android/os/Process.java

/*
 * Copyright (C) 2006 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.system.Os;
import android.util.Log;
import com.android.internal.os.Zygote;
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.List;

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

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

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

/**
 * Tools for managing OS processes.
 */
public class Process {
    private static final String LOG_TAG = "Process";

    /**
     * @hide for internal use only.
     */
    public static final String ZYGOTE_SOCKET = "zygote";

    /**
     * @hide for internal use only.
     */
    public static final String SECONDARY_ZYGOTE_SOCKET = "zygote_secondary";

    /**
     * Defines the UID/GID under which system code runs.
     */
    public static final int SYSTEM_UID = 1000;

    /**
     * Defines the UID/GID under which the telephony code runs.
     */
    public static final int PHONE_UID = 1001;

    /**
     * Defines the UID/GID for the user shell.
     * @hide
     */
    public static final int SHELL_UID = 2000;

    /**
     * Defines the UID/GID for the log group.
     * @hide
     */
    public static final int LOG_UID = 1007;

    /**
     * Defines the UID/GID for the WIFI supplicant process.
     * @hide
     */
    public static final int WIFI_UID = 1010;

    /**
     * Defines the UID/GID for the mediaserver process.
     * @hide
     */
    public static final int MEDIA_UID = 1013;

    /**
     * Defines the UID/GID for the DRM process.
     * @hide
     */
    public static final int DRM_UID = 1019;

    /**
     * Defines the UID/GID for the group that controls VPN services.
     * @hide
     */
    public static final int VPN_UID = 1016;

    /**
     * Defines the UID/GID for the NFC service process.
     * @hide
     */
    public static final int NFC_UID = 1027;

    /**
     * Defines the UID/GID for the Bluetooth service process.
     * @hide
     */
    public static final int BLUETOOTH_UID = 1002;

    /**
     * Defines the GID for the group that allows write access to the internal media storage.
     * @hide
     */
    public static final int MEDIA_RW_GID = 1023;

    /**
     * Access to installed package details
     * @hide
     */
    public static final int PACKAGE_INFO_GID = 1032;

    /**
     * Defines the start of a range of UIDs (and GIDs), going from this
     * number to {@link #LAST_APPLICATION_UID} that are reserved for assigning
     * to applications.
     */
    public static final int FIRST_APPLICATION_UID = 10000;

    /**
     * Last of application-specific UIDs starting at
     * {@link #FIRST_APPLICATION_UID}.
     */
    public static final int LAST_APPLICATION_UID = 19999;

    /**
     * First uid used for fully isolated sandboxed processes (with no permissions of their own)
     * @hide
     */
    public static final int FIRST_ISOLATED_UID = 99000;

    /**
     * Last uid used for fully isolated sandboxed processes (with no permissions of their own)
     * @hide
     */
    public static final int LAST_ISOLATED_UID = 99999;

    /**
     * Defines the gid shared by all applications running under the same profile.
     * @hide
     */
    public static final int SHARED_USER_GID = 9997;

    /**
     * First gid for applications to share resources. Used when forward-locking
     * is enabled but all UserHandles need to be able to read the resources.
     * @hide
     */
    public static final int FIRST_SHARED_APPLICATION_GID = 50000;

    /**
     * Last gid for applications to share resources. Used when forward-locking
     * is enabled but all UserHandles need to be able to read the resources.
     * @hide
     */
    public static final int LAST_SHARED_APPLICATION_GID = 59999;

    /**
     * Standard priority of application threads.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_DEFAULT = 0;

    /*
     * ***************************************
     * ** Keep in sync with utils/threads.h **
     * ***************************************
     */

    /**
     * Lowest available thread priority.  Only for those who really, really
     * don't want to run if anything else is happening.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_LOWEST = 19;

    /**
     * Standard priority background threads.  This gives your thread a slightly
     * lower than normal priority, so that it will have less chance of impacting
     * the responsiveness of the user interface.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_BACKGROUND = 10;

    /**
     * Standard priority of threads that are currently running a user interface
     * that the user is interacting with.  Applications can not normally
     * change to this priority; the system will automatically adjust your
     * application threads as the user moves through the UI.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_FOREGROUND = -2;

    /**
     * Standard priority of system display threads, involved in updating
     * the user interface.  Applications can not
     * normally change to this priority.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_DISPLAY = -4;

    /**
     * Standard priority of the most important display threads, for compositing
     * the screen and retrieving input events.  Applications can not normally
     * change to this priority.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_URGENT_DISPLAY = -8;

    /**
     * Standard priority of audio threads.  Applications can not normally
     * change to this priority.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_AUDIO = -16;

    /**
     * Standard priority of the most important audio threads.
     * Applications can not normally change to this priority.
     * Use with {@link #setThreadPriority(int)} and
     * {@link #setThreadPriority(int, int)}, <b>not</b> with the normal
     * {@link java.lang.Thread} class.
     */
    public static final int THREAD_PRIORITY_URGENT_AUDIO = -19;

    /**
     * Minimum increment to make a priority more favorable.
     */
    public static final int THREAD_PRIORITY_MORE_FAVORABLE = -1;

    /**
     * Minimum increment to make a priority less favorable.
     */
    public static final int THREAD_PRIORITY_LESS_FAVORABLE = +1;

    /**
     * Default scheduling policy
     * @hide
     */
    public static final int SCHED_OTHER = 0;

    /**
     * First-In First-Out scheduling policy
     * @hide
     */
    public static final int SCHED_FIFO = 1;

    /**
     * Round-Robin scheduling policy
     * @hide
     */
    public static final int SCHED_RR = 2;

    /**
     * Batch scheduling policy
     * @hide
     */
    public static final int SCHED_BATCH = 3;

    /**
     * Idle scheduling policy
     * @hide
     */
    public static final int SCHED_IDLE = 5;

    // Keep in sync with SP_* constants of enum type SchedPolicy
    // declared in system/core/include/cutils/sched_policy.h,
    // except THREAD_GROUP_DEFAULT does not correspond to any SP_* value.

    /**
     * Default thread group -
     * has meaning with setProcessGroup() only, cannot be used with setThreadGroup().
     * When used with setProcessGroup(), the group of each thread in the process
     * is conditionally changed based on that thread's current priority, as follows:
     * threads with priority numerically less than THREAD_PRIORITY_BACKGROUND
     * are moved to foreground thread group.  All other threads are left unchanged.
     * @hide
     */
    public static final int THREAD_GROUP_DEFAULT = -1;

    /**
     * Background thread group - All threads in
     * this group are scheduled with a reduced share of the CPU.
     * Value is same as constant SP_BACKGROUND of enum SchedPolicy.
     * FIXME rename to THREAD_GROUP_BACKGROUND.
     * @hide
     */
    public static final int THREAD_GROUP_BG_NONINTERACTIVE = 0;

    /**
     * Foreground thread group - All threads in
     * this group are scheduled with a normal share of the CPU.
     * Value is same as constant SP_FOREGROUND of enum SchedPolicy.
     * Not used at this level.
     * @hide
     **/
    private static final int THREAD_GROUP_FOREGROUND = 1;

    /**
     * System thread group.
     * @hide
     **/
    public static final int THREAD_GROUP_SYSTEM = 2;

    /**
     * Application audio thread group.
     * @hide
     **/
    public static final int THREAD_GROUP_AUDIO_APP = 3;

    /**
     * System audio thread group.
     * @hide
     **/
    public static final int THREAD_GROUP_AUDIO_SYS = 4;

    public static final int SIGNAL_QUIT = 3;
    public static final int SIGNAL_KILL = 9;
    public static final int SIGNAL_USR1 = 10;

    /**
     * State for communicating with the zygote process.
     *
     * @hide for internal use only.
     */
    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(String socketAddress) throws IOException {
            DataInputStream zygoteInputStream = null;
            BufferedWriter zygoteWriter = null;
            final LocalSocket zygoteSocket = new LocalSocket();

            try {
                zygoteSocket.connect(new LocalSocketAddress(socketAddress,
                        LocalSocketAddress.Namespace.RESERVED));

                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 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;
        }
    }

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

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

    /**
     * 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.
     *
     * @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 debugFlags 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 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
     *
     * {@hide}
     */
    public static final ProcessStartResult start(final String processClass,
                                  final String niceName,
                                  int uid, int gid, int[] gids,
                                  int debugFlags, int mountExternal,
                                  int targetSdkVersion,
                                  String seInfo,
                                  String abi,
                                  String instructionSet,
                                  String appDataDir,
                                  String[] zygoteArgs) {
        try {
            return startViaZygote(processClass, niceName, uid, gid, gids,
                    debugFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, 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 */
    static final int ZYGOTE_RETRY_MILLIS = 500;

    /**
     * Queries the zygote for the list of ABIS it supports.
     *
     * @throws ZygoteStartFailedEx if the query failed.
     */
    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
     */
    private static ProcessStartResult zygoteSendArgsAndGetResult(
            ZygoteState zygoteState, ArrayList<String> args)
            throws ZygoteStartFailedEx {
        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, 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();

            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");
                }
                writer.write(arg);
                writer.newLine();
            }

            writer.flush();

            // Should there be a timeout on this?
            ProcessStartResult result = new ProcessStartResult();
            result.pid = inputStream.readInt();
            if (result.pid < 0) {
                throw new ZygoteStartFailedEx("fork() failed");
            }
            result.usingWrapper = inputStream.readBoolean();
            return result;
        } catch (IOException ex) {
            zygoteState.close();
            throw new ZygoteStartFailedEx(ex);
        }
    }

    /**
     * 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 debugFlags Additional flags.
     * @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 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 static ProcessStartResult startViaZygote(final String processClass,
                                  final String niceName,
                                  final int uid, final int gid,
                                  final int[] gids,
                                  int debugFlags, int mountExternal,
                                  int targetSdkVersion,
                                  String seInfo,
                                  String abi,
                                  String instructionSet,
                                  String appDataDir,
                                  String[] extraArgs)
                                  throws ZygoteStartFailedEx {
        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_JNI_LOGGING) != 0) {
                argsForZygote.add("--enable-jni-logging");
            }
            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");
            }
            if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER) {
                argsForZygote.add("--mount-external-multiuser");
            } else if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER_ALL) {
                argsForZygote.add("--mount-external-multiuser-all");
            }
            argsForZygote.add("--target-sdk-version=" + targetSdkVersion);

            //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);
            }

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

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

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

            argsForZygote.add(processClass);

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

            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
        }
    }

    /**
     * Tries to open socket to Zygote process if not already open. If
     * already open, does nothing.  May block and retry.
     */
    private static ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
        if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
            try {
                primaryZygoteState = ZygoteState.connect(ZYGOTE_SOCKET);
            } catch (IOException ioe) {
                throw new ZygoteStartFailedEx("Error connecting to primary zygote", ioe);
            }
        }

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

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

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

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

    /**
     * Returns elapsed milliseconds of the time this process has run.
     * @return  Returns the number of milliseconds this process has return.
     */
    public static final native long getElapsedCpuTime();

    /**
     * Returns the identifier of this process, which can be used with
     * {@link #killProcess} and {@link #sendSignal}.
     */
    public static final int myPid() {
        return Os.getpid();
    }

    /**
     * Returns the identifier of this process' parent.
     * @hide
     */
    public static final int myPpid() {
        return Os.getppid();
    }

    /**
     * Returns the identifier of the calling thread, which be used with
     * {@link #setThreadPriority(int, int)}.
     */
    public static final int myTid() {
        return Os.gettid();
    }

    /**
     * Returns the identifier of this process's uid.  This is the kernel uid
     * that the process is running under, which is the identity of its
     * app-specific sandbox.  It is different from {@link #myUserHandle} in that
     * a uid identifies a specific app sandbox in a specific user.
     */
    public static final int myUid() {
        return Os.getuid();
    }

    /**
     * Returns this process's user handle.  This is the
     * user the process is running under.  It is distinct from
     * {@link #myUid()} in that a particular user will have multiple
     * distinct apps running under it each with their own uid.
     */
    public static final UserHandle myUserHandle() {
        return new UserHandle(UserHandle.getUserId(myUid()));
    }

    /**
     * Returns whether the current process is in an isolated sandbox.
     * @hide
     */
    public static final boolean isIsolated() {
        int uid = UserHandle.getAppId(myUid());
        return uid >= FIRST_ISOLATED_UID && uid <= LAST_ISOLATED_UID;
    }

    /**
     * Returns the UID assigned to a particular user name, or -1 if there is
     * none.  If the given string consists of only numbers, it is converted
     * directly to a uid.
     */
    public static final native int getUidForName(String name);

    /**
     * Returns the GID assigned to a particular user name, or -1 if there is
     * none.  If the given string consists of only numbers, it is converted
     * directly to a gid.
     */
    public static final native int getGidForName(String name);

    /**
     * Returns a uid for a currently running process.
     * @param pid the process id
     * @return the uid of the process, or -1 if the process is not running.
     * @hide pending API council review
     */
    public static final int getUidForPid(int pid) {
        String[] procStatusLabels = { "Uid:" };
        long[] procStatusValues = new long[1];
        procStatusValues[0] = -1;
        Process.readProcLines("/proc/" + pid + "/status", procStatusLabels, procStatusValues);
        return (int) procStatusValues[0];
    }

    /**
     * Returns the parent process id for a currently running process.
     * @param pid the process id
     * @return the parent process id of the process, or -1 if the process is not running.
     * @hide
     */
    public static final int getParentPid(int pid) {
        String[] procStatusLabels = { "PPid:" };
        long[] procStatusValues = new long[1];
        procStatusValues[0] = -1;
        Process.readProcLines("/proc/" + pid + "/status", procStatusLabels, procStatusValues);
        return (int) procStatusValues[0];
    }

    /**
     * Returns the thread group leader id for a currently running thread.
     * @param tid the thread id
     * @return the thread group leader id of the thread, or -1 if the thread is not running.
     *         This is same as what getpid(2) would return if called by tid.
     * @hide
     */
    public static final int getThreadGroupLeader(int tid) {
        String[] procStatusLabels = { "Tgid:" };
        long[] procStatusValues = new long[1];
        procStatusValues[0] = -1;
        Process.readProcLines("/proc/" + tid + "/status", procStatusLabels, procStatusValues);
        return (int) procStatusValues[0];
    }

    /**
     * Set the priority of a thread, based on Linux priorities.
     *
     * @param tid The identifier of the thread/process to change.
     * @param priority A Linux priority level, from -20 for highest scheduling
     * priority to 19 for lowest scheduling priority.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * priority.
     */
    public static final native void setThreadPriority(int tid, int priority)
            throws IllegalArgumentException, SecurityException;

    /**
     * Call with 'false' to cause future calls to {@link #setThreadPriority(int)} to
     * throw an exception if passed a background-level thread priority.  This is only
     * effective if the JNI layer is built with GUARD_THREAD_PRIORITY defined to 1.
     *
     * @hide
     */
    public static final native void setCanSelfBackground(boolean backgroundOk);

    /**
     * Sets the scheduling group for a thread.
     * @hide
     * @param tid The identifier of the thread to change.
     * @param group The target group for this thread from THREAD_GROUP_*.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * priority.
     * If the thread is a thread group leader, that is it's gettid() == getpid(),
     * then the other threads in the same thread group are _not_ affected.
     */
    public static final native void setThreadGroup(int tid, int group)
            throws IllegalArgumentException, SecurityException;

    /**
     * Sets the scheduling group for a process and all child threads
     * @hide
     * @param pid The identifier of the process to change.
     * @param group The target group for this process from THREAD_GROUP_*.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * priority.
     *
     * group == THREAD_GROUP_DEFAULT means to move all non-background priority
     * threads to the foreground scheduling group, but to leave background
     * priority threads alone.  group == THREAD_GROUP_BG_NONINTERACTIVE moves all
     * threads, regardless of priority, to the background scheduling group.
     * group == THREAD_GROUP_FOREGROUND is not allowed.
     */
    public static final native void setProcessGroup(int pid, int group)
            throws IllegalArgumentException, SecurityException;

    /**
     * Return the scheduling group of requested process.
     *
     * @hide
     */
    public static final native int getProcessGroup(int pid)
            throws IllegalArgumentException, SecurityException;

    /**
     * Set the priority of the calling thread, based on Linux priorities.  See
     * {@link #setThreadPriority(int, int)} for more information.
     *
     * @param priority A Linux priority level, from -20 for highest scheduling
     * priority to 19 for lowest scheduling priority.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * priority.
     *
     * @see #setThreadPriority(int, int)
     */
    public static final native void setThreadPriority(int priority)
            throws IllegalArgumentException, SecurityException;

    /**
     * Return the current priority of a thread, based on Linux priorities.
     *
     * @param tid The identifier of the thread/process to change.
     *
     * @return Returns the current priority, as a Linux priority level,
     * from -20 for highest scheduling priority to 19 for lowest scheduling
     * priority.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     */
    public static final native int getThreadPriority(int tid)
            throws IllegalArgumentException;

    /**
     * Set the scheduling policy and priority of a thread, based on Linux.
     *
     * @param tid The identifier of the thread/process to change.
     * @param policy A Linux scheduling policy such as SCHED_OTHER etc.
     * @param priority A Linux priority level in a range appropriate for the given policy.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist, or if <var>priority</var> is out of range for the policy.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * scheduling policy or priority.
     *
     * {@hide}
     */
    public static final native void setThreadScheduler(int tid, int policy, int priority)
            throws IllegalArgumentException;

    /**
     * Determine whether the current environment supports multiple processes.
     *
     * @return Returns true if the system can run in multiple processes, else
     * false if everything is running in a single process.
     *
     * @deprecated This method always returns true.  Do not use.
     */
    @Deprecated
    public static final boolean supportsProcesses() {
        return true;
    }

    /**
     * Set the out-of-memory badness adjustment for a process.
     *
     * @param pid The process identifier to set.
     * @param amt Adjustment value -- linux allows -16 to +15.
     *
     * @return Returns true if the underlying system supports this
     *         feature, else false.
     *
     * {@hide}
     */
    public static final native boolean setOomAdj(int pid, int amt);

    /**
     * Adjust the swappiness level for a process.
     *
     * @param pid The process identifier to set.
     * @param is_increased Whether swappiness should be increased or default.
     *
     * @return Returns true if the underlying system supports this
     *         feature, else false.
     *
     * {@hide}
     */
    public static final native boolean setSwappiness(int pid, boolean is_increased);

    /**
     * Change this process's argv[0] parameter.  This can be useful to show
     * more descriptive information in things like the 'ps' command.
     *
     * @param text The new name of this process.
     *
     * {@hide}
     */
    public static final native void setArgV0(String text);

    /**
     * Kill the process with the given PID.
     * Note that, though this API allows us to request to
     * kill any process based on its PID, the kernel will
     * still impose standard restrictions on which PIDs you
     * are actually able to kill.  Typically this means only
     * the process running the caller's packages/application
     * and any additional processes created by that app; packages
     * sharing a common UID will also be able to kill each
     * other's processes.
     */
    public static final void killProcess(int pid) {
        sendSignal(pid, SIGNAL_KILL);
    }

    /** @hide */
    public static final native int setUid(int uid);

    /** @hide */
    public static final native int setGid(int uid);

    /**
     * Send a signal to the given process.
     *
     * @param pid The pid of the target process.
     * @param signal The signal to send.
     */
    public static final native void sendSignal(int pid, int signal);

    /**
     * @hide
     * Private impl for avoiding a log message...  DO NOT USE without doing
     * your own log, or the Android Illuminati will find you some night and
     * beat you up.
     */
    public static final void killProcessQuiet(int pid) {
        sendSignalQuiet(pid, SIGNAL_KILL);
    }

    /**
     * @hide
     * Private impl for avoiding a log message...  DO NOT USE without doing
     * your own log, or the Android Illuminati will find you some night and
     * beat you up.
     */
    public static final native void sendSignalQuiet(int pid, int signal);

    /** @hide */
    public static final native long getFreeMemory();

    /** @hide */
    public static final native long getTotalMemory();

    /** @hide */
    public static final native void readProcLines(String path,
            String[] reqFields, long[] outSizes);

    /** @hide */
    public static final native int[] getPids(String path, int[] lastArray);

    /** @hide */
    public static final int PROC_TERM_MASK = 0xff;
    /** @hide */
    public static final int PROC_ZERO_TERM = 0;
    /** @hide */
    public static final int PROC_SPACE_TERM = (int)' ';
    /** @hide */
    public static final int PROC_TAB_TERM = (int)'\t';
    /** @hide */
    public static final int PROC_COMBINE = 0x100;
    /** @hide */
    public static final int PROC_PARENS = 0x200;
    /** @hide */
    public static final int PROC_QUOTES = 0x400;
    /** @hide */
    public static final int PROC_OUT_STRING = 0x1000;
    /** @hide */
    public static final int PROC_OUT_LONG = 0x2000;
    /** @hide */
    public static final int PROC_OUT_FLOAT = 0x4000;

    /** @hide */
    public static final native boolean readProcFile(String file, int[] format,
            String[] outStrings, long[] outLongs, float[] outFloats);

    /** @hide */
    public static final native boolean parseProcLine(byte[] buffer, int startIndex,
            int endIndex, int[] format, String[] outStrings, long[] outLongs, float[] outFloats);

    /** @hide */
    public static final native int[] getPidsForCommands(String[] cmds);

    /**
     * Gets the total Pss value for a given process, in bytes.
     *
     * @param pid the process to the Pss for
     * @return the total Pss value for the given process in bytes,
     *  or -1 if the value cannot be determined
     * @hide
     */
    public static final native long getPss(int pid);

    /**
     * Specifies the outcome of having started a process.
     * @hide
     */
    public static final class ProcessStartResult {
        /**
         * The PID of the newly started process.
         * Always >= 0.  (If the start failed, an exception will have been thrown instead.)
         */
        public int pid;

        /**
         * True if the process was started with a wrapper attached.
         */
        public boolean usingWrapper;
    }
}