A DESCRIPTION OF THE PROBLEM :
During refactoring, the priority was changed from Thread.MAX_PRIORITY - 2 to instead state Thread.MIN_PRIORITY - 2, which results in a negative priority, and is thus set to Thread.NORM_PRIORITY. Thus the Cleaner by default now has threads with priority 5, instead of 8.

The change was done in git revision # 992b50087d2ec8878dfcbbd1820a00b6b6bdf644 and label 8261036 by Claes Redestad

REGRESSION : Last worked in version 16.0.2

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the class below with Java 16.0.2 and Java 17

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
My cleaner thread priority is 8
ACTUAL -
My cleaner thread priority is 5

---------- BEGIN SOURCE ----------
import java.lang.ref.*;

public class CleanerDemo {
    public static void main(String... args) throws InterruptedException {
        Cleaner cleaner = Cleaner.create();
        Cleaner.Cleanable cleanable = cleaner.register(new Object(),
                () -> System.out.println("My cleaner thread priority is " +
                        Thread.currentThread().getPriority()));
        System.gc();
        Thread.sleep(1000);
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
It is not a serious bug, since thread priorities are usually of not much significance. However, one could provide a thread factory with a different priority.

FREQUENCY : always