src/test/java/org/apache/bcel/HandleTest.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.bcel;

import org.apache.bcel.generic.GOTO;
import org.apache.bcel.generic.ILOAD;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.InstructionList;
import org.apache.bcel.generic.NOP;
import org.junit.jupiter.api.Test;

/**
 * Test for https://issues.apache.org/jira/browse/BCEL-267 "Race conditions on static fields in BranchHandle and
 * InstructionHandle".
 */
class HandleTest {

    static Throwable exception;
    static final int MAXI = 100;
    static final int MAXJ = 1000;

    /**
     * Asserts that branch handles can be added an instruction list, without corrupting the list.
     */
    static void branchHandles() {
        for (int i = 0; i < MAXI; i++) {
            final InstructionList list = new InstructionList();
            final InstructionHandle start = list.append(new NOP());
            try {
                for (int j = 0; j < MAXJ; j++) {
                    list.append(new GOTO(start));
                }
                final InstructionHandle[] instructionHandles = list.getInstructionHandles();
                for (int j = 0; j < instructionHandles.length; j++) {
                    final InstructionHandle handle = instructionHandles[j];
                    if (j > 0) {
                        checkLinkage(handle, j);
                        if (start != ((GOTO) handle.getInstruction()).getTarget()) {
                            final AssertionError error = new AssertionError("unexpected instruction at index " + j);
                            exception = error;
                            throw error;
                        }
                    }
                }
                if (exception != null) {
                    return;
                }
            } catch (final NullPointerException e) {
                System.out.println("NPE at i=" + i);
                exception = e;
                throw e;
            }
            list.dispose(); // this initializes caching of unused instruction handles
        }
    }

    /**
     * Assert that opposite next/prev pairs always match.
     */
    static void checkLinkage(final InstructionHandle ih, final int index) {
        final InstructionHandle prev = ih.getPrev();
        final InstructionHandle next = ih.getNext();
        if (prev != null && prev.getNext() != ih || next != null && next.getPrev() != ih) {
            final AssertionError error = new AssertionError("corrupt instruction list at index " + index);
            exception = error;
            throw error;
        }
    }

    /**
     * Asserts that instruction handles can be added an instruction list, without corrupting the list.
     */
    static void handles() {
        for (int i = 0; i < MAXI; i++) {
            final InstructionList list = new InstructionList();
            try {
                for (int j = 0; j < MAXJ; j++) {
                    list.append(new ILOAD(j));
                }
                final InstructionHandle[] instructionHandles = list.getInstructionHandles();
                for (int j = 0; j < instructionHandles.length; j++) {
                    final InstructionHandle handle = instructionHandles[j];
                    checkLinkage(handle, j);
                    if (j != ((ILOAD) handle.getInstruction()).getIndex()) {
                        final AssertionError error = new AssertionError("unexpected instruction at index " + j);
                        exception = error;
                        throw error;
                    }
                }
                if (exception != null) {
                    return;
                }
            } catch (final NullPointerException e) {
                System.out.println("NPE at i=" + i);
                exception = e;
                throw e;
            }
            list.dispose(); // this initializes caching of unused instruction handles
        }
    }

    /**
     * Concurrently run the given runnable in two threads.
     */
    private void perform(final Runnable r) throws Throwable {
        exception = null;
        final Thread t1 = new Thread(r);
        final Thread t2 = new Thread(r);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        if (exception != null) {
            throw exception;
        }
    }

    /**
     * Assert that two independent instruction lists can be modified concurrently. Here: inserting branch instructions.
     */
    @Test
    void testBranchHandle() throws Throwable {
        perform(HandleTest::branchHandles);
    }

    /**
     * Assert that two independent instruction lists can be modified concurrently. Here: inserting regular instructions.
     */
    @Test
    void testInstructionHandle() throws Throwable {
        perform(HandleTest::handles);
    }
}