Android应用框架之应用启动过程详解

public final class ActivityManagerService extends ActivityManagerNative     implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {   ......   private final void startProcessLocked(ProcessRecord app,         String hostingType, String hostingNameStr) {     ......     try {       int uid = app.info.uid;       int[] gids = null;       try {         gids = mContext.getPackageManager().getPackageGids(           app.info.packageName);       } catch (PackageManager.NameNotFoundException e) {         ......       }       ......       int debugFlags = 0;       ......       int pid = Process.start("android.app.ActivityThread",         mSimpleProcessManagement ? app.processName : null, uid, uid,         gids, debugFlags, null);       ......     } catch (RuntimeException e) {       ......     }   }   ...... } 

public class Process {  ......  public static final int start(final String processClass,    final String niceName,    int uid, int gid, int[] gids,    int debugFlags,    String[] zygoteArgs)  {    if (supportsProcesses()) {      try {        return startViaZygote(processClass, niceName, uid, gid, gids,          debugFlags, zygoteArgs);      } catch (ZygoteStartFailedEx ex) {        ......      }    } else {      ......      return 0;    }  }  ......}

public class Process {  ......  private static int startViaZygote(final String processClass,      final String niceName,      final int uid, final int gid,      final int[] gids,      int debugFlags,      String[] extraArgs)      throws ZygoteStartFailedEx {    int pid;    synchronized(Process.class) {      ArrayList<String> argsForZygote = new ArrayList<String>();      // --runtime-init, --setuid=, --setgid=,      // and --setgroups= must go first      argsForZygote.add("--runtime-init");      argsForZygote.add("--setuid=" + uid);      argsForZygote.add("--setgid=" + gid);      if ((debugFlags & Zygote.DEBUG_ENABLE_SAFEMODE) != 0) {        argsForZygote.add("--enable-safemode");      }      if ((debugFlags & Zygote.DEBUG_ENABLE_DEBUGGER) != 0) {        argsForZygote.add("--enable-debugger");      }      if ((debugFlags & Zygote.DEBUG_ENABLE_CHECKJNI) != 0) {        argsForZygote.add("--enable-checkjni");      }      if ((debugFlags & Zygote.DEBUG_ENABLE_ASSERT) != 0) {        argsForZygote.add("--enable-assert");      }      //TODO optionally enable debuger      //argsForZygote.add("--enable-debugger");      // --setgroups is a comma-separated list      if (gids != null && gids.length > 0) {        StringBuilder sb = new StringBuilder();        sb.append("--setgroups=");        int sz = gids.length;        for (int i = 0; i < sz; i++) {          if (i != 0) {            sb.append(',');          }          sb.append(gids[i]);        }        argsForZygote.add(sb.toString());      }      if (niceName != null) {        argsForZygote.add("--nice-name=" + niceName);      }      argsForZygote.add(processClass);      if (extraArgs != null) {        for (String arg : extraArgs) {          argsForZygote.add(arg);        }      }      pid = zygoteSendArgsAndGetPid(argsForZygote);    }  }  ......}

public class Process {  ......  private static int zygoteSendArgsAndGetPid(ArrayList<String> args)      throws ZygoteStartFailedEx {    int pid;    openZygoteSocketIfNeeded();    try {      /**      * See com.android.internal.os.ZygoteInit.readArgumentList()      * Presently the wire format to the zygote process is:      * a) a count of arguments (argc, in essence)      * b) a number of newline-separated argument strings equal to count      *      * After the zygote process reads these it will write the pid of      * the child or -1 on failure.      */      sZygoteWriter.write(Integer.toString(args.size()));      sZygoteWriter.newLine();      int sz = args.size();      for (int i = 0; i < sz; i++) {        String arg = args.get(i);        if (arg.indexOf('/n') >= 0) {          throw new ZygoteStartFailedEx(            "embedded newlines not allowed");        }        sZygoteWriter.write(arg);        sZygoteWriter.newLine();      }      sZygoteWriter.flush();      // Should there be a timeout on this?      pid = sZygoteInputStream.readInt();      if (pid < 0) {        throw new ZygoteStartFailedEx("fork() failed");      }    } catch (IOException ex) {      ......    }    return pid;  }  ......}这里的sZygoteWriter

class ZygoteConnection {  ......  boolean runOnce() throws ZygoteInit.MethodAndArgsCaller {    String args[];    Arguments parsedArgs = null;    FileDescriptor[] descriptors;    try {      args = readArgumentList();      descriptors = mSocket.getAncillaryFileDescriptors();    } catch (IOException ex) {      ......      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;    try {      parsedArgs = new Arguments(args);      applyUidSecurityPolicy(parsedArgs, peer);      applyDebuggerSecurityPolicy(parsedArgs);      applyRlimitSecurityPolicy(parsedArgs, peer);      applyCapabilitiesSecurityPolicy(parsedArgs, peer);      int[][] rlimits = null;      if (parsedArgs.rlimits != null) {        rlimits = parsedArgs.rlimits.toArray(intArray2d);      }      pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid,        parsedArgs.gids, parsedArgs.debugFlags, rlimits);    } catch (IllegalArgumentException ex) {      ......    } catch (ZygoteSecurityException ex) {      ......    }    if (pid == 0) {      // in child      handleChildProc(parsedArgs, descriptors, newStderr);      // should never happen      return true;    } else { /* pid != 0 */      // in parent...pid of < 0 means failure      return handleParentProc(pid, descriptors, parsedArgs);    }  }  ......}

class ZygoteConnection {  ......  private void handleChildProc(Arguments parsedArgs,      FileDescriptor[] descriptors, PrintStream newStderr)      throws ZygoteInit.MethodAndArgsCaller {    ......    if (parsedArgs.runtimeInit) {      RuntimeInit.zygoteInit(parsedArgs.remainingArgs);    } else {      ......    }  }  ......}

public class RuntimeInit {  ......  public static final void zygoteInit(String[] argv)      throws ZygoteInit.MethodAndArgsCaller {    // TODO: Doing this here works, but it seems kind of arbitrary. Find    // a better place. The goal is to set it up for applications, but not    // tools like am.    System.setOut(new AndroidPrintStream(Log.INFO, "System.out"));    System.setErr(new AndroidPrintStream(Log.WARN, "System.err"));    commonInit();    zygoteInitNative();    int curArg = 0;    for ( /* curArg */ ; curArg < argv.length; curArg++) {      String arg = argv[curArg];      if (arg.equals("--")) {        curArg++;        break;      } else if (!arg.startsWith("--")) {        break;      } else if (arg.startsWith("--nice-name=")) {        String niceName = arg.substring(arg.indexOf('=') + 1);        Process.setArgV0(niceName);      }    }    if (curArg == argv.length) {      Slog.e(TAG, "Missing classname argument to RuntimeInit!");      // let the process exit      return;    }    // Remaining arguments are passed to the start class's static main    String startClass = argv[curArg++];    String[] startArgs = new String[argv.length - curArg];    System.arraycopy(argv, curArg, startArgs, 0, startArgs.length);    invokeStaticMain(startClass, startArgs);  }  ......}

public class ZygoteInit {  ......  static void invokeStaticMain(ClassLoader loader,      String className, String[] argv)      throws ZygoteInit.MethodAndArgsCaller {    Class<?> cl;    try {      cl = loader.loadClass(className);    } catch (ClassNotFoundException ex) {      ......    }    Method m;    try {      m = cl.getMethod("main", new Class[] { String[].class });    } catch (NoSuchMethodException ex) {      ......    } catch (SecurityException ex) {      ......    }    int modifiers = m.getModifiers();    ......    /*    * 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);  }  ......}

public final class ActivityThread {  ......  public static final void main(String[] args) {    SamplingProfilerIntegration.start();    Process.setArgV0("<pre-initialized>");    Looper.prepareMainLooper();    if (sMainThreadHandler == null) {      sMainThreadHandler = new Handler();    }    ActivityThread thread = new ActivityThread();    thread.attach(false);    if (false) {      Looper.myLooper().setMessageLogging(new        LogPrinter(Log.DEBUG, "ActivityThread"));    }    Looper.loop();    if (Process.supportsProcesses()) {      throw new RuntimeException("Main thread loop unexpectedly exited");    }    thread.detach();    String name = (thread.mInitialApplication != null)      ? thread.mInitialApplication.getPackageName()      : "<unknown>";    Slog.i(TAG, "Main thread of " + name + " is now exiting");  }  ......}