xref: /libcore/dalvik/src/main/java/dalvik/system/Zygote.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 dalvik.system;

import java.io.File;

/**
 * Provides access to the Dalvik "zygote" feature, which allows a VM instance to
 * be partially initialized and then fork()'d from the partially initialized
 * state.
 *
 * @hide
 */
public class Zygote {
    /*
     * Bit values for "debugFlags" argument.  The definitions are duplicated
     * in the native code.
     */
    /** enable debugging over JDWP */
    public static final int DEBUG_ENABLE_DEBUGGER   = 1;
    /** enable JNI checks */
    public static final int DEBUG_ENABLE_CHECKJNI   = 1 << 1;
    /** enable Java programming language "assert" statements */
    public static final int DEBUG_ENABLE_ASSERT     = 1 << 2;
    /** disable the JIT compiler */
    public static final int DEBUG_ENABLE_SAFEMODE   = 1 << 3;
    /** Enable logging of third-party JNI activity. */
    public static final int DEBUG_ENABLE_JNI_LOGGING = 1 << 4;

    /** No external storage should be mounted. */
    public static final int MOUNT_EXTERNAL_NONE = 0;
    /** Single-user external storage should be mounted. */
    public static final int MOUNT_EXTERNAL_SINGLEUSER = 1;
    /** Multi-user external storage should be mounted. */
    public static final int MOUNT_EXTERNAL_MULTIUSER = 2;
    /** All multi-user external storage should be mounted. */
    public static final int MOUNT_EXTERNAL_MULTIUSER_ALL = 3;

    /**
     * When set by the system server, all subsequent apps will be launched in
     * VM safe mode.
     */
    public static boolean systemInSafeMode = false;

    private Zygote() {}

    private static void preFork() {
        Daemons.stop();
        waitUntilAllThreadsStopped();
    }

    /**
     * We must not fork until we're single-threaded again. Wait until /proc shows we're
     * down to just one thread.
     */
    private static void waitUntilAllThreadsStopped() {
        File tasks = new File("/proc/self/task");
        while (tasks.list().length > 1) {
            try {
                // Experimentally, booting and playing about with a stingray, I never saw us
                // go round this loop more than once with a 10ms sleep.
                Thread.sleep(10);
            } catch (InterruptedException ignored) {
            }
        }
    }

    private static void postFork() {
        Daemons.start();
    }

    /**
     * Forks a new Zygote instance, but does not leave the zygote mode.
     * The current VM must have been started with the -Xzygote flag. The
     * new child is expected to eventually call forkAndSpecialize()
     *
     * @return 0 if this is the child, pid of the child
     * if this is the parent, or -1 on error
     */
    public static int fork() {
        preFork();
        int pid = nativeFork();
        postFork();
        return pid;
    }

    native public static int nativeFork();

    /**
     * Forks a new VM instance.  The current VM must have been started
     * with the -Xzygote flag. <b>NOTE: new instance keeps all
     * root capabilities. The new process is expected to call capset()</b>.
     *
     * @param uid the UNIX uid that the new process should setuid() to after
     * fork()ing and and before spawning any threads.
     * @param gid the UNIX gid that the new process should setgid() to after
     * fork()ing and and before spawning any threads.
     * @param gids null-ok; a list of UNIX gids that the new process should
     * setgroups() to after fork and before spawning any threads.
     * @param debugFlags bit flags that enable debugging features.
     * @param rlimits null-ok an array of rlimit tuples, with the second
     * dimension having a length of 3 and representing
     * (resource, rlim_cur, rlim_max). These are set via the posix
     * setrlimit(2) call.
     * @param seInfo null-ok a string specifying SEAndroid information for
     * the new process.
     * @param niceName null-ok a string specifying the process name.
     *
     * @return 0 if this is the child, pid of the child
     * if this is the parent, or -1 on error.
     */
    public static int forkAndSpecialize(int uid, int gid, int[] gids, int debugFlags,
            int[][] rlimits, int mountExternal, String seInfo, String niceName) {
        preFork();
        int pid = nativeForkAndSpecialize(
                uid, gid, gids, debugFlags, rlimits, mountExternal, seInfo, niceName);
        postFork();
        return pid;
    }

    native public static int nativeForkAndSpecialize(int uid, int gid, int[] gids, int debugFlags,
            int[][] rlimits, int mountExternal, String seInfo, String niceName);

    /**
     * Special method to start the system server process. In addition to the
     * common actions performed in forkAndSpecialize, the pid of the child
     * process is recorded such that the death of the child process will cause
     * zygote to exit.
     *
     * @param uid the UNIX uid that the new process should setuid() to after
     * fork()ing and and before spawning any threads.
     * @param gid the UNIX gid that the new process should setgid() to after
     * fork()ing and and before spawning any threads.
     * @param gids null-ok; a list of UNIX gids that the new process should
     * setgroups() to after fork and before spawning any threads.
     * @param debugFlags bit flags that enable debugging features.
     * @param rlimits null-ok an array of rlimit tuples, with the second
     * dimension having a length of 3 and representing
     * (resource, rlim_cur, rlim_max). These are set via the posix
     * setrlimit(2) call.
     * @param permittedCapabilities argument for setcap()
     * @param effectiveCapabilities argument for setcap()
     *
     * @return 0 if this is the child, pid of the child
     * if this is the parent, or -1 on error.
     */
    public static int forkSystemServer(int uid, int gid, int[] gids, int debugFlags,
            int[][] rlimits, long permittedCapabilities, long effectiveCapabilities) {
        preFork();
        int pid = nativeForkSystemServer(
                uid, gid, gids, debugFlags, rlimits, permittedCapabilities, effectiveCapabilities);
        postFork();
        return pid;
    }

    native public static int nativeForkSystemServer(int uid, int gid, int[] gids, int debugFlags,
            int[][] rlimits, long permittedCapabilities, long effectiveCapabilities);

    /**
     * Executes "/system/bin/sh -c &lt;command&gt;" using the exec() system call.
     * This method never returns.
     *
     * @param command The shell command to execute.
     */
    public static void execShell(String command) {
        nativeExecShell(command);
    }

    /**
     * Appends quotes shell arguments to the specified string builder.
     * The arguments are quoted using single-quotes, escaped if necessary,
     * prefixed with a space, and appended to the command.
     *
     * @param command A string builder for the shell command being constructed.
     * @param args An array of argument strings to be quoted and appended to the command.
     * @see #execShell(String)
     */
    public static void appendQuotedShellArgs(StringBuilder command, String[] args) {
        for (String arg : args) {
            command.append(" '").append(arg.replace("'", "'\\''")).append("'");
        }
    }

    native private static void nativeExecShell(String command);
}