calls.)
*/
androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc); //创建线程
ALOGV("--- registering native functions ---\n");
/*
* Every "register" function calls one or more things that return
* a local reference (e.g. FindClass). Because we haven't really
* started the VM yet, they're all getting stored in the base frame
* and never released. Use Push/Pop to manage the storage.
*/
env->PushLocalFrame(200);
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) { //执行注册JNI函数
env->PopLocalFrame(NULL);
return -1;
}
env->PopLocalFrame(NULL);
//createJavaThread("fubar", quickTest, (void*) "hello");
return 0;
}Android系统孵化流程
framework/base/core/java/com/android/internel/os/ZygoteInit.java
public static void main(String argv[]) { // 由JAVA虚拟机启动，具体见AndroidRuntime.start()
ZygoteServer zygoteServer = new ZygoteServer(); //孵化服务端
// Mark zygote start. This ensures that thread creation will throw
// an error.
ZygoteHooks.startZygoteNoThreadCreation();
// Zygote goes into its own process group.
try {
Os.setpgid(0, 0); //进入进程组
} catch (ErrnoException ex) {
throw new RuntimeException("Failed to setpgid(0,0)", ex);
}
try {
// Report Zygote start time to tron unless it is a runtime restart
if (!"1".equals(SystemProperties.get("sys.boot_completed"))) {
MetricsLogger.histogram(null, "boot_zygote_init",
(int) SystemClock.elapsedRealtime());
}
String bootTimeTag = Process.is64Bit() ? "Zygote64Timing" : "Zygote32Timing";
BootTimingsTraceLog bootTimingsTraceLog = new BootTimingsTraceLog(bootTimeTag,
Trace.TRACE_TAG_DALVIK);
bootTimingsTraceLog.traceBegin("ZygoteInit"); //跟踪孵化
RuntimeInit.enableDdms(); //使能DDMS
// Start profiling the zygote initialization.
SamplingProfilerIntegration.start(); //采样初始化
boolean startSystemServer = false;
String socketName = "zygote";
String abiList = null;
boolean enableLazyPreload = false;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
startSystemServer = true; //加载系统服务
} else if ("--enable-lazy-preload".equals(argv[i])) {
enableLazyPreload = true; // 预加载类
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length()); //处理器架构列表
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName = argv[i].substring(SOCKET_NAME_ARG.length()); //套接名 zygote
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}
if (abiList == null) {
throw new RuntimeException("No ABI list supplied.");
}
zygoteServer.registerServerSocket(socketName); //注册孵化套接
// In some configurations, we avoid preloading resources and classes eagerly.
// In such cases, we will preload things prior to our first fork.
if (!enableLazyPreload) {
bootTimingsTraceLog.traceBegin("ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload(bootTimingsTraceLog); //3.1类加载，耗时操作
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
bootTimingsTraceLog.traceEnd(); // ZygotePreload
} else {
Zygote.resetNicePriority(); //重置 nice 优先级
}
// Finish profiling the zygote initialization.
SamplingProfilerIntegration.writeZygoteSnapshot(); //套接快照
// Do an initial gc to clean up after startup
bootTimingsTraceLog.traceBegin("PostZygoteInitGC"); //孵化GC
gcAndFinalize(); //GC和回收
bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC
bootTimingsTraceLog.traceEnd(); // ZygoteInit
// Disable tracing so that forked processes do not inherit stale tracing tags from
// Zygote.
Trace.setTracingEnabled(false);
// Zygote process unmounts root storage spaces.
Zygote.nativeUnmountStorageOnInit();
// Set seccomp policy
Seccomp.setPolicy();
ZygoteHooks.stopZygoteNoThreadCreation();
if (startSystemServer) {
startSystemServer(abiList, socketName, zygoteServer); //3.2启动系统服务
}
Log.i(TAG, "Accepting command socket connections");
zygoteServer.runSelectLoop(abiList); //3.2进入循环
zygoteServer.closeServerSocket(); // 关闭套接
} catch (Zygote.MethodAndArgsCaller caller) { // 3.4 异常回调
caller.run(); // 非常有趣
} catch (Throwable ex) {
Log.e(TAG, "System zygote died with exception", ex);
zygoteServer.closeServerSocket();
throw ex;
}
}3.1 加载系统类，启动耗时操作
static void preload(BootTimingsTraceLog bootTimingsTraceLog) {
Log.d(TAG, "begin preload");
bootTimingsTraceLog.traceBegin("BeginIcuCachePinning");
beginIcuCachePinning();
bootTimingsTraceLog.traceEnd(); // BeginIcuCachePinning
bootTimingsTraceLog.traceBegin("PreloadClasses");
preloadClasses(); //预加载框架类
bootTimingsTraceLog.traceEnd(); // PreloadClasses
bootTimingsTraceLog.traceBegin("PreloadResources");
preloadResources(); //预加载系统资源
bootTimingsTraceLog.traceEnd(); // PreloadResources
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "PreloadOpenGL");
preloadOpenGL(); //预加载OpenGl
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
preloadSharedLibraries(); //预加载共享库
preloadTextResources(); //预加载文理资源
// Ask the WebViewFactory to do any initialization that must run in the zygote process,
// for memory sharing purposes.
WebViewFactory.prepareWebViewInZygote();
endIcuCachePinning();
warmUpJcaProviders();
Log.d(TAG, "end preload");
sPreloadComplete = true; //加载完成
}3.2 启动系统服务
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_PTRACE,
OsConstants.CAP_SYS_TIME,
OsConstants.CAP_SYS_TTY_CONFIG,
OsConstants.CAP_WAKE_ALARM
);
/* Containers run without this capability, so avoid setting it in that case */
if (!SystemProperties.getBoolean(PROPERTY_RUNNING_IN_CONTAINER, false)) {
capabilities |= posixCapabilitiesAsBits(OsConstants.CAP_BLOCK_SUSPEND);
}
/* Hardcoded command line to start the system server */
//硬编码指令启动系统服务
String args[] = {
"--setuid=1000",
"--setgid=1000",
"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,1032,3001,3002,3003,3006,3007,3009,3010",
"--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); //使用ZygoteConnection启动连接
ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
/* Request to fork the system server process */
//启动系统服务进程
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
/* For child process */
if (pid == 0) {
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
zygoteServer.closeServerSocket();
handleSystemServerProcess(parsedArgs);
}
return true;
}
}处理系统服务进程，载入SystemServer类，并执行Zygote初始化
private static void handleSystemServerProcess(
ZygoteConnection.Arguments parsedArgs)
throws Zygote.MethodAndArgsCaller {
// set umask to 0077 so new files and directories will default to owner-only permissions.
Os.umask(S_IRWXG | S_IRWXO);
if (parsedArgs.niceName != null) {
Process.setArgV0(parsedArgs.niceName);
}
final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
if (systemServerClasspath != null) {
performSystemServerDexOpt(systemServerClasspath); //执行dexOpt操作
// Capturing profiles is only supported for debug or eng builds since selinux normally
// prevents it.
boolean profileSystemServer = SystemProperties.getBoolean(
"dalvik.vm.profilesystemserver", false);
if (profileSystemServer && (Build.IS_USERDEBUG || Build.IS_ENG)) {
try {
File profileDir = Environment.getDataProfilesDePackageDirectory(
Process.SYSTEM_UID, "system_server");
File profile = new File(profileDir, "primary.prof");
profile.getParentFile().mkdirs();
profile.createNewFile();
String[] codePaths = systemServerClasspath.split(":");
VMRuntime.registerAppInfo(profile.getPath(), codePaths);
} catch (Exception e) {
Log.wtf(TAG, "Failed to set up system server profile", e);
}
}
}
if (parsedArgs.invokeWith != null) {
String[] args = parsedArgs.remainingArgs;
// If we have a non-null system server class path, we'll have to duplicate the
// existing arguments and append the classpath to it. ART will handle the classpath
// correctly when we exec a new process.
if (systemServerClasspath != null) {
String[] amendedArgs = new String[args.length + 2];
amendedArgs[0] = "-cp";
amendedArgs[1] = systemServerClasspath;
System.arraycopy(args, 0, amendedArgs, 2, args.length);
args = amendedArgs;
}
WrapperInit.execApplication(parsedArgs.invokeWith,
parsedArgs.niceName, parsedArgs.targetSdkVersion,
VMRuntime.getCurrentInstructionSet(), null, args);
} else {
//重新载入SystemServer类
ClassLoader cl = null;
if (systemServerClasspath != null) {
cl = createPathClassLoader(systemServerClasspath, parsedArgs.targetSdkVersion);
Thread.currentThread().setContextClassLoader(cl);
}
/*
* Pass the remaining arguments to SystemServer.
*/
ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion, parsedArgs.remainingArgs, cl);
}
/* should never reach here */
}3.3 接收来自系统或应用层的创建诉求
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framework/base/core/java/com/android/internel/os/ZygoteServer.java
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) {
ZygoteConnection newPeer = acceptCommandPeer(abiList);
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
boolean done = peers.get(i).runOnce(this); //3.4调用runOnce创建进程
if (done) {
peers.remove(i);
fds.remove(i);
}
}
}
}
}接受来自系统的连接请求
framework/base/core/java/com/android/internel/os/ZygoteConnection .java
private ZygoteConnection acceptCommandPeer(String abiList) {
try {
return createNewConnection(mServerSocket.accept(), abiList);
} catch (IOException ex) {
throw new RuntimeException(
"IOException during accept()", ex);
}
}
protected ZygoteConnection createNewConnection(LocalSocket socket, String abiList)
throws IOException {
return new ZygoteConnection(socket, abiList);
}3.4 创建应用进程
boolean runOnce(ZygoteServer zygoteServer) throws Zygote.MethodAndArgsCaller {
String args[];
Arguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
args = readArgumentList();
descriptors = mSocket.getAncillaryFileDescriptors();
} catch (IOException ex) {
Log.w(TAG, "IOException on command socket " + ex.getMessage());
closeSocket();
return true;
}
if (args == null) {
// EOF reached.
closeSocket();
return true;
}
/** the stderr of the most recent request, if avail */
PrintStream newStderr = null;
if (descriptors != null && descriptors.length >= 3) {
newStderr = new PrintStream(
new FileOutputStream(descriptors[2]));
}
int pid = -1;
FileDescriptor childPipeFd = null;
FileDescriptor serverPipeFd = null;
try {
parsedArgs = new Arguments(args);
if (parsedArgs.abiListQuery) {
return handleAbiListQuery();
}
if (parsedArgs.preloadDefault) {
return handlePreload();
}
if (parsedArgs.preloadPackage != null) {
return handlePreloadPackage(parsedArgs.preloadPackage,
parsedArgs.preloadPackageLibs, parsedArgs.preloadPackageCacheKey);
}
if (parsedArgs.permittedCapabilities != 0 || parsedArgs.effectiveCapabilities != 0) {
throw new ZygoteSecurityException("Client may not specify capabilities: " +
"permitted=0x" + Long.toHexString(parsedArgs.permittedCapabilities) +
", effective=0x" + Long.toHexString(parsedArgs.effectiveCapabilities));
}
applyUidSecurityPolicy(parsedArgs, peer);
applyInvokeWithSecurityPolicy(parsedArgs, peer);
applyDebuggerSystemProperty(parsedArgs);
applyInvokeWithSystemProperty(parsedArgs);
int[][] rlimits = null;
if (parsedArgs.rlimits != null) {
rlimits = parsedArgs.rlimits.toArray(intArray2d);
}
int[] fdsToIgnore = null;
if (parsedArgs.invokeWith != null) {
FileDescriptor[] pipeFds = Os.pipe2(O_CLOEXEC);
childPipeFd = pipeFds[1];
serverPipeFd = pipeFds[0];
Os.fcntlInt(childPipeFd, F_SETFD, 0);
fdsToIgnore = new int[] { childPipeFd.getInt$(), serverPipeFd.getInt$() };
}
/**
* In order to avoid leaking descriptors to the Zygote child,
* the native code must close the two Zygote socket descriptors
* in the child process before it switches from Zygote-root to
* the UID and privileges of the application being launched.
*
* In order to avoid "bad file descriptor" errors when the
* two LocalSocket objects are closed, the Posix file
* descriptors are released via a dup2() call which closes
* the socket and substitutes an open descriptor to /dev/null.
*/
int [] fdsToClose = { -1, -1 };
FileDescriptor fd = mSocket.getFileDescriptor();
if (fd != null) {
fdsToClose[0] = fd.getInt$();
}
fd = zygoteServer.getServerSocketFileDescriptor();
if (fd != null) {
fdsToClose[1] = fd.getInt$();
}
fd = null;
// 创建线程
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
parsedArgs.niceName, fdsToClose, fdsToIgnore, parsedArgs.instructionSet,
parsedArgs.appDataDir);
} catch (ErrnoException ex) {
logAndPrintError(newStderr, "Exception creating pipe", ex);
} catch (IllegalArgumentException ex) {
logAndPrintError(newStderr, "Invalid zygote arguments", ex);
} catch (ZygoteSecurityException ex) {
logAndPrintError(newStderr,
"Zygote security policy prevents request: ", ex);
}
try {
if (pid == 0) {
// in child
zygoteServer.closeServerSocket();
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
//处理子进程
handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);
// should never get here, the child is expected to either
// throw Zygote.MethodAndArgsCaller or exec().
return true;
} else {
// in parent...pid of < 0 means failure
IoUtils.closeQuietly(childPipeFd);
childPipeFd = null;
return handleParentProc(pid, descriptors, serverPipeFd, parsedArgs);
}
} finally {
IoUtils.closeQuietly(childPipeFd);
IoUtils.closeQuietly(serverPipeFd);
}
}处理子进程
private void handleChildProc(Arguments parsedArgs,
FileDescriptor[] descriptors, FileDescriptor pipeFd, PrintStream newStderr)
throws Zygote.MethodAndArgsCaller {
/**
* By the time we get here, the native code has closed the two actual Zygote
* socket connections, and substituted /dev/null in their place. The LocalSocket
* objects still need to be closed properly.
*/
closeSocket();
if (descriptors != null) {
try {
Os.dup2(descriptors[0], STDIN_FILENO);
Os.dup2(descriptors[1], STDOUT_FILENO);
Os.dup2(descriptors[2], STDERR_FILENO);
for (FileDescriptor fd: descriptors) {
IoUtils.closeQuietly(fd);
}
newStderr = System.err;
} catch (ErrnoException ex) {
Log.e(TAG, "Error reopening stdio", ex);
}
}
if (parsedArgs.niceName != null) {
Process.setArgV0(parsedArgs.niceName);
}
// End of the postFork event.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
if (parsedArgs.invokeWith != null) {
WrapperInit.execApplication(parsedArgs.invokeWith, //exec Appllication
parsedArgs.niceName, parsedArgs.targetSdkVersion,
VMRuntime.getCurrentInstructionSet(),
pipeFd, parsedArgs.remainingArgs);
} else {
ZygoteInit.zygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs, null /* classLoader */);
}
} public static final void zygoteInit(int targetSdkVersion, String[] argv, //zygoteInit.java
ClassLoader classLoader) throws Zygote.MethodAndArgsCaller {
if (RuntimeInit.DEBUG) {
Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams();
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit(); //启动线程池
RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader); //执行
}int register_com_android_internal_os_ZygoteInit(JNIEnv* env) //AndroidRuntime.cpp
{
const JNINativeMethod methods[] = {
{ "nativeZygoteInit", "()V",
(void*) com_android_internal_os_ZygoteInit_nativeZygoteInit },
};
return jniRegisterNativeMethods(env, "com/android/internal/os/ZygoteInit",
methods, NELEM(methods));
}static void com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env, jobject clazz)
{
gCurRuntime->onZygoteInit();
}加入线程池
virtual void onZygoteInit() //app_main.cpp
{
sp<ProcessState> proc = ProcessState::self();
ALOGV("App process: starting thread pool.\n");
proc->startThreadPool();
}应用初始化
framework/base/core/java/com/android/internel/os/RuntimeInit .java
protected static void applicationInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws Zygote.MethodAndArgsCaller {
// If the application calls System.exit(), terminate the process
// immediately without running any shutdown hooks. It is not possible to
// shutdown an Android application gracefully. Among other things, the
// Android runtime shutdown hooks close the Binder driver, which can cause
// leftover running threads to crash before the process actually exits.
nativeSetExitWithoutCleanup(true);
// We want to be fairly aggressive about heap utilization, to avoid
// holding on to a lot of memory that isn't needed.
VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
final Arguments args;
try {
args = new Arguments(argv);
} catch (IllegalArgumentException ex) {
Slog.e(TAG, ex.getMessage());
// let the process exit
return;
}
// The end of of the RuntimeInit event (see #zygoteInit).
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
// Remaining arguments are passed to the start class's static main
invokeStaticMain(args.startClass, args.startArgs, classLoader);
}执行类加载并抛出异常，该异常一直会随着方法链，返回到ZygoteInit的main函数，然后被捕获
private static void invokeStaticMain(String className, String[] argv, ClassLoader classLoader)
throws Zygote.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) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
/*
* 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 Zygote.MethodAndArgsCaller(m, argv); //抛出异常
}使用异常和反射机制处理诉求
framework/base/core/java/com/android/internel/os/Zygote.java
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 }); // 反射调用
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
Throwable cause = ex.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException(ex);
}
}
}至此系统孵化完毕，runSelectLoop函数将一直等待系统诉求；下一篇我们讲Binder机制，Android8.0最大的更新就是Binder架构的变动，Google推出的Treble计划旨在提升系统更新的速度，在系统中将存在三个binder，一个用于系统框架，一个用于vnd, 最后一个用于HAL硬件抽象层。理解Binder对理解Android系统至关重要，它在Android系统中可以说无处不在；