/*

 * Copyright (c) 2019, 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

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 */

package jdk.internal.vm.compiler.libgraal;

import jdk.vm.ci.hotspot.HotSpotJVMCIRuntime;

/**

 * Scope for calling CEntryPoints in libgraal. {@linkplain #LibGraalScope(HotSpotJVMCIRuntime)

 * Opening} a scope attaches the current thread to libgraal and {@linkplain #close() closing} it

 * detaches the current thread.

 */

public final class LibGraalScope implements AutoCloseable {

    static final ThreadLocal<LibGraalScope> currentScope = new ThreadLocal<>();

    private final LibGraalScope parent;

    private final boolean topLevel;

    private final HotSpotJVMCIRuntime runtime;

    private final long isolateThread;

    /**

     * Gets the isolate thread associated with the current thread. The current thread must be in an

     * {@linkplain #LibGraalScope(HotSpotJVMCIRuntime) opened} scope.

     *

     * @returns a value that can be used for the IsolateThreadContext argument of a {@code native}

     *          method {@link LibGraal#registerNativeMethods linked} to a CEntryPoint function in

     *          libgraal

     * @throws IllegalStateException if not the current thread is not attached to libgraal

     */

    public static long getIsolateThread() {

        LibGraalScope scope = currentScope.get();

        if (scope == null) {

            throw new IllegalStateException("Cannot get isolate thread outside of a " + LibGraalScope.class.getSimpleName());

        }

        return scope.isolateThread;

    }

    /**

     * Enters a scope for making calls into libgraal. If there is no existing libgraal scope for the

     * current thread, the current thread is attached to libgraal. When the outer most scope is

     * closed, the current thread is detached from libgraal.

     *

     * This must be used in a try-with-resources statement.

     *

     * This cannot be called from {@linkplain LibGraal#inLibGraal() within} libgraal.

     *

     * @throws IllegalStateException if libgraal is {@linkplain LibGraal#isAvailable() unavailable}

     *             or {@link LibGraal#inLibGraal()} returns true

     */

    public LibGraalScope(HotSpotJVMCIRuntime runtime) {

        if (LibGraal.inLibGraal() || !LibGraal.isAvailable()) {

            throw new IllegalStateException();

        }

        this.runtime = runtime;

        parent = currentScope.get();

        boolean top = false;

        if (parent == null) {

            top = LibGraal.attachCurrentThread(runtime, false);

            isolateThread = LibGraal.getCurrentIsolateThread(LibGraal.isolate);

        } else {

            isolateThread = parent.isolateThread;

        }

        topLevel = top;

        currentScope.set(this);

    }

    @Override

    public void close() {

        if (topLevel) {

            LibGraal.detachCurrentThread(runtime);

        }

        currentScope.set(parent);

    }

}