多个线程持有相同的锁？

Question

  "dashboardRefreshContainer-8" - Thread t@1384
   java.lang.Thread.State: RUNNABLE
    at sun.util.calendar.ZoneInfo.getLastRule(ZoneInfo.java:638)
    - locked <4d70153e> (a sun.util.calendar.ZoneInfo)
    at sun.util.calendar.ZoneInfo.getOffsets(ZoneInfo.java:275)
    at sun.util.calendar.ZoneInfo.getOffsets(ZoneInfo.java:225)
    at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2024)
    at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:1996)
    at java.util.Calendar.setTimeInMillis(Calendar.java:1109)
    at java.util.Calendar.setTime(Calendar.java:1075)

"TP-Processor38" - Thread t@158
   java.lang.Thread.State: RUNNABLE
    at sun.util.calendar.ZoneInfo.getLastRule(ZoneInfo.java:638)
    - locked <4d70153e> (a sun.util.calendar.ZoneInfo)
    at sun.util.calendar.ZoneInfo.getOffsets(ZoneInfo.java:275)
    at sun.util.calendar.ZoneInfo.getOffsets(ZoneInfo.java:225)
    at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2024)
    at java.util.GregorianCalendar.computeFields(GregorianCalendar.java:1996)
    at java.util.Calendar.setTimeInMillis(Calendar.java:1109)
    at java.util.Calendar.setTime(Calendar.java:1075)

线程都是Runnable,它们拥有相同的锁.两个线程都可以锁定相同的地址,而它们都是RUNNABLE吗？这是一个JRE错误吗？

Answer 1

该问题仅存在于线程转储中.实际上,在任何时间点,锁只由一个线程保持.但是,线程转储显示具有相同锁的两个不同线程,因为它不是原子的.

可以使用以下程序轻松复制该行为:

public class Test {
    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            public void run() {
                for (;;) {
                    synchronized (this) { }
                }
            }
        };
        new Thread(runnable).start();
        new Thread(runnable).start();
    }
}