com/android/internal/os/ZygoteServer.java

/*
 * 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 static android.system.OsConstants.POLLIN;

import android.net.LocalServerSocket;
import android.net.LocalSocket;
import android.os.SystemClock;
import android.os.Trace;
import android.system.ErrnoException;
import android.system.Os;
import android.system.StructPollfd;
import android.util.Log;
import android.util.Slog;

import dalvik.system.ZygoteHooks;

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.FileDescriptor;
import java.io.IOException;
import java.util.ArrayList;

/**
 * Server socket class for zygote processes.
 *
 * Provides functions to wait for commands on a UNIX domain socket, and fork
 * off child processes that inherit the initial state of the VM.%
 *
 * Please see {@link ZygoteArguments} for documentation on the
 * client protocol.
 */
class ZygoteServer {
    // TODO (chriswailes): Change this so it is set with Zygote or ZygoteSecondary as appropriate
    public static final String TAG = "ZygoteServer";

    /**
     * The maximim value that will be accepted from the USAP_POOL_SIZE_MAX device property.
     * is a mirror of USAP_POOL_MAX_LIMIT found in com_android_internal_os_Zygote.cpp.
     */
    private static final int USAP_POOL_SIZE_MAX_LIMIT = 100;

    /**
     * The minimum value that will be accepted from the USAP_POOL_SIZE_MIN device property.
     */
    private static final int USAP_POOL_SIZE_MIN_LIMIT = 1;

    /** The default value used for the USAP_POOL_SIZE_MAX device property */
    private static final String USAP_POOL_SIZE_MAX_DEFAULT = "10";

    /** The default value used for the USAP_POOL_SIZE_MIN device property */
    private static final String USAP_POOL_SIZE_MIN_DEFAULT = "1";

    /**
     * Indicates if this Zygote server can support a unspecialized app process pool.  Currently this
     * should only be true for the primary and secondary Zygotes, and not the App Zygotes or the
     * WebView Zygote.
     *
     * TODO (chriswailes): Make this an explicit argument to the constructor
     */

    private final boolean mUsapPoolSupported;

    /**
     * If the unspecialized app process pool should be created and used to start applications.
     *
     * Setting this value to false will disable the creation, maintenance, and use of the USAP
     * pool.  When the USAP pool is disabled the application lifecycle will be identical to
     * previous versions of Android.
     */
    private boolean mUsapPoolEnabled = false;

    /**
     * Listening socket that accepts new server connections.
     */
    private LocalServerSocket mZygoteSocket;

    /**
     * The name of the unspecialized app process pool socket to use if the USAP pool is enabled.
     */
    private LocalServerSocket mUsapPoolSocket;

    /**
     * File descriptor used for communication between the signal handler and the ZygoteServer poll
     * loop.
     * */
    private FileDescriptor mUsapPoolEventFD;

    /**
     * Whether or not mZygoteSocket's underlying FD should be closed directly.
     * If mZygoteSocket is created with an existing FD, closing the socket does
     * not close the FD and it must be closed explicitly. If the socket is created
     * with a name instead, then closing the socket will close the underlying FD
     * and it should not be double-closed.
     */
    private boolean mCloseSocketFd;

    /**
     * Set by the child process, immediately after a call to {@code Zygote.forkAndSpecialize}.
     */
    private boolean mIsForkChild;

    /**
     * The runtime-adjustable maximum USAP pool size.
     */
    private int mUsapPoolSizeMax = 0;

    /**
     * The runtime-adjustable minimum USAP pool size.
     */
    private int mUsapPoolSizeMin = 0;

    /**
     * The runtime-adjustable value used to determine when to re-fill the USAP pool.  The pool will
     * be re-filled when (mUsapPoolMax - gUsapPoolCount) >= sUsapPoolRefillThreshold.
     */
    private int mUsapPoolRefillThreshold = 0;

    ZygoteServer() {
        mUsapPoolEventFD = null;
        mZygoteSocket = null;
        mUsapPoolSocket = null;

        mUsapPoolSupported = false;
    }

    /**
     * Initialize the Zygote server with the Zygote server socket, USAP pool server socket, and USAP
     * pool event FD.
     *
     * @param isPrimaryZygote  If this is the primary Zygote or not.
     */
    ZygoteServer(boolean isPrimaryZygote) {
        mUsapPoolEventFD = Zygote.getUsapPoolEventFD();

        if (isPrimaryZygote) {
            mZygoteSocket = Zygote.createManagedSocketFromInitSocket(Zygote.PRIMARY_SOCKET_NAME);
            mUsapPoolSocket =
                    Zygote.createManagedSocketFromInitSocket(
                            Zygote.USAP_POOL_PRIMARY_SOCKET_NAME);
        } else {
            mZygoteSocket = Zygote.createManagedSocketFromInitSocket(Zygote.SECONDARY_SOCKET_NAME);
            mUsapPoolSocket =
                    Zygote.createManagedSocketFromInitSocket(
                            Zygote.USAP_POOL_SECONDARY_SOCKET_NAME);
        }

        fetchUsapPoolPolicyProps();

        mUsapPoolSupported = true;
    }

    void setForkChild() {
        mIsForkChild = true;
    }

    public boolean isUsapPoolEnabled() {
        return mUsapPoolEnabled;
    }

    /**
     * Registers a server socket for zygote command connections. This opens the server socket
     * at the specified name in the abstract socket namespace.
     */
    void registerServerSocketAtAbstractName(String socketName) {
        if (mZygoteSocket == null) {
            try {
                mZygoteSocket = new LocalServerSocket(socketName);
                mCloseSocketFd = false;
            } catch (IOException ex) {
                throw new RuntimeException(
                        "Error binding to abstract socket '" + socketName + "'", ex);
            }
        }
    }

    /**
     * Waits for and accepts a single command connection. Throws
     * RuntimeException on failure.
     */
    private ZygoteConnection acceptCommandPeer(String abiList) {
        try {
            return createNewConnection(mZygoteSocket.accept(), abiList);
        } catch (IOException ex) {
            throw new RuntimeException(
                    "IOException during accept()", ex);
        }
    }

    protected ZygoteConnection createNewConnection(LocalSocket socket, String abiList)
            throws IOException {
        return new ZygoteConnection(socket, abiList);
    }

    /**
     * Close and clean up zygote sockets. Called on shutdown and on the
     * child's exit path.
     */
    void closeServerSocket() {
        try {
            if (mZygoteSocket != null) {
                FileDescriptor fd = mZygoteSocket.getFileDescriptor();
                mZygoteSocket.close();
                if (fd != null && mCloseSocketFd) {
                    Os.close(fd);
                }
            }
        } catch (IOException ex) {
            Log.e(TAG, "Zygote:  error closing sockets", ex);
        } catch (ErrnoException ex) {
            Log.e(TAG, "Zygote:  error closing descriptor", ex);
        }

        mZygoteSocket = null;
    }

    /**
     * Return the server socket's underlying file descriptor, so that
     * ZygoteConnection can pass it to the native code for proper
     * closure after a child process is forked off.
     */

    FileDescriptor getZygoteSocketFileDescriptor() {
        return mZygoteSocket.getFileDescriptor();
    }

    private void fetchUsapPoolPolicyProps() {
        if (mUsapPoolSupported) {
            final String usapPoolSizeMaxPropString = Zygote.getConfigurationProperty(
                    ZygoteConfig.USAP_POOL_SIZE_MAX, USAP_POOL_SIZE_MAX_DEFAULT);

            if (!usapPoolSizeMaxPropString.isEmpty()) {
                mUsapPoolSizeMax = Integer.min(Integer.parseInt(
                        usapPoolSizeMaxPropString), USAP_POOL_SIZE_MAX_LIMIT);
            }

            final String usapPoolSizeMinPropString = Zygote.getConfigurationProperty(
                    ZygoteConfig.USAP_POOL_SIZE_MIN, USAP_POOL_SIZE_MIN_DEFAULT);

            if (!usapPoolSizeMinPropString.isEmpty()) {
                mUsapPoolSizeMin = Integer.max(
                        Integer.parseInt(usapPoolSizeMinPropString), USAP_POOL_SIZE_MIN_LIMIT);
            }

            final String usapPoolRefillThresholdPropString = Zygote.getConfigurationProperty(
                    ZygoteConfig.USAP_POOL_REFILL_THRESHOLD,
                    Integer.toString(mUsapPoolSizeMax / 2));

            if (!usapPoolRefillThresholdPropString.isEmpty()) {
                mUsapPoolRefillThreshold = Integer.min(
                        Integer.parseInt(usapPoolRefillThresholdPropString),
                        mUsapPoolSizeMax);
            }

            // Sanity check
            if (mUsapPoolSizeMin >= mUsapPoolSizeMax) {
                Log.w(TAG, "The max size of the USAP pool must be greater than the minimum size."
                        + "  Restoring default values.");

                mUsapPoolSizeMax = Integer.parseInt(USAP_POOL_SIZE_MAX_DEFAULT);
                mUsapPoolSizeMin = Integer.parseInt(USAP_POOL_SIZE_MIN_DEFAULT);
                mUsapPoolRefillThreshold = mUsapPoolSizeMax / 2;
            }
        }
    }

    private boolean mIsFirstPropertyCheck = true;
    private long mLastPropCheckTimestamp = 0;

    private void fetchUsapPoolPolicyPropsWithMinInterval() {
        final long currentTimestamp = SystemClock.elapsedRealtime();

        if (mIsFirstPropertyCheck
                || (currentTimestamp - mLastPropCheckTimestamp >= Zygote.PROPERTY_CHECK_INTERVAL)) {
            mIsFirstPropertyCheck = false;
            mLastPropCheckTimestamp = currentTimestamp;
            fetchUsapPoolPolicyProps();
        }
    }

    /**
     * Checks to see if the current policy says that pool should be refilled, and spawns new USAPs
     * if necessary.
     *
     * @param sessionSocketRawFDs  Anonymous session sockets that are currently open
     * @return In the Zygote process this function will always return null; in unspecialized app
     *         processes this function will return a Runnable object representing the new
     *         application that is passed up from usapMain.
     */

    Runnable fillUsapPool(int[] sessionSocketRawFDs) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Zygote:FillUsapPool");

        // Ensure that the pool properties have been fetched.
        fetchUsapPoolPolicyPropsWithMinInterval();

        int usapPoolCount = Zygote.getUsapPoolCount();
        int numUsapsToSpawn = mUsapPoolSizeMax - usapPoolCount;

        if (usapPoolCount < mUsapPoolSizeMin
                || numUsapsToSpawn >= mUsapPoolRefillThreshold) {

            // Disable some VM functionality and reset some system values
            // before forking.
            ZygoteHooks.preFork();
            Zygote.resetNicePriority();

            while (usapPoolCount++ < mUsapPoolSizeMax) {
                Runnable caller = Zygote.forkUsap(mUsapPoolSocket, sessionSocketRawFDs);

                if (caller != null) {
                    return caller;
                }
            }

            // Re-enable runtime services for the Zygote.  Services for unspecialized app process
            // are re-enabled in specializeAppProcess.
            ZygoteHooks.postForkCommon();

            Log.i("zygote",
                    "Filled the USAP pool. New USAPs: " + numUsapsToSpawn);
        }

        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

        return null;
    }

    /**
     * Empty or fill the USAP pool as dictated by the current and new USAP pool statuses.
     */
    Runnable setUsapPoolStatus(boolean newStatus, LocalSocket sessionSocket) {
        if (!mUsapPoolSupported) {
            Log.w(TAG,
                    "Attempting to enable a USAP pool for a Zygote that doesn't support it.");
            return null;
        } else if (mUsapPoolEnabled == newStatus) {
            return null;
        }

        Log.i(TAG, "USAP Pool status change: " + (newStatus ? "ENABLED" : "DISABLED"));

        mUsapPoolEnabled = newStatus;

        if (newStatus) {
            return fillUsapPool(new int[]{ sessionSocket.getFileDescriptor().getInt$() });
        } else {
            Zygote.emptyUsapPool();
            return null;
        }
    }

    /**
     * Runs the zygote process's select loop. Accepts new connections as
     * they happen, and reads commands from connections one spawn-request's
     * worth at a time.
     */
    Runnable runSelectLoop(String abiList) {
        ArrayList<FileDescriptor> socketFDs = new ArrayList<FileDescriptor>();
        ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();

        socketFDs.add(mZygoteSocket.getFileDescriptor());
        peers.add(null);

        while (true) {
            fetchUsapPoolPolicyPropsWithMinInterval();

            int[] usapPipeFDs = null;
            StructPollfd[] pollFDs = null;

            // Allocate enough space for the poll structs, taking into account
            // the state of the USAP pool for this Zygote (could be a
            // regular Zygote, a WebView Zygote, or an AppZygote).
            if (mUsapPoolEnabled) {
                usapPipeFDs = Zygote.getUsapPipeFDs();
                pollFDs = new StructPollfd[socketFDs.size() + 1 + usapPipeFDs.length];
            } else {
                pollFDs = new StructPollfd[socketFDs.size()];
            }

            /*
             * For reasons of correctness the USAP pool pipe and event FDs
             * must be processed before the session and server sockets.  This
             * is to ensure that the USAP pool accounting information is
             * accurate when handling other requests like API blacklist
             * exemptions.
             */

            int pollIndex = 0;
            for (FileDescriptor socketFD : socketFDs) {
                pollFDs[pollIndex] = new StructPollfd();
                pollFDs[pollIndex].fd = socketFD;
                pollFDs[pollIndex].events = (short) POLLIN;
                ++pollIndex;
            }

            final int usapPoolEventFDIndex = pollIndex;

            if (mUsapPoolEnabled) {
                pollFDs[pollIndex] = new StructPollfd();
                pollFDs[pollIndex].fd = mUsapPoolEventFD;
                pollFDs[pollIndex].events = (short) POLLIN;
                ++pollIndex;

                for (int usapPipeFD : usapPipeFDs) {
                    FileDescriptor managedFd = new FileDescriptor();
                    managedFd.setInt$(usapPipeFD);

                    pollFDs[pollIndex] = new StructPollfd();
                    pollFDs[pollIndex].fd = managedFd;
                    pollFDs[pollIndex].events = (short) POLLIN;
                    ++pollIndex;
                }
            }

            try {
                Os.poll(pollFDs, -1);
            } catch (ErrnoException ex) {
                throw new RuntimeException("poll failed", ex);
            }

            boolean usapPoolFDRead = false;

            while (--pollIndex >= 0) {
                if ((pollFDs[pollIndex].revents & POLLIN) == 0) {
                    continue;
                }

                if (pollIndex == 0) {
                    // Zygote server socket

                    ZygoteConnection newPeer = acceptCommandPeer(abiList);
                    peers.add(newPeer);
                    socketFDs.add(newPeer.getFileDescriptor());

                } else if (pollIndex < usapPoolEventFDIndex) {
                    // Session socket accepted from the Zygote server socket

                    try {
                        ZygoteConnection connection = peers.get(pollIndex);
                        final Runnable command = connection.processOneCommand(this);

                        // TODO (chriswailes): Is this extra check necessary?
                        if (mIsForkChild) {
                            // We're in the child. We should always have a command to run at this
                            // stage if processOneCommand hasn't called "exec".
                            if (command == null) {
                                throw new IllegalStateException("command == null");
                            }

                            return command;
                        } else {
                            // We're in the server - we should never have any commands to run.
                            if (command != null) {
                                throw new IllegalStateException("command != null");
                            }

                            // We don't know whether the remote side of the socket was closed or
                            // not until we attempt to read from it from processOneCommand. This
                            // shows up as a regular POLLIN event in our regular processing loop.
                            if (connection.isClosedByPeer()) {
                                connection.closeSocket();
                                peers.remove(pollIndex);
                                socketFDs.remove(pollIndex);
                            }
                        }
                    } catch (Exception e) {
                        if (!mIsForkChild) {
                            // We're in the server so any exception here is one that has taken place
                            // pre-fork while processing commands or reading / writing from the
                            // control socket. Make a loud noise about any such exceptions so that
                            // we know exactly what failed and why.

                            Slog.e(TAG, "Exception executing zygote command: ", e);

                            // Make sure the socket is closed so that the other end knows
                            // immediately that something has gone wrong and doesn't time out
                            // waiting for a response.
                            ZygoteConnection conn = peers.remove(pollIndex);
                            conn.closeSocket();

                            socketFDs.remove(pollIndex);
                        } else {
                            // We're in the child so any exception caught here has happened post
                            // fork and before we execute ActivityThread.main (or any other main()
                            // method). Log the details of the exception and bring down the process.
                            Log.e(TAG, "Caught post-fork exception in child process.", e);
                            throw e;
                        }
                    } finally {
                        // Reset the child flag, in the event that the child process is a child-
                        // zygote. The flag will not be consulted this loop pass after the Runnable
                        // is returned.
                        mIsForkChild = false;
                    }
                } else {
                    // Either the USAP pool event FD or a USAP reporting pipe.

                    // If this is the event FD the payload will be the number of USAPs removed.
                    // If this is a reporting pipe FD the payload will be the PID of the USAP
                    // that was just specialized.
                    long messagePayload = -1;

                    try {
                        byte[] buffer = new byte[Zygote.USAP_MANAGEMENT_MESSAGE_BYTES];
                        int readBytes = Os.read(pollFDs[pollIndex].fd, buffer, 0, buffer.length);

                        if (readBytes == Zygote.USAP_MANAGEMENT_MESSAGE_BYTES) {
                            DataInputStream inputStream =
                                    new DataInputStream(new ByteArrayInputStream(buffer));

                            messagePayload = inputStream.readLong();
                        } else {
                            Log.e(TAG, "Incomplete read from USAP management FD of size "
                                    + readBytes);
                            continue;
                        }
                    } catch (Exception ex) {
                        if (pollIndex == usapPoolEventFDIndex) {
                            Log.e(TAG, "Failed to read from USAP pool event FD: "
                                    + ex.getMessage());
                        } else {
                            Log.e(TAG, "Failed to read from USAP reporting pipe: "
                                    + ex.getMessage());
                        }

                        continue;
                    }

                    if (pollIndex > usapPoolEventFDIndex) {
                        Zygote.removeUsapTableEntry((int) messagePayload);
                    }

                    usapPoolFDRead = true;
                }
            }

            // Check to see if the USAP pool needs to be refilled.
            if (usapPoolFDRead) {
                int[] sessionSocketRawFDs =
                        socketFDs.subList(1, socketFDs.size())
                                .stream()
                                .mapToInt(fd -> fd.getInt$())
                                .toArray();

                final Runnable command = fillUsapPool(sessionSocketRawFDs);

                if (command != null) {
                    return command;
                }
            }
        }
    }
}