/*
 * Copyright (C) 2016 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 android.os;

import android.net.LocalSocket;
import android.net.LocalSocketAddress;
import android.util.Log;
import android.util.Slog;

import com.android.internal.annotations.GuardedBy;
import com.android.internal.os.Zygote;
import com.android.internal.util.Preconditions;

import java.io.BufferedWriter;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.UUID;

/*package*/ class ZygoteStartFailedEx extends Exception {
    ZygoteStartFailedEx(String s) {
        super(s);
    }

    ZygoteStartFailedEx(Throwable cause) {
        super(cause);
    }

    ZygoteStartFailedEx(String s, Throwable cause) {
        super(s, cause);
    }
}

Maintains communication state with the zygote processes. This class is responsible for the sockets opened to the zygotes and for starting processes on behalf of the Process class. {@hide} /**
 * Maintains communication state with the zygote processes. This class is responsible
 * for the sockets opened to the zygotes and for starting processes on behalf of the
 * {@link android.os.Process} class.
 *
 * {@hide}
 */
public class ZygoteProcess {
    private static final String LOG_TAG = "ZygoteProcess";

    
The name of the socket used to communicate with the primary zygote.
/**
     * The name of the socket used to communicate with the primary zygote.
     */
    private final LocalSocketAddress mSocket;

    
The name of the secondary (alternate ABI) zygote socket.
/**
     * The name of the secondary (alternate ABI) zygote socket.
     */
    private final LocalSocketAddress mSecondarySocket;

    public ZygoteProcess(String primarySocket, String secondarySocket) {
        this(new LocalSocketAddress(primarySocket, LocalSocketAddress.Namespace.RESERVED),
                new LocalSocketAddress(secondarySocket, LocalSocketAddress.Namespace.RESERVED));
    }

    public ZygoteProcess(LocalSocketAddress primarySocket, LocalSocketAddress secondarySocket) {
        mSocket = primarySocket;
        mSecondarySocket = secondarySocket;
    }

    public LocalSocketAddress getPrimarySocketAddress() {
        return mSocket;
    }

    
State for communicating with the zygote process.
/**
     * State for communicating with the zygote process.
     */
    public static class ZygoteState {
        final LocalSocket socket;
        final DataInputStream inputStream;
        final BufferedWriter writer;
        final List<String> abiList;

        boolean mClosed;

        private ZygoteState(LocalSocket socket, DataInputStream inputStream,
                BufferedWriter writer, List<String> abiList) {
            this.socket = socket;
            this.inputStream = inputStream;
            this.writer = writer;
            this.abiList = abiList;
        }

        public static ZygoteState connect(LocalSocketAddress address) throws IOException {
            DataInputStream zygoteInputStream = null;
            BufferedWriter zygoteWriter = null;
            final LocalSocket zygoteSocket = new LocalSocket();

            try {
                zygoteSocket.connect(address);

                zygoteInputStream = new DataInputStream(zygoteSocket.getInputStream());

                zygoteWriter = new BufferedWriter(new OutputStreamWriter(
                        zygoteSocket.getOutputStream()), 256);
            } catch (IOException ex) {
                try {
                    zygoteSocket.close();
                } catch (IOException ignore) {
                }

                throw ex;
            }

            String abiListString = getAbiList(zygoteWriter, zygoteInputStream);
            Log.i("Zygote", "Process: zygote socket " + address.getNamespace() + "/"
                    + address.getName() + " opened, supported ABIS: " + abiListString);

            return new ZygoteState(zygoteSocket, zygoteInputStream, zygoteWriter,
                    Arrays.asList(abiListString.split(",")));
        }

        boolean matches(String abi) {
            return abiList.contains(abi);
        }

        public void close() {
            try {
                socket.close();
            } catch (IOException ex) {
                Log.e(LOG_TAG,"I/O exception on routine close", ex);
            }

            mClosed = true;
        }

        boolean isClosed() {
            return mClosed;
        }
    }

    
Lock object to protect access to the two ZygoteStates below. This lock must be
acquired while communicating over the ZygoteState's socket, to prevent
interleaved access.
/**
     * Lock object to protect access to the two ZygoteStates below. This lock must be
     * acquired while communicating over the ZygoteState's socket, to prevent
     * interleaved access.
     */
    private final Object mLock = new Object();

    
List of exemptions to the API blacklist. These are prefix matches on the runtime format
symbol signature. Any matching symbol is treated by the runtime as being on the light grey
list.
/**
     * List of exemptions to the API blacklist. These are prefix matches on the runtime format
     * symbol signature. Any matching symbol is treated by the runtime as being on the light grey
     * list.
     */
    private List<String> mApiBlacklistExemptions = Collections.emptyList();

    
Proportion of hidden API accesses that should be logged to the event log; 0 - 0x10000.
/**
     * Proportion of hidden API accesses that should be logged to the event log; 0 - 0x10000.
     */
    private int mHiddenApiAccessLogSampleRate;

    
The state of the connection to the primary zygote.
/**
     * The state of the connection to the primary zygote.
     */
    private ZygoteState primaryZygoteState;

    
The state of the connection to the secondary zygote.
/**
     * The state of the connection to the secondary zygote.
     */
    private ZygoteState secondaryZygoteState;

    
Start a new process.
If processes are enabled, a new process is created and the
static main() function of a processClass is executed there.
The process will continue running after this function returns.
If processes are not enabled, a new thread in the caller's
process is created and main() of processclass called there.
The niceName parameter, if not an empty string, is a custom name to
give to the process instead of using processClass.  This allows you to
make easily identifyable processes even if you are using the same base
processClass to start them.
When invokeWith is not null, the process will be started as a fresh app
and not a zygote fork. Note that this is only allowed for uid 0 or when
runtimeFlags contains DEBUG_ENABLE_DEBUGGER.
Params:
processClass – The class to use as the process's main entry
                    point.
niceName – A more readable name to use for the process.
uid – The user-id under which the process will run.
gid – The group-id under which the process will run.
gids – Additional group-ids associated with the process.
runtimeFlags – Additional flags.
targetSdkVersion – The target SDK version for the app.
seInfo – null-ok SELinux information for the new process.
abi – non-null the ABI this app should be started with.
instructionSet – null-ok the instruction set to use.
appDataDir – null-ok the data directory of the app.
invokeWith – null-ok the command to invoke with.
zygoteArgs – Additional arguments to supply to the zygote process.
Throws:
RuntimeException – on fatal start failure
Returns:
An object that describes the result of the attempt to start the process./**
     * Start a new process.
     *
     * <p>If processes are enabled, a new process is created and the
     * static main() function of a <var>processClass</var> is executed there.
     * The process will continue running after this function returns.
     *
     * <p>If processes are not enabled, a new thread in the caller's
     * process is created and main() of <var>processclass</var> called there.
     *
     * <p>The niceName parameter, if not an empty string, is a custom name to
     * give to the process instead of using processClass.  This allows you to
     * make easily identifyable processes even if you are using the same base
     * <var>processClass</var> to start them.
     *
     * When invokeWith is not null, the process will be started as a fresh app
     * and not a zygote fork. Note that this is only allowed for uid 0 or when
     * runtimeFlags contains DEBUG_ENABLE_DEBUGGER.
     *
     * @param processClass The class to use as the process's main entry
     *                     point.
     * @param niceName A more readable name to use for the process.
     * @param uid The user-id under which the process will run.
     * @param gid The group-id under which the process will run.
     * @param gids Additional group-ids associated with the process.
     * @param runtimeFlags Additional flags.
     * @param targetSdkVersion The target SDK version for the app.
     * @param seInfo null-ok SELinux information for the new process.
     * @param abi non-null the ABI this app should be started with.
     * @param instructionSet null-ok the instruction set to use.
     * @param appDataDir null-ok the data directory of the app.
     * @param invokeWith null-ok the command to invoke with.
     * @param zygoteArgs Additional arguments to supply to the zygote process.
     *
     * @return An object that describes the result of the attempt to start the process.
     * @throws RuntimeException on fatal start failure
     */
    public final Process.ProcessStartResult start(final String processClass,
                                                  final String niceName,
                                                  int uid, int gid, int[] gids,
                                                  int runtimeFlags, int mountExternal,
                                                  int targetSdkVersion,
                                                  String seInfo,
                                                  String abi,
                                                  String instructionSet,
                                                  String appDataDir,
                                                  String invokeWith,
                                                  String[] zygoteArgs) {
        try {
            return startViaZygote(processClass, niceName, uid, gid, gids,
                    runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, invokeWith, false /* startChildZygote */,
                    zygoteArgs);
        } catch (ZygoteStartFailedEx ex) {
            Log.e(LOG_TAG,
                    "Starting VM process through Zygote failed");
            throw new RuntimeException(
                    "Starting VM process through Zygote failed", ex);
        }
    }

    
retry interval for opening a zygote socket /** retry interval for opening a zygote socket */
    static final int ZYGOTE_RETRY_MILLIS = 500;

    
Queries the zygote for the list of ABIS it supports.
Throws:
ZygoteStartFailedEx – if the query failed./**
     * Queries the zygote for the list of ABIS it supports.
     *
     * @throws ZygoteStartFailedEx if the query failed.
     */
    @GuardedBy("mLock")
    private static String getAbiList(BufferedWriter writer, DataInputStream inputStream)
            throws IOException {
        // Each query starts with the argument count (1 in this case)
        writer.write("1");
        // ... followed by a new-line.
        writer.newLine();
        // ... followed by our only argument.
        writer.write("--query-abi-list");
        writer.newLine();
        writer.flush();

        // The response is a length prefixed stream of ASCII bytes.
        int numBytes = inputStream.readInt();
        byte[] bytes = new byte[numBytes];
        inputStream.readFully(bytes);

        return new String(bytes, StandardCharsets.US_ASCII);
    }

    
Sends an argument list to the zygote process, which starts a new child
and returns the child's pid. Please note: the present implementation
replaces newlines in the argument list with spaces.
Throws:
ZygoteStartFailedEx – if process start failed for any reason/**
     * Sends an argument list to the zygote process, which starts a new child
     * and returns the child's pid. Please note: the present implementation
     * replaces newlines in the argument list with spaces.
     *
     * @throws ZygoteStartFailedEx if process start failed for any reason
     */
    @GuardedBy("mLock")
    private static Process.ProcessStartResult zygoteSendArgsAndGetResult(
            ZygoteState zygoteState, ArrayList<String> args)
            throws ZygoteStartFailedEx {
        try {
            // Throw early if any of the arguments are malformed. This means we can
            // avoid writing a partial response to the zygote.
            int sz = args.size();
            for (int i = 0; i < sz; i++) {
                if (args.get(i).indexOf('\n') >= 0) {
                    throw new ZygoteStartFailedEx("embedded newlines not allowed");
                }
            }

            /**
             * See com.android.internal.os.SystemZygoteInit.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, followed by boolean to
             * indicate whether a wrapper process was used.
             */
            final BufferedWriter writer = zygoteState.writer;
            final DataInputStream inputStream = zygoteState.inputStream;

            writer.write(Integer.toString(args.size()));
            writer.newLine();

            for (int i = 0; i < sz; i++) {
                String arg = args.get(i);
                writer.write(arg);
                writer.newLine();
            }

            writer.flush();

            // Should there be a timeout on this?
            Process.ProcessStartResult result = new Process.ProcessStartResult();

            // Always read the entire result from the input stream to avoid leaving
            // bytes in the stream for future process starts to accidentally stumble
            // upon.
            result.pid = inputStream.readInt();
            result.usingWrapper = inputStream.readBoolean();

            if (result.pid < 0) {
                throw new ZygoteStartFailedEx("fork() failed");
            }
            return result;
        } catch (IOException ex) {
            zygoteState.close();
            throw new ZygoteStartFailedEx(ex);
        }
    }

    
Starts a new process via the zygote mechanism.
Params:
processClass – Class name whose static main() to run
niceName – 'nice' process name to appear in ps
uid – a POSIX uid that the new process should setuid() to
gid – a POSIX gid that the new process shuold setgid() to
gids – null-ok; a list of supplementary group IDs that the
new process should setgroup() to.
runtimeFlags – Additional flags for the runtime.
targetSdkVersion – The target SDK version for the app.
seInfo – null-ok SELinux information for the new process.
abi – the ABI the process should use.
instructionSet – null-ok the instruction set to use.
appDataDir – null-ok the data directory of the app.
startChildZygote – Start a sub-zygote. This creates a new zygote process
that has its state cloned from this zygote process.
extraArgs – Additional arguments to supply to the zygote process.
Throws:
ZygoteStartFailedEx – if process start failed for any reason
Returns:
An object that describes the result of the attempt to start the process./**
     * Starts a new process via the zygote mechanism.
     *
     * @param processClass Class name whose static main() to run
     * @param niceName 'nice' process name to appear in ps
     * @param uid a POSIX uid that the new process should setuid() to
     * @param gid a POSIX gid that the new process shuold setgid() to
     * @param gids null-ok; a list of supplementary group IDs that the
     * new process should setgroup() to.
     * @param runtimeFlags Additional flags for the runtime.
     * @param targetSdkVersion The target SDK version for the app.
     * @param seInfo null-ok SELinux information for the new process.
     * @param abi the ABI the process should use.
     * @param instructionSet null-ok the instruction set to use.
     * @param appDataDir null-ok the data directory of the app.
     * @param startChildZygote Start a sub-zygote. This creates a new zygote process
     * that has its state cloned from this zygote process.
     * @param extraArgs Additional arguments to supply to the zygote process.
     * @return An object that describes the result of the attempt to start the process.
     * @throws ZygoteStartFailedEx if process start failed for any reason
     */
    private Process.ProcessStartResult startViaZygote(final String processClass,
                                                      final String niceName,
                                                      final int uid, final int gid,
                                                      final int[] gids,
                                                      int runtimeFlags, int mountExternal,
                                                      int targetSdkVersion,
                                                      String seInfo,
                                                      String abi,
                                                      String instructionSet,
                                                      String appDataDir,
                                                      String invokeWith,
                                                      boolean startChildZygote,
                                                      String[] extraArgs)
                                                      throws ZygoteStartFailedEx {
        ArrayList<String> argsForZygote = new ArrayList<String>();

        // --runtime-args, --setuid=, --setgid=,
        // and --setgroups= must go first
        argsForZygote.add("--runtime-args");
        argsForZygote.add("--setuid=" + uid);
        argsForZygote.add("--setgid=" + gid);
        argsForZygote.add("--runtime-flags=" + runtimeFlags);
        if (mountExternal == Zygote.MOUNT_EXTERNAL_DEFAULT) {
            argsForZygote.add("--mount-external-default");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_READ) {
            argsForZygote.add("--mount-external-read");
        } else if (mountExternal == Zygote.MOUNT_EXTERNAL_WRITE) {
            argsForZygote.add("--mount-external-write");
        }
        argsForZygote.add("--target-sdk-version=" + targetSdkVersion);

        // --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);
        }

        if (seInfo != null) {
            argsForZygote.add("--seinfo=" + seInfo);
        }

        if (instructionSet != null) {
            argsForZygote.add("--instruction-set=" + instructionSet);
        }

        if (appDataDir != null) {
            argsForZygote.add("--app-data-dir=" + appDataDir);
        }

        if (invokeWith != null) {
            argsForZygote.add("--invoke-with");
            argsForZygote.add(invokeWith);
        }

        if (startChildZygote) {
            argsForZygote.add("--start-child-zygote");
        }

        argsForZygote.add(processClass);

        if (extraArgs != null) {
            for (String arg : extraArgs) {
                argsForZygote.add(arg);
            }
        }

        synchronized(mLock) {
            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
        }
    }

    
Closes the connections to the zygote, if they exist.
/**
     * Closes the connections to the zygote, if they exist.
     */
    public void close() {
        if (primaryZygoteState != null) {
            primaryZygoteState.close();
        }
        if (secondaryZygoteState != null) {
            secondaryZygoteState.close();
        }
    }

    
Tries to establish a connection to the zygote that handles a given abi. Might block and retry if the zygote is unresponsive. This method is a no-op if a connection is already open. /**
     * Tries to establish a connection to the zygote that handles a given {@code abi}. Might block
     * and retry if the zygote is unresponsive. This method is a no-op if a connection is
     * already open.
     */
    public void establishZygoteConnectionForAbi(String abi) {
        try {
            synchronized(mLock) {
                openZygoteSocketIfNeeded(abi);
            }
        } catch (ZygoteStartFailedEx ex) {
            throw new RuntimeException("Unable to connect to zygote for abi: " + abi, ex);
        }
    }

    
Push hidden API blacklisting exemptions into the zygote process(es).
The list of exemptions will take affect for all new processes forked from the zygote after
this call.
Params:
exemptions – List of hidden API exemption prefixes. Any matching members are treated as
       whitelisted/public APIs (i.e. allowed, no logging of usage)./**
     * Push hidden API blacklisting exemptions into the zygote process(es).
     *
     * <p>The list of exemptions will take affect for all new processes forked from the zygote after
     * this call.
     *
     * @param exemptions List of hidden API exemption prefixes. Any matching members are treated as
     *        whitelisted/public APIs (i.e. allowed, no logging of usage).
     */
    public boolean setApiBlacklistExemptions(List<String> exemptions) {
        synchronized (mLock) {
            mApiBlacklistExemptions = exemptions;
            boolean ok = maybeSetApiBlacklistExemptions(primaryZygoteState, true);
            if (ok) {
                ok = maybeSetApiBlacklistExemptions(secondaryZygoteState, true);
            }
            return ok;
        }
    }

    
Set the precentage of detected hidden API accesses that are logged to the event log.
This rate will take affect for all new processes forked from the zygote after this call.
Params:
rate – An integer between 0 and 0x10000 inclusive. 0 means no event logging./**
     * Set the precentage of detected hidden API accesses that are logged to the event log.
     *
     * <p>This rate will take affect for all new processes forked from the zygote after this call.
     *
     * @param rate An integer between 0 and 0x10000 inclusive. 0 means no event logging.
     */
    public void setHiddenApiAccessLogSampleRate(int rate) {
        synchronized (mLock) {
            mHiddenApiAccessLogSampleRate = rate;
            maybeSetHiddenApiAccessLogSampleRate(primaryZygoteState);
            maybeSetHiddenApiAccessLogSampleRate(secondaryZygoteState);
        }
    }

    @GuardedBy("mLock")
    private boolean maybeSetApiBlacklistExemptions(ZygoteState state, boolean sendIfEmpty) {
        if (state == null || state.isClosed()) {
            Slog.e(LOG_TAG, "Can't set API blacklist exemptions: no zygote connection");
            return false;
        }
        if (!sendIfEmpty && mApiBlacklistExemptions.isEmpty()) {
            return true;
        }
        try {
            state.writer.write(Integer.toString(mApiBlacklistExemptions.size() + 1));
            state.writer.newLine();
            state.writer.write("--set-api-blacklist-exemptions");
            state.writer.newLine();
            for (int i = 0; i < mApiBlacklistExemptions.size(); ++i) {
                state.writer.write(mApiBlacklistExemptions.get(i));
                state.writer.newLine();
            }
            state.writer.flush();
            int status = state.inputStream.readInt();
            if (status != 0) {
                Slog.e(LOG_TAG, "Failed to set API blacklist exemptions; status " + status);
            }
            return true;
        } catch (IOException ioe) {
            Slog.e(LOG_TAG, "Failed to set API blacklist exemptions", ioe);
            mApiBlacklistExemptions = Collections.emptyList();
            return false;
        }
    }

    private void maybeSetHiddenApiAccessLogSampleRate(ZygoteState state) {
        if (state == null || state.isClosed()) {
            return;
        }
        if (mHiddenApiAccessLogSampleRate == -1) {
            return;
        }
        try {
            state.writer.write(Integer.toString(1));
            state.writer.newLine();
            state.writer.write("--hidden-api-log-sampling-rate="
                    + Integer.toString(mHiddenApiAccessLogSampleRate));
            state.writer.newLine();
            state.writer.flush();
            int status = state.inputStream.readInt();
            if (status != 0) {
                Slog.e(LOG_TAG, "Failed to set hidden API log sampling rate; status " + status);
            }
        } catch (IOException ioe) {
            Slog.e(LOG_TAG, "Failed to set hidden API log sampling rate", ioe);
        }
    }

    
Tries to open socket to Zygote process if not already open. If
already open, does nothing.  May block and retry.  Requires that mLock be held.
/**
     * Tries to open socket to Zygote process if not already open. If
     * already open, does nothing.  May block and retry.  Requires that mLock be held.
     */
    @GuardedBy("mLock")
    private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
        Preconditions.checkState(Thread.holdsLock(mLock), "ZygoteProcess lock not held");

        if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
            try {
                primaryZygoteState = ZygoteState.connect(mSocket);
            } catch (IOException ioe) {
                throw new ZygoteStartFailedEx("Error connecting to primary zygote", ioe);
            }
            maybeSetApiBlacklistExemptions(primaryZygoteState, false);
            maybeSetHiddenApiAccessLogSampleRate(primaryZygoteState);
        }
        if (primaryZygoteState.matches(abi)) {
            return primaryZygoteState;
        }

        // The primary zygote didn't match. Try the secondary.
        if (secondaryZygoteState == null || secondaryZygoteState.isClosed()) {
            try {
                secondaryZygoteState = ZygoteState.connect(mSecondarySocket);
            } catch (IOException ioe) {
                throw new ZygoteStartFailedEx("Error connecting to secondary zygote", ioe);
            }
            maybeSetApiBlacklistExemptions(secondaryZygoteState, false);
            maybeSetHiddenApiAccessLogSampleRate(secondaryZygoteState);
        }

        if (secondaryZygoteState.matches(abi)) {
            return secondaryZygoteState;
        }

        throw new ZygoteStartFailedEx("Unsupported zygote ABI: " + abi);
    }

    
Instructs the zygote to pre-load the classes and native libraries at the given paths
for the specified abi. Not all zygotes support this function.
/**
     * Instructs the zygote to pre-load the classes and native libraries at the given paths
     * for the specified abi. Not all zygotes support this function.
     */
    public boolean preloadPackageForAbi(String packagePath, String libsPath, String libFileName,
                                        String cacheKey, String abi) throws ZygoteStartFailedEx,
                                                                            IOException {
        synchronized(mLock) {
            ZygoteState state = openZygoteSocketIfNeeded(abi);
            state.writer.write("5");
            state.writer.newLine();

            state.writer.write("--preload-package");
            state.writer.newLine();

            state.writer.write(packagePath);
            state.writer.newLine();

            state.writer.write(libsPath);
            state.writer.newLine();

            state.writer.write(libFileName);
            state.writer.newLine();

            state.writer.write(cacheKey);
            state.writer.newLine();

            state.writer.flush();

            return (state.inputStream.readInt() == 0);
        }
    }

    
Instructs the zygote to preload the default set of classes and resources. Returns true if a preload was performed as a result of this call, and false otherwise. The latter usually means that the zygote eagerly preloaded at startup or due to a previous call to preloadDefault. Note that this call is synchronous. /**
     * Instructs the zygote to preload the default set of classes and resources. Returns
     * {@code true} if a preload was performed as a result of this call, and {@code false}
     * otherwise. The latter usually means that the zygote eagerly preloaded at startup
     * or due to a previous call to {@code preloadDefault}. Note that this call is synchronous.
     */
    public boolean preloadDefault(String abi) throws ZygoteStartFailedEx, IOException {
        synchronized (mLock) {
            ZygoteState state = openZygoteSocketIfNeeded(abi);
            // Each query starts with the argument count (1 in this case)
            state.writer.write("1");
            state.writer.newLine();
            state.writer.write("--preload-default");
            state.writer.newLine();
            state.writer.flush();

            return (state.inputStream.readInt() == 0);
        }
    }

    
Try connecting to the Zygote over and over again until we hit a time-out.
Params:
socketName – The name of the socket to connect to./**
     * Try connecting to the Zygote over and over again until we hit a time-out.
     * @param socketName The name of the socket to connect to.
     */
    public static void waitForConnectionToZygote(String socketName) {
        final LocalSocketAddress address =
                new LocalSocketAddress(socketName, LocalSocketAddress.Namespace.RESERVED);
        waitForConnectionToZygote(address);
    }

    
Try connecting to the Zygote over and over again until we hit a time-out.
Params:
address – The name of the socket to connect to./**
     * Try connecting to the Zygote over and over again until we hit a time-out.
     * @param address The name of the socket to connect to.
     */
    public static void waitForConnectionToZygote(LocalSocketAddress address) {
        for (int n = 20; n >= 0; n--) {
            try {
                final ZygoteState zs = ZygoteState.connect(address);
                zs.close();
                return;
            } catch (IOException ioe) {
                Log.w(LOG_TAG,
                        "Got error connecting to zygote, retrying. msg= " + ioe.getMessage());
            }

            try {
                Thread.sleep(1000);
            } catch (InterruptedException ie) {
            }
        }
        Slog.wtf(LOG_TAG, "Failed to connect to Zygote through socket " + address.getName());
    }

    
Starts a new zygote process as a child of this zygote. This is used to create
secondary zygotes that inherit data from the zygote that this object
communicates with. This returns a new ZygoteProcess representing a connection
to the newly created zygote. Throws an exception if the zygote cannot be started.
/**
     * Starts a new zygote process as a child of this zygote. This is used to create
     * secondary zygotes that inherit data from the zygote that this object
     * communicates with. This returns a new ZygoteProcess representing a connection
     * to the newly created zygote. Throws an exception if the zygote cannot be started.
     */
    public ChildZygoteProcess startChildZygote(final String processClass,
                                               final String niceName,
                                               int uid, int gid, int[] gids,
                                               int runtimeFlags,
                                               String seInfo,
                                               String abi,
                                               String instructionSet) {
        // Create an unguessable address in the global abstract namespace.
        final LocalSocketAddress serverAddress = new LocalSocketAddress(
                processClass + "/" + UUID.randomUUID().toString());

        final String[] extraArgs = {Zygote.CHILD_ZYGOTE_SOCKET_NAME_ARG + serverAddress.getName()};

        Process.ProcessStartResult result;
        try {
            result = startViaZygote(processClass, niceName, uid, gid,
                    gids, runtimeFlags, 0 /* mountExternal */, 0 /* targetSdkVersion */, seInfo,
                    abi, instructionSet, null /* appDataDir */, null /* invokeWith */,
                    true /* startChildZygote */, extraArgs);
        } catch (ZygoteStartFailedEx ex) {
            throw new RuntimeException("Starting child-zygote through Zygote failed", ex);
        }

        return new ChildZygoteProcess(serverAddress, result.pid);
    }
}