Как выгрузить dll из Java-машины / forpes.ru

11:16

java -jar my-program.jar
private void addLibraryPath(String pathToAdd) throws ReflectiveOperationException {
    Field usrPathsField = ClassLoader.class.getDeclaredField("usr_paths");
    usrPathsField.setAccessible(true);
    String[] paths = (String[]) usrPathsField.get(null);
    String[] newPaths = Arrays.copyOf(paths, paths.length + 1);
    newPaths[newPaths.length - 1] = pathToAdd;
    usrPathsField.set(null, newPaths);
}
private Path prepareLibrary() throws IOException, ReflectiveOperationException {
    Path dir = Files.createTempDirectory("lib");
    try (InputStream input = ExampleClass.class.getResourceAsStream("custom.dll")) {
        if (input == null) {
            throw new FileNotFoundException("Can't load resource custom.dll");
        }
        Files.copy(input, dir.resolve("custom.dll"));
    }
    addLibraryPath(dir.toAbsolutePath().toString());
    return dir;
}

try {
    ...
} finally {
    delete(dir);
}

if (!delete(dir)) {
    forceDelete(dir);
}

ClassLoader parentCl = ExampleClass.class.getClassLoader();
classLoader = new URLClassLoader(new URL[0], parentCl);
Class.forName("org.jdbc.CustomDriver", classLoader, true);
try (Connection connection = DriverManager.getConnection(dbUrl, dbProperties)) {
    if (connection.getClass().getClassLoader() != classLoader) {
        System.out.printf("Что-то пошло не так%n");
    }
    ...
}

ClassLoader cl = ExampleClass.class.getClassLoader();
URL url = UnloadableDriver.class.getResource("CustomJDBCDriver.jar");
if (url == null) {
    throw new FileNotFoundException("Can't load resource CustomJDBCDriver.jar");
}
Path dir = prepareLibrary();
try (InputStream stream = url.openStream()) {
    Path target = dir.resolve("CustromJDBCDriver.jar");
    Files.copy(stream, target);
    url = target.toUri().toURL();
}
ClassLoader classLoader = new URLClassLoader(new URL[] {url}, cl);
Class.forName("org.jdbc.CustomDriver", true, classLoader);
try (Connection connection = DriverManager.getConnection(dbUrl, dbProperties)) {
    if (connection.getClass().getClassLoader() != classLoader) {
        System.out.printf("Что-то пошло не так%n");
    } else {
        System.out.printf("Получилось, можно идти дальше%n");
    }
    ...
}

public class ExampleClass implements AutoCloseable {
    private final Path dir;
    private URLClassLoader classLoader;

    public ExampleClass() {
        ...
    }

    public void doWork() {
        ...
    }

    @Override
    public void close() {
        ...
        this.classLoader.close();
        this.classloader = null;
        System.gc(); // где-то здесь должна выгрузиться dll
        if (!delete(this.dir)) {
            scheduleRemovalToTaskschd(this.dir);
        }
    }
}

public class Main {
    public static void main(String args[]) {
        try (ExampleClass example = new ExampleClass()) {
            example.doWork();
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
}

@Override
public void close() {
    ...
    this.classLoader.close();
    this.classloader = null;
    System.gc();
    System.runFinalization(); // где-то здесь должна выгрузиться dll
    if (!delete(this.dir)) {
        scheduleRemovalToTaskschd(this.dir);
    }
}

if (needConnection) {
    try (Connection connection = DriverManager.connect()) {
        ...
    }
}
// Вот здесь переменна connection еще считается живой.

Enumeration<Driver> drivers = driverManager.getDrivers();
while (drivers.hasMoreElements()) {
    Driver driver = drivers.nextElement();
    if (driver.getClass().getClassLoader() == classLoader) {
        DriverManager.deregisterDriver(driver);
        break;
    }
}

public interface DriverManagerProxy {
    void deregisterDriver(Driver driver) throws SQLException;
}

public class DriverManagerProxyImpl implements DriverManagerProxy {
    @Override
    public void deregisterDriver(Driver driver) throws SQLException {
        DriverManager.deregisterDriver(driver);
    }
}

public class ExampleClass implements AutoCloseable {
    private final Path dir;
    private URLClassLoader classLoader;
    private DriverManagerProxy driverManager;

    public ExampleClass() {
        ...
        this.classLoader = ...;
        Class.forName("org.jdbc.CustomDriver", true, classLoader);
        Class<?> dmClass = Class.forName("ru.example.DriverManagerProxyImpl",
                                         true,
                                         classLoader);
        this.driverManager = (DriverManagerProxy) dmClass.newInstance();
    }

    public void doWork() {
        ...
    }

    @Override
    public void close() {
        ...
        Enumeration<Driver> drivers = driverManager.getDrivers();
        while (drivers.hasMoreElements()) {
            Driver driver = drivers.nextElement();
            if (driver.getClass().getClassLoader() == classLoader) {
                driverManager.deregisterDriver(driver);
                break;
            }
        }
        this.driverManager = null;
        this.classLoader.close();
        this.classloader = null;
        System.gc();
        System.runFinalization(); // где-то здесь должна выгрузиться dll
        if (!delete(this.dir)) {
            scheduleRemovalToTaskschd(this.dir);
        }
    }
}

ResourceBundle.clearCache(classLoader);

private static void cleanupThreadLocals(ClassLoader cl)
        throws ReflectiveOperationException {
    int length = 1;
    Thread threads[] = new Thread[length];
    int cnt = Thread.enumerate(threads);
    while (cnt >= length) {
        length *= 2;
        threads = new Thread[length];
        cnt = Thread.enumerate(threads);
    }
    for (int i = 0; i < cnt; i++) {
        Thread thread = threads[i];
        if (thread == null) {
            continue;
        }
        cleanupThreadLocals(thread, cl);
    }
}

private static void cleanupThreadLocals(Thread thread, ClassLoader cl)
        throws ReflectiveOperationException {
    Field threadLocalsField = Thread.class.getDeclaredField("threadLocals");
    threadLocalsField.setAccessible(true);
    Object threadLocals = threadLocalsField.get(thread);
    if (threadLocals == null) {
        return;
    }
    Class<?> threadLocalsClass = threadLocals.getClass();
    Field tableField = threadLocalsClass.getDeclaredField("table");
    tableField.setAccessible(true);
    Object table = tableField.get(threadLocals);
    Object entries[] = (Object[]) table;
    Class<?> entryClass = table.getClass().getComponentType();
    Field valueField = entryClass.getDeclaredField("value");
    valueField.setAccessible(true);
    Method expungeStaleEntry = threadLocalsClass.getDeclaredMethod("expungeStaleEntry", Integer.TYPE);
    expungeStaleEntry.setAccessible(true);
    for (int i = 0; i < entries.length; i++) {
        Object entry = entries[i];
        if (entry == null) {
            continue;
        }
        Object value = valueField.get(entry);
        if (value != null) {
            ClassLoader valueClassLoader = value.getClass().getClassLoader();
            if (valueClassLoader == cl) {
                ((java.lang.ref.Reference<?>) entry).clear();
                expungeStaleEntry.invoke(threadLocals, i);
            }
        }
    }
}

try {
    ...
} catch (RuntimeException e) {
    if (e.getClass().getClassLoader() == this.getClass().getClassLoader()) {
        throw e;
    }
    RuntimeException exception = new RuntimeException(String.format("%s: %s", e.getClass(), e.getMessage()));
    exception.setStackTrace(e.getStackTrace());
    throw exception;
} catch (SQLException e) {
    if (e.getClass().getClassLoader() == this.getClass().getClassLoader()) {
        throw e;
    }
    SQLException exception = new SQLException(String.format("%s: %s", e.getClass(), e.getMessage()));
    exception.setStackTrace(e.getStackTrace());
    throw exception;
}

System.gc();
System.runFinalization();
System.gc();
System.runFinalization();

private static void dumpHeap() {
    try {
        Class<?> clazz = Class.forName("com.sun.management.HotSpotDiagnosticMXBean");
        MBeanServer server = ManagementFactory.getPlatformMBeanServer();
        Object hotspotMBean =
                ManagementFactory.newPlatformMXBeanProxy(
                        server, "com.sun.management:type=HotSpotDiagnostic", clazz);
        Method m = clazz.getMethod("dumpHeap", String.class, boolean.class);
        m.invoke(hotspotMBean, "nul", true);
    } catch (@SuppressWarnings("unused") RuntimeException e) {
        return;
    } catch (@SuppressWarnings("unused") ReflectiveOperationException e) {
        return;
    } catch (@SuppressWarnings("unused") IOException e) {
        return;
    }
}

this.classLoader = null;
System.gc();
System.runFinalization();
System.gc();
System.runFinalization();
if (!delete(this.dir)) {
    dumpHeap();
    if (!delete(this.dir)) {
        scheduleRemovalToTaskschd(this.dir);
    }
}

public class UnloadableDriver implements Driver, AutoCloseable {
    private final Path dir; // временный каталог, подлежащий удалению
    private URLClassLoader classLoader;
    private DriverManagerProxy driverManager;
    private Driver driver;

    public UnloadableDriver() throws SQLException {
        ...
    }

    @Override
    public void close() {
        ...
    }

    ...
}

public interface JDBCService {
    Connection getConnection(String url, Properties properties) throws SQLException;
}

@Service(JDBCService.class)
public class JDBCServiceImpl implements JDBCService {
    private UnloadableDriver driver;

    @Activate
    public void activate(ComponentContext ctx) throws SQLException {
        this.driver = new UnloadableDriver();
    }

    @Deactivate
    public void deactivate() {
        this.driver.close();
        this.driver = null;
    }

    @Override
    public Connection getConnection(String url, Properties info) throws SQLException {
        return this.driver.connect(url, properties);
    }
}

import java.lang.reflect.*;
import java.util.*;

public class Test {
  public static void main(String[] args) throws Exception {
    Field usrPathsField = ClassLoader.class.getDeclaredField("usr_paths");
    usrPathsField.setAccessible(true);
    String[] paths = (String[]) usrPathsField.get(null);
    System.out.println(Arrays.toString(paths));
  }
}
System.gc();
System.runFinalization();

Как выгрузить dll из Java-машины +23

Попытка решения

Использование класслоадера

Эксперименты со сборщиком мусора

Локальные переменные

DriverManager

ResourceBundle

ThreadLocals

Исключения

Java наносит ответный удар

Проверка при помощи OSGI

Выводы

Комментарии (21)

apangin

sergey-b

barker

lany

apangin

lany

apangin

sergey-b

apangin

izzholtik

Pngv

lany

sergey-b

apangin

sergey-b

lany

sergey-b

Pngv

lany

Ilias

sergey-b