_sharedContextCache is not thread safe

[dadadong]

I am using the swift version of ANTLR4.13.1 to parse the objc code file, and I always encounter a crash. My code structure is as follows:

        let queue = OperationQueue()
        for path in paths {
            let opt = BlockOperation {
                guard let input = try? ANTLRFileStream(path) else {
                    return nil
                }
                let lexer = ObjectiveCLexer(input)
                let tokens = CommonTokenStream(lexer)
                guard let parser = try? ObjectiveCParser(tokens) else {
                    return nil
                }
                parser.setErrorHandler(BailErrorStrategy())
                guard let unit = try? parser.translationUnit(),
                      unit.exception == nil
                else {
                    return nil
                }
                // soming....
            }
            queue.addOperation(opt)
        }

Crash stack：

[dadadong]

I use the following code to solve the thread-safety problem and do not know if there is a risk，any help me ：）

private class OC_Parsor: ObjectiveCParser {
    private let _cache = PredictionContextCache()

    override init(_ input: TokenStream) throws {
        RuntimeMetaData.checkVersion("4.13.1", RuntimeMetaData.VERSION)
        try super.init(input)
        _interp = ParserATNSimulator(self, ObjectiveCParser._ATN, ObjectiveCParser._decisionToDFA, _cache)
    }
}