Android example source code file (ZygoteConnection.java)

This example Android source code file (ZygoteConnection.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, arguments, arraylist, credentials, duplicate, error, filedescriptor, illegalargumentexception, internet, io, ioexception, localsocket, net, network, os, printstream, string, uid, zygoteconnection, zygotesecurityexception

The ZygoteConnection.java Android example source code

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.internal.os;

import android.net.Credentials;
import android.net.LocalSocket;
import android.os.Process;
import android.os.SystemProperties;
import android.util.Log;

import dalvik.system.PathClassLoader;
import dalvik.system.Zygote;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.util.ArrayList;

/**
 * A connection that can make spawn requests.
 */
class ZygoteConnection {
    private static final String TAG = "Zygote";

    /** a prototype instance for a future List.toArray() */
    private static final int[][] intArray2d = new int[0][0];

    /**
     * {@link android.net.LocalSocket#setSoTimeout} value for connections.
     * Effectively, the amount of time a requestor has between the start of
     * the request and the completed request. The select-loop mode Zygote
     * doesn't have the logic to return to the select loop in the middle of
     * a request, so we need to time out here to avoid being denial-of-serviced.
     */
    private static final int CONNECTION_TIMEOUT_MILLIS = 1000;

    /** max number of arguments that a connection can specify */
    private static final int MAX_ZYGOTE_ARGC=1024;

    /**
     * The command socket.
     *
     * mSocket is retained in the child process in "peer wait" mode, so
     * that it closes when the child process terminates. In other cases,
     * it is closed in the peer.
     */
    private final LocalSocket mSocket;
    private final DataOutputStream mSocketOutStream;
    private final BufferedReader mSocketReader;
    private final Credentials peer;

    /**
     * A long-lived reference to the original command socket used to launch
     * this peer. If "peer wait" mode is specified, the process that requested
     * the new VM instance intends to track the lifetime of the spawned instance
     * via the command socket. In this case, the command socket is closed
     * in the Zygote and placed here in the spawned instance so that it will
     * not be collected and finalized. This field remains null at all times
     * in the original Zygote process, and in all spawned processes where
     * "peer-wait" mode was not requested.
     */
    private static LocalSocket sPeerWaitSocket = null;

    /**
     * Constructs instance from connected socket.
     *
     * @param socket non-null; connected socket
     * @throws IOException
     */
    ZygoteConnection(LocalSocket socket) throws IOException {
        mSocket = socket;

        mSocketOutStream
                = new DataOutputStream(socket.getOutputStream());

        mSocketReader = new BufferedReader(
                new InputStreamReader(socket.getInputStream()), 256);

        mSocket.setSoTimeout(CONNECTION_TIMEOUT_MILLIS);
                
        try {
            peer = mSocket.getPeerCredentials();
        } catch (IOException ex) {
            Log.e(TAG, "Cannot read peer credentials", ex);
            throw ex;
        }
    }

    /**
     * Returns the file descriptor of the associated socket.
     *
     * @return null-ok; file descriptor
     */
    FileDescriptor getFileDesciptor() {
        return mSocket.getFileDescriptor();
    }

    /**
     * Reads start commands from an open command socket.
     * Start commands are presently a pair of newline-delimited lines
     * indicating a) class to invoke main() on b) nice name to set argv[0] to.
     * Continues to read commands and forkAndSpecialize children until
     * the socket is closed. This method is used in ZYGOTE_FORK_MODE
     *
     * @throws ZygoteInit.MethodAndArgsCaller trampoline to invoke main()
     * method in child process
     */
    void run() throws ZygoteInit.MethodAndArgsCaller {

        int loopCount = ZygoteInit.GC_LOOP_COUNT;

        while (true) {
            /*
             * Call gc() before we block in readArgumentList().
             * It's work that has to be done anyway, and it's better
             * to avoid making every child do it.  It will also
             * madvise() any free memory as a side-effect.
             *
             * Don't call it every time, because walking the entire
             * heap is a lot of overhead to free a few hundred bytes.
             */
            if (loopCount <= 0) {
                ZygoteInit.gc();
                loopCount = ZygoteInit.GC_LOOP_COUNT;
            } else {
                loopCount--;
            }

            if (runOnce()) {
                break;
            }
        }
    }

    /**
     * Reads one start command from the command socket. If successful,
     * a child is forked and a {@link ZygoteInit.MethodAndArgsCaller}
     * exception is thrown in that child while in the parent process,
     * the method returns normally. On failure, the child is not
     * spawned and messages are printed to the log and stderr. Returns
     * a boolean status value indicating whether an end-of-file on the command
     * socket has been encountered.
     *
     * @return false if command socket should continue to be read from, or
     * true if an end-of-file has been encountered.
     * @throws ZygoteInit.MethodAndArgsCaller trampoline to invoke main()
     * method in child process
     */
    boolean runOnce() throws ZygoteInit.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;

        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) {
            logAndPrintError (newStderr, "Invalid zygote arguments", ex);
            pid = -1;
        } catch (ZygoteSecurityException ex) {
            logAndPrintError(newStderr,
                    "Zygote security policy prevents request: ", ex);
            pid = -1;
        }

        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);
        }
    }

    /**
     * Closes socket associated with this connection.
     */
    void closeSocket() {
        try {
            mSocket.close();
        } catch (IOException ex) {
            Log.e(TAG, "Exception while closing command "
                    + "socket in parent", ex);
        }
    }

    /**
     * Handles argument parsing for args related to the zygote spawner.<p>

     * Current recognized args:
     * <ul>
     *   <li> --setuid=uid of child process, defaults to 0
     *   <li> --setgid=gid of child process, defaults to 0
     *   <li> --setgroups=comma-separated list of supplimentary gid's
     *   <li> --capabilities=a pair of comma-separated integer strings
     * indicating Linux capabilities(2) set for child. The first string
     * represents the <code>permitted set, and the second the
     * <code>effective set. Precede each with 0 or
     * 0x for octal or hexidecimal value. If unspecified, both default to 0.
     * This parameter is only applied if the uid of the new process will
     * be non-0. </i>
     *   <li> --rlimit=r,c,mtuple of values for setrlimit() call.
     *    <code>r is the resource, c and m
     *    are the settings for current and max value.</i>
     *   <li> --peer-wait indicates that the command socket should
     * be inherited by (and set to close-on-exec in) the spawned process
     * and used to track the lifetime of that process. The spawning process
     * then exits. Without this flag, it is retained by the spawning process
     * (and closed in the child) in expectation of a new spawn request.
     *   <li> --classpath=colon-separated classpath indicates
     * that the specified class (which must b first non-flag argument) should
     * be loaded from jar files in the specified classpath. Incompatible with
     * --runtime-init
     *   <li> --runtime-init indicates that the remaining arg list should
     * be handed off to com.android.internal.os.RuntimeInit, rather than
     * processed directly
     * Android runtime startup (eg, Binder initialization) is also eschewed.
     *   <li> If --runtime-init is present:
     *      [--] <args for RuntimeInit >
     *   <li> If --runtime-init is absent:
     *      [--] <classname> [args...]
     * </ul>
     */
    static class Arguments {
        /** from --setuid */
        int uid = 0;
        boolean uidSpecified;

        /** from --setgid */
        int gid = 0;
        boolean gidSpecified;

        /** from --setgroups */
        int[] gids;

        /** from --peer-wait */
        boolean peerWait;

        /**
         * From --enable-debugger, --enable-checkjni, --enable-assert, and
         * --enable-safemode
         */
        int debugFlags;

        /** from --classpath */
        String classpath;

        /** from --runtime-init */
        boolean runtimeInit;

        /** from --capabilities */
        boolean capabilitiesSpecified;
        long permittedCapabilities;
        long effectiveCapabilities;

        /** from all --rlimit=r,c,m */
        ArrayList<int[]> rlimits;

        /**
         * Any args after and including the first non-option arg
         * (or after a '--')
         */
        String remainingArgs[];

        /**
         * Constructs instance and parses args
         * @param args zygote command-line args
         * @throws IllegalArgumentException
         */
        Arguments(String args[]) throws IllegalArgumentException {
            parseArgs(args);
        }

        /**
         * Parses the commandline arguments intended for the Zygote spawner
         * (such as "--setuid=" and "--setgid=") and creates an array
         * containing the remaining args.
         *
         * Per security review bug #1112214, duplicate args are disallowed in
         * critical cases to make injection harder.
         */
        private void parseArgs(String args[])
                throws IllegalArgumentException {
            int curArg = 0;

            for ( /* curArg */ ; curArg < args.length; curArg++) {
                String arg = args[curArg];

                if (arg.equals("--")) {
                    curArg++;
                    break;
                } else if (arg.startsWith("--setuid=")) {
                    if (uidSpecified) {
                        throw new IllegalArgumentException(
                                "Duplicate arg specified");
                    }
                    uidSpecified = true;
                    uid = Integer.parseInt(
                            arg.substring(arg.indexOf('=') + 1));
                } else if (arg.startsWith("--setgid=")) {
                    if (gidSpecified) {
                        throw new IllegalArgumentException(
                                "Duplicate arg specified");
                    }
                    gidSpecified = true;
                    gid = Integer.parseInt(
                            arg.substring(arg.indexOf('=') + 1));
                } else if (arg.equals("--enable-debugger")) {
                    debugFlags |= Zygote.DEBUG_ENABLE_DEBUGGER;
                } else if (arg.equals("--enable-safemode")) {
                    debugFlags |= Zygote.DEBUG_ENABLE_SAFEMODE;
                } else if (arg.equals("--enable-checkjni")) {
                    debugFlags |= Zygote.DEBUG_ENABLE_CHECKJNI;
                } else if (arg.equals("--enable-assert")) {
                    debugFlags |= Zygote.DEBUG_ENABLE_ASSERT;
                } else if (arg.equals("--peer-wait")) {
                    peerWait = true;
                } else if (arg.equals("--runtime-init")) {
                    runtimeInit = true;
                } else if (arg.startsWith("--capabilities=")) {
                    if (capabilitiesSpecified) {
                        throw new IllegalArgumentException(
                                "Duplicate arg specified");
                    }
                    capabilitiesSpecified = true;
                    String capString = arg.substring(arg.indexOf('=')+1);

                    String[] capStrings = capString.split(",", 2);

                    if (capStrings.length == 1) {
                        effectiveCapabilities = Long.decode(capStrings[0]);
                        permittedCapabilities = effectiveCapabilities;
                    } else {
                        permittedCapabilities = Long.decode(capStrings[0]);
                        effectiveCapabilities = Long.decode(capStrings[1]);
                    }
                } else if (arg.startsWith("--rlimit=")) {
                    // Duplicate --rlimit arguments are specifically allowed.
                    String[] limitStrings
                            = arg.substring(arg.indexOf('=')+1).split(",");

                    if (limitStrings.length != 3) {
                        throw new IllegalArgumentException(
                                "--rlimit= should have 3 comma-delimited ints");
                    }
                    int[] rlimitTuple = new int[limitStrings.length];

                    for(int i=0; i < limitStrings.length; i++) {
                        rlimitTuple[i] = Integer.parseInt(limitStrings[i]);
                    }

                    if (rlimits == null) {
                        rlimits = new ArrayList();
                    }

                    rlimits.add(rlimitTuple);
                } else if (arg.equals("-classpath")) {
                    if (classpath != null) {
                        throw new IllegalArgumentException(
                                "Duplicate arg specified");
                    }
                    try {
                        classpath = args[++curArg];
                    } catch (IndexOutOfBoundsException ex) {
                        throw new IllegalArgumentException(
                                "-classpath requires argument");
                    }
                } else if (arg.startsWith("--setgroups=")) {
                    if (gids != null) {
                        throw new IllegalArgumentException(
                                "Duplicate arg specified");
                    }

                    String[] params
                            = arg.substring(arg.indexOf('=') + 1).split(",");

                    gids = new int[params.length];

                    for (int i = params.length - 1; i >= 0 ; i--) {
                        gids[i] = Integer.parseInt(params[i]);
                    }
                } else {
                    break;
                }
            }

            if (runtimeInit && classpath != null) {
                throw new IllegalArgumentException(
                        "--runtime-init and -classpath are incompatible");
            }

            remainingArgs = new String[args.length - curArg];

            System.arraycopy(args, curArg, remainingArgs, 0,
                    remainingArgs.length);
        }
    }

    /**
     * Reads an argument list from the command socket/
     * @return Argument list or null if EOF is reached
     * @throws IOException passed straight through
     */
    private String[] readArgumentList()
            throws IOException {

        /**
         * See android.os.Process.zygoteSendArgsAndGetPid()
         * 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.
         */

        int argc;

        try {
            String s = mSocketReader.readLine();

            if (s == null) {
                // EOF reached.
                return null;
            }
            argc = Integer.parseInt(s);
        } catch (NumberFormatException ex) {
            Log.e(TAG, "invalid Zygote wire format: non-int at argc");
            throw new IOException("invalid wire format");
        }

        // See bug 1092107: large argc can be used for a DOS attack
        if (argc > MAX_ZYGOTE_ARGC) {   
            throw new IOException("max arg count exceeded");
        }

        String[] result = new String[argc];
        for (int i = 0; i < argc; i++) {
            result[i] = mSocketReader.readLine();
            if (result[i] == null) {
                // We got an unexpected EOF.
                throw new IOException("truncated request");
            }
        }

        return result;
    }

    /**
     * Applies zygote security policy per bugs #875058 and #1082165. 
     * Based on the credentials of the process issuing a zygote command:
     * <ol>
     * <li> uid 0 (root) may specify any uid, gid, and setgroups() list
     * <li> uid 1000 (Process.SYSTEM_UID) may specify any uid > 1000 in normal
     * operation. It may also specify any gid and setgroups() list it chooses.
     * In factory test mode, it may specify any UID.
     * <li> Any other uid may not specify any uid, gid, or setgroups list. The
     * uid and gid will be inherited from the requesting process.
     * </ul>
     *
     * @param args non-null; zygote spawner arguments
     * @param peer non-null; peer credentials
     * @throws ZygoteSecurityException
     */
    private static void applyUidSecurityPolicy(Arguments args, Credentials peer)
            throws ZygoteSecurityException {

        int peerUid = peer.getUid();

        if (peerUid == 0) {
            // Root can do what it wants
        } else if (peerUid == Process.SYSTEM_UID ) {
            // System UID is restricted, except in factory test mode
            String factoryTest = SystemProperties.get("ro.factorytest");
            boolean uidRestricted;

            /* In normal operation, SYSTEM_UID can only specify a restricted
             * set of UIDs. In factory test mode, SYSTEM_UID may specify any uid.
             */
            uidRestricted  
                 = !(factoryTest.equals("1") || factoryTest.equals("2"));

            if (uidRestricted
                    && args.uidSpecified && (args.uid < Process.SYSTEM_UID)) {
                throw new ZygoteSecurityException(
                        "System UID may not launch process with UID < "
                                + Process.SYSTEM_UID);
            }
        } else {
            // Everything else
            if (args.uidSpecified || args.gidSpecified
                || args.gids != null) {
                throw new ZygoteSecurityException(
                        "App UIDs may not specify uid's or gid's");
            }
        }

        // If not otherwise specified, uid and gid are inherited from peer
        if (!args.uidSpecified) {
            args.uid = peer.getUid();
            args.uidSpecified = true;
        }
        if (!args.gidSpecified) {
            args.gid = peer.getGid();
            args.gidSpecified = true;
        }
    }


    /**
     * Applies debugger security policy.
     * If "ro.debuggable" is "1", all apps are debuggable. Otherwise,
     * the debugger state is specified via the "--enable-debugger" flag
     * in the spawn request.
     *
     * @param args non-null; zygote spawner args
     */
    private static void applyDebuggerSecurityPolicy(Arguments args) {
        if ("1".equals(SystemProperties.get("ro.debuggable"))) {
            args.debugFlags |= Zygote.DEBUG_ENABLE_DEBUGGER;
        }
    }

    /**
     * Applies zygote security policy per bug #1042973. Based on the credentials
     * of the process issuing a zygote command:
     * <ol>
     * <li> peers of  uid 0 (root) and uid 1000 (Process.SYSTEM_UID)
     * may specify any rlimits.
     * <li> All other uids may not specify rlimits.
     * </ul>
     * @param args non-null; zygote spawner arguments
     * @param peer non-null; peer credentials
     * @throws ZygoteSecurityException
     */
    private static void applyRlimitSecurityPolicy(
            Arguments args, Credentials peer)
            throws ZygoteSecurityException {

        int peerUid = peer.getUid();

        if (!(peerUid == 0 || peerUid == Process.SYSTEM_UID)) {
            // All peers with UID other than root or SYSTEM_UID
            if (args.rlimits != null) {
                throw new ZygoteSecurityException(
                        "This UID may not specify rlimits.");
            }
        }
    }

    /**
     * Applies zygote security policy per bug #1042973. A root peer may
     * spawn an instance with any capabilities. All other uids may spawn
     * instances with any of the capabilities in the peer's permitted set
     * but no more.
     *
     * @param args non-null; zygote spawner arguments
     * @param peer non-null; peer credentials
     * @throws ZygoteSecurityException
     */
    private static void applyCapabilitiesSecurityPolicy(
            Arguments args, Credentials peer)
            throws ZygoteSecurityException {

        if (args.permittedCapabilities == 0
                && args.effectiveCapabilities == 0) {
            // nothing to check
            return;
        }

        if (peer.getUid() == 0) {
            // root may specify anything
            return;
        }

        long permittedCaps;

        try {
            permittedCaps = ZygoteInit.capgetPermitted(peer.getPid());
        } catch (IOException ex) {
            throw new ZygoteSecurityException(
                    "Error retrieving peer's capabilities.");
        }

        /*
         * Ensure that the client did not specify an effective set larger
         * than the permitted set. The kernel will enforce this too, but we
         * do it here to make the following check easier.
         */
        if (((~args.permittedCapabilities) & args.effectiveCapabilities) != 0) {
            throw new ZygoteSecurityException(
                    "Effective capabilities cannot be superset of "
                            + " permitted capabilities" );
        }

        /*
         * Ensure that the new permitted (and thus the new effective) set is
         * a subset of the peer process's permitted set
         */

        if (((~permittedCaps) & args.permittedCapabilities) != 0) {
            throw new ZygoteSecurityException(
                    "Peer specified unpermitted capabilities" );
        }
    }

    /**
     * Handles post-fork setup of child proc, closing sockets as appropriate,
     * reopen stdio as appropriate, and ultimately throwing MethodAndArgsCaller
     * if successful or returning if failed.
     *
     * @param parsedArgs non-null; zygote args
     * @param descriptors null-ok; new file descriptors for stdio if available.
     * @param newStderr null-ok; stream to use for stderr until stdio
     * is reopened.
     *
     * @throws ZygoteInit.MethodAndArgsCaller on success to
     * trampoline to code that invokes static main.
     */
    private void handleChildProc(Arguments parsedArgs,
            FileDescriptor[] descriptors, PrintStream newStderr)
            throws ZygoteInit.MethodAndArgsCaller {

        /*
         * First, set the capabilities if necessary
         */

        if (parsedArgs.uid != 0) {
            try {
                ZygoteInit.setCapabilities(parsedArgs.permittedCapabilities,
                        parsedArgs.effectiveCapabilities);
            } catch (IOException ex) {
                Log.e(TAG, "Error setting capabilities", ex);
            }
        }

        /*
         * Close the socket, unless we're in "peer wait" mode, in which
         * case it's used to track the liveness of this process.
         */

        if (parsedArgs.peerWait) {
            try {
                ZygoteInit.setCloseOnExec(mSocket.getFileDescriptor(), true);
                sPeerWaitSocket = mSocket;
            } catch (IOException ex) {
                Log.e(TAG, "Zygote Child: error setting peer wait "
                        + "socket to be close-on-exec", ex);
            }
        } else {
            closeSocket();
            ZygoteInit.closeServerSocket();
        }

        if (descriptors != null) {
            try {
                ZygoteInit.reopenStdio(descriptors[0],
                        descriptors[1], descriptors[2]);

                for (FileDescriptor fd: descriptors) {
                    ZygoteInit.closeDescriptor(fd);
                }
                newStderr = System.err;
            } catch (IOException ex) {
                Log.e(TAG, "Error reopening stdio", ex);
            }
        }

        if (parsedArgs.runtimeInit) {
            RuntimeInit.zygoteInit(parsedArgs.remainingArgs);
        } else {
            ClassLoader cloader;

            if (parsedArgs.classpath != null) {
                cloader
                    = new PathClassLoader(parsedArgs.classpath,
                    ClassLoader.getSystemClassLoader());
            } else {
                cloader = ClassLoader.getSystemClassLoader();
            }

            String className;
            try {
                className = parsedArgs.remainingArgs[0];
            } catch (ArrayIndexOutOfBoundsException ex) {
                logAndPrintError (newStderr,
                        "Missing required class name argument", null);
                return;
            }
            String[] mainArgs
                    = new String[parsedArgs.remainingArgs.length - 1];

            System.arraycopy(parsedArgs.remainingArgs, 1,
                    mainArgs, 0, mainArgs.length);

            try {
                ZygoteInit.invokeStaticMain(cloader, className, mainArgs);
            } catch (RuntimeException ex) {
                logAndPrintError (newStderr, "Error starting. ", ex);
            }
        }
    }

    /**
     * Handles post-fork cleanup of parent proc
     *
     * @param pid != 0; pid of child if > 0 or indication of failed fork
     * if < 0;
     * @param descriptors null-ok; file descriptors for child's new stdio if
     * specified.
     * @param parsedArgs non-null; zygote args
     * @return true for "exit command loop" and false for "continue command
     * loop"
     */
    private boolean handleParentProc(int pid,
            FileDescriptor[] descriptors, Arguments parsedArgs) {

        if(pid > 0) {
            // Try to move the new child into the peer's process group.
            try {
                ZygoteInit.setpgid(pid, ZygoteInit.getpgid(peer.getPid()));
            } catch (IOException ex) {
                // This exception is expected in the case where
                // the peer is not in our session
                // TODO get rid of this log message in the case where
                // getsid(0) != getsid(peer.getPid())
                Log.i(TAG, "Zygote: setpgid failed. This is "
                    + "normal if peer is not in our session");
            }
        }

        try {
            if (descriptors != null) {
                for (FileDescriptor fd: descriptors) {
                    ZygoteInit.closeDescriptor(fd);
                }
            }
        } catch (IOException ex) {
            Log.e(TAG, "Error closing passed descriptors in "
                    + "parent process", ex);
        }

        try {
            mSocketOutStream.writeInt(pid);
        } catch (IOException ex) {
            Log.e(TAG, "Error reading from command socket", ex);
            return true;
        }

        /*
         * If the peer wants to use the socket to wait on the
         * newly spawned process, then we're all done.
         */
        if (parsedArgs.peerWait) {
            try {
                mSocket.close();
            } catch (IOException ex) {
                Log.e(TAG, "Zygote: error closing sockets", ex);
            }
            return true;
        }
        return false;
    }

    /**
     * Logs an error message and prints it to the specified stream, if
     * provided
     *
     * @param newStderr null-ok; a standard error stream
     * @param message non-null; error message
     * @param ex null-ok an exception
     */
    private static void logAndPrintError (PrintStream newStderr,
            String message, Throwable ex) {
        Log.e(TAG, message, ex);
        if (newStderr != null) {
            newStderr.println(message + (ex == null ? "" : ex));
        }
    }
}