[GR-10322] Preliminary thread-safety of statically cached parse trees

PullRequest: graalpython/90

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/parser/PythonParserImpl.java

@@ -27,8 +27,7 @@
 
 import static com.oracle.graal.python.runtime.exception.PythonErrorType.SyntaxError;
 
-import java.util.HashMap;
-import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.regex.Pattern;
 
 import org.antlr.v4.runtime.CharStreams;
@@ -52,7 +51,7 @@
 import com.oracle.truffle.api.source.SourceSection;
 
 public final class PythonParserImpl implements PythonParser {
-    private static final Map<String, ParserRuleContext> cachedParseTrees = new HashMap<>();
+    private static final ConcurrentHashMap<String, ParserRuleContext> cachedParseTrees = new ConcurrentHashMap<>();
 
     private static Python3Parser getPython3Parser(CodePointCharStream fromString) {
         Python3Parser parser = new Builder.Parser(fromString).build();
@@ -75,11 +74,7 @@ private static ParserRuleContext preParseWithAntlr(PythonCore core, Source sourc
         Python3Parser parser = getPython3Parser(fromString);
         ParserRuleContext input;
         if (!core.isInitialized()) {
-            input = cachedParseTrees.get(fileDirAndName);
-            if (input == null) {
-                input = parser.file_input();
-                cachedParseTrees.put(fileDirAndName, input);
-            }
+            input = cachedParseTrees.computeIfAbsent(fileDirAndName, (key) -> parser.file_input());
         } else {
             try {
                 if (source.isInteractive()) {