More fix: two validation records would collide if generated at the

same millisecond. Use a persistent random, and include the userId
and a bit of the timestamp to make a secret that cannot collide
with another user's secret.

src/main/java/com/threerings/user/OOOUserRepository.java

@@ -21,7 +21,6 @@ import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Random;
 
 import com.google.common.collect.Lists;
 
@@ -952,11 +951,7 @@ public class OOOUserRepository extends UserRepository
         update("delete from penders where userId = '" + userId + "'");
 
         // create a new one and insert it into the database
-        ValidateRecord rec = new ValidateRecord();
-        rec.secret = Long.toString(Math.abs((new Random()).nextLong()), 16);
-        rec.userId = userId;
-        rec.persist = persist;
-        rec.inserted = new Date(System.currentTimeMillis());
+        ValidateRecord rec = ValidateRecord.create(userId, persist);
         insert(_vtable, rec);
         return rec;
     }

src/main/java/com/threerings/user/ValidateRecord.java

@@ -4,6 +4,9 @@
 package com.threerings.user;
 
 import java.sql.Date;
+import java.util.Random;
+
+import com.samskivert.util.StringUtil;
 
 /**
  * Maintains information on users that have not yet validated their
@@ -18,4 +21,28 @@ public class ValidateRecord
     public boolean persist;
 
     public Date inserted;
+
+    /**
+     * Create a new ValidateRecord for the specified userId.
+     */
+    public static ValidateRecord create (int userId, boolean persist)
+    {
+        ValidateRecord rec = new ValidateRecord();
+        rec.userId = userId;
+        rec.persist = persist;
+        long now = System.currentTimeMillis();
+        long secret;
+        do {
+            secret = rand.nextLong();
+        } while (secret == Long.MIN_VALUE); // MIN_VALUE doesn't "abs" nicely
+        // guarantee that secret cannot collide with another user by prepending the userId
+        rec.secret = Integer.toString(userId, 16) +
+            StringUtil.prepad(Integer.toString((int) (now & 0xFFFF), 16), 4, '0') +
+            StringUtil.prepad(Long.toString(Math.abs(secret), 16), 16, '0');
+        rec.inserted = new Date(now);
+        return rec;
+    }
+
+    /** Generates random numbers for validate records. */
+    protected static final Random rand = new Random();
 }

src/main/java/com/threerings/user/depot/DepotUserRepository.java

@@ -13,7 +13,6 @@ import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Random;
 import java.util.Set;
 
 import com.google.common.collect.Lists;
@@ -937,11 +936,7 @@ public class DepotUserRepository extends DepotRepository
         deleteAll(ValidateDepotRecord.class, new Where(ValidateDepotRecord.USER_ID.eq(userId)));
 
         // create a new one and insert it into the database
-        ValidateRecord rec = new ValidateRecord();
-        rec.secret = Long.toString(Math.abs((new Random()).nextLong()), 16);
-        rec.userId = userId;
-        rec.persist = persist;
-        rec.inserted = new Date(System.currentTimeMillis());
+        ValidateRecord rec = ValidateRecord.create(userId, persist);
         insert(ValidateDepotRecord.fromValidateRecord(rec));
         return rec;
     }