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 * 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.
 *
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 */
package jdk.vm.ci.hotspot;

/**
 * Scope used to potentially change whether the current thread can make VM-to-Java calls.
 * A scope is exited by the {@link #close()} method so it should be used in a
 * try-with-resources statement.
 *
 * The scope does nothing if the current thread is not a HotSpot VM CompilerThread
 * for a JVMCI compiler.
 */
public class CompilerThreadCanCallJavaScope implements AutoCloseable {

    /**
     * Thread state used during the scope.
     */
    private final boolean state;

    /**
     * Non-null iff the thread state needs resetting in {@link #close()}.
     */
    private final CompilerToVM vm;

    /**
     * The thread on which the constructor was called.
     */
    private final Thread thread;

    /**
     * Opens a scope to allow/disallow the current thread to make VM-to-Java calls.
     * The scope is a no-op if the current thread is not a HotSpot VM CompilerThread
     * for a JVMCI compiler.
     *
     * @param newState true/false to allow/disallow VM-to-Java calls within the scope
     */
    public CompilerThreadCanCallJavaScope(boolean newState) {
        this.state = newState;
        this.thread = Thread.currentThread();
        CompilerToVM vm = HotSpotJVMCIRuntime.runtime().getCompilerToVM();
        if (vm.updateCompilerThreadCanCallJava(newState)) {
            this.vm = vm;
        } else {
            this.vm = null;
        }
    }

    /**
     * Resets the state of the current thread with respect to whether it can make
     * VM-to-Java calls to what it was before the constructor was called.
     *
     * @throws IllegalStateException if called on a different thread than the constructor
     */
    @Override
    public void close() {
        if (this.thread != Thread.currentThread()) {
            throw new IllegalStateException();
        }

        if (vm != null) {
            vm.updateCompilerThreadCanCallJava(!state);
        }
    }
}