Propagating ThreadLocal to a new Thread fetched from a ExecutorService

Question

I\'m running a process in a separate thread with a timeout, using an ExecutorService and a Future (example code here) (the thread \"spawning\" takes place in a AOP Aspect).<

Answer 1

Here is an example to pass the current LocaleContext in parent thread to the child thread spanned by CompletableFuture[By default it used ForkJoinPool].

Just define all the things you wanted to do in a child thread inside a Runnable block. So when the CompletableFuture execute the Runnable block, its the child thread who is in control and voila you have the parent's ThreadLocal stuff set in Child's ThreadLocal.

The problem here is not the entire ThreadLocal is copied over. Only the LocaleContext is copied. Since the ThreadLocal is of private access to only the Thread it belongs too using Reflection and trying to get and set in Child is all too much of wacky stuff which might lead to memory leaks or performance hit.

So if you know the parameters you are interested from the ThreadLocal, then this solution works way cleaner.

 public void parentClassMethod(Request request) {
        LocaleContext currentLocale = LocaleContextHolder.getLocaleContext();
        executeInChildThread(() -> {
                LocaleContextHolder.setLocaleContext(currentLocale);
                //Do whatever else you wanna do
            }));

        //Continue stuff you want to do with parent thread
}


private void executeInChildThread(Runnable runnable) {
    try {
        CompletableFuture.runAsync(runnable)
            .get();
    } catch (Exception e) {
        LOGGER.error("something is wrong");
    }
}