src/jdk.jshell/share/classes/jdk/jshell/execution/LocalExecutionControl.java

/*
 * Copyright (c) 2016, 2025, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.jshell.execution;

import java.lang.constant.ClassDesc;
import java.lang.constant.ConstantDescs;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Stream;
import java.lang.classfile.ClassFile;
import java.lang.classfile.ClassTransform;
import java.lang.classfile.CodeBuilder;
import java.lang.classfile.CodeElement;
import java.lang.classfile.CodeTransform;
import java.lang.classfile.Label;
import java.lang.classfile.instruction.BranchInstruction;
import java.lang.classfile.instruction.LabelTarget;

/**
 * An implementation of {@link jdk.jshell.spi.ExecutionControl} which executes
 * in the same JVM as the JShell-core.
 *
 * @author Grigory Ptashko
 * @since 9
 */
public class LocalExecutionControl extends DirectExecutionControl {

    private final Object STOP_LOCK = new Object();
    private boolean userCodeRunning = false;
    private ThreadGroup execThreadGroup;
    private Field allStop = null;

    /**
     * Creates an instance, delegating loader operations to the specified
     * delegate.
     *
     * @param loaderDelegate the delegate to handle loading classes
     */
    public LocalExecutionControl(LoaderDelegate loaderDelegate) {
        super(loaderDelegate);
    }

    /**
     * Create an instance using the default class loading, which delegates to the system class loader.
     */
    public LocalExecutionControl() {
    }

    /**
     * Create an instance using the default class loading, but delegating to the specified parent class loader.
     *
     * @param parent parent class loader
     * @since 22
     */
    public LocalExecutionControl(ClassLoader parent) {
        super(new DefaultLoaderDelegate(parent));
    }

    @Override
    public void load(ClassBytecodes[] cbcs)
            throws ClassInstallException, NotImplementedException, EngineTerminationException {
        super.load(Stream.of(cbcs)
                .map(cbc -> new ClassBytecodes(cbc.name(), instrument(cbc.bytecodes())))
                .toArray(ClassBytecodes[]::new));
    }

    private static final String CANCEL_CLASS = "REPL.$Cancel$";
    private static final ClassDesc CD_Cancel = ClassDesc.of(CANCEL_CLASS);
    private static final String STOP_CHECK = "stopCheck";
    private static final ClassDesc CD_ThreadDeath = ClassDesc.of("java.lang.ThreadDeath");

    private static byte[] instrument(byte[] classFile) {
        var cc = ClassFile.of();
        return cc.transformClass(cc.parse(classFile),
                        ClassTransform.transformingMethodBodies(
                            CodeTransform.ofStateful(StopCheckWeaver::new)));
    }

    private static ClassBytecodes genCancelClass() {
        return new ClassBytecodes(CANCEL_CLASS, ClassFile.of().build(CD_Cancel, clb ->
             clb.withFlags(ClassFile.ACC_PUBLIC)
                .withField("allStop", ConstantDescs.CD_boolean, ClassFile.ACC_PUBLIC | ClassFile.ACC_STATIC | ClassFile.ACC_VOLATILE)
                .withMethodBody(STOP_CHECK, ConstantDescs.MTD_void, ClassFile.ACC_PUBLIC | ClassFile.ACC_STATIC, cob ->
                        cob.getstatic(CD_Cancel, "allStop", ConstantDescs.CD_boolean)
                           .ifThenElse(tb -> tb.new_(CD_ThreadDeath)
                                               .dup()
                                               .invokespecial(CD_ThreadDeath, ConstantDescs.INIT_NAME, ConstantDescs.MTD_void)
                                               .athrow(),
                                       eb -> eb.return_()))));
    }

    // This inserts calls to REPL.$Cancel$.stopCheck() at method start and prior to any backward branch
    private static class StopCheckWeaver implements CodeTransform {

        private final Set<Label> priorLabels = new HashSet<>();

        @Override
        public void atStart(CodeBuilder builder) {
            stopCheck(builder);
        }

        @Override
        public void accept(CodeBuilder builder, CodeElement element) {
            switch (element) {
                case LabelTarget target -> priorLabels.add(target.label());
                case BranchInstruction branch when priorLabels.contains(branch.target()) -> stopCheck(builder);
                default -> { }
            }
            builder.with(element);
        };

        private void stopCheck(CodeBuilder builder) {
            builder.invokestatic(CD_Cancel, STOP_CHECK, ConstantDescs.MTD_void);
        }
    }

    @Override
    @SuppressWarnings("removal")
    protected String invoke(Method doitMethod) throws Exception {
        if (allStop == null) {
            super.load(new ClassBytecodes[]{ genCancelClass() });
            allStop = findClass(CANCEL_CLASS).getDeclaredField("allStop");
        }
        allStop.set(null, false);

        AtomicReference<InvocationTargetException> iteEx = new AtomicReference<>();
        AtomicReference<IllegalAccessException> iaeEx = new AtomicReference<>();
        AtomicReference<NoSuchMethodException> nmeEx = new AtomicReference<>();
        AtomicReference<Boolean> stopped = new AtomicReference<>(false);

        execThreadGroup = new ThreadGroup("JShell process local execution") {
            @Override
            public void uncaughtException(Thread t, Throwable e) {
                if (e instanceof InvocationTargetException) {
                    if (e.getCause() instanceof ThreadDeath) {
                        stopped.set(true);
                    } else {
                        iteEx.set((InvocationTargetException) e);
                    }
                } else if (e instanceof IllegalAccessException) {
                    iaeEx.set((IllegalAccessException) e);
                } else if (e instanceof NoSuchMethodException) {
                    nmeEx.set((NoSuchMethodException) e);
                } else if (e instanceof ThreadDeath) {
                    stopped.set(true);
                }
            }
        };

        final Object[] res = new Object[1];
        Thread snippetThread = new Thread(execThreadGroup, () -> {
            try {
                res[0] = doitMethod.invoke(null, new Object[0]);
            } catch (InvocationTargetException e) {
                if (e.getCause() instanceof ThreadDeath) {
                    stopped.set(true);
                } else {
                    iteEx.set(e);
                }
            } catch (IllegalAccessException e) {
                iaeEx.set(e);
            } catch (ThreadDeath e) {
                stopped.set(true);
            }
        });

        snippetThread.start();
        Thread[] threadList = new Thread[execThreadGroup.activeCount()];
        execThreadGroup.enumerate(threadList);
        for (Thread thread : threadList) {
            if (thread != null) {
                thread.join();
            }
        }

        if (stopped.get()) {
            throw new StoppedException();
        }

        if (iteEx.get() != null) {
            throw iteEx.get();
        } else if (nmeEx.get() != null) {
            throw nmeEx.get();
        } else if (iaeEx.get() != null) {
            throw iaeEx.get();
        }

        return valueString(res[0]);
    }

    @Override
    public void stop() throws EngineTerminationException, InternalException {
        synchronized (STOP_LOCK) {
            if (!userCodeRunning) {
                return;
            }
            if (execThreadGroup == null) {
                throw new InternalException("Process-local code snippets thread group is null. Aborting stop.");
            }
            try {
                allStop.set(null, true);
            } catch (IllegalArgumentException | IllegalAccessException ex) {
                throw new InternalException("Exception on local stop: " + ex);
            }
            Thread[] threads;
            int len, threadCount;
            do {
                len = execThreadGroup.activeCount() + 4;
                threads = new Thread[len];
                threadCount = execThreadGroup.enumerate(threads);
            } while (threadCount == len);
            for (int i = 0; i < threadCount; i++) {
                threads[i].interrupt();
            }
        }
    }

    @Override
    protected void clientCodeEnter() {
        synchronized (STOP_LOCK) {
            userCodeRunning = true;
        }
    }

    @Override
    protected void clientCodeLeave() {
        synchronized (STOP_LOCK) {
            userCodeRunning = false;
        }
    }

}