目录

AntlrV4的内存泄漏问题

victorchutian 收录于类别 Java

2022-08-03 2022-08-03 约 638 字预计阅读 3 分钟

目录

警告

本文最后更新于 2022-08-03，文中内容可能已过时。

在使用antlr生成的语法解析器处理多个文件后，JVM 最终会产生内存不足异常,PredictionContextCache中的hashMap和DFA数组_decisionToDFA会不断增长。因为 PredictionContextCache和_decisionToDFA在生成Parser和Lexer中是类共享的。

public class XXXParser extends Parser {
	protected static final DFA[] _decisionToDFA;
	protected static final PredictionContextCache _sharedContextCache =
		new PredictionContextCache();
  // ...
}

修复方案

/**
 * fix antlr memory leak
 * @see <a href="https://github.com/antlr/antlr4/issues/499"> Memory Leak </a>
 * @author victorchu
 * @date 2022/8/8 11:29
 */
import org.antlr.v4.runtime.Lexer;
import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.atn.ATN;
import org.antlr.v4.runtime.atn.LexerATNSimulator;
import org.antlr.v4.runtime.atn.ParserATNSimulator;
import org.antlr.v4.runtime.atn.PredictionContextCache;
import org.antlr.v4.runtime.dfa.DFA;

import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiConsumer;

import static com.google.common.base.Preconditions.checkArgument;
import static java.util.Objects.requireNonNull;

public class RefreshableParserInitializer<L extends Lexer, P extends Parser>
        implements BiConsumer<L, P>
{
    private final AtomicReference<ParserAndLexerATNCaches<L, P>> caches;

    public RefreshableParserInitializer()
    {
        caches = new AtomicReference<>();
    }

    private ParserAndLexerATNCaches<L, P> buildATNCache(L l, P p)
    {
        ATN lexerATN = l.getATN();
        ATN parserATN = p.getATN();
        return new ParserAndLexerATNCaches(new AntlrATNCacheFields(lexerATN), new AntlrATNCacheFields(parserATN));
    }
    // ================= 泛型处理 =====================

    @Override
    public void accept(L l, P p)
    {

        ParserAndLexerATNCaches<L, P> newCache = buildATNCache(l, p);
        ParserAndLexerATNCaches<L, P> oldCaches = caches.getAndSet(newCache);
        newCache.config(l,p);
    }

    private static final class ParserAndLexerATNCaches<L extends Lexer, P extends Parser>
    {
        public ParserAndLexerATNCaches(AntlrATNCacheFields lexer, AntlrATNCacheFields parser)
        {
            this.lexer = lexer;
            this.parser = parser;
        }

        public final AntlrATNCacheFields lexer;
        public final AntlrATNCacheFields parser;

        public void config(L l, P p){
            lexer.configureLexer(l);
            parser.configureParser(p);
        }
    }

    public static final class AntlrATNCacheFields
    {
        private final ATN atn;
        private final PredictionContextCache predictionContextCache;
        private final DFA[] decisionToDFA;

        public AntlrATNCacheFields(ATN atn)
        {
            this.atn = requireNonNull(atn, "atn is null");
            this.predictionContextCache = new PredictionContextCache();
            this.decisionToDFA = createDecisionToDFA(atn);
        }

        @SuppressWarnings("ObjectEquality")
        public void configureLexer(Lexer lexer)
        {
            requireNonNull(lexer, "lexer is null");
            // Intentional identity equals comparison
            checkArgument(atn == lexer.getATN(), "Lexer ATN mismatch: expected %s, found %s", atn, lexer.getATN());
            lexer.setInterpreter(new LexerATNSimulator(lexer, atn, decisionToDFA, predictionContextCache));
        }

        @SuppressWarnings("ObjectEquality")
        public void configureParser(Parser parser)
        {
            requireNonNull(parser, "parser is null");
            // Intentional identity equals comparison
            checkArgument(atn == parser.getATN(), "Parser ATN mismatch: expected %s, found %s", atn, parser.getATN());
            parser.setInterpreter(new ParserATNSimulator(parser, atn, decisionToDFA, predictionContextCache));
        }

        private static DFA[] createDecisionToDFA(ATN atn)
        {
            DFA[] decisionToDFA = new DFA[atn.getNumberOfDecisions()];
            for (int i = 0; i < decisionToDFA.length; i++) {
                decisionToDFA[i] = new DFA(atn.getDecisionState(i), i);
            }
            return decisionToDFA;
        }
    }
}

如何使用RefreshableParserInitializer？

 SqlBaseLexer baseLexer = xxx;
 SqlBaseParser baseParser = xxx;

 // 注意，每次解析前调用
 BiConsumer<SqlBaseLexer, SqlBaseParser> initializer = new RefreshableParserInitializer<SqlBaseLexer, SqlBaseParser>(){};
 initializer.accept(baseLexer,baseParser);

由于 cache有助于提升 Parser的性能，应该选择定时，按照运行次数或者是内存占用来间断地淘汰缓存。
参考代码见AntlrCacheManager - chutian0610’s github

资料