[HDFS-16798] SerialNumberMap should decrease current counter if the item exist

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0
• Fix Version/s: 3.4.0
• Component/s: namenode
• Labels: pull-request-available
• Target Version/s: 3.4.0
• Hadoop Flags: Reviewed
• Assignee: ZanderXu
• Reporter: ZanderXu
• Created: 08/Oct/22 11:02
• Updated: 16/Oct/24 18:29
• Resolved: 09/Oct/22 11:07

Description

During looking into some code related XATTR, I found there is a bug in SerialNumberMap, as bellow:

public int get(T t) {
  if (t == null) {
    return 0;
  }
  Integer sn = t2i.get(t);
  if (sn == null) {
    sn = current.getAndIncrement();
    if (sn > max) {
      current.getAndDecrement();
      throw new IllegalStateException(name + ": serial number map is full");
    }
    Integer old = t2i.putIfAbsent(t, sn);
    if (old != null) {
      // here: if the old is not null, we should decrease the current value.
      return old;
    }
    i2t.put(sn, t);
  }
  return sn;
} 

This bug will only cause that the capacity of serialNumberMap is less than expected, no other impact.

Issue Links

• links to: GitHub Pull Request #4987