zygote进程实际是通过init.zygote64.rc文件解析
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
//main方法
class main
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart media
onrestart restart netd
writepid /dev/cpuset/foreground/tasks
对应的是 /frameworks/base/cmds/app_process/app_main.cpp的main方法
int main(int argc, char* const argv[])
{
//过滤第一个参数
argc--;
argv++;
String8 niceName;
String8 className;
++i;
//解析参数
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) {
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);
} else {
maybeCreateDalvikCache();
//如果startSystemServer为true的话(默认是true)，将start-system-server放到启动的参数args
if (startSystemServer) {
args.add(String8("start-system-server"));
}
.....
}
if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string());
set_process_name(niceName.string());
}
if (zygote) {
//runtime实际是AndroidRuntime
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.");
return 10;
}
}
实际最终走的是AndroidRuntime的start方法
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
//className是com.android.internal.os.ZygoteInit
JNIEnv* env;
//1、创建jvm虚拟机
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
/*
* 2、注册Android JNI
*/
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);
//创建数组
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
assert(strArray != NULL);
//className=com.android.internal.os.ZygoteInit
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) {
} else {
//通过JNI调用ZygoteInit的main函数
jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
"([Ljava/lang/String;)V");
}
free(slashClassName);
}
AndroidRuntime.start主要做以下几件事情
- 创建jvm
- 注册JNI方法
- 找到ZygoteInit的main方法
- 通过JNI执行ZygoteInit.main方法,回到Java层
image.png
Zygote的Java世界
public static void main(String argv[]) {
try {
//1、创建一个服务端zygote的socket
registerZygoteSocket(socketName);
//2、预加载资源
preload();
if (startSystemServer) {
//3、启动SystemServer
startSystemServer(abiList, socketName);
}
Log.i(TAG, "Accepting command socket connections");
//4、等待客户端请求
runSelectLoop(abiList);
closeServerSocket();
} catch (MethodAndArgsCaller caller) {
caller.run();
} catch (RuntimeException ex) {
Log.e(TAG, "Zygote died with exception", ex);
closeServerSocket();
throw ex;
}
}
registerZygoteSocket源码分析
private static void registerZygoteSocket(String socketName) {
if (sServerSocket == null) {
int fileDesc;
final String fullSocketName = ANDROID_SOCKET_PREFIX + socketName;
try {
String env = System.getenv(fullSocketName);
fileDesc = Integer.parseInt(env);
} catch (RuntimeException ex) {
throw new RuntimeException(fullSocketName + " unset or invalid", ex);
}
try {
FileDescriptor fd = new FileDescriptor();
fd.setInt$(fileDesc);
sServerSocket = new LocalServerSocket(fd);
} catch (IOException ex) {
throw new RuntimeException(
"Error binding to local socket '" + fileDesc + "'", ex);
}
}
}
实际就是创建了一个LocalServerSocket,也就是Socket的本地服务端
preload源码分析
static void preload() {
//预加载类
preloadClasses();
//预加载资源，如drawable和color
preloadResources();
//预加载opengl
preloadOpenGL();
//预加载 "android", "compiler_rt", "jnigraphics" 这3个共享库
preloadSharedLibraries();
//预加载文本资源
preloadTextResources();
// 仅用于 zygote 进程，用于内存共享的进程
WebViewFactory.prepareWebViewInZygote();
}
启动SystemServer进程
private static boolean startSystemServer(String abiList, String socketName)
throws MethodAndArgsCaller, RuntimeException {
//1、设置启动参数，进程和进程组为1000，进程名为system_server，启动名字为"com.android.server.SystemServer"
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",
"--capabilities=" + capabilities + "," + capabilities,
"--nice-name=system_server",
"--runtime-args",
"com.android.server.SystemServer",
};
ZygoteConnection.Arguments parsedArgs = null;
int pid;
try {
//2、参数封装成Arguments对象
parsedArgs = new ZygoteConnection.Arguments(args);
ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);
ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
//3、创建一个子进程
pid = Zygote.forkSystemServer(
parsedArgs.uid, parsedArgs.gid,
parsedArgs.gids,
parsedArgs.debugFlags,
null,
parsedArgs.permittedCapabilities,
parsedArgs.effectiveCapabilities);
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
if (pid == 0) {
if (hasSecondZygote(abiList)) {
waitForSecondaryZygote(socketName);
}
//4、启动SystemServer进程
handleSystemServerProcess(parsedArgs);
}
return true;
}
runSelectLoop
private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {
ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();
ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
//sServerSocket是刚才registerZygoteSocket 创建的LocalServerSocket
fds.add(sServerSocket.getFileDescriptor());
peers.add(null);
while (true) {
//死循环获取ActivityManagerService请求Zygote进程创建新的应用程序进程
StructPollfd[] pollFds = new StructPollfd[fds.size()];
//fds转移到pollFds
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) {
//0则表示服务端和客户端连接上
ZygoteConnection newPeer = acceptCommandPeer(abiList);
//将得到的ZygoteConnection 添加到peers中
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
//创建一个新的应用程序进程
boolean done = peers.get(i).runOnce();
if (done) {
peers.remove(i);
fds.remove(i);
}
}
}
}
}
boolean runOnce() throws ZygoteInit.MethodAndArgsCaller {
String args[];
Arguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
//读取socket的参数列表
args = readArgumentList();
descriptors = mSocket.getAncillaryFileDescriptors();
} catch (IOException ex) {
closeSocket();
return true;
}
try {
//将读取到参数封装成Arguments
parsedArgs = new Arguments(args);
if (parsedArgs.abiListQuery) {
return handleAbiListQuery();
}
//创建子进程
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
parsedArgs.niceName, fdsToClose, parsedArgs.instructionSet,
parsedArgs.appDataDir);
} catch (ErrnoException ex) {
}
try {
if (pid == 0) {
// i子进程
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);
return true;
} else {
//父进程
IoUtils.closeQuietly(childPipeFd);
childPipeFd = null;
return handleParentProc(pid, descriptors, serverPipeFd, parsedArgs);
}
} finally {
IoUtils.closeQuietly(childPipeFd);
IoUtils.closeQuietly(serverPipeFd);
}
}
总结
- 创建AppRuntime并调用start方法，创建zygote进程
- 注册JNI方法
- 通过JNI调用ZygoteInit的main函数进入Zygote的Java框架层
- 通过registerZygoteSocket创建本地socket的服务端，并通过runSelectLoop等待ActivityManagerService的请求来创建新的进程
- 启动SystemServer进程
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