Clean up the caching of ATN instances with bypass alternatives

runtime/Java/src/org/antlr/v4/runtime/Parser.java

@@ -51,6 +51,8 @@ import org.antlr.v4.runtime.tree.pattern.ParseTreePatternMatcher;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
+import java.util.WeakHashMap;
 
 /** This is all the parsing support code essentially; most of it is error recovery stuff. */
 public abstract class Parser extends Recognizer<Token, ParserATNSimulator> {
@@ -98,6 +100,15 @@ public abstract class Parser extends Recognizer<Token, ParserATNSimulator> {
 		}
 	}
 
+	/**
+	 * This field maps from the serialized ATN string to the deserialized {@link ATN} with
+	 * bypass alternatives.
+	 *
+	 * @see ATNDeserializationOptions#isGenerateRuleBypassTransitions()
+	 */
+	private static final Map<String, ATN> bypassAltsAtnCache =
+		new WeakHashMap<String, ATN>();
+
 	/**
 	 * The error handling strategy for the parser. The default value is a new
 	 * instance of {@link DefaultErrorStrategy}.
@@ -435,26 +446,30 @@ public abstract class Parser extends Recognizer<Token, ParserATNSimulator> {
 		_input.getTokenSource().setTokenFactory(factory);
 	}
 
-	/** The ATN with bypass alternatives is expensive to create so we create it lazily.
-	 *  The actual generated parsers override this method. These are just
-	 *  setters/getters. createATNWithBypassAlts() does the creation.
+	/**
+	 * The ATN with bypass alternatives is expensive to create so we create it
+	 * lazily.
+	 *
+	 * @throws UnsupportedOperationException if the current parser does not
+	 * implement the {@link #getSerializedATN()} method.
 	 */
-	public void setATNWithBypassAlts(ATN atn) { }
-	public ATN getATNWithBypassAlts() { return null; }
+	@NotNull
+	public ATN getATNWithBypassAlts() {
+		String serializedAtn = getSerializedATN();
+		if (serializedAtn == null) {
+			throw new UnsupportedOperationException("The current parser does not support an ATN with bypass alternatives.");
+		}
 
-	/** Create and cache the ATN with bypass alternatives. This is not
-	 *  part of the typical API--use compileParseTreePattern().
-	 */
-	public void createATNWithBypassAlts() {
-		if ( getATNWithBypassAlts()==null ) {
-			synchronized (Parser.class) { // create just one pattern matcher
-				if ( getATNWithBypassAlts()==null ) { // double-check
-					String sATN = getSerializedATN();
+		synchronized (bypassAltsAtnCache) {
+			ATN result = bypassAltsAtnCache.get(serializedAtn);
+			if (result == null) {
 				ATNDeserializationOptions deserializationOptions = new ATNDeserializationOptions();
 				deserializationOptions.setGenerateRuleBypassTransitions(true);
-					setATNWithBypassAlts( new ATNDeserializer(deserializationOptions).deserialize(sATN.toCharArray()) );
-				}
+				result = new ATNDeserializer(deserializationOptions).deserialize(serializedAtn.toCharArray());
+				bypassAltsAtnCache.put(serializedAtn, result);
 			}
+
+			return result;
 		}
 	}
 
@@ -483,7 +498,6 @@ public abstract class Parser extends Recognizer<Token, ParserATNSimulator> {
 	public ParseTreePattern compileParseTreePattern(String pattern, int patternRuleIndex,
 													Lexer lexer)
 	{
-		createATNWithBypassAlts();
 		ParseTreePatternMatcher m = new ParseTreePatternMatcher(lexer, this);
 		return m.compile(pattern, patternRuleIndex);
 	}

runtime/Java/src/org/antlr/v4/runtime/tree/pattern/ParseTreePatternMatcher.java

@@ -132,9 +132,6 @@ public class ParseTreePatternMatcher {
 	public ParseTreePatternMatcher(Lexer lexer, Parser parser) {
 		this.lexer = lexer;
 		this.parser = parser;
-		if ( parser!=null ) {
-			parser.createATNWithBypassAlts();
-		}
 	}
 
 	public void setDelimiters(String start, String stop, String escapeLeft) {

tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg

@@ -247,10 +247,6 @@ public class <parser.name> extends <superClass> {
 
 	@Override
 	public ATN getATN() { return _ATN; }
-	@Override
-	public ATN getATNWithBypassAlts() { return _ATNWithBypassAlts; }
-	@Override
-	public void setATNWithBypassAlts(ATN atn) { _ATNWithBypassAlts = atn; }
 
 	@Override
 	public Map\<String, Integer> getTokenTypeMap() { return tokenNameToType; }
@@ -935,7 +931,6 @@ public static final String _serializedATN =
 <endif>
 public static final ATN _ATN =
 	new ATNDeserializer().deserialize(_serializedATN.toCharArray());
-public static ATN _ATNWithBypassAlts;
 static {
 	_decisionToDFA = new DFA[_ATN.getNumberOfDecisions()];
 	for (int i = 0; i \< _ATN.getNumberOfDecisions(); i++) {