DlOpen implementation using the Foreign Linker API

DlOpen.java

/*
 * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

import jdk.incubator.foreign.CLinker;
import jdk.incubator.foreign.FunctionDescriptor;
import jdk.incubator.foreign.MemoryAddress;
import jdk.incubator.foreign.ResourceScope;
import jdk.incubator.foreign.SymbolLookup;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import java.util.Optional;

class DlOpen {
    static final MethodHandle DL_OPEN = CLinker.getInstance().downcallHandle(
            CLinker.systemLookup().lookup("dlopen").get(),
            MethodType.methodType(MemoryAddress.class, MemoryAddress.class, int.class),
            FunctionDescriptor.of(CLinker.C_POINTER, CLinker.C_POINTER, CLinker.C_INT));

    static final MethodHandle DL_SYM = CLinker.getInstance().downcallHandle(
            CLinker.systemLookup().lookup("dlsym").get(),
            MethodType.methodType(MemoryAddress.class, MemoryAddress.class, MemoryAddress.class),
            FunctionDescriptor.of(CLinker.C_POINTER, CLinker.C_POINTER, CLinker.C_POINTER));

    static final MethodHandle DL_CLOSE = CLinker.getInstance().downcallHandle(
            CLinker.systemLookup().lookup("dlclose").get(),
            MethodType.methodType(int.class, MemoryAddress.class),
            FunctionDescriptor.of(CLinker.C_INT, CLinker.C_POINTER));

    private static MemoryAddress dlopen(MemoryAddress libName, int dlopenOptions) {
        try {
            return (MemoryAddress)DL_OPEN.invokeExact(libName, dlopenOptions);
        } catch (Throwable ex) {
            throw new IllegalStateException();
        }
    }

    private static MemoryAddress dlsym(MemoryAddress handle, MemoryAddress symbolName) {
        try {
            return (MemoryAddress)DL_SYM.invokeExact(handle, symbolName);
        } catch (Throwable ex) {
            throw new IllegalStateException();
        }
    }

    private static int dlclose(MemoryAddress handle) {
        try {
            return (int)DL_CLOSE.invokeExact(handle);
        } catch (Throwable ex) {
            throw new IllegalStateException();
        }
    }

    public static SymbolLookup lookup(String libraryName, ResourceScope scope) {
        try (ResourceScope openScope = ResourceScope.newConfinedScope()) {
            final MemoryAddress handle = dlopen(CLinker.toCString(libraryName, openScope).address(), 1);
            if (handle == MemoryAddress.NULL) {
                throw new IllegalArgumentException("Cannot find library: " + libraryName);
            }
            scope.addCloseAction(() -> dlclose(handle));
            return name -> {
                try (ResourceScope lookupScope = ResourceScope.newConfinedScope()) {
                    MemoryAddress sym = dlsym(handle, CLinker.toCString(name, lookupScope).address());
                    return sym == MemoryAddress.NULL ?
                            Optional.empty() : Optional.of(sym);
                }
            };
        }
    }

    public static void main(String[] args) {
        // quick test
        try (ResourceScope scope = ResourceScope.newConfinedScope()) {
            SymbolLookup clib = DlOpen.lookup("libc.so.6", scope);
            System.out.println(clib.lookup("qsort"));
        } // library unloaded here
    }
}