Android学习（八）Zygote
Zygote
Zygote同ServiceManager都是由init解析rc脚本时启动的，相关脚本如下：
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server 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 |
Zygote的class所属为main，而不是core，和其同属组的系统进程有netd、debuggerd、rild等。
app_process的实现代码：
\Android4.4\frameworks\base\cmds\app_process\app_main.cpp
int main(int argc, char* const argv[]) {
mArgC = argc; mArgV = argv;
mArgLen = 0; for (int i=0; i<argc; i++) { mArgLen += strlen(argv[i]) + 1; } mArgLen--;
AppRuntime runtime; const char* 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);
// Parse runtime arguments. Stop at first unrecognized option. bool zygote = false; bool startSystemServer = false; bool application = false; const char* parentDir = NULL; const char* niceName = NULL; const char* className = NULL; while (i < argc) { const char* arg = argv[i++]; if (!parentDir) { parentDir = arg; } else if (strcmp(arg, "--zygote") == 0) { zygote = true; niceName = "zygote"; } 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 = arg + 12; } else { className = arg; break; } }
if (niceName && *niceName) { setArgv0(argv0, niceName); set_process_name(niceName); }
runtime.mParentDir = parentDir;
if (zygote) { runtime.start("com.android.internal.os.ZygoteInit", startSystemServer ? "start-system-server" : ""); } else if (className) { // Remainder of args get passed to startup class main() runtime.mClassName = className; runtime.mArgC = argc - i; runtime.mArgV = argv + i; runtime.start("com.android.internal.os.RuntimeInit", application ? "application" : "tool"); } 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; } } |
init.rc指定了—zygote选项，因此app_process会启动ZygoteInit并传入"start-system-server"参数。
AppRuntime runtime;的定义：class AppRuntime : public AndroidRuntime
runtime.start("com.android.internal.os.ZygoteInit",
startSystemServer ? "start-system-server" : "");
void AndroidRuntime::start(const char* className, const char* options) {
/* start the virtual machine */ JniInvocation jni_invocation; jni_invocation.Init(NULL); JNIEnv* env; if (startVm(&mJavaVM, &env) != 0) { return; } onVmCreated(env);
/* * Register android functions. */ if (startReg(env) < 0) { 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. */ jclass stringClass; jobjectArray strArray; jstring classNameStr; jstring optionsStr;
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); optionsStr = env->NewStringUTF(options); env->SetObjectArrayElement(strArray, 1, optionsStr);
/* * Start VM. This thread becomes the main thread of the VM, and will * not return until the VM exits. */ char* slashClassName = toSlashClassName(className); jclass startClass = env->FindClass(slashClassName); if (startClass == NULL) { ALOGE("JavaVM unable to locate class '%s'\n", slashClassName); /* keep going */ } else { 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);
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"); }
|
com.android.internal.os.ZygoteInit运行在java虚拟机状态。
看ZygoteInit.java：
public static void main(String argv[]) { try { // Start profiling the zygote initialization. SamplingProfilerIntegration.start();
registerZygoteSocket(); EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START, SystemClock.uptimeMillis()); preload(); EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END, SystemClock.uptimeMillis());
// Finish profiling the zygote initialization. SamplingProfilerIntegration.writeZygoteSnapshot();
// Do an initial gc to clean up after startup gc();
// Disable tracing so that forked processes do not inherit stale tracing tags from // Zygote. Trace.setTracingEnabled(false);
// If requested, start system server directly from Zygote if (argv.length != 2) { throw new RuntimeException(argv[0] + USAGE_STRING); }
if (argv[1].equals("start-system-server")) { startSystemServer(); } else if (!argv[1].equals("")) { throw new RuntimeException(argv[0] + USAGE_STRING); }
Log.i(TAG, "Accepting command socket connections");
runSelectLoop();
closeServerSocket(); } catch (MethodAndArgsCaller caller) { caller.run(); } catch (RuntimeException ex) { Log.e(TAG, "Zygote died with exception", ex); closeServerSocket(); throw ex; } } |
刚才传入了参数"start-system-server"所以会调用startSystemServer();来启动SystemServer。
private static boolean startSystemServer() throws MethodAndArgsCaller, RuntimeException { long capabilities = posixCapabilitiesAsBits( 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 ); /* Hardcoded command line to start the system server */ String args[] = { "--setuid=1000", "--setgid=1000", "--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1032,3001,3002,3003,3006,3007", "--capabilities=" + capabilities + "," + capabilities, "--runtime-init", "--nice-name=system_server", "com.android.server.SystemServer", }; ZygoteConnection.Arguments parsedArgs = null;
int pid;
try { parsedArgs = new ZygoteConnection.Arguments(args); ZygoteConnection.applyDebuggerSystemProperty(parsedArgs); ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);
/* Request to fork the system server process */ 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) { handleSystemServerProcess(parsedArgs); }
return true; } |
"com.android.server.SystemServer"作为子进程被创建：
public static void main(String[] args) { if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) { // If a device's clock is before 1970 (before 0), a lot of // APIs crash dealing with negative numbers, notably // java.io.File#setLastModified, so instead we fake it and // hope that time from cell towers or NTP fixes it // shortly. Slog.w(TAG, "System clock is before 1970; setting to 1970."); SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME); }
if (SamplingProfilerIntegration.isEnabled()) { SamplingProfilerIntegration.start(); timer = new Timer(); timer.schedule(new TimerTask() { @Override public void run() { SamplingProfilerIntegration.writeSnapshot("system_server", null); } }, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL); }
// Mmmmmm... more memory! dalvik.system.VMRuntime.getRuntime().clearGrowthLimit();
// The system server has to run all of the time, so it needs to be // as efficient as possible with its memory usage. VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
Environment.setUserRequired(true);
System.loadLibrary("android_servers");
Slog.i(TAG, "Entered the Android system server!");
// Initialize native services. nativeInit();
// This used to be its own separate thread, but now it is // just the loop we run on the main thread. ServerThread thr = new ServerThread(); thr.initAndLoop(); } |
这个地方4.4的代码与2.3的代码有些区别，4.4代码中不再system_init.cpp文件，其他服务的初始化都是在ServerThread thr = new ServerThread();中进行的。
SystemServer中加载android_servers.so库文件，nativeInit是一个jni调用：
\Android4.4\frameworks\base\services\jni\ com_android_server_SystemServer.cpp
#include <jni.h> #include <JNIHelp.h>
#include <sensorservice/SensorService.h>
#include <cutils/properties.h> #include <utils/Log.h> #include <utils/misc.h>
namespace android {
static void android_server_SystemServer_nativeInit(JNIEnv* env, jobject clazz) { char propBuf[PROPERTY_VALUE_MAX]; property_get("system_init.startsensorservice", propBuf, "1"); if (strcmp(propBuf, "1") == 0) { // Start the sensor service SensorService::instantiate(); } }
/* * JNI registration. */ static JNINativeMethod gMethods[] = { /* name, signature, funcPtr */ { "nativeInit", "()V", (void*) android_server_SystemServer_nativeInit }, };
int register_android_server_SystemServer(JNIEnv* env) { return jniRegisterNativeMethods(env, "com/android/server/SystemServer", gMethods, NELEM(gMethods)); }
}; // namespace android |
可见4.4中的nativeInit中只做了SensorService的初始化。
这里只看到了Zygote的启动流程，对一系列系统服务做了初始操作，4.4的代码和2.3的代码在结构上有些差别，进一步的学习，后面继续。