Android系统启动-zygote篇

/frameworks/base/cmds/app_process/App_main.cpp （内含AppRuntime类）  /frameworks/base/core/jni/AndroidRuntime.cpp  /frameworks/base/core/java/com/android/internal/os/ZygoteInit.java  /frameworks/base/core/java/com/android/internal/os/Zygote.java  /frameworks/base/core/java/android/net/LocalServerSocket.java

App_main.main      AndroidRuntime.start          startVm          startReg          ZygoteInit.main              registerZygoteSocket              preload              startSystemServer              runSelectLoop

int main(int argc, char* const argv[])  {      AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));        //忽略第一个参数      argc--;      argv++;        int i;      for (i = 0; i < argc; i++) {          if (argv[i][0] != '-') {              break;          }          if (argv[i][1] == '-' && argv[i][2] == 0) {              ++i;              break;          }          runtime.addOption(strdup(argv[i]));      }      //参数解析      bool zygote = false;      bool startSystemServer = false;      bool application = false;      String8 niceName;      String8 className;      ++i;      while (i < argc) {          const char* arg = argv[i++];          if (strcmp(arg, "--zygote") == 0) {              zygote = true;              niceName = ZYGOTE_NICE_NAME; //对于64位系统nice_name为zygote64,32位系统为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.setTo(arg + 12);          } else if (strncmp(arg, "--", 2) != 0) {              className.setTo(arg);              break;          } else {              --i;              break;          }      }      Vector<String8> args;      if (!className.isEmpty()) {          // 运行application或tool程序          args.add(application ? String8("application") : String8("tool"));          runtime.setClassNameAndArgs(className, argc - i, argv + i);      } else {          //进入zygote模式，创建 /data/dalvik-cache路径          maybeCreateDalvikCache();          if (startSystemServer) {              args.add(String8("start-system-server"));          }          char prop[PROP_VALUE_MAX];          if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {              return 11;          }          String8 abiFlag("--abi-list=");          abiFlag.append(prop);          args.add(abiFlag);            for (; i < argc; ++i) {              args.add(String8(argv[i]));          }      }        //设置进程名      if (!niceName.isEmpty()) {          runtime.setArgv0(niceName.string());          set_process_name(niceName.string());      }      if (zygote) {          // 启动AppRuntime 【见小节3】          runtime.start("com.android.internal.os.ZygoteInit", args, zygote);      } else if (className) {          runtime.start("com.android.internal.os.RuntimeInit", args, zygote);      } else {          //没有指定类名或zygote，参数错误          return 10;      }  }

 app_process [可选参数] 命令所在路径 启动的类名 [可选参数]

void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)  {      static const String8 startSystemServer("start-system-server");        for (size_t i = 0; i < options.size(); ++i) {          if (options[i] == startSystemServer) {             const int LOG_BOOT_PROGRESS_START = 3000;          }      }      const char* rootDir = getenv("ANDROID_ROOT");      if (rootDir == NULL) {          rootDir = "/system";          if (!hasDir("/system")) {              return;          }          setenv("ANDROID_ROOT", rootDir, 1);      }      JniInvocation jni_invocation;      jni_invocation.Init(NULL);      JNIEnv* env;      // 虚拟机创建【见小节3.1】      if (startVm(&mJavaVM, &env, zygote) != 0) {          return;      }      onVmCreated(env);      // JNI方法注册【见小节3.2】      if (startReg(env) < 0) {          ALOGE("Unable to register all android natives\n");          return;      }        jclass stringClass;      jobjectArray strArray;      jstring classNameStr;        //等价 strArray= new String[options.size() + 1];      stringClass = env->FindClass("java/lang/String");      strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);        //等价 strArray[0] = "com.android.internal.os.ZygoteInit"      classNameStr = env->NewStringUTF(className);      env->SetObjectArrayElement(strArray, 0, classNameStr);        //等价 strArray[1] = "start-system-server"；      //   strArray[2] = "--abi-list=xxx"；其中xxx为系统响应的cpu架构类型，比如arm64-v8a.      for (size_t i = 0; i < options.size(); ++i) {          jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());          env->SetObjectArrayElement(strArray, i + 1, optionsStr);      }        //将"com.android.internal.os.ZygoteInit"转换为"com/android/internal/os/ZygoteInit"      char* slashClassName = toSlashClassName(className);      jclass startClass = env->FindClass(slashClassName);      if (startClass == NULL) {          ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);      } else {          jmethodID startMeth = env->GetStaticMethodID(startClass, "main",              "([Ljava/lang/String;)V");          if (startMeth == NULL) {              ALOGE("JavaVM unable to find main() in '%s'\n", className);          } else {              // 调用ZygoteInit.main()方法【见小节4.0】              env->CallStaticVoidMethod(startClass, startMeth, strArray);          }      }      free(slashClassName); //释放相应对象的内存空间      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");  }

int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)  {      // JNI检测功能，用于native层调用jni函数时进行常规检测，比较弱字符串格式是否符合要求，资源是否正确释放。该功能一般用于早期系统调试或手机Eng版，对于User版往往不会开启，引用该功能比较消耗系统CPU资源，降低系统性能。      bool checkJni = false;      property_get("dalvik.vm.checkjni", propBuf, "");      if (strcmp(propBuf, "true") == 0) {          checkJni = true;      } else if (strcmp(propBuf, "false") != 0) {          property_get("ro.kernel.android.checkjni", propBuf, "");          if (propBuf[0] == '1') {              checkJni = true;          }      }      if (checkJni) {          addOption("-Xcheck:jni");      }        //虚拟机产生的trace文件，主要用于分析系统问题，路径默认为/data/anr/traces.txt      parseRuntimeOption("dalvik.vm.stack-trace-file", stackTraceFileBuf, "-Xstacktracefile:");        //对于不同的软硬件环境，这些参数往往需要调整、优化，从而使系统达到最佳性能      parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");      parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");      parseRuntimeOption("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");      parseRuntimeOption("dalvik.vm.heapminfree", heapminfreeOptsBuf, "-XX:HeapMinFree=");      parseRuntimeOption("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");      parseRuntimeOption("dalvik.vm.heaptargetutilization",                         heaptargetutilizationOptsBuf, "-XX:HeapTargetUtilization=");        //preloaded-classes文件内容是由WritePreloadedClassFile.java生成的，在ZygoteInit类中会预加载工作将其中的classes提前加载到内存，以提高系统性能      if (!hasFile("/system/etc/preloaded-classes")) {          return -1;      }            //创建虚拟机      if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {          ALOGE("JNI_CreateJavaVM failed\n");          return -1;      }  }

int AndroidRuntime::startReg(JNIEnv* env)  {      //设置线程创建方法为javaCreateThreadEtc      androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);        env->PushLocalFrame(200);      //进程NI方法的注册      if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {          env->PopLocalFrame(NULL);          return -1;      }      env->PopLocalFrame(NULL);      return 0;  }

static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env)  {      for (size_t i = 0; i < count; i++) {          if (array[i].mProc(env) < 0) { 【见下文】              return -1;          }      }      return 0;  }

static const RegJNIRec gRegJNI[] = {      REG_JNI(register_com_android_internal_os_RuntimeInit),      REG_JNI(register_android_os_Binder)，      ...  }；

#define REG_JNI(name)      { name }  struct RegJNIRec {      int (*mProc)(JNIEnv*);  };

int register_com_android_internal_os_RuntimeInit(JNIEnv* env)  {      return jniRegisterNativeMethods(env, "com/android/internal/os/RuntimeInit",          gMethods, NELEM(gMethods));  }    //gMethods：java层方法名与jni层的方法的一一映射关系  static JNINativeMethod gMethods[] = {      { "nativeFinishInit", "()V",          (void*) com_android_internal_os_RuntimeInit_nativeFinishInit },      { "nativeZygoteInit", "()V",          (void*) com_android_internal_os_RuntimeInit_nativeZygoteInit },      { "nativeSetExitWithoutCleanup", "(Z)V",          (void*) com_android_internal_os_RuntimeInit_nativeSetExitWithoutCleanup },  };

public static void main(String argv[]) {      try {          RuntimeInit.enableDdms(); //开启DDMS功能          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.");          }          registerZygoteSocket(socketName); //为Zygote注册socket【见小节4.1】          preload(); // 预加载类和资源【见小节4.2】          SamplingProfilerIntegration.writeZygoteSnapshot();          gcAndFinalize(); //GC操作          if (startSystemServer) {              startSystemServer(abiList, socketName);//启动system_server【见小节4.3】          }          runSelectLoop(abiList); //进入循环模式【见小节4.4】          closeServerSocket();      } catch (MethodAndArgsCaller caller) {          caller.run(); //启动system_server中会讲到。      } catch (RuntimeException ex) {          closeServerSocket();          throw ex;      }  }

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); //设置文件描述符              sServerSocket = new LocalServerSocket(fd); //创建Socket的本地服务端          } catch (IOException ex) {              throw new RuntimeException("Error binding to local socket '" + fileDesc + "'", ex);          }      }  }

static void preload() {      //预加载位于/system/etc/preloaded-classes文件中的类      preloadClasses();         //预加载资源，包含drawable和color资源      preloadResources();        //预加载OpenGL      preloadOpenGL();        //通过System.loadLibrary()方法，      //预加载"android","compiler_rt","jnigraphics"这3个共享库      preloadSharedLibraries();        //预加载  文本连接符资源      preloadTextResources();        //仅用于zygote进程，用于内存共享的进程      WebViewFactory.prepareWebViewInZygote();  }

private static boolean startSystemServer(String abiList, String socketName)          throws MethodAndArgsCaller, RuntimeException {      long capabilities = posixCapabilitiesAsBits(          OsConstants.CAP_BLOCK_SUSPEND,          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      );      //参数准备      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 {          //用于解析参数，生成目标格式          parsedArgs = new ZygoteConnection.Arguments(args);          ZygoteConnection.applyDebuggerSystemProperty(parsedArgs);          ZygoteConnection.applyInvokeWithSystemProperty(parsedArgs);            // fork子进程，用于运行system_server          pid = Zygote.forkSystemServer(                  parsedArgs.uid, parsedArgs.gid,                  parsedArgs.gids,                  parsedArgs.debugFlags,                  null,                  parsedArgs.permittedCapabilities,                  parsedArgs.effectiveCapabilities);      } catch (IllegalArgumentException ex) {          throw new RuntimeException(ex);      }        //进入子进程system_server      if (pid == 0) {          if (hasSecondZygote(abiList)) {              waitForSecondaryZygote(socketName);          }          // 完成system_server进程剩余的工作          handleSystemServerProcess(parsedArgs);      }      return true;  }

private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {      ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();      ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();      //sServerSocket是socket通信中的服务端，即zygote进程      fds.add(sServerSocket.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) {              //采用I/O多路复用机制，当客户端发出连接请求或者数据处理请求时，跳过continue，执行后面的代码              if ((pollFds[i].revents & POLLIN) == 0) {                  continue;              }              if (i == 0) {                  //创建客户端连接                  ZygoteConnection newPeer = acceptCommandPeer(abiList);                  peers.add(newPeer);                  fds.add(newPeer.getFileDesciptor());              } else {                  //处理客户端数据事务                  boolean done = peers.get(i).runOnce();                  if (done) {                      peers.remove(i);                      fds.remove(i);                  }              }          }      }  }