[Bug classpath/28035] New: java.rmi.server.UID does not return unique IDs

[dpirkle at symyx dot com]

A loop like the following will show duplicate ID's returned by the toString()
method of java.rmi.server.UID:

  for (int i = 1; i <=20; ++i) {
    System.out.println(new UID().toString());
  }

Within the first few lines, you'll see an ID that appears twice in two
consecutive lines.

I believe the problem is due to this line at the end of the constructor:

  count = uidCounter++;

Any time the clock advances, count and uidCounter are set to Short.MIN_VALUE. 
The next iteration, the else branch is taken, and count will stay at
Short.MIN_VALUE, since a postfix operator is used on uidCounter (see line
above).  All subsequent iterations, count and uidCounter will continue to
increment, until the clock ticks again, at which point the duplication
reocccurs.

If I change the line above to the following, it seems to fix the problem:

  count = ++uidCounter;

By the way, shouldn't the whole constructor be synchronized?  Seems like
there's potential for what's going on in the if branch to conflict with what's
going on in the else branch (if you had 2 threads at each branch at the same
time), but the if is not synchronized and the else is synchronized, so one can
clobber the other.


-- 
           Summary: java.rmi.server.UID does not return unique IDs
           Product: classpath
           Version: 0.91
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: classpath
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dpirkle at symyx dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28035