public static IllegalStateException newIllegalContextPushingException(
            RequestContext newCtx, RequestContext oldCtx) {
        requireNonNull(newCtx, "newCtx");
        requireNonNull(oldCtx, "oldCtx");
        final IllegalStateException ex = new IllegalStateException(
                "Trying to call object wrapped with context " + newCtx + ", but context is currently " +
                "set to " + oldCtx + ". This means the callback was called from " +
                "unexpected thread or forgetting to close previous context.");
        if (REPORTED_THREADS.add(Thread.currentThread())) {
            logger.warn("An error occurred while pushing a context", ex);
        }
        return ex;
    }
Returns an {@link IllegalStateException} which is raised when pushing a context from
the unexpected thread or forgetting to close the previous context.
core/src/main/java/com/linecorp/armeria/internal/common/RequestContextUtil.java